Club Lamb Fungus (Sheep Ringworm)—Winter precautions

By Melissa Holahan, DVM, DACVECC, WSU Veterinary Medicine Extension

Taking winter precautions now prevents spring spread.

Sheep dermatophytosis (wool rot, lumpy wool, sheep ringworm) is commonly referred to as club lamb fungus. There has been an increase in prevalence over recent years due to the popularity of sheep exhibitions without a concurrent expansion of biosecurity protocols. Club lamb fungus is highly contagious to both humans and other animals. If infected, one should inform their physician promptly as sheep ringworm is more likely to cause deep infections which lead to permanent scarring.

Transmission

Disease occurs when the fungus, Trichophyton verrucosum, invades the skin/hair follicles. Small micro cuts from slick shearing and repetitive washing can breakdown the skin’s natural defenses (the physical skin barrier of wool and the protective layer of lanolin oil). In addition, the stress of travel/exhibition and high-performance diets lead to a breakdown in the immune system making animals more susceptible to infection. Producers can help mitigate these effects by changing diets slower and earlier in the season, shaving prior to show day, limiting bathes, using show blankets to improve cleanliness and avoid exposure, and minimizing travel trips/distance.

While the spread of disease occurs mostly at exhibitions, you can easily bring home contaminated equipment and then expose your animals during the next show season. This includes halters, lead ropes, shearing tools, brushes, blankets, feed/water bins, and don’t forget clothing (esp. FFA jackets, show clothing, etc.). Trichophyton spores can survive several years in the environment. It is best practice to have exhibition equipment in a specific color (e.g., red) that stays with the trailer and is never taken into the barn.

Diagnoses

Early shearing can help identify lesions which are most commonly found on the head, back and neck. Initially the skin is thickened and inflamed, eventually turning into crusty and scaly scabs which often form very characteristic circular lesions (Figure 1). The wool may appear clumped or lumpy at first due to discharge. These spots can take up to a month to appear after initial exposure (which is why it is important to keep your show string separated to avoid spread during asymptomatic stages). Lesions are seen at 4-8 weeks and infection can heal spontaneously in 8-16 weeks, although treatment can shorten this time frame. Keep in mind, however, that all stages of fungal infection are contagious. The presumptive diagnosis of sheep ringworm is based on clinical signs and history; however, fungal culture is the confirmatory test. procedures.

Treatment

The use of anti-fungal medication in sheep is considered an extra-label drug use and requires a valid veterinary-client-patient relationship. Most cases of club lamb fungus will recover over time if given proper nutrition and appropriate treatment while reducing stress. However, it will put a halt to a show season, so prevention is key including developing a post-show protocol to prevent spread (e.g., use a prophylactic anti-fungal shampoo before loading on trailer, have a quarantine area for the show string, and feed these animals last during chores).

Winter prevention

Prevention is the key to avoiding disease during show season. Ringworm can survive on fomites for years, so it is commonly brought home from shows with exposure/disease occurring during the springtime when pens, shearing equipment, jackets, etc. are brought out of storage. Remember to clean housing areas and all items at the end of show season and prior to lambing season for the best prevention. Common disinfectants that are appropriate to use include: Rescue, Virkon, and bleach. Keep in mind that disinfectants are only effective if organic material is removed.

Biosecurity at exhibition events

The responsibility lies with the producer to take an active role in preventing the spread of this contagious fungus. Talk with your club shearers to avoid transmission of this disease. Show/fair committee members, 4H/FFA leaders and veterinarians are the next level of prevention by prohibiting entry of any animal exhibiting ringworm. Animal handling should be done with separate gloves for each exhibitor’s sheep. Many show committees have now adopted a zero-tolerance rule (ringworm at any stage of healing) which has greatly reduced the risks of spread because this approach avoids exposure from asymptomatic carriers as well as those that are potentially still contagious.