NAVLE Integumentary

Equine Dermatophilosis Study Guide

Dermatophilosis (also known as rain rot, rain scald, mud fever, or streptothricosis) is one of the most common bacterial skin infections affecting horses worldwide.

Overview and Clinical Importance

Dermatophilosis (also known as rain rot, rain scald, mud fever, or streptothricosis) is one of the most common bacterial skin infections affecting horses worldwide. This exudative, crusting dermatitis is caused by Dermatophilus congolensis, a gram-positive, facultative anaerobic actinomycete bacterium with unique fungal-like characteristics. The disease has significant clinical importance due to its painful nature, impact on equine performance, and potential for secondary complications if left untreated.

Understanding this condition is essential for the NAVLE because it frequently appears on board examinations due to its distinctive clinical presentation, characteristic cytological findings (the pathognomonic "railroad track" appearance), and specific management requirements involving environmental control alongside antimicrobial therapy.

Characteristic Description
Classification Actinomycete bacterium (filamentous, fungus-like bacteria)
Gram Stain Gram-positive
Oxygen Requirements Facultative anaerobe (can survive with or without oxygen)
Acid-Fast Staining Non-acid-fast
Morphologic Forms Two forms: Branching filamentous hyphae (1-5 micrometers diameter) and motile flagellated zoospores (0.6-1.0 micrometers)
Environmental Survival Survives up to 42 months in dried crusts; not isolated from soil

Etiology

Causative Agent

Dermatophilus congolensis is a unique pathogen with the following characteristics:

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