Ringworm is an important disease of the skin, as it is highly infectious to other animals. The disease derives its name from the circular appearance of the lesions on the sufferer’s skin. The cause of the disease has nothing to do with any worm parasite, but is a fungus.
The most common form of ringworm is caused by a fungus called Microsporum canis.
This is responsible for most infections in the cat, and more than 60 percent of the infections in dogs. The parasite is almost ideally adapted to life on the cat’s skin, so that very little reaction in the form of scratching or inflammation of the skin is seen.
The most common site of infection is around the head and face. Commonly, areas of complete loss of hair can be detected. In other cases small areas of discolored skin and broken hairs may be all that is evident to alert the owner that a skin disease may be present. In long-standing cases there may be large areas where the hair appears singed, and bare areas where the skin is obviously thickened.
In dogs the areas most commonly affected are the face and nose, the outside of the limbs, and the abdomen.
The fungus usually produces a more marked reaction in the dog, and the lesions are more typically circular where the skin is raised and the hair completely missing or broken.
Humans tend to react to the presence of the fungi on the skin more intensely than the dog or cat. Circular reddened areas that can be quite itchy appear on the face and forearms, which are the most likely areas to first come in contact with spores from an infected animal. If the spores have been distributed in furniture, bedding or clothing, the lesions can appear all over the body.
Transmission of the disease is by spores and fragments of skin that contain spores, and infective strands of the fungus. Direct contact with an infected animal is not necessary. Spore-laden hairs and skin fragments may be transmitted over long distances and remain infective for years in carpets, or upholstery until a suitable host comes in contact with it.
Children’s skin seems much more susceptible than adults, and infective spores may be transmitted from child to child without the involvement of dog or cat.
Diagnosis of Microsporum canis is helped by the characteristic of the spore to fluoresce under ultraviolet light.
When suspected animals are examined in a darkened room, even very small areas of infection can be detected. In long-haired cats small infected areas can be surrounded by dense normal fur, so that detection of these areas is impossible without the aid of the lamp.
Other methods of diagnosis involve taking skin scrapings of suspected areas for microscopic examination, or the culture fragments of skin or hair in a special medium that changes color in the presence of the colony of a pathogenic fungus. This last method is useful in the detection of fungi other than Microsporum canis that do not exhibit the fluorescence under ultraviolet light.
Ringworm can be successfully treated, provided steps are taken to not only eliminate the fungus from the skin of the animal but also to remove it from the environment.
Treatment of the animal must be undertaken over many weeks. An antibiotic, Griseofulvin, is active against the fungus in the skin and hair and is given by mouth. It is important to keep the hair in the infected areas as short as possible, as this progressively retains the infected material as it is inactivated by the drug.
Local applications of lotions and ointments can be applied, but are not a successful treatment for ringworm if used without Griseofulvin. Cats often become quite sensitive to many of the commonly used ringworm ointments and their continual use can cause severe skin inflammations.
A more-effective topical treatment is to bathe the animal in the disinfectant solution, Halamid. This is completely non-toxic and is also useful to soak bedding and to scrub carpets and chairs that have been in contact with the infected animal.
Vacuum cleaning frequently and vigorously helps to remove the infective spores. Of course, the patient must be kept isolated so that it is not continually reinfecting the surroundings.
Re-examination of the patient at regular intervals after the treatment with Griseofulvin has ceased is essential if reoccurrence of the infection and subsequent massive contamination of the environment is to be prevented.