Introduction

• Superficial bacterial dermatitis.
• Cause: Dermatophilus congolensis Dermatophilus spp.
• Signs: alopecia and crusting .
• Diagnosis: microscopic identification ofDermatophilus congolensis .
• Treatment: keep dry +/- topical antibacterials +/- systemic antibiotics.
• Prognosis: good.

Pathogenesis

Etiology

• Dermatophilus congolensis infection Dermatophilus spp.

Predisposing factors

General

• Exposure to persistently wet weather/wet ground.
• Trauma, secondary to allergies or insect exposure.
• Intercurrent disease.
• Malnutrition.
• Stress.

Specific

• Prolonged heavy rain.
• Muddy paddocks.
• Sweating.
• Non-pigmented areas.
• Trauma (grooming, rubbing tack, gravel thrown up by hooves, sharp vegetation).
• Use of contaminated equipment allowing spread from infected horses.
• Forceful spraying with water.
• Ectoparasites, particularly biting flies Biting and nuisance flies.
• Primary or secondary photodermatitis Dermatitis: solar.

Pathophysiology

• Source: chronically infected carrier animals, or environment (saprophytic soil organism).
• Transmission: direct contact, fomites or biting and non-biting flies and ticks.
• Dermatophilus can be isolated in the soil where affected animals are kept.
• Organic matter was found to have a protective effect on the micro-organism. Dermatophilus can also survive as a commensal and opportunistic pathogen in the skin of animals that are clinically normal, therefore potentially acting as a source of infection once favorable conditions are present.
• Entry: requires abrasion in skin.
• Infection: requires moist environment.
• Dermatophilus congolensis from chronically infected carrier animals or saprophytic infection from soil → transmission by direct contact, fomites (persists for up to 42 months in crusts in the environment) or biting and non-biting flies and ticks → entry into epidermis through abrasion in skin → germination of motile coccoid zoospores in a moist defect of stratum corneum → proliferation mycelium within living layers of epidermis → primarily neutrophilic inflammatory response → barrier that Dermatophilus congolensis organisms are unable to penetrate → elimination of organisms as epidermis re-epithelializes .
• Non-pigmented areas with dermatophilosis infection may be associated with, and exacerbated by, photodermatitis.
• Occasional severe cases of deeper, generalized exudative, neutrophilic dermatitis may be seen in immunocompromised horses.
• Lymph nodes and/or systemic involvement may also occur with possible fever and weight loss.

Timecourse

• Depends on time taken between exposure to organism and exposure to wet environment, and on the health and immune status of the host.

Diagnosis

Treatment

Prevention

Outcomes