Sir Arnold Theiler and the discovery of anaplasmosis: a centennial perspective.

Sir Arnold Theiler's research in 1908/09 led to the discovery of the first rickettsial pathogen, Anaplasma marginale, and set the stage for his development and implementation of an effective live vaccine based on a less virulent strain, A. marginale ss. centrale. His 1910 report, describing A. marginale, is among the classic monographs in infectious disease research, presenting not only observations in exacting detail but also highlighting the deductive reasoning leading to association of a new pathogen with a specific disease. With a centennial perspective and both conceptual frameworks and molecular tools unimaginable in Theiler's time, the significance of several observations in the original report--cyclic bacteremia, strain superinfection, and taxonomic position--is now clear and highlight the broad applicability of key principles of pathogen biology.

Epizootiology and control of anaplasmosis in south africa.

The history of bovine anaplasmosis, or tick-born gallsickness, since the discovery of Anaplasma marginale by Sir Arnold Theiler is briefly reviewed. The development of the Anaplasma centrale vaccine by Theiler, up to the composition of the present vaccine issued by Onderstepoort in which the original isolate is still passaged, is discussed in detail. Recent transmission studies at Onderstepoort have shown that 5 tick species are capable of transmitting anaplasmosis intrastadially, and intrastadial transmission, especially by adult male ticks, it is believed, could play an important role in the epizootiology of bovine anaplasmosis in South Africa. Disease incidence and tick distribution are discussed in relation to enzootic and epizootic conditions. Investigations have proved that the Onderstepoort A. centrale vaccine is not as avirulent in adult cattle as it was previously thought to be. The results of a field trial undertaken to test the infectivity of the vaccine, are given.