Studies on bovine anaplasmosis The comparative pathogenicity and immunological relationship of anaplasma centrale to anaplasma marginale

Abstract

A limited serological surrey of the inoidenoe of borine anaplasmosis in east afrioa indicates a high lerel of infeotion* it is probable that anaplasmosis is endemic in most areas of east afrioa where oattle are produoed commercially* the marked reduction of inoidenoe in a well managed herd where regular dipping is practiced does, however, reveal the probable presenoe of large numbers of highly susoeptible adult animals* The presenoe of susoeptible oattle indioate the need for oontinued tick oontrol to prevent future spread of infection* the presenoe of speoifio complement-fixing antibodies in sera of game animals has been demonstrated. This is not necessarily indioative of anaplasma marginals infection, but does suggest the presence of or past exposure to anaplasma antigens, if not identical, at least, resembling a* marginals. Comparative pathogenesis studies on 72 animals have been oomplete* k% oentrale produoed a markedly milder course of infection in spleneotomised oalves, and adult oattle, than virulent east african a. Marginals (eah)* Mild a. Marginals strains obtained from the u.S* resulted in infections of approximately equal virulenoe to a* centrale. Differences in virulence of 1. Oentrale (eac), and eam infections in young non-spleneotomised animals are not as readily demonstrable* Complement-fixation antigens were prepared using blood collected from animals showing both a,, oentrale and a* marginals (eam) infections. These antigens were used in addition to an antigen obtained from the u.S. Department of agriculture, prepared from a,, marginals infeotions. Complement-fixation (cf) studies show that the mild strains of a* marginals 165 Are serologieally indistinguishable from the east ifrioan virulent a- marginale. In low serum dilutlons9 cross reactions between jl. Centrals And jk. Marginale sense and antigens occur, but serum titrations reweal marked serological differences not observed between different marginals strains. These findings indioate that pentrale should not be considered A mild strain if a. Marginals. A total of 62 oross infectivity trials further oonfirms the distinot nature of the a. Centrals pathogen. A. Centrals produces a degree of immunity against challenge with ju marginals. In most instances, such a challenge produoes an infection of reduced severity. A total of three deaths occurred among 12 spleneotomised oalves when challenged with eax, after first hawing been premunised with a. Centrals. Of 11 controls, all died from anaplasmosia, following a similar challenge. Al. Oentrale was responsible for significant protection against eam challenge in adult oattls, but was of questionable walus among non-spleneotomised oalwss and yearling oattle. Animals first inf so ted with a. Marginals and then ohallenged with a. Centrals, generally react to the ohallenge with Almost equal severity as animals showing a primary iu oentrale infection. ✓ • Eo detectable protection la produced by jl. Marginals to a subsequent a. Oentrale infeotioa. A homologous ohallenge of anaplasma oarrier oattle failed to produce clear out ewidenoe of reaction to ohallenge. Difference in virulenoe among _a. Marginals isolates has been demonstrated. Evaluation of a. Oentrale or other premunising vacoines is influenced by the relative virulenoe of the a. Marginals ohallenge Administered