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Title: Protective immunity induced by immunization with a live, cultured anaplasma marginale strain

item KENITRA HAMMAC, GENA - Washington State University
item KU, PEI-SHIN - Washington State University
item GALLETTI, MARIA - Universidad De Sao Paulo
item Noh, Susan
item Scoles, Glen
item PALMER, GUY - Washington State University
item BRAYTON, KELLY - Washington State University

Submitted to: Vaccine
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/24/2013
Publication Date: 8/2/2013
Citation: Kenitra Hammac, G., Ku, P., Galletti, M.F., Noh, S.M., Scoles, G.A., Palmer, G.A., Brayton, K.A. 2013. Protective immunity induced by immunization with a live, cultured anaplasma marginale strain. Vaccine. 31:3617-3622.

Interpretive Summary: Anaplasmosis, caused by Anaplasma marginale, causes significant morbidity and mortality in cattle and is found worldwide. This bacterial pathogen colonizes erythrocytes, causes anemia and fever, and is transmitted by ticks. The methods of disease prevention are limited. In many parts of the world, animals are inoculated with Anaplasma marginale subsp centrale, which is a naturally attenuated strain of A. marginale. Infection with this organism results in minimal disease and an immune response which provides partial protection against the development of clinical signs of anaplasmosis when an animal is subsequently exposed to A. marginale. Live A. centrale must be grown in cattle and stored in liquid nitrogen until just prior to inoculation. This process is difficult, expensive, and carries the risk of introduction of other blood borne pathogens, such as bovine leukosis virus, into the inoculated population. In this study, a strain of A. marginale (A. marginale-GFP) that can be grown in culture and is labeled with a fluorescent protein was tested as a vaccine strain which could serve as an alternative to A. centrale. The advantages of this approach are that the organism can be grown in culture thus reducing both the cost of production and risk of transmission of cattle pathogens, and the fluorescent protein is a potentially convenient means to differentiate between infected and immunized animals. In this study, the A. marginale-GFP induced minimal disease in inoculated animals and provided protection against anemia and fever when immunized animals were challenged with wild type A. marginale. Thus, this cultured product is safe and produces protection against disease caused by a homologous strain. The next step will be to determine if this strain can induce protection against a wider variety of A. marginale strains.

Technical Abstract: Despite significant economic losses resulting from infection with Anaplasma marginale, a tick-transmitted rickettsial disease of cattle, available vaccines provide, at best, only partial protection against clinical disease. The green-fluorescent protein (GFP) expressing mutant of the A. marginale St. Maries strain is a live, marked vaccine candidate (AmStM-GFP). To test whether AmStM-GFP is safe and provides clinical protection, a group of calves was vaccinated and clinical parameters, including percent infected erythrocytes, packed cell volume and days required to reach peak bacteremia were measured following inoculation and following tick challenge with wild type St. Maries strain (AmStM). These clinical parameters were compared to those obtained during infection with the A. marginale subsp. centrale vaccine strain or wild type AmStM. AmStM-GFP resulted in similar clinical parameters to A. centrale, but had a lower maximum percent infected erythrocytes, smaller drop in PCV and took longer to reach peak bacteremia than wild type AmStM. AmStM-GFP provided clinical protection, yielding a stable PCV and low bacteremia following challenge, whereas A. centrale only afforded partial clinical protection.