Vector control, drug infusion to check filariasis

 
By Indrajit Bose
Last Updated: Saturday 04 July 2015

-- (Credit: Source: WHO)lymphatic filariasis, commonly known as elephantiasis, has long been a major cause of acute and chronic morbidity among people in tropical and subtropical areas of Asia, Africa, the western Pacific and some parts of the Americas. Of the estimated 128 million cases of lymphatic filariasis, 91 per cent are caused by Wuchereria bancrofti.

A study carried out by researchers of the Centre for Research in Medical Entomology, Tamil Nadu, and the National Institute of Malaria Research, Delhi, says that with the help of mass drug administration (mda), vector control reduces transmission of filariasis. The group suggests that vector control should be included in the Global Programme to Eliminate Lymphatic Filariasis (gpelf). gpelf was launched in 2000 based on the principles of interruption of transmission, and alleviation and prevention of disability due to lymphatic filariasis. Currently, gpelf depends largely on mda to interrupt the transmission of W bancrofti. This strategy is based on the evidence that a single annual dose of antifilarial drugs (diethylcarbamazine, dec, with or without ivermectin, ivr, or albendazole) can suppress microfilaraemia for prolonged periods and the cumulative effect is expected to lead towards the elimination of lymphatic filariasis.

"In this paper, we have emphasised that vector control is expected to bring down the time frame of the period of filariasis elimination campaign, by complementing the benefits brought about in by the action of mda therapy. The maintenance of low transmission levels (by repeated mdas) for sufficiently longer periods to interrupt transmission is a more practical and sustainable proposition to eliminate filariasis, when communities can be empowered to carry out simple vector control operations along with mda," says I P Sunish of the Madurai-based Centre for Research in Medical Entomology.

Currently, there are 31.6 million microfilaraemics, 20.32 million cases of symptomatic filariasis, and about 450 million individuals potentially at risk of infection. India loses about 1.2 billion man-days due to lymphatic filariasis, says Sunish. "According to the national health policy, India's elimination target year is 2015," Sunish adds.

Globally, the majority of Wbancrofti is transmitted by Culex quinquefasciatus, which typically breeds in stagnant and polluted water. "It seems unlikely that mda would be sufficient for sustained interruption of transmission in areas of Culex transmission of lymphatic filariasis, due to their high vectorial efficiency. Therefore, vector control would be an important supplement," the authors note.

The study has been carried out in filarial endemic villages of Tirukoilur in Villupuram district, Tamil Nadu. "We have been conducting lymphatic filariasis control studies in nine villages from 1995-1999 and in six villages since 2000," say the authors. It found a drastic decrease in the vector density in villages receiving mda with vector control. "We also found the prevalence and intensities of microfilararmia fell sharply in villages receiving both mda and vector control," say the researchers.

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