Gastroenteritis viruses (norovirus, rotavirus) — MCQs

10 questions

A 3-year-old boy is brought to the pediatrician by his parents with a presentation of severe diarrhea, vomiting, and fever for the past 2 days. The child is enrolled at a daycare where several other children have had similar symptoms in the past week. On physical exam, the child is noted to have dry mucous membranes. His temperature is 102°F (39°C). Questions regarding previous medical history reveal that the child’s parents pursued vaccine exemption to opt out of most routine vaccinations for their child. The RNA virus that is most likely causing this child’s condition has which of the following structural features?

A 7-year-old boy is brought to the emergency room because of severe, acute diarrhea. He is drowsy with a dull, lethargic appearance. He has sunken eyes, poor skin turgor, and dry oral mucous membranes and tongue. He has a rapid, thready pulse with a systolic blood pressure of 60 mm Hg and his respirations are 33/min. His capillary refill time is 6 sec. He has had no urine output for the past 24 hours. Which of the following is the most appropriate next step in treatment?

A 55-year-old man presents to the emergency department with nausea and vomiting. The patient states that he has felt nauseous for the past week and began vomiting last night. He thought his symptoms would resolve but decided to come in when his symptoms worsened. He feels that his symptoms are exacerbated with large fatty meals and when he drinks alcohol. His wife recently returned from a cruise with symptoms of vomiting and diarrhea. The patient has a past medical history of poorly managed diabetes, constipation, anxiety, dyslipidemia, and hypertension. His temperature is 99.5°F (37.5°C), blood pressure is 197/128 mmHg, pulse is 100/min, respirations are 17/min, and oxygen saturation is 95% on room air. Physical exam reveals a systolic murmur heard loudest along the left upper sternal border. Abdominal exam reveals an obese, tympanitic and distended abdomen with a 3 cm scar in the right lower quadrant. Vascular exam reveals weak pulses in the lower extremities. Which of the following is the most likely diagnosis?

A 4-year-old boy presents to the emergency department with diarrhea. Several days ago, he experienced a fever which has progressed to vomiting and diarrhea. He has had multiple episodes of non-bloody diarrhea and states that he feels fatigued. He is not up to date on his vaccinations and takes many different herbal supplements from his parents. His temperature is 101°F (38.3°C), blood pressure is 100/55 mmHg, pulse is 111/min, respirations are 19/min, and oxygen saturation is 100% on room air. Physical exam is notable for dry mucous membranes and a fatigued appearing child. Which of the following is the most likely etiology of this patient’s symptoms?

A 48-year-old man presents to the clinic with several weeks of watery diarrhea and right upper quadrant pain with fever. He also endorses malaise, nausea, and anorexia. He is HIV-positive and is currently on antiretroviral therapy. He admits to not being compliant with his current medications. His temperature is 37°C (98.6°F), respiratory rate is 15/min, pulse is 70/min, and blood pressure is 100/84 mm Hg. A physical examination is performed which is within normal limits. His blood tests results are given below: Hb%: 11 gm/dL Total count (WBC): 3,400 /mm3 Differential count: Neutrophils: 70% Lymphocytes: 25% Monocytes: 5% CD4+ cell count: 88/mm3 Stool microscopy results are pending. What is the most likely diagnosis?

A 24-year-old woman presents with 3 days of diarrhea. She was recently on vacation in Peru and admits that on her last day of the trip she enjoyed a dinner of the local food and drink. Upon return to the United States the next day, she developed abdominal cramps and watery diarrhea, occurring about 3-5 times per day. She has not noticed any blood or mucous in her stool. Vital signs are stable. On physical examination, she is well appearing in no acute distress. Which of the following is commonly associated with the likely underlying illness?

A scientist is studying the influenza A virus. He focuses on two strains – one from humans (H7N1) and one from horses (H3N8). He takes cells from chickens and coinfects these cells with both influenza strains. From these chicken cells, the scientist isolates a new strain and finds that this new strain can infect human cells. He further characterizes the new strain’s hemagglutinin and neuraminidase description as H7N8. What term best describes the process that underlies these experimental results?

