Serological diagnosis of Trypanosoma evansi (Steel, 1885) in horses using a direct agglutination test.

The research article presents a study on the use of a “direct agglutination test” to diagnose ‘Mal de Caderas’, a disease in horses caused by the parasite Trypanosoma evansi. The test has proved effective and reliable, providing a new tool for the diagnosis of the disease and allowing differentiation between current and past infections.

Test Methodology

• The researchers used an antigen, a substance that causes an immune response, made from a suspension of trypsin-treated parasites that were stabilized with formalin. Trypsin is an enzyme that breaks down proteins, while formalin is a solution used to preserve biological samples.
• The direct agglutination test involves mixing the antigen with a serum sample from the horse. If the horse has been infected with T. evansi, the antibodies in the serum will bind to the antigen, causing visible clumping or agglutination.

Test Evaluation and Results

• The test was evaluated on horses with both natural and experimental infections of T. evansi. The results showed quite high sensitivity and specificity of 94% and 97% respectively. Sensitivity indicates the test’s ability to correctly identify those with the disease, while specificity measures the test’s ability to correctly identify those without the disease.
• The researchers found that treating the serum with a compound called 2-mercaptoethanol before testing allowed the test to differentiate between IgM and IgG antibodies. This is significant as it offers insight on the status of the infection; presence of IgM antibodies usually signifies a current infection while IgG antibodies indicate past exposure to the parasite.
• The antigen used in the test was stable over a period of six months and showed good reproducibility between different batches, indicating consistency in test results over time and across different test conditions.

Conclusion and Implications

• Despite the success of the test in diagnosing T. evansi in horses, the researchers propose that the direct agglutination test should be used alongside other diagnostic methods. This is to increase the overall accuracy and reliability of the results.
• The direct agglutination test could be used both to detect clinical cases of the disease and for larger scale seroepidemiological studies, which aim to understand the frequency, distribution and determinants of the disease within a specific population.