Cheap urine test for lymphatic filariasis
[COLOMBO] An international team of researchers has developed a simple but effective urine test to diagnose lymphatic filariasis, a neglected parasitic disease that affects more than 120 million people globally.
The test is more affordable and less cumbersome than existing diagnostic methods, scientists from Bangladesh, Japan and Sri Lanka reported in Parasitology International, on 13 September.
Lymphatic filariasis, also called elephantiasis, is caused by the Wuchereria bancrofti, Brugia malayi and B. timori species of the nematode that is spread by mosquito bites. The worms settle in the lymph vessels, causing limbs to swell.
An enzyme-linked immunosorbent assay (ELISA) test to detect filarial antigen in urine is available, but it requires equipment that may not be available in endemic areas. Antigens – including toxins, bacteria, and parasites – stimulate the production of defensive antibodies by the body’s immune system.
"The new visual test can be carried out with ordinary facilities which are generally available in the peripheral units of the national programme to eliminate lymphatic filariasis in Sri Lanka," said Thishan Channa Yahathugoda, head of the department of parasitology, faculty of medicine, University of Ruhuna.
Yahathugoda told SciDev.Net that the new test, using coloured latex beads, costs US$0.50 (50 cents) – a fraction of the cost for the immunochromatographic card test (ICT) for filarial antigen in blood samples that costs about US$15.
The new urine test detects filarial antigen with 87 per cent sensitivity (ability to detect true infections) and 97 per cent specificity (ability to reject healthy individuals) with ICT on antigen positive people taken as standard.
"We are in the elimination stages (of filariasis), according to World Health Organisation (WHO) guidelines," said Udaya Ranasinghe, director of Sri Lanka’s anti-filariasis campaign in the ministry of health.
In 2002, health authorities initiated a five-year, WHO-recommended mass drug administration programme in eight endemic districts which brought down infection rates to 0.03 per cent, Sunil Settinayake, special coordinator of the campaign, said. But pockets of infections remain.
The new test has been deployed in Bangladesh, where 54 out of 64 districts are affected – up from 34 in 2001.
"The highest rates of infection are in the northern part of the country where up to 16.8 per cent of the population is positive and 3.9 per cent has chronic disease," said Moazzem Hossain, chairman, Institute of Allergy and Clinical Immunology of Bangladesh, and a member of the international research team.