INTRODUCTION TO HEPATITIS A VIRUS (HAV)
⇒ Hepatitis A virus (HAV) was first demonstrated by the Feinstone & co-workers in 1973 by using immunoelectron microscopy (IEM).
⇒ HAV causes Type A hepatitis or Infectious Hepatitis, a subacute disease occurring mainly in children & young adults.
MORPHOLOGY OF HEPATITIS A VIRUS
⇒ HAV is a 27 nm, non-enveloped, single-stranded RNA virus with an icosahedral symmetry.
⇒ HAV belongs to the Picornavirus family.
⇒ Only one serotype of this virus exists.
TRANSMISSION ROUTE OF HEPATITIS A VIRUS
⇒ The Hepatitis A virus enters the body by the oral route through contaminated food, water or milk.
RESISTANCE SHOWN BY HEPATITIS A VIRUS
⇒ HAV is resistant to inactivation by heat at 60o C for 1 hour, ether & to pH 3, can survive at 4o C or below.
⇒ HAV is destroyed by autoclaving at 121oC, boiling for five minutes, formaldehyde (1:4000), by chlorine at 10-15 ppm for 30 minutes & inactivate by UV rays.
CLINICAL FEATURES OF HEPATITIS A VIRUS
⇒ The large majority of infections are asymptomatic.
⇒ The incubation period is 2-6 weeks.
⇒ Symptoms include Fever, Malaise, Anorexia, Nausea, Vomiting, Liver tenderness, usually subsides with Jaundice.
⇒ Rapidly fatal fulminant hepatitis is very rare.
LABORATORY DIAGNOSIS OF HEPATITIS A VIRUS
⇒ Specimen:- Feces or serum may be collected for the demonstration of the virus or its antibodies.
⇒ Direct demonstration:– The virus can be visualized by IEM in feces.
⇒ Serology:– IgM anti-HAV antibody appears during the late incubation period, reaches peak levels in 2-3 weeks & disappears after 3-4 months. IgG antibodies also appear & peaks in 3-4 months and persist much longer. ELISA kits are used to detect the presence of these antibodies in the feces & also can be detected by radioimmunoassay.
⇒ Biochemical tests:– Liver function tests such as serum alanine aminotransferase (ALT) and bilirubin level supplements the diagnosis.
PROPHYLAXIS OF THE HEPATITIS A VIRUS INFECTION
⇒ Improved sanitation & prevention of fecal contamination of food & water.
⇒ HAV vaccination is available, the full course consists of two intramuscular injections of the vaccine. Protection lasts for 10-20 years.
⇒ One attack of the disease gives life-long protection against HAV.