Rapid accurate field diagnosis of Indian visceral leishmaniasis.
BACKGROUND
A firm diagnosis of visceral leishmaniasis (kala-azar) requires demonstration of the parasite in organ aspirates or tissue biopsy samples. The aim of this prospective study was to assess the diagnostic usefulness of non-invasive testing for antibody to the leishmanial antigen K39 by means of antigen-impregnated nitrocellulose paper strips adapted for use under field conditions.


METHODS
One drop of peripheral blood is applied to the hitrocellulose strip. Three drops of test buffer (phosphate-buffered saline plus bovine serum albumin) are added to the dried blood. The development of two visible bands indicates presence of IgG anti-K39. 323 consecutive patients with suspected kala-azar referred to two specialist units in India, and 25 healthy controls, provided fingerstick blood samples for the test. Spleen aspirates were taken from 250 patients.


RESULTS
Kala-azar was confirmed by microscopy of spleen-aspirate smears in 127 patients. The K39 strip test was positive in all 127; the estimated sensitivity was therefore 100% (95% CI 98-100). Four patients had positive strip tests but negative aspirate smears; all four responded to treatment for leishmaniasis. 217 individuals, including the 25 healthy controls, 73 patients with malaria or tuberculosis, and 119 spleen-aspirate-negative patients who had presumed malaria or cirrhosis (79) or no final diagnosis (40), had negative strip-test results. None of the 119 aspirate-negative patients developed evidence of kala-azar during 3-6 months of follow-up. The estimated specificity of the strip test was 98% (95-100; 217/221).


CONCLUSIONS
Detection of anti-K39 by immunochromatographic strip testing is a rapid and non-invasive method of diagnosing kala-azar, which has good sensitivity and specificity and is well suited for use in field conditions.
Sundar
S
S
Kala-Azar Medical Research Center, Banaras Hindu University, Varanasi, India.
Reed
S G
SG
Singh
V P
VP
Kumar
P C
PC
Murray
H W
HW
D000293:Adolescent; D000328:Adult; D000818:Animals; D000913:Antibodies, Protozoan / Q000032:analysis*; D000953:Antigens, Protozoan / Q000276:immunology; D002648:Child; D002845:Chromatography; D005260:Female; D006801:Humans; D007159:Immunologic Tests; D007893:Leishmania donovani / Q000276:immunology*; D007898:Leishmaniasis, Visceral / Q000175:diagnosis*; D008297:Male; D011446:Prospective Studies; D015800:Protozoan Proteins / Q000276:immunology; D011934:Reagent Strips; D012680:Sensitivity and Specificity
D000913:Antibodies, Protozoan; D000953:Antigens, Protozoan; D015800:Protozoan Proteins; D011934:Reagent Strips; C079253:K39 antigen, Leishmania