Rain scald is a relatively common skin infection caused by the bacteria Dermatophilus congolensis. The infection often affects the skin on the back and rump of horses.

Rain scald can develop when skin is exposed to excessive moisture which weakens and damages the skin. Once the skin barrier is compromised, Dermatophilus congolensis enters and spreads in the top layer of the skin.

In mild cases, the most common symptoms are dry and scaly skin. Advanced cases involve the development and spread of crusty lesions and scabs.

Prompt treatment is required to stop the spread of rain scald. Treatment involves cleansing the skin with an antiseptic wash and applying topical antibacterial agents. In severe cases of the condition, systemic antibiotics may be administered.

Key management strategies to prevent rain scald include reducing exposure to moisture by providing proper shelter and blanketing your horse appropriately. Regular grooming and good nutrition also help to prevent the condition.

What is Rain Scald

A relatively common skin condition first identified in cattle in Africa, rain scald is also referred to as rain rot, mud fever, dermatophilosis, and streptothricosis.

Rain scald is a type of infection (dermatitis) caused by the bacteria Dermatophilus congolensis. [1][2][3] This pathogenic bacteria lives on the skin in a dormant statem but can cause an inflammatory infection if activated.

When skin is exposed to moisture, the bacteria can replicate and spread in the top layer of the skin (epidermis) by causing infectious lesions.

Rain scald can cause lesions to form on the back, rump and sometimes on the face of affected horses. Dermatophilus congolensis is sometimes present in the skin of horses that have mud fever lesions on their pasterns. [6]

Rain scald is contagious through direct contact and through sharing of blankets, tack, brushes or other equipment. Horses living together may also contract the infection at the same time because they are exposed to the same environmental conditions.

Risk of Infection in Horses

Horses affected by rain scald often have cracked, damaged skin that facilitates the entry of additional types of microorganisms such as Staphylococcus. When additional microorganisms enter the skin, they can cause secondary infections.

Because Dermatophilus congolensis thrives in damp conditions, skin infections caused by this type of bacteria are most common during the wettest seasons of the year.

Rain scald affects horses around the globe, especially those living in areas where it is humid and when rain is abundant and frequent. [4][5]

Skin infection with Dermatophilus congolensis affects horses of all breeds and ages. Horses with lowered immunity or poorly developed immune systems also have an increased risk.

Horses affected do not become immune to dermatophilosis infection once they have had rain scald. The infection can reoccur again in the future, especially in wet and muddy conditions.

The spores of Dermatophilus congolensis can remain infective for months if present on skin, hair, and dried scabs from healed lesions. These spores can infect new animals through direct contact or can reinfect the original host. Biting insects can also transmit the infection by spreading the bacteria’s spores to other animals.

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Signs of Rain Scald

The bacterial infection caused by Dermatophilus congolensis can vary from mild to severe. If left untreated, the condition can spread along the skin covering an increasingly larger area over time.

In mild cases, the infection may appear as dry and scaly skin. Crusty lesions and scabs develop as the condition progresses to a more advanced state.

The infection results in the discharge of a sticky secretion that causes the hair to matt together and leads to the development of crusty scabs of varying sizes. [7] These scabs have attached hairs that stand up like the bristles on a paintbrush. Hair loss occurs in areas where the scabs have come detached from the skin.

Underneath scabs, the skin may be raw and ooze yellow exudate (pus). In serious cases of rain scald, large areas of skin can become covered in hardened scabs and the skin is left raw in areas where they have come off.

Risk Factors

Environmental

Horses living in humid and tropical climates where rainfall occurs often have a greater risk of rain scald. Excessive exposure to rain weakens the skin’s protective barrier leaving it susceptible to bacterial infection with Dermatophilus congolensis, an opportunistic microorganism with a complex lifecycle.

Skin Damage

Any physical trauma to the skin leaves it vulnerable to infection with Dermatophilus congolensis. Bug bites can cause damage to the skin and increase infection risk by facilitating an opening for bacteria to enter the skin.

Rough plants can scratch, cut, and puncture the skin, also leaving it prone to infection by microorganisms including Dermatophilus congolensis.

Poor Hygiene

Inadequate grooming promotes unhealthy skin that becomes prone to infection. Proper grooming is necessary to allow the pores to breathe by removing dirt from the skin to reduce the accumulation of microorganisms in the hair and on the skin.

The bacteria that cause rain scald are easily transmitted from horse to horse through contact with one another. Using shared tack and grooming tools on horses can facilitate the spread of bacteria between horses.

Lack of Skin Pigment

Some types of dermatitis are more comm