A 55-year-old man comes to the physician because of a 2-month history of headaches, facial numbness, recurrent epistaxis, and a 5-kg (11-lb) weight loss. He recently immigrated from Hong Kong. Examination shows right-sided cervical lymphadenopathy. Endoscopy shows an exophytic nasopharyngeal mass. Histologic examination of a biopsy specimen of the mass shows sheets of undifferentiated cells with nuclear pleomorphism and abundant mitotic figures. The patient most likely acquired the causal pathogen of his nasopharyngeal mass via which of the following routes of transmission?
Q92
A 53-year-old man presents to an urgent care center with severe fever that began during the day along with muscle and joint pains. He states that he felt fine the day before but then developed a fever to 103°F (39.4°C) and had to leave work after which he developed a headache and body pains. The patient states that he was recently in South Asia for a business trip and was otherwise feeling well since returning 2 weeks ago. On exam, the patient’s temperature is 103.3°F (39.6°C), blood pressure is 110/84 mmHg, pulse is 94/min, and respirations are 14/min. On physical exam, the patient appears flushed and has a rash that blanches when touched. On laboratory workup, the pathogen was identified as an enveloped virus with an icosahedral capsid and had positive-sense, single-stranded linear RNA. Which of the following is the most likely cause of this patient's presentation?
Q93
A 12-year-old girl is brought to the physician because of fatigue, dyspnea, and mild chest pain on exertion for 1 week. She does not have a fever or a rash. She had an upper respiratory infection 3 weeks ago. She returned from summer camp in Colorado 3 days ago. She says they went hiking and camping as part of their activities. Her temperature is 36.9°C (98.4°F), heart rate is 96/min, and blood pressure is 106/74 mm Hg. Pulse oximetry on room air shows an oxygen saturation of 96%. Physical examination reveals jugular venous distention and 1+ pitting edema on both ankles. A few scattered inspiratory crackles are heard in the thorax and an S3 is heard at the apex. Abdominal examination is unremarkable. Her hemoglobin concentration is 11.6 g/dL, leukocyte count is 8900/mm3, and ESR is 10 mm/hr. An x-ray of the chest shows mild cardiac enlargement. Which of the following is the most likely cause of this patient's symptoms?
Q94
A 9-year-old boy is brought to the physician for evaluation of a 3-day history of fever, sore throat, and itchy, red eyes. His symptoms began while he was away at summer camp. His immunizations are not up-to-date. He appears ill. His temperature is 39.1°C (102.3°F). Physical examination shows erythema and edema of the conjunctivae and posterior pharyngeal wall. There is bilateral, tender, preauricular lymphadenopathy. Further evaluation shows infection with a DNA virus. Which of the following is the most likely causal pathogen?
Q95
Lipidator is a nonionic surfactant that is used to disrupt the lipid membranes of cells. This disruption of the lipid membrane results in the release of all of its cytoplasmic contents. Which of the following viruses would not be disrupted if treated with this detergent?
Q96
A 17-year-old girl presents to the family doctor with fever, headache, sore throat, dry cough, myalgias, and weakness. Her symptoms began acutely 2 days ago. On presentation, her blood pressure is 110/80 mm Hg, heart rate is 86/min, respiratory rate is 18/min, and temperature is 39.0°C (102.2°F). Physical examination reveals conjunctival injection and posterior pharyngeal wall erythema. Rapid diagnostic testing of a throat swab for influenza A+B shows positive results. Which of the following statements is true regarding the process of B cell clonal selection and the formation of specific IgG antibodies against influenza virus antigens in this patient?
