Pathology, microbiology, and molecular evaluation of tissues from equids serologically positive for Burkholderia mallei in Midwestern Brazil

ABSTRACT: Glanders is a disease caused by the bacterium Burkholderia mallei that primarily affects horses, mules and donkeys. The disease can cause lesions in the skin, lungs and several other organs. However, it often manifests as an asymptomatic disease. In Brazil, serological tests of high sensitivity and specificity are used to assist in the detection of antibodies against B. mallei and to contribute to the control of the disease. However, due to the mandatory euthanasia of seroreactive animals, equids with positive serology for B. mallei and asymptomatic generated great conflicts between breeders, veterinarians and diagnostic laboratories. This study clarifies the limitations of complementary diagnostic tests for detecting B. mallei. It describes the clinical, morphological and laboratory findings in 24 equines from different municipalities in the Mato Grosso State, Brazil, which reacted to the complement fixation test and were positive in the western blotting test for glanders. Data and tissue samples were collected from 24 horses for histological, microbiological and molecular analysis. In 23 horses, no clinical signs, morphological alterations, microbiological isolation, or molecular detection would characterize B. mallei infection. On the other hand, samples from an asymptomatic horse without lesional alterations showed sequence amplification compatible with B. mallei in the PCR. Considering that the infection by B. mallei is subject to the application of animal sanitary defense measures and that, by international requirement and national legislation, the serological results are tools that should support the sanitation procedures for the error of the bacteria in the Mato Grosso State, Brazil.