Preliminary evaluation of diagnostic tests using horses experimentally infected with trypanosoma evansi.
Authors: Wernery U, Zachariah R, Mumford J A, Luckins T
Journal: Veterinary journal (London, England : 1997)
Summary
# Editorial Summary: Diagnostic Tests for Equine Trypanosomiasis Surra, caused by *Trypanosoma evansi*, presents significant diagnostic challenges in endemic regions, yet few studies have systematically evaluated detection methods in horses. Researchers at the University of Dubai experimentally infected seven horses with camel-derived *T. evansi* parasites and compared six diagnostic approaches, tracking parasitaemia, antigen presence and antibody responses over several months post-infection and following trypanocidal treatment. The microhaematocrit centrifugation test proved most sensitive, detecting parasites within 1–3 days of infection, whilst antibody tests (IFAT, CATT, and ab-ELISA) reliably detected infection in all seven horses but not in the uninfected control—though the ab-ELISA showed unacceptably high background readings in 15% of surra-negative UK horses. Critically, antigen detection using latex agglutination persisted at variable levels after successful drug treatment (declining to pre-infection levels in only five of six horses by day 92–279), whereas the ag-ELISA antigen test remained elevated indefinitely, complicating post-treatment surveillance and potentially limiting its use for confirming treatment success. For equine practitioners in endemic or at-risk areas, these findings suggest combining direct parasite detection early in infection with antibody serology for confirmatory diagnosis, but relying on antigen tests alone for post-treatment clearance assessment may be unreliable—a consideration particularly important when importing horses or managing herd health protocols.
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Practical Takeaways
- •MHCT provides earliest diagnosis of T. evansi infection in horses (within 1-3 days); consider this test for acute clinical suspicion
- •Post-treatment monitoring is problematic as ag-ELISA remains positive indefinitely while LAT may normalize, requiring careful interpretation depending on clinical context
- •Antibody tests are reliable for confirming infection but ab-ELISA shows unacceptable false-positive rates in some populations; IFAT and CATT appear more specific for clinical use
Key Findings
- •Microhaematocrit centrifugation test (MHCT) was most sensitive, detecting parasites 1-3 days post-infection
- •Antigen-ELISA detected antigen 3-10 days post-infection; ag-ELISA antigen levels did not return to pre-infection levels in any of 6 horses after treatment
- •Latex agglutination test (LAT) first positive on day 3 post-infection with antigen levels declining to pre-infection levels in 5 of 6 horses
- •Antibody detection tests (ab-ELISA, CATT, IFAT) detected antibodies in all 7 infected horses but ab-ELISA had 15% false positive rate in surra-negative horses; IFAT detected antibodies at 15.7 days post-infection