Q97
A 38-year-old man presents to the physician with fever and malaise for 4 days. He has headaches and joint pain. A pruritic rash appeared on the trunk yesterday. He had blood in his ejaculate twice. His hearing has become partially impaired. There is no history of serious illnesses or the use of medications. Ten days ago, he traveled to Brazil where he spent most of the time outdoors in the evenings. He did not use any control measures for mosquito bites. His temperature is 38.2℃ (100.8℉); the pulse is 88/min; the respiratory rate is 13/min, and the blood pressure is 125/60 mm Hg. Conjunctival suffusion is noted. A maculopapular rash is present over the trunk and proximal extremities without the involvement of the palms or soles. Several joints of the hands are tender to palpation. The abdomen is soft with no organomegaly. A peripheral blood smear shows no pathogenic organisms. Which of the following is the most likely diagnosis?
Q98
A medical student is performing research on the properties of viruses in order to determine the transmission patterns of various organisms. He accidentally drops a rack of tubes and spills various virus samples on the benchtop. Upon seeing this, the laboratory technician wipes down the workbench with alcohol in order to clean up the spill. Which of the following organisms would most likely still be alive after this cleaning?
Q99
A scientist performed an experiment to produce hybrid viruses by mixing two different serotypes of influenza virus, H1N1 and H2N2, in a respiratory epithelium cell line. Several days later, the scientist collected the media and analyzed the viral progeny. She found the following serotypes of virus: H1N1, H2N2, H1N2, and H2N1. Which of the following terms best explains the appearance of new serotypes?
Q100
A previously healthy 24-year-old male is brought to the emergency department because of fevers, congestion, and chest pain for 3 days. The chest pain is exacerbated by deep inspiration. He takes no medications. His temperature is 37.5°C (99.5°F), blood pressure is 118/75 mm Hg, pulse is 130/min, and respirations are 12/min. He appears weak and lethargic. Cardiac examination shows a scratchy sound best heard along the left sternal border when the patient leans forward. There are crackles in both lung bases. Examination of the lower extremities shows pitting edema. Results of a rapid influenza test are negative. EKG shows diffuse ST-elevations with depressed PR interval. An echocardiogram shows left ventricular chamber enlargement with contractile dysfunction. Infection with which of the following pathogens is the most likely cause of this patient's symptoms?
Viruses US Medical PG Practice Questions and MCQs
Question 91: A 55-year-old man comes to the physician because of a 2-month history of headaches, facial numbness, recurrent epistaxis, and a 5-kg (11-lb) weight loss. He recently immigrated from Hong Kong. Examination shows right-sided cervical lymphadenopathy. Endoscopy shows an exophytic nasopharyngeal mass. Histologic examination of a biopsy specimen of the mass shows sheets of undifferentiated cells with nuclear pleomorphism and abundant mitotic figures. The patient most likely acquired the causal pathogen of his nasopharyngeal mass via which of the following routes of transmission?
A. Tick bite
B. Fecal-oral
C. Transfer of saliva (Correct Answer)
D. Sexual contact
E. Mother to baby
Explanation: ***Transfer of saliva***
- The clinical presentation with headaches, facial numbness, epistaxis, weight loss, cervical lymphadenopathy, and an exophytic nasopharyngeal mass, particularly in a patient from Hong Kong, is highly suggestive of **Nasopharyngeal Carcinoma (NPC)**.
- NPC is strongly associated with the **Epstein-Barr virus (EBV)**, which is commonly transmitted via **saliva** (e.g., through kissing or sharing utensils), leading to infectious mononucleosis in most cases but can cause NPC in susceptible individuals.
*Tick bite*
- Transmission via a **tick bite** is characteristic of diseases like **Lyme disease**, **Rocky Mountain spotted fever**, or **ehrlichiosis**, which present with different symptoms (e.g., rash, fever, widespread arthralgia) and are not associated with nasopharyngeal masses or EBV infection.
- This route is not relevant to the development of **nasopharyngeal carcinoma**.
*Fecal-oral*
- The **fecal-oral route** is responsible for transmitting pathogens like **Hepatitis A**, **poliovirus**, and **norovirus**, which primarily cause gastrointestinal or systemic infections distinct from nasopharyngeal carcinoma.
- This mode of transmission is not associated with **EBV** or the development of NPC.
