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Title: Association of anaplasma marginale strain superinfection with infection prevalence within tropical regions

item CASTAÑEDA-ORTIZ, ELIZABETH - Autonomous National University Of Mexico
item Ueti, Massaro
item MINERVA, CAMACHO-NUEZ - Autonomous National University Of Mexico
item MOSQUEDA, JUAN - Autonomous University Of Chiapas
item Mousel, Michelle
item Johnson, Wendell
item PALMER, GUY - Washington State University

Submitted to: PLOS ONE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/13/2015
Publication Date: 3/20/2015
Citation: Castañeda-Ortiz, E.J., Ueti, M.W., Minerva, C., Mosqueda, J.J., Mousel, M.R., Johnson, W.C., Palmer, G.H. 2015. Association of anaplasma marginale strain superinfection with infection prevalence within tropical regions. PLoS One. doi: 10.1371/journal.pone.0120748.

Interpretive Summary: Tick-borne pathogens including Anaplasma marginale infect ruminates worldwide and negatively impact the cattle industry by approximately $20 billion U.S. dollars due to vaccination, loss of production, treatment, abortion and death of cattle. It is unknown if herds of cattle with high infection rates are infected with a greater number of different strains of Anaplasma marginale than herds with low infection rates in the tropics. In this study, two herds of cattle in tropical Mexico, were tested for infection rate and number of strains. A larger number of different strains were identified in the herd with high infection rates compared with the herd with low infection rates. This information can be used to better understand outbreaks of this costly disease and possibly develop strategies to control Anaplasma marginale in cattle.

Technical Abstract: Strain superinfection occurs when a second strain infects a host already infected with a primary strain. The incidence of superinfection with Anaplasma marginale, a tick-borne rickettsial pathogen of domestic and wild ruminants, has been shown to be higher in tropical versus temperate regions. This has been attributed to the higher prevalence of infection, with consequent immunity against primary strains and thus greater selective pressure for superinfection with antigenically distinct strains. However an alternative explanation would be the differences in the transmitting vector, Dermacentor andersoni in the studied temperate regions and Rhipicephalus microplus in the studied tropical regions. To address this question, we examined two tropical populations sharing the same vector, R. microplus, but with significantly different infection prevalence. Using two separate markers, msp1a (one allele per genome) and msp2 (multiple alleles per genome), there was higher levels of multiple strain infections in the high infection prevalence as compared to the low prevalence population. The association of higher strain diversity with infection prevalence supports the hypothesis that high levels of infection prevalence and consequent population immunity is the predominant driver of strain superinfection.