New Delhi: Indian researchers have identified a key protein that plays an important role in regulating the survival, infectivity and drug response of the parasite that causes visceral leishmaniasis - better known as 'kala-azar'. Kala-azar is the most severe form of leishmaniasis, and is caused by a parasite called Leishmania donovani, which spreads to people through the bite of an infected female sandfly, Scidev.Net reported.

Jitesh P. Iyer and co-workers from the National Institute of Immunology, found that higher levels of an enzyme called cTXNPx made the L. donovani parasite more virulent at certain times in its life cycle. Laboratory tests also showed a higher parasite burden in immune cells.

cTXNPx belongs to the group of enzymes that detoxify peroxides, chemicals that are toxic to L. donovani. When humans are infected by L. donovani, their immune cells release hydrogen peroxide to destroy the parasite.

Parasites with higher levels of cTXNPx were more able to withstand high levels of hydrogren peroxide, and were also resistant to an antileishmanial drug.

"This study provides a link between cTXNPx expression to survival, virulence and drug response in L. donovani," the researchers write in a paper published in the April issue of the journal Molecular Microbiology.

"This study invites further studies to explore the plausibility of any new drug molecule targeting this enzyme," said Swapan Jana of the Society for Social Pharmacology.

"The study is impressive - given the emerging drug resistance of Leishmania donovani, it's important to work on the ways to combat the parasite through newer drugs."

Drug-resistance of L. donovani is a major issue in developing countries like India, said Jana.

"Even though different centres have reported different findings, it is a fact that resistance [of L. donovani] to the first line drug sodium antimony gluconate has been increasing since the late 1970s," said Sarman Singh of the All India Institute of Medical Sciences.

Kala-azar is endemic in four Indian states, the worst affected being Bihar. The disease infects about 300,000 people and kills 20,000 in India each year.

"In some areas of Bihar, drug resistance is reported in up to 70 percent of cases," added Singh. IANS