Submitted to: Journal of Veterinary Diagnostic Investigation
Publication Type: Peer reviewed journal
Publication Acceptance Date: 4/25/1994
Publication Date: N/A
Citation: Interpretive Summary: One of the more important microbial pathogens of cattle in the U.S. is a rickettsia (similar to a bacterium) called Anaplasma marginale, that invades and divides in the red blood cells of cattle. The organisms are spread in a variety of ways, but the most important natural way is by ticks. Several strains, or isolets of this species have been described in the U.S. Among the several strains identified in the U.S., some are not capable of being spread by ticks, and some are more pathogenic than others. Thus, being able to characterize new strains when they are discovered is important in the overall control of the disease. In this study, a newly identified strain from cattle in northern Idaho was compared to other well characterized strains, two of which were from relatively nearby Washington and southern Idaho. This strain was shown to be different than other strains, including those in close proximity but, was shown to be capable of fspread by ticks, and in fact, ticks removed from the sick animal in question, was shown to be harboring the organisms. This study accomplished two important concerns: 1) that the sophisticated biotechniques developed over the past several years in our laboratories can be successfully employed in the characterization of disease organisms when they are first identified, and 2) that there may be more strains in nature than first thought.
Technical Abstract: Anaplasma marginale, a hemoparasite of cattle a results in significant economic losses worldwide. Distinct strains of A. marginale has been identified based on differences in tick transmissibility, molecular size of surface proteins and DNA restriction fragments, and reactivity to a panel of monoclonal antibodies. In this paper, we report on the molecular characterization of a newly isolated strain of A. marginale, designated St Maries, recovered from an acutely infected cow in northern Idaho. Dermacentor andersoni ticks taken from the infected animal were tested for infection by RNA probe analysis. The infection rate of male ticks was 100%, and the infection rate of female ticks was 83%. Infected male ticks were able to transmit St. Maries strain to a susceptible calf. The high infection rate in male ticks is important in transmission of A. marginale because of their intermittent feeding behavior, which promotes interhost transfer. The newly isolated strain differs from other US strains, including strains previously isolated in Idaho and Washington, based on reactivity to a panel of monoclonal antibodies and restriction fragment length polymorphisms. These results imply that antigenically distinct strains of A. marginale may arise within the same region.