*Sexual contact*
- **Sexual contact** is the primary mode of transmission for sexually transmitted infections (STIs) such as **HPV**, **HIV**, and **herpes simplex virus (HSV)**. While some of these (e.g., HPV) can cause cancers, they are generally not associated with nasopharyngeal carcinoma linked to EBV.
- The symptoms presented are not characteristic of a sexually transmitted disease.
*Mother to baby*
- **Mother-to-baby** (vertical) transmission occurs with infections like **HIV**, **syphilis**, or **CMV**, which cause congenital abnormalities or early childhood diseases. This route is not typically associated with the acquisition of EBV leading to nasopharyngeal carcinoma in a 55-year-old adult.
- While EBV can be transmitted vertically, it's not the primary route for the development of NPC in adulthood.
Question 92: A 53-year-old man presents to an urgent care center with severe fever that began during the day along with muscle and joint pains. He states that he felt fine the day before but then developed a fever to 103°F (39.4°C) and had to leave work after which he developed a headache and body pains. The patient states that he was recently in South Asia for a business trip and was otherwise feeling well since returning 2 weeks ago. On exam, the patient’s temperature is 103.3°F (39.6°C), blood pressure is 110/84 mmHg, pulse is 94/min, and respirations are 14/min. On physical exam, the patient appears flushed and has a rash that blanches when touched. On laboratory workup, the pathogen was identified as an enveloped virus with an icosahedral capsid and had positive-sense, single-stranded linear RNA. Which of the following is the most likely cause of this patient's presentation?
A. Dengue virus (Correct Answer)
B. Norovirus
C. Coronavirus
D. Marburg virus
E. Saint Louis encephalitis virus
Explanation: ***Dengue virus***
- The patient's presentation with **acute onset of high fever**, severe **muscle and joint pains** ("breakbone fever"), headache, and a **blanching rash** after recent travel to **South Asia** is highly characteristic of dengue fever.
- The description of the pathogen as an **enveloped virus** with an **icosahedral capsid** and **positive-sense, single-stranded linear RNA** perfectly matches the **Flaviviridae family** to which the dengue virus belongs.
- Among the options, only dengue virus and Saint Louis encephalitis virus have these exact structural characteristics (both are flaviviruses), but the **clinical presentation** with severe myalgia/arthralgia and travel to South Asia clearly points to dengue.
*Norovirus*
- Norovirus typically causes **gastroenteritis**, characterized primarily by **vomiting, diarrhea**, and abdominal cramps, which are not the dominant symptoms in this patient.
- While fever can occur, it's usually **mild** and not as prominent as the high fever and severe myalgia/arthralgia seen in dengue.
- **Structurally**, norovirus is **non-enveloped** (naked capsid), which does not match the pathogen description.
*Coronavirus*
- Coronaviruses are associated with **respiratory illnesses** (e.g., common cold, SARS, MERS, COVID-19) causing symptoms like cough, shortness of breath, and sore throat.
- While fever and body aches can occur, the **severe joint pains** and typical rash are not hallmarks of coronavirus infections.
- **Structurally**, coronaviruses have **helical nucleocapsid symmetry**, not icosahedral, which excludes this option based on the pathogen description.
*Marburg virus*
- Marburg virus causes a severe **hemorrhagic fever** with symptoms including high fever, severe headache, malaise, followed by gastrointestinal symptoms, and eventually **hemorrhagic manifestations** (e.g., bleeding from orifices, petechiae, purpura).
- The patient's presentation does not describe any hemorrhagic signs, and the rash is blanching, not petechial or purpuric.
- **Structurally**, Marburg is a filovirus with **helical symmetry** and **negative-sense ssRNA**, not positive-sense with icosahedral capsid, which excludes this option.
*Saint Louis encephalitis virus*
- Saint Louis encephalitis virus causes a **neuroinvasive disease** characterized by encephalitis, presenting with altered mental status, seizures, and focal neurological deficits, although some patients may have milder fever and headache.
- While it shares the **same viral structure** as dengue (both are flaviviruses with enveloped, icosahedral, (+)ssRNA), the **clinical presentation** differs significantly—this patient lacks neurological symptoms.
