Hepatitis A virus is transmitted principally by
Answer: A
Spread is by person-to-person contact and by food or water contaminated with faeces, which is why outbreaks follow poor sanitation and food handled by an infected worker. Blood-borne transmission is possible but rare, and there is no arthropod or respiratory route.
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The average incubation period of hepatitis A is about
Answer: B
Correct answer: 28 days
Hepatitis A incubates for about a month, with a usual range of two to six weeks. That is long enough for an infected food handler to expose a great many people before anyone falls ill, which is why outbreak investigation has to look back several weeks and why post-exposure vaccination is still worth giving.
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Hepatitis A differs from hepatitis B and C in that it
Answer: C
Hepatitis A produces an acute illness from which people recover, and no carrier state or chronic infection follows, so cirrhosis and liver cancer are not among its consequences. Its severity lies in the acute illness itself, which can occasionally be fulminant.
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In children under six years of age, hepatitis A infection is
Answer: D
Most infections in young children pass unnoticed and usually without jaundice, whereas older children and adults are typically jaundiced. Unrecognised infection in children is exactly what makes them effective spreaders within a household or nursery.
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Hepatitis A virus belongs to the family
Answer: A
It is a small naked icosahedral virus with a positive-sense single-stranded RNA genome, sharing the family with poliovirus and the rhinoviruses. Being naked is part of why it survives so well in the environment and resists many disinfectants.
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Hepatitis A virus can survive outside the body for
Answer: B
Lacking an envelope, the virion tolerates drying and a wide range of conditions and remains infectious for long periods on surfaces and in water. That persistence underlies its transmission by shellfish, salads and contaminated water supplies.
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Immune globulin given after exposure to hepatitis A is effective if administered within
Answer: C
Because the incubation period averages four weeks, passive antibody given inside the first two weeks can still prevent or attenuate illness. Vaccine is now often preferred for healthy contacts, with immune globulin reserved for the very young, the elderly and the immunocompromised.
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The marker indicating acute hepatitis A infection is
Answer: D
IgM appears with the illness and disappears over some months, so its presence dates the infection as recent. IgG persists for life and marks immunity, whether from past infection or from vaccination, and hepatitis A virus has no surface or e antigen of the kind hepatitis B carries.
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The family containing the virus of serum hepatitis is
Answer: A
The hepadnaviruses are enveloped viruses with a small circular, partially double-stranded DNA genome of about 3.2 kilobases. Their use of reverse transcription during replication is unusual for a DNA virus and is why some antiretroviral drugs are active against them.
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The genome of hepatitis B virus is
Answer: B
The genome is remarkably compact at about 3.2 kilobases and is only partly double-stranded, the gap being completed in the infected cell. Despite being DNA it is copied through an RNA intermediate by a reverse transcriptase.
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