HIV — MCQs

Q: Four scientists were trying to measure the effect of a new inhibitor X on the expression levels of transcription factor, HNF4alpha. They measured the inhibition levels by using RT-qPCR. In short they converted the total mRNA of the cells to cDNA (RT part), and used PCR to amplify the cDNA quantifying the amplification with a dsDNA binding dye (qPCR part). Which of the following group characteristics contains a virus(es) that has the enzyme necessary to convert the mRNA to cDNA used in the above scenario?

Enveloped, dimeric (+) ssRNA. ***Enveloped, dimeric (+) ssRNA*** - This group describes **retroviruses**, which possess the enzyme **reverse transcriptase**. - **Reverse transcriptase** is essential for converting their **RNA genome** into **cDNA**, a process analogous to the RT step in RT-qPCR. - Examples include **HIV**, which is tagged to this topic. *Enveloped, circular (-) ssRNA* - This description does not accurately represent a major viral family. - Most enveloped negative-sense RNA viruses have **linear or segmented genomes** (e.g., **Orthomyxoviruses**, **Bunyaviruses**), not circular. - These viruses replicate using an **RNA-dependent RNA polymerase** to synthesize mRNA from their negative-sense RNA genome. - They do not inherently carry or require **reverse transcriptase** for their life cycle. *Nonenveloped, (+) ssRNA* - These viruses, like **Picornaviruses**, directly use their positive-sense RNA as mRNA and replicate via an **RNA-dependent RNA polymerase**. - They do not possess **reverse transcriptase** for cDNA synthesis. *Nonenveloped, ssDNA* - Viruses with a **single-stranded DNA genome**, such as **Parvoviruses**, replicate by first synthesizing a double-stranded DNA intermediate. - Their replication machinery does not involve **reverse transcriptase** to convert RNA to DNA. *Nonenveloped, circular dsDNA* - Viruses in this group, like **Papillomaviruses** and **Polyomaviruses**, have a circular double-stranded DNA genome and replicate within the host nucleus using the host's DNA polymerase. - They do not utilize or encode **reverse transcriptase** for their replication cycle.

Q: A 41-year-old HIV-positive male presents to the ER with a 4-day history of headaches and nuchal rigidity. A lumbar puncture shows an increase in CSF protein and a decrease in CSF glucose. When stained with India ink, light microscopy of the patient’s CSF reveals encapsulated yeast with narrow-based buds. Assuming a single pathogenic organism is responsible for this patient’s symptoms, which of the following diagnostic test results would also be expected in this patient?

Latex agglutination of CSF. **Latex agglutination of CSF** - The presence of **encapsulated yeast with narrow-based buds** in the cerebrospinal fluid (CSF) on **India ink stain** is pathognomonic for **Cryptococcus neoformans**, the causative agent of **cryptococcal meningitis**. - **Latex agglutination** is a rapid and highly sensitive test that detects the **cryptococcal capsular polysaccharide antigen** in CSF, making it an expected diagnostic finding. *Ring-enhancing lesions on CT imaging* - **Ring-enhancing lesions** are typically associated with **Toxoplasma gondii encephalitis** (toxoplasmosis) in HIV-positive patients, which would also present with focal neurological deficits. - While cryptococcal meningitis can sometimes cause cryptococcomas that may enhance, these are less common and not the primary diagnostic feature. *Cotton-wool spots on funduscopic exam* - **Cotton-wool spots** are associated with **HIV retinopathy** or sometimes **cytomegalovirus (CMV) retinitis**, presenting as fluffy white lesions on the retina. - These findings are indicative of microinfarctions in the retinal nerve fiber layer due to various causes, but not directly linked to fungal meningitis. *Acid-fast oocysts in stool* - **Acid-fast oocysts in stool** are characteristic of infections such as **cryptosporidiosis** or **isosporiasis**, which cause chronic diarrhea in immunocompromised individuals. - These are gastrointestinal pathogens and would not directly lead to the neurological symptoms and CSF findings described in the patient. *Frontotemporal atrophy on MRI* - **Frontotemporal atrophy** is a feature of **neurocognitive disorders** such as **frontotemporal dementia** or **HIV-associated dementia (HAD)**, a chronic neurocognitive decline. - While HAD can occur in HIV-positive individuals, it does not explain the acute presentation of headaches, nuchal rigidity, and specific CSF findings suggestive of an acute infectious process like meningitis.

Q: A 24-year-old male presents to the emergency room with a cough and shortness of breath for the past 3 weeks. You diagnose Pneumocystis jiroveci pneumonia (PCP). An assay of the patient's serum reveals the presence of viral protein p24. Which of the following viral genes codes for this protein?

gag. ***gag*** - The **gag gene** (group-specific antigen) in HIV codes for structural proteins of the virus, including **p24**, which forms the viral capsid. - The presence of **p24 protein** in the serum is a key marker for **HIV infection**, particularly in the early stages, as it indicates active viral replication. *pol* - The **pol gene** codes for essential viral enzymes such as **reverse transcriptase**, **integrase**, and **protease**, which are crucial for the HIV life cycle. - While vital for viral replication, the **pol gene products** are enzymes involved in processing and replication, not the structural capsid protein p24. *rev* - The **rev gene** (regulator of expression of virion proteins) codes for the **Rev protein**, which regulates the export of HIV mRNAs from the nucleus to the cytoplasm. - This regulatory protein ensures the efficient synthesis of structural and enzymatic proteins but does not directly code for the p24 capsid protein. *env* - The **env gene** (envelope) codes for the viral envelope glycoproteins **gp160**, which is cleaved into **gp120** and **gp41**. - These proteins are critical for viral entry into host cells by binding to CD4 receptors and co-receptors, but they are distinct from the p24 capsid protein. *tat* - The **tat gene** (trans-activator of transcription) codes for the **Tat protein**, a powerful trans-activator that enhances the transcription of HIV RNA. - Tat plays a crucial role in increasing the efficiency of viral gene expression but does not code for structural components like the p24 capsid.

Q: A 45-year-old man presents with a 2-week history of night sweats, cough, and a fever. Past medical history includes HIV infection diagnosed 10 years ago, managed with HAART. He says he hasn’t been compliant with his HAART therapy as prescribed because it is too expensive and he is currently unemployed without insurance. A chest radiograph is performed and reveals a cavity in the right upper lobe of his lung. Which of the following lung infections is most likely causing this patient’s symptoms?

M. tuberculosis. ***M. tuberculosis*** - This patient's symptoms (night sweats, cough, fever), along with a cavitary lesion on chest X-ray, are classic for **pulmonary tuberculosis**, especially in an immunocompromised individual with HIV and likely poor HAART adherence. - **HIV infection** significantly increases the risk for reactivation of latent TB and progression to active disease. *Cytomegalovirus* - **CMV pneumonia** is rare in HIV patients unless their CD4 count is severely low and they are not on ART. It typically presents with dyspnea and hypoxemia, and imaging may show diffuse interstitial infiltrates rather than a cavitary lesion. - While CMV can cause **retinitis**, esophagitis, or colitis in HIV/AIDS patients, isolated cavitary lung lesions are not a typical presentation. *Mycobacterium avium complex* - **MAC infection** typically occurs in advanced HIV disease (CD4 < 50 cells/mm3) and usually presents as disseminated disease with symptoms like wasting, diarrhea, and anemia, rather than primarily cavitary lung lesions. - While pulmonary MAC can occur, it's less likely to present with a cavitary lesion than M. tuberculosis and would be in a more severely immunocompromised state. *Pneumocystis jirovecii* - **Pneumocystis pneumonia (PJP)** is a common opportunistic infection in HIV patients with low CD4 counts, presenting with dyspnea, non-productive cough, and hypoxemia. - Chest imaging typically shows **diffuse bilateral interstitial infiltrates**, not a cavitary lesion. *Histoplasmosis* - **Histoplasmosis** is more prevalent in specific geographic regions (e.g., Ohio and Mississippi River valleys) and can cause pulmonary infiltrates or disseminated disease in immunocompromised individuals. - While cavitary lesions can occur, the combination of night sweats, cough, and a cavitary lesion in an HIV patient points more strongly towards **tuberculosis** as the most common and classic presentation.

