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Anaplasma Centrale

Anaplasma centrale is a species of Gram-negative bacteria causing mild anaplasmosis in cattle (bovine species), sheep, and wild ruminants. The primary vectors are ticks, but mechanical trasmission by biting flies, contaminated fomites, and transplacentally also has been reported 1,5. Although infection with A. centrale may result in severe disease, it usually causes only a mild anemia cases. The organism is widely distributed in the world but has never been reported in North America 2,7.

Anaplasma centrale was first isolated in 1910 by Sir Arnold Theiler who described it as a naturally occurring, generally less pathogenic strain of Anaplasma marginale, the cause of a fatal infectious disease of cattle in South Africa. The question of whether A. centrale is a subspecies of A. marginale, as originally suggested by Theiler, or a separate species is unresolved.

Anaplasma centrale Source: Vet Microbiol. 2015 Sep 30; 179(3-4): 270–276 under the CC BY license

Anaplasma species are intra-erythrocytic parasites that are found in the membrane-bound round vacuole, called "inclusion body." The vacuole may contain several parasites. The scientific name is based on the staining characteristics and location within the host cell. "Anaplasma" refers to the lack of stained cytoplasm, and the species name refers to the location of the inclusion body in the erythrocyte 4. A. centrale is located more centrally when viewed on stained blood films.



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After invasion of a red blood cell (RBC), the organism divides into 6 initial bodies and enlarges within its thin outer membrane. When the infected red blood cell ruptures, the parasite's membrane also ruptures, releasing the initial bodies into the blood stream to invade other RBCs. As the infection progresses, more and more RBCs are destroyed causing hemolytic anemia 9.

Anaplasma centrale has been used to immunize cattle against A. marginale for almost 100 years. The vaccine does not prevent the infection with A. marginale, but reduces the severity of symptoms 3,6. A. centrale vaccine is a live, blood-based vaccine which carries with it risk of vaccine-induced disease as well as transmission of known and unknown contaminating pathogens. This concern has prevented its licensure in both the United States and the European Union. The vaccine is used in Africa, Asia, Australia, and the Americas, but despite its long history of field use, the basis for protective immunity against virulent strains is not fully understood. Current understanding of immunity to A. marginale has been derived both from experimental vaccine trials, which identified major surface protein 2 (MSP-2) as a protection-inducing immunogen, and from the study of infection-induced immunity.6,8.

References

  1. Carlton L. Gyles, J.F. Prescott, Glenn Songer, Charles O. Thoen (editors). Pathogenesis of Bacterial Infections in Animals
  2. Douglas J. Weiss, K. Jane Wardrop (editor). Schalm's Veterinary Hematology
  3. Alister G. Craig, Artur Scherf. Antigenic Variation
  4. M. W. Service (editor). The Encyclopedia of Arthropod-transmitted Infections
  5. B.F. Eldridge, J.D. Edman (editors). Medical Entomology
  6. Joseph T. Agnes, Kelly A. Brayton, Megan LaFollett, Junzo Norimine, Wendy C. Brown, and Guy H. Palmer. Identification of Anaplasma marginale Outer Membrane Protein Antigens Conserved between A. marginale Sensu Stricto Strains and the Live A. marginale subsp. centrale Vaccine
  7. Hisashi Inokuma, Yutaka Terada, Tugihiko Kamio, Didier Raoult, and Philippe Brouqui. Analysis of the 16S rRNA Gene Sequence of Anaplasma centrale and Its Phylogenetic Relatedness to Other Ehrlichiae
  8. Varda Shkap, Thea Molad, Kelly A. Brayton, Wendy C. Brown, and Guy H. Palmer. Expression of Major Surface Protein 2 Variants with Conserved T-Cell Epitopes in Anaplasma centrale Vaccinates


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