Evaluation of a standardized direct agglutination test (DAT) for the diagnosis of visceral leishmaniasis in Kenya

A prototype test kit being developed, by the World Health Organization (WHO), for the diagnosis of visceral leishmaniasis (VL) was evaluated in the Baringo district of Rift Valley province in Kenya. The screening of approximately 10,000 individuals for the signs of VL produced 305 suspected cases. These cases and 304 controls matched for sex and age (+/- 2 years) were then tested with the kit, which is based on a direct agglutination test (DAT). The evaluation was a three-stage process. The first stage, the field screening, involved screening filter-paper samples of dried blood from the suspects and controls at a DAT titre of 1:500. The second stage, the laboratory titration, involved screening of the same individuals by testing freshly eluted filter-paper samples at 1:500 to 1:2000 dilution. In the third stage, the full-scale titration, all samples that had been positive at 1:2000 were titrated at 1:500-1:512,000. All the suspects giving DAT titres of 1:2000 or higher were considered positive for VL. This diagnosis was checked, whenever possible, by the examination of smears and/or cultures of splenic aspirates for leishmanial parasites. Those found to be parasitologically positive were put on a standard treatment regime of 20 mg sodium stibogluconate (Pentostam)/kg.day. Although 42 (13.8%) of the 305 clinical suspects investigated were DAT-positive (at 1:2000), it was only possible to take splenic aspirates from 32. Four (12.5%) of these 32 were apparently false-positives by DAT, as no parasites could be detected in their splenic aspirates. The others provided positive smears and cultures (27 cases) or a negative smear but a positive culture (one case). It was possible to re-examine two of the four serologically positive but parasitologically negative VL suspects at a 3-month follow-up: neither had a palpable spleen, one had seroconverted and the other had much lower DAT titre (1:32,000) than when investigated previously (1:128,000). All the parasitologically confirmed cases remained DAT-positive (1:2000) at this follow-up. The low cut-off titre (1:2000) and the simple procedure should make the kit suitable for use by health workers at all levels of primary-health care, including those with limited training and skills, for screening rural communities at risk of VL.     

Evaluation of direct agglutination test (DAT) as an immunodiagnostic tool for diagnosis of visceral leishmaniasis in Nepal

Before field application of the direct agglutination test (DAT) for leishmaniasis, it was assessed as a diagnostic tool. Fifteen confirmed visceral leishmaniasis cases (bone marrow aspiration positive), 120 tuberculosis, 58 leprosy, 15 malaria, 26 intestinal parasitic infection cases, 24 endemic healthy controls from adjacent to the study area, and 18 controls from Kathmandu (who had never visited the VL endemic areas) were tested for anti-leishmanial antibody agglutination titers. Two of the tuberculosis cases were positive for anti-leishmanial agglutinating antibodies at 1:800. All the visceral leishmaniasis confirmed cases were reactive to anti-leishmanial antibody at > or = 1:3,200. Other specimens were negative for serology. The sensitivity of the direct agglutination test was 100% and the specificity was 99.2%. The direct agglutination test had positive and negative predictive values of 100% and 99.2% respectively. The direct agglutination test has been found to be simple, rapid, reliable, economic, safe and adaptable to micro-techniques using microtiter plates. It is specific and sensitive. The direct agglutination test is simple enough for it to be performed in a field laboratory.     

Evaluation of two rK39 dipstick tests, direct agglutination test, and indirect fluorescent antibody test for diagnosis of visceral leishmaniasis in a new epidemic site in highland Ethiopia

We assessed the performance characteristics of two rK39 immunochromatographic tests, a direct agglutination test (DAT), and an indirect immunofluorescent antibody test (IFAT) in the site of a new epidemic of visceral leishmaniasis (VL) in northwestern Ethiopia. The study population was composed of 179 patients with suspected VL and 67 controls. The sensitivities of Kalazar Detect^®, DiaMed-IT Leish^®, DAT, and IFAT in 35 polymerase chain reaction–confirmed VL cases were 94.3%, 91.4%, 91.4%, and 100%, respectively, and the specificities were 98.5%, 94%, 98.5%, and 98.5%, respectively. In a Bayesian latent class analysis of all 246 specimens, the estimated sensitivities were 90.5%, 89%, 88.8%, and 96% for Kalazar Detect^®, DiaMed-IT Leish^®, DAT, and IFAT, respectively; DAT showed the highest estimated specificity (97.4%). Both rK39 immunochromatographic tests perform as well as DAT, and are suitable for VL diagnosis in first-level health centers in this area of Ethiopia.     

