K39 strip test--easy, reliable and cost-effective field diagnosis for visceral leishmaniasis in India.

OBJECTIVE: A firm diagnosis of visceral leishmaniasis (VL) requires demonstration of the parasite in splenic or bone marrow aspirate. The aim of this prospective study was to assess the usefulness of K39 strip test as a noninvasive method of diagnosing visceral leishmaniasis under field conditions by testing serum antibody to the leishmanial antigen K39.
MATERIAL AND METHODS: One drop of serum/blood was applied to the sample application pad on the test strip, which was diluted with 2 drops of chase buffer solution. The development of two visible red lines indicates the presence of IgG anti-K39. In the first phase of the study (2001), a total of 200 patients (Active VL-70, ex-VL-30, healthy endemic control-20 and patients with other tropical diseases-80) were tested with the K39 strip test at the School of Tropical Medicine, Kolkata. In the second phase of the study (2002), the test was applied in a remote tribal area of West Bengal where an epidemic of VL had occurred. Thirty-two patients were identified in 207 villagers of the affected area; all of them were tested with the K39 strip test.
RESULTS: In the first phase, all VL and ex-VL cases gave positive results (100%). Ten percent of the healthy endemic controls were positive. The test results were negative in all other prevalent tropical diseases (100%). The estimated sensitivity of the test was 100% and the specificity was 98.18%. In the second phase of the study, all 32 patients of the epidemic were shown to be positive. All patients were treated with sodium stibogluconate injections and they recovered uneventfully.
CONCLUSIONS: K39 strip test is ideal for rapid reliable field diagnosis of visceral leishmaniasis. The test has high sensitivity and specificity but it remains positive long after treatment (up to 3 years).