Contagious Pustular Dermatitis (Orf Disease) - Epidemiology, Diagnosis, Control and Public Health Concerns

摘要

Contagious pustular dermatitis (CPD), also known as Orf or contagious ecthyma is an important viral disease of sheep and goats. It is mainly seen as a benign disease but malignant form has also been reported from few parts of the world. The rates of morbidity and mortality are higher, particularly in lambs and kids experiencing the disease for the first time. The causative agent of disease is Orf virus, type species of the genus Parapoxvirus belonging to family Poxviridae. The virus produces localized persistent proliferative skin lesions and affected hosts are infected repeatedly owing to its host immune evasive strategy. These viruses have been found uniformly labile to chloroform but resistant to ether and also exhibit antigenic variations among them. Clinically, the disease is enzootic and occurs in three forms viz. labial, genital / mammary and generalized forms. The incubation period in natural cases is 2-3 weeks. The disease outbreaks mostly occur between autumn and spring but its severity is more in autumn and winter than spring. The virus grows well in cell cultures of caprine, ovine and bovine origin. Confounding symptoms impose laboratory affirmation by serological assays or molecular techniques. The disease can be diagnosed by electron microscopy, serological tests and PCR/ quantitative real-time PCR. Virus specific antibody response to structural proteins of capripox and orf viruses in western-blot analysis readily differentiates these two infections. The antibody response to the 32 kDa and 26 kDa proteins of capripox viruses provides a firm basis for differentiation. Although, the role of humoral immunity is well established but probably cell mediated immunity plays a major role in recovery from natural infections. A number of inactivated and live or live modified vaccines have been tried with variable success. The duration of immunity after vaccination is controversial; outbreaks have occurred in vaccinated animals. The disease is also of public health significance as it causes infection in human beings.