Usefulness of the direct agglutination test in the early detection of subclinicalLeishmania donovaniinfection: a community-based study

Abstract

The value of a direct agglutination test (DAT) in the detection of subclinical infections with Leishmania donovani has recently been investigated in the Indian state of Bihar, after the sensitivity and specificity of the test had been determined. When used to screen sera from 108 parasitologically confirmed cases of visceral leishmaniasis, 50 patients with active, non-leishmanial infection, and 641 healthy controls living close to, or distant from, an endemic area, the test was found to be 91.7% sensitive and 100% specific if a titre of 1:800 was used as the threshold for seropositivity. During a longitudinal clinical study in a rural, VL-endemic area of the Indian state of Bihar, the test was used, with 1:800 set as the threshold titre, to determine the baseline prevalence of infection with L. donovani among villagers who, though showing no symptoms of VL, had recently been febrile for at least 2 weeks. The 234 subjects of this study were either VL-case contacts [i.e. members of households in which there were active or cured VL cases (N=78)] or the members of control households with no cases or history of the disease (N=156). The results of DAT at the start of the study indicated that 49 (20.9%) of the subjects--29 (37.2%) of the VL-case contacts and 20 (12.8%) of the other subjects--were seropositive and therefore probably had subclinical infections with L. donovani. During the subsequent 9 months of follow-up, however, only eight of the subjects found seropositive at the start of the study--seven (24.1%) of the seropositive case contacts but only one (5.0%) of the other seropositives--developed symptomatic VL, all by month 6 of the follow-up. Compared with their neighbours, therefore, individuals who shared households with active or cured cases of VL appeared at greater risk not only of L. donovani infection (indicating focal transmission) but also of developing symptomatic disease once infected. Curiously, among the seropositive case contacts, those from the households that harboured active cases of VL at the baseline survey were less likely to develop symptomatic VL during the 9 months of follow-up than those from households that harboured only cured cases (18.8% v. 30.8%). The wide-spread use of DAT could allow the detection and early treatment of latent L. donovani infections and so contribute to the elimination of VL, at least as a public-health problem, from India.

Incidence of Symptomatic and Asymptomatic Leishmania donovani Infections in High-Endemic Foci in India and Nepal: A Prospective Study

“…In the observed seroconverters who remained asymptomatic, we found that seropositivity did not last into the second year in 86.7%. This is in line with what is reported elsewhere [7], [13], [17]. Six-monthly serological testing might therefore have detected more seroconversions, which would have led to a higher ratio.…”

Evaluación de una prueba de aglutinación directa como método alternativo para el diagnóstico de leishmaniasis visceral canina y humana en Venezuela

“…The test showed very high sensitivity and specificity for human sera, similar to previous reports (20)(21)(22)(23). Positive and negative predictive values of 100% were obtained at a cut-off titer of 1:800.…”

Asymptomatic Infection with Visceral Leishmaniasis in a Disease-Endemic Area in Bihar, India

“…A 96-hour, stationary-phase culture of promastigotes of a laboratory-adapted reference strain of L. donovani (WHOM/IN/80DD8) was grown in monophasic medium containing 20% fetal calf serum and used to prepare DAT antigen. 13,14 For sub-clinical infections, the DAT has a sensitivity of 91.7% and a specificity of 100%.…”