Q: A 23-year-old male with a homozygous CCR5 mutation is found to be immune to HIV infection. The patient’s CCR5 mutation interferes with the function of which viral protein?

gp120. ***gp120*** - The **gp120 protein** on the HIV envelope is responsible for binding to the **CD4 receptor** and the **coreceptor CCR5** or CXCR4 on host cells, which is the initial step for viral entry. - A homozygous **CCR5 mutation** (specifically the **CCR5-Δ32** deletion) prevents HIV from using this coreceptor, thereby blocking the binding of gp120 and subsequent viral entry. *gp41* - **gp41** is another envelope protein that, after gp120 binds to CD4 and a coreceptor, undergoes a conformational change to mediate **fusion** of the viral and host cell membranes. - While essential for entry, gp41 acts downstream of gp120's primary binding to the coreceptor, so a CCR5 mutation primarily affects gp120's ability to engage with the cell. *Reverse transcriptase* - **Reverse transcriptase** is a viral enzyme responsible for **converting viral RNA into DNA** once the virus has already entered the host cell cytoplasm. - A CCR5 mutation prevents viral entry, thus the activity of reverse transcriptase is not directly interfered with by the mutation itself but rather by the lack of cellular access. *pp17* - **pp17**, also known as **matrix protein**, is an internal structural protein that plays a role in the assembly of new virions and guiding the **reverse transcribed DNA** into the nucleus. - This protein is involved in later stages of the viral life cycle *after* entry and integration, and its function is not directly blocked by a CCR5 mutation. *p24* - **p24** is the major **capsid protein** that forms the core of the HIV virus, enclosing the viral RNA and enzymes. - It is critical for maintaining the structural integrity of the virus and is a key target for diagnostic tests, but it does not directly participate in the initial binding and entry process that is affected by a CCR5 mutation.

Q: A 49-year-old homeless man comes to the emergency department because of fatigue, cough, and worsening shortness of breath for 2 weeks. He was diagnosed with HIV-infection 25 years ago but has never had any symptoms. He has always refused to take antiretroviral medication. Pulmonary examination shows diffuse crackles over bilateral lower lung fields. An x-ray of the chest shows diffuse, symmetrical interstitial infiltrates. His serum level of beta-d-glucan is elevated. Further testing shows a heterozygous mutation that prevents entry of HIV into macrophages. Which of the following proteins is most likely affected by the mutation in this patient?

CCR5. ***CCR5*** - The mutation preventing HIV entry into **macrophages** points to an issue with a coreceptor, most commonly **CCR5**, which is crucial for macrophage-tropic HIV strains. - A **heterozygous mutation** in CCR5 (CCR5-Δ32) can confer partial resistance to HIV-1 infection, explaining why the patient has been asymptomatic for 25 years despite refusing antiretroviral therapy. - This is a well-documented host genetic factor that slows HIV disease progression. *ICAM-1* - **ICAM-1 (Intercellular Adhesion Molecule 1)** is involved in cell adhesion and immune cell trafficking, but not directly in HIV entry into macrophages. - Mutations in ICAM-1 would not specifically prevent HIV entry, nor would it explain the long-term asymptomatic status in an HIV-positive individual. *Gp120* - **Gp120** is an HIV envelope glycoprotein that binds to the **CD4 receptor** and a coreceptor (CCR5 or CXCR4) on host cells. - While gp120 is essential for HIV entry, it is a **viral protein**; the question asks about a mutation in a **host protein** that prevents viral entry. *CD4* - **CD4** is the primary receptor for HIV on T cells and macrophages, essential for viral entry. - However, a **heterozygous CD4 mutation** would not provide meaningful protection against HIV, as one functional copy would be sufficient for viral entry. - In contrast, heterozygous **CCR5-Δ32** mutation provides documented partial resistance, making CCR5 the better answer given this patient's 25-year asymptomatic course. *P antigen* - **P antigen** typically refers to a red blood cell antigen and is not involved in HIV entry into macrophages. - There is no known direct association between P antigen and HIV susceptibility or disease progression.

Four scientists were trying to measure the effect of a new inhibitor X on the expression levels of transcription factor, HNF4alpha. They measured the inhibition levels by using RT-qPCR. In short they converted the total mRNA of the cells to cDNA (RT part), and used PCR to amplify the cDNA quantifying the amplification with a dsDNA binding dye (qPCR part). Which of the following group characteristics contains a virus(es) that has the enzyme necessary to convert the mRNA to cDNA used in the above scenario?

A 44-year-old with a past medical history significant for human immunodeficiency virus infection presents to the emergency department after he was found to be experiencing worsening confusion. The patient was noted to be disoriented by residents and staff at the homeless shelter where he resides. On presentation he reports headache and muscle aches but is unable to provide more information. His temperature is 102.2°F (39°C), blood pressure is 112/71 mmHg, pulse is 115/min, and respirations are 24/min. Knee extension with hips flexed produces significant resistance and pain. A lumbar puncture is performed with the following results: Opening pressure: Normal Fluid color: Clear Cell count: Increased lymphocytes Protein: Slightly elevated Which of the following is the most likely cause of this patient's symptoms?

A 27-year-old man interested in pre-exposure therapy for HIV (PrEP) is being evaluated to qualify for a PrEP study. In order to qualify, patients must be HIV- and hepatitis B- and C-negative. Any other sexually transmitted infections require treatment prior to initiation of PrEP. The medical history is positive for a prior syphilis infection and bipolar affective disorder, for which he takes lithium. On his next visit, the liver and renal enzymes are within normal ranges. HIV and hepatitis B and C tests are negative. Which of the following about the HIV test is true?

A 32-year-old HIV positive male presents to the office complaining of difficulty swallowing and bad breath for the past couple of months. Upon further questioning, he says, "it feels like there’s something in my throat". He says that the difficulty is sometimes severe enough that he has to skip meals. He added that it mainly occurs with solid foods. He is concerned about his bad breath since he has regular meetings with his clients. Although he is on antiretroviral medications, he admits that he is noncompliant. On examination, the patient is cachectic with pale conjunctiva. On lab evaluation, the patient’s CD4+ count is 70/mm3. What is the most likely cause of his symptoms?

A 33-year-old man with HIV comes to the physician because of a nonproductive cough and shortness of breath for 3 weeks. He feels tired after walking up a flight of stairs and after long conversations on the phone. He appears chronically ill. His temperature is 38.5°C (101.3°F), and pulse is 110/min. Pulse oximetry on room air shows an oxygen saturation of 95%. Upon walking, his oxygen saturation decreases to 85%. Cardiopulmonary examination is normal. Laboratory studies show a CD4+ T-lymphocyte count of 176/mm3 (N > 500). Results of urine Legionella antigen testing are negative. A CT scan of the chest shows diffuse, bilateral ground-glass opacities. Microscopic examination of fluid obtained from bronchoalveolar lavage will most likely show which of the following findings?

