title: Attempted transmission of Ehrlichia risticii by field-captured Dermacentor variabilis (Acari: Ixodidae).
abstract: The capability of field-collected American dog ticks, Dermacentor variabilis, to infect horses with Ehrlichia risticii, causative agent of Potomac horse fever (PHF), was examined by allowing adult ticks collected from horse farms with a history of PHF to feed on susceptible horses. More than 500 male and female ticks attached and fed on 3 test horses; however, no clinical or serologic evidence of PHF was observed in treated or control horses. All horses were challenge exposed with E risticii-infective blood by inoculation at 60 to 65 days after ticks fed, and all developed clinical PHF with subsequent seroconversion. The data, therefore, indicated that adult D variabilis, a common parasite of horses on Maryland premises where PHF is enzootic, may not serve as a vector of E risticii.
mesh_terms: D000818:Animals; D001096:Arachnid Vectors / Q000469:parasitology / Q000502:physiology*; D003870:Dermacentor / Q000469:parasitology / Q000502:physiology*; D004536:Ehrlichia; D005247:Feeding Behavior; D005260:Female; D006734:Horse Diseases / Q000635:transmission*; D006736:Horses; D008297:Male; D012288:Rickettsiaceae Infections / Q000635:transmission / Q000662:veterinary*; D013987:Ticks / Q000502:physiology*