A 15-year-old girl presents to her primary care physician with her parents. She is complaining of fever and a sore throat for the past 4 days. She was born at 39 weeks gestation via spontaneous vaginal delivery and is up to date on all vaccines and is meeting all developmental milestones. Her boyfriend at school has the same symptoms including fever and sore throat. Today, her heart rate is 90/min, respiratory rate is 17/min, blood pressure is 110/65 mm Hg, and temperature is 38.2°C (100.8°F). Examination revealed cervical lymphadenopathy and mild hepatosplenomegaly. Oral exam reveals focal tonsillar exudate. A monospot test is positive. This patient is most likely infected with which of the following viruses?

A previously healthy 53-year-old man is brought to the emergency department 45 minutes after the onset of a severe headache. He returned from a vacation in the mountains 4 days ago, during which he went swimming in a freshwater lake. On arrival, he is confused. His temperature is 39°C (102.2°F) and blood pressure is 105/68 mm Hg. Neurologic examination shows diffuse hyperreflexia. An MRI of the brain shows asymmetrical, bitemporal hyperintensities. A lumbar puncture is performed. Cerebrospinal fluid analysis shows: Leukocyte count 120/mm3 Segmented neutrophils 10% Lymphocytes 90% Erythrocyte count 15/mm3 Glucose 45 mg/dL Opening pressure 130 mm Hg Protein 75 mg/dL Which of the following is the most likely causal pathogen?

Q10

A previously healthy 5-year-old boy is brought to the physician because of increasing weakness and a retroauricular rash that started 2 days ago. The rash spread rapidly and involves the trunk and extremities. Last week, he had a mild sore throat, pink eyes, and a headache. His family recently immigrated from Ethiopia. His immunization status is unknown. The patient appears severely ill. His temperature is 38.5°C (101.3°F). Examination shows tender postauricular and suboccipital lymphadenopathy. There is a nonconfluent, maculopapular rash over the torso and extremities. Infection with which of the following is the most likely cause of this patient's symptoms?

Gastroenteritis viruses (norovirus, rotavirus) US Medical PG Practice Questions and MCQs

Question 1: A 3-year-old boy is brought to the pediatrician by his parents with a presentation of severe diarrhea, vomiting, and fever for the past 2 days. The child is enrolled at a daycare where several other children have had similar symptoms in the past week. On physical exam, the child is noted to have dry mucous membranes. His temperature is 102°F (39°C). Questions regarding previous medical history reveal that the child’s parents pursued vaccine exemption to opt out of most routine vaccinations for their child. The RNA virus that is most likely causing this child’s condition has which of the following structural features?

A. Single-stranded, icosahedral, non-enveloped
B. Double-stranded, icosahedral, non-enveloped (Correct Answer)
C. Single-stranded, helical, enveloped
D. Single-stranded, icosahedral, enveloped
E. Double-stranded, helical, non-enveloped

Explanation: ***Double-stranded, icosahedral, non-enveloped*** - The clinical presentation of severe diarrhea, vomiting, and fever in a young child, especially in a daycare setting with a history of vaccine exemption, is highly suggestive of **Rotavirus infection**. - **Rotavirus** is a member of the Reoviridae family and is characterized by its **double-stranded RNA (dsRNA) genome**, **icosahedral capsid**, and **lack of an envelope**. *Single-stranded, icosahedral, non-enveloped* - This describes viruses like **Picornaviruses** (e.g., Poliovirus, Rhinovirus) or **Caliciviruses** (e.g., Norovirus), which can cause gastrointestinal symptoms but lack the dsRNA genome of Rotavirus. - While Norovirus can cause outbreaks of gastroenteritis, the structural features provided do not align with the most likely pathogen given the severity and typical age group for Rotavirus. *Single-stranded, helical, enveloped* - This describes viruses such as **Paramyxoviruses** (e.g., Measles, Mumps) or **Orthomyxoviruses** (e.g., Influenza), which typically cause respiratory or systemic infections, not primarily severe gastroenteritis in this manner. - The presence of an **envelope** and **helical symmetry** rule out Rotavirus. *Single-stranded, icosahedral, enveloped* - This describes viruses such as **Togaviruses** (e.g., Rubella) or **Flaviviruses** (e.g., Dengue), which cause a variety of systemic diseases but are not common causes of severe diarrheal illness in this demographic. - The combination of **enveloped** and an **icosahedral capsid** does not match Rotavirus structure. *Double-stranded, helical, non-enveloped* - While some viruses have **double-stranded RNA**, none of the medically significant viruses are known to be **helical** and **non-enveloped** simultaneously. - **Helical symmetry** is usually associated with enveloped viruses in RNA viruses; therefore, this combination is not characteristic of common human viral pathogens causing gastroenteritis.

