Losing immunity to hepatitis A
THE outbreak of hepatitis A in Depok near Jakarta (Sunday Star, Dec 1) has alerted me of this Cinderella hepatitis. Hepatitis B is well known to Malaysians while hepatitis C is newsworthy because of the tremendous advances achieved in its treatment.
However, hepatitis A is often confused with hepatitis B, as is clearly shown whenever a hepatitis B carrier asks his doctor what he can’t eat or when his well-meaning friends advise him to discard the clams from his char koay teow.
It is hepatitis A that is transmitted through the foods we consume, especially filter feeders like bi-valve molluscs. Contaminated water supply and hence uncooked foods washed in it, like fruits, salads and ulam, are other possible sources.
The severity of hepatitis A varies with age. In the very young, it may be a silent disease, the so-called asymptomatic hepatitis. Older children may just experience flu-like symptoms without jaundice. In adults, the classical symptoms of fever, fatigue, nausea, vomiting, anorexia and jaundice predominate. At the most severe end of this continuum is fulminant hepatitis
A. Analysis of data from the United States’ Centre for Disease Control demonstrated that there is a striking correlation between increasing age and death from fulminant hepatitis A, with mortality rates in excess of 2% among the over 40s.
In under-developed countries, overcrowding, poor housing conditions and standards of sanitation favour the spread of the hepatitis A virus. Children in these high endemicity areas are exposed to the virus at a very young age. They hence develop the milder form of hepatitis A, which often go unrecognised among the vast array of other acute infectious diseases present in the area.
On the other hand, as a country develops, modern sewerage systems and the provision of clean drinking water significantly reduce the circulation of the hepatitis A virus in the population. Exposure to the virus in childhood and hence natural immunity becomes less common, leaving an ever-increasing pool of adults susceptible to hepatitis A.
This is what is happening in Malaysia where many adults are now no longer immune to hepatitis A. When these active working and travelling adults visit areas of high endemicity, they may become infected and develop the more severe form of the disease.
With the recent growth in international travel, they are likely to take the virus home with them within the incubation period of two to six weeks before they develop any symptoms. During this period, they would be at their most infectious.
Importing the hepatitis A virus this way could result in an outbreak or epidemic among a largely vulnerable low endemicity population back home. I have had patients who developed hepatitis A after returning from Vietnam, Laos and Cambodia. And now Indonesia is also on the list.
It has been estimated that about 80% of international travellers are tourists, but one should not forget other regular travellers who would also benefit from hepatitis A vaccination, including athletes competing in countries of high endemicity. There is no specific treatment for hepatitis A. Vaccination is the way to prevent the disease.