Question 1

Clinical virology — Hydrophobia (fear of water during painful spasms of swallowing) is classically associated with which viral infection?

Accepted Answer

Introduction / Context: Hydrophobia is a dramatic clinical sign in encephalitic rabies. Painful pharyngeal spasms are triggered by attempts to drink or even by the sight/sound of water, reflecting involvement of brainstem centers and autonomic dysfunction. Given Data / Assumptions: Rabies virus is a neurotropic, enveloped, negative-sense RNA virus (genus Lyssavirus). Clinical features include agitation, aerophobia, hydrophobia, hypersalivation, and rapidly progressive encephalitis. Other listed infections do not cause hydrophobia as a hallmark sign. Concept / Approach: Identify the one infection uniquely linked to hydrophobia. While dysphagia can accompany other neurological diseases, hydrophobia with pharyngeal spasms is a classic rabies presentation in humans. Step-by-Step Solution: Match clinical sign (hydrophobia) to disease (rabies).Exclude influenza, polio, and hepatitis which have different primary organ targets and symptom complexes.Select “Rabies.” Verification / Alternative check: Public health manuals list hydrophobia and aerophobia as key clues in suspected rabies encephalitis. Why Other Options Are Wrong: Influenza: respiratory illness with myalgias and fever; no hydrophobia. Polio: flaccid paralysis without hydrophobic spasms. Hepatitis: hepatic inflammation; unrelated neurologic syndrome. Common Pitfalls: Assuming any CNS infection could present similarly; hydrophobia is notably rabies-specific in classic descriptions. Final Answer: Rabies

Question 2

Antemortem diagnosis of rabies — Which clinical specimens are suitable for demonstrating rabies antigen by direct immunofluorescence in living patients?

Accepted Answer

Introduction / Context: Early diagnosis of rabies is critical because the disease is almost uniformly fatal once symptomatic. Antemortem testing leverages direct immunofluorescence (DFA/IF) on accessible tissues to detect viral antigen. Given Data / Assumptions: Direct immunofluorescence targets rabies nucleocapsid antigens in exfoliated epithelial cells or tissue imprints. Sampling must be minimally invasive and repeatable. Multiple sites increase diagnostic yield when combined with RT-PCR on saliva/CSF and skin biopsies. Concept / Approach: Saliva contains infected epithelial cells and virions; corneal and conjunctival impression smears capture infected epithelial cells. These are recognized clinical specimens for antemortem antigen detection by direct IF in appropriate laboratory settings. Step-by-Step Solution: Identify all acceptable antemortem samples for DFA.Confirm that salivary, corneal, and conjunctival smears are used in practice to detect antigen.Select the inclusive choice “All of these.” Verification / Alternative check: Diagnostic algorithms also include nuchal skin biopsy (hair follicles) for DFA and RT-PCR, but this does not invalidate the listed smear specimens for antigen detection. Why Other Options Are Wrong: Selecting only one smear type lowers sensitivity; standard protocols may use multiple specimen types. Common Pitfalls: Assuming brain biopsy is required antemortem; less invasive smears and biopsies are preferred initially. Final Answer: All of these

Question 3

Host range — Among the animal species listed, which is classically considered most susceptible to rabies infection?

Accepted Answer

Introduction / Context: Rabies affects all mammals to varying degrees, but practical public health emphasis is on species with high susceptibility and close human contact. Reservoirs and vectors vary by region, with dogs representing the dominant source of human exposures in many countries. Given Data / Assumptions: All mammals are susceptible; birds (fowl) are relatively resistant and rarely infected. In endemic regions, domestic dogs constitute the principal reservoir and transmit most human cases. “Most susceptible” in basic MCQs usually contrasts mammals with avian species and highlights the dog’s epidemiological role. Concept / Approach: Between the provided options, dogs are both highly susceptible and epidemiologically central. Cats and cattle can be infected, but dogs contribute the majority of human rabies deaths worldwide due to frequency of bites and urban reservoirs. Step-by-Step Solution: Exclude fowl (avian; comparatively resistant).Compare mammals: dog is a key reservoir with high case frequency.Select “dog” as the most susceptible/epidemiologically important from the list. Verification / Alternative check: Global health data consistently attribute most human rabies transmissions to dog bites in endemic areas. Why Other Options Are Wrong: Cat: susceptible but less central globally. Cow: herbivore; cases occur but do not drive human epidemics. Fowl: relatively resistant; not a typical host. Common Pitfalls: Confusing reservoir importance with mere possibility of infection; practical susceptibility and transmission risk point to dogs. Final Answer: dog

Question 4

Viral gastroenteritis — Which of the following agents are well-recognized causes of acute diarrhea outbreaks?

