Hepatitis B virus.
DNA virus, transmitted perinatally (mom-fetus), percutaneously (blood; needles, IV drug use), horizontally (mucosa, blood, body fluids). Incubation 45-180 days (avg. 56-96). 90% of infected neonates develop chronic Hep B. Serum surface antigen (HBsAg) that persists 6 to 12+ months after infection indicates carrier state. Serum surface antibodies (anti-HBs or HBsAB) indicate immunity from HBV vaccine or past HBV infection. With chronic HBV infection, liver enzymes may be normal, elevated with low-grade disease, or severe liver disease.