A 7-year-old boy is brought to the emergency department because of photophobia and pruritus on the periocular area of the right eye for the last 2 days. He also had crusts over the eyelashes of the right eye that morning. The boy has a history of asthma and atopic dermatitis. His medications include inhaled steroids and salbutamol. Vital signs are within normal limits. Physical examination shows conjunctival injection and redness in the affected eye, as well as a watery discharge from it. There are multiple vesicles with an erythematous base located on the upper and lower eyelids. Visual acuity is within normal limits. Which of the following is the most likely cause?
Q62
A 38-year-old woman presented to a clinic because of dementia, hemiparesis, ataxia, aphasia, and dysarthria that developed over the last 5 days. She had a 15-year history of intravenous drug abuse and was treated for fever, cough, and shortness of breath before the onset of neurological symptoms. Her MRI shows multiple white matter lesions, as seen in the picture. Over the course of 2 weeks, the patient's condition worsens. Despite aggressive treatment, she lapses into a coma and dies. At autopsy, histologic examination of her brain tissue reveals gigantic, deformed astrocytes and oligodendrocytes with abnormal nuclei. Which of the following is the most likely cause of this woman's neurological symptoms?
Q63
A 24-year-old man presents to the clinic with the complaint of a new rash. The lesions are not bothersome, but he is worried as he has never seen anything like this on his body. Upon further questioning the patient states has been generally healthy except for a one time "horrible" flu-like episode two months ago in June. He has since gotten better. On physical exam the following rash is observed (Figure 1). What is the cause of this patient's rash?
Q64
A 3-year-old boy presents to an urgent care clinic with his mother. She states that his behavior has been lethargic for the past 3 days. She also notes that he has had a runny nose, mild cough, and sore throat during this time. She does not believe that he has been febrile. His temperature is 99.1°F (37.2°C), blood pressure is 105/67 mmHg, pulse is 100/min, respirations are 18/min, and SpO2 97% on room air. Which nucleic acid structure most accurately describes the most likely virus responsible for this boy’s clinical condition?
Q65
A 52-year-old woman presents to the clinic with several days of vomiting and diarrhea. She also complains of headaches, muscle aches, and fever, but denies tenesmus, urgency, and bloody diarrhea. Past medical history is insignificant. When asked about any recent travel she says that she just came back from a cruise ship vacation. Her temperature is 37°C (98.6° F), respiratory rate is 15/min, pulse is 67/min, and blood pressure is 122/98 mm Hg. Physical examination is non-contributory. Microscopic examination of the stool is negative for ova or parasites. What is the most likely diagnosis?
Q66
A group of scientists is conducting an experiment on the human cells involved in the immune response. They genetically modify B cells so they do not express the cluster of differentiation 21 (CD21) on their cell surfaces. The pathogenesis of which of the following organisms would most likely be affected by this genetic modification?
Q67
An investigator studying patients with symptoms of arthritis detects a nonenveloped virus with a single-stranded DNA genome in the serum of a pregnant patient. Fetal infection with this pathogen is most likely to cause which of the following manifestations?
Q68
A 32-year-old man with a past medical history significant for HIV and a social history of multiple sexual partners presents with new skin findings. His past surgical and family histories are noncontributory. The patient's blood pressure is 129/75 mm Hg, the pulse is 66/min, the respiratory rate is 16/min, and the temperature is 37.5°C (99.6°F). Physical examination reveals numerous painless skin-colored, flattened and papilliform lesions along the penile shaft and around the anus on physical exam. The application of 5% acetic acid solution causes the lesions to turn white. What is the etiology of these lesions?
Q69
An investigator studying influenza virus variability isolates several distinct influenza virus strains from the respiratory secretions of a study subject. Mass spectrometry analysis of one strain shows that it expresses neuraminidase on its surface. Subsequent sequencing of this strain shows that its genome lacks the neuraminidase gene. Which of the following is the most likely explanation for this finding?
Q70
An investigator studying viral mutation isolates a virus strain from the gastric contents of an infant with gastroenteritis. This virus has a nonenveloped RNA genome with 11 segments and an icosahedral symmetrical capsid. The investigator finds that if 2 strains of this virus coinfect a single host cell, some of the resulting viral progeny have genome segments derived from both parental viruses. The observed phenomenon is most likely also seen in which of the following viral families?