- The prominent **severe myalgia, arthralgia**, typical blanching rash, and **travel history to dengue-endemic South Asia** distinguish dengue from Saint Louis encephalitis.
Question 93: A 12-year-old girl is brought to the physician because of fatigue, dyspnea, and mild chest pain on exertion for 1 week. She does not have a fever or a rash. She had an upper respiratory infection 3 weeks ago. She returned from summer camp in Colorado 3 days ago. She says they went hiking and camping as part of their activities. Her temperature is 36.9°C (98.4°F), heart rate is 96/min, and blood pressure is 106/74 mm Hg. Pulse oximetry on room air shows an oxygen saturation of 96%. Physical examination reveals jugular venous distention and 1+ pitting edema on both ankles. A few scattered inspiratory crackles are heard in the thorax and an S3 is heard at the apex. Abdominal examination is unremarkable. Her hemoglobin concentration is 11.6 g/dL, leukocyte count is 8900/mm3, and ESR is 10 mm/hr. An x-ray of the chest shows mild cardiac enlargement. Which of the following is the most likely cause of this patient's symptoms?
A. Coxsackie virus infection (Correct Answer)
B. Rhinovirus infection
C. Borrelia burgdorferi infection
D. Giant cell myocarditis
E. Acute rheumatic fever
Explanation: ***Coxsackie virus infection***
- The patient's symptoms (fatigue, dyspnea, chest pain, S3 gallop, jugular venous distention, edema, crackles, and cardiac enlargement) suggest **myocarditis** and **congestive heart failure**.
- **Coxsackie B virus** is the most common viral cause of myocarditis, often following an upper respiratory infection.
- The **temporal relationship** (symptoms developing 2-3 weeks after URI) is classic for viral myocarditis.
*Rhinovirus infection*
- **Rhinovirus** typically causes the common cold and does not usually lead to severe cardiac complications like myocarditis and heart failure.
- While it can cause an upper respiratory infection, it lacks the typical association with later development of **myocardial inflammation**.
*Borrelia burgdorferi infection*
- **Borrelia burgdorferi** (Lyme disease) can cause **Lyme carditis**, but Lyme disease is uncommon in Colorado (endemic in Northeast and Upper Midwest US).
- Lyme carditis typically presents as **AV block or pericarditis**, not diffuse myocarditis with dilated cardiomyopathy and heart failure.
- The patient lacks other key features of Lyme disease, such as a **bull's-eye rash (erythema migrans)**, joint pain, or neurological symptoms.
*Giant cell myocarditis*
- **Giant cell myocarditis** is a rare and aggressive form of myocarditis, often presenting with rapid onset heart failure and arrhythmias.
- While it causes severe cardiac dysfunction, it's less common in this age group and usually has a more fulminant course requiring urgent diagnosis and immunosuppressive therapy.
*Acute rheumatic fever*
- **Acute rheumatic fever** typically follows a **Streptococcal pharyngitis** and can cause pancarditis (myocarditis, pericarditis, endocarditis).
- However, the absence of fever, migratory arthritis, skin rash (erythema marginatum), or chorea makes acute rheumatic fever less likely in this case.
Question 94: A 9-year-old boy is brought to the physician for evaluation of a 3-day history of fever, sore throat, and itchy, red eyes. His symptoms began while he was away at summer camp. His immunizations are not up-to-date. He appears ill. His temperature is 39.1°C (102.3°F). Physical examination shows erythema and edema of the conjunctivae and posterior pharyngeal wall. There is bilateral, tender, preauricular lymphadenopathy. Further evaluation shows infection with a DNA virus. Which of the following is the most likely causal pathogen?
A. Adenovirus (Correct Answer)
B. Picornavirus
C. Human herpes virus 4
D. Paramyxovirus
E. Parvovirus
Explanation: ***Adenovirus***
- The constellation of **fever**, **sore throat**, **conjunctivitis** (itchy, red eyes), and **preauricular lymphadenopathy** is classic for **pharyngoconjunctival fever**, which is most commonly caused by adenovirus.