Question 2: A 7-year-old boy is brought to the emergency room because of severe, acute diarrhea. He is drowsy with a dull, lethargic appearance. He has sunken eyes, poor skin turgor, and dry oral mucous membranes and tongue. He has a rapid, thready pulse with a systolic blood pressure of 60 mm Hg and his respirations are 33/min. His capillary refill time is 6 sec. He has had no urine output for the past 24 hours. Which of the following is the most appropriate next step in treatment?

A. Start IV fluid resuscitation by administering colloid solutions
B. Provide oral rehydration therapy to correct dehydration
C. Give initial IV bolus of 2 L of Ringer’s lactate, followed by packed red cells, fresh frozen plasma, and platelets in a ratio of 1:1:1
D. Start IV fluid resuscitation with normal saline or Ringer’s lactate, along with monitoring of vitals and urine output (Correct Answer)
E. Give antidiarrheal drugs

Explanation: ***Start IV fluid resuscitation with normal saline or Ringer's lactate, along with monitoring of vitals and urine output*** - This patient presents with **severe dehydration** and **hypovolemic shock** (lethargy, sunken eyes, poor skin turgor, dry mucous membranes, rapid thready pulse, hypotension [systolic BP 60 mmHg], tachypnea, prolonged capillary refill >5 seconds, and anuria). - According to **PALS guidelines**, the immediate priority is rapid intravenous administration of **isotonic crystalloids** (normal saline or Ringer's lactate) given as **20 mL/kg boluses** over 5-20 minutes, repeated as needed based on clinical response. - Close monitoring of vital signs, mental status, perfusion (capillary refill), and urine output is essential to assess response to resuscitation and guide further fluid management. *Start IV fluid resuscitation by administering colloid solutions* - While colloids (albumin, synthetic colloids) can expand intravascular volume, **isotonic crystalloids** are preferred for initial resuscitation in severe dehydration per **WHO and PALS guidelines**. - Crystalloids are equally effective, more readily available, less expensive, and have fewer potential adverse effects compared to colloids in pediatric dehydration. - There is no proven survival benefit of colloids over crystalloids in this clinical scenario. *Provide oral rehydration therapy to correct dehydration* - **Oral rehydration therapy (ORT)** is the appropriate first-line treatment for **mild to moderate dehydration** in children who can tolerate oral intake. - However, ORT is **contraindicated** in patients with **severe dehydration** or **hypovolemic shock**, particularly those with altered mental status, inability to drink, or hemodynamic instability. - This patient's drowsiness, hypotension, and signs of shock require immediate IV resuscitation; ORT would be too slow and potentially dangerous. *Give initial IV bolus of 2 L of Ringer's lactate, followed by packed red cells, fresh frozen plasma, and platelets in a ratio of 1:1:1* - A 2-liter bolus is **excessive and dangerous** for a 7-year-old child (average weight ~23 kg); the appropriate initial bolus is **20 mL/kg** (~460 mL), which can be repeated based on response. - The **1:1:1 massive transfusion protocol** (packed RBCs, FFP, platelets) is indicated for **hemorrhagic shock** with significant blood loss, not for hypovolemic shock from dehydration. - There is no evidence of bleeding or coagulopathy in this patient; blood products are not indicated. *Give antidiarrheal drugs* - **Antidiarrheal agents** (loperamide, diphenoxylate) are **contraindicated** in young children with acute infectious diarrhea, as they can prolong illness, increase risk of complications (toxic megacolon, bacterial overgrowth), and mask serious underlying conditions. - The priority in severe dehydration is **fluid and electrolyte resuscitation**, not stopping the diarrhea. - The diarrhea typically resolves once the underlying infection is controlled and hydration is restored.