Viruses US Medical PG Practice Questions and MCQs
Question 61: A 7-year-old boy is brought to the emergency department because of photophobia and pruritus on the periocular area of the right eye for the last 2 days. He also had crusts over the eyelashes of the right eye that morning. The boy has a history of asthma and atopic dermatitis. His medications include inhaled steroids and salbutamol. Vital signs are within normal limits. Physical examination shows conjunctival injection and redness in the affected eye, as well as a watery discharge from it. There are multiple vesicles with an erythematous base located on the upper and lower eyelids. Visual acuity is within normal limits. Which of the following is the most likely cause?
A. Adenovirus
B. Molluscum contagiosum virus
C. Herpes simplex virus (Correct Answer)
D. Chlamydia trachomatis
E. Staphylococcus aureus
Explanation: ***Herpes simplex virus***
- The presence of **vesicles with an erythematous base** on the eyelids is highly characteristic of a **herpes simplex virus (HSV)** infection.
- In a child with a history of **atopic dermatitis**, there is an increased risk for severe or disseminated HSV infections, including **eczema herpeticum**.
*Adenovirus*
- Adenovirus typically causes **epidemic keratoconjunctivitis**, characterized by **follicular conjunctivitis** and preauricular lymphadenopathy, not vesicular lesions.
- While it can cause watery discharge and conjunctival injection, the absence of vesicles makes it less likely than HSV.
*Molluscum contagiosum virus*
- Molluscum contagiosum causes **dome-shaped, pearly papules with central umbilication**, which are distinct from the vesicles described.
- Lesions are usually chronic and can lead to follicular conjunctivitis through viral shedding into the conjunctival sac, but not acute vesicular eruptions.
*Chlamydia trachomatis*
- **Chlamydia trachomatis** is a common cause of **bacterial conjunctivitis** in newborns and sexually active adults, presenting as a **mucopurulent discharge**.
- While chronic forms can cause scarring and pannus, it does not typically cause acute vesicular lesions on the eyelids.
*Staphylococcus aureus*
- **Staphylococcus aureus** is a common cause of **bacterial conjunctivitis**, characterized by **purulent discharge** and crusting, and can cause cellulitis or abscesses.
- However, it does not typically cause the distinct **vesicular lesions** described on the eyelids.
Question 62: A 38-year-old woman presented to a clinic because of dementia, hemiparesis, ataxia, aphasia, and dysarthria that developed over the last 5 days. She had a 15-year history of intravenous drug abuse and was treated for fever, cough, and shortness of breath before the onset of neurological symptoms. Her MRI shows multiple white matter lesions, as seen in the picture. Over the course of 2 weeks, the patient's condition worsens. Despite aggressive treatment, she lapses into a coma and dies. At autopsy, histologic examination of her brain tissue reveals gigantic, deformed astrocytes and oligodendrocytes with abnormal nuclei. Which of the following is the most likely cause of this woman's neurological symptoms?
A. A double-stranded circular DNA virus (Correct Answer)
B. A proteinaceous infectious particle
C. Autoimmune attack of myelin sheaths
D. An autosomal recessive lysosomal storage disease
E. A single-stranded linear RNA virus
Explanation: ***A double-stranded circular DNA virus***
- The clinical presentation of rapidly progressive multifocal neurological deficits in an immunocompromised patient (due to IV drug abuse and recent infection) is highly suggestive of **Progressive Multifocal Leukoencephalopathy (PML)**.
- PML is caused by the **JC virus (JCV)**, a **double-stranded circular DNA virus**, which infects and destroys **oligodendrocytes**, leading to demyelination and the characteristic white matter lesions and bizarre astrocytes seen on histology. At autopsy, histological examination reveals **gigantic, deformed astrocytes and oligodendrocytes with abnormal nuclei** which is a classic finding in PML.
*A proteinaceous infectious particle*
- A proteinaceous infectious particle refers to a **prion**, which causes spongiform encephalopathies like **Creutzfeldt-Jakob disease (CJD)**.
- While CJD causes rapidly progressive dementia, the typical MRI findings are **cortical ribboning** and **basal ganglia hyperintensity**, and the characteristic histological feature is **spongiform change**, not deformed glial cells, and there is no typical association with IV drug abuse.
*Autoimmune attack of myelin sheaths*
- This describes conditions like **multiple sclerosis (MS)**, which also involve demyelination and white matter lesions.
- However, MS typically has a relapsing-remitting or progressive course over years, not days, and histological findings show inflammation and demyelination with astrogliosis, but not the specific bizarre and gigantic glial cells characteristic of PML, and is not directly linked to IV drug abuse in this manner.
