How Long Should I Isolate New Horses?
Quarantine can be a very useful tool to reduce the risk of infectious diseases making it onto a farm. New horses, or horses that have been off the farm, can bring various infectious diseases onto the farm with them, and horse movement is probably the key driving force for many infectious diseases. Isolation of new horses can be beneficial for a few reasons:
- It allows for identification of infectious diseases that the new horse is incubating. A horse could be brewing an infection, but look normal at the time it arrives. Giving it some time to determine whether it is incubating a disease and keeping it isolated during that time can reduce the risk of it spreading the disease to other animals on the farm. For this to be effective, horses need to be monitored for signs of infection (e.g. fever, diarrhea, cough, nasal discharge) and there needs to be a plan in place to address any problems before the horse is released from quarantine.
- A new horse could have been infected or exposed to an infectious disease prior to arrival, and be shedding the virus or bacterium when it reached the farm. For example, if the horse had influenza, it can continue to shed influenza virus for a short period of time after it recovers. Also, some infectious microorganisms can be transiently acquired during transportation, or infectious organisms that are dormant in the horse's body (e.g. equine herpesvirus) might re-awaken and be shed for a period of time following transportation. In these situations, the horse would probably appear to be completely healthy, but would still be infectious. Keeping the horse isolated after arrival provides a wash-out period during which shedding of these infectious agents will decline.
- While not widely performed, testing of horses for certain pathogens (such as Streptococcus equi, the cause of strangles) is useful in many situations. However, it's of limited use if horses are not kept isolated while awaiting results. Short-term isolation while awaiting results is necessary.
An important and contentious consideration is how long to keep new horses isolated from resident horses. Unfortunately there's no straight answer. In general, longer is better, but there's no exact number of days that's known to provide the best result. It really depends on what infectious diseases are of greatest concern, the facilities that are available for quarantine and the risk aversity of the farm. Ideally, a three week quarantine would be used, since that is beyond the typical shedding period for several important infectious diseases. However, it's not foolproof. Quarantine without testing will not identify long-term strangles carriers, horses shedding various intestinal bacteria like Salmonella, and herpesvirus carriers. Isolation is just one infection control tool that can be used to reduce the risk of disease on farms.