Question 3: A 55-year-old man presents to the emergency department with nausea and vomiting. The patient states that he has felt nauseous for the past week and began vomiting last night. He thought his symptoms would resolve but decided to come in when his symptoms worsened. He feels that his symptoms are exacerbated with large fatty meals and when he drinks alcohol. His wife recently returned from a cruise with symptoms of vomiting and diarrhea. The patient has a past medical history of poorly managed diabetes, constipation, anxiety, dyslipidemia, and hypertension. His temperature is 99.5°F (37.5°C), blood pressure is 197/128 mmHg, pulse is 100/min, respirations are 17/min, and oxygen saturation is 95% on room air. Physical exam reveals a systolic murmur heard loudest along the left upper sternal border. Abdominal exam reveals an obese, tympanitic and distended abdomen with a 3 cm scar in the right lower quadrant. Vascular exam reveals weak pulses in the lower extremities. Which of the following is the most likely diagnosis?

A. Enteric nervous system damage
B. Twisting of the bowel
C. Adhesions (Correct Answer)
D. Norovirus
E. Impacted stool

Explanation: ***Adhesions*** - The patient's history of a 3 cm scar in the right lower quadrant suggests a prior abdominal surgery, which is the most common cause of **intra-abdominal adhesions**. - **Adhesions** can lead to **small bowel obstruction**, causing symptoms like nausea, vomiting, abdominal distension, and tympany, which are all present in this patient. *Enteric nervous system damage* - Poorly managed diabetes can cause **diabetic gastroparesis**, which involves damage to the **enteric nervous system** leading to delayed gastric emptying. - While it can cause nausea and vomiting, it doesn't typically present with significant abdominal distension or tympany, which are indicative of a mechanical obstruction. *Twisting of the bowel* - **Volvulus**, or twisting of the bowel, causes acute abdominal pain, distension, and often complete obstruction. - While it's a possibility for bowel obstruction, the presence of a surgical scar and gradual worsening of symptoms over a week makes **adhesions** a more likely cause in this scenario. *Norovirus* - **Norovirus** is a common cause of acute gastroenteritis, characterized by abrupt onset of vomiting and diarrhea, often with a rapid resolution. - Although his wife has similar symptoms, the patient's symptoms have been ongoing for a week, are exacerbated by fatty meals, and include abdominal distension, which is inconsistent with typical norovirus infection. *Impacted stool* - **Fecal impaction** can cause constipation, abdominal pain, and sometimes paradoxical diarrhea. - While the patient has a history of constipation, the significant **tympanic distension** and persistent vomiting suggest a mechanical obstruction rather than just impacted stool.

Question 4: A 4-year-old boy presents to the emergency department with diarrhea. Several days ago, he experienced a fever which has progressed to vomiting and diarrhea. He has had multiple episodes of non-bloody diarrhea and states that he feels fatigued. He is not up to date on his vaccinations and takes many different herbal supplements from his parents. His temperature is 101°F (38.3°C), blood pressure is 100/55 mmHg, pulse is 111/min, respirations are 19/min, and oxygen saturation is 100% on room air. Physical exam is notable for dry mucous membranes and a fatigued appearing child. Which of the following is the most likely etiology of this patient’s symptoms?

