Virology, NEET PG & INI-CET Microbiology MCQs

Explanation

In the window period HBsAg has cleared and anti-HBs has not yet appeared, so anti-HBc IgM is the only marker indicating recent infection. It is essential for diagnosis at this stage.

Explanation

HBeAg positivity reflects active viral replication and high infectivity. Anti-HBs indicates immunity from vaccination or recovery, while isolated HBsAg indicates infection but not necessarily high replication.

Explanation

The CD4 T-cell count reflects immune status and susceptibility to opportunistic infections, and a count below 200 cells per microlitre defines AIDS. Viral load, by contrast, monitors treatment response and infectivity.

Explanation

A reactive HIV screening ELISA is confirmed with a Western blot or an antigen-antibody differentiation immunoassay. Modern algorithms use a fourth-generation antigen-antibody test followed by a differentiation assay and, if needed, nucleic acid testing.

Explanation

Negri bodies are eosinophilic intracytoplasmic inclusions in neurons, especially in the hippocampus and cerebellum, and are diagnostic of rabies. Rabies is almost invariably fatal once symptomatic, which makes post-exposure prophylaxis crucial.

Explanation

Antigenic shift is a major, abrupt change from reassortment of influenza A genome segments, producing novel strains capable of causing pandemics. Antigenic drift is gradual point mutation causing seasonal epidemics.

Explanation

High-risk human papillomavirus types 16 and 18 cause most cervical cancers via the E6 and E7 oncoproteins, which inactivate p53 and Rb. HPV vaccination targets these types.

Explanation

EBV is linked to infectious mononucleosis, Burkitt lymphoma, nasopharyngeal carcinoma and Hodgkin lymphoma. Cervical carcinoma is caused by human papillomavirus, not EBV.

Explanation

Hepatitis A and E spread by the faecal-oral route and cause acute, self-limiting hepatitis, though E is dangerous in pregnancy. Hepatitis B, C and D spread parenterally and can cause chronic disease.

Explanation

Dengue is transmitted by the day-biting Aedes aegypti mosquito, which also spreads chikungunya and Zika. Anopheles transmits malaria, Culex transmits Japanese encephalitis and filariasis, and sandflies transmit leishmaniasis.

Explanation

OPV is a live attenuated vaccine that induces both mucosal IgA and systemic immunity. The injectable IPV is a killed vaccine. Live vaccines are generally avoided in pregnancy and severe immunodeficiency.

Explanation

Reverse transcriptase transcribes the retroviral RNA genome into DNA, which integrase then inserts into the host genome. Reverse transcriptase inhibitors are a cornerstone of antiretroviral therapy.