A simple and economical direct agglutination test for serodiagnosis and sero-epidemiological studies of visceral leishmaniasis.

A simple and economical direct agglutination test for the detection of visceral leishmaniasis is described. Trypsin-treated, Coomassie Brilliant Blue-stained, formalin-preserved promastigotes were used as antigen in re-usable V-well microtitre plates. In 21 patients with recent kala-azar, titres of 1:51200 or higher were found. Cured kala-azar patients treated 4 to 14 months before testing, showed titres in the range of 1:3,200 to greater than 1:51,200. Healthy and diseased controls had titres below 1:1,600 with the exception of African trypanosomiasis patients who showed titres of 1:200 to 1:12,800, overlapping with the titres of cured kala-azar patients. Where trypanosomiasis is not a consideration, a titre of 1:1,600 could be considered indicative of visceral leishmaniasis, the sensitivity and specificity were then 100%. The test was applied to sera of 280 inhabitants of Baringo District, a known focus of visceral leishmaniasis in Kenya. When treated cases were included, the test showed a sensitivity of 100% and specificity of 99.3%. This test could be used in district hospitals and health centres in endemic areas as an aid in diagnosis of kala-azar and in the field for sero-epidemiological studies.

Evaluation of a newly developed direct agglutination test (DAT) for serodiagnosis and sero-epidemiological studies of visceral leishmaniasis: comparison with IFAT and ELISA.

A newly developed direct agglutination test (DAT) for visceral leishmaniasis, IFAT and ELISA were applied to sera of patients with visceral leishmaniasis, African and American trypanosomiasis, other parasitic infections and healthy controls. The sensitivities of the 3 tests were comparable (96.3% to 100%); excluding patients with African and American trypanosomiasis, the specificities of DAT and IFAT were 100% and ELISA 87.3%. When trypanosomiasis sera were included, the specificities were 72.6%, 94.3% and 79.4% in DAT, IFAT and ELISA respectively. In 273 sera from a leishmaniasis endemic area (Baringo District, Kenya), the sensitivity was 80% in DAT and IFAT and 60% in ELISA, specificities being 99.6% (DAT), 98.5% (IFAT) and 62.5% (ELISA). As the new DAT is economical and easy to perform, it is recommended for sero-epidemiological field work on visceral leishmaniasis.

Detection of antibodies to Leishmania donovani in animals in a kala-azar endemic region in eastern Sudan: a preliminary report.

The prevalence of antibodies against Leishmania donovani in selected domestic and wild animal species in 2 villages in Sudan with active L. donovani transmission in humans was investigated. Screening of domestic animals (donkeys, cows, sheep, goats, camels and dogs) with the direct agglutination test (DAT) detected reaction rates above the cut-off titres in donkeys (68.7%), cows (21.4%) and goats (8.5%), and which were also found in wild rats (5.5%). Sera of sheep, camels and dogs had a weak agglutination reaction below the cut-off titre. Testing of the same sera by enzyme-linked immunosorbent assay (ELISA), against a lysate of L. donovani promastigotes, showed reaction rates above the cut-off optical density in cows (47.6%), goats (13.6%), and in rats (4.1%). No Leishmania parasite was isolated from spleen, liver, bone-marrow or spleen of Nile rats.

Potential of a direct agglutination test (DAT) for detection of visceral leishmaniasis in a known endemic area in Sudan.

Hawata District (Kassala Province) is one of the known endemic areas for visceral leishmaniasis in Sudan. The co-endemicity with malaria, enteric fever, tuberculosis and brucellosis together with the limited medical laboratory facilities, rendered differential diagnosis of visceral leishmaniasis in this area, rather difficult. Two-hundred and three serum samples, including 49 collected from patients treated earlier as visceral leishmaniasis cases, were tested in a developed direct agglutination test (DAT). 100% concordance was found between the DAT results and the parasitological diagnosis in 40 confirmed cases. In nine unconfirmed, however highly suspected cases, the DAT results indicated visceral leishmaniasis. Significant improvements in the condition of those nine patients was observed during the therapeutic test and later on after a full course of treatment with sodium antimony gluconate (pentostam). DAT titres in the other serum samples (154), collected from patients with malaria, enteric fever, brucellosis and schistosomiasis and from endemic controls were below the cut-off titre (1:3200). Considering the low costs involved, easiness in performance and stability of the antigen, the DAT appears to possess high potential for routine application in Sudan.

Introduction of an improved direct agglutination test for the detection of Leishmania infantum infection in southern France.

An improved direct agglutination test (DAT) is assessed for the detection of Leishmania infantum antibodies in man and in the canine reservoir in Southern France. The test performance in 32 human visceral leishmaniasis patients was in agreement with the parasitological diagnosis and the immunofluorescence (IFAT) results. In six patients diagnosed earlier as kala-azar cases, both DAT and IFAT revealed negative results. The specificity of the DAT was reproduced in this study by the absence of cross-reactions with sera from other patients. In the dog reservoir, the DAT results were compared with those obtained by IFAT, the enzyme-linked immunosorbent assay (ELISA), cross-over electrophoresis and the latex agglutination test. All 34 dogs with parasitologically positive lymph node aspirates also had positive DAT titres (less than or equal to 1:640); the sensitivity in the other four tests was relatively low. Positive DAT and IFAT results were found in 16 unconfirmed cases of canine leishmaniasis, most probably due to prepatent L. infantum infections.

A direct agglutination test discriminative toward Chagas' disease for the diagnosis of visceral leishmaniasis in Brazil: preliminary results.

Two-hundred and sixty-five human sera from Brazil were tested in a direct agglutination assay using trypsinated Leishmania donovani donovani antigen. The assay proved to be of value for the diagnosis of American visceral leishmaniasis in that it was discriminative toward Chagas' disease.

Epidemiology of canine leishmaniasis: prevalence, incidence and basic reproduction number calculated from a cross-sectional serological survey on the island of Gozo, Malta.

Assessment of the resilience of canine leishmaniasis to control or, more ambitiously, the effort needed to eradicate infection, requires an estimate of the basic case reproduction number (R0). This paper applies the theoretical results of Hasibeder, Dye & Carpenter (1992) to data from a cross-sectional survey on the Maltese island of Gozo in which dogs of known age, sex and occupation (pet, guard etc) were subjected to three different serological tests for the presence of specific antibody (IFAT, DAT and ELISA). Difficulties in interpreting these test results, and hence of determining the proportion of dogs infected, present the main obstacle to estimating R0: estimates are critically dependent on the choice of threshold separating seropositives from seronegatives. The data do, however, allow a robust comparative analysis of risk which shows that the force of infection experienced by working dogs is about three times higher than that of pet dogs, a degree of non-homogeneous contact which actually has little effect on estimates of R0. We suggest a cautious point estimate of R0 congruent to 11, and comment briefly on its significance for leishmaniasis control.