Leishmaniasis DAT (Direct Agglutination Test)
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Visceral leishmaniasis (VL) or kala-azar is one of the most important parasitic tropical diseases. Untreated, VL is fatal; hence early and accurate diagnosis is essential. Two methods are commonly used in the routine diagnosis of the disease: parasitology and serology.
Parasitology
Parasitological testing comprises microscopical examination of tissue smears/aspirates and parasite culture. The latter method may be more sensitive and reliable than microscopy in diagnosis of VL, especially when there are few parasites present. Culture may give information on the viability of the parasite, which can be important in evaluating VL chemotherapy. The parasitological methods are highly specific, but their sensitivity can be as low as 50–60% depending on the type of tissue and method employed. Therefore, serology is often used in the diagnosis of VL.
Serology
The direct agglutination test (DAT) remains the first-line diagnostic tool in Sudan as it appears to be a simple and economical test with high sensitivity and specificity. The test is very suitable for use in the field. The development of a freeze-dried (FD) antigen increased the applicability of the test under rural conditions as, in contrast to liquid antigen, a cold chain for preserving the antigen is not necessary.
Many studies have been conducted towards the sensitivity and specificity of the test and in general it is accepted that the DAT is the most robust of currently available tests for use in clinical settings in disease endemic countries. Furthermore, cost-effectiveness analysis of VL diagnostic-therapeutic strategies demonstrated DAT as the most effective test when used after screening of patients based on clinical case definition.
Approach
Since it initial development by scientists from KIT, the antigen is produced in large batches on the premises of the institute. In order to increase the product stability, the antigen is freeze-dried (FD) by a commercial company. The FD DAT antigen remains stable at ambient temperature for at least 1 year. The test fulfills all requirements to be used under harsh field conditions: no electricity, no cold chain and only simple equipment are needed to perform the test. Appropriate quality control procedures are in place in order to ensure batch-to-batch reliability of the antigen.
The DAT can be used for the sero-diagnosis of human visceral leishmaniasis and canine leishmaniosis. Interestingly, the DAT is reported to be able to identify at least a substantial proportion of HIV positive VL co-infected cases.
KIT Biomedical Research holds workshops, often on request of organizations like MSF, WHO, AMREF or Health NET, to support local operators in the use and interpretation of the test.
KIT Biomedical Research supports local laboratories in the production of DAT antigen and/or the implementation of the test in their routine diagnostic procedures. The local implementation is supported by Quality Control by KIT Biomedical Research.
Focal points
- Production of DAT antigen for the sero-diagnosis of visceral leishmaniasis and canine leishmaniosis
- Perform batch quality control of produced DAT antigen (in the Netherlands and disease endemic countries)
- Technology transfer and training
- Perform quality control of DAT procedures carried out in local laboratories and field settings in disease endemic countries
Example
The DAT is at present extensively being used in several research projects all over the world. KIT Biomedical Research has provided DAT antigen for research purposes to scientists in the following countries: Brazil, Ecuador, Colombia, Venezuela, India, Nepal, Ethiopia, Sudan, Kenya, Uganda, Syria, Turkey, Portugal, Spain, Belgium and the Netherlands.
In support of test use, staff members of KIT Biomedical Research trained local operators in Kenya (Nairobi and Lokichoggio), Ethiopia (Addis Ababa and Gondar), Sudan (Khartoum and Wad Medani) and Brasil (Recife, Manaus, Rio de Janeiro and Teresina) on request. For this purpose small workshops were organised during which 6 – 10 people were trained in performing and interpretation of the test.
Projects
- To perform batch quality control of liquid cultured antigen for serological diagnosis of visceral leishmaniasis prepared in Ethiopia
- Evaluation of simple diagnostics for the detection of leishmania infections in humans and dogs in endemic regions
Publications
- Schallig, H.D.F.H. - Development and application of 'simple' diagnostic tools for visceral leishmaniasis
- Schallig, H.D. - Evaluation of the direct agglutination test and the rK39 dipstick test for the sero-diagnosis of visceral leishmaniasis.
- Cardoso, L. - Serological survey of Leishmania infection in dogs from the municipality of Peso da Régua (Alto Douro, Portugal) using the direct agglutination test (DAT) and fast agglutination screening test (FAST)
- da Silva, E.S. - Diagnosis of canine leishmaniasis in the endemic area of Belo Horizonte, Minas Gerais, Brazil by parasite, antibody and DNA detection assays.