Q.79 Which of the following diseases are caused by family of DNA viruses?
(A) Hepatitis B
(B) Smallpox
(C) Influenza
(D) Rabies
Hepatitis B and Smallpox are caused by DNA viruses, making options (A) and (B) correct.
Hepatitis B virus belongs to the Hepadnaviridae family with a partially double-stranded circular DNA genome, while the smallpox virus (variola) is from the Poxviridae family featuring a large linear double-stranded DNA genome. Influenza and rabies, however, involve RNA genomes, so they do not qualify.
Option Analysis
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(A) Hepatitis B: Caused by hepatitis B virus (HBV), a member of the Hepadnaviridae family. Its genome is 3,020–3,320 nucleotides of relaxed circular, partially double-stranded DNA, encoding genes like C, P, S, and X. HBV replicates via reverse transcription but remains classified as a DNA virus.
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(B) Smallpox: Caused by variola virus in the Poxviridae family (genus Orthopoxvirus). The genome is linear double-stranded DNA, approximately 186,000 base pairs long, with about 200 genes for replication in the host cytoplasm.
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(C) Influenza: Caused by influenza viruses (Orthomyxoviridae family), which have a segmented, single-stranded negative-sense RNA genome (eight segments for types A and B).
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(D) Rabies: Caused by rabies virus (Rhabdoviridae family), featuring a non-segmented single-stranded negative-sense RNA genome (~12 kb) encoding five proteins: N, P, M, G, and L.
Correct Answer
(A) and (B). Both diseases stem from distinct DNA virus families, unlike the RNA-based influenza and rabies viruses.
Diseases caused by DNA viruses, such as Hepatitis B and Smallpox, highlight key distinctions in viral genomics relevant for exams like CSIR NET Life Sciences. These pathogens use double-stranded or partially double-stranded DNA genomes, contrasting with RNA viruses like Influenza and Rabies.
DNA Virus Families and Key Examples
DNA viruses encompass families like Hepadnaviridae and Poxviridae, infecting humans via blood, bodily fluids, or respiratory routes.
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Hepadnaviridae (Hepatitis B): HBV’s compact ~3.2 kb circular DNA genome replicates in hepatocytes, leading to acute or chronic liver disease. Eight genotypes (A-H) vary globally, with reverse transcription during replication.
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Poxviridae (Smallpox): Variola virus’s 186 kb linear dsDNA genome encodes cytoplasmic replication machinery, causing severe rash and fever; eradicated in 1980 via vaccination.
RNA Viruses: Why Not Included
Influenza (Orthomyxoviridae) and Rabies (Rhabdoviridae) rely on ssRNA genomes for rapid mutation and antigenic drift/shift.
| Disease | Virus Family | Genome Type | Key Feature |
|---|---|---|---|
| Hepatitis B | Hepadnaviridae | Partially dsDNA (circular) | Liver tropism, chronic carrier state |
| Smallpox | Poxviridae | dsDNA (linear) | Cytoplasmic replication, eradicated |
| Influenza | Orthomyxoviridae | ssRNA (-sense, segmented) | Annual epidemics, vaccines updated |
| Rabies | Rhabdoviridae | ssRNA (-sense, non-segmented) | Neurotropic, nearly 100% fatal post-symptoms |
This table clarifies genome-based classification for competitive exams.
Exam Relevance for CSIR NET
Understanding diseases caused by DNA viruses aids in virology questions on Baltimore classification (Groups I, II for DNA viruses). HBV integrates into host DNA in chronic cases, while poxviruses avoid nucleus dependency.
