Dermatophilosis is a skin infection caused by the bacterium Dermatophilus congolensis [1][2]. It used to go by names such as rain rot and rain scald [2].
It is mainly a disease of horses and farm animals. A veterinary dermatology handbook describes it in horses, cattle, sheep, goats and llamas [1], and a CDC journal note says it affects mostly cattle [2]. Dogs and cats are not on that list, and published reports in pets are few. Most of what is known comes from large animals, so the descriptions below are about the disease in animals in general.
Dermatophilosis can pass to people, although this is rare. If your vet suspects it, wear gloves when you handle your pet and wash your hands afterward [1][2].
What triggers it
- Wet skin and skin damage: the handbook names long-lasting wetness of the skin and damage to the skin as the two biggest risk factors [1]. Water softens the outer skin layer and lets the bacteria release their infective form, and infection only takes hold once the skin is injured [1]. Outbreaks tend to follow wet, rainy weather [1].
- Bites and scratches: insect and tick bites and prickly plants can damage the skin [1]. Flies and shared clippers can carry the bacteria from one animal to another [1].
- Hidden infection: some animals carry the bacteria without signs, and the infection can flare when conditions turn favorable [1].
- Other illness: another disease at the same time can make infection more likely, and ticks or a weak immune system can make it more severe [1].
- Where it is found: it occurs worldwide [1].
Signs
- Thick scabs: the typical sign is a thick crust with a tuft of hairs stuck in it [1]. When the crust comes off, the hairs come with it and the skin underneath looks pink and moist [1].
- Where on the body: in horses the upper surfaces of the body, such as the back, are hit most [1]. Animals that stand in wet pasture may have scabs only on the lower legs and muzzle [1].
- Pain more than itch: in horses, new scabs are described as painful rather than itchy [1].
- Older patches: long-standing areas can show hair loss and scaling [1].
- Severe cases: farm animals with large parts of the body affected can lose weight quickly [1].
Reports in cats are few. One described a lump under the skin near the knee of a young feral cat [3].
Scabs have many other causes. The handbook lists fungal skin infection, bacterial hair follicle infection and the autoimmune disease pemphigus foliaceus among the look-alikes [1]; see ringworm in dogs and cats. For more common bacterial skin infections, see pyoderma in dogs and pyoderma in cats.
How vets diagnose it
The quickest test is to look at material from the crusts under a microscope [1]. Your vet may break up a crust on a slide, or press a slide against the moist skin under a fresh crust, then stain it [1]. Under the microscope the bacteria line up in parallel rows that look like a railroad track [1].
In older or dried-out patches the bacteria are harder to find, so the lab may need to grow them in culture or look at a small skin sample (biopsy) [1].
How vets treat it
In horses, many cases clear up on their own once the weather turns dry [1]. Even so, the handbook advises keeping the animal dry, supporting its general health and controlling parasites and biting insects [1]. When treatment is needed, vets use skin washes or medicines by mouth or injection [1]. Your vet will decide whether your pet needs treatment and which one.
Crusts from affected animals are a main source of the bacteria [1]. Ask your vet how to keep your pet’s skin dry and free of parasites, and how to handle any crusts that come off.
At home, as directed by a vet:
- wear gloves when you touch the affected skin, and wash your hands afterward;
- give all medicines exactly as prescribed;
- do not pick or pull off the scabs unless your vet tells you to;
- go back for every recheck.
Outlook
- In horses, most cases settle when dry weather returns [1].
- Having had the infection once does not give strong protection, so it can come back [1]. Later infections tend to be milder and clear faster than the first one [1].
- Some animals seem to resist the disease naturally [1].
These are statements about groups of animals, mostly not dogs and cats. They cannot predict how one pet will do. Your vet can explain what this means for your pet.
Can people catch it?
Yes, but rarely. The handbook says people can pick it up through contact with infected animals [1], and the CDC journal note says it affects humans more rarely than animals [2].
If you have a skin problem after handling an affected pet, see your doctor.
When to see your vet
See your vet if your dog or cat has:
- thick scabs on the skin, especially scabs with tufts of hair stuck in them [1];
- scabs that spread to new patches of skin;
- a lump under the skin [3];
- scabs that seem painful, or a pet that is off its food or less active.
FAQ
Is dermatophilosis common in dogs and cats?
No. It is mainly a disease of horses and farm animals [1][2], and reports in pets are few [3].
Can I catch it from my pet?
It is rare, but it can pass to people through contact with an infected animal [1]. Wear gloves and wash your hands after handling an affected pet.
Why does wet weather matter?
Long-lasting wetness softens the skin and lets the bacteria release their infective form, so the disease often follows rainy spells [1].
The bottom line
Dermatophilosis is a bacterial skin infection seen mostly in horses and farm animals, with few reports in dogs and cats. Wet skin and skin damage are the main triggers, and it causes thick scabs with tufts of hair stuck in them. Vets diagnose it by looking at crust samples under a microscope. It can rarely pass to people, so wear gloves and wash your hands, and see your vet about any scabs on the skin.
This article is for general information only and does not replace advice from your veterinarian. If your pet has crusts or scabs on the skin, see your vet.
Sources
- Torres SMF, et al. 1.5 Dermatophilosis. Small and Large Animal Dermatology Handbook, Vol. 1. University of Minnesota Libraries Publishing, 2025 (CC BY 4.0). https://open.lib.umn.edu/animaldermatology/chapter/dermatophilosis-2/
- Ollhoff RD, Pogliani FC, Sellera FP. Dermatophilus congolensis. Emerg Infect Dis. 2022;28(8):1663. Centers for Disease Control and Prevention (public domain). https://doi.org/10.3201/eid2808.212573
- Barger AM, Weedon GR, Maddox CW, Galloway KA. Dermatophilus congolensis in a feral cat. J Feline Med Surg. 2014;16(10):840-1. https://pubmed.ncbi.nlm.nih.gov/24496323/