Expression of polymorphic msp1beta genes during acute anaplasma Marginale rickettsemia.

Immunization of cattle with native MSP1 induces protection against Anaplasma marginale. The native immunogen is composed of a single MSP1a protein and multiple, undefined MSP1b polypeptides. In addition to the originally sequenced gene, designated msp1beta(F1), we identified three complete msp1beta genes in the Florida strain: msp1beta(F2), msp1beta(F3), and msp1beta(F4). Each of these polymorphic genes encodes a structurally unique MSP1b protein, and unique transcripts can be identified during acute A. marginale rickettsemia. The structural polymorphism is clustered in discrete variable regions, and each MSP1b protein results from a unique mosaic of five variable regions. Although each of the MSP1b proteins in the Florida strain contains epitopes recognized by serum antibody induced by protective immunization with the native MSP1 complex, the variable regions also include epitopes expressed by some but not all of the MSP1b proteins. These data support testing recombinant vaccines composed of the multiple antigenically and structurally unique MSP1b proteins combined with MSP1a in order to mimic the efficacy of native MSP1 immunization.

Detection of cattle naturally infected with Anaplasma marginale in a region of endemicity by nested PCR and a competitive enzyme-linked immunosorbent assay using recombinant major surface protein 5.

A competitive enzyme-linked immunosorbent assay using recombinant major surface protein 5 (rMSP5-cELISA) of Anaplasma marginale was validated in a naturally infected cattle herd in an area of eastern Oregon where A. marginale is endemic. The true positive and negative A. marginale infection status of 235 randomly selected cattle was determined by using a nested PCR (nPCR) coupled with msp5 sequence analysis and hybridization. Judgment of the reliability of the nPCR and hybridization for detection of persistent infections was based on three observations. First, the nPCR was able to detect as few as 30 infected erythrocytes per ml. Second, the nPCR was able to consistently detect low levels of rickettsemia in seven carrier cattle experimentally infected with A. marginale. Third, msp5 sequence analysis showed >95% identity among 30 nPCR amplicons from cattle naturally infected with field strains of A. marginale. The nPCR and hybridization identified 151 infected and 84 uninfected cattle among the 235 animals tested. With a cutoff point of 28%, the rMSP5-cELISA showed a sensitivity of 96% and a specificity of 95%. These results indicate that the rMSP5-cELISA can sensitively and specifically detect cattle with naturally acquired persistent A. marginale infections and suggest that it is an excellent assay for epidemiological studies, eradication programs, and regulation of international cattle movement.

Animal health research in the Small Ruminant Collaborative Research Support Program.

Disease is a major constraint in small ruminant production systems in lesser-developed countries throughout the world. Animal health projects have been an integral part of the Small Ruminant Collaborative Research Support Program (SR-CRSP) from its inception. At the onset, these projects were oriented toward herd health care and veterinary extension activities. Later, all the projects developed a sharper focus in that they were directed to more basic studies of infectious disease. Diseases currently being investigated include caseous lymphadenitis, contagious caprine pleuropneumonia, caprine arthritis-encephalitis, ovine pulmonary carcinoma, ovine progressive pneumonia and neonatal mortality of alpaca. Continued, sharply focused studies are projected for the future to take advantage of recombinant technology in the development of multivalent vaccines.