- Adenoviruses are **non-enveloped DNA viruses** that frequently cause respiratory and ocular infections, especially in children and in crowded settings such as summer camps.
- The **preauricular lymphadenopathy** is a key finding that distinguishes adenoviral conjunctivitis from other causes.
*Picornavirus*
- Picornaviruses (e.g., rhinoviruses, enteroviruses) are **RNA viruses**, not DNA viruses, which contradicts the information given in the prompt.
- While enteroviruses can cause hand-foot-and-mouth disease or herpangina, they typically do not present with prominent **pharyngoconjunctival fever** symptoms like those described.
*Human herpes virus 4*
- Human herpesvirus 4, also known as **Epstein-Barr virus (EBV)**, causes **infectious mononucleosis**, characterized by fatigue, fever, **lymphadenopathy** (often cervical), and **pharyngitis**, but typically not conjunctivitis.
- While EBV is a DNA virus, the clinical picture with prominent conjunctivitis and preauricular lymphadenopathy is less characteristic of mononucleosis.
*Paramyxovirus*
- Paramyxoviruses (e.g., measles, mumps) are **RNA viruses**, which contradicts the prompt's finding of a DNA virus.
- While measles can cause conjunctivitis, it presents with a characteristic **rash**, **Koplik spots**, and more severe systemic symptoms not described here.
*Parvovirus*
- Parvovirus B19 is a **DNA virus** that causes **erythema infectiosum** (fifth disease), characterized by a "slapped cheek" rash and lacy rash on the extremities, often preceded by mild flu-like symptoms.
- It does not typically cause the combination of severe pharyngitis, conjunctivitis, and preauricular lymphadenopathy seen in this case.
Question 95: Lipidator is a nonionic surfactant that is used to disrupt the lipid membranes of cells. This disruption of the lipid membrane results in the release of all of its cytoplasmic contents. Which of the following viruses would not be disrupted if treated with this detergent?
A. Flavivirus
B. Herpesvirus
C. Picornavirus (Correct Answer)
D. HIV
E. Hepadnavirus
Explanation: ***Picornavirus***
- Picornaviruses are **non-enveloped viruses**, meaning they lack a lipid outer membrane.
- As they do not possess a lipid membrane, they would not be susceptible to disruption by a detergent like Lipidator, which targets lipid bilayers.
*Flavivirus*
- Flaviviruses are **enveloped viruses**, possessing an outer lipid membrane derived from the host cell.
- This lipid envelope would be disrupted by a nonionic surfactant, leading to the inactivation of the virus.
*Herpesvirus*
- Herpesviruses are also **enveloped viruses**, characterized by a complex lipid-containing outer membrane.
- Their envelopes are susceptible to disruption by detergents, which would compromise viral integrity and infectivity.
*HIV*
- HIV is an **enveloped retrovirus**, meaning it has a lipid bilayer that surrounds its capsid.
- This lipid envelope is essential for its infectious cycle and would be easily destroyed by a detergent, rendering the virus non-functional.
*Hepadnavirus*
- Hepadnaviruses, such as Hepatitis B virus, are **enveloped viruses** that contain an outer lipid membrane crucial for their structure and entry into host cells.
- A detergent like Lipidator would disrupt this lipid envelope, thereby inactivating the virus.
Question 96: A 17-year-old girl presents to the family doctor with fever, headache, sore throat, dry cough, myalgias, and weakness. Her symptoms began acutely 2 days ago. On presentation, her blood pressure is 110/80 mm Hg, heart rate is 86/min, respiratory rate is 18/min, and temperature is 39.0°C (102.2°F). Physical examination reveals conjunctival injection and posterior pharyngeal wall erythema. Rapid diagnostic testing of a throat swab for influenza A+B shows positive results. Which of the following statements is true regarding the process of B cell clonal selection and the formation of specific IgG antibodies against influenza virus antigens in this patient?