A 41-year-old HIV-positive male presents to the ER with a 4-day history of headaches and nuchal rigidity. A lumbar puncture shows an increase in CSF protein and a decrease in CSF glucose. When stained with India ink, light microscopy of the patient’s CSF reveals encapsulated yeast with narrow-based buds. Assuming a single pathogenic organism is responsible for this patient’s symptoms, which of the following diagnostic test results would also be expected in this patient?

A 24-year-old male presents to the emergency room with a cough and shortness of breath for the past 3 weeks. You diagnose Pneumocystis jiroveci pneumonia (PCP). An assay of the patient's serum reveals the presence of viral protein p24. Which of the following viral genes codes for this protein?

A 45-year-old man presents with a 2-week history of night sweats, cough, and a fever. Past medical history includes HIV infection diagnosed 10 years ago, managed with HAART. He says he hasn’t been compliant with his HAART therapy as prescribed because it is too expensive and he is currently unemployed without insurance. A chest radiograph is performed and reveals a cavity in the right upper lobe of his lung. Which of the following lung infections is most likely causing this patient’s symptoms?

A 23-year-old male with a homozygous CCR5 mutation is found to be immune to HIV infection. The patient’s CCR5 mutation interferes with the function of which viral protein?

Q10

A 49-year-old homeless man comes to the emergency department because of fatigue, cough, and worsening shortness of breath for 2 weeks. He was diagnosed with HIV-infection 25 years ago but has never had any symptoms. He has always refused to take antiretroviral medication. Pulmonary examination shows diffuse crackles over bilateral lower lung fields. An x-ray of the chest shows diffuse, symmetrical interstitial infiltrates. His serum level of beta-d-glucan is elevated. Further testing shows a heterozygous mutation that prevents entry of HIV into macrophages. Which of the following proteins is most likely affected by the mutation in this patient?

HIV US Medical PG Practice Questions and MCQs

Question 1: Four scientists were trying to measure the effect of a new inhibitor X on the expression levels of transcription factor, HNF4alpha. They measured the inhibition levels by using RT-qPCR. In short they converted the total mRNA of the cells to cDNA (RT part), and used PCR to amplify the cDNA quantifying the amplification with a dsDNA binding dye (qPCR part). Which of the following group characteristics contains a virus(es) that has the enzyme necessary to convert the mRNA to cDNA used in the above scenario?

A. Enveloped, dimeric (+) ssRNA (Correct Answer)
B. Enveloped, circular (-) ssRNA
C. Nonenveloped, (+) ssRNA
D. Nonenveloped, ssDNA
E. Nonenveloped, circular dsDNA

Explanation: ***Enveloped, dimeric (+) ssRNA*** - This group describes **retroviruses**, which possess the enzyme **reverse transcriptase**. - **Reverse transcriptase** is essential for converting their **RNA genome** into **cDNA**, a process analogous to the RT step in RT-qPCR. - Examples include **HIV**, which is tagged to this topic. *Enveloped, circular (-) ssRNA* - This description does not accurately represent a major viral family. - Most enveloped negative-sense RNA viruses have **linear or segmented genomes** (e.g., **Orthomyxoviruses**, **Bunyaviruses**), not circular. - These viruses replicate using an **RNA-dependent RNA polymerase** to synthesize mRNA from their negative-sense RNA genome. - They do not inherently carry or require **reverse transcriptase** for their life cycle. *Nonenveloped, (+) ssRNA* - These viruses, like **Picornaviruses**, directly use their positive-sense RNA as mRNA and replicate via an **RNA-dependent RNA polymerase**. - They do not possess **reverse transcriptase** for cDNA synthesis. *Nonenveloped, ssDNA* - Viruses with a **single-stranded DNA genome**, such as **Parvoviruses**, replicate by first synthesizing a double-stranded DNA intermediate. - Their replication machinery does not involve **reverse transcriptase** to convert RNA to DNA. *Nonenveloped, circular dsDNA* - Viruses in this group, like **Papillomaviruses** and **Polyomaviruses**, have a circular double-stranded DNA genome and replicate within the host nucleus using the host's DNA polymerase. - They do not utilize or encode **reverse transcriptase** for their replication cycle.

Question 2: A 44-year-old with a past medical history significant for human immunodeficiency virus infection presents to the emergency department after he was found to be experiencing worsening confusion. The patient was noted to be disoriented by residents and staff at the homeless shelter where he resides. On presentation he reports headache and muscle aches but is unable to provide more information. His temperature is 102.2°F (39°C), blood pressure is 112/71 mmHg, pulse is 115/min, and respirations are 24/min. Knee extension with hips flexed produces significant resistance and pain. A lumbar puncture is performed with the following results: Opening pressure: Normal Fluid color: Clear Cell count: Increased lymphocytes Protein: Slightly elevated Which of the following is the most likely cause of this patient's symptoms?

A. Herpes simplex virus
B. Group B streptococcus
C. Cryptococcus (Correct Answer)
D. Tuberculosis
E. Neisseria meningitidis

Explanation: ***Cryptococcus*** - **Cryptococcus neoformans** is the **most common cause of meningitis** in HIV-positive patients, particularly those with CD4 counts <100 cells/μL. - The CSF findings are **classic for cryptococcal meningitis**: clear fluid, **lymphocytic pleocytosis**, normal or mildly elevated opening pressure, and **slightly elevated protein** with normal or mildly decreased glucose. - The patient's **subacute presentation** with confusion, fever, and meningeal signs in the context of **HIV infection** strongly suggests cryptococcal meningitis as the most likely diagnosis. - Diagnosis is confirmed with **CSF cryptococcal antigen**, India ink stain, or fungal culture. *Herpes simplex virus* - While HSV can cause meningitis or encephalitis, it is **not the most common cause** of meningitis in HIV-positive patients. - **HSV encephalitis** typically presents with more prominent temporal lobe involvement, including personality changes, seizures, and focal neurological deficits. - HSV meningitis is more common in **immunocompetent individuals** and would be less likely than cryptococcal infection in an HIV patient. *Group B streptococcus* - This causes **bacterial meningitis** with a **neutrophilic predominance** in CSF, not lymphocytic. - CSF would show **markedly elevated protein**, **decreased glucose**, and cloudy appearance. - More common in neonates and elderly patients, not typically associated with HIV. *Neisseria meningitidis* - This is a cause of **acute bacterial meningitis** with rapid onset and often a **petechial rash**. - CSF would show **neutrophilic predominance**, **high protein**, **low glucose**, and turbid appearance. - The lymphocytic pleocytosis rules out typical bacterial meningitis. *Tuberculosis* - **Tuberculous (TB) meningitis** is an important consideration in HIV-positive patients and can present with lymphocytic pleocytosis. - However, TB meningitis typically shows **markedly elevated protein** (often >100 mg/dL, not "slightly elevated"), **low glucose** (<45 mg/dL), and may have a "spider-web clot" on standing CSF. - The **more subacute to chronic course** (weeks) and absence of very high protein make TB less likely than cryptococcal meningitis in this acute presentation.