A. Rotavirus (Correct Answer)
B. Campylobacter jejuni
C. Norovirus
D. Vibrio cholerae
E. Adenovirus

Explanation: ***Rotavirus*** - The patient's age (4-year-old), symptoms of **fever, vomiting, and non-bloody diarrhea**, and being **unvaccinated** against rotavirus strongly point to this diagnosis. - Rotavirus is a common cause of **severe gastroenteritis** in unvaccinated infants and young children, often leading to dehydration as evidenced by **dry mucous membranes**. - The rotavirus vaccine has dramatically reduced cases in vaccinated populations, making unvaccinated children particularly vulnerable. *Campylobacter jejuni* - This typically causes **bloody diarrhea**, which is not seen in this patient's presentation. - **Campylobacter jejuni** is often associated with consumption of raw poultry or contaminated water, and usually presents with more severe abdominal pain. *Norovirus* - While Norovirus can cause vomiting and non-bloody diarrhea, it typically affects individuals of **all ages** and often occurs in outbreaks in close-knit communities. - Though possible, **rotavirus** is a more common cause of severe gastroenteritis in unvaccinated young children. *Vibrio cholerae* - **Cholera** is characterized by **profuse watery diarrhea** (rice-water stools) leading to rapid dehydration. - It is typically seen in endemic areas or after exposure to contaminated water sources, and the patient's symptoms are not as extreme to suggest cholera. *Adenovirus* - While adenovirus can cause gastroenteritis in children, it typically presents with **respiratory symptoms** (pharyngitis, conjunctivitis) in addition to gastrointestinal symptoms. - Adenovirus gastroenteritis is generally **less severe** than rotavirus and lacks the classic vaccine-preventable epidemiology that makes rotavirus more likely in this unvaccinated child.

Question 5: A 48-year-old man presents to the clinic with several weeks of watery diarrhea and right upper quadrant pain with fever. He also endorses malaise, nausea, and anorexia. He is HIV-positive and is currently on antiretroviral therapy. He admits to not being compliant with his current medications. His temperature is 37°C (98.6°F), respiratory rate is 15/min, pulse is 70/min, and blood pressure is 100/84 mm Hg. A physical examination is performed which is within normal limits. His blood tests results are given below: Hb%: 11 gm/dL Total count (WBC): 3,400 /mm3 Differential count: Neutrophils: 70% Lymphocytes: 25% Monocytes: 5% CD4+ cell count: 88/mm3 Stool microscopy results are pending. What is the most likely diagnosis?

A. C. difficile colitis
B. Traveler’s diarrhea due to ETEC
C. Cryptosporidiosis (Correct Answer)
D. Norovirus infection
E. Irritable bowel syndrome

Explanation: ***Cryptosporidiosis*** - This patient's **HIV-positive status** with a **CD4+ count of 88/mm3** indicates severe immunosuppression, making them highly susceptible to opportunistic infections. The combination of **watery diarrhea**, **right upper quadrant pain with fever** (suggestive of biliary involvement), and general malaise is characteristic of cryptosporidiosis in immunocompromised individuals. - **Cryptosporidium** infection often causes **chronic, severe watery diarrhea** in patients with AIDS, and can also lead to **cholangitis or cholecystitis**, explaining the right upper quadrant pain and fever. *C. difficile colitis* - While *C. difficile* can cause watery diarrhea, especially in hospitalized patients or those on antibiotics, the **right upper quadrant pain with fever** and the patient's profound **immunocompromise (CD4+ <200)** makes opportunistic infections like *Cryptosporidium* more likely. - *C. difficile* typically presents with **colitis**, which may include abdominal pain but less commonly high-grade fever or specific right upper quadrant pain indicative of biliary involvement. *Traveler’s diarrhea due to ETEC* - **ETEC (Enterotoxigenic *E. coli*)** is a common cause of traveler's diarrhea, usually self-limiting and associated with recent travel, which is not mentioned here. - While it causes watery diarrhea, it typically does not present with **fever or right upper quadrant pain** suggestive of biliary disease, especially not in a patient with severe immunosuppression where opportunistic pathogens are more expected. *Norovirus infection* - **Norovirus** causes acute gastroenteritis with **vomiting and watery diarrhea**, sometimes low-grade fever, but it is typically a self-limiting illness lasting 1-3 days. - It does not explain the **right upper quadrant pain with fever** suggestive of biliary involvement, nor the prolonged "several weeks" duration of symptoms. *Irritable bowel syndrome* - **Irritable bowel syndrome (IBS)** is a functional gastrointestinal disorder characterized by chronic abdominal pain and altered bowel habits (diarrhea, constipation, or both), but it does not cause **fever, laboratory abnormalities (low CD4 count), or acute onset of symptoms** in an immunocompromised patient. - IBS is a diagnosis of exclusion and does not account for the systemic symptoms like **fever, malaise**, or the specific right upper quadrant pain.