Accepted Answer

Introduction / Context: Acute viral gastroenteritis is a leading cause of morbidity worldwide, especially in children and in closed communities. Multiple unrelated RNA virus families cause similar clinical syndromes with vomiting and watery diarrhea. Given Data / Assumptions: Rotaviruses are a major pediatric pathogen. Norwalk virus (norovirus) commonly causes explosive outbreaks in schools, cruise ships, and nursing homes. Astroviruses are established causes of pediatric and institutional gastroenteritis. Concept / Approach: Each listed virus group is a documented etiologic agent of acute diarrheal disease. Therefore, the most correct choice is the inclusive “All of these.” Step-by-Step Solution: Associate each virus with clinical gastroenteritis.Recognize overlapping epidemiology (fecal-oral transmission, seasonal trends).Choose the inclusive option encompassing all three agents. Verification / Alternative check: Laboratory panels for gastroenteritis routinely include rotavirus, norovirus, and astrovirus assays in pediatric and outbreak settings. Why Other Options Are Wrong: Selecting any single virus ignores the multifactorial viral causes of diarrhea. Common Pitfalls: Assuming rotavirus is exclusively pediatric; adults can be infected, and norovirus affects all ages. Final Answer: All of these

Question 5

Star-shaped enteric virus — Which virus appears star-like under electron microscopy and is transmitted via the fecal–oral route?

Accepted Answer

Introduction / Context: Electron microscopy historically aided in distinguishing small, non-enveloped enteric viruses. Morphology plus transmission route can help identify likely pathogens in gastroenteritis outbreaks. Given Data / Assumptions: “Star-shaped” refers to a characteristic surface pattern seen in astroviruses. Transmission for these small enteric viruses is predominantly fecal–oral, often through contaminated food, water, or fomites. Caliciviruses (e.g., norovirus) have distinct morphology; hepatitis E is a separate enteric hepatitis agent with different imaging features; hepatitis D depends on hepatitis B and is parenteral/sexual. Concept / Approach: Astroviruses are named from “astron” (star) due to their 5- to 6-pointed star-like appearance on EM after negative staining. They are recognized causes of pediatric diarrhea and institutional outbreaks. Step-by-Step Solution: Match the unique “star-like” morphology to astrovirus.Confirm fecal–oral epidemiology consistent with enteric transmission.Select “Astrovirus.” Verification / Alternative check: Molecular diagnostics (RT-PCR) corroborate EM findings in epidemiologic investigations of diarrheal disease. Why Other Options Are Wrong: Calicivirus (norovirus): not star-shaped; EM shows distinct cup-like depressions. Hepatitis E virus: enterically transmitted but not star-shaped; causes hepatitis rather than classic short-incubation gastroenteritis. Hepatitis D virus: requires HBV and spreads mainly via blood/sexual routes. Common Pitfalls: Confusing different small RNA enteric viruses based solely on size; morphology and clinical syndromes provide helpful clues. Final Answer: Astrovirus

Question 6

Hepatitis E virus (HEV): What is the principal route of human-to-human transmission in community outbreaks?