Question 3: A 27-year-old man interested in pre-exposure therapy for HIV (PrEP) is being evaluated to qualify for a PrEP study. In order to qualify, patients must be HIV- and hepatitis B- and C-negative. Any other sexually transmitted infections require treatment prior to initiation of PrEP. The medical history is positive for a prior syphilis infection and bipolar affective disorder, for which he takes lithium. On his next visit, the liver and renal enzymes are within normal ranges. HIV and hepatitis B and C tests are negative. Which of the following about the HIV test is true?

A. It is a quantitative test used for screening purposes.
B. It is a qualitative test used for screening purposes. (Correct Answer)
C. A secondary reagent is needed to interpret the results.
D. A known antigen binds directly to the patient's serum.
E. An unknown antigen binds to the known serum.

Explanation: ***It is a qualitative test used for screening purposes.*** - **HIV screening tests** (e.g., 4th generation antibody/antigen combination assays) are typically **qualitative**, meaning they detect the presence or absence of HIV markers, not their exact amount. - These tests are primarily used for broad **screening** of populations to identify potential cases of HIV infection. *It is a quantitative test used for screening purposes.* - **Quantitative tests** for HIV, such as viral load tests, measure the amount of virus in the blood and are typically used for monitoring disease progression or treatment effectiveness, not for initial screening. - Screening tests are designed for high sensitivity to detect infection, even with low viral loads or early antibody responses, making a quantitative measurement less relevant for initial screening. *A secondary reagent is needed to interpret the results.* - While some complex immunoassays might involve multiple steps, modern **HIV screening tests** often use advanced technologies that directly yield results, making a separate secondary reagent for interpretation generally unnecessary. - The results are typically indicated by a color change or a signal detected by an instrument, without requiring an additional interpretive reagent. *A known antigen binds directly to the patient's serum.* - **HIV antibody tests** detect **antibodies** produced by the patient's immune system in response to HIV infection. - In such tests, **known HIV antigens** (from the test kit) bind to **HIV-specific antibodies present in the patient's serum**, not to serum components directly. - This option is incorrect because it omits the critical role of antibodies as the target molecules being detected. *An unknown antigen binds to the known serum.* - This statement describes a different type of immunological assay where an unknown antigen is being identified using a known antibody, which is contrary to how **HIV screening tests** for infection are typically structured. - **HIV screening tests** use known components (e.g., HIV antigens or antibodies) in the test kit to detect unknown components (e.g., HIV antibodies or viral antigens) in the patient's sample.

Question 4: A 32-year-old HIV positive male presents to the office complaining of difficulty swallowing and bad breath for the past couple of months. Upon further questioning, he says, "it feels like there’s something in my throat". He says that the difficulty is sometimes severe enough that he has to skip meals. He added that it mainly occurs with solid foods. He is concerned about his bad breath since he has regular meetings with his clients. Although he is on antiretroviral medications, he admits that he is noncompliant. On examination, the patient is cachectic with pale conjunctiva. On lab evaluation, the patient’s CD4+ count is 70/mm3. What is the most likely cause of his symptoms?

A. Candida albicans (Correct Answer)
B. Human papilloma virus
C. Cytomegalovirus
D. HHV-8
E. Irritation due to medication therapy

Explanation: ***Candida albicans*** - The patient's presentation with **dysphagia** (difficulty swallowing), **bad breath**, and sensation of something in the throat, combined with **HIV positive status** and a very **low CD4+ count (70/mm³)**, is highly suggestive of **esophageal candidiasis**. - **Esophageal candidiasis** is a common **opportunistic infection** in immunocompromised individuals, particularly those with advanced HIV (typically CD4+ <100/mm³), and presents with difficulty swallowing (especially solids), halitosis, sensation of food impaction, and can lead to malnutrition and cachexia. *Human papilloma virus* - While **HPV infections** can occur in HIV-positive individuals and cause squamous lesions, they typically manifest as warts or papillomas and are less likely to be the primary cause of such severe, obstructive dysphagia without other characteristic findings. - HPV-related lesions in the esophagus are relatively rare and usually do not present with the specific "something in my throat" sensation or the degree of malnourishment seen in this patient due to diffuse candidal inflammation. *Cytomegalovirus* - **Cytomegalovirus (CMV) esophagitis** is a serious opportunistic infection in HIV patients with very low CD4+ counts (typically <50/mm³), and it can cause dysphagia. - However, CMV esophagitis typically presents with **painful swallowing (odynophagia)** and **linear or deep ulcers** on endoscopy rather than the diffuse inflammation and white plaques characteristic of candidiasis. The patient's presentation of difficulty (not pain) with solids and the "something in the throat" sensation is more typical of candidiasis. *HHV-8* - **Human Herpesvirus 8 (HHV-8)** is primarily associated with **Kaposi's sarcoma (KS)**, which can affect the gastrointestinal tract, including the esophagus. - While KS lesions in the esophagus can cause dysphagia, they are typically described as **purplish, raised lesions**, and the patient's symptoms of bad breath and a feeling of "something in my throat" are not the most common presentation for esophageal Kaposi's sarcoma. *Irritation due to medication therapy* - Although some medications, including certain antiretrovirals, can cause **pill esophagitis** or irritation, the patient's symptoms are chronic ("past couple of months"), severe enough to cause **cachexia**, and his **noncompliance** would make medication-induced irritation less likely to be the sole cause of such severe and prolonged symptoms. - The patient's **compromised immune status** (low CD4+ count) strongly points towards an opportunistic infection rather than merely drug-induced irritation.

Question 5: A 33-year-old man with HIV comes to the physician because of a nonproductive cough and shortness of breath for 3 weeks. He feels tired after walking up a flight of stairs and after long conversations on the phone. He appears chronically ill. His temperature is 38.5°C (101.3°F), and pulse is 110/min. Pulse oximetry on room air shows an oxygen saturation of 95%. Upon walking, his oxygen saturation decreases to 85%. Cardiopulmonary examination is normal. Laboratory studies show a CD4+ T-lymphocyte count of 176/mm3 (N > 500). Results of urine Legionella antigen testing are negative. A CT scan of the chest shows diffuse, bilateral ground-glass opacities. Microscopic examination of fluid obtained from bronchoalveolar lavage will most likely show which of the following findings?

A. Silver-staining, disc-shaped cysts (Correct Answer)
B. Silver-staining, gram-negative bacilli
C. Septate, acute-angle branching hyphae
D. Gram-positive, catalase-positive cocci
E. Intracellular, acid-fast bacteria

Explanation: **Silver-staining, disc-shaped cysts** - The patient's presentation with **nonproductive cough**, **shortness of breath**, fever, and **exertional hypoxemia** (desaturation upon walking) in the context of **HIV with a low CD4+ count (176/mm3)** is highly suggestive of **Pneumocystis pneumonia (PCP)**. - **Pneumocystis jirovecii** (formerly *Pneumocystis carinii*) is the causative agent and is characterized by **disc-shaped cysts that stain with silver stains** (e.g., GMS stain) in bronchoalveolar lavage (BAL) fluid. *Silver-staining, gram-negative bacilli* - This description is characteristic of **Legionella pneumophila**, which can cause pneumonia, but the **urine Legionella antigen test was negative**, making this diagnosis less likely. - While Legionella is a gram-negative bacillus and can be stained with silver, the overall clinical picture and negative antigen test point away from it. *Septate, acute-branching hyphae* - This morphology is characteristic of **Aspergillus species**, which can cause invasive aspergillosis, particularly in immunocompromised patients. - However, aspergillosis typically presents with different radiological findings (e.g., nodules, cavitations, halo sign, or air crescent sign), and the clinical picture in this case is more typical of PCP. *Gram-positive, catalase-positive cocci* - This description is typical for **Staphylococcus aureus**, which can cause bacterial pneumonia. - While *S. aureus* can cause pneumonia in immunocompromised patients, the diffuse **ground-glass opacities** and exertional hypoxemia, coupled with a low CD4 count, are not typical for staphylococcal pneumonia. *Intracellular, acid-fast bacteria* - This morphology is characteristic of **Mycobacterium species**, such as **Mycobacterium tuberculosis** or **Mycobacterium avium complex (MAC)**. - While TB and MAC infections are common in HIV patients with low CD4 counts, they usually present with different radiological patterns (e.g., cavitations, lymphadenopathy for TB; disseminated disease for MAC) and the sudden onset of profound exertional hypoxemia is less typical.

