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United States Department of Agriculture

Agricultural Research Service

Research Project: DETERMINANTS OF ANAPLASMA MARGINALE TRANSMISSION AT THE VECTOR/PATHOGEN INTERFACE

Location: Animal Diseases Research

Title: Transmission of Babesia caballi by Dermacentor nitens (Acari: Ixodidae) Is Restricted to One Generation in the Absense of Alimentary Reinfection on a Susceptible Equine Host

Authors
item Schwint, Nicolas - WSU
item Knowles, Donald
item Ueti, Massaro - WSU
item Kappmeyer, Lowell
item Scoles, Glen

Submitted to: Journal of Medical Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 18, 2008
Publication Date: July 28, 2008
Citation: Schwint, N.O., Knowles Jr, D.P., Ueti, M.W., Kappmeyer, L.S., Scoles, G.A. 2008. Transmission of Babesia caballi by Dermacentor nitens (Acari: Ixodidae) Is Restricted to One Generation in the Absense of Alimentary Reinfection on a Susceptible Equine Host. Journal of Medical Entomology. 45(6):1152-1155.

Interpretive Summary: The tropical horse tick, Dermacentor nitens, is the natural vector of one of the parasites that causes Equine Piroplasmosis in the Americas; the distribution of this tick in the United States is limited to the southernmost parts of Florida and Texas. The parasite, Babesia caballi, occurs widely throughout the world, but the United States and a few other countries are considered to be free of infection by the International Organization for Animal Health (OIE). This has led to non-tariff trade barriers that negatively impact the economy of the horse industry. The objective of this study was to test the ability of B. caballi to persist in D. nitens for more than one generation. Partially engorged female ticks were collected off of a B. caballi infected horse in Puerto Rico and were allowed to reattach and feed on an uninfected horse. That horse became infected with B. caballi. These field collected ticks fed to repletion and were then held for oviposition and hatching. The larval offspring of these field-collected ticks, the parental generation of larvae (P1), was fed on a calf, a host that is not susceptible to infection with B. caballi, to clear them from B. caballi infection. The following generations of ticks (F1, F2, and F3) were also reared on calves and each generation was test fed on two naive horses. The F1 generation transmitted B. caballi infection whereas F2 and F3 did not. These results demonstrate that D. nitens can become persistently infected with B. caballi for at least one generation. These data suggest that in the event of the introduction of this pathogen into areas of the continental United States where D. nitens occurs, the tick could become a reservoir of B. caballi, making it very difficult to eradicate once established.

Technical Abstract: The tropical horse tick, Dermacentor nitens, is the natural vector of Babesia caballi in the Americas; the distribution of this tick in the United States is limited to the southernmost parts of Florida and Texas. Babesia caballi, one of the etiologic agents of equine babesiosis, occurs widely throughout the world, but the United States and a few other countries are considered to be free of infection. This has led to non-tariff trade barriers that negatively impact the economy of the horse industry. The objective was to test the ability of B. caballi to persist in D. nitens for more than one generation. Partially engorged female D. nitens were collected from a B. caballi infected horse in Puerto Rico and were allowed to reattach and feed on an uninfected horse. That horse became infected with B. caballi. These field collected ticks fed to repletion on the horse and were then held for oviposition and hatching. The larval offspring of these field collected ticks, the parental generation of larvae (P1), was fed on a calf (a non-susceptible host for B. caballi) to clear them from B. caballi infection. The following generations of ticks (F1, F2, and F3) were also reared on calves and each generation was also test fed on two naive horses. The F1 generation transmitted B. caballi infection whereas F2 and F3 did not. These results demonstrate that D. nitens can become persistently infected with B. caballi for at least one generation, calling into question aspects of the accepted life cycle paradigm of the parasite. These data suggest that in the event of the introduction of this pathogen into areas of the continental United States where D. nitens occurs, the tick could become a reservoir of B. caballi, making it very difficult to eradicate once established.

Last Modified: 8/27/2014
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