Contagious ecthyma is an infectious dermatitis of sheep and goats that primarily affects the lips of young animals. The lesions are characteristic, and diagnosis is confirmed by PCR assay. The disease is typically more severe in goats than in sheep. Treatment usually focuses on secondary infections. Humans are occasionally affected through direct contact.
Contagious ecthyma is a viral, pustular dermatitis of young sheep and goats. Lesions usually involve the lips but can involve other cutaneous junctions such as the coronet, and can extend onto the face and ears as well. Diagnosis is confirmed by PCR assay. Affected animals go off feed, fail to gain weight, and may develop serious secondary infections at the lesion sites, all of which result in production losses.
Etiologia e epidemiologia do ectima contagioso em ovinos e caprinos
The parapoxvirus that causes contagious ecthyma is related to the viruses that cause pseudocowpox and bovine papular stomatitis. The virus is transmitted by contact. It is highly resistant to desiccation in the environment and has been recovered from dried crusts after 12 years. In the laboratory, it is also resistant to glycerol and to ether.
Contagious ecthyma is found worldwide and is common in young lambs reared artificially and in older lambs during late summer, fall, and winter on pasture, and during winter in feedlots.
Achados clínicos e diagnóstico do ectima contagioso em ovinos e caprinos
Clinical evaluation
Laboratory confirmation
The effect of contagious ecthyma on the ear of a goat. Note the proliferative dermatitis in the pinna.
Courtesy of Dr. Robert Dunstan.
An ulcerative lesion of proliferative contagious ecthyma (orf), extending from the mucocutaneous junction of the lips in a sheep and covering both the lips and the nasal region.
Courtesy of Dr. Philip Scott.
Lesions of chronic proliferative contagious ecthyma, extending from the mucocutaneous junction of the lips of a sheep. The chronic hyperkeratosis covers both the upper and lower lips.
Courtesy of Dr. Philip Scott.
Chronic proliferative contagious ecthyma lesions, extending from the mucocutaneous junction of the lips of a lamb. Scabs are present on the nasal and buccal regions and, to a lesser extent, the pinna.
Courtesy of Dr. Philip Scott.
The scabby lip crusts on this lamb are a proliferative contagious ecthyma lesion that extends from the mucocutaneous junction of the lips.
Courtesy of Dr. Philip Scott.
Strawberry footrot, a lesion resulting from secondary infection of a contagious ecthyma lesion at the coronary band due to the bacterium Dermatophilus congolensis.
Courtesy of Dr. Philip Scott.
The primary lesion of contagious ecthyma develops at the mucocutaneous junction of the lips and around erupting incisor teeth, and it may extend to the mucosa of the buccal cavity. Occasionally, lesions are found on the feet and around the coronet, where secondary bacterial infection with Dermatophilus congolensis commonly leads to strawberry footrot. Ewes nursing infected lambs may develop lesions on the teats that extend onto the udder skin. The lesions develop as papules and progress through vesicular and pustular stages before encrusting. Coalescence of numerous discrete lesions often leads to the formation of large scabs, and the proliferation of dermal tissue produces a verrucose mass under them. When the lesion extends to the oral mucosa, secondary necrobacillosis frequently develops.
During the course of the disease (1–4 weeks), the scabs drop off and the tissues heal without scarring. During active stages of infection, more severely affected lambs do not eat normally, and they lose condition. Extensive lesions on the feet result in lameness. Mastitis, sometimes gangrenous, may occur in ewes with lesions on the teats.
The ecthyma lesion is characteristic. The disease must be differentiated from ulcerative dermatosis, which produces tissue destruction and crateriform ulcers. Compared to ulcerative dermatosis, ecthyma usually affects younger animals; however, this criterion can be used only presumptively. Foot-and-mouth disease and bluetongue infection should also be considered as differential diagnoses if morbidity is high and the clinical signs include salivation, lameness, and fever. Staphyloccocal folliculitis affects the skin of the muzzle and surrounding the eyes. Electron microscopic direct demonstration of virus in scab material has now been replaced by PCR assay as the diagnostic method of choice for ecthyma. Historically, inoculation of susceptible and ecthyma-immunized sheep confirmed the diagnosis.
Tratamento e controle da ectima contagiosa em ovinos e caprinos
Secondary infection
Live vaccines
Both parenteral and topical antimicrobials may help combat secondary bacterial infection of the skin lesions of contagious ecthyma. In endemic areas, appropriate repellents and larvicides should be applied to the lesions to prevent myiasis. The virus is transmissible to humans; lesions in humans are usually confined to the hands and face, are more proliferative, and can be very distressing. Veterinarians and sheep handlers should exercise reasonable protective precautions and wear disposable gloves. Most cases in humans are misdiagnosed and mistaken for other diseases (eg, anthrax) which often leads to unnecessary treatment with antibiotics or cryosurgery. Typically, physicians suspect ecthyma only when the patient reports a history of contact with sheep or goats. At this time biopsy of the lesion is performed for diagnostic confirmation by means of PCR testing.
Sheep that have recovered from natural infection are highly resistant to reinfection. Despite there being many immunogenic virus strains, the current commercial single-strain live vaccines have produced fair immunity in all parts of the US (with an occasional exception usually occurring in goats). Vaccine breaks appear to be due to the virulence of the infecting strain rather than to differences in antigenicity of the vaccine. Sheep immunized against contagious ecthyma remain susceptible to ulcerative dermatosis.
Live vaccines should be administered cautiously to avoid contaminating uninfected premises, and vaccinated animals should be segregated from unprotected stock until the scabs have fallen off. A small amount of the live vaccine is brushed over light scarifications of the skin, usually on the inside of the thigh or behind the elbow or caudal fold. Lambs should be vaccinated when ~1 month old. For best results, a second vaccination ~2–3 months later is suggested. Nonimmunized lambs should be vaccinated ~1–2 months before entering infected feedlots.
Although ecthyma is a vesicular disease that could be mistaken for foot-and-mouth disease, its notification is not mandatory by World Organization for Animal Health (formerly OIE) rules. Currently, there is no eradication program or procedure to investigate outbreaks.
Pontos-chave
Contagious ecthyma is an infectious zoonotic disease, affecting mainly sheep and goats.
Lesions are characteristic and usually affect the lips and face, creating vesicles, ulcers and hyperkeratosis.
Although it is considered a mild disease, new strategies for diagnosis and vaccination are needed.
Referências
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