Ringworm is caused by a fungus, and it is most frequently seen in young animals because they may have less immunity than adults. The skin disease is contagious from animal to animal — and can also be transmitted between species. A person may be at risk for ringworm when handling affected animals, says Andi Lear, veterinarian in the Department of Large Animal Clinical Services at the University of Tennessee.

“Nearly any type of ringworm can be spread from one species to another, though certain types appear most frequently in cattle,” Lear says. “Animals or humans can get ringworm if they have a skin abrasion and a compromised immune system.”

Ringworm is often a winter problem because these fungi thrive in a damp, dark environment.

“In many herds, about 20% of the cows carry some of these fungi, but these organisms may not always cause ringworm, except in susceptible individuals,” she says. Young animals, such as a group of yearlings, may be more vulnerable, as are old or immune-compromised animals. Animals with skin abrasions — scraped while fighting one another or when put through a chute or traveling through brush — may get ringworm.

“Even though the fungal spores are present in the environment and animals are always exposed, if they have a functional immune system, they can fight it off. The lesions are dry in the middle and flat and crusty on the outside. Even though they keep growing for a while, these lesions are self-limiting,” she says. “The fungus is its own worst enemy. It needs oxygen. As it kills the hair follicles and affects the skin tissue, it creates a crust and tends to suffocate itself. This is why the lesion is always spreading outward in circular fashion — because it has to keep getting air. Eventually the immune system takes care of it, and it goes away.”

Ringworm may have economic importance if very many animals in the herd have ringworm (hair loss in winter) or it goes through a group of animals slated for sale. Even though it’s mainly a cosmetic problem, animals with ringworm tend to bring a lower price. Bulls and breeding stock would also be harder to sell as potential buyers hesitate to introduce this into their own herd. Ringworm is always a problem in show animals and club calves; there are rules against bringing affected animals to a show because ringworm is contagious.

“Some people treat for ringworm, but many ‘cures’ are probably due to the fact the treatment was given just before the lesions started to resolve on their own.” — Andi Lear

“Some people treat for ringworm, but many ‘cures’ are probably due to the fact the treatment was given just before the lesions started to resolve on their own,” Lear explains. Several types of disinfectants can be applied topically to lesions. Iodine solutions, lime sulfur, chlorhexidine, etc., can be diluted and sprayed onto the animal. Rarely is an animal treated with a systemic antifungal drug because issues of labeling and withdrawal times arise. Also, there aren’t any really good antifungal drugs labeled for systemic use in livestock. Treatment is generally just topical application and time.

Lear is aware of one ringworm vaccine that has been used in cattle and horses in Europe, but it is not available in the United States. She says the best prevention is to have healthy young animals in a clean environment, and make sure they are not immune-suppressed. BVD (bovine viral diarrhea) or malnutrition may predispose young animals to ringworm. Having a good nutritional program is important, she recommends. The unfortunate calf that gets orphaned out on the range, or whose dam doesn’t milk very well, or any animal with a mineral deficiency could be a prime candidate for ringworm.

Ringworm is fairly easy to diagnose because there are not many other things that look similar, though scabies can sometimes be mistaken for ringworm.

“Scabies is very itchy, however, and ringworm is not,” Lear explains. “We can do a quick screening of a tissue sample, if necessary, under the microscope. If we see fungi, we know it’s ringworm and can treat it.”

Editor’s note: Heather Smith Thomas is a freelance writer and cattlewoman from Salmon, Idaho.

Angus Beef Bulletin EXTRA, Vol. 16, No. 10-A