Direct agglutination test with urine samples for the diagnosis of visceral leishmaniasis

A new direct agglutination test (DAT) for use with urine samples for the diagnosis of visceral leishmaniasis (VL) has been developed and compared with the conventional DAT with serum samples and our previously reported enzyme-linked immunosorbent assay (ELISA) with urine samples (urine ELISA). The new DAT, in which anti-human IgG was used as enhancing antibody, was tested with urine samples from 75 VL patients and 225 non-VL patients and healthy people. The sensitivity of the new DAT (90.7%), was almost the same as that of the conventional DAT (91.0%) and the urine ELISA (93.3%). The specificity of the new DAT (96.4%) was nearly identical with that of the urine ELISA (97.3%). A urine-based DAT has several advantages over the conventional DAT: sample collection is non-invasive and it can process larger numbers of samples with smaller amounts of antigen.     

Multi-centre evaluation of repeatability and reproducibility of the direct agglutination test for visceral leishmaniasis

OBJECTIVE: To evaluate the repeatability and reproducibility of the serological direct agglutination test (DAT) for visceral leishmaniasis (VL) with aqueous antigen in a multi-centre study in VL-endemic areas in Sudan, Kenya and Nepal. METHODS: Repeatability within each centre and reproducibility between the centres' results and an external reference laboratory (Belgium) was assessed on 1596 triplicate plain blood samples collected on filter paper. RESULTS: High kappa values (range 0.86-0.97) indicated excellent DAT repeatability within the centres. The means of the titre differences between the reference laboratory and the centres in Sudan, Kenya and Nepal (2.3, 2.4 and 1.1, respectively, all significantly different from 0) showed weak reproducibility across centres. 95% of the titre differences between the reference laboratory and the respective centres were accounted for by large intervals: 0.6-9 fold titre variation for Sudan, 0.7-8 fold for Kenya and 0.26-4 fold for Nepal. CONCLUSION: High repeatability of DAT confirms its potential, but reproducibility problems remain an obstacle to its routine use in the field. Reproducibility was hindered by alteration of the antigen through temperature and shaking, especially in Kenya and Sudan, and by nonstandardization of the test reading. DAT handling procedures and antigen quality must be carefully standardized and monitored when introducing this test into routine practice.     

Use of the recombinant K39 dipstick test and the direct agglutination test in a setting endemic for visceral leishmaniasis in Nepal

We evaluated the field use of two serologic tests for visceral leishmaniasis (VL), the direct agglutination test (DAT) and rK39 dipstick test, in the context of a case-control study. Most VL cases in Nepal are currently diagnosed on clinical grounds and with relatively non-specific tests such as the formol-gel test. Among 14 newly diagnosed VL patients with bone-marrow slides confirmed positive in two independent laboratories, the sensitivity of both tests was 100%. Among 113 controls with no personal or household history of VL, the specificity of the rK39 was 100% while that of the DAT was 93%. The rK39 was less expensive than DAT, and has the advantages of ease of use and obtaining results within minutes. The wider use of the rK39 dipstick test could improve the specificity of VL diagnosis in Nepal.     

Latex agglutination test for the detection of urinary antigens in visceral leishmaniasis

This paper describes a new latex agglutination test ('KATEX') for the detection of leishmanial antigen in the urine of patients with visceral leishmaniasis. In preliminary laboratory trials, using urine collected from well-defined cases and controls from Brazil, Yemen and Nepal, the test had 100% specificity and a sensitivity between 68 and 100%. When used in a time-course experiment in cotton rats infected with Leishmania donovani, the test became positive 1 week after inoculation and antigen levels in urine declined rapidly after chemotherapy (the test was negative before the end of the course of treatment). Finally, in an integrated study performed in Sudan, KATEX was compared to microscopy and four different serological tests in a group of 73 patients having presented with clinical manifestations suggestive of visceral leishmaniasis. Compared to microscopy, KATEX performed better than any single serological test in predicting positivity and a particularly good result was obtained by combining KATEX and the direct agglutination test (DAT).     

Usefulness of the rK39-immunochromatographic test, direct agglutination test, and leishmanin skin test for detecting asymptomatic Leishmania infection in children in a new visceral leishmaniasis focus in Amhara State, Ethiopia

In areas where visceral leishmaniasis is anthroponotic, asymptomatically infected patients may play a role in transmission. Additionally, the number of asymptomatic patients in a disease-endemic area will also provide information on transmission dynamics. Libo Kemkem and Fogera districts (Amhara State, Ethiopia) are now considered newly established areas to which visceral leishmaniasis is endemic. In selected villages in these districts, we conducted a study to assess the usefulness of different approaches to estimate the asymptomatic infection rate. Of 605 participants, the rK39 immunochromatographic test was able to detect asymptomatic infection in 1.5% (9 of 605), direct agglutination test in 5.3% (32 of 605), and leishmanin skin test in 5.6% (33 of 589); the combined use of serologic methods and leishmanin skin test enabled detecting asymptomatic infection in 10.1% (61 of 605). We conclude that the best option to detect asymptomatic infection in this new visceral leishmaniasis-endemic focus is the combined use of the direct agglutination test and the leishmanin skin test.     

