Pox

INTRODUCTION Pox is a slow-spreading disease characterized by the development of discrete nodular proliferative skin lesions on the nonfeathered parts of the body (cutaneous form) or fibrino-necrotic and proliferative lesions in the mucous membrane of the upper respiratory tract, mouth, and esophagus (diphtheritic form). A concurrent systemic infection may also occur.

ETIOLOGY Avian poxviruses (fowl, turkey, pigeon, canary, junco, mynah, psittacine, quail, sparrow, crow, peacock, penguin, alala, apapane, condor, and starling) are members of the genus Avipoxvirus of the Family Poxviridae. FPV is the type species of the genus.

Transmission Poxvirus infection occurs through mechanical transmission of the virus to the injured or lacerated skin. Individuals handling birds at the time of vaccination may carry the virus on their hands and clothing and may unknowingly deposit the virus in the eyes of susceptible birds.

Incubation Period Incubation period of the naturally occurring disease varies from about 4—10 days in chickens, turkeys, and pigeons and is about 4 days in canaries.

Clinical Signs The disease may occur in one of the two forms, cutaneous or diphtheritic, or both. The signs vary depending upon the susceptibility of the host, virulence of the virus, distribution of the lesions,and other complicating factors.

The cutaneous form of the disease is characterized by the appearance of nodular lesions on the comb, wattle, eyelids, and other nonfeathered areas of the body. Cutaneous eye lesions will interfere with the bird’s ability to reach food and water.

In the diphtheritic form (wet pox), cankers or diphtheritic yellowish lesions occur on the mucous membranes of the mouth, esophagus, or trachea with accompanying Coryza-like mild or severe respiratory signs similar to those caused by infectious laryngotracheitis virus infection of the trachea.

Diphtheritic FPV lesions in the mouth of a chicken

Cutaneous FPV lesions on the comb of a chicken.

Lesions in the corner of the mouth, on the tongue, throat, and upper part of the trachea interfere with eating, drinking, and breathing. In pullets coming into lay and in older birds, the disease often runs a slow course accompanied by unthriftiness and reduced egg production.

Gross The characteristic lesion of the cutaneous form of pox in chickens is a local epithelial hyperplasia involving epidermis and underlying feather follicles, with formation of nodules that first appear as small white foci and then rapidly increase in size and become yellow.

In the diphtheritic form, slightly elevated, white opaque nodules or yellowish patches develop on the mucous membranes of mouth, esophagus, tongue, or upper trachea. Nodules rapidly increase in size and often coalesce to become a yellow, cheesy, necrotic, pseudodiphtheritic, or diphtheritic membrane

DIAGNOSIS Microscopy Isolation and Identification of Virus Serology Differential Diagnosis Infectious laryngotracheitis

INTERVENTION STRATEGIES Management Procedures Types of Vaccines Vaccines of fowlpox and pigeonpox virus origin are routinely used for vaccination of chickens and turkeys in areas where the disease is endemic.

Vaccine Takes The flock should be examined about 7—10 days after vaccination for evidence of “takes.” A “take” consists of swelling of the skin or a scab at the site where the vaccine was applied and is evidence of successful vaccination.

The lack of a take could be the result of vaccine being applied to an immune bird, use of a vaccine of inadequate potency (after the expiration date or subjected to deleterious influences), or improper application.

In-ovo Vaccination. Recent success with in-ovo administration of FPV vaccines to 18-day-old chicken embryos has provided encouraging results