Antifungal Therapy in Cats

Fungal infections in the cat are relatively common. Those most likely to be encountered are ringworm (Dermatophytosis) or malassezia. Ringworm is a potential zoonosis to people, and whilst in healthy individuals it is rarely serious, for those people with suppressed immune systems it could prove a serious complication. 

Whilst a wide range of antifungals are available that are highly effective, they are not without side effects. Treatments can be topical such as a cream or ointment that incorporates an antifungal, or they can be systemic such as an oral liquid or tablet. The latter is often necessary for ringworm as it invades deep into the hair follicle.  It is also important to disinfect and clean the environment to prevent accidental reinfection or cross infection.

Most cats are treated as out patients in first opinion practice. 

In the case of ringworm, long-haired cats may be clipped at the beginning of therapy in order to reduce the shed of infected hairs. Cats that tolerate bathing can be washed in anti-fungal shampoo containing miconazole and chlorhexidine every three to four days, which again reduces shed of contaminated hair. 

Once ringworm is diagnosed, systemic therapy is started. This is either an oral medicated liquid or tablets. Liquid medications are better suited to the cat as it is easier to adjust to give an accurate dosage. The most frequently used oral liquid, containing itraconazole, is given on a 'week-on, week-off' basis until repeat fungal cultures come back negative. Older therapies such as griseofulvin tablets are given daily and unfortunately this older drug, although cheaper, is linked to a greater risk of side effects. 

Modern antifungal drugs are extremely effective, although several weeks of therapy is often required, so the response is not quick.  Owners also need to be mindful of the risk of infection posed by environmental contamination. A cat with ringworm sheds infected hairs during the course of their treatment. These hairs pose a potential infection risk to other mammals, including people. 

Thus restricting the cat under treatment to one room is a good idea, to make daily cleaning and vacuuming more realistic. In addition, cats with suppressed immune systems are less able to keep fungal infections in check, so prolonged treatment may be necessary. 

For a severe ringworm infection it can take several weeks for infected hair to be shed and a healthy coat to grow back. For less serious infections, the cat may be able to mix with others again after two to three weeks. 

It is advisable for the owner to wear latex gloves whilst applying topical treatments to cats with ringworm. In addition collars, bowls, bedding, and toys should be considered infected and regularly washed and disinfected. 

Skin and ear infections caused by malassezia are less contagious, and usually due to an overgrowth of a normal skin inhabitant. These cats do not need to be isolated during treatment and don't pose an infection risk to people. A topical treatment such as an ointment containing miconazole or medicated ear drops is usually sufficient to bring the problem under control. A typical course of treatment for an ear infection is 10 to 14 days.

The cost of diagnosis of ringworm can vary depending on the test. Shining a Wood's lamp on the cat (detects 50% of cases) may be included as part of the consultation fee. However, sending hair plucks away for culture ranges in cost from $100 to $150. 

Itrafungol solution requires a prescription and retails for around $80 a bottle. However, this provides sufficient solution to medicate several cats. Your vet may have an open bottle and be prepared to sell you just the amount needed for one cat. 

Griseofulvin tablets (prescription required) can be bought for around $30.

Ringworm is highly contagious and a zoonosis, therefore treatment is essential. However, the systemic treatments do carry the risk of side effects, including loss of appetite, vomiting, diarrhea, and in a worse case scenario, liver or kidney damage. It is, therefore, important to monitor the patient, stop treatment if complications occur, and speak to your vet. 

The dose of medication can be minimized by administering it with a fatty meal, such as giving a knob of butter with food. This improves the penetration of the drug into the skin where it is most needed. 

Treatment also needs to be given for prolonged periods of time. Three weeks is a common minimum, with longer needed in some cases, depending on the severity of the infection. 

Key to preventing ringworm or malassezia infections are keeping the cat in optimal health. Those cats that are in good physical conditions will have a strong immune system which is better able to police the skin and fight off infection. 

Those cats most at risk are kittens, stressed cats, or those with feline immunodeficiency virus or feline leukaemia. Given the infectious nature of ringworm, places where groups of stressed cats live in close conditions is the perfect environment for spread. Unfortunately, this sets up many shelters as potential hotspots of infection. 

Observing good hygiene when groups of cats are housed together is crucial. This means not sharing brushes, frequent washing of food and water bowls along with litter trays, regular bedding changes, and disinfection of the cattery accommodation. 

It is also essential to identify infection promptly and isolate the affected individuals so they don't act as a source of infection for others.