Poxviruses

Parapoxviruses

Contagious ecthyma

• AKA contagious pustular dermatitis, Orf, etc

General information

• CE is an acute debilitating but rarely fatal skin disease of sheep, goats and incidentally of ruminants and humans.
• The disease is generally mild.
• Morbidity may reach 90%, but mortality rarely exceeds 1%, unless secondary infection or myiasis occurs.
• The course of the disease without complications is 2‑6 weeks, and it takes about 10 weeks to run a course through a naive flock, but often lingers indefinitely in the flock because it can reinfect the same animal many times and is resistant to desiccation.
• PPV's generally exhibit a highly restricted host range but in all cases can also infect man.

Aetiological agent

• The virus is a large, enveloped, highly epitheliotropic, DNA virus which is ovoid in shape and measures 220‑300 x 140‑170 nm. *There are over 100 polypeptides in the virion.
• The core proteins include a transcriptase and several other enzymes.
• The virus is immunologically related to those causing bovine papular stomatitis, pseudocowpox, sealpox, deer PPV, red squirrel PPV and camel PPV.
• There is extensive cross‑neutralization and cross‑protection between viruses belonging to the same genus, but not between those of different genera.
• The virus is resistant to desiccation.

Pathology

Differential diagnosis

• Sheep pox: A more severe disease, it is characterized by elevated papules distributed diffusely over the skin surface. Inclusion bodies are often seen, but there is no down‑growth of epidermis. There is a high mortality.
• Ulcerative dermatosis: Characterized by ulcers and crusts on the skin of the face, feet and genitalia. The lesions are not elevated because there is no epithelial hyperplasia.
• Blue‑tongue: There is a lower morbidity but a high mortality. The disease is usually seen in adult animals. This is a severe systemic disease which is a differential only for the rare, systemic form of CE.
• Mycotic dermatitis: The scabs are smaller and thinner and lighter and usually yellowish in color. The crusts are not firmly attached.
• Foot and mouth disease: When lesions occur in the mouth.