Bench notes: Brucella canis serologic testing
Brucella canis is a potentially zoonotic disease that can be transmitted from an infected dog to humans. Those in close contact with infectious body fluids and tissues (e.g., veterinarians and technicians, kennel workers, laboratory staff) are at increased risk.
There are two serological tests performed at the VDL to test for B. canis antibodies in dogs. Rapid Slide Agglutination Test (RSAT) is initially used to screen for B. canis antibodies. The RSAT is specific for B. canis and is based on direct agglutination of killed whole-cell antigen. In addition, the 2-mercaptoethanol (2ME)-RSAT also is performed. This second test improves specificity by reducing antibodies in the sample that may cross-react with other bacteria. The 2ME-RSAT is less sensitive but more specific than the RSAT. Thus, the more sensitive test is performed first, and the more specific test follows.
If the serum is negative on the RSAT, the animal is considered either not infected with B. canis or early in infection prior to the development of an antibody response. An additional sample should be submitted in 4 to 6 weeks to detect recent infection. If a serum sample is positive on both the RSAT and 2ME-RSAT, the animal is presumptively diagnosed as being infected with B. canis, and bacterial culture samples should be forwarded to the National Veterinary Laboratory Service (NVSL) for definitive diagnosis. In some cases, the RSAT is positive, but the 2ME-RSAT is negative. This can be due to early infection or non-specific/cross reactive antibodies. Repeat 2ME-RSAT is recommended in 30 days.
Heidi Pecoraro, DVM, PhD, Diplomate, ACVP
|Gram stain of Brucella sp., a Gram-negative coccobacillus.|
Photo courtesy of the Public Health Image Library, #19255