An outbreak of strangles associated with a novel genotype of Streptococcus equi subspecies equi in donkeys in China during 2018

Abstract

Summary Background Strangles is a highly contagious respiratory disease of equids caused by the bacterium Streptococcus equi subspecies equi. Objectives To identify the cause of an outbreak of strangles that occurred on donkey farms within the Shandong Province of China and determine the prevalence of the disease. Study design Cross‐sectional. Methods Samples were taken from clinically affected animals to measure the prevalence of strangles within the population of donkeys at six intensive farms in China and identify the SeM type of isolate recovered from affected animals. Diagnosis was confirmed by bacterial isolation, biochemical tests and PCR. Epidemiological data were analysed using Chi‐square test and a Fisher's exact two‐sided test. The SeM gene of S. equi isolates recovered from affected animals was determined and compared with the SeM database PubMLST‐seM. Results In July and August 2018, an outbreak of strangles occurred on six donkey farms within the Shandong Province of China. The overall prevalence of disease within the different donkey herds was 13.4%. Younger animals were worst affected with 40.3% (83/206) of donkey foals aged under 1 year exhibiting clinical signs compared with 12.5% (191/1525) of donkeys aged one to 2 years and 3.8% (17/442) of donkeys over 2 years of age. Analysis of SeM sequencing data identified that the farms were affected by the same strain of S. equi, SD201807, which contains the novel 136 allele of SeM. Main limitations Healthy donkeys were not sampled in this study. Conclusions The number of intensive donkey breeding farms in China has risen recently. The higher numbers of animals that are in closer proximity to one another raise the potential for the transmission of infectious diseases such as strangles. This is the first description of a strangles outbreak among donkey herds in China. The Summary is available in Chinese – see Supporting information.

Identification of a Novel Genotype of Streptococcus equi Subspecies equi in a Donkey Suffering from Strangles

“…Comparing with equivalent N-terminal variable regions from all SeM alleles available in databases (Kelly et al, 2006), identified that the 5' SeM sequence of the CN190402 strain (GenBank accession number MK988511) contained a novel SeM allele, i.e., SeM-138 (https://pubmlst.org/szooepidemicus/seM/). Phylogenetic analysis showed that CN190402 was clustered into a group with SeM-88 and SeM-136, closely related to the SeM-136 that was associated with a strangles outbreak in an intensive donkey farm located in middle-east of China during 2019 (Dong et al, 2019). Comparison of the nucleotide sequences among SeM-3 (4047 strain; GenBank FM204883), SeM-88, SeM-136, and SeM-138 identified that SeM-138 shares 94.2, 96.6 and 98.5% identities, respectively.…”

“…Although strangles is widely reported in horses, only a few strangles cases have been reported in donkeys with severe clinical signs. In our previous study, the strangles outbreak in donkey was first reported in intensive donkey farming (Dong et al, 2019). The investigation presumed that the causative S. equi entered the farm with newly introduced donkeys, which suggested it is important to use quarantine measures effectively and screening methods should be used to identify the infected animals and carriers of S. equi to prevent the spread of strangles.…”

The Potential for New Donkey Farming Systems to Supply the Growing Demand for Hides

“…Nevertheless, compared to Animals 2020, 10, 718 4 of 22 horses and other domesticated animals, knowledge about the reproductive physiology of donkeys and donkey breeding management is still very limited [34][35][36][37][38][39][40]. In addition, intensive donkey farming is a relatively recent development, mainly for the production of donkey dairy products in Europe and for donkey hides but also meat and dairy in China [23,34,[41][42][43][44][45]. To date, intensive donkey farming is still under-researched and knowledge on donkey farming systems is very limited.…”

“…The farming system starts with an initial female breeding stock. Intensive farming of donkeys is already happening in China [23,44,47]. The latest donkey population estimate is 2.5 million donkeys in China in 2018 [15].…”

“…In this paper, we focus on the potential to supply donkey hides (not meat, milk or other donkey derived products) from donkey farming systems. New donkey farms for the supply of hides have been set up in China in recent years [23]. It is reported that, in recent years, 15 provinces and 22 cities have announced their intention to provide subsidies to stimulate donkey breeding [17].…”