Strangles occurs when Streptococcus equi subsp equi, a gram-positive, aerobic coccal bacteria, enters the mouth or nose and attaches to the tonsillar crypts, writes Kate L. Hepworth-Warren, DVM, DACVIM. Chronic shedders are often the culprit in new outbreaks when horses suddenly develop signs of strangles with no known exposure. A chronic shedder also can make it difficult to end an outbreak once it begins.
Source: DVM 360, February 4, 20212. Link. Through use of appropriate biosecurity measures, endoscopic examination and sampling of the guttural pouches, chronic carriers can be identified and treated so that they no longer pose a risk to the rest of the herd.