Genesis of malaria

A study links malaria to farming

Published: Friday 31 August 2001

the origin of malaria is associated with the beginning of cultivation thousands of years ago, confirm two recent studies.

In 1958, Frank Livingstone had proposed a hypothesis that the emergence of malaria might be linked with the beginning of agriculture. According to Livingstone, the introduction of slash and burn system in West Africa about 2000 to 4000 years ago resulted in the clearing of tropical forest. This gave rise to sunlit pools of water, a breeding hotspot for Anopheles Gambiae (vector for Plasmodium Falciparum parasite).

This hypothesis was endorsed by two studies conducted recently by Sarah Volkman, Harvard University and Sarah Tishkoff, Maryland University.

Volkman and her team tested a range of genetic variations found in Plasmodium falciparum , a parasite causing the deadliest form of malaria.

In general, greater the gene variation in the population of the species, longer the gene has lived on earth. Therefore, variation in gene population acts as a 'molecular clock', deducing the age of the gene ancestor. Volkman studied the neutral genes or those genes that are not subject to excessive pressures causing an increased and random rate of mutation. Previous studies of variation in P falciparum concentrated on those genes that were subject to a lot of pressures in trying to evade the human immune system or protecting it from pesticide spraying and made poor molecular clocks. She applied the speed of mutation and found the time coincided with the Neolithic agricultural revolution.

Tishkoff did a similar test with genes of Homo sapiens . With the appearance of malaria, humans also must have developed genetic variations to counter the attack of malaria. Most human genes that supposedly reduce risk of malaria show up in red blood cells or in the immune system. These include human leukocyte antigen ( hla ), alpha and beta globin, duffy factor ( fy ), tumor necrosis factor ( tnf ) and glucose-6-phosphate-dehydrogenase ( g6pd ). She studied the functioning of g6pd gene. It produces an enzyme needed for transfer of oxygen to the blood stream. The g6pd enzyme deficiency resulted in mutation in the g6pd gene that caused a host of other health problems but increased resistance to malaria. Tishkoff studied the g6pd gene of 450 Africans and through the speed of variation, computed time of the ancestor gene. It again coincided with the findings of Volkman and traced back to the Neolithic age.

"This is just a historic study which does not in any way hold relevance to future cure of malaria. It only explains the origin of the disease", says, V P Sharma, director, Malaria Research Centre, New Delhi. The study does not throw any light on future care but is an indicator of the emergence of new diseases in future.

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