Ringworm, medically known as dermatophytosis or tinea, is a fungal infection of the skin, hair, and nails, despite its misleading name that suggests a worm is involved. This common condition is caused by microscopic organisms called dermatophytes, which feed on keratin, the material found in the outer layer of skin. Feline ringworm is readily transmissible to people, defining it as a zoonotic disease.
The Zoonotic Nature of Feline Ringworm
The spread of ringworm from cats to humans is primarily facilitated by the fungus Microsporum canis, the most common species found in felines. Transmission occurs through infective fungal spores, which are microscopic, dust-like particles produced by the fungus. These spores are shed into the environment, mainly attached to infected hairs, and serve as the main source of infection.
Infection happens through two main routes: direct contact with an infected cat or indirect contact with contaminated objects. Direct contact involves petting or handling a cat that is shedding spores, even if the cat appears healthy. Indirect transmission occurs when a person touches contaminated items (fomites), such as bedding, grooming tools, or carpet fibers. The spores are particularly hardy and can remain infectious in the home environment for months. People with compromised immune systems, the very young, and the elderly are at a higher risk of contracting the infection upon exposure.
Identifying Signs of Infection in Pets and People
Ringworm symptoms vary, and some cats may not show obvious signs, making them asymptomatic carriers. In cats that exhibit symptoms, the sign is circular patches of hair loss (alopecia), often seen on the head, ears, or limbs. Within these patches, the skin may look scaly, crusty, or inflamed, and the surrounding hairs might appear broken or stubbly.
Identifying the infection in humans is usually more straightforward, as the rash typically appears as a distinct ring shape, which is how the condition got its name. This ring-shaped rash, often referred to as tinea corporis, has raised, red, and sometimes scaly borders, while the center of the patch may look clearer. The affected areas, commonly on the arms, legs, or torso, are frequently itchy. In some cases, the rash can become crusted or develop small blisters. Symptoms in people usually begin to appear within one to six weeks after exposure to the fungus.
Treatment and Environmental Decontamination
Treating ringworm involves a dual approach: treating the infected host and decontaminating the environment to prevent re-infection. For humans, mild cases are often treated with over-the-counter antifungal creams containing ingredients like miconazole or clotrimazole. If the rash is widespread, persistent, or involves the scalp, a doctor may prescribe oral antifungal medications.
In cats, veterinary consultation is necessary, as treatment often combines topical and systemic therapies. Topical treatments include antifungal shampoos or dips, such as lime sulfur, which is highly effective but has a strong odor. Oral antifungal drugs are also commonly used to eliminate the infection from the hair follicles and shorten the duration of the disease. Environmental decontamination is a non-negotiable step because spores can survive for long periods. This process involves mechanical cleaning, such as vacuuming all surfaces and immediate disposal of the vacuum bag, followed by disinfection. Hard surfaces should be cleaned with a specialized disinfectant or a diluted bleach solution to kill remaining spores.