Serological and Molecular Detection of Anaplasma spp. in Blood From Healthy Horses: A Preliminary Study of Horses in East Texas.
Authors: Russell Alyssa, Shost Nichola, Burch Megan, Salazara Luis Lopez, Fikes Kalley, Bechelli Jeremy, Suagee-Bedore Jessica
Journal: Journal of equine veterinary science
Summary
# Serological and Molecular Detection of Anaplasma spp. in Blood From Healthy Horses: East Texas Evidence Anaplasma phagocytophilum, transmitted by infected ticks, typically causes acute febrile illness in horses characterised by fever, lethargy, ventral oedema, petechiae and neurological signs; however, the true prevalence of exposure and active infection within asymptomatic populations remains unclear. Researchers collected blood samples from 133 horses across Texas, New York and New Jersey, using immunofluorescence antibody assays to detect anti-Anaplasma antibodies and PCR to identify current bacterial DNA in white blood cells. Molecular testing revealed active A. phagocytophilum infection in 24 horses (18%), with 20 cases concentrated in East Texas, whilst 107 horses (80%) tested seropositive; notably, eight currently infected horses showed no detectable antibody response, suggesting recent acquisition or variable immune responses. Geographic variation emerged prominently—seropositivity was 100% in New York and New Jersey but only 66% in Texas—indicating differential exposure patterns or possible strain differences affecting immune development. The detection of active bacterial DNA in clinically normal horses, combined with the absence of any reported anaplasmosis treatments in these East Texas populations, suggests endemic circulation with variable disease manifestation and raises important questions about carrier status, tick vector ecology and population-level susceptibility differences that warrant further investigation.
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Practical Takeaways
- •A. phagocytophilum is present and actively circulating in East Texas horse populations; consider anaplasmosis in differential diagnoses for febrile, lethargic horses even without owner-reported history
- •Horses can carry active bacterial infection without showing clinical signs at the time of testing; subclinical infections may be more common than symptomatic disease
- •Serology alone is insufficient for determining current infection status—PCR testing is necessary to identify actively infected horses, as some infected horses may be seronegative
Key Findings
- •24 of 133 horses (18%) tested positive for A. phagocytophilum DNA, with 20 of these cases located in East Texas
- •107 of 133 horses (80%) tested positive for serum antibodies to A. phagocytophilum, indicating prior exposure
- •8 horses with active A. phagocytophilum infection were seronegative, suggesting recent or early infection
- •100% of New York and New Jersey horses tested positive for antibodies compared to 66% of Texas horses, yet active infection was primarily found in Texas