Q. My yearling has broken out with warts around his mouth. These warts have become quite unsightly. How do I treat him, and will they come back? Should I quarantine him so he does not spread the warts to my other horses?

A. Warts are caused by the papillomavirus, and they usually appear as blemishes on the face, mouth, or nose regions in younger horses. They appear as either single warts, or as clusters of warts that have a "cauliflower" appearance. While unsightly, they usually pose no threat to the horse's overall health and are considered merely a cosmetic blemish. In most cases, the warts will disappear on their own in a matter of time. But it is important to remember that warts are a viral, contagious disease and that proper steps should be taken in order to prevent them from spreading from one horse to another, especially if the horse is kept in the vicinity of other horses.

Younger horses are more susceptible to warts because they have less-efficient immune systems than older horses. Their skin also is not as tough, and they have less hair to ward off the insects that can carry the papillomavirus. The good news is that once a horse has been infected, it builds up an immunity and is less susceptible to future infections. Provided the horse is in good physical condition, has a good nutrition program, is wormed regularly, and is under good management, the warts should disappear within six to nine months. Short-term, the warts will not reappear because of the immunity the horse has developed for the virus.

If a horse on a farm becomes affected with warts, it is best to keep the youngster away from other horses as much as possible. Also, as a general management practice, and especially if there is an animal on the farm that is infected with warts, do not use the same equipment such as brushes, halters, bridles, etc., on both infected and non-infected horses. While there might be no way to really isolate the infected horse, good hygiene practices will help keep the warts from spreading.

Complications that can arise as a result of warts are secondary, but they do sometimes occur. Some of the most common secondary problems arise because the warts are banged or scraped on barn doors, fences, halters, bridles, etc. When this happens, it creates an open sore on the wart that could allow a secondary infection to enter the open wound. During hot months, "summer sores" can become superimposed on the warts if the wart has been rubbed raw. There also is the possibility that maggots or larvae might take up housekeeping in the warts. Again, this would be during the summer months when the horse is most active and there is a greater chance that the horse will aggravate the warts, allowing these problems to arise.

Generally, however, beyond secondary infections and infestations, there are no real health consequences associated with warts. The only time warts become dangerous is when a horse has an immune deficiency such as CID, which compromises the immune system. In these cases, the warts could become much more extensive and cover wider areas of the body because the animal's immune system will not contribute to self-curing. Theoretically, in these animals, the warts can persist and all sorts of health problems can occur as a result.

It is thought that warts can be cleared up faster if they are surgically removed. In many cases, where there are numerous warts present, the removal of some of the warts seems to accelerate the immune response, therefore clearing up all the warts more quickly. This does not always work, and it is hard to prove because warts are a self curing disease in horses anyway.

Warts rarely go beyond being more than just a cosmetic defect. Most horses which get warts are youngsters which probably are not out on the track or in competition. Something to keep in mind when dealing with warts is your show schedule. If a horse has warts, it is not a good idea to take it to shows where it will come in contact with other horses.

Ultimately, warts are a fairly trivial disease, provided the horse is given good nutrition and care. In most circumstances, the infection is self-limiting and there should be no complications. The key to managing warts is management of the horse itself. Management will depend on whether the horse is stabled alone or with other animals. Since warts are caused by a highly contagious virus, if the horse is stabled with other animals, then common-sense hygiene should be utilized because warts appear more often in this type of situation.

About the Author

William Miller, Jr., VMD, Dipl. ACVD

William H. Miller, Jr. VMD, Dipl. ACVD, is a Professor of Dermatology at Cornell University.

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