Serological markers for leishmania donovani infection in Nepal: Agreement between direct agglutination test and rK39 ELISA

Visceral leishmaniasis (VL) is an important vector-borne disease caused by Leishmania donovani in the Indian subcontinent. The actual incidence and role of asymptomatic infections in the region are not wellknown. We used the direct agglutination test (DAT) and the rK39 ELISA as L. donovani infection markers in 10 VL endemic villages in Nepal. DAT titre distribution showed two subgroups in the population (infected and non-infected individuals), while rK39 did not. The agreement between both tests was moderate (j = 0.53; 95% CI 0.49–0.57). More research is needed to develop validated markers for Leishmania infection.     

Evaluation of complement fixation procedures for the diagnosis of visceral leishmaniasis

Three complement fixation (CF) procedures were evaluated for their ability to detect serum antibodies to visceral leishmaniasis. These tests differ in their use of buffers, volumes of complement and sensitized erythrocyte concentrations, incubation times and percentage haemolysis endpoints. Freeze-thawed sonicates of Leishmania donovani promastignotes were used as antigen. Test sensitivity was determined using sera from 46 Kenyans with parasitologically proven leishmaniasis. The frequencies of positive reactions in all three tests were 96-97% and positive antibody titres ranged from 1:16 to 1:4096. Specificity was determined with 20 sera from healthy individuals with no known exposure to leishmaniasis. The frequencies of false positive reactions were 0-10% in the control sera, with titres up to 1:16. No cross-reactions were observed with sera from patients with bacterial, fungal and other parasitic diseases. In replicate experiments, 99-100% of the sera tested were within one titre dilution of each other. All three CF procedures provide very good sensitivity, specificity and low cross-reactivity and are statistically similar in their capacity to diagnose visceral leishmaniasis.     

rK39 antigen for the diagnosis of visceral leishmaniasis by using human saliva

The rK39 rapid immunochromatographic test (ICT) is now being widely used in the diagnosis of visceral leishmaniasis (VL) using serum. We evaluated the presence of anti-rK-39 antibody in human saliva being noninvasive to replace the invasive procedures of diagnosis. Enzyme-linked immunosorbent assay (ELISA) and ICT assays were performed in 300 subjects: 114-confirmed VL patients, 95 and 47 healthy controls from endemic and nonendemic regions, respectively, and 44 subjects with different diseases. Sensitivity in saliva was 83.3% by ELISA and 82.5% by ICT, compared with 100% for both ICT and ELISA in serum. Specificity in saliva was 100%, 90.5%, and 88.6% with ELISA, and 91.48%, 91.57%, and 84.06% using ICT, in nonendemic, endemic, and different diseases, respectively. In serum, specificity was 97%, 88.5%, and 89% by ELISA and 100%, 94.7%, and 95.5% by ICT in nonendemic, endemic, and different diseases, respectively. Saliva is not suitable for diagnosis of VL because of low sensitivity.     

Comparison of an rK39 dipstick rapid test with direct agglutination test and splenic aspiration for the diagnosis of kala-azar in Sudan

We compared an rK39 dipstick rapid test (Amrad ICT, Australia) with a direct agglutination test (DAT) and splenic aspirate for the diagnosis of kala-azar in 77 patients. The study was carried out under field conditions in an endemic area of north-east Sudan. The sensitivity of the rK39 test compared with splenic aspiration was 92% (46/50), the specificity 59% (16/27), and the positive predictive value 81% (46/57). Compared with the diagnostic protocol used by Médecins sans Frontières, the sensitivity of the rK39 test was 93% (50/54), the specificity 70% (16/23), and the positive predictive value 88% (50/57). Compared with splenic aspirates, the sensitivity of a DAT with a titre > or =1:400 was 100% (50/50), but its specificity only 55% (15/27) and the positive predictive value was 80% (50/62). Using a DAT titre > or =1:6400, the sensitivity was 84% (42/50), the specificity 85% (23/27) and the positive predictive value 91% (42/46). All four patients with DAT titre > or =1:6400 but negative splenic aspirate were also rK39 positive; we consider these are probably 'true' cases of kala-azar, i.e. false negative aspirates, rather than false DAT and rK39 seropositives. There were no false negative DATs (DAT titre < or =1:400 and aspirate positive), but there were four false negative rK39 tests (rK39 negative and aspirate positive). The rK39 dipstick is a good screening test for kala-azar; but further development is required before it can replace the DAT as a diagnostic test in endemic areas of the Sudan.     

