Hepatitis Viruses HAV, HBV NonA-NonB: HCV, HDV, HEV
HAV Disease Hepatitis A Important properties Typical enterovirus (enterovirus72) classified in Picornavirus Single-stranded RNA genome Non- enveloped icosahedral nucleocapsid Replicates in the cytoplasm of the cell. One serotype. Humans and chimpanzees are the only natural hosts.
Replicative cycle A positive strand RNA: Genome replication occurs by synthesis of a complementary negative strand which then serves as the template for the positive strands which are needed both for replication and protein synthesis.
Transmission & Epidemiology Transmitted by fecal-oral rote. Virus in feces 2 weeks before the symptoms. So quarantine of patients is ineffective. Children the most frequently infected group. Outbreaks arise from fecally contaminated water or food. The level of viremia is low and chronic infection does not occur.
Pathogenesis HAV replicates in gasterointestinal tract epithelial cells and spreads to the liver via the blood. Very low level of viremia Hepatocytes are infected. HAV infection of cultured cells produces no cytopathic effect. Immune attack on the hepatocytes plays no role in pathogenesis (against HBV). No chronic infection. The infection cannot be distinguished pathologically from other hepatitis infections.
Clinical findings (HAV) Clinical manifestations of hepatitis are virtually the same Fever Anorexia Nausea Vomiting Jaundice fatigue
Clinical findings (HAV) Usually resolve spontaneously in 2-4 weeks. Incubation period: average 1 month
Immunity Immune response is initially IgM antibody detectable at the time jaundice appears. The appearance of IgM is followed 1-3 weeks later by the production of IgG antibody which provides lifelong protection.
Laboratory diagnosis Detection IgM (the most important test). 4-fold rise in IgG titer. Treatment & Prevention No antiviral therapy. vaccine is available. Immune prophylaxy is available Resolves itselfe spontaneously.
A member of hepadenavirus. 42-nm enveloped virion with an icosahedral nucleocapsid. Partially double-strand circular DNA genome.
Antigenes and fragments HBsAg (important both in diagnosis and immunization). DNA-dependent DNA polymerase 3 different types of particles: 42-nm virions, 22-nm spheres, long filaments 22 nm wide. HBcAg (Core antigen ) HBe Ag (an indicator of transmissibility)
Serotypes based on HBsAg HBsAg: A group-specific antigen, ‘a’ and 2 sets of exclusive epitopes, d or y and w or r leading to 4 serotypes: adw, adr, ayw, ayr which are useful in epidemiologic studies. Humans are the only natural host of HBV.
Replicative cycle DNA polymerase synthesize the missing portion of DNA --- Fully double-strand circular DNA in nucleus --- Some DNA copies integrates into hepatocyte DNA /// Some DNA copies serves as a template for mRNA synthesis --- mRNA functions both in protein synthesis and template for the DNA minus strand (by RNA-dependent DNA polymerase) --- DNA minus strand serves as template for plus strand.
Transmission & Epidemiology Blood is Most important way of transmission. In addicts using intravenous drugs. Sexual transmission. Mother to child during birth or breast feeding. Immunization reduces the incidence.
Clinical finding Incubation period: 2-3 months The acute disease is similar to that of HAV. Symptoms in HBV tend to be more severe than HAV. Most chronic carriers are asymptomatic.
Pathogenesis Entering HBV the blood --- infecting hepatocytes --- necrosis and inflammation (Immune attack against viral antigens on infected hepatocytes). 10% of patients become chronic carriers of HBV (probably due a persistent infection of hepatocytes mediated DNA integrated into cell DNA): Chronic persistent hepatitisChronic persistent hepatitis Some chronic carriers have chronic active hepatitis may leading to cirrhosis, hepatocellular carcinoma and death.
Laboratory diagnosis Immunoassay for HBs Ag HBsAg during the incubation period and mostly during the prodome and acute disease. Prolonged presence of HBsAg indicates carrier state and the risk of chronic hepatitis. Windows phase: no HBsAg and HBsAb but HBcAb HbeAg: During incubation period and is present during prodrome and early acute disease (an indicator of transmissibility). HBeAb indicates low transmissibility. DNA polymerase during incubation and early in the disease but assay not available in clinical lab.
Treatment & Prevention Alpha interferon Lamivudine (inhibits hepatitis B viral DNA synthesis) Baraclude (inhibiting hepatitis B viral DNA synthesis) Rest, combined with a high protein/high carbohydrate diet to repair damaged liver cells. Prevention by using vaccine and hyperimmune globulin (HBIG) No one with a history of hepatitis (of any type) should donate blood.
NON-A, NON-B hepatitis viruses HCV -Distributed worldwide -The most major agent of Non-A, Non-B -An enveloped single-strand RNA virus (a flavivirus). -Incubation period: an average of 2 months -No immunity
80% of cases go to chronic forms tend to cause cirrhosis (20-50%) or hepatocellular carcinoma (5-25%). Mild infection and only 25% show jaundice. Most cases are asymptomatic There are at least 6 genotypes of HCV Diagnosis is based on serologic methods (ELISA)
HEV An enterically transmited virus Nonenveloped, single-stranded RNA virus (from calcivirus). Diagnosis is serologic (ELISA) based on IgM and IgG No antiviral agent for treatment
HVD (Delta agent) Single-stranded circle RNA RNA genome surrounded by an envelope composed of HBsAg. A defective virus as its genome does not code for its own envelope protein. HDV can only replicate in HBV-infected cells. Delta antigen is a distinctive determinant present in this virus but not in HBV.
HDV HDV + HBV infection tends to be a fulminant hepatitis. Transmission the same as HBV A chronic carrier state can occur. Infection can be detected by the appearance of IgM to delta antigen. No treatment No vaccine