*An autosomal recessive lysosomal storage disease*
- Lysosomal storage diseases (e.g., Krabbe disease, Tay-Sachs) cause neurological dysfunction due to enzyme deficiencies leading to substrate accumulation.
- These are typically **genetic conditions** presenting in childhood or early adulthood with a more chronic and progressive course, and they would not usually manifest as an acute, rapidly fatal illness in a 38-year-old with a history of IV drug abuse.
*A single-stranded linear RNA virus*
- Many neurotropic viruses are single-stranded linear RNA viruses (e.g., HIV,Measles virus causing SSPE, rabies virus).
- While HIV can cause dementia (HIV-associated dementia), the rapid progression with multiple focal neurological deficits and specific histological findings of bizarre astrocytes and oligodendrocytes points more specifically to PML, which is often seen in advanced HIV infection but is caused by JCV (a DNA virus), not HIV itself. Measles causing SSPE is a much slower process.
Question 63: A 24-year-old man presents to the clinic with the complaint of a new rash. The lesions are not bothersome, but he is worried as he has never seen anything like this on his body. Upon further questioning the patient states has been generally healthy except for a one time "horrible" flu-like episode two months ago in June. He has since gotten better. On physical exam the following rash is observed (Figure 1). What is the cause of this patient's rash?
A. Molluscum contagiosum virus (Correct Answer)
B. Varicella zoster virus (VZV)
C. Human immunodeficiency virus (HIV)
D. Human papilloma virus (HPV)
E. Staphylococcus aureus cellulitis
Explanation: ***Molluscum contagiosum virus***
- The image displays characteristic **umbilicated papules**, which are pathognomonic for **molluscum contagiosum**, a viral skin infection.
- The history of a "horrible" flu-like episode two months prior could suggest recent **immunocompromise** or an acute retroviral syndrome, making the patient more susceptible to or exacerbating molluscum contagiosum.
*Varicella zoster virus (VZV)*
- VZV typically causes **vesicles on an erythematous base** that evolve into **crusted lesions** in a dermatomal distribution (shingles) or widespread (chickenpox), which is not consistent with the described rash.
- While VZV can reactivate due to immunocompromise, the morphology of the rash does not fit a typical VZV presentation like chickenpox or shingles.
*Human immunodeficiency virus (HIV)*
- While **HIV infection** can lead to various skin manifestations, including increased susceptibility to molluscum contagiosum, it is not the direct cause of the rash itself.
- The flu-like episode could represent acute retroviral syndrome, but HIV itself does not cause this specific papular rash, rather it creates an environment for opportunistic infections or conditions like molluscum.
*Human papilloma virus (HPV)*
- HPV causes **warts** (verrucae) which are typically **rough, hyperkeratotic papules** or lesions with a cauliflower-like appearance, a different morphology than seen in the image.
- While HPV infections are common, the characteristic smooth, umbilicated papules seen here are not consistent with typical HPV-induced lesions.
*Staphylococcus aureus cellulitis*
- **Cellulitis** is a **bacterial skin infection** characterized by localized areas of **redness, warmth, swelling, and pain**, often with poorly defined borders, which are absent in this presentation.
- **Staphylococcus aureus** can cause various skin infections, but not the distinct umbilicated papules observed in the image; these lesions are viral, not bacterial.
Question 64: A 3-year-old boy presents to an urgent care clinic with his mother. She states that his behavior has been lethargic for the past 3 days. She also notes that he has had a runny nose, mild cough, and sore throat during this time. She does not believe that he has been febrile. His temperature is 99.1°F (37.2°C), blood pressure is 105/67 mmHg, pulse is 100/min, respirations are 18/min, and SpO2 97% on room air. Which nucleic acid structure most accurately describes the most likely virus responsible for this boy’s clinical condition?
A. Double-stranded DNA
B. Single-stranded, negative-sense RNA
C. Double-stranded RNA
D. Single-stranded DNA
E. Single-stranded, positive-sense RNA (Correct Answer)
Explanation: ***Single-stranded, positive-sense RNA***
- The constellation of a runny nose, mild cough, sore throat, and lethargy in a 3-year-old child strongly suggests a **common cold** (viral upper respiratory infection).
- The most frequent causes of the common cold are **rhinoviruses** and **coronaviruses**, both of which possess **single-stranded, positive-sense RNA genomes**.
*Double-stranded DNA*
- Viruses with double-stranded DNA genomes include **adenoviruses** and **herpesviruses**, which can cause respiratory infections but often present with more severe or distinct symptoms (e.g., adenoviral conjunctivitis, herpetic stomatitis).
