Viral Disease

Viral Disease infectious diseases caused by the virus pathogen. There is about a dozen different groups or families of viruses that cause significant human diseases. Some common viral diseases are yellow fever, dengue fever, poliomyelitis, hepatitis, rabies, influenza, mumps, measles, pox, herpes, rotavirus diarrhoea, Chron's disease and a variety of encephalitis. Many types of cancers are also believed to be caused by oncogenic viruses.

Small pox had been a scourge to mankind which is caused by the virus variola major belonging to the poxvirus family. There are somewhat less virulent viruses of the poxvirus family which cause less severe disease. These less virulent viruses have been used to advantage in the formulation of vaccines for protection against small pox. Vaccinia virus is one such virus that has been extensively used for vaccination against small pox in many countries.

In the process of vaccine making, the vaccinia virus is first inoculated in the skin of cow. The fluid from the lesion that develops at the site of inoculation is collected and used as vaccine or, the virus collected from the lesion is multiplied by injecting in chicken embryo before being used. In 1967 the World Health Organisation (WHO) undertook a global small pox eradication campaign and successfully executed the programme so that within a few years small pox was completely eradicated from the world. The last small pox case to be recorded in the Asian subcontinent was detected in Bangladesh in 1975; the last natural victim of small pox occurred in Somalia in 1977. To the success of small pox eradication from Bangladesh, the Institute of Public Health (IPH) played a vital role in preparing the vaccine and making the vaccination programme successful.

Common viral diseases in Bangladesh include hepatitis, poliomyelitis, rabies, measles, mumps, rotavirus diarrhoea, and 'chicken pox'. Chicken pox is caused by a virus, but the virus is not related to pox virus. The above diseases are among the list of viral diseases for which a diagnosis is usually made by the physician based on well known clinical symptoms and in a small number of cases, by laboratory tests. In most cities and smaller towns, the extent of facilities that are available allow only ordinary clinical tests to be performed such as blood picture examination which is used by physicians as the sole laboratory test for diagnosis of a bacterial or viral infections. Only in the major cities there exists facilities for immunological diagnosis of viral infections. Tests for hepatitis B virus is the most common immunological test presently available in the country. Cases of possible viral encephalitis and tests for oncogenic viruses associated with cancers are not investigated at present as to their possible viral basis because these tests are not routinely available in the country.

Incidence of different viral diseases are not well recorded as part of a national documentation and reporting programme, because such surveillance programmes are costly and beyond the resources of the country to introduce and sustain. In recent years, the incidence of hepatitis is being recorded in some of the larger cities because immunological diagnostic tests are available. So far seven hepatitis viruses that are designated as hepatitis A virus (HAV), hepatitis B Virus (HBV), and similarly HCV, HDV, HEV, HFV and HGV have been identified. Of these types, type A and E are transmitted through the enteric route, while types B, C, D and G are transmitted parenterally, that is, through wounds, injections and blood transfusion. About 83% of the population of Bangladesh appear to carry antibodies against hepatitis A virus suggesting that an infection with this virus probably occur at stage of life. Hepatitis B virus is carried by about 7.5% of our population, that is by approximately 10 million people. Estimates on the incidence of other hepatitis-causing viruses in Bangladesh are not available at present.

Rotavirus diarrhoea, also called teething diarrhoea, is a very common viral disease. Every baby probably experiences an attack of rotavirus diarrhoea within the first few months of life. Rotavirus diarrhoea is of special interest because unlike bacterial or parasitic diarrhoeas in which case the disease incidence correlates with poor hygienic conditions and unsafe drinking water which is a common feature of the third world countries, rotavirus diarrhoea appears to have global distribution independent of sanitation condition or economic status of the people. It is thus as frequent in the industrialised countries as it is so in the third world countries. There is some information available on incidence of rotavirus diarrhoea in Bangladesh which comes for the research work done at the International Centre for Diarrhoeal Disease Research, Bangladesh (ICDDR,B). ICDDR,B has carried out extensive studies on rotavirus diarrhoea for the last two decades as part of developing a prevention strategy against rotavirus diarrhoea by using an oral vaccine. [Zia Uddin Ahmed]

See also hepatitis; measles; mumps; pox.