Dermatophilosis

Also known as:

'Cutaneous streptothrichosis Lumpy wool - sheep Strawberry foot rot - sheep' Rain Scald - horses

Description

This is a group of diseases affecting the epidermis caused by Dermatophilus congolensis. It causes a range of conditions in large animals including rain scald in horses and strawberry foot rot in sheep. The disease is associated with skin trauma, prolonged wetting or parasites. Lesions typically involve exudative dermatitis with scab formation. It is a zoonosis affecting humans in close contact with infected animals.

Signalment

Can be seen in animals of all ages but most commonly occurs in young animals who are chronically exposed to moisture. Affects horses, sheep, cattle, goats, pigs and rarely dogs and cats.

History and Clinical signs

Lesions commonly occur following heavy rainfall and commonly affects the dorsum of animals. Any previous trauma or damage to the skin can predispose to infection. Blood-sucking insects are also thought to be involved in transmission.

Equine dermatophilosis

Dermatophilosis - Horse

Ovine dermatophilosis

Also see General Dermatophilosis

Three clinical syndromes have been documented:

• Lumpy wool
• Strawberry foot rot
• Fleece rot

Fleece infection is known as lumpy wool. Infection passes from ewe to lamb during suckling and hence lesions first appear on the head which leads to infection on the trunk. In wet weather can result in high morbidity outbreaks. Large areas of the fleece can be affected where crusts of varying thickness become evident. On haired skin, crusts can become very thick and can form horn like structures. In severe infecions of rams the scrotum and surrounding skin can become affected.

Strawberry foot rot is a condition affecting the skin from the coronet to the carpus or hock. The disease occurs as a result of Orf and Dermatophilus infection. Scabs get rubbed away leaving the granulating surface which resembles a strawberry.

Fleece rot A condition thought to be assosiated with dermatophilosis, but also involves pigment producing bacteria which stains the wool a characteristic yellow colour. Predisposes to fly strike.

Bovine dermatophilosis

Also see General Dermatophilosis

Dermatophilosis in a cow (Courtesy of Bristol BioMed Image Archive)

Is rarely reported but causes lesions which are distributed over the head, dorsum, neck and chest. Cattle that stand for long periods in deep water and mud develop lesions over the flexor surfaces of the joints. Dairy cows may develop lesions on the udder.

Lesions may resolve within weeks if dry weather or prolonged wetting of infected areas can lead to secondary bacterial infection which can result in limb oedema and cellulitis.

Diagnosis

Can often make a diagnosis on history and physical exam. Impression smears can also be useful when stained with either gram stain or Giemsa and examined microscopically. Additionally it is possible to culture material from the crusts however this can be difficult due to the slow growing nature of the pathogen.

Pathology

Grossly: Papules, pustules, crusts may coalesce and mat the coat.

Microscopically:

• • Hyperplastic superficial perivascular dermatitis
  • Multilaminated crusts, alternating keratin and inflammatory cell layers

Treatment

Farm animals: Bring affected animals into a dry environment. Investigate any underlying problems which may predispose to the infection. Antibiotics can be given intramuscularly and typically work following one dose. However if signs do not resolve a 5 day course should be administered. Penicillin and streptomycin are good choices for this disease. Additionally Dips containing 0.2% Copper Sulphate or 0.5% Zinc sulphate can be effective.

Prognosis

Good if animals are kept dry. Often re-occurs in wet weather.

References

Merck & Co (2008) The Merck Veterinary Manual (Eighth Edition) Merial

4th year Veterinary Dermatology notes. Royal Veterinary college. October-November 2008. p60-64.