Pseudocowpox, Parapoxvirus, in Cattle (Milker’s nodes, Paravaccinia)
Description Pseudocowpox (SUE-doe-cowpox) is a viral skin disease that causesmild sores on the teats and udders of cattle. This virus can also infecthumans and the condition is commonly referred to as milker’s nodule.A PARAPOXVIRUS related to the orf and papular stomatitis viruses causes pseudocowpox, a mild pox-like lesion of the teats that can spread to humans causing ‘milker’s nodules’. Has also been isolated from scrotal lesions of adult bulls.
The initial signs of pseudocowpox are small, reddish, raised sores on the teats and udders of cows. This is followed by the formation of vesicles, scabs, and nodules on the udder and teats. The extension of sores often forms a “ring” or “horseshoe” of scabs that are characteristic for pseudocowpox and this occurs over the course of several weeks. Although the disease spreads slowly through milking herds, it is common for the entire herd to eventually be aff ected. The length of immunity after infection is usually short and reinfection is common.
Lesions begin as small, red papules on the teats or udder. These may be followed rapidly by scabbing, or small vesicles or pustules may develop before scabs form. Scabs may be abundant but can be removed without causing pain. Granulation occurs beneath the scabs, resulting in a raised lesion that heals from the center and leaves a characteristic horseshoe or circular ring of small scabs. This stage is reached in ~7-12 days. Some lesions persist for several months, giving the affected teats a rough feel and appearance, and more scabs may form. The infection spreads slowly throughout milking herds, and a variable percentage of cows shows lesions at any time. Cattle may become reinfected in subsequent lactations. The scabbed lesions may be confused with mild traumatic injuries to the teats and udder. Scabs examined with an electron microscope frequently show characteristic virus particles.