HAV, HBV, and HCV are the most clinically-significant viruses that give rise to hepatitis. However, we now know of the existence of hepatitis E and hepatitis D viruses.
Hepatitis E infects approximately 2 billion people worldwide. The World Health Organization (WHO) reported that approximately 20 million people are infected yearly, and of those cases approximately 3 million progress to an acute hepatitis syndrome. The mode of transmission and the risk factors for Hepatitis E infection are not fully understood. Transmission is predominantly thought to be via the fecal-oral route, through contaminated water. Animal transmission to humans may also play a role. In developed countries, hepatitis E has a prevalence of less than 1%. Interestingly, as many as 1%-3% of people in the US have antibodies to hepatitis E, making it more widespread than previously thought. Hepatitis E virus usually causes acute hepatic inflammation that is self-limiting.
Hepatitis D, which is also known as 'delta hepatitis,' only occurs in people who are first infected with HBV. Hepatitis D is an incomplete virus that requires HBV antigen to replicate. Hepatitis D can be an acute or chronic infection. Hepatitis D is transmitted through percutaneous or mucosal contact with infected blood or body fluids. Transmission of HDV can occur either simultaneously with HBV infection (coinfection) or superimposed on chronic hepatitis B or hepatitis B carrier state (superinfection). HBV vaccination will also prevent hepatitis D infection.
Serologic laboratory assays now exist for Hepatitis E and D. While still relatively rare, testing for these antibodies may be performed when viral hepatitis appears to be present but HAV, HBV, and HCV have been ruled out.
