Comparison of nasopharyngeal and guttural pouch specimens to determine the optimal sampling site to detect Streptococcus equi subsp equi carriers by DNA amplification

Abstract

Background Streptococcus equi subsp equi (S. equi) is the cause of “equine strangles” which is a highly infectious upper respiratory disease. Detection of S. equi is influenced by site of specimen collection, method of sampling, and type of diagnostic test that is performed. We hypothesized i) that a loop-mediated isothermal amplification (LAMP) assay that targets the S. equi-specific eqbE gene would be more sensitive than a realtime PCR assay that targets the S. equi-specific seeI gene and ii) that LAMP of specimens obtained by guttural pouch lavage (GPL) would be more sensitive than LAMP of nasopharyngeal specimens to identify S. equi carriers.MethodsA nasopharyngeal flocked swab, nasopharyngeal wash, and GPL specimen was collected from 44 convalescent horses and the eqbE LAMP assay was performed. The seeI realtime PCR assay and aerobic culture were also performed on the GPL specimen. Logistic regression was performed to compare sampling sites and test methods (P-values ≤0.05 were considered significant).ResultsOne of 41 nasopharyngeal flocked swabs, 6/38 nasopharyngeal wash and 24/44 GPL specimens were positive by eqbE LAMP. 18/44 GPL specimens were positive by seeI PCR and S. equi was isolated from 4/44 of these specimens. Detection of S. equi DNA was 51 times more likely from the GPL samples than nasopharyngeal samples (OR 51.0, P < 0.0001). When eqbE LAMP GPL samples were positive, it was eight times more likely that the guttural pouch had any abnormality on endoscopy (OR 8.2, P ≤ 0.005), almost 20 times more likely that mild empyema was found (OR 19.7, P ≤ 0.002), and eight times more likely that the SeeI PCR was positive for S. equi DNA (OR 8.1, P ≤ 0.006).ConclusionThis study demonstrates that guttural pouch lavage specimens should be used to detect S. equi and that the eqbE LAMP assay was comparable to the seeI PCR.Electronic supplementary materialThe online version of this article (doi:10.1186/s12917-017-0989-4) contains supplementary material, which is available to authorized users.

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

“…13 With regards to endoscopic scoring, earlier reports suggest that clear differences should be noted in many carriers. 14 to Streptococcus zooepidemicus alone. 11 Despite recent evidence to the contrary, 15 the iELISA has also been suggested for use to detect animals that have been exposed to S. equi that may remain persistently infected.…”

Comparison of flocked and rayon swabs for the molecular detection of selected equine viruses and bacteria from nasal secretions of healthy horses

“…Previous work has shown that the molecular detection of S equi improves when more than one sample per horse is processed at the same time 13 . A recent study by Boyle and others 16 determined that the molecular detection of S equi from guttural pouch washes from convalescent horses was 51 times more successful than from nasopharyngeal flocked swabs.…”

Strangles Awareness Week: a new initiative to help stamp out strangles

“…Around 10 per cent of horses that appear to have recovered become subclinical carriers, persistently harbouring S equi in their guttural pouches, from which they will intermittently shed bacteria into their local environment 6…”

“…Around 10 per cent of horses that appear to have recovered become subclinical carriers, persistently harbouring S equi in their guttural pouches, from which they will intermittently shed bacteria into their local environment. 6 Strangles affects the health and welfare of infected horses and can be financially and emotionally draining for horse owners and equestrian businesses. Unfortunately, the stigma around strangles can deter those affected from being open about an outbreak -something that is an essential part of preventing the spread of disease.…”