Question 6: A 41-year-old HIV-positive male presents to the ER with a 4-day history of headaches and nuchal rigidity. A lumbar puncture shows an increase in CSF protein and a decrease in CSF glucose. When stained with India ink, light microscopy of the patient’s CSF reveals encapsulated yeast with narrow-based buds. Assuming a single pathogenic organism is responsible for this patient’s symptoms, which of the following diagnostic test results would also be expected in this patient?

A. Ring-enhancing lesions on CT imaging
B. Latex agglutination of CSF (Correct Answer)
C. Cotton-wool spots on funduscopic exam
D. Acid-fast oocysts in stool
E. Frontotemporal atrophy on MRI

Explanation: **Latex agglutination of CSF** - The presence of **encapsulated yeast with narrow-based buds** in the cerebrospinal fluid (CSF) on **India ink stain** is pathognomonic for **Cryptococcus neoformans**, the causative agent of **cryptococcal meningitis**. - **Latex agglutination** is a rapid and highly sensitive test that detects the **cryptococcal capsular polysaccharide antigen** in CSF, making it an expected diagnostic finding. *Ring-enhancing lesions on CT imaging* - **Ring-enhancing lesions** are typically associated with **Toxoplasma gondii encephalitis** (toxoplasmosis) in HIV-positive patients, which would also present with focal neurological deficits. - While cryptococcal meningitis can sometimes cause cryptococcomas that may enhance, these are less common and not the primary diagnostic feature. *Cotton-wool spots on funduscopic exam* - **Cotton-wool spots** are associated with **HIV retinopathy** or sometimes **cytomegalovirus (CMV) retinitis**, presenting as fluffy white lesions on the retina. - These findings are indicative of microinfarctions in the retinal nerve fiber layer due to various causes, but not directly linked to fungal meningitis. *Acid-fast oocysts in stool* - **Acid-fast oocysts in stool** are characteristic of infections such as **cryptosporidiosis** or **isosporiasis**, which cause chronic diarrhea in immunocompromised individuals. - These are gastrointestinal pathogens and would not directly lead to the neurological symptoms and CSF findings described in the patient. *Frontotemporal atrophy on MRI* - **Frontotemporal atrophy** is a feature of **neurocognitive disorders** such as **frontotemporal dementia** or **HIV-associated dementia (HAD)**, a chronic neurocognitive decline. - While HAD can occur in HIV-positive individuals, it does not explain the acute presentation of headaches, nuchal rigidity, and specific CSF findings suggestive of an acute infectious process like meningitis.

Question 7: A 24-year-old male presents to the emergency room with a cough and shortness of breath for the past 3 weeks. You diagnose Pneumocystis jiroveci pneumonia (PCP). An assay of the patient's serum reveals the presence of viral protein p24. Which of the following viral genes codes for this protein?

A. gag (Correct Answer)
B. pol
C. rev
D. env
E. tat

Explanation: ***gag*** - The **gag gene** (group-specific antigen) in HIV codes for structural proteins of the virus, including **p24**, which forms the viral capsid. - The presence of **p24 protein** in the serum is a key marker for **HIV infection**, particularly in the early stages, as it indicates active viral replication. *pol* - The **pol gene** codes for essential viral enzymes such as **reverse transcriptase**, **integrase**, and **protease**, which are crucial for the HIV life cycle. - While vital for viral replication, the **pol gene products** are enzymes involved in processing and replication, not the structural capsid protein p24. *rev* - The **rev gene** (regulator of expression of virion proteins) codes for the **Rev protein**, which regulates the export of HIV mRNAs from the nucleus to the cytoplasm. - This regulatory protein ensures the efficient synthesis of structural and enzymatic proteins but does not directly code for the p24 capsid protein. *env* - The **env gene** (envelope) codes for the viral envelope glycoproteins **gp160**, which is cleaved into **gp120** and **gp41**. - These proteins are critical for viral entry into host cells by binding to CD4 receptors and co-receptors, but they are distinct from the p24 capsid protein. *tat* - The **tat gene** (trans-activator of transcription) codes for the **Tat protein**, a powerful trans-activator that enhances the transcription of HIV RNA. - Tat plays a crucial role in increasing the efficiency of viral gene expression but does not code for structural components like the p24 capsid.

Question 8: A 45-year-old man presents with a 2-week history of night sweats, cough, and a fever. Past medical history includes HIV infection diagnosed 10 years ago, managed with HAART. He says he hasn’t been compliant with his HAART therapy as prescribed because it is too expensive and he is currently unemployed without insurance. A chest radiograph is performed and reveals a cavity in the right upper lobe of his lung. Which of the following lung infections is most likely causing this patient’s symptoms?

A. M. tuberculosis (Correct Answer)
B. Cytomegalovirus
C. Mycobacterium avium complex
D. Pneumocystis jirovecii
E. Histoplasmosis

Explanation: ***M. tuberculosis*** - This patient's symptoms (night sweats, cough, fever), along with a cavitary lesion on chest X-ray, are classic for **pulmonary tuberculosis**, especially in an immunocompromised individual with HIV and likely poor HAART adherence. - **HIV infection** significantly increases the risk for reactivation of latent TB and progression to active disease. *Cytomegalovirus* - **CMV pneumonia** is rare in HIV patients unless their CD4 count is severely low and they are not on ART. It typically presents with dyspnea and hypoxemia, and imaging may show diffuse interstitial infiltrates rather than a cavitary lesion. - While CMV can cause **retinitis**, esophagitis, or colitis in HIV/AIDS patients, isolated cavitary lung lesions are not a typical presentation. *Mycobacterium avium complex* - **MAC infection** typically occurs in advanced HIV disease (CD4 < 50 cells/mm3) and usually presents as disseminated disease with symptoms like wasting, diarrhea, and anemia, rather than primarily cavitary lung lesions. - While pulmonary MAC can occur, it's less likely to present with a cavitary lesion than M. tuberculosis and would be in a more severely immunocompromised state. *Pneumocystis jirovecii* - **Pneumocystis pneumonia (PJP)** is a common opportunistic infection in HIV patients with low CD4 counts, presenting with dyspnea, non-productive cough, and hypoxemia. - Chest imaging typically shows **diffuse bilateral interstitial infiltrates**, not a cavitary lesion. *Histoplasmosis* - **Histoplasmosis** is more prevalent in specific geographic regions (e.g., Ohio and Mississippi River valleys) and can cause pulmonary infiltrates or disseminated disease in immunocompromised individuals. - While cavitary lesions can occur, the combination of night sweats, cough, and a cavitary lesion in an HIV patient points more strongly towards **tuberculosis** as the most common and classic presentation.

