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Title: Independence of Anaplasma marginale Strains with High and Low Transmission Efficiencies in the Tick Vector following Simultaneous Acquisition by Feeding on a Superinfected Mammalian Reservoir Host

Author
item GALLETTI, MARIA - Washington State University
item UETI, MASSARO - Washington State University
item Knowles Jr, Donald
item BRAYTON, KELLY - Washington State University
item PALMER, GUY - Washington State University

Submitted to: Infection and Immunity
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/26/2009
Publication Date: 4/1/2009
Citation: Galletti, M.F., Ueti, M.W., Knowles Jr, D.P., Brayton, K.A., Palmer, G.H. 2009. Independence of Anaplasma marginale Strains with High and Low Transmission Efficiencies in the Tick Vector following Simultaneous Acquisition by Feeding on a Superinfected Mammalian Reservoir Host. Infection and Immunity. 77(4):1459-1464.

Interpretive Summary: Vaccine development for infectious agents which persist in their host and are transmitted during the chronic, subclinical phase requires knowledge concerning the strain transmission efficiency of these agents. These data show that even in the face of superinfection (defined as the infection of a persistently infected host with a new strain of in this case Anaplasma marginale) transmission of strain is dependent on strain characteristics and not impacted by superinfection. Importantly a vaccine strain used in the development of these data was not transmitted, even from ticks infected with both the vaccine and wild-type strain.

Technical Abstract: Strain superinfection occurs when a second pathogen strain infects a host already carrying a primary strain. Anaplasma marginale superinfection occurs when the second strain encodes a unique variant surface repertoire as compared to the primary strain and the epidemiologic consequences depend on the relative tick-borne transmission efficiency of the two strains. Following strain superinfection in the reservoir host, we tested whether the presence of two A. marginale (senso lato) strains that differed in transmission efficiency altered the transmission phenotypes as compared to single strain infections. Dermacentor andersoni males were fed on animals superinfected with the A. marginale ss. centrale Israel vaccine strain (low transmission efficiency) and the A. marginale St. Maries strain (high transmission efficiency). Ticks most commonly acquired both strains (co-infection) although single infections with each strain were also detected. Within co-infected ticks, the St. Maries strain had a marked competitive advantage and replicated to significantly higher levels as compared to the vaccine strain. The St. Maries strain was subsequently transmitted to naïve hosts by ticks previously fed either on superinfected animals or on animals singly infected with the St. Maries strain. In contrast, the vaccine strain was not transmitted by either singly or co-infected ticks. These results support that the observed strain predominance in endemic regions is mediated by the intrinsic transmission efficiency of specific strains regardless of occurrence of superinfection.