What are Dermatophytosis?
Dermatophytosis is a highly contagious fungal infection that can occur in humans, dogs and cats. It is commonly called ringworm but there are no parasitic worms involved. 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.
The fungi that causes dermatophytosis belong to a specialized group known as dermatophytes. Dermatophytosis fungi feed on the keratin found in the outer layer of the skin, hair and nails. This fungal disease usually infects the hair follicles of the canine. It causes the hair to break off at the skin line, resulting in round patches of hair loss. As the disease spreads over the dog’s body, the lesions may be irregular shaped. Dermatophytosis is not usually itchy but the lesions may lead to skin sores caused by your dog licking at the infected area.
Some dogs may be asymptomatic carriers, which means they do not show outward symptoms of the disease but are able to transmit the disease to other animals or humans.
If you believe that your pet has dermatophytosis, it is imperative that you take him to a veterinarian to help ensure the disease does is not transmitted to other members of your household.
Dermatophytosis is a fungal infection that affects the superficial layers of the skin, hair and nails. It typically causes a raised, red, circular rash on the skin; symptoms appear within 4 to 14 days after being infected.
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Symptoms of Dermatophytosis in Dogs
Dogs infected with dermatophytosis may show one or more of the following symptoms:
- Round raised areas of hair loss
- Irregular patches of hair loss
- Scaly or crusty skin
- Irritated and inflamed hair follicles
- Pustules on the skin
- Dry, brittle or cracked nails
- Secondary bacterial skin infections
There are three most common fungal species that may cause ringworm in dogs; all three are zoonotic and may be transmitted from pet to human.
- Microsporum canis - Fungus that affects the upper layers of the skin on cats, dogs and humans
- Microsporum gypseum - Is a soil associated dermatophyte
- Trichophyton mentagrophytes - Affects 30% of dogs, especially Terrier breeds
Causes of Dermatophytosis in Dogs
- Dermatophytosis is contagious and is transmitted by direct exposure to the fungus
- It may be transferred by contact with an infected animal or human
- Dermatophytosis may also be passed by handling contaminated soil
- Fungal spores may transferred by a pet’s bedding, brushes and furniture
- Puppies, canines with a suppressed immune system, or pets on steroid medications are more susceptible to contracting dermatophytosis
- Contact with infected rodents may transmit dermatophytosis
- Flea bite may transmit the fungi
Diagnosis of Dermatophytosis in Dogs
Your veterinarian will take a thorough history of your pet. You will be asked questions on what the symptoms are and the timeline as to when they started. Your veterinarian will perform a physical exam. A common screening test used in dermatophytosis is the use of a specialized ultraviolet light called a Wood’s lamp. There are several types of the ringworm fungus that will glow with a yellow-green hue in a dark room when exposed to a Wood’s lamp. The Wood lamp is not always accurate because not all fungi fluoresce.
A more reliable test is to perform a fungal culture, using a sample of your pet’s skin or hair. There are special culture mediums designed specifically for identifying ringworm infections. A positive culture can sometimes be confirmed within a couple of days but some fungi take longer to grow. Your veterinarian may also examine your dog’s hair under a microscope to see if he can identify the fungal spores.
Treatment of Dermatophytosis in Dogs
Once dermatophytosis is diagnosed the treatment goals will be to eliminate the fungi from the dog’s skin, restore hair and skin to a normal condition and prevent the spread of infection to other family members. Therefore, treatment for dermatophytosis will involve the combination of topical, systemic therapy and sanitizing environmental contamination.
Topical treatments are best if applied to the dog’s whole body, in the form of shampoos, rinses or dips. Your veterinarian may suggest clipping or shaving your pet’s hair to help aid with the treatment. Topical treatments usually must be continued for at least 4 to 6 weeks. Some topical solutions that have been found effective against dermatophytosis include sulfur sulfide, enilconazole, chlorhexidine + miconazole and chlorhexidine + ketoconazole.
Isolated lesions may be spot treated with a prescribed anti-fungal ointment. After bathing or applying ointment to your pet make sure to wash your hands and sanitize any surfaces the dog had contacted with.
Oral antifungal drugs that your veterinarian may prescribe include griseofulvin, terbinafine, lufenuron and itraconazole. Each of these medications may have side effects, so must have close direct veterinary supervision. Antifungals never should be given to pregnant pets because they may cause defects in the litter.
Oral treatment usually must be continued for at least six weeks. Your veterinarian team will take dermatophytosis cultures one to two weeks after the start of treatment to help determine if your pet is still infected. Commonly, two consecutive negative cultures will indicate that your pet is no longer infected.
Fungal spores can be shed into the environment and infect other animals or humans in the household. Your pet’s living environment must be frequently disinfected, vacuumed and mopped. Your pet’s bed and toys must be washed. A bleach diluted solution is recommended in areas that can be disinfected. Air filters should be changed frequently. Your veterinarian may recommend restricting your pet to an area that is easy to maintain as sanitary.
Recovery of Dermatophytosis in Dogs
Prognosis that your pet will recover from dermatophytosis is very good. Follow up visits will be necessary to check on your pet’s progress, monitor prescribed medications, and repeat cultures.
Make sure to let your veterinarian know if you observe any side effects or new symptoms while your pet is on antifungal medication. It is extremely important that you follow your veterinarian team’s treatment plan to avoid the recurrence of the dermatophytosis.