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Title: Equine Piroplasmosis Associated with Amblyomma cajennense Ticks, Texas, USA

item Scoles, Glen
item Hutcheson, H
item Schlater, Jack
item Hennager, Steve
item Pelzel, Angela
item Knowles, Donald - Don

Submitted to: Emerging Infectious Diseases
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/23/2011
Publication Date: 10/1/2011
Publication URL:
Citation: Scoles, G.A., Hutcheson, H.J., Schlater, J.L., Hennager, S.G., Pelzel, A.M., Knowles Jr, D.P. 2011. Equine Piroplasmosis Associated with Amblyomma cajennense Ticks, Texas, USA. Emerging Infectious Diseases. 17(10)1903-1905.

Interpretive Summary: The international Organization for Animal Health (OIE) has considered the United States to be free of equine piroplasmosis (EP) since 1978, however a recent large outbreak in southern Texas has jeopardized the EP free status of the US. Unlike previous cases of EP that have occurred sporadically in the US, this outbreak appears tpo be, at least in part, the result of endemic tick-borne transmission. The overall infection prevalence on the index ranch is 80% but in some divisions 100% of the horses are positive. The cayenne tick, Amblyomma cajennense was the predominant species found on horses at the ranch. This species has not previously been shown to be a competent vector, but adult cayenne ticks collected from positive horses at the ranch that were allowed to re-attach and feed on a naïve horse successfully transmitted Babesia equi. We propose that transmission by this tick species is primarily responsible for the high prevalence of infection in this outbreak.

Technical Abstract: We report an outbreak of equine piroplasmosis in southern Texas, USA. Infection prevalence reached 100% in some areas (292 positive horses). Amblyomma cajennense was the predominant tick and experimentally transmitted Theileria equi to a uninfected horse. We suggest transmission by this tick species played a role in this outbreak.