Survival of Streptococcus equi
Streptococcus equi is the bacterium that causes of strangles, and important and highly infectious disease of horses. This bacterium is widespread in the horse population and outbreaks of strangles are not uncommon. Outbreaks are manageable if adequate time and resources are available, but some aspects of strangles control are complicated by a lack of good information.
One area that people often ask questions about is the ability of S. equi to survive outside of a horse, and how to handle the general environment (e.g. barn, paddocks) during an outbreak of strangles. Two older studies reported that S. equi can survive on environmental surfaces for up to 60 days. This has led some people to recommend prolonged quarantine of pastures that have been used by infected horses. However, these studies were conducted in the controlled and relatively hospitable environment of a laboratory, without exposure to sunlight, temperature changes and competing bacteria that are found in the "real world".
A recent study, presented the 2008 Forum of the American College of Veterinary Internal Medicine (ACVIM), evaluated S. equi survival in a more "real world" situation: outdoors, on objects like fence rails, feed bins and water buckets. These items were experimentally contaminated with S. equi, and the length of time that the bacteria survived was studied. Surprisingly, S. equi only lived for a short period of time under these conditions, typically a day or less.
Does this mean that we should allow horses into potentially contaminated areas after only a couple days? Probably not. The results of this study only apply to the conditions that were studied, that is outside with exposure to sunlight, and during the summer. It is safe to assume that survival is short term on farms under these conditions, but it could be longer during cloudy periods and in shady areas. We don’t know the optimal time for which to quarantine stalls and paddocks, but it is reasonable to assume that long-term quarantine, as has been recommended in the past, is not needed in most situations. If it is sunny and there is exposure to sunlight, 1 to 2 weeks is probably well beyond the survival period of S. equi.
More information about strangles will soon be available on the equIDblog Resources page.
