Dermatophilosis

This fact sheet was updated 10/29/20.

Other names: Rain rot, Contagious dermatitis, Streptothricosis, Strawberry foot rot, Lumpy wool

Cause

Dermatophilosis is a bacterial skin infection of many animal species, and sometimes humans, caused by the spore-forming bacterium Dermatophilus congolensis. This species of bacteria is unusual because its characteristics and life cycle are similar to that of a fungus. It thrives in wet weather and is thought to exist in soil but has not been isolated from the environment. Dermatophilosis occurs most frequently in domestic animals, but is increasingly recognized in wildlife. D. congolensis was first described in domestic cattle in Zaire, Africa in 1910. 

Significance

Dermatophilosis occurs in wildlife when environmental conditions are moist, but it does not seem to have a significant impact on wildlife populations. The young and immunocompromised animals, or animals chronically exposed to wet conditions, are most commonly affected.

Dermatophilosis has occasionally been transmitted to humans working closely with infected animals. Human infection usually results in mild, self-limiting skin lesions, though people with deficiencies of their immune system may experience more severe infections. 

Species Affected

Dermatophilosis has been reported in at least 21 species of wild mammals, though all mammals are likely susceptible. The disease has been reported in several species of wild ungulates (hooved mammals), including white-tailed deer, mule deer, elk and moose. It has also been found in rabbits, rodents, woodchucks, striped skunks, camels, buffalo, primates, and several species of carnivores including a captive polar bear. 

Dermatophilosis is also known to occur in reptiles, and has been described in crocodiles, alligators, lizards, snakes, and tortoises. Domestic animals commonly infected include cattle, sheep, goats, and horses. Humans, pigs, dogs, and cats are also rarely infected. 

Distribution

Dermatophilosis has been reported in animals worldwide, with the exception of Antarctica. This disease does occur in temperate regions but is more common in tropical and subtropical climates.

Transmission

D. congolensis spores can remain infective for months on skin, hair, and dried crusts from healed lesions. These can infect new animals through direct contact or can act as a source of re-infection for the original host. Biting insects, such as ticks and flies, as well as contaminated surroundings, can also transmit or spread the spores to other naïve individuals.

Outbreaks are often associated with rain, high humidity and high temperature because these factors disrupt the natural protective barriers of skin leading to infection. The spores also readily enter cuts or abrasions of the skin. Animals that congregate naturally as in winter yards, or do so because of human influence such as at feeders, are at particular risk.

Clinical Signs

D. congolensis infections result in exudates that form crusty scabs on the skin, matted tufts of hair and areas of patchy or extensive hair loss. The scabs can become detached and reveal raw, red, inflamed, and often bleeding deeper layers of skin. Infections can range from mild and barely visible to severe. Lesions can be small or large and may occur on any part of the body, though the top line and sloping areas of the body that become wet are often affected. Lesions caused by biting flies are found mostly on the back. In contrast, lesions caused by ticks commonly affect the head, ears, armpit and groin areas and scrotum.

The most severely affected animals may rarely become emaciated and die, but most infections are mild and will heal spontaneously with time in animals with a normally functioning immune system. Dry weather helps to accelerate the healing process.

Diagnosis

Dermatophilosis is diagnosed by isolating the bacteria from skin lesions or from impression smears of the crusts. D. congolensis should be suspected in any scabby skin lesion or pustule, particularly if the lesions are in the characteristic patterns as described above.

Treatment

Antibiotics may be used to treat this disease, but treatment is usually not attempted in wildlife. Spontaneous resolution is common.

Management

Dermatophilosis is not currently considered a significant disease in wildlife, so management and prevention are not necessary.

Anyone handling wildlife is at risk of exposure to D. congolensis. Washing hands with warm soapy water after any contact with animals is recommended to prevent infection.

 

Suggested Reading

Images

White-tailed deer buck fawn with papules of dermatophilosis on the muzzle and ear margin. Image from Roscoe et al. 1975White-tailed deer buck fawn with papules of dermatophilosis on the muzzle and ear margin. Image from Roscoe et al. 1975