| Strangles is a highly contagious respiratory disease of equi caused by Streptococcus equi subspecies equi(S.equi)and is one of the most prevalent equine infectious disease worldwide.It is classically characterized by abrupt pyrexia,pharyngitis,abscess formation in the submandibular and retropharyngeal lymph nodes,and profuse mucopurulent nasal discharge.Since the disease is highly infectious and usually causes death in foals,and the pathogen is hard to eliminated,it has caused huge economic losses in horse industry.Recently,with the driving of market demand and the support of a series of targeted poverty alleviation policies,the donkey industry have been developing rapidly and the breeding scale have been expanding.The breeding mode has been rapidly moving to intensivefarm.However,while intensive breeding mode improves economic benefits,due to the high-density and the lack of biosecurity,infectious disease appears to be more frequent,which has become one of the main problems for donkey industry.Intensive donkey farms have suffered from strangles in Shandong,Henan,Hebei,Liaoning,Shanxi,Shaanxi,Inner Mongolia,Gansu and Xinjiangprovinces from 2018,which has caused considerable economic losses to the local donkey industry.Since strangles was first reported,the scientific research has been mainly focusing on horse strangle,but only few of them on donkey strangles,especially in intensive donkey farms.Moreover,almost no research has been done for susceptibility,morbidity and mortality,transmission route,molecular biological characteristics of pathogens,prevention and control of S.equi infection in intensive donkey farms,which results in the lack of research data supporting for the prevention and control of strangles in intensive donkey farms.Therefore,the present study has carried on the scientific research to the above questions.First of all,six intensive donkey farms with strangles outbreaks(2 breeding farms and 4 fatten farms)were selected as research objects.the outbreak caused by S.equi was confirmed by clinical diagnosis,staining,bacterial isolation and PCR diagnosis.the prevalence of strangles in this population of donkeys was 13.4 %.The prevalence of strangles was found to be significantly higher(P <0.00001)in donkey foals under 1 year of age(40.3%(83/206)),compared with those between 1 and 2 years of age(12.5%(191/1525))or over 2 years of age(3.8%(17/442)).In addition,11 of 83(13%)affected donkey foals died due to strangles,but there were no deaths in affected donkeys over one year of age(P <0.0001).The result indicated that the foal under the age of 1 years is most susceptible to strangles and with high morbidity and mortality which were decreased with ages.In addition,the horse strangles usually happens in the spring and autumn,especially from September to next April?But the current large-scale outbreak began in July 2018 and lasted until August 2019,which may due to the change of life style and status in intensive donkey farms.It suggested that the outbreak of strangle is no seasonal in intensive donkey farms.Total 7 novel genotypes of S.equi(SeM-136?SeM-138?SeM-142?SeM-144?SeM-145?SeM-146 and SeM-149)were indentified in 667 sample collected from 49 intensive donkey farms located in 9 provinces including Shandong,Henan,Hebei,Liaoning,Shanxi,Shaanxi,Inner Mongolia,Gansu and Xinjiang during July 2018 to August 2019,and there no known genotype was detected.Among the novel genotypes identified,SeM-136 was detected in 37 of the 49 intensive donkey farms in above provinces except Shaanxi,and all the 37 farms had introduced donkeys during the period of the outbreaks.Since other genotypes were regional,it is suggested that the SeM-136 was responsible for the pandemic of strangles.The phylogenetic analysis was performed by using the fragment of 327 bp coding the N-terminal virable region of SeM protein,and the result showed all S.equi strains isolated from donkeys close to each other and form a cluster,but keep a relatively long genetic distance from horse isolates.It is suggested that the S.equi strain that caused the outbreak may not have originated in horses,but has been present in donkeys.In addition,the study on genotype SeM-138 indicated that the introduction of donkeys can introduce S.equi strains into farms,which showed the importance of establishing isolation zones for donkey introduction in intensive donkey farms.Veterinary opinion remains divided as to whether antibiotic treatment is necessary for strangles or not.Antimicrobial susceptibility test was performed for 133 isolates of 7 novel genotypes with penicillin and cephalosporin cefuroxime sodium.The result showed that no resistant strains emerge,and bacterial inhibition ring of penicillin was of 31 to 37 mm while that of cephalosporin cefuroxime sodium was 30 to 35 mm.All of them are sensitive.Meanwhile,a randomized trial of 12 to 14-month-old donkeys with enlarged submaxillary lymph nodeswas performed to check the time required from begin to mature,it was 6-13 days in the untreated control group,but 10-92 days in the group with 7-day penicillin treatment.The treatment group required significantly longer time than the control group(P<0.01).It suggested that antibiotic treatment for donkeys with enlarged lymph nodes can significantly prolong the disease course.Based on the result of the present study and own clinical experience,the biosecurity strategy,treatment principles and treatment methods were preliminarily formulated,contributingto prevention,control and treatment of strangles in intensive donkey farms.In summary,based on the practical problems associated outbreak of strangles in intensive donkey farms,the present study focused on clinical characteristic,transmission route,molecular biological characteristic,the sensitivity of commonly used drugs,biosecurity strategies,treatment principle andmethod,and so on.The results will lead to a greater understanding about the strangles in intensive donkey farms,and will contribute to prevention and control of strangles and other infectious diseases. |
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