The performance of direct agglutination tests (DAT) in the diagnosis of visceral leishmaniasis among Ethiopian patients with HIV co-infection

The incidence of visceral leishmaniasis (VL) in Ethiopia has dramatically increased over the last 10 years, coinciding with the advent of the HIV epidemic. HIV co-infection in VL patients results in atypical, clinical and serological presentations, and may hamper serological diagnosis of VL. The performance of direct agglutination tests (DAT) in the diagnosis of VL in 103 Ethiopian patients with or without HIV infection was therefore investigated. The DAT results indicated that 96 of the patients had leishmanial infections, although amastigotes were only detected in samples from 91. Data on HIV status showed that 50.7% of all patients but 56.0% of the parasitologically confirmed cases of VL patients were HIV-positive. Based on the 95 patients who were each examined both by DAT and parasitological methods, the overall sensitivity of the DAT was 97.7%. Among the parasitologically confirmed cases of VL, a false-negative DAT result was obtained for two (3.9%) of the 51 cases who had HIV co-infection and for none of the 40 HIV-negative cases. In contrast to the observations made in Europe, DAT in Ethiopia therefore remain reasonably sensitive in the diagnosis of VL during HIV co-infection. The results are discussed in view of the possibility of distinctive antibody responses induced by Leishmania donovani donovani and L. d. infantum in HIV-infected patients.     

Performance of recombinant K39 antigen in the diagnosis of Brazilian visceral leishmaniasis

This study evaluated the performance of recombinant K39 (rK39) antigen in a immunochromatographic format (strip test) and a crude antigen enzyme-linked immunosorbent assay in the diagnosis of Brazilian visceral leishmaniasis (VL) in 128 consecutive patients with parasitologically proven infections (by microscopy and/or culture). For each patient, a medical history was obtained and a complete physical examination was performed. Controls included 10 healthy volunteers and 50 patients with other diseases: malaria (10), leprosy (9), Chagas' disease (10), tuberculosis (10), and cutaneous leishmaniasis (11). The sensitivities of the rK39 antigen strip test and the ELISA were 90% and 89%, respectively, while the specificities were 100% and 98%, respectively. Our study confirms the accuracy of the rK39 antigen strip test in the diagnosis of VL in a high prevalence population.     

Detection of leishmanial antigen in the urine of patients with visceral leishmaniasis by a latex agglutination test

Diagnosis of visceral leishmaniasis (VL) is usually done by demonstration of parasites in tissue smears. However, obtaining these smears may be risky, painful, and difficult. Antibody-based diagnostics are limited by their inability to predict active disease. In this study, a new latex agglutination test (KAtex), which detects parasite antigen in freshly voided and boiled urine, was evaluated in patients with VL before the start (n = 382) and at the end of treatment (n = 273); 185 healthy controls from leishmaniasis-endemic region were also studied. The KAtex result was positive in 87% (95% confidence interval [CI] = 83.3-90.3). However, at the end of treatment only 3% (95% CI = 1.6-6.2) patients were positive. The specificity of the test was 99% and 2 of 185 healthy controls tested positive. Positive and negative predictive values were 0.994 and 0.788, respectively. KAtex is a promising test, and in a simplified and improved format it could be applied meaningfully in the diagnosis of VL.     

Serodiagnosis and screening of canine visceral leishmaniasis in an endemic area of Corsica: applicability of a direct agglutination test and immunoblot analysis.

For effective control of visceral leishmaniasis caused by Leishmania infantum in the Mediterranean area, the detection of infected dogs is of utmost importance. To assess the suitability of a direct agglutination test (DAT) and immunoblot analysis in serodiagnosis and screening of infected dogs under field conditions, a study was performed on 113 dogs in an endemic area of Corsica. Twenty one of 22 parasitologically confirmed cases were correctly diagnosed by both tests, and 100% specificity was found when 11 dogs with other diseases were examined. Interestingly, eight of 80 apparently healthy dogs from the same area were found to be parasite-positive by the DAT test as well as by the immunoblot. Although both tests were equally sensitive and specific, based on both the feasibility of its application in field conditions and ease of performance, we consider the DAT to be more suitable for serodiagnosis and large-scale screening of infected dogs.