الفهرس 
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Abstract
Strangles is a highly infectious, worldwide disease that affects the upper respiratory tract of equine caused by Streptococcus species. Rapid identification of the causative agents is critical to initiate early targeted antibiotic therapy and minimize death and economic losses in horses. Hence, to facilitate a rapid diagnosis of strangles, the aim of the present study was to evaluate the direct sample multiplex PCR for detection and identification of the three most important β-hemolytic streptococci in clinical samples from Arabian horses.
Out of 465 clinically examined Arabian horses during the period from November 2015 to January 2019, 100 horses (21.50%) showed clinical signs of strangles including fever (39.5 to 41.5oC), anorexia, serous nasal discharge that later becomes mucopurulent and even purulent (yellowish) discharge from the nostrils and enlarged submaxillary, retropharyngeal and parotid lymph nodes. The prevalence of strangles was found to be significant in foals under one year of age (22%), compared with those between one and 2 years of age (15.29%) or over 2 years of age (25.29%). Age, seasonality and strangles being diagnosed in the previous year have significant association with the occurrence of strangles in the examined Arabian horse population. It was found that that chance that horses develop strangles is 3.1 times higher if the strangles was diagnosed in the station during the previous year than if it is not.
All samples (n=100) were collected from horses displaying clinical signs of strangles and cultural and biochemical characters of 95 positive samples (95%) revealed S. equi (n=86; 90.52 %), S. zooepidemicus (n=6; 6.31%) and 3 samples were positive for S. equisimilis (3.15%). The diagnostic multiplex PCR targeting SeeI, sodA, eqsim genes and 16S rRNA control gene successfully discriminated the three streptococci S. equi, S. zooepidemicus and S. equisimilis. Using the direct sample multiplex PRC assay, S. equi were present in 91/100 samples of which 86 were identified by culture and 5 culture-negative. Moreover, 1 sample (1%) that was S. equi by phenotypic methods was PCR- positive for S. zooepidemicus (n=6), and 1 sample was identified phenotypically as S. zooepidemicus was S. equi by PCR. S. equisimilis present in 3 samples by both culture and direct PCR. This explained the significant overall correlation between phenotypic and genotypic identification of Streptococcus spp.