A single vaccine may not help in the control of malaria

Syed Akbar

Hyderabad, Nov 10: A single vaccine may not help in the control of malaria and this major health nuisance has to be tackled through specific vaccines for different strains of malarial parasite.

A study by the city-based Centre for Cellular and Molecular Biology and the National Institute for Malaria Research revealed that different vaccines need to be developed to prevent different isolates of Plasmodium falciparum, the causative agent of malaria.

"The C-terminal region of merozoite surface protein-1 is one of the leading candidates for vaccination against the erythrocytic stages of malaria. However, a major concern in the development of MSP-1 based malaria vaccine is the polymorphism observed in different geographical Plasmodium falciparum isolates," the study points out.

The results from the study also revealed predominance of a particular type of allele among Indian field isolates. Seven such variant forms were isolated in a singe geographical location. This simply means there should be seven different vaccines each targeting a particular isolate, in the Indian context.

The study demonstrated the existence of allele specific antibodies in Plasmodium falciparum-infected patient sera. The scientists suggested the importance of a multi-allelic based vaccine for an effective malaria control in the country.

Malaria is one of the major causes of death from infection in India as in other developing countries.  Development of an effective malaria vaccine may reduce malaria-associated severe morbidity and mortality in malaria-endemic areas.

A number of parasite surface antigens of asexual blood stages are being investigated as vaccine candidate antigens. Among these antigens, merozoite surface protein-1 is a leading candidate antigen.

"A substantial proportion of antibodies directed to MSP-119 in Plasmodium falciparum-infected human sera have been shown to inhibit erythrocyte invasion in vitro. Sequence comparison of Plasmodium falciparum msp1 sequences among different geographical isolates shows a great deal of variations," the study said.

Malaria transmission is perennial in the country but is markedly low in the plain area than forest area. Plasmodium falciparum accounted for 85 per cent of total malaria cases during the study period. In forest and plain areas, the number of falciparum cases per thousand populations were 284.1 and 31.2 respectively, whereas the parasite rate was 14 per cent and 1.7 per cent respectively.

In forest areas, clinical malaria occurred more frequently in children aged 0-5 years and declined gradually with increasing age.