In this essay we will discuss about Hepatitis A Virus (HAV). After reading this essay you will learn about: 1. Introduction to Hepatitis A Virus (HAV) 2. Resistance 3. Laboratory Diagnosis of Hepatitis A Virus (HAV) 4. Serum Concentration of ALT 5. Epidemiology of Hepatitis A Virus (HAV) 6. Prophylaxis of Hepatitis A Virus (HAV).
Contents:
- Essay on the Introduction to Hepatitis A Virus (HAV)
- Essay on Resistance
- Essay on the Laboratory Diagnosis of Hepatitis A Virus (HAV)
- Essay on the Serum Concentration of ALT
- Essay on the Epidemiology of Hepatitis A Virus (HAV)
- Essay on the Prophylaxis of Hepatitis A Virus (HAV)
Essay # Introduction to Hepatitis A Virus (HAV):
In 1973, HAV (Fig. 52.1) was discovered in faeces of infected patients by immune microscopy. World Health Organisation (WHO) considered that this infection is prevalent worldwide, in countries where overcrowding; poor hygiene and sanitation are common. HAV was classified as picorna virus. It is a 27 to 32 mm spherical with cubic symmetry.
However, there is now more evidence to support that HAV is different from other well defined four genera. The pathogenic mechanism of liver cell damage in acute HAV infection is not yet understood. HAV is destroyed by boiling in water for 5 minutes. Usually it causes a minor or unnoticed illness in children and young adults and high mortality in patients over 60 years of age.
More sensitive serological assays, the microtiter solid phase immuno-radiometric assay and immune adherence could detect HAV in stools, liver homogenates and bile and to measure specific antibody in serum. High titre serum immunoglobulin preparations have value in the prophylaxis of HAV infection. Killed HAV vaccine is under clinical trials.
Essay # Resistance:
(a) HAV is stable to treatment with 20% ether; pH 2.4 and at a temperature of 60°C for one hour.
(b) It can be destroyed by autoclaving, boiling for 5 minutes, dry heat, ultraviolet radiation (UV) and by formalin (1: 4,000 for 3 days at 37°C).
Essay # Laboratory Diagnosis of Hepatitis A Virus (HAV):
Laboratory diagnosis can be done by demonstration of virus and its antibody along with biochemical tests:
(A) HAV Antigen Tests:
Only one type of Hepatitis A virus (HAV) is known—HAV viraemia—occurs only transiently in the incubation period and the excretion of the virus occurs only for 7-10 days after onset of clinical illness.
(1) Isolation:
It is not possible to grow routinely from faeces of patients, though HAV was grown in human and simian cell culture.
(2) Immunofluorescence:
It can detect HAV in faeces during their excretion in faeces.
(B) Hepatitis A Virus Antibodies:
Since it is difficult to isolate HAV from faeces, it is possible to demonstrate specific Ig M antibody to HAV which is found in the blood during early stage of clinical illness and at the time of jaundice appearance.
Though Ig M antibody can be detected in serum for 2-6 months after onset of clinical symptoms. After 3 months the titre falls to a low level. Ig G anti-HAV appears during convalescence and persists for many years. It indicates immunity and past infection.
(C) Biochemical Tests:
The pathological and clinical diagnosis is supported by biochemical tests (Liver function tests like ALT and bilirubin).
(1) Alanine Amino-Transferase (ALT):
Alanine amino-transferase (ALT, previously called as SGPT), a cytoplasmic enzyme and asparagine amino-transferase (AST formerly known as SGOT) are present in cytoplasm and mitochondria. Normal serum contains low activities of these two enzymes.
The source of which is not known. ALT and AST are not specific to the liver, but ALT occurs in much higher concentration in hepatic cells than elsewhere; thus a rise in serum ALT activity reflects more specifically liver damage.
Essay # Serum Concentration of ALT:
(a) During recovery phase of Acute Hepatitis A, titre of 500-2,000 units decrease progressively.
(b) In HAV infection, there is a sharp rise of ALT with short duration (4-20 days).
(c) In HBV infection, there is gradual rise over a longer period (35-200 days).
(d) In non-A-non-B hepatitis, there is fluctuation in serum ALT levels.
Bilirubin and Protein:
With the appearance of jaundice, serum bilirubin level usually reaches 5 to 20 mg/dl. Serum globulin is increased with fall in albumin level.
Essay # Epidemiology of Hepatitis A Virus (HAV):
The spread of the infection is usually from case to case, through contaminated food (raw oysters, shell fish milk) and water.
Essay # Prophylaxis of Hepatitis A Virus (HAV):
The prevention can be by:
(a) Improving the sanitation;
(b) By avoiding the faecal contamination of food and water;
(c) By administrating immune human globulin (Ig G) before or within 1-2 weeks after exposure to HAV infection;
(d) By disinfecting water by sodium hypochlorite (0.5%) for half an hour inactivates virus; one attack can give life-long protection.