Contagious Pustular Dermatitis (Orf)
· Also known as CPD, Scabby Mouth or Contagious Ecthyma.
· Caused by a pox virus. This virus can remain active and infective in the environment through dried scabs in the environment. CPD virus most commonly results in proliferative lesions following trauma of the coronary band and lips/gums; seen most severely in hand-reared lambs less than two months old. Outbreaks of CPD are associated with pasture change, where the new pasture features thistles or gorse; causing superficial trauma to the lips/mouth. This change usually shows outbreaks of CPD after 10-14 days of pasture change.
· CPD is a zoonotic disease.
· Clinical presentation: this virus most commonly results in proliferative lesions at the hoof/horn junctions and on the lips. Lesions persist for 4-8 weeks then regress. Initial papule and vesicle stages are rarely observed. The most common presentation seen is scabs progressing to large wart-like structures, which bleed profusely following trauma to their base. Commonly there are scabs at the lip commissure (joining) and along the gum margins surrounding the incisor teeth. Rarely but not unheard-of, there can be scabs present on the tongue and hard palate.
Incidence can be high but mortality is usually fairly low in uncomplicated cases.
· Spread of the virus is rapid between orphan lambs that share the same feeding equipment. In sucking lambs, lesions develop on the medial aspect of the ewe’s teat; due to trauma of the teat via the lambs sucking, which permits entry for the virus. These teat lesions are painful and may stop a ewe allowing a lamb to nurse. Occasionally, mastitis (which may be gangrenous in nature) will follow the development of CPD teat lesions.
Facial dermatitis: CPD virus and various bacteria (including S. aureus) may act together to cause severe facial dermatitis. This presents as sharply-demarcated areas on the muzzle and lower lip with scab material also palpable within the hairs extending for a further 2-3cms from the periphery of the visible lesions. The skin is oedematous with serious exudation and superficial pus accumulation with adherent straw/foreign objects becoming dessicated, forming hard scabs separated by deep fissure. Removal of the scab reveals a deep bed of exuberant granulation tissue.
Strawberry Footrot: CPD virus and Dermatophilus congolensis may act together to produce large granulomatous masses extending 4-8cms proximally from the coronary band often referred to as “strawberry footrot”. These lesions bleed profusely when traumatised. Usually they only affect one leg and are seen in weaned lambs recently moved to stubble pasture. Lesions are often severe, but incidence is generally fairly low.
Diagnosis is based on findings of large proliferative lesions around the lips and nostrils of growing lambs. On ewes the scabs are seen on the teats most commonly.
Treatment is largely unsuccessful except for lambs with superficial secondary bacterial infection of scabs which show a good response to either intramuscular procaine penicillin or oxytetracycline injections and topical oxytetracycline spray for 3-5 days.
Prevention & Control: disease is introduced into a flock by carrier sheep with no obvious skin lesions. Infection can remain active and viable in dry scab material in housing/pasture for many months; this is likely the reason for year-year infection. Cleaning and disinfection of lambing accommodation may therefore be help to break the usual annual appearance.