A. Deletions are the most common form of mutations that occur during somatic hypermutation in this patient’s B cells.
B. V(D)J recombination results in the formation of a B cell clone, which produces specific antibodies against influenza virus antigens.
C. During antibody class switching, variable region of antibody heavy chain changes, and the constant one stays the same.
D. The first event that occurs after B lymphocyte activation is V(D)J recombination.
E. After somatic hypermutation, only a small proportion of B cell antigen receptors have increased affinity for the antigen. (Correct Answer)
Explanation: ***After somatic hypermutation, only a small amount of B cells antigen receptors have increased affinity for the antigen.***
* **Somatic hypermutation** introduces random mutations in the **variable regions** of immunoglobulin genes, leading to a spectrum of B cells with varying affinities for the antigen; only a small fraction will have significantly **increased affinity**.
* B cells with higher-affinity receptors are preferentially selected to proliferate and differentiate through a process called **affinity maturation**, ensuring a more effective immune response.
*Deletions are the most common form of mutations that occur during somatic hypermutation in this patient’s B cells.*
* **Point mutations**, specifically **substitutions**, are the predominant type of mutations introduced during **somatic hypermutation**, not deletions.
* These point mutations lead to subtle changes in the **antibody binding site**, enabling refinement of antigen affinity.
*V(D)J recombination results in the formation of a B cell clone, which produces specific antibodies against influenza virus antigens.*
* **V(D)J recombination** occurs *before* antigen exposure and is responsible for generating the diverse repertoire of B cell receptors; it does not directly "form a B cell clone" after antigen binding.
* **Clonal selection**—the proliferation of a specific B cell upon antigen recognition—is what forms the clone responsible for producing specific antibodies.
*During antibody class switching, variable region of antibody heavy chain changes, and the constant one stays the same.*
* During **antibody class switching**, the **constant region** of the heavy chain gene changes (e.g., from IgM to IgG), while the **variable region** remains the same.
* This allows the B cell to produce antibodies with different effector functions (e.g., complement activation, opsonization) but with the same **antigen specificity**.
*The first event that occurs after B lymphocyte activation is V(D)J recombination.*
* **V(D)J recombination** is a process that occurs during **B cell development** in the bone marrow, *before* the B cell encounters an antigen and becomes activated.
* After **B lymphocyte activation** by an antigen, subsequent events include proliferation, differentiation into plasma cells and memory cells, **somatic hypermutation**, and **class switching**.
Question 97: A 38-year-old man presents to the physician with fever and malaise for 4 days. He has headaches and joint pain. A pruritic rash appeared on the trunk yesterday. He had blood in his ejaculate twice. His hearing has become partially impaired. There is no history of serious illnesses or the use of medications. Ten days ago, he traveled to Brazil where he spent most of the time outdoors in the evenings. He did not use any control measures for mosquito bites. His temperature is 38.2℃ (100.8℉); the pulse is 88/min; the respiratory rate is 13/min, and the blood pressure is 125/60 mm Hg. Conjunctival suffusion is noted. A maculopapular rash is present over the trunk and proximal extremities without the involvement of the palms or soles. Several joints of the hands are tender to palpation. The abdomen is soft with no organomegaly. A peripheral blood smear shows no pathogenic organisms. Which of the following is the most likely diagnosis?
A. Rocky Mountain spotted fever
B. Chagas disease
C. Whipple’s disease
D. Zika virus disease (Correct Answer)
E. Malaria
Explanation: ***Zika virus disease***
- The patient's travel to **Brazil**, **mosquito exposure**, fever, malaise, headache, arthralgia, and **maculopapular rash** (without palm/sole involvement) are classic symptoms of Zika virus.
- Additional findings like **conjunctival suffusion**, **hematospermia**, and **hearing impairment** are consistent with atypical presentations or complications of Zika.
*Rocky Mountain spotted fever*
- While it presents with fever, headache, and rash, the rash typically involves the **palms and soles** and can be **petechial**, which is not described.
