Equine Review

In the Equine Veterinary Journal, Andy Durham and Jeremy Kemp-Symonds presented the results of screening tests from horses admitted to the Bransby horses sanctuary (2020. 10.1111/evj.13276). At admission, horses undergo both paired serological testing for antibodies against Streptococcus equi antigens A and C and bilateral guttural pouch lavage to identify strangles carriers. Of 287 horses examined, nine (3.1%) were found to be guttural pouch carriers. There was no significant association between serological status and guttural pouch carriage of S. equi. Only one of the nine carriers (11%) was seropositive using a cut-off of OD ≥0.5, and only three of nine (33%) using a cut-off of OD ≥0.3. Of the 35 seropositive horses, only one was positive on polymerase chain reaction (PCR) of bilateral guttural pouch lavage samples. The authors advised caution when relying on serology as a screening test for chronic carriage of S. equi.

In an editorial in the same issue, Philip Ivens and Scott Pirie discussed the diagnosis of S. equi (2020. 10.1111/evj.13319). They postulated that a proportion of S. equi carriers undergo a temporal reduction in serological response to the residual bacteria present within the guttural pouch; for example through reduced epitope exposure, bacterial genetic mutation or immunological adaptation.