What are dermatophytosis (Ringworm)?
Ringworm (Dermatophytosis) is a highly contagious fungal infection that can occur in humans, dogs and cats. It is an infection of skin, hair, or claws caused by a type of fungus. The fungal spores shed from an infected animal can live in the environment for over 18 months. Dermatophytosis fungus is more common in hot and humid climates.
Types of Dermatohytosis
There are three most common fungal species that may cause ringworm in dogs:
- Microsporum canis – Fungus that affects the upper layers of the skin on cats, dogs and humans
- Trichophyton mentagrophytes – Affects 30% of dogs, especially Terrier breeds
Most cases of ringworm are spread by contact with infected animals or contaminated objects such as furniture or grooming tools. Broken hairs with associated spores are important sources for spread of the disease. Contact does not always result in infection. Whether infection is established depends on the fungal species and on host factors, including age, health, condition of exposed skin surfaces, grooming behaviour, and nutrition. Infection leads to short-lived resistance to reinfection. Under most circumstances, dermatophytes grow only in the dead cells of skin and hair, and infection stops on reaching living cells or inflamed tissue. As inflammation and host immunity develop, further spread of infection stops, but this process may take several weeks.
How long does it take for the lesions to appear?
The incubation period between exposure to ringworm fungus and the development of ringworm lesions usually ranges from seven to fourteen days; some cases may take up to 21 days before signs of infection develop.
Symptoms of Dermatophytosis
Deratophytosis may cause your dog to have one or more of the following symptom:
- Irregular patches of hair loss
- Bald scaly patches
- Irritated and inflamed hair follicles
- Pustules on the skin
- Dry, brittle or cracked nails
- Broken hairs
- Secondary bacterial skin infections
- Dog may also develop acne-like bumps on the skin
How is a ringworm in dogs diagnosed
Diagnosis is made in one or more of the following three ways:
- Identification of the typical ‘ringworm’ lesions on the skin. This method is not very accurate and may lead to misdiagnosis. Additional diagnostic tests are usually required to confirm that ringworm fungi is present.
- Fluorescence of infected hairs under a special ultraviolet light known as a Wood’s lamp. Most cases of canine ringworm caused by M. canis will glow with a yellow-green florescence when the skin and coat are examined in a dark room with a Wood’s lamp. However, not all cases of M. canis will fluoresce, and neither T. mentagrophytes or M. gypseum fluoresce under a Wood’s lamp. Some skin ointments and other materials also fluoresce and may give a false positive result. While this technique is acceptable in certain situations as a rapid screening tool in multi-animal facilities, diagnosis made on Wood’s lamp evaluation is not always reliable.
- The most accurate method for diagnosing ringworm in dogs is by fungal culture of a sample of hair or skin cells. A positive culture can sometimes be confirmed within a couple of days, but in some cases the fungal spores may be slow to grow, and culture results can take up to four weeks. Therefore, a suspected sample cannot be called negative for at least a month.
There are numerous causes for hair loss in dogs. Before making a diagnosis of ringworm, your veterinarian may recommend additional testing to rule out some of these causes.
How is ringworm in dogs treated
Regardless of the severity of the case, treatment of ringworm in dogs is always necessary to avoid the spread of infection to children or other pets. The specific method of treatment recommended by your veterinarian to treat your dog will depend on the severity of the infection, how many pets are involved, if there are children or susceptible adults in the household, and how difficult it will be to disinfect your pet’s environment.
- Topical therapy
Occasionally, topical therapy is used alone for treatment of ringworm, but more commonly it is used in combination with oral medications. Various creams and ointments are available to apply to localised areas of skin affected by ringworm. Shaving the hair in small areas, if only one or two areas are affected, or clipping all of your dog’s hair may be recommended by your veterinarian, along with bathing your dog with a medicated shampoo at least twice weekly. It is extremely important to only use preparations that have been specifically provided or recommended by your veterinarian for topical treatment of dogs. Topical treatment will usually be necessary for a period of several weeks to several months.
After bathing or treating your dog, be sure to wash your hands, and sanitise any surfaces your dog has been in contact with using a bleach solution (see Environmental cleaning below). - Oral treatment
In the majority of cases of ringworm, effective treatment will require administration of an oral anti-fungal drug. The most widely used drug for this purpose is griseofulvin. Newer drugs such as itraconazole or terbinafine (Lamasil) are being used more frequently and are often preferred since they have fewer side effects. The response of individual dogs to treatment varies. And if therapy is stopped too soon, the disease may recur.
Typically two consecutive negative ringworm cultures indicate your pet has been successfully treated, at which time treatment can be discontinued.
DO NOT stop treatment unless your veterinarian has made this recommendation. Stopping treatment too soon can result in a recurrence of the fungus.
If there is more than one pet in the household, try to separate infected from non-infected animals and just treat the infected ones. In some situations it may be preferable to treat all of the pets. Your veterinarian will advise you on the best treatment given your individual circumstances.
- Environmental cleaning
Infected hairs contain numerous microscopic fungal spores that can be shed into the environment. Infection of other animals and humans can occur, either by direct contact with an infected dog or through contact with fungal spores in a contaminated environment. In addition to minimising direct contact with an infected dog, it is also important to keep the environment as free of spores as possible. Clipping the hair (with its careful disposal) combined with topical anti-fungal treatment of affected areas of skin may help to reduce environmental contamination.
How long will my dog
How long will my dog be contagious?
Infected pets remain contagious for about three weeks if aggressive treatment is used. The ringworm infection will last longer and remain contagious for an extended period of time. This if only minimal measures are taken or if you are not faithful with the prescribed approach. Minimising exposure to other dogs or cats and to your family members is recommended during this period.
Will my dog recover from ringworm?
The vast majority of dogs, if treated appropriately, will recover from a ringworm infection. Symptoms may recur if the treatment is discontinued, too early or is not aggressive enough (i.e., only topical treatment was used). And also if the pet has an underlying disease compromising the immune system. Occasionally symptoms recur because the dog is a carrier of ringworm.
