Bartonella Infection among Cats Adopted from a San Francisco Shelter, Revisited

Bartonella infection among cats from shelters can pose a health risk to adopters. Bartonella henselae is the most common species, with B. clarridgeiae and B. koehlerae being less common. The lower rates of infection by the latter species may reflect their rarity or an inefficiency of culture techniques. To assess the incidence of infection, blood cultures, serology, and PCR testing were performed on 193 kittens (6 to 17 weeks old) and 158 young adult cats (5 to 12 months old) from a modern regional shelter. Classical B. henselae culture medium was compared to a medium supplemented with insect cell growth factors. Bartonella colonies were isolated from 115 (32.8%) animals, including 50 (25.9%) kittens and 65 (41.1%) young adults. Therefore, young adults were twice as likely to be culture positive as kittens. Enhanced culture methods did not improve either the isolation rate or species profile. B. henselae was isolated from 40 kittens and 55 young adults, while B. clarridgeiae was cultured from 10 animals in each group. B. koehlerae was detected in one young adult by PCR only. B. henselae genotype II was more commonly isolated from young adults, and genotype I was more frequently isolated from kittens. Kittens were 4.7 times more likely to have a very high bacterial load than young adults. A significantly higher incidence of bacteremia in the fall and winter than in the spring and summer was observed. Bartonella antibodies were detected in 10% (19/193) of kittens and 46.2% (73/158) of young adults, with culture-positive kittens being 9.4 times more likely to be seronegative than young adults.