Microbiology for NEET-PG
Hepatitis Viruses for NEET-PG
Five hepatotropic viruses cause viral hepatitis: HAV, HBV, HCV, HDV, and HEV. HAV and HEV spread by the faeco-oral route and cause acute self-limiting disease, while HBV, HCV, and HDV spread parenterally or sexually and can progress to chronic hepatitis, cirrhosis, and hepatocellular carcinoma. For NEET-PG, the highest-yield discriminators are genome type, transmission, chronicity potential, and serological markers. HAV is a non-enveloped RNA picornavirus; HEV is a non-enveloped RNA hepevirus notorious for fulminant hepatitis in pregnant women, especially in the third trimester, with mortality reaching around 20 percent. HBV is the only DNA virus of the group, a partially double-stranded hepadnavirus that replicates through reverse transcription and carries the classic surface, core, and e antigen serology. HCV is an enveloped RNA flavivirus with the highest tendency to chronicity, historically the leading cause of post-transfusion hepatitis before screening. HDV is a defective RNA virus that needs HBsAg to assemble, so it occurs only as co-infection or superinfection with HBV. Diagnosis rests on serology and nucleic acid testing. Vaccines exist for HAV and HBV, and HBV vaccination protects against HDV. HEV vaccine is licensed in China but not widely used. Interpreting the HBV serological panel, distinguishing acute from chronic infection, recognising the window period, and reading the anti-HBc IgM versus IgG pattern are recurrent exam themes.
MedNext Academy | 3 min read
Hepatitis Viruses for NEET-PG
Five hepatotropic viruses cause viral hepatitis: HAV, HBV, HCV, HDV, and HEV. HAV and HEV spread by the faeco-oral route and cause acute self-limiting disease, while HBV, HCV, and HDV spread parenterally or sexually and can progress to chronic hepatitis, cirrhosis, and hepatocellular carcinoma. For NEET-PG, the highest-yield discriminators are genome type, transmission, chronicity potential, and serological markers. HAV is a non-enveloped RNA picornavirus; HEV is a non-enveloped RNA hepevirus notorious for fulminant hepatitis in pregnant women, especially in the third trimester, with mortality reaching around 20 percent. HBV is the only DNA virus of the group, a partially double-stranded hepadnavirus that replicates through reverse transcription and carries the classic surface, core, and e antigen serology. HCV is an enveloped RNA flavivirus with the highest tendency to chronicity, historically the leading cause of post-transfusion hepatitis before screening. HDV is a defective RNA virus that needs HBsAg to assemble, so it occurs only as co-infection or superinfection with HBV. Diagnosis rests on serology and nucleic acid testing. Vaccines exist for HAV and HBV, and HBV vaccination protects against HDV. HEV vaccine is licensed in China but not widely used. Interpreting the HBV serological panel, distinguishing acute from chronic infection, recognising the window period, and reading the anti-HBc IgM versus IgG pattern are recurrent exam themes.
Five hepatotropic viruses cause viral hepatitis: HAV, HBV, HCV, HDV, and HEV. HAV and HEV spread by the faeco-oral route and cause acute self-limiting disease, while HBV, HCV, and HDV spread parenterally or sexually and can progress to chronic hepatitis, cirrhosis, and hepatocellular carcinoma. For NEET-PG, the highest-yield discriminators are genome type, transmission, chronicity potential, and serological markers. HAV is a non-enveloped RNA picornavirus; HEV is a non-enveloped RNA hepevirus notorious for fulminant hepatitis in pregnant women, especially in the third trimester, with mortality reaching around 20 percent. HBV is the only DNA virus of the group, a partially double-stranded hepadnavirus that replicates through reverse transcription and carries the classic surface, core, and e antigen serology. HCV is an enveloped RNA flavivirus with the highest tendency to chronicity, historically the leading cause of post-transfusion hepatitis before screening. HDV is a defective RNA virus that needs HBsAg to assemble, so it occurs only as co-infection or superinfection with HBV. Diagnosis rests on serology and nucleic acid testing. Vaccines exist for HAV and HBV, and HBV vaccination protects against HDV. HEV vaccine is licensed in China but not widely used. Interpreting the HBV serological panel, distinguishing acute from chronic infection, recognising the window period, and reading the anti-HBc IgM versus IgG pattern are recurrent exam themes.
Key points
- **Genome and family:** HAV picornavirus RNA, HEV hepevirus RNA, HCV flavivirus RNA, HDV deltavirus RNA, HBV hepadnavirus DNA. HBV is the only DNA virus.
- **Faeco-oral pair:** HAV and HEV spread through contaminated water and food, cause acute self-limiting hepatitis, and never become chronic.
- **HEV in pregnancy:** HEV causes fulminant hepatic failure in pregnant women, worst in the third trimester, with high maternal mortality around 20 percent.
- **Parenteral group:** HBV, HCV, and HDV transmit through blood, sexual contact, and vertically. HCV has the greatest chronicity potential.
- **HBsAg:** First serological marker to appear and the marker of active infection. Persistence beyond six months defines chronic HBV.
- **Window period:** HBsAg has cleared but anti-HBs not yet detectable. Anti-HBc IgM is the only positive marker and confirms recent infection here.
- **HBeAg:** Marker of high viral replication and infectivity. Anti-HBe seroconversion signals falling infectivity.
- **Immunity versus infection:** Isolated anti-HBs indicates vaccination. Anti-HBs with anti-HBc indicates resolved natural infection.
- **HDV dependence:** HDV needs HBsAg envelope to propagate. Superinfection on chronic HBV carries worse prognosis than co-infection.
- **Oncogenesis:** Chronic HBV and HCV are leading causes of hepatocellular carcinoma. HBV can integrate into host genome and act directly.
- **Vaccination:** HAV and HBV have effective vaccines. HBV vaccine indirectly prevents HDV. No routine vaccine for HCV.
Frequently Asked Questions
Which hepatitis viruses cause chronic infection?
HBV, HCV, and HDV can become chronic. HCV has the highest chronicity rate. HAV and HEV are always acute and self-limiting.
What is the window period in hepatitis B?
It is the interval when HBsAg has disappeared but anti-HBs has not yet risen. Anti-HBc IgM is the only detectable marker and confirms recent HBV infection.
Why is hepatitis E dangerous in pregnancy?
HEV causes fulminant hepatic failure in pregnant women, particularly in the third trimester, with maternal mortality reported near 20 percent.
How does hepatitis D depend on hepatitis B?
HDV is a defective virus that cannot make its own envelope. It uses HBsAg from HBV, so it infects only patients who already carry HBV.
What marker indicates immunity from hepatitis B vaccination?
Isolated anti-HBs positivity with negative anti-HBc indicates vaccine-induced immunity, since the vaccine contains only surface antigen.
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