UPSC CSE Prelims
Communicable Diseases Previous Year Questions (PYQs)

Detailed Explanation:

Answer: Option 2 — 2 Only

Statement 1 is incorrect because adenoviruses have double-stranded DNA genomes, not single-stranded DNA. Retroviruses have single-stranded RNA genomes (not double-stranded DNA), which they reverse-transcribe into DNA using reverse transcriptase. Statement 2 is correct as adenoviruses are a common cause of the common cold, and AIDS is indeed caused by HIV, a retrovirus.

❌ Statement 1 – Incorrect: Adenoviruses have double-stranded DNA genomes; retroviruses have single-stranded RNA genomes, not double-stranded DNA.
✅ Statement 2 – Correct: The common cold can be caused by adenoviruses, and AIDS is caused by HIV, which is a retrovirus.

📝 Short Notes: Viral Genome Types

• DNA Viruses: Generally replicate in the nucleus using host cell machinery (exceptions: poxviruses replicate in cytoplasm)
• RNA Viruses: Most replicate in the cytoplasm; carry their own RNA polymerase
• Retroviruses: Unique in possessing reverse transcriptase enzyme that synthesizes DNA from RNA template
• Common Cold Causes: Rhinoviruses (most common), coronaviruses, adenoviruses, and others
• HIV Classification: Lentivirus genus of the Retroviridae family; targets CD4+ T cells

Detailed Explanation:

Answer: Option 3 — Both 1 and 2

✅ Statement 1 – Correct: Zika virus is primarily transmitted by the Aedes aegypti mosquito in tropical regions. This is the same mosquito species that transmits dengue, chikungunya, and yellow fever. The mosquito becomes infected when it bites an infected person and can then transmit the virus to other people through subsequent bites.

✅ Statement 2 – Correct: Sexual transmission of Zika virus is well-documented and possible. The virus can be transmitted through vaginal, anal, and oral sex. It can persist in semen for several months, making sexual transmission a significant route of infection even in areas without active mosquito transmission. Pregnant women are particularly at risk as Zika can cause severe birth defects.

Therefore, both statements are correct.

Detailed Explanation:

The 2014–2016 Ebola outbreak was the most widespread epidemic of Ebola virus disease (EVD) in history, primarily affecting West African countries.

The outbreak began in Guinea in December 2013 and rapidly spread to neighboring Liberia and Sierra Leone, causing over 11,000 deaths and massive socio-economic disruption. These three countries accounted for the vast majority of cases and were frequently mentioned in global news coverage.

Detailed Explanation:

H1N1 virus is a subtype of Influenza A virus that causes Swine flu, which was declared a pandemic by WHO in June 2009.

The virus contains glycoproteins haemagglutinin (H) and neuraminidase (N), hence named H1N1, and was also responsible for the 1918 Spanish Flu outbreak.

Detailed Explanation:

❌ Statement 1 – Incorrect: Diphtheria has not been eradicated; India still administers the Pentavalent vaccine (introduced in 2011–12) which includes DPT (Diphtheria, Pertussis, Tetanus) component, indicating ongoing disease burden.

❌ Statement 2 – Incorrect: Chickenpox (Varicella) remains endemic in India; the Varicella vaccine is available but not part of the Universal Immunization Programme (UIP), and cases occur regularly across the country.

✅ Statement 3 – Correct: Smallpox was declared eradicated from India in 1975 (last case in 1975), and WHO certified global eradication in 1980; India played a key role in the worldwide eradication campaign.

Detailed Explanation:

❌ Statement 1 – Incorrect: Chikungunya is a mosquito-borne viral disease transmitted by Aedes mosquitoes, not through blood contact or tattooing.

✅ Statement 2 – Correct: Hepatitis B is a bloodborne viral infection that can be transmitted through contaminated tattooing needles and equipment.

✅ Statement 3 – Correct: HIV-AIDS spreads through contact with infected blood, making transmission possible via unsterilized tattooing equipment.