Question 6: A 24-year-old woman presents with 3 days of diarrhea. She was recently on vacation in Peru and admits that on her last day of the trip she enjoyed a dinner of the local food and drink. Upon return to the United States the next day, she developed abdominal cramps and watery diarrhea, occurring about 3-5 times per day. She has not noticed any blood or mucous in her stool. Vital signs are stable. On physical examination, she is well appearing in no acute distress. Which of the following is commonly associated with the likely underlying illness?

A. Raw oysters
B. Soft cheese
C. Unwashed fruits and vegetables (Correct Answer)
D. Fried rice
E. Ground meat

Explanation: ***Unwashed fruits and vegetables*** - The patient's symptoms (watery diarrhea, abdominal cramps, recent travel to Peru, and consuming local food/drink) are highly suggestive of **Traveler's Diarrhea (TD)**. This condition is most commonly caused by **enterotoxigenic E. coli (ETEC)**. - **Unwashed fruits and vegetables** are a common vehicle for the transmission of ETEC and other pathogens associated with TD, as they can be contaminated with fecal matter. *Raw oysters* - **Raw oysters** are typically associated with **Vibrio parahaemolyticus** or **norovirus** infections, which can cause gastroenteritis but are not the most common cause of Traveler's Diarrhea from contaminated food in a country like Peru. - While they can cause diarrhea, the clinical picture is classic for Traveler's Diarrhea, where produce is a more frequent culprit. *Soft cheese* - **Soft cheeses**, especially unpasteurized ones, are more commonly associated with bacterial infections like **Listeria monocytogenes**, which can cause severe illness, but usually presents differently than typical Traveler's Diarrhea, often with fever and systemic symptoms. - They are not a primary source for the common pathogens causing acute watery diarrhea in travelers. *Fried rice* - **Fried rice** is a common source of **Bacillus cereus** food poisoning, which typically causes a very rapid onset of vomiting within 1-6 hours (emetic form) or diarrhea within 6-15 hours (diarrheal form) after consumption. - The patient's symptoms started the day after returning, suggesting a longer incubation period than typically seen with *B. cereus* from fried rice. *Ground meat* - **Ground meat**, particularly undercooked, is a common source of **enterohemorrhagic E. coli (EHEC)**, especially O157:H7, and **Salmonella** or **Campylobacter**. - These typically cause more severe diarrhea, often with **bloody stools**, which the patient explicitly denied.

Question 7: A scientist is studying the influenza A virus. He focuses on two strains – one from humans (H7N1) and one from horses (H3N8). He takes cells from chickens and coinfects these cells with both influenza strains. From these chicken cells, the scientist isolates a new strain and finds that this new strain can infect human cells. He further characterizes the new strain’s hemagglutinin and neuraminidase description as H7N8. What term best describes the process that underlies these experimental results?

A. Transduction
B. Antigenic drift
C. Transformation
D. Conjugation
E. Antigenic shift (Correct Answer)

Explanation: ***Antigenic shift*** - **Antigenic shift** in influenza viruses refers to the process where two different influenza strains **coinfect** the same host cell, leading to a **reassortment** of their segmented genomes. - This reassortment creates a novel viral strain with a new combination of hemagglutinin (H) and neuraminidase (N) antigens (e.g., H7N1 + H3N8 → H7N8), which can lead to pandemics. *Transduction* - **Transduction** is a process where foreign DNA is introduced into a cell by a virus or viral vector, primarily seen in bacteria. - It involves the transfer of genetic material via **bacteriophages** and does not describe the reassortment of influenza virus segments. *Antigenic drift* - **Antigenic drift** involves small, gradual changes in the H and N antigens of influenza viruses due to **point mutations** during replication. - These slow mutations lead to seasonal epidemics, but not the creation of a completely new subtype as described. *Transformation* - **Transformation** is the process by which a cell takes up naked DNA from its environment, incorporating it into its own genome. - This mechanism is common in bacteria for acquiring new genetic traits and is not applicable to the reassortment of viral segments within a coinfected host cell. *Conjugation* - **Conjugation** is a process of genetic material transfer between bacteria through direct cell-to-cell contact, typically via a **pilus**. - This mechanism is distinct from viral genetic reassortment and does not involve the coinfection of a host cell by different viral strains.

