Submitted to: Infection and Immunity
Publication Type: Peer reviewed journal
Publication Acceptance Date: 1/26/2009
Publication Date: 4/1/2009
Publication URL: iai.asm.org/cgi/reprint/77/4/1459
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):1459-64. Interpretive Summary: These data show that in the case of Anaplasma marginale, a pathogen of cattle and other ruminant red blood cells the strain that predominates in areas with infection and disease the transmission of one strain compared to another is intrinsic within the genetics of a given pathogen. This information aids in the design of vaccines to block transmission and the understanding of outbreaks of infection and disease.
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 carries a variant repertoire different from that of the primary strain, and the epidemiologic consequences depend on the relative efficiencies of tick-borne transmission of the two strains. Following strain superinfection in the reservoir host, we tested whether the presence of two A. marginale (sensu lato) strains that differed in transmission efficiency altered the transmission phenotypes in comparison to those for single-strain infections. Dermacentor andersoni ticks were fed on animals superinfected with the Anaplasma marginale subsp. centrale vaccine strain (low transmission efficiency) and the A. marginale St. Maries strain (high transmission efficiency). Within ticks that acquired both strains, the St. Maries strain had a competitive advantage and replicated to significantly higher levels than 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, consistent with the predicted transmission phenotype of this strain and the lack of interference due to the presence of a competing low-efficiency strain. The vaccine strain was not transmitted by either singly infected or coinfected ticks, consistent with the predicted transmission phenotype and the lack of enhancement due to the presence of a high-efficiency strain. These results support the idea that the strain predominance in regions of endemicity is mediated by the intrinsic transmission efficiency of specific strains regardless of occurrence of superinfection.