- While adenoviruses can cause common cold-like symptoms, rhinoviruses and coronaviruses are statistically more prevalent in this clinical picture.
*Single-stranded, negative-sense RNA*
- Viruses with single-stranded, negative-sense RNA genomes include **influenza viruses**, **respiratory syncytial virus (RSV)**, and **paramyxoviruses**.
- While these can cause respiratory symptoms, influenza often presents with more significant **fever** and myalgia, and RSV more commonly causes **bronchiolitis** in young children.
*Double-stranded RNA*
- **Rotaviruses**, which have double-stranded RNA genomes, are primarily associated with **gastroenteritis**, causing severe diarrhea and vomiting, not typical respiratory symptoms.
- Though some reoviruses (a family of double-stranded RNA viruses) can cause respiratory illness, it is less common in this context than the positive-sense RNA viruses.
*Single-stranded DNA*
- **Parvovirus B19**, a single-stranded DNA virus, is known for causing **erythema infectiosum** (fifth disease) and aplastic crises, not general upper respiratory symptoms associated with the common cold.
- There are very few human pathogens with single-stranded DNA genomes that would cause this specific set of symptoms.
Question 65: A 52-year-old woman presents to the clinic with several days of vomiting and diarrhea. She also complains of headaches, muscle aches, and fever, but denies tenesmus, urgency, and bloody diarrhea. Past medical history is insignificant. When asked about any recent travel she says that she just came back from a cruise ship vacation. Her temperature is 37°C (98.6° F), respiratory rate is 15/min, pulse is 67/min, and blood pressure is 122/98 mm Hg. Physical examination is non-contributory. Microscopic examination of the stool is negative for ova or parasites. What is the most likely diagnosis?
A. Traveler’s diarrhea due to ETEC
B. Irritable bowel syndrome
C. Norovirus infection (Correct Answer)
D. Giardiasis
E. C. difficile colitis
Explanation: ***Norovirus infection***
- The combination of **vomiting** and **diarrhea** along with a history of **cruise ship travel** is highly suggestive of norovirus. Norovirus is a common cause of gastroenteritis outbreaks in crowded settings like cruise ships, schools, and nursing homes.
- While fever, headaches, and muscle aches can be present, the absence of **bloody diarrhea** and **tenesmus** points away from bacterial dysentery.
*Traveler’s diarrhea due to ETEC*
- **Enterotoxigenic *E. coli* (ETEC)** is a common cause of traveler's diarrhea, but the primary symptom is typically **watery diarrhea** often without significant vomiting.
- While travel is a risk factor, **cruise ship outbreaks** are more characteristic of norovirus due to its highly contagious nature and short incubation period.
*Irritable bowel syndrome*
- **Irritable bowel syndrome (IBS)** is a chronic functional gastrointestinal disorder characterized by recurrent abdominal pain associated with altered bowel habits.
- It does not typically present with an acute onset of **vomiting, diarrhea, fever, and muscle aches** following a specific exposure like a cruise.
*Giardiasis*
- **Giardiasis** is caused by the parasite *Giardia lamblia* and typically presents with **prolonged watery diarrhea**, abdominal cramps, bloating, and malabsorption.
- The acute, self-limiting nature and prominent **vomiting** in this case are less typical for giardiasis, and stool microscopy was negative for ova or parasites.
*C. difficile colitis*
- ***C. difficile* colitis** is primarily associated with **recent antibiotic use** and symptoms include **severe watery diarrhea**, abdominal pain, and fever.
- There is no history of antibiotic use, and the cruise travel context and prominent vomiting are not typical for *C. difficile* infection.
Question 66: A group of scientists is conducting an experiment on the human cells involved in the immune response. They genetically modify B cells so they do not express the cluster of differentiation 21 (CD21) on their cell surfaces. The pathogenesis of which of the following organisms would most likely be affected by this genetic modification?
A. Human papillomavirus
B. Human immunodeficiency virus (HIV)
C. Parvovirus B19
D. Epstein-Barr virus (EBV) (Correct Answer)
E. Measles virus
Explanation: ***Epstein-Barr virus (EBV)***
- EBV primarily infects B cells by binding to **CD21**, also known as the **C3d receptor** or CR2.
- Absence of CD21 would prevent EBV from entering B cells, thereby disrupting its **pathogenesis** and replication cycle.
*Human papillomavirus*
- HPV primarily infects **epithelial cells** and uses entry receptors other than CD21, such as alpha-6 integrins and heparan sulfate proteoglycans.