Question 8: A 15-year-old girl presents to her primary care physician with her parents. She is complaining of fever and a sore throat for the past 4 days. She was born at 39 weeks gestation via spontaneous vaginal delivery and is up to date on all vaccines and is meeting all developmental milestones. Her boyfriend at school has the same symptoms including fever and sore throat. Today, her heart rate is 90/min, respiratory rate is 17/min, blood pressure is 110/65 mm Hg, and temperature is 38.2°C (100.8°F). Examination revealed cervical lymphadenopathy and mild hepatosplenomegaly. Oral exam reveals focal tonsillar exudate. A monospot test is positive. This patient is most likely infected with which of the following viruses?

A. Varicella virus
B. Cytomegalovirus
C. Herpes simplex virus
D. Epstein-Barr virus (Correct Answer)
E. Variola virus

Explanation: ***Epstein-Barr virus*** - The symptoms of fever, sore throat, **cervical lymphadenopathy**, **hepatosplenomegaly**, and **tonsillar exudates** in an adolescent, coupled with a **positive Monospot test**, are highly characteristic of **infectious mononucleosis** caused by the Epstein-Barr virus (EBV) - The positive Monospot test detects **heterophile antibodies**, which are a hallmark of acute EBV infection and essentially confirms the diagnosis *Varicella virus* - Varicella virus (chickenpox) typically presents with a **pruritic vesicular rash** that progresses through different stages (macules → papules → vesicles → crusts), which is not described in this patient - While fever can be present, the distinctive rash, rather than lymphadenopathy and tonsillar exudates, is the defining feature *Cytomegalovirus* - Cytomegalovirus (CMV) can cause a **mononucleosis-like syndrome** with similar clinical features - However, CMV mononucleosis typically presents with **negative heterophile antibodies** (negative Monospot test), which distinguishes it from EBV - This patient's positive Monospot test makes CMV unlikely as the primary cause *Herpes simplex virus* - Herpes simplex virus (HSV) infections typically cause **oral ulcers** (cold sores), **gingivostomatitis**, or **genital lesions** - While HSV can cause fever and sore throat, it would not typically lead to the diffuse lymphadenopathy, hepatosplenomegaly, and positive Monospot test seen in this case *Variola virus* - Variola virus (smallpox) is characterized by a **distinctive rash** of deep-seated pustules that begin on the face and extremities, often with systemic symptoms like high fever and malaise - Smallpox has been **eradicated worldwide since 1980**, making this diagnosis impossible in contemporary practice - The presentation is distinctly different from the symptoms described, especially with the absence of the characteristic rash

Question 9: A previously healthy 53-year-old man is brought to the emergency department 45 minutes after the onset of a severe headache. He returned from a vacation in the mountains 4 days ago, during which he went swimming in a freshwater lake. On arrival, he is confused. His temperature is 39°C (102.2°F) and blood pressure is 105/68 mm Hg. Neurologic examination shows diffuse hyperreflexia. An MRI of the brain shows asymmetrical, bitemporal hyperintensities. A lumbar puncture is performed. Cerebrospinal fluid analysis shows: Leukocyte count 120/mm3 Segmented neutrophils 10% Lymphocytes 90% Erythrocyte count 15/mm3 Glucose 45 mg/dL Opening pressure 130 mm Hg Protein 75 mg/dL Which of the following is the most likely causal pathogen?

