LABORATORY DIAGNOSIS OF HEPATITIS A VIRUS

Hepatitis A is a fecal-oral transmitted infection often acquired through contaminated food. Hepatitis A Virus causes infectious hepatitis. It is a subacute disease of global distribution, which affects mainly children and young adults.

Some Key Features of Hepatitis A Virus

Hepatitis A History:

1. Epidemic jaundice described by Hippocrates
2. Differentiated from Hepatitis B in 1940s
3. Serologic tests developed in 1970s
4. Vaccine licensed in 1995 and 1996

Hepatitis A Properties:

1. Picornavirus (RNA)
2. Human are only natural host
3. Stable at low pH
4. Inactivated by high temperature (185oF or higher), formalin, chlorine

Hepatitis A Pathogenesis

1. Entry into mouth
2. Viral replication in the liver
3. Virus present in blood and feces 10-12 days after infection
4. Virus excretion may continue for upto 3 weeks after onset of symptoms

Hepatitis A Clinical Features

1. Incubation period 28 days (range 15-50 days)
2. illness not specific for hepatitis A
3. Likelihood of symptomatic illness directly related to age
4. Children generally asymptomatic, adults symptomatic

Hepatitis A Epidemiology

1. Reservoir: Human
2. Transmission: Fecal-oral
3. Temporal pattern: None
4. Communicability: 2 weeks before to one week after onset

Hepatitis A can not be distinguished from other types of viral hepatitis on the basis of clinical or epidemiologic features alone. Serologic testing is required to confirm the diagnosis. 

1. Electron microscopy: Hepatitis A Virus is present in stools before the onset of clinical symptoms and can be demonstrated by electron microscopy. Virus appear early in the disease and disappears within 2 weeks following the onset of jaundice.
   
2. Virus isolation:  Hepatitis A Virus can be grown in human simian cell cultures. Isolation in cell cultures is difficult and not practical for diagnostic use.
   
3. Polymerase chain reaction: Detection of nucleic acid with PCR can be useful both as an epidemiological tool and in environmental studies but it is not indicated for clinical use. HAV can be detected in the liver, stool, bile, and blood of naturally infected humans and experimentally infected nonhuman primates by immunoassays, nucleic acid hybridization assays or PCR. HAV is detected in the stool from about 2 weeks prior to the onset of jaundice up to 2 weeks after.
   
4. Serology:  Antibodies  against Hepatitis A Virus can be demonstrated from the onset of the clinical symptoms.  Hepatitis A antibody testing is performed first. IgM antibody tests are performed on all reactive specimens. Hepatitis A IgM indicates acute infection.
   Diagnosis of acute infection requires demonstration of anti-HAV IgM antibodies or seroconversion. IgM antibodies disappear about 3–6 months after the onset of disease. IgG antibodies on the other hand persist for life and indicate immunity against reinfection. Antibodies are demonstrated by means of EIA or RIA.

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