Accepted Answer

Introduction / Context: Hepatitis E virus (HEV) is a non-enveloped, single-stranded RNA virus that commonly causes acute viral hepatitis in regions with limited sanitation. Exam questions often test recognition of its classic faecal–oral transmission, especially via contaminated municipal water during monsoon or flood-related disruptions. Given Data / Assumptions: Disease focus: Hepatitis E (classically epidemic waterborne hepatitis). Population setting: community outbreaks, particularly in areas with compromised water and sewage systems. We seek the most common and epidemiologically dominant transmission route. Concept / Approach: Unlike hepatitis B and C (bloodborne and parenteral), HEV spreads primarily via the faecal–oral route. Large outbreaks follow ingestion of water contaminated with human sewage. Sporadic zoonotic genotypes exist, but the exam emphasis remains on waterborne spread in endemic regions. Step-by-Step Solution: Identify hallmark: faecal–oral transmission dominates HEV epidemiology. Link to outbreaks: community water contamination causes explosive epidemics. Contrast with other options: parenteral and sexual routes are not typical for HEV outbreaks. Select the best match: faecally contaminated drinking water. Verification / Alternative check: Public health reports repeatedly implicate contaminated piped water or wells in HEV outbreaks; case control studies show strong association with unsafe drinking water and inadequate sanitation. Why Other Options Are Wrong: Infected syringes/needles: characteristic of HBV/HCV, not the main HEV route. Sexual intercourse: not a dominant HEV pathway. “None of these” and shellfish-only are too restrictive and miss the classic waterborne pattern. Common Pitfalls: Confusing HEV with HAV or HBV; assuming all hepatitis viruses share the same transmission route. HEV is best remembered as “epidemic waterborne hepatitis.” Final Answer: Faecally contaminated drinking water.

Question 7

Rabies virology: What is the characteristic morphology (shape) of the rabies virus particle?

Accepted Answer

Introduction / Context: Rabies virus, a member of the Rhabdoviridae family (genus Lyssavirus), displays a unique virion morphology that is a favorite viva and MCQ point in microbiology and pathology exams. Recognizing its classic shape helps link clinical suspicion to lab and imaging descriptions. Given Data / Assumptions: Organism: Rabies virus (enveloped, negative-sense RNA). Question: Identify the canonical virion shape. Answer should reflect standard textbook morphology. Concept / Approach: Rhabdoviruses are famously “bullet-shaped” on electron microscopy, with one rounded end and one flattened end, a helical nucleocapsid, and an envelope studded with glycoprotein spikes. This contrasts with the roughly spherical shape of many orthomyxoviruses and coronaviruses. Step-by-Step Solution: Recall family hallmark: Rhabdoviridae → bullet-shaped virions. Differentiate from common distractors (spherical, filamentous). Choose the textbook descriptor: bullet-shaped. Verification / Alternative check: Electron micrographs and standard references consistently describe rabies virions as bullet-like with a helical ribonucleoprotein core. Why Other Options Are Wrong: Spherical/polygonal/tubular/filamentous forms better fit other viral families; they do not capture rabies morphology. Common Pitfalls: Confusing “helical symmetry” of the nucleocapsid with overall particle shape; for rabies, the envelope gives the distinctive bullet outline. Final Answer: Bullet-shaped.

Question 8

Respiratory viruses with club-shaped peplomers: Which agent classically has surface spikes (peplomers) that appear club-shaped and commonly infects the human respiratory tract?

Accepted Answer

Introduction / Context: “Peplomers” are the glycoprotein spikes seen on the surface of enveloped viruses. Coronaviruses are named for their corona-like appearance due to prominent, club-shaped spike (S) proteins, and they commonly infect the upper and lower respiratory tract. Given Data / Assumptions: We are comparing surface morphology across common viruses. Target organ system: respiratory tract. Select the agent with club-shaped peplomers. Concept / Approach: Coronaviruses are enveloped and have large, club-shaped spikes responsible for receptor binding and membrane fusion. Astroviruses and noroviruses are non-enveloped enteric viruses lacking peplomer spikes; their infections primarily involve the gastrointestinal tract. Step-by-Step Solution: Identify peplomers → requires an enveloped virus. Coronaviruses: enveloped with club-shaped S glycoprotein; respiratory tropism common. Astrovirus and norovirus → non-enveloped, GI pathogens, no peplomers. Select Coronavirus. Verification / Alternative check: Electron micrographs show a “crown” of clubs on coronaviruses; clinical correlation with colds, SARS-like illnesses, and other respiratory syndromes supports the choice. Why Other Options Are Wrong: Astrovirus and norovirus lack envelopes and do not have club-shaped spikes; “All of these” is therefore incorrect; adenovirus has fiber projections but is non-enveloped and not club-peplomer based. Common Pitfalls: Assuming all surface projections are “peplomers.” Only enveloped viruses display peplomer spikes; non-enveloped viruses have capsid features instead. Final Answer: Coronavirus.

Rhabdoviridae, Caliciviridae and Astroviridae Questions