Brucella suis type 4 in foxes and their role as reservoirs/vectors among reindeer

Abstract

Field and laboratory studies were conducted to test the hypotheses that (1) the reindeer/caribou organism, Brucella suis type 4, is incidentally transmitted to reindeer predators such as foxes but does not cause reproductive disease in them, and (2) infected predators such as foxes are terminal hosts and do not serve as reservoirs of infection for reindeer. In field collections, serologic prevalence of brucellosis was similar for male and female foxes (Vulpes vulpes and Alopex lagopus). B. suis type 4 was isolated from female Vulpes and Alopex. No association between reproductive status of foxes and brucellosis infections was observed. Serologic titers in Vulpes experimentally infected by oral exposure to Brucella suis type 4 were detected first by the standard tube and plate agglutination tests which were followed by the buffered Brucella antigen, rivanol, and complement fixation tests. Brucella suis type 4 was isolated from the feces 4 to 6 days post-exposure (PE) and from the oral cavity for as long as 3 weeks PE in Vulpes challenged with 10$\sp9$ or 10$\sp{11}$ colony forming units. Brucella suis type 4 was isolated frequently from regional lymph nodes in the head up to 18 weeks PE, and from only more distant nodes at 22 and 66 weeks PE. Organisms did not localize in the reproductive tract. Clinical effects of brucellosis in Vulpes experimentally-infected were not observed. Pathologic lesions were not detected in the male and non-gravid female reproductive tract. Due to breeding failure, effects of Brucella suis type 4 on the pregnant fox reproductive tract were not determined in experimental infections. Gross and microscopic pathology was limited to lymph nodes. Fox to fox transmission attributed to aerosols from products shed by infected foxes occurred readily. Transmission from Vulpes to lemmings (Dicrostonyx rubricatus) that were exposed to urine from infected fox occurred frequently. Transmission from infected Vulpes to two reindeer (Rangifer tarandus) occurred under conditions of close confinement. Ingestion of organisms passed mechanically in the fox feces was considered the probable source of infection. Fox saliva containing Brucella was also implicated in transmitting the organism through bites or aerosols.