Diagnosis of equine infectious anaemia during the 2006 outbreak in Ireland.
Authors: Cullinane A, Quinlivan M, Nelly M, Patterson H, Kenna R, Garvey M, Gildea S, Lyons P, Flynn M, Galvin P, Neylon M, Jankowska K
Journal: The Veterinary record
Summary
# Equine Infectious Anaemia: Diagnostic challenges during the 2006 Irish outbreak When equine infectious anaemia emerged across Ireland in 2006, identifying infected animals proved more complex than existing diagnostic protocols suggested. Researchers compared multiple detection methods—ELISA, immunoblot, and agar gel immunodiffusion (AGID)—across acute and subclinical cases, supplemented by RT-PCR and PCR analysis of post-mortem tissues and plasma samples. ELISA and immunoblot assays outperformed AGID in acute cases, whilst notably, one mare exhibited fluctuating antibody levels across all serological tests before eventually seroconverting on AGID, highlighting the inconsistency of early detection. Molecular methods proved particularly valuable: PCR reliably detected viral DNA in plasma regardless of disease stage, whereas RT-PCR identified viral RNA in only 52% of seropositive animals but showed superior sensitivity early in infection, potentially identifying infected horses weeks before conventional serological tests. With seroconversion typically occurring around 37 days post-infection (though delayed beyond 60 days in some cases), these findings suggest PCR-based screening could substantially reduce the diagnostic window and improve outbreak control—a critical consideration for practitioners implementing biosecurity protocols and for regulatory authorities designing surveillance strategies.
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Practical Takeaways
- •ELISA and immunoblot are preferable to AGID for detecting acute EIA cases; AGID may miss early infections due to delayed seroconversion
- •PCR testing offers earlier detection of acutely infected horses compared to standard serological tests and should be considered during suspected outbreaks
- •Allow at least 37–60 days before confirming negative status in potentially exposed horses, as seroconversion can be delayed; repeat testing may be necessary
Key Findings
- •ELISAs and immunoblot were more sensitive than AGID in acute EIA cases during the 2006 Irish outbreak
- •PCR detected viral DNA in plasma at all disease stages, while RT-PCR detected RNA in only 52% of seropositive animals and was most sensitive early in infection
- •Seroconversion period for this virus strain was approximately 37 days but may exceed 60 days in some cases
- •One mare exhibited fluctuating antibody levels across all serological assays before AGID seroconversion, demonstrating diagnostic challenges