Glanders and the risk for its introduction through the international movement of horses

Glanders is the contagious zoonotic disease caused by infection with Burkholderia mallei. It affects primarily horses, donkeys and mules. The disease was eradicated from large areas of the Western world in the early 20th century, but, over the last 10-20 years, has emerged and re-emerged in areas in which it was previously unknown or had been eradicated. Although glanders was previously thought to manifest in only acute or chronic presentations, it now appears that B. mallei can produce latent infections similar to those caused by Burkholderia pseudomallei. These latent infections may or may not be detectable by current diagnostic tests. The diagnostic test currently recommended by the World Organisation for Animal Health (Office International des Epizooties [OIE]) for international trade in equids is the complement fixation test (CFT). This test has been shown to have varying sensitivities and specificities depending on the antigen and methodology used. False positives are problematic for the horse-owner and veterinary authority, whereas false negatives may allow the reintroduction of B. mallei into B. mallei-free areas. These gaps in knowledge of the epidemiology of glanders, and weaknesses in its diagnosis, coupled with the increased movement of equids, indicate that infection with B. mallei remains a major risk in the context of international movement of equids.