- Its pathogenesis is not directly dependent on B cell CD21 expression.
*Human immunodeficiency virus (HIV)*
- HIV primarily infects **CD4+ T cells and macrophages** by binding to CD4 and chemokine co-receptors (CCR5 or CXCR4).
- CD21 on B cells is not a primary receptor for HIV entry or infection.
*Parvovirus B19*
- Parvovirus B19 primarily targets **erythroid progenitor cells** by binding to the **P antigen** (globoside) on their surface.
- Its infection pathway does not involve CD21 on B cells.
*Measles virus*
- Measles virus primarily uses **CD150 (SLAM)** as its receptor on immune cells (including B cells and T cells) and nectin-4 on epithelial cells.
- While B cells can be infected, CD21 is not the primary receptor for measles virus entry.
Question 67: An investigator studying patients with symptoms of arthritis detects a nonenveloped virus with a single-stranded DNA genome in the serum of a pregnant patient. Fetal infection with this pathogen is most likely to cause which of the following manifestations?
A. Hydrops fetalis (Correct Answer)
B. Notched teeth
C. Microcephaly
D. Chorioretinitis
E. Vesicular rash
Explanation: ***Hydrops fetalis***
- The description of a nonenveloped virus with a **single-stranded DNA genome** is characteristic of **Parvovirus B19**. This virus commonly causes hydrops fetalis due to **fetal anemia** and subsequent heart failure.
- Parvovirus B19 infection in pregnant women can lead to severe complications for the fetus, primarily due to tropism for **erythroid progenitor cells**, resulting in anemia.
*Notched teeth*
- **Hutchinson's teeth**, characterized by notches, are a classic manifestation of **congenital syphilis**, caused by the bacterium *Treponema pallidum*, not a virus.
- Syphilis is a spirochete and not a single-stranded DNA virus.
*Microcephaly*
- **Microcephaly** is a severe neurological abnormality often associated with congenital infections like **Zika virus** or **cytomegalovirus (CMV)**, which are RNA and double-stranded DNA viruses, respectively.
- While viral infections can cause microcephaly, Parvovirus B19 is primarily known for causing fetal anemia and hydrops, not typically microcephaly.
*Chorioretinitis*
- **Chorioretinitis** is a common ocular manifestation of congenital infections such as **toxoplasmosis**, **CMV**, and **rubella**, but it is not a hallmark of Parvovirus B19 infection.
- These pathogens have different genomic structures and disease presentations.
*Vesicular rash*
- A **vesicular rash** is characteristic of infections caused by **herpesviruses**, such as **varicella-zoster virus (VZV)** or herpes simplex virus.
- These are **double-stranded DNA viruses**, not single-stranded DNA viruses like Parvovirus B19.
Question 68: A 32-year-old man with a past medical history significant for HIV and a social history of multiple sexual partners presents with new skin findings. His past surgical and family histories are noncontributory. The patient's blood pressure is 129/75 mm Hg, the pulse is 66/min, the respiratory rate is 16/min, and the temperature is 37.5°C (99.6°F). Physical examination reveals numerous painless skin-colored, flattened and papilliform lesions along the penile shaft and around the anus on physical exam. The application of 5% acetic acid solution causes the lesions to turn white. What is the etiology of these lesions?
A. HSV (type 2)
B. HPV (types 6 & 11) (Correct Answer)
C. Neisseria gonorrhoeae
D. HPV (types 16 & 18)
E. Molluscum contagiosum
Explanation: ***HPV (types 6 & 11)***
- These types of **Human Papillomavirus** are responsible for the vast majority of **genital warts (condyloma acuminata)**, which typically present as **painless, skin-colored, flattened, and papilliform lesions**.
- The lesions turning white upon application of **5% acetic acid solution (acetowhitening)** is a characteristic finding that helps visualize and identify HPV-related lesions.
*HSV (type 2)*
- **Herpes Simplex Virus type 2** causes **genital herpes**, which presents as painful, vesicular lesions that typically rupture to form ulcers.
- The lesions described in the question are painless and papilliform, not vesicular or ulcerated.
*Neisseria gonorrhoeae*
- **Neisseria gonorrhoeae** causes **gonorrhea**, a bacterial infection that typically presents as urethritis with purulent discharge in men, or can be asymptomatic.
- It does not cause wart-like lesions on the skin.
*HPV (types 16 & 18)*
- While these are high-risk types of **Human Papillomavirus**, they are primarily associated with **cervical, anal, and other anogenital cancers**, rather than benign genital warts.
