Markers of long term silent carriers of Streptococcus equi ssp. equi in horses

Abstract

Background: Difficulty in detection of silent carriers of Streptococcus equi is a key reason for its continued spread to immunologically naïve groups of horses. Objective: To determine whether clinical examination, markers of inflammation, or serology differentiate silent carriers of S. equi in recovered comingled horses. Animals: Ninety-eight warmblood yearlings and 72 unaffected mares on a large breeding farm (outbreak A), 38 mature Icelandic horses at a riding stable (outbreak B), and 27 mixed breed horses at a boarding stable (outbreak C). Methods: Prospective observational study 6 months to 2 years after strangles outbreaks. Carriers were defined as any animal positive on culture or qPCR to S. equi from nasopharyngeal lavage or guttural pouch endoscopy and lavage. Most horses had complete physical exams and 1 group included evaluation of white blood cell counts and serum amyloid A. Sera from all horses was tested for antibodies to antigens A and C of S. equi using an enhanced indirect ELISA. Descriptive statistics were calculated. Data were compared using paired t tests, Wilcoxon ranked test, chi square, or the Fishers exact test. Significance was set at P < .05.

Repeated nasopharyngeal lavage predicts freedom from silent carriage of Streptococcus equi after a strangles outbreak

“…Although such a method would preclude visual detection of the chondroids, such changes are reported to represent only a small proportion of horses identified as silent carriers. 12 , 16 …”

“…Although such a method would preclude visual detection of the chondroids, such changes are reported to represent only a small proportion of horses identified as silent carriers. 12,16 On the other hand, although use of other less invasive markers of silent carrier status, such as serology, continue to be recommended, 18 hypothesis-based studies have failed to support their clinical value in identification of carriers 11 or distinguishing noncarrier herdmates poststrangles. 12…”

“…12,16 On the other hand, although use of other less invasive markers of silent carrier status, such as serology, continue to be recommended, 18 hypothesis-based studies have failed to support their clinical value in identification of carriers 11 or distinguishing noncarrier herdmates poststrangles. 12…”

“… 9 Other minimally invasive alternatives to carrier testing, such as use of serology after strangles outbreaks, have lacked clinically useful discriminatory power because carriers can be seronegative, 11 even when culture positive. 12 …”

“…Moreover, it has been shown that combined sampling by both NPL and GPL is required for optimal testing for the carrier state because single guttural pouch samples also can be falsely negative in silent carriers of S. equi 9 . Other minimally invasive alternatives to carrier testing, such as use of serology after strangles outbreaks, have lacked clinically useful discriminatory power because carriers can be seronegative, 11 even when culture positive 12 …”