Markers of long term silent carriers of Streptococcus equiss p.equiin horses

Background Difficulty in detection of silent carriers ofStreptococcus equiis a key reason for its continued spread to immunologically naive groups of horses. Objective To determine whether clinical examination, markers of inflammation, or serology differentiate silent carriers ofS. equiin 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 toS. equifrom 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 ofS. equiusing an enhanced indirect ELISA. Descriptive statistics were calculated. Data were compared using pairedttests, Wilcoxon ranked test, chi square, or the Fishers exact test. Significance was set atP < .05. Results Apart from weanlings at 6 months in outbreak A, there was no significant association between any clinical markers or serology with carrier state (P= .06-1). Moreover, 3/12 culture positive carriers were seronegative toS. equi. Conclusions and Clinical Importance Silent carriers ofS. equido not differ clinically or on markers of inflammation to their noncarrier herd-mates. Moreover, serology alone will not distinguish carriers in comingled horses.