- This disease is common in the **southeastern and south-central US**, not typically Brazil, and is transmitted by ticks, not mosquitoes.
*Chagas disease*
- This is a parasitic disease (Trypanosoma cruzi) transmitted by **reduviid bugs** (kissing bugs) in Central and South America.
- Acute symptoms often include a **chagoma** (local swelling at the bite site) or **Romaña's sign** (periorbital swelling), followed by chronic cardiac or gastrointestinal involvement, which don't fit the current presentation.
*Whipple’s disease*
- This rare systemic bacterial infection (Tropheryma whipplei) primarily affects the **gastrointestinal tract**, leading to malabsorption, diarrhea, and weight loss.
- While it can cause arthralgia, fever, and neurological symptoms, the prominent rash, conjunctival suffusion, and recent travel/mosquito exposure are not characteristic.
*Malaria*
- Malaria presents with cyclical **fevers** and **chills**, headache, and myalgia, often with **anemia** and **splenomegaly**.
- A **rash is uncommon** in malaria, and the other specific symptoms like conjunctival suffusion, hematospermia, and hearing impairment are not typical.
Question 98: A medical student is performing research on the properties of viruses in order to determine the transmission patterns of various organisms. He accidentally drops a rack of tubes and spills various virus samples on the benchtop. Upon seeing this, the laboratory technician wipes down the workbench with alcohol in order to clean up the spill. Which of the following organisms would most likely still be alive after this cleaning?
A. Coronavirus and herpesvirus
B. Adenovirus and coronavirus
C. Coronavirus and rhinovirus
D. Adenovirus and rhinovirus (Correct Answer)
E. Adenovirus and herpesvirus
Explanation: ***Adenovirus and rhinovirus***
- **Adenovirus** and **rhinovirus** are both **non-enveloped viruses**, meaning they lack a lipid envelope.
- Non-enveloped viruses are generally **more resistant** to inactivation by alcohol-based disinfectants because alcohol primarily acts by dissolving lipid envelopes.
*Coronavirus and herpesvirus*
- Both **coronavirus** and **herpesvirus** are **enveloped viruses**.
- **Enveloped viruses** are highly susceptible to destruction by alcohol, which disrupts their lipid envelope.
*Adenovirus and coronavirus*
- While **adenovirus** is non-enveloped and resistant, **coronavirus** is enveloped and thus susceptible to alcohol.
- Therefore, the coronavirus component of this pair would likely be inactivated.
*Coronavirus and rhinovirus*
- While **rhinovirus** is non-enveloped and resistant, **coronavirus** is enveloped and thus susceptible to alcohol.
- As a result, the coronavirus would likely be destroyed by the alcohol.
*Adenovirus and herpesvirus*
- While **adenovirus** is non-enveloped and resistant, **herpesvirus** is enveloped and susceptible to alcohol.
- The herpesvirus would likely be inactivated by the alcohol cleaning.
Question 99: A scientist performed an experiment to produce hybrid viruses by mixing two different serotypes of influenza virus, H1N1 and H2N2, in a respiratory epithelium cell line. Several days later, the scientist collected the media and analyzed the viral progeny. She found the following serotypes of virus: H1N1, H2N2, H1N2, and H2N1. Which of the following terms best explains the appearance of new serotypes?
A. Phenotypic mixing
B. Complementation
C. Reassortment (Correct Answer)
D. Transformation
E. Recombination
Explanation: ***Reassortment***
- **Reassortment** occurs in viruses with **segmented genomes**, like influenza, when a host cell is co-infected with two different viral strains.
- During replication, the progeny viruses can package segments from either parent, leading to novel combinations of surface proteins (**H** and **N** antigens), as seen with the emergence of H1N2 and H2N1.
*Phenotypic mixing*
- **Phenotypic mixing** involves the packaging of the genome of one virus into the capsid or envelope proteins derived from another virus, without genetic exchange.
