Avian pox (AP) is a viral disease of birds caused by a member of the poxvirus family. It is a widespread disease that is found in a large number of bird families and is naturally occurring in North America. There are different AP strains. Most are species specific - that is, each strain infects a certain species or group of birds. However, strains have been known to cross family groups and infect new individuals. To date, there is no evidence that AP can infect humans. Avian Pox is a slow-developing disease that generally causes mild/moderate skin lesions and rarely causes death. These lesions mostly occur on the featherless regions on the face, legs and feet. However, when AP affects the mucous membranes in the oral cavity or respiratory tract, respiration can be impaired and result in death. The first reported case of a Bald Eagle infected by poxvirus was in 1979 from Alaska and was a lethal infection. The first reported case of poxvirus in a Bald Eagle in Virginia was in 1981.
There are three different clinical forms of the disease:
- 1. Cutaneous form or "dry pox". This is the most common form in raptors and is the presentation seen in the Norfolk Botanical Gardens Bald Eagle;
- 2. Diphtheritic form or "wet pox". This form infects the mucosa of the oral or respiratory tract;
- 3. Septicemic (generalized) form. This form is rare and is seen more often in canaries, causing depression, anorexia and death in the majority of cases.
Transmission of avian pox virus occurs only when active virus particles enter the body of a susceptible host through a breach in the skin. The most common form of transmission is by mechanical transfer of the virus by biting insects after they have fed on an infected bird and then bite a susceptible individual. The virus may also be transferred by means of direct contact with an infected animal, contaminated objects (bird feeders, perches, nesting material), or by aerosol particles. Avian pox virus is very resistant to environmental degradation and can survive for years in dry scabs or in dry surfaces. For this reason