Viral Infections Classification for NEET PG 2026: Complete Guide

Virology in NEET PG is structured around two big buckets: DNA vs RNA. Examiners drill on classification (capsid symmetry, envelope, segmented vs non-segmented), the viral cycle, and the clinical syndrome — most stems lead with a vignette and ask "Which virus?" or "Which antiviral?".

This NEETPGAI deep dive maps every high-yield virus to its family, genome type, transmission, classic clinical features, diagnostic test, and treatment. Pair this with the Microbiology subject hub and the bacterial infections classification guide for full microbio coverage.

Classification at a glance

Mnemonic for non-enveloped viruses (PAPP-CR): Picorna, Adeno, Papilloma, Polyoma, Calici, Reo. Non-enveloped = stable in environment, faeco-oral common.

DNA viruses

Herpesviruses

• Acyclovir activated by viral thymidine kinase (HSV/VZV) → triphosphate → blocks viral DNA polymerase. Resistance via TK loss (foscarnet for resistant cases).
• Ganciclovir/valganciclovir for CMV; activated by viral UL97 kinase. Side effect: marrow suppression.

Hepatitis B virus (HBV — Hepadnavirus)

• Partial dsDNA, enveloped, reverse transcriptase in life cycle (only DNA virus with RT).
• Serology high-yield:
  • HBsAg+ → infection (acute or chronic).
  • HBeAg+ → high infectivity and active replication.
  • Anti-HBs+ → immunity (vaccine or recovered).
  • Anti-HBc IgM → acute infection (window-period marker).
  • Anti-HBe → seroconversion, less infectious.
• Treat chronic HBV with tenofovir or entecavir; HBV vaccine in UIP from birth.

Human papillomavirus (HPV)

• Non-enveloped dsDNA. High-risk types 16, 18, 31, 33, 45 drive cervical, anal, oropharyngeal cancers.
• E6 binds and degrades p53; E7 binds and inactivates Rb.
• Vaccines: bivalent (16, 18), quadrivalent (6, 11, 16, 18), 9-valent (adds 31, 33, 45, 52, 58). Indian Cervavac (quadrivalent) is now in HPV programme.

Parvovirus B19

• Single-stranded DNA, non-enveloped. Tropism for erythroid progenitors via P-antigen.
• Erythema infectiosum (slapped-cheek, 5th disease), aplastic crisis in sickle cell, hydrops fetalis in pregnancy.

Other DNA viruses

• Adenovirus — pharyngoconjunctival fever, military recruit ARDS, gastroenteritis (types 40, 41).
• Smallpox — eradicated 1980; monkeypox (mpox) — re-emergence 2022; tecovirimat is the antiviral.

RNA viruses — respiratory

Influenza

• (−)ssRNA, segmented, enveloped. Surface antigens: HA (attachment) and NA (release). Antigenic shift causes pandemics.
• H1N1 (2009 pandemic), H5N1 (avian), H7N9.
• Treatment: oseltamivir, zanamivir (NA inhibitors); baloxavir (cap-dependent endonuclease inhibitor).

RSV

• (−)ssRNA, paramyxo. Leading cause of bronchiolitis <2 years.
• Palivizumab (monoclonal anti-F protein) prophylaxis in high-risk preterms.

SARS-CoV-2 (COVID-19)

• (+)ssRNA, enveloped, corona. Spike protein binds ACE2.
• Antivirals: remdesivir (RdRp inhibitor), nirmatrelvir-ritonavir (Mpro inhibitor), molnupiravir (mutagenic).
• Vaccines used in India: Covishield (ChAdOx1), Covaxin (whole-virion inactivated), Corbevax (RBD subunit), iNCOVACC (intranasal).

Other respiratory

• Measles (paramyxo, rubeola) — 3 Cs (cough, coryza, conjunctivitis), Koplik spots, maculopapular rash, SSPE late complication.
• Mumps (paramyxo) — parotitis, orchitis, aseptic meningitis.
• Rubella (toga) — maternal infection in 1st trimester causes congenital rubella syndrome (cataract, heart defects, deafness — Gregg triad).

RNA viruses — enteric and hepatitis

Hepatitis viruses summary

• HCV cure: direct-acting antivirals (sofosbuvir + velpatasvir or daclatasvir; glecaprevir + pibrentasvir) — >95% SVR12 in 8–12 weeks.

RNA viruses — arboviruses (NEET PG India favourites)

Dengue specifics

• WHO 2009 classification: dengue without warning signs, with warning signs, severe dengue.
• Warning signs: abdominal pain, persistent vomiting, mucosal bleed, lethargy, hepatomegaly, rising HCT with falling platelets.
• Diagnosis: NS1 days 1–9 (peaks 1–5); IgM days 5+; PCR in early phase.
• Severe dengue triggered by antibody-dependent enhancement with secondary heterotypic infection.

