A guide to understanding the use and limitations of strangles blood tests Positive resultHorses exposed to the bacteria recently, i.e. from 10 days to a few months ago, probably WILL test positive on the antibody blood test. This is regardless of whether they have exhibited clinical disease, and whether they successfully cleared the disease or became carriers. This can lead to a positive result but no risk of transmitting disease. Negative resultHorses exposed to the bacteria more than a few months ago probably WILL NOT test positive on the antibody blood test. This is regardless of whether they became carriers or not. This can lead to a negative result, but with risk of transmitting disease. Inconclusive resultResults can sometimes come back as borderline or inconclusive. This is either because the antibody levels are on the way up and will soon become positive, or because they or on the way down and soon will be negative, or because the individual horse has a slightly higher level of cross-reactivity from other antibodies. Detecting asymptomatic carriersThe only reliable way to detect a long-term carrier is to perform a guttural pouch wash, which involves passing an endoscope up the nasal passages into the guttural pouches and taking a sample of fluid, which can be checked for bacterial DNA using a PCR test.Regardless of which tests are used, if any, we recommend that for the purpose of biosecurity all premises implement a strict isolation policy for a minimum of 14 days for all new entrants. Useful linksStrangles vaccination information Strangles testing and prevention information Tags Equine Publication date 12 Aug, 2025