Question 9: A 23-year-old male with a homozygous CCR5 mutation is found to be immune to HIV infection. The patient’s CCR5 mutation interferes with the function of which viral protein?

A. gp41
B. Reverse transcriptase
C. pp17
D. gp120 (Correct Answer)
E. p24

Explanation: ***gp120*** - The **gp120 protein** on the HIV envelope is responsible for binding to the **CD4 receptor** and the **coreceptor CCR5** or CXCR4 on host cells, which is the initial step for viral entry. - A homozygous **CCR5 mutation** (specifically the **CCR5-Δ32** deletion) prevents HIV from using this coreceptor, thereby blocking the binding of gp120 and subsequent viral entry. *gp41* - **gp41** is another envelope protein that, after gp120 binds to CD4 and a coreceptor, undergoes a conformational change to mediate **fusion** of the viral and host cell membranes. - While essential for entry, gp41 acts downstream of gp120's primary binding to the coreceptor, so a CCR5 mutation primarily affects gp120's ability to engage with the cell. *Reverse transcriptase* - **Reverse transcriptase** is a viral enzyme responsible for **converting viral RNA into DNA** once the virus has already entered the host cell cytoplasm. - A CCR5 mutation prevents viral entry, thus the activity of reverse transcriptase is not directly interfered with by the mutation itself but rather by the lack of cellular access. *pp17* - **pp17**, also known as **matrix protein**, is an internal structural protein that plays a role in the assembly of new virions and guiding the **reverse transcribed DNA** into the nucleus. - This protein is involved in later stages of the viral life cycle *after* entry and integration, and its function is not directly blocked by a CCR5 mutation. *p24* - **p24** is the major **capsid protein** that forms the core of the HIV virus, enclosing the viral RNA and enzymes. - It is critical for maintaining the structural integrity of the virus and is a key target for diagnostic tests, but it does not directly participate in the initial binding and entry process that is affected by a CCR5 mutation.

Question 10: A 49-year-old homeless man comes to the emergency department because of fatigue, cough, and worsening shortness of breath for 2 weeks. He was diagnosed with HIV-infection 25 years ago but has never had any symptoms. He has always refused to take antiretroviral medication. Pulmonary examination shows diffuse crackles over bilateral lower lung fields. An x-ray of the chest shows diffuse, symmetrical interstitial infiltrates. His serum level of beta-d-glucan is elevated. Further testing shows a heterozygous mutation that prevents entry of HIV into macrophages. Which of the following proteins is most likely affected by the mutation in this patient?

A. ICAM-1
B. Gp120
C. CD4
D. P antigen
E. CCR5 (Correct Answer)

Explanation: ***CCR5*** - The mutation preventing HIV entry into **macrophages** points to an issue with a coreceptor, most commonly **CCR5**, which is crucial for macrophage-tropic HIV strains. - A **heterozygous mutation** in CCR5 (CCR5-Δ32) can confer partial resistance to HIV-1 infection, explaining why the patient has been asymptomatic for 25 years despite refusing antiretroviral therapy. - This is a well-documented host genetic factor that slows HIV disease progression. *ICAM-1* - **ICAM-1 (Intercellular Adhesion Molecule 1)** is involved in cell adhesion and immune cell trafficking, but not directly in HIV entry into macrophages. - Mutations in ICAM-1 would not specifically prevent HIV entry, nor would it explain the long-term asymptomatic status in an HIV-positive individual. *Gp120* - **Gp120** is an HIV envelope glycoprotein that binds to the **CD4 receptor** and a coreceptor (CCR5 or CXCR4) on host cells. - While gp120 is essential for HIV entry, it is a **viral protein**; the question asks about a mutation in a **host protein** that prevents viral entry. *CD4* - **CD4** is the primary receptor for HIV on T cells and macrophages, essential for viral entry. - However, a **heterozygous CD4 mutation** would not provide meaningful protection against HIV, as one functional copy would be sufficient for viral entry. - In contrast, heterozygous **CCR5-Δ32** mutation provides documented partial resistance, making CCR5 the better answer given this patient's 25-year asymptomatic course. *P antigen* - **P antigen** typically refers to a red blood cell antigen and is not involved in HIV entry into macrophages. - There is no known direct association between P antigen and HIV susceptibility or disease progression.

Question 11: A 45-year-old man with a history of poorly controlled human immunodeficiency virus (HIV) infection presents to the emergency room complaining of clumsiness and weakness. He reports a 3-month history of worsening balance, asymmetric muscle weakness, and speech difficulties. He recently returned from a trip to Guatemala to visit his family. He has been poorly compliant with his anti-retroviral therapy and his most recent CD4 count was 195. His history is also notable for rheumatoid arthritis and hepatitis C. His temperature is 99°F (37.2°C), blood pressure is 140/90 mmHg, pulse is 95/min, and respirations are 18/min. On exam, he has 4/5 strength in his right upper extremity, 5/5 strength in his left upper extremity, 5/5 strength in his right lower extremity, and 3/5 strength in his left lower extremity. His speech is disjointed with intermittent long pauses between words. Vision is 20/100 in the left eye and 20/40 in his right eye; previously, his eyesight was 20/30 bilaterally. This patient most likely has a condition caused by which of the following types of pathogens?

A. Arenavirus
B. Bunyavirus
C. Herpesvirus
D. Polyomavirus (Correct Answer)
E. Picornavirus

Explanation: ***Polyomavirus*** - The patient's **poorly controlled HIV**, **low CD4 count (195)**, and progressive neurological symptoms (clumsiness, weakness, speech difficulties, vision changes) are highly suggestive of **Progressive Multifocal Leukoencephalopathy (PML)**. - PML is caused by the **JC virus**, which is a type of **polyomavirus**, typically reactivating in immunocompromised individuals. *Arenavirus* - Arenaviruses (e.g., Lassa fever virus) are known to cause **hemorrhagic fevers** and can lead to neurological complications, but the clinical presentation described (progressive focal neurological deficits in an HIV patient) is not typical for an arenavirus infection. - While some arenaviruses cause **meningoencephalitis**, the progressive, demyelinating-like course seen in this patient points away from arenavirus. *Bunyavirus* - Bunyaviruses (e.g., Hantavirus, La Crosse encephalitis virus) can cause **encephalitis**, fever, and myalgia, but they don't typically present with the specific constellation of **progressive white matter lesions** and focal neurological signs characteristic of PML in an HIV patient. - Hantaviruses are more associated with **hemorrhagic fever with renal syndrome** or **hantavirus cardiopulmonary syndrome**. *Herpesvirus* - While herpesviruses (e.g., HSV, CMV, VZV) can cause severe neurological disease in HIV patients (e.g., **CMV encephalitis**, **HSV encephalitis**, **VZV vasculopathy**), the described progressive multifocal deficits, especially with rapid worsening, in an HIV patient with a low CD4 count strongly favor PML. - Herpesviral encephalitides often present with more acute onset, fever, and seizures, or specific radiographic patterns not directly matching PML. *Picornavirus* - Picornaviruses, such as enteroviruses, can cause **aseptic meningitis** or **encephalitis**, particularly in immunocompromised individuals. - However, the progressive, multifocal neurological deficits, particularly affecting **white matter**, are not characteristic of picornavirus infections, which tend to cause more diffuse or acute inflammatory processes.

