Thursday, November 20, 2008

A case report of Pigeon Pox-Histopathologic Diagnosis

Avian pox is a well-known disease in chickens, turkeys, pigeons, and canaries, and it has been identified in more than 60 wild bird species (Tripathy, 1991). Avian pox is a transmissible disease that is spread by several kinds of vectors: biting arthropods such as mosquitoes and mites, and aerosols generated from infected birds, or the ingestion of contaminated food or water. The disease has two forms: cutaneous and diphtheritic. Pigeon pox is a slowly developing disease resulting in morbidity and mortality among all age groups and sexes. The disease may be complicated with parasitism or poor condition of the flock. A case of cutaneous form of pigeon pox is presented.

Case History and Discussion

During March 2006, two local breed of pigeons were brought by local people to the dispensary with the history that they were found dead and lying along the roadside. On examination, they were found to be dehydrated and emaciated in nature. Several 0.5-1 cm diameter coalescing, round, yellowish, rough and firm masses were found at the eyelids, beak, and the mouth, and some were superficially ulcerated. Diphtheritic lesions were not found in birds. Histologic sections of skin containing the nodular lesions had cords and large clusters of markedly hypertrophic and hyperplastic epidermal stratified squamous epithelium, surrounded by dense fibroblastic stroma. Lesions consisted of swollen and pale keratinocytes with a foamy, vacuolated cytoplasm and single, round, dense eosinophilic intracytoplasmic viral inclusions (identified as Bollinger bodies). Inclusions distended the cell cytoplasm, producing cell necrosis. Some of them had clear, unstained, central rounded spaces. The superficial epidermis of the lesions was ulcerated with eosinophilic, amorphous keratinaceous crusts and necrosis.

On the basis of necropsy results, histopathologic features, and the presence of viral intracytoplasmic inclusions in epidermal cells, a diagnosis of poxvirus infection was made. In some cases, the diagnosis of a pox virus infection can be suspected by external clinical examination and gross lesions (Heuschele, 1986), but it is necessary to confirm the disease in the cutaneous form by the presence of characteristic Bollinger bodies in epithelial cells of epidermis observed in histopathologic analysis, by electron microscopy for viral particles in epidermal cells, or by virus isolation (Heuschele, 1986 and Randall and Reece, 1996). In this bird, gross lesions were compatible with an avian pox diagnosis, and this fact was confirmed by the histopathologic analysis performed on bird. An outbreak of pigeon pox involving eight local golla breed of pigeons in rural areas of Bareilly district was reported. Deaths in a few cases was recorded which might have been aided by heavy parasite load (Rajendra Singh et al., 1990).

Mortality and morbidity due to poxvirus infection may be very high in pigeons (Tripathy, 1991). Nevertheless, Pox virus is not fatal in all infected individuals, but it can reduce viability and predispose affected birds to predation, secondary infection, and accident (Reece, 1989). Thus Pox virus infection was an important, if not the direct, cause of death in bird.

by : M. Mohan and Trevor Francis Fernandez
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