ABSTRACT
The latex agglutination test (KAtex), direct agglutination test (DAT), and the rK39 immuno-chromatographic strip test (dipstick test) were evaluated for their role in the diagnosis and prognosis of visceral leishmaniasis (kala-azar) in India. Sera and urine samples from 455 subjects—150 confirmed visceral leishmaniasis cases, 160 endemic controls, 100 non-endemic controls, and 45 other febrile diseases—were included in the study. The sensitivity of the KAtex, DAT, and rK39 strip test was 87% [95% confidence interval (CI) 80-96], 93.3% (95% CI 88-100), and 98% (95% CI 93-100) respectively. The specificity of these tests was 98% (95% CI 93-100), 93% (95% CI 87-100), and 89% (95% CI 82-97) for the KAtex, DAT, and rK39 strip test respectively. Fifty cases were followed up and subjected to the KAtex, DAT, and rK39 strip test after 30 days of successful treatment. The DAT and rK39 strip test showed positive results in all the 50 cases whereas the KAtex showed no positive reaction in any case. Based on the results, it is concluded that the sensitivity and specificity of the DAT and rK39 strip test are comparable but the greater convenience of use of the strip test makes it a better tool for the diagnosis of visceral leishmaniasis in the peripheral areas of endemic regions whereas the sensitivity of the KAtex needs to be improved to promote its use as a first-line diagnostic test in the field-setting. It may be used for the prognosis of the disease as antigen becomes undetectable in urine after 30 days of the completion of the treatment. Alternatively, it can be used as an adjunct with rK39 for sero-epidemiological surveys.
ABSTRACT
Background: A new unique latex agglutination test (KAtex) that detects a stable, nonprotein, disease specific parasite antigen in the freshly voided urine of patients suffering from active kala-azar has been introduced by Kalon Biological Ltd. UK. This is absolutely non-invasive method of diagnosis for visceral leishmaniasis and suitable for implementation as a rapid diagnostic tool at the point of care. Objective: Diagnostic potential of KAtex was evaluated among clinically suspected kala-azar patients in an endemic zone of Bangladesh. Methodology: KAtex was done using freshly voided urine according to the manufacturer’s instructions for sixty (60) clinically suspected patients of kala-azar admitted in Rajshahi Medical College Hospital (RMCH), Bangladesh and forty (40) healthy controls during December 2005 to June 2006. Leishmania nested Polymerase Chain Reaction (Ln-PCR) using peripheral blood buffy coat was performed for all study population (100) and Ln-PCR positive cases were considered as confirmed cases of kalaazar. Results: Out of 60 clinically suspected kala-azar patients, 56 were Ln-PCR positive and 53 of 56 Ln-PCR positive cases were KAtex positive (sensitivity, 94.64%; Mantel- Haenszel Chi sq. 79.66, p= 0.0000, confidence interval [CI], >95 to 100%). None of the healthy controls was found positive by Ln-PCR but 2 of 40 were KAtex positive (specificity, 95%; confidence interval [CI], >95 to 100%). The positive and negative predictive values of KAtex were noted as 98.10% and 92.85% respectively. Conclusion: This limited prospective study suggests that KAtex is an absolutely non-invasive urinebased antigen detection test with high sensitivity and specificity and may be useful for screening active kala-azar patients, particularly suitable for field use.