What Is Ringworm in Cats?
Despite its name, ringworm has nothing to do with worms. It is a fungal infection of the skin, hair and occasionally nails, known medically as dermatophytosis. In cats, the most common causative organism is Microsporum canis, which is responsible for the vast majority of feline ringworm cases. Less frequently, Trichophyton mentagrophytes and Microsporum gypseum are implicated. Understanding what ringworm actually is helps explain why treatment works so differently from antiparasitic treatments — antifungal drugs, not antiparasitics, are required.
Ringworm is one of the most commonly diagnosed skin conditions in cats, particularly in kittens, rescue animals and cats in multi-cat households. It is also one of the most clinically significant because of its zoonotic potential.
Zoonotic Risk: Can Ringworm Spread From Cats to Humans?
Yes — this is one of the most important aspects of feline ringworm. Microsporum canis can be transmitted from cats to humans through direct contact with infected skin or hair, or through contact with contaminated objects such as bedding, grooming tools and furniture. In humans, ringworm typically presents as a circular, scaly, mildly itchy rash on the skin, or as scalp infection in children.
Certain groups are at significantly higher risk of contracting ringworm from an infected cat: children, who tend to handle animals more closely and whose immune systems are still developing; elderly individuals; and anyone who is immunocompromised, including those undergoing chemotherapy, taking long-term corticosteroids, or living with conditions such as HIV. In immunocompromised individuals, ringworm can be more extensive and more difficult to treat. If anyone in the household is in a high-risk group, extra precautions and prompt veterinary treatment for the cat are particularly important.
Symptoms in Cats
The classic presentation of ringworm in cats is circular patches of hair loss with scaly skin at the edges. The lesions most commonly appear on the face, ears, paws and tail, though they can develop anywhere on the body. The name ringworm comes from the ring-like appearance of lesions in humans — in cats, the pattern is often less well-defined.
Itching in cats with ringworm is variable. Some cats scratch at the affected areas, while others show little apparent discomfort. This variation is clinically significant because cats that are not itchy may be overlooked for longer, allowing the infection to spread.
Of particular note is the phenomenon of asymptomatic carriage. Some cats, particularly Persian cats and other long-haired breeds, can carry Microsporum canis without showing any obvious skin lesions whatsoever. These carrier cats can silently infect other animals and humans in the household, making diagnosis particularly challenging. If ringworm is diagnosed in one cat in a multi-cat household, all cats should be evaluated.
How Is Ringworm Diagnosed?
Several diagnostic methods are available, each with different advantages and limitations:
- Wood's lamp examination: a Wood's lamp emits ultraviolet light, under which certain strains of Microsporum canis fluoresce apple-green. This is a quick and convenient screening tool, but it has significant limitations — not all strains of M. canis fluoresce, and the test produces both false positives and false negatives. A positive fluorescence is useful, but a negative result does not rule out ringworm.
- Fungal culture: this is considered the gold standard for diagnosis. Hair and scale from the lesion are cultured on a specialist medium and monitored for fungal growth. The key limitation is time — cultures typically take two to three weeks to produce a definitive result. This means treatment is often initiated before culture results are available.
- PCR testing: polymerase chain reaction testing for dermatophytes is increasingly available through veterinary laboratories and offers a faster result than culture. It is becoming a more common diagnostic option in veterinary practice.
Treatment of Ringworm in Cats
Ringworm treatment in cats requires a combination of systemic antifungal therapy, topical treatment and environmental decontamination. Treating the cat alone, without addressing the environment, almost always leads to reinfection.
Systemic Antifungal Treatment
Itraconazole is the antifungal of choice for cats with ringworm. It is well tolerated in cats and is typically administered on a pulsed schedule under veterinary guidance. Griseofulvin, an older antifungal, is no longer recommended in cats due to concerns about toxicity and its potential to cause severe bone marrow suppression, particularly in cats co-infected with feline immunodeficiency virus. Any cat scheduled for antifungal treatment should ideally be tested for FIV and FeLV prior to starting therapy.
Topical Treatment
Topical antifungal treatment is used alongside systemic therapy to reduce surface fungal load and decrease environmental contamination. Lime sulphur dips, enilconazole rinses and antifungal shampoos are all used in practice. These treatments require careful handling — lime sulphur in particular has a strong smell and can stain surfaces — and gloves should always be worn when applying topical treatments to infected cats.
All cats in the household should be treated simultaneously, even those that appear clinically unaffected.
Environmental Decontamination
Environmental decontamination is a critical and often underestimated component of ringworm management. Fungal spores from Microsporum canis are extraordinarily resilient — they can survive in the environment for up to 18 months under the right conditions. Inadequate decontamination is one of the most common reasons for treatment failure and recurrence.
- Vacuum all carpets, upholstered furniture and soft furnishings thoroughly and frequently throughout the treatment period. Dispose of vacuum bags carefully.
- Wash all bedding, cat beds and fabric items at the highest temperature they can tolerate.
- Clean hard surfaces with a dilute bleach solution — a ratio of 1:10 bleach to water is effective against dermatophyte spores.
- Replace or thoroughly clean grooming tools, brushes and combs.
- Restrict the affected cat's access to as small an area of the home as possible during treatment to limit environmental contamination.
Human Treatment and the Ping-Pong Problem
If any person in the household develops suspicious skin lesions during the cat's treatment, they should see their general practitioner promptly. In humans, ringworm is typically treated with topical antifungal creams, which are available over the counter, though scalp infections in children generally require systemic antifungal treatment.
It is essential that human and feline cases are treated simultaneously. If the cat is treated and clears the infection, but a human family member's ringworm is left untreated, the fungus can be passed back to the cat — and vice versa. This ping-pong reinfection cycle is a recognised problem and the reason why close communication between the veterinary surgeon and the family's general practitioner is sometimes necessary.
How Long Does Treatment Take?
Ringworm treatment in cats is not a short process. A typical treatment course lasts six to twelve weeks, and it is vital that the full course is completed even if lesions appear to have resolved. Early discontinuation of treatment is a common cause of relapse. Two consecutive negative fungal cultures, taken two to four weeks apart, are generally used to confirm that the infection has cleared before treatment is stopped.
Quarantine of new kittens before introduction to an existing multi-cat household is strongly recommended, as ringworm is particularly common in rescue kittens and young cats from breeding environments.