Strangles displays a major challenge to veterinary medicine worldwide. However, no data on Streptococcus equi subsp. equi (S. equi) M protein alleles have been reported so far from Arabian horses. We report here for the first time the S. equi SeM alleles causing strangles in Arabian horses, and the associated risk factors for the disease. Duplicate samples from one hundred Arabian horses with acute strangles in confirmed outbreaks and sporadic cases were analysed by phenotypic methods and multiplex polymerase chain reaction (PCR) targeting streptokinase precursor, seeI and sodA genes. PCR and sequencing of S. equi SeM gene were employed for strains typing, and the four superantigens were determined among the allelic variants. Directsample PCR confirmed and highly positively correlated (r = .85) with the phenotypic results, and detected S. equi in five samples more than the conventional culture. A combination of multiplex PCR from samples and culture could successfully identify S. equi (92%), S. zooepidemicus (5%) and S. equisimilis (3%). SeM typing demonstrated five SeM alleles, including four previously unidentified alleles that were deposited in the PubMLST-SeM database. SeM-139 and SeM-141 are related to some strains that were recently recovered from donkeys in China. SeM-140 and SeM-199 are related to a group of alleles from horses in Europe. Variation in the presence of seeM, seeH and seeL superantigens was found across the four novel alleles without interference with the severity of strangles and clinical presentation seen in different outbreaks. Horse age was the most important factor in developing strangles, followed by seasonality and the diagnosis of strangles in the previous year. These new findings comprise a significant contribution to the horse industry through the identification of novel S. equi SeM types that may bolster measures for strangles control as the identified SeM alleles will certainly help in the development of SeM-containing vaccine.
Strangles is a highly infectious, worldwide, costly disease, affects the upper respiratory system of equine and is caused by Streptococcus equi. Early diagnosis ought to be performed for infected and carrier horses by rapid and accurate diagnostic methods. Bacteriological culture, Matrix assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS), polymerase chain reaction (PCR) and DNA sequencing of S. equi M-protein (SeM) were the common methods for detection and differentiation of different subtypes of S. equi. In forty percent of suspected strangles cases, bacteriological culture may fail to detect S. equi. Recently, the development of direct sample PCR for estimation of S. equi in samples provides an alternative and potentially more sensitive method for diagnosis of equine strangles. This review article highlights the different methods of diagnosis, the role of chronic carrier in transmission of infection to susceptible animals and the different methods for identification and discrimination of β-haemolytic streptococci in respiratory samples of horses.
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