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?
Q2
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?
Q3
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?
Q4
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?
Q5
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?
Q6
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?
Q7
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?
Q8
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?
Q9
A 36-year-old woman with HIV comes to the physician because of a 3-day history of pain and watery discharge in her left eye. She also has blurry vision and noticed that she is more sensitive to light. Her right eye is asymptomatic. She had an episode of shingles 7 years ago. She was diagnosed with HIV 5 years ago. She admits that she takes her medication inconsistently. She wears contact lenses. Current medications include abacavir, lamivudine, efavirenz, and a nutritional supplement. Her temperature is 37°C (98.6°F), pulse is 89/min, and blood pressure is 110/70 mm Hg. Examination shows conjunctival injection of the left eye. Visual acuity is 20/20 in the right eye and 20/80 in the left eye. Extraocular movements are normal. Her CD4+ T-lymphocyte count is 90/mm3. A photograph of the left eye after fluorescein administration is shown. Which of the following is the most likely diagnosis?
Q10
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?
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 36-year-old woman with HIV comes to the physician because of a 3-day history of pain and watery discharge in her left eye. She also has blurry vision and noticed that she is more sensitive to light. Her right eye is asymptomatic. She had an episode of shingles 7 years ago. She was diagnosed with HIV 5 years ago. She admits that she takes her medication inconsistently. She wears contact lenses. Current medications include abacavir, lamivudine, efavirenz, and a nutritional supplement. Her temperature is 37°C (98.6°F), pulse is 89/min, and blood pressure is 110/70 mm Hg. Examination shows conjunctival injection of the left eye. Visual acuity is 20/20 in the right eye and 20/80 in the left eye. Extraocular movements are normal. Her CD4+ T-lymphocyte count is 90/mm3. A photograph of the left eye after fluorescein administration is shown. Which of the following is the most likely diagnosis?
A. Pseudomonas keratitis
B. Fusarium keratitis
C. Neurotrophic keratopathy
D. Herpes simplex keratitis (Correct Answer)
E. Herpes zoster keratitis
Explanation: ***Herpes simplex keratitis***
- The fluorescein staining shows a **dendritic ulcer**, which is **pathognomonic** for herpes simplex keratitis.
- The patient's **immunosuppressed state** due to HIV with a low CD4+ count (90/mm3) makes her susceptible to opportunistic viral infections like HSV.
*Pseudomonas keratitis*
- Often seen in **contact lens wearers**, but it typically presents with a rapidly progressive, painful, circumferential stromal infiltrate, and often a **hypopyon**, which are not described.
- The classic dendritic pattern on fluorescein staining is not characteristic of bacterial keratitis.
*Fusarium keratitis*
- This is a **fungal infection** often associated with contact lens use, especially after corneal trauma involving vegetable matter.
- It presents with feathery, elevated infiltrates and satellite lesions, which differ from the dendritic pattern seen.
*Neurotrophic keratopathy*
- This condition results from **corneal denervation**, leading to impaired epithelial healing.
- While it can cause persistent epithelial defects, it typically appears as an oval or irregular epithelial defect without the distinct dendritic branching pattern.
*Herpes zoster keratitis*
- While caused by a herpesvirus (VZV), it typically presents with a characteristic **pseudodendrite** (not true dendrite) that stains poorly with fluorescein and is associated with a **rash in the V1 dermatome**.
- The patient's history of shingles 7 years ago is less relevant than the current classic dendritic pattern for HSV.
Question 10: 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.