Systematic monitoring of glanders-infected horses by complement fixation test, bacterial isolation, and PCR

Glanders is an equine zoonosis caused by Burkholderia mallei that is responsible for considerable economic loss. Complement fixation testing (CFT) using warm or cold incubation are recommended by the OIE, but many routinely used detection tests may present misleading results. To increase accuracy of glanders diagnosis and establish an appropriate protocol in collaboration with the National Equine Health Program, seven horses positive for glanders kept in isolation in Brazil were examined fortnightly by CFT, microbiological screening, and molecular testing. Warm and cold serologies with USDA and c.c.Pro antigens, respectively, were performed on 132 samples using the US Department of Agriculture protocol. The warm and cold serologies showed, respectively,12.9% and 17.3% seroreactive, 85.7% and 65.2% non-reactive, 0.8% and 3% inconclusive, and 0% and 2.3% anticomplementary. The agreement of CFT protocols was moderate. Of 213 clinical samples submitted to selective culture (167 nasal swabs, 5 ocular swabs, 3 lymph node punctures, and 38 tissue samples from four horses that died), 1.9% tested positive for B. mallei. Fourteen samples and one nasal swab (7%) tested positive with PCR. Cold CFT with the USDA and c.c.Pro antigens, in combination with PCR to increase sensitivity, may be useful for diagnosis of chronic glanders.