Överlevnad av Streptococcus equi subspecies equi på olika material i hästens omgivning
Abstract: Strangles, caused by the bacteria Streptococcus equi subspecies equi (S. equi) is the most commonly diagnosed infectious disease in horses worldwide. Infection by S. equi in the upper respiratory tract results in fever, nasal discharge and enlarged lymph nodes that can contain abscesses. Strangles is highly contagious and can also in some cases cause serious complications and even fatalities. Spread of S. equi most commonly occurs via direct contact between horses, but also spreads indirectly via for example stable interior and equipment. While strangles as a clinical disease has been well described, whether, and if so, for how long the bacteria can survive on inanimate objects in the stable environment is poorly understood. The aim of this master’s thesis was to address clinically relevant aspects of the survival of S. equi in a stable environment. The study was divided in two parts. Firstly, materials in horses’ near environment, including wooden posts, filled plastic water buckets and plastic twitches were contaminated with a standardized broth of live S. equi. For the first two materials, the time of survival of S. equi was investigated. For the twitches, as they are commonly used by veterinarians when sampling a horse with suspicion of strangles, the effectiveness of different cleaning protocols on complete removal of S equi DNA was examined. In the second part of the study, environmental samples were obtained from confirmed strangles outbreaks three to six weeks after all horses had recovered clinically. The purpose was to examine if live bacteria and/or its DNA could be detected in horses’ near environment after full recovery from a naturally occurring outbreak of strangles. Culture and qPCR were used as diagnostics in both parts of the study, with culture detecting live bacteria and qPCR DNA from both live and nonviable bacteria. The results show that S. equi survived maximum 19 days in the water buckets under summer conditions and at least 73 days in winter conditions. The culture-results from the wooden posts were positive for maximum 4 days in the summer and 10 days in the winter. Regarding twitches, no live S equi could be recovered on culture after thorough cleaning and disinfection. However, the twitches remained positive to S. equi on qPCR for all disinfectants except for bleach. For the natural outbreaks, three out of four stables from the second part of the study had culture- or qPCR-results that were positive for S. equi. Several different materials were positive; wood, metal, polyester and cotton. In contrast to the experimental inoculation study, none of the sampled water buckets in any of the stables were positive on culture or qPCR. This may indicate that water sources in a natural outbreak of strangles may have far less contamination by S. equi than was done in the experimental work. Similarly, none of the wooden posts sampled in these stables yielded any positive results, which correlates with the results from the first part of the study which showed that S. equi did not survive a longer time on wooden material outdoors. Strikingly, all the positive samples from the stables were from surfaces not exposed to direct sunlight. The results highlight that environmental factors affect the survival of S. equi in a stable environment, and thorough cleaning is necessary to get rid of live bacteria. The environmental samples from affected stables may have had positive results because contamination during the outbreak or continued shedding of S. equi from the previously ill horses. Nonetheless, it was clear that even following full clinical recovery from outbreaks S. equi can be found in stable environments. More studies of the environmental survival with concurrent sampling of the horses are in order.
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