Question 12: A 45-year-old man comes to the physician for the evaluation of painful swallowing and retrosternal pain over the past 2 days. He was recently diagnosed with HIV infection, for which he now takes tenofovir, emtricitabine, and raltegravir. There is no family history of serious illness. He has smoked one pack of cigarettes daily for the past 20 years. He drinks 2–3 beers per day. He does not use illicit drugs. Vital signs are within normal limits. Physical examination of the oral cavity shows no abnormalities. The patient's CD4+ T-lymphocyte count is 80/mm3 (normal ≥ 500). Empiric treatment is started. Two weeks later, he reports no improvement in his symptoms. Esophagogastroduodenoscopy is performed and shows multiple well-circumscribed, round, superficial ulcers in the upper esophagus. Which of the following is the most likely underlying cause of this patient's symptoms?

A. Degeneration of inhibitory neurons within the myenteric plexuses
B. Infection with cytomegalovirus
C. Infection with herpes simplex virus (Correct Answer)
D. Transient lower esophageal sphincter relaxation
E. Allergic inflammation of the esophagus

Explanation: ***Infection with herpes simplex virus*** - The patient's **HIV infection** and **low CD4+ T-lymphocyte count (80/mm3)** indicate severe immunosuppression, making him highly susceptible to opportunistic infections like HSV esophagitis. - The EGD findings of **multiple well-circumscribed, round, superficial ulcers** predominantly in the **upper esophagus** are classic endoscopic features of HSV esophagitis. *Degeneration of inhibitory neurons within the myenteric plexuses* - This condition, known as **achalasia**, typically presents with **dysphagia for both liquids and solids**, regurgitation, and chest pain, which can be confused with retrosternal pain. - However, achalasia does not typically cause **ulcers in the esophagus** and is not primarily linked to HIV or immunosuppression. *Infection with cytomegalovirus* - While CMV esophagitis can occur in immunosuppressed patients and cause odynophagia and retrosternal pain, the ulcers are typically **linear**, **serpiginous**, or **giant** and located more commonly in the **distal esophagus**, unlike the round, superficial ulcers seen here. - CMV infection often presents with other systemic symptoms like fever, fatigue, and leukopenia, which are not mentioned in this case. *Transient lower esophageal sphincter relaxation* - This is a common mechanism contributing to **gastroesophageal reflux disease (GERD)**, which can cause retrosternal pain and dysphagia due to esophageal strictures or erosions. - However, GERD typically causes **diffuse inflammation** and **erosions** rather than discrete, well-circumscribed ulcers, and it's not directly linked to the patient's immunosuppressed state. *Allergic inflammation of the esophagus* - This describes **eosinophilic esophagitis (EoE)**, which presents with dysphagia and food impaction, especially in younger individuals or those with other atopic conditions. - Endoscopy in EoE often shows **trachealization** (concentric rings), **linear furrows**, or **white exudates**, not well-circumscribed ulcers, and it's not associated with HIV infection or severe immunosuppression.

Question 13: A laboratory method uses chromogenic substrates, in which a reaction may be interpreted according to an enzyme-mediated color change. The detection of which of the substances below is routinely used in clinical practice and applies the above-described method?

A. Epstein-Barr virus infection
B. ABO blood types
C. Anti-D antibodies
D. Antibodies in autoimmune hemolytic anemia
E. P24 antigen (Correct Answer)

Explanation: ***P24 antigen*** - The **P24 antigen** test for **HIV** often utilizes **ELISA (Enzyme-Linked Immunosorbent Assay)**, which relies on an enzyme-mediated color change reaction (chromogenic substrate) for detection. - The intensity of the color change is proportional to the amount of **P24 antigen** present, indicating recent **HIV infection**. *Epstein-Barr virus infection* - Detection of **Epstein-Barr virus (EBV)** infection commonly involves serological tests for specific **antibodies (e.g., VCA-IgM, VCA-IgG, EBNA-IgG)**, not typically direct antigen detection via chromogenic substrates. - While some **ELISA-based antibody tests** use chromogenic reactions, the primary target is the antibody response, not a direct viral antigen (like P24 in HIV). *ABO blood types* - **ABO blood typing** is primarily performed using **agglutination reactions** where red blood cells clump in the presence of specific antibodies, visible macroscopically. - This method does not involve an enzyme-mediated color change with **chromogenic substrates**. *Anti-D antibodies* - Detection of **anti-D antibodies** (e.g., in Rh-negative pregnant women or for transfusion reactions) is typically done via **indirect antiglobulin test (IAT or Coombs test)**, which identifies antibodies bound to red blood cells or free in serum. - The **IAT** relies on agglutination, not an enzyme-linked chromogenic reaction. *Antibodies in autoimmune hemolytic anemia* - **Autoimmune hemolytic anemia (AIHA)** is diagnosed primarily using the **direct antiglobulin test (DAT or Coombs test)**, which detects antibodies already coating the patient's red blood cells. - The **DAT** works by inducing agglutination, not through an enzyme-mediated chromogenic substrate detection system.

Question 14: A 20-year-old female arrives at the urgent care clinic at her university’s health plan asking for an HIV test. She is an undergraduate at the university and just started having sexual intercourse with her new boyfriend. They use protection only occasionally so she wants to get tested to make sure everything is okay. She has never been tested for STDs before. She reports no symptoms and has not seen a physician regularly for any medical conditions in the past. Her family history is uncertain because she was adopted. Her HIV immunoassay and HIV-1/HIV-2 differentiation immunoassay both come back positive. She asks on the phone, “Doctor, tell it to me straight. Do I have AIDS?” Which of the following is the most accurate response?

A. We need your partner's information to be sure of your diagnosis.
B. We have to get a confirmatory PCR test to see if you have AIDS.
C. You have AIDS but this disease is now a manageable condition.
D. We need additional bloodwork to see if you have AIDS. (Correct Answer)
E. You do not have AIDS because you just started having sex recently.

Explanation: ***We need additional bloodwork to see if you have AIDS.*** - A patient receives an **AIDS diagnosis** when their **CD4+ T-cell count drops below 200 cells/µL** or if they develop an **AIDS-defining illness**, such as *Pneumocystis jirovecii* pneumonia or Kaposi's sarcoma. - While the **positive HIV tests** indicate she has **HIV infection**, additional tests are required to assess her immune status and confirm an AIDS diagnosis. *We need your partner's information to be sure of your diagnosis.* - A person's HIV status is determined by **their own test results**, not by their partner's information. - While partner notification is important for public health, it is not necessary to confirm an individual's HIV diagnosis. *We have to get a confirmatory PCR test to see if you have AIDS.* - A **PCR test** (specifically a **nucleic acid test**) is used to **confirm HIV infection** by detecting viral RNA or DNA, especially in early stages or when antibody tests are indeterminate. - However, a PCR test alone does not diagnose AIDS; a diagnosis of AIDS requires monitoring of **CD4+ T-cell count** and/or the presence of AIDS-defining illnesses. *You have AIDS but this disease is now a manageable condition.* - This statement is **premature and potentially inaccurate**, as her AIDS status has not yet been determined. - While HIV infection is manageable with treatment, misinforming a patient about an AIDS diagnosis before full evaluation is inappropriate. *You do not have AIDS because you just started having sex recently.* - The **time since exposure** to HIV does not definitively rule out an AIDS diagnosis. - While it typically takes years for **HIV to progress to AIDS**, individual progression rates can vary, and it is crucial to perform appropriate diagnostic tests rather than making assumptions based on exposure history.