- While progeny viruses might temporarily display characteristics of both parents, their genetic material remains unchanged, so subsequent generations would revert to the original serotype unless continuous co-infection occurs.
*Complementation*
- **Complementation** happens when one virus provides a functional protein that is deficient in another co-infecting virus, allowing the deficient virus to replicate.
- This process does not lead to the formation of new hybrid serotypes but rather allows a 'defective' virus to replicate alongside a 'helper' virus.
*Transformation*
- **Transformation** in microbiology typically refers to the uptake of foreign genetic material (DNA) by a bacterial cell, altering its genetic makeup.
- In virology, it can also refer to the process by which some viruses induce uncontrolled cell growth in eukaryotic cells, leading to oncogenesis, which is unrelated to the formation of hybrid serotypes.
*Recombination*
- **Recombination** involves the exchange of genetic material between two homologous chromosomes or DNA molecules, leading to a new genetic sequence.
- While it results in new genetic combinations, the term **reassortment** is specifically used for the exchange of entire genome segments characteristic of viruses like influenza.
Question 100: A previously healthy 24-year-old male is brought to the emergency department because of fevers, congestion, and chest pain for 3 days. The chest pain is exacerbated by deep inspiration. He takes no medications. His temperature is 37.5°C (99.5°F), blood pressure is 118/75 mm Hg, pulse is 130/min, and respirations are 12/min. He appears weak and lethargic. Cardiac examination shows a scratchy sound best heard along the left sternal border when the patient leans forward. There are crackles in both lung bases. Examination of the lower extremities shows pitting edema. Results of a rapid influenza test are negative. EKG shows diffuse ST-elevations with depressed PR interval. An echocardiogram shows left ventricular chamber enlargement with contractile dysfunction. Infection with which of the following pathogens is the most likely cause of this patient's symptoms?
A. Orthomyxovirus
B. Flavivirus
C. Togavirus
D. Paramyxovirus
E. Picornavirus (Correct Answer)
Explanation: ***Picornavirus***
- This patient presents with **myopericarditis** (concurrent myocarditis and pericarditis), which is particularly characteristic of **picornavirus** infection, specifically **coxsackievirus B**.
- **Pericarditis features:** Pleuritic chest pain, pericardial friction rub (scratchy sound), diffuse ST elevations with PR depression on EKG.
- **Myocarditis features:** Left ventricular enlargement with contractile dysfunction, signs of heart failure (pitting edema, tachycardia, weakness).
- **Coxsackievirus B** is the **most common viral cause** of acute myocarditis and pericarditis in previously healthy young adults, often following a prodrome of respiratory or gastrointestinal symptoms.
*Orthomyxovirus*
- **Orthomyxoviruses** (influenza virus) can cause myocarditis, but the **negative rapid influenza test** makes this diagnosis unlikely in this case.
- While influenza commonly causes respiratory symptoms and fever, the combination of classic pericarditis findings with severe myocarditis points more strongly toward coxsackievirus infection.
*Flavivirus*
- **Flaviviruses** (e.g., Dengue, Zika, West Nile) typically present with **fever, arthralgias, rash**, or **neurological symptoms**, which are not described here.
- Cardiac complications from flaviviruses are rare and would typically occur in the context of their characteristic systemic manifestations. They are not a common cause of acute myopericarditis.
*Togavirus*
- **Togaviruses** include **rubella virus** and **alphaviruses** (e.g., Chikungunya). Rubella presents with diffuse rash and lymphadenopathy, while alphaviruses cause prominent arthralgias.
- While rubella can rarely cause myocarditis, it is not a common cause of acute myopericarditis, and the characteristic rash and joint symptoms are absent in this patient.
*Paramyxovirus*
- **Paramyxoviruses** include measles, mumps, RSV, and parainfluenza. **Mumps virus** is the paramyxovirus most associated with myocarditis.
- However, mumps typically presents with characteristic **parotitis** (parotid gland swelling), which is absent in this patient, making it less likely than coxsackievirus as the cause of this myopericarditis presentation.
