Equine Piroplasmosis Associated with Amblyomma cajennense Ticks, Texas, USA - Emerging Infectious Diseases Journal Homepage | CDC EID

DOI: 10.3201/eid1710.101182
Suggested citation for this article: Scoles GA, Hutcheson HJ, Schlater JL, Hennager SG, Pelzel AM, Knowles DP. Equine piroplasmosis associated with Amblyomma cajennense ticks, Texas, USA. Emerg Infect Dis. 2011 Oct; [Epub ahead of print].
Equine Piroplasmosis Associated with Amblyomma cajennense Ticks, Texas, USA
Glen A. Scoles, H. Joel Hutcheson, Jack L. Schlater, Steven G. Hennager, Angela M. Pelzel, and Don P. Knowles

Author affiliations: US Department of Agriculture, Pullman, Washington, USA (G.A. Scoles, D.P. Knowles); US Department of Agriculture, Ames, Iowa, USA (H.J. Hutcheson, J.L. Schlater, S.G. Hennager); and US Department of Agriculture, Fort Collins, Colorado, USA (A.M. Pelzel)
We report an outbreak of equine piroplasmosis in southern Texas, USA, in 2009. Infection prevalence reached 100% in some areas (292 infected horses). Amblyomma cajennense was the predominant tick and experimentally transmitted Theileria equi to an uninfected horse. We suggest that transmission by this tick species played a role in this outbreak.

Theileria equi (incertae sedis; Piroplasma equi Laveran, 1901) is one of the etiologic agents of equine piroplasmosis. This parasite infects equids worldwide, but a few countries (Australia, Great Britain, Japan, United States, and Canada) are classified as free of this disease. These and several other countries restrict entry or internal movement of horses on the basis of their serologic response to T. equi antigen.

Particular tick species are obligate intermediate hosts and vectors for T. equi (1), which undergoes a complex developmental cycle in the vector similar to that of other apicomplexan hemoparasites (2,3). Asymptomatic persistent parasitemia detectable by serologic analysis or PCR develops in equids that survive acute infection. International movement of asymptomatic carriers poses a risk for introduction of equine piroplasmosis into regions free of this disease, but endemic transmission occurs only in regions that have competent vectors.

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