Question 15: A 48-year-old woman is brought to her primary care physician by her sister who is concerned about a deterioration in the patient's general status. The patient was diagnosed with HIV 7 years ago. She says that her last T cell count was "good enough", so she has been skipping every other dose of her antiretroviral medications and trimethoprim-sulfamethoxazole. Her sister has had to drive her home from work several times this month because she has become disoriented and confused about her surroundings. Motor strength is 4/5 on the right and 3/5 on the left. She is able to walk unassisted, but her gait appears mildly uncoordinated. There is diplopia when the right eye is covered. Her CD4 count is 75 cells/µL. MRI shows numerous asymmetric, hyperintense, non-enhancing lesions bilaterally without mass effect. Brain biopsy shows demyelination and atypical astrocytes. Which of the following is most likely responsible for this patient's current condition?

A. Autoimmune demyelination
B. John Cunningham virus (JC virus) (Correct Answer)
C. Toxoplasma gondii
D. Primary CNS lymphoma (PCNSL)
E. HIV associated neurocognitive disorder (HAND)

Explanation: ***John Cunningham virus (JC virus)*** - This patient presents with **progressive neurological deficits**, disorientation, motor weakness, uncoordinated gait, and diplopia, in the setting of severe **immunocompromise** (CD4 count 75 cells/µL) due to non-adherence to HIV medication. The MRI findings of **asymmetric, non-enhancing, hyperintense lesions without mass effect** are classic for **Progressive Multifocal Leukoencephalopathy (PML)**, which is caused by the **JC virus**. - **Brain biopsy** showing **demyelination and atypical astrocytes** further confirms the diagnosis of PML, as the JC virus primarily infects and destroys oligodendrocytes, leading to demyelination, and causes characteristic cytopathic effects on astrocytes. *Autoimmune demyelination* - While there is demyelination, the patient's severe **immunocompromised state (CD4 = 75 cells/µL)** makes an opportunistic infection far more likely than an autoimmune process. - Autoimmune demyelination, such as multiple sclerosis, typically does not present with such rapid deterioration in a profoundly immunocompromised individual and is usually not characterized by non-enhancing lesions. *Toxoplasma gondii* - **Toxoplasmosis** is a common opportunistic infection in HIV patients with low CD4 counts, often presenting with focal neurological deficits, seizures, and headache. - However, MRI lesions are typically **ring-enhancing** and often associated with **mass effect**, which is contrary to the non-enhancing lesions without mass effect described in this case. *Primary CNS lymphoma (PCNSL)* - PCNSL can also occur in immunocompromised HIV patients and presents with neurological symptoms. - However, PCNSL lesions are typically **contrast-enhancing** (often homogeneously) and frequently demonstrate **mass effect**, which is not seen here. *HIV associated neurocognitive disorder (HAND)* - HAND causes cognitive impairment, but typically involves a more **diffuse process** rather than discrete focal lesions. - It does not usually present with the dramatic asymmetric motor deficits, diplopia, and characteristic MRI findings of asymmetric, non-enhancing lesions seen in this patient.

Question 16: During an experiment conducted to alter the infectivity of common viruses that affect humans, an investigator successfully increases the host range of human immunodeficiency virus (HIV). The new strain of the virus can infect fibroblast-like cells in addition to the usual target of HIV. Which of the following is the most likely explanation for the increase in the host range of the virus?

A. Reassortment of genetic material between segments of two viruses
B. Increased rate of budding out of host cells
C. Excessive activity of viral RNA polymerase
D. Point mutations in the hemagglutinin gene
E. Mutation of the gene coding for viral surface glycoproteins (Correct Answer)

Explanation: ***Mutation of the gene coding for viral surface glycoproteins*** - Viral **surface glycoproteins** are crucial for initial host cell recognition and binding, determining **cell tropism** and **host range**. A mutation in these genes can alter the binding specificity, allowing the virus to infect new cell types. - Changes in these glycoproteins can enable interaction with different host cell receptors, thereby expanding the range of cells the virus can infect. *Reassortment of genetic material between segments of two viruses* - **Reassortment** typically occurs in viruses with segmented genomes (e.g., influenza virus), leading to rapid genetic shifts. HIV has a non-segmented RNA genome, so reassortment as described is not applicable. - While reassortment can increase virulence or transmissibility, it's not the primary mechanism by which non-segmented RNA viruses like HIV would expand their host range to a new cell type through a single event in a controlled experiment. *Increased rate of budding out of host cells* - An increased rate of budding affects the **viral load** and potentially the efficiency of spread, but it does not alter the fundamental ability of the virus to infect new cell types by changing its **cellular tropism**. - This mechanism relates to the release of new virions from infected cells rather than the initial entry or binding to a host cell. *Excessive activity of viral RNA polymerase* - **RNA polymerase activity** can impact replication efficiency and mutation rates, but it does not directly determine the host cell specificity or the ability to bind to new cell surface receptors. - While increased activity might lead to more mutations overall, the specific mechanism for increased host range would still involve a change in a gene coding for a surface protein responsible for cell binding. *Point mutations in the hemagglutinin gene* - **Hemagglutinin** is a surface glycoprotein explicitly found in **influenza viruses**, involved in binding to sialic acid receptors. HIV does not possess a hemagglutinin gene. - Therefore, mutations in this gene cannot explain changes in HIV's host range.

Question 17: An investigator is studying the mechanism of HIV infection in cells obtained from a human donor. The effect of a drug that impairs viral fusion and entry is being evaluated. This drug acts on a protein that is cleaved off of a larger glycosylated protein in the endoplasmic reticulum of the host cell. The protein that is affected by the drug is most likely encoded by which of the following genes?

A. gag
B. env (Correct Answer)
C. tat
D. pol
E. rev

Explanation: ***env*** - The **env (envelope) gene** of HIV encodes for the precursor protein **gp160**, which is then cleaved by host cellular proteases into **gp120** and **gp41** within the endoplasmic reticulum. - **gp120** and **gp41** together form the viral envelope glycoproteins responsible for viral binding to host cells and **fusion/entry**, making them the target of drugs that impair these processes. *gag* - The **gag (group-specific antigen) gene** encodes for structural proteins of the viral core, such as **p24 (capsid protein)**, p17 (matrix protein), and p7 (nucleocapsid protein). - These proteins are primarily involved in the assembly of new virions and do not directly mediate viral fusion and entry. *tat* - The **tat (trans-activator of transcription) gene** encodes a regulatory protein that significantly enhances the transcription of viral genes. - It plays a crucial role in the viral life cycle by increasing the efficiency of HIV gene expression, but it is not directly involved in viral fusion or entry. *pol* - The **pol (polymerase) gene** encodes for essential viral enzymes, including **reverse transcriptase**, integrase, and protease. - These enzymes are critical for converting viral RNA into DNA, integrating viral DNA into the host genome, and cleaving viral polyproteins, respectively, but they are not involved in mediating viral entry. *rev* - The **rev (regulator of virion expression) gene** encodes a regulatory protein that facilitates the transport of unspliced and partially spliced viral RNAs from the nucleus to the cytoplasm. - This transport is crucial for the synthesis of structural and enzymatic proteins and for packaging viral RNA into new virions, but it does not directly participate in viral fusion and entry.

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