A. Herpes simplex virus (Correct Answer)
B. La Crosse virus
C. Rabies virus
D. Enterovirus
E. Naegleria fowleri

Explanation: ***Herpes simplex virus*** - The combination of **acute severe headache**, **fever**, **confusion**, **bitemporal hyperintensities** on MRI, and CSF showing a **lymphocytic pleocytosis** with some red blood cells (erythrocytes) is highly suggestive of **herpes simplex encephalitis (HSV encephalitis)**. - HSV encephalitis characteristically causes **temporal lobe involvement**, leading to focal neurological deficits and neuropsychiatric symptoms, and CSF often has **lymphocytic predominance** with a slightly elevated protein. *La Crosse virus* - This virus causes **encephalitis** primarily in children and adolescents, often preceded by fever, headache, and nausea; seizures are common. - While it can cause encephalitis, the **bitemporal hyperintensities** and specific CSF findings (lymphocytic pleocytosis, erythrocytes) are more classic for HSV. *Rabies virus* - Rabies presents as **encephalitis** with symptoms escalating from non-specific flu-like illness to neurological symptoms like hydrophobia, hallucinations, and paralysis. - The patient's presentation with **acute severe headache** and rapid onset of confusion, without a history of animal bite, makes rabies less likely. *Enterovirus* - Enteroviruses are a common cause of **aseptic meningitis** and can cause **encephalitis**, especially in children. - While they can cause fever, headache, and CSF lymphocytic pleocytosis, **bitemporal hyperintensities** and significant confusion pointing to focal neurological involvement are less characteristic. *Naegleria fowleri* - *Naegleria fowleri* causes **primary amoebic meningoencephalitis (PAM)**, typically in individuals with recent freshwater exposure, leading to rapid onset of severe headache, fever, and altered mental status. - CSF analysis in PAM usually shows a **neutrophilic pleocytosis** rather than lymphocytic predominance, differentiating it from HSV encephalitis.

Question 10: A previously healthy 5-year-old boy is brought to the physician because of increasing weakness and a retroauricular rash that started 2 days ago. The rash spread rapidly and involves the trunk and extremities. Last week, he had a mild sore throat, pink eyes, and a headache. His family recently immigrated from Ethiopia. His immunization status is unknown. The patient appears severely ill. His temperature is 38.5°C (101.3°F). Examination shows tender postauricular and suboccipital lymphadenopathy. There is a nonconfluent, maculopapular rash over the torso and extremities. Infection with which of the following is the most likely cause of this patient's symptoms?

A. Togavirus (Correct Answer)
B. Human herpesvirus 6
C. Parvovirus
D. Varicella zoster virus
E. Paramyxovirus

Explanation: ***Togavirus*** - This patient's presentation is classic for **rubella** (German measles), caused by the **rubella virus**, a **togavirus**. - The hallmark clinical finding is **tender postauricular and suboccipital lymphadenopathy**, which appears before the rash and is pathognomonic for rubella. - The **maculopapular rash** begins on the face (retroauricular region) and spreads cephalocaudally to the trunk and extremities over 2-3 days. - The prodrome includes **mild symptoms** (low-grade fever, sore throat, mild conjunctivitis, headache), which is characteristic of rubella. - The patient's **unknown immunization status** and immigration from a region with lower vaccination coverage increases the likelihood of rubella infection. *Paramyxovirus* - **Measles virus** is a paramyxovirus that causes rubeola, but the clinical presentation differs significantly from this case. - Measles typically presents with the **"3 Cs"**: severe **cough**, **coryza** (profuse nasal discharge), and **conjunctivitis** (more prominent than rubella). - **Koplik spots** (white spots on buccal mucosa) are pathognomonic for measles and appear before the rash. - Measles causes **higher fever** (often >40°C) and more severe systemic illness than described here. - While measles can have lymphadenopathy, the **prominent postauricular and suboccipital nodes are characteristic of rubella, not measles**. *Human herpesvirus 6* - **HHV-6** causes **roseola infantum** (exanthem subitum), typically in infants 6-24 months old. - The classic presentation is **high fever for 3-5 days** that suddenly resolves, followed immediately by a rash (**"fever then rash"**). - This patient had prodromal symptoms followed by rash while still febrile, which does not fit roseola. - Roseola does not cause significant lymphadenopathy or conjunctivitis. *Parvovirus* - **Parvovirus B19** causes **erythema infectiosum** (fifth disease), characterized by a **"slapped cheek"** facial erythema followed by a reticular (lacy) rash on the trunk and extremities. - The rash pattern and prominent lymphadenopathy in this case are not consistent with fifth disease. - Fifth disease typically causes mild or no fever and lacks the retroauricular distribution seen here. *Varicella zoster virus* - **VZV** causes **chickenpox**, which presents with a **pruritic, vesicular rash** that appears in successive crops and progresses through stages (macule → papule → vesicle → crust). - This patient has a **maculopapular, nonconfluent rash** without vesicles, which is inconsistent with chickenpox. - Chickenpox does not typically cause prominent postauricular lymphadenopathy.

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