Retroviruses — HIV

• (+)ssRNA, enveloped, RT, integrase. Gp120 binds CD4 + CCR5/CXCR4 co-receptor.
• Acute retroviral syndrome (mononucleosis-like) → seroconversion.
• Diagnosis: 4th-generation Ag/Ab combo (p24 antigen + antibodies). Confirm with HIV-1/2 differentiation immunoassay; viral load by PCR.
• First-line ART (NACO, India): TLD (Tenofovir + Lamivudine + Dolutegravir) for adults, adolescents, and most children >30 kg.
• PrEP: tenofovir + emtricitabine.
• PMTCT: ART for life (Option B+); single-dose nevirapine to neonate plus 6-week zidovudine.

Rhabdo and other notable RNA viruses

• Rabies (rhabdo) — bullet-shaped, Negri bodies in hippocampus and Purkinje cells. Almost 100% fatal once symptomatic. Post-exposure prophylaxis: wound wash, RIG (passive), 5-dose Essen or 4-dose Zagreb regimen of cell-culture vaccine.
• Ebola (filo) — enveloped, filamentous, devastating haemorrhagic fever; remdesivir, monoclonal Abs (REGN-EB3, mAb114).
• Lassa (arena) — Africa rodent-borne haemorrhagic fever; ribavirin treatment.
• Hantavirus (bunya) — pulmonary syndrome (Sin Nombre), HFRS in Eurasia.

Antivirals at a glance

High-yield NEET PG MCQ traps

1. Only DNA virus with RT — Hepatitis B (Hepadnavirus).
2. Negative-sense RNA viruses carry their own RNA-dependent RNA polymerase in the virion.
3. Antibody-dependent enhancement — secondary heterotypic dengue infection drives DHF/DSS.
4. Slapped cheek + aplastic crisis + hydrops — Parvo B19.
5. Owl's-eye intranuclear inclusion — CMV; Cowdry A — HSV/VZV; Negri body — rabies.
6. Roseola (high fever 3 days, rash on defervescence) — HHV-6 or HHV-7.
7. HEV in pregnancy — fulminant hepatic failure with up to 25% mortality.
8. Burkitt lymphoma c-MYC translocation t(8;14) — EBV-driven.
9. Tzanck smear — multinucleated giant cells in HSV/VZV.
10. HIV first-line in India — TLD, regardless of CD4 count.

Recent updates and Indian context

• Mpox (2022 outbreak) — clade IIb spread globally; tecovirimat under expanded access; smallpox vaccine (JYNNEOS) cross-protective.
• HPV vaccine in UIP — Cervavac (quadrivalent, Indian-made by SII) included for adolescent girls.
• NACO ART policy — universal "test and treat" since 2017; TLD first-line.
• Dengue surveillance — IDSP weekly P-form; Tamil Nadu, Kerala, West Bengal report highest case loads pre-monsoon.
• Influenza — H3N2 wave (early 2023) tested NEET PG knowledge of oseltamivir dosing and high-risk groups.

Frequently Asked Questions

Which DNA viruses establish latency and where?

Herpesviruses are the classic latent DNA viruses. HSV-1/2 latent in trigeminal/sacral ganglia, VZV in dorsal root ganglia, EBV in B-lymphocytes, CMV in monocytes and CD34+ progenitors, HHV-6 and HHV-7 in T-cells, HHV-8 (KSHV) in B-cells. Reactivation drives recurrent disease, especially under immunosuppression.

What are the seven oncogenic viruses tested in NEET PG?

EBV (Burkitt lymphoma, nasopharyngeal carcinoma, post-transplant lymphoma), HBV and HCV (hepatocellular carcinoma), HPV (cervical, anal, oropharyngeal cancer — types 16/18), HTLV-1 (adult T-cell leukaemia), HHV-8 (Kaposi sarcoma), and Merkel cell polyomavirus (Merkel cell carcinoma). Mnemonic — 7 viruses, 1 hallmark of cancer.

What is the dengue NS1 antigen window?

NS1 antigen is detectable from day 1 to day 9 of illness — peaking days 1–5 and overlapping the febrile phase. IgM appears day 5 and persists 6 weeks; IgG from day 7 in primary, earlier and higher in secondary. Best diagnostic strategy: NS1 in days 1–5; IgM/IgG paired serology after day 5.

Which antiviral drugs target HIV reverse transcriptase?

NRTIs (zidovudine, tenofovir, abacavir, lamivudine, emtricitabine) competitively inhibit reverse transcriptase by chain termination. NNRTIs (efavirenz, nevirapine, rilpivirine, doravirine) bind allosterically and inhibit non-competitively. Modern first-line ART in India is tenofovir + lamivudine + dolutegravir (TLD) — dolutegravir is an integrase inhibitor.

What is the difference between hepatitis A and hepatitis E in pregnancy?

Hepatitis A (RNA, picornavirus, faeco-oral) is mostly self-limited in pregnancy. Hepatitis E (RNA, hepevirus, faeco-oral) is associated with up to 25% mortality in third-trimester pregnancy due to fulminant hepatic failure — a high-yield Indian-context exam stem. Both are transmitted via contaminated water; HEV outbreaks are common in India.

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Written by: NEETPGAI Editorial Team Reviewed by: Pending SME Review Last reviewed: April 2026