Ringworm is a highly contagious and unsightly skin infection that can
have financial consequences if afflicted cattle are banned from shows
or exhibitions.
Despite its name, it is caused by a fungus and is characterized by
circular hairless lesions on the neck and head, especially around the
eyes.
The fungus infects an animal’s hairs, weakening them so they break off.
It also feeds on the outer layers of skin as it expands from the
periphery of the lesions. The grey, crusted, hairless ringworm areas
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can reach up to 10 centimetres in diameter.
Though a solitary ringworm lesion is rare, so is entire body infection.
Most calves have multiple lesions. In severe infections, several
ringworm sites may coalesce into large hairless areas.
The fungal spores that cause ringworm are passed directly from one
animal to another, and can also be transferred by grooming equipment
and halters.
Calves sharing feed bunks can easily pass the infection among
themselves. Head butting may also spread the fungus, which could be why
there are so many lesions on calves’ heads.
The incubation period, which is the time from when the fungus invades
the skin to when signs of infection are evident, varies from seven days
to six weeks.
It is easy to think the infection is under control until it suddenly
shows up in more calves – obviously those that were incubating the
disease.
Young calves that are exposed to ringworm for the first time are
likely to develop lesions because they have no immunity. They are more
likely to contract ringworm if their immune systems are depressed due
to disease or poor nutrition, or if they are overcrowded, which allows
a greater chance of contact.
In severely immunocompromised calves, the fungus may advance down to
the lower skin levels, causing inflammation and
itchiness.
Ringworm is seen more in calves that are housed indoors, with no
access to sunlight. Mineral deficiencies are also thought to play a
role in susceptibility.
“Old-time” producers treat ringworm with a range of miracle topicals
from toothpaste to used crankcase oil. These products seem to work
because spontaneous regression of ringworm is common.
However, the substance put on the skin is of little consequence under
these circumstances. The disease probably resolves when the calf
develops immunity.
Most producers treat ringworm to stop existing lesions from
progressing and to reduce its spread to other animals. The first step
is to remove the crusts with a brush and mild soap.
The calf can then be treated topically with 0.5 percent sodium
hypochlorite (1:10 chlorine bleach), 0.5 percent chlorhexidene, 0.5
percent lime-sulfur, or one percent Povidone-iodine.
These solutions are applied to the entire animal daily for five days,
then weekly until the infection is controlled.
A prevention program might be worthwhile for valuable animals or for
those expected to be in a show. Cleaning and disinfecting grooming
equipment with a bleach solution is critical. One gallon of bleach
added to three gallons of water is an effective disinfectant.
It also helps to reduce housing density and to increase the herd’s
exposure to sunlight. Ringworm vaccinations are available, but results
have been variable.
Jeff Grognet is a veterinarian and writer practicing in Qualicum Beach,
B.C.
