Ringworm in Dogs

Ringworm is a fungus called dermatophytes. Dermatophtytes means ‘plants that live on the skin’. In the past, because of the circular lesions made by the fungi they were thought to be caused by worms, hence the name ringworm. The fungi live on the surface of the skin and in the skin follicles feeding on dead skin tissue and hair. There are three different types of fungus that can cause ringworm, but the most predominant ones found on dogs and cats is microsporum canis.

Signs and Symptoms

The usual symptom is a round hairless lesion. The characteristic “ring” that we see on humans doesn’t always appear as a ring on dogs. This lesion will grow in size and often become irregular in shape. The fungi cause the hair shafts to break off and this results in patches of hair loss. Ringworm are commonly found on the face, ears, tail and paws. The lesions are scaly and may or may not be itchy; often the skin is reddened and inflamed.

Causes

Transmission of ringworm can happen by direct contact with another infected animal or person. It can be passed from dogs to cats and vice versa, and from pets to humans and from humans to pets. The fungal spores can live in the environment for a long time and can be found in carpets, bedding, grooming equipment, etc. and can infect your dog when it comes into contact with them. The incubation period is 10-12 days. This means that following exposure to the fungus, about 10-12 days will pass before any lesions occur.

In rare cases ringworm can be spread by contact with infected soil. The fungus can live for months in soil if the nutrients are right.

You can contract ringworm by touching an animal with ringworm. Ringworm can spread while petting or grooming dogs or cats. You can also get ringworm from cows, goats, pigs and horses.

Healthy adult dogs usually have a resistance to ringworm. Young dogs and puppies are more susceptible because their immune system hasn’t fully developed. Many dogs are carriers of ringworm but show no symptoms. They can, however, infect other animals or humans.

Diagnosis

To diagnose ringworm your vet will need to do one of the following tests. It is not possible by just looking at the skin to make the diagnosis.

Wood’s Lamp – An ultra violet lamp also known as a black light. Your vet may use this as 50% of microsporum canis will glow under the lamp.

Microscopic diagnosis – Your vet may look at part of the hair or skin from the lesion under a microscope.

Culture – Your vet may decide to take a scraping from the lesion and send it away to the laboratory to see what the culture grows.

Treatment

If no treatment is carried out, ringworm will run its course in two to four months and the symptoms will resolve themselves. However, treatment is recommended to save your dog from suffering any longer than necessary and to cut down the period of time that they are contagious.

Recommended treatment can consist of one or more – or all – of the following:

An anti-fungal drug which inhibits fungal reproduction, usually taken over the course of 5-7 days.

Lime sulphur dip is very often beneficial. The dip, mixed with water, should be given twice a week and can be done at home.

NOTE: Be prepared that Lime sulphur smells very much like rotten eggs or stink bombs. And it will stain clothing and jewellery, and cause temporary yellowing of your dog’s hair.

Decontaminate the environment. Use bleach mixed at 1:10 on any surface that you can. It will kill 80% of the spores. Vacuum on a daily basis and, if possible, steam clean carpets and furnishings which will kill off a large number of the fungus spores. Wash your dog’s bedding in very hot water and use a bleach solution to clean the dog kennel. If your dog is an indoors dog try to confine him to only one room of the house.