- The lesions described are characteristic of condyloma acuminata, which are typically caused by low-risk HPV types.
*Molluscum contagiosum*
- **Molluscum contagiosum** manifests as **umbilicated papules**, meaning they have a central indention, which is distinct from the papilliform lesions described.
- These lesions are typically small, flesh-colored to pearly, and dome-shaped.
Question 69: An investigator studying influenza virus variability isolates several distinct influenza virus strains from the respiratory secretions of a study subject. Mass spectrometry analysis of one strain shows that it expresses neuraminidase on its surface. Subsequent sequencing of this strain shows that its genome lacks the neuraminidase gene. Which of the following is the most likely explanation for this finding?
A. Complementation
B. Recombination
C. Transduction
D. Phenotypic mixing (Correct Answer)
E. Reassortment
Explanation: ***Phenotypic mixing***
- **Phenotypic mixing** occurs when a virus genome is packaged into a capsid or envelope proteins derived from a *different* but co-infecting virus. In this case, the influenza strain's genome lacks the **neuraminidase gene**, but it expresses neuraminidase on its surface because it acquired the protein from another co-infecting strain.
- This process is temporary, as the progeny of this mixed virus will replicate normally according to its own **genome**, and thus would not express neuraminidase unless it also inherited the gene.
*Complementation*
- **Complementation** occurs when two viruses infect the same cell, and one virus provides a **gene product** (a protein) that the other virus, which has a defective gene, needs to replicate.
- In complementation, the defective virus *replicates its own genome*, but uses the protein supplied by the other virus; it would not express a protein derived directly from another virus's genome on its surface if its own genome did not encode it.
*Recombination*
- **Recombination** involves the exchange of genetic material between two different but related viruses, resulting in a **hybrid genome** containing genes from both parental viruses.
- If recombination had occurred, the virus's genome *would* contain the neuraminidase gene, which is contradicted by the finding that the genome *lacks* it.
*Transduction*
- **Transduction** is a process where **bacteriophages** (viruses that infect bacteria) transfer bacterial DNA from one bacterium to another. This mechanism is specific to bacteria and their phages, and is not applicable to human influenza viruses.
- This process involves the transfer of genetic material between bacteria via a viral vector, which is unrelated to the expression of a surface protein from a *non-encoded gene* in influenza.
*Reassortment*
- **Reassortment** is a unique characteristic of viruses with **segmented genomes**, such as influenza, where segments can be exchanged between different strains during co-infection.
- If reassortment had occurred, the influenza strain's genome *would have acquired* the neuraminidase gene segment, which contradicts the finding that the genome *lacks* the neuraminidase gene.
Question 70: An investigator studying viral mutation isolates a virus strain from the gastric contents of an infant with gastroenteritis. This virus has a nonenveloped RNA genome with 11 segments and an icosahedral symmetrical capsid. The investigator finds that if 2 strains of this virus coinfect a single host cell, some of the resulting viral progeny have genome segments derived from both parental viruses. The observed phenomenon is most likely also seen in which of the following viral families?
A. Caliciviruses
B. Orthomyxoviruses (Correct Answer)
C. Flaviviruses
D. Retroviruses
E. Picornaviruses
Explanation: ***Orthomyxoviruses***
- The description of a virus with a **segmented RNA genome** undergoing reassortment (mixing segments from coinfecting strains) is characteristic of **Orthomyxoviruses**, which notably include the influenza virus.
- Influenza virus is well-known for its ability to **reassort** its **8 segmented RNA genome**, leading to antigenic shifts responsible for pandemics.
*Caliciviruses*
- **Caliciviruses** (e.g., Norovirus) have a **single-stranded, non-segmented RNA genome** and do not undergo genomic reassortment.
- They are a common cause of **gastroenteritis** but their genetic features differ.
*Flaviviruses*
- **Flaviviruses** (e.g., Dengue, Yellow Fever, Zika) possess a **single-stranded, non-segmented RNA genome**.
- They replicate via a polyprotein cleavage mechanism and do not exhibit genomic reassortment.
*Retroviruses*
- **Retroviruses** (e.g., HIV) have a **diploid, positive-sense, single-stranded RNA genome** that is reverse transcribed into DNA.
- While they can undergo **recombination** during reverse transcription, this is distinct from the described reassortment of segmented genomes.
*Picornaviruses*
- **Picornaviruses** (e.g., Poliovirus, Rhinovirus) have a **single-stranded, non-segmented RNA genome**.
- They are known for their rapid replication but do not exhibit genomic segmentation or reassortment.
