There appears to be no GSKJ4 trend towards increased numbers of SNPs or decreased conservation when comparing omps that are transcribed in either ticks or cattle [33]. Development of vaccines against anaplasmosis has received considerable attention over the last 50 years and has resulted in several marketed live and inactivated whole-organism vaccines [28]. None are currently available in the U.S. because of varying efficacy against heterologous Modulators strains and/or side-effects such as isoerythrolysis due to contaminating erythrocyte proteins in the vaccines. This has stimulated the search for improved vaccines and also attempts to understand the reasons for

the breaks in vaccine protection against heterologous strains [29], [30] and [31]. The reason for breaks in protection appear to be due to a sophisticated system for antigenic variation, whereby the expressed MSP2 and MSP3 outer membrane proteins continually change in sequence [32]. This is caused by segmental gene conversion of genomic expression sites for MSP2 and MSP3 by genomic

pseudogenes [10]. The repertoire of pseudogenes determines the ability of an incoming strain to superinfect a persistently infected carrier animal [13]. We show here that the pseudogene repertoire is extremely diverse for both MSP2 and MSP3 across the U.S., even within A. marginale strains from the same state. No msp2 or msp3 pseudogene was present in all U.S. strains. Therefore, it is unlikely that a vaccine could be developed by trying to include a full repertoire of potential MSP2/MSP3

variants in a vaccine. the However, check details other members of pfam01617 (to which both msp2 and msp3 belong) encode conserved OMPs and are expressed in A. marginale [33] and, therefore, still remain viable vaccine candidates. Two other vaccine strategies have also been proposed recently. The first [16] relies on the protection afforded by the less virulent strain A. marginale subspecies centrale. This strain has been extensively used in the field in Australia, South Africa, Argentina, Uruguay, Israel, Zimbabwe and Malawi. Recent research has found proteins with immunogenic epitopes shared between marginale and centrale, although the overall protein sequence identities were less than 90% [16], and these have been proposed for inclusion in a subunit vaccine. Although A. marginale subsp. centrale undoubtedly provides some protection against A. marginale strains [35], controlled trials have shown low efficacy of this vaccine against heterologous isolates from South America and Africa [36], [37], [38] and [39], and infection by A. marginale subspecies centrale does not prevent subsequent superinfection by A. marginale [40]. These data have stimulated the search for less virulent strains of A. marginale to potentially replace the A. marginale subspecies centrale vaccine, and such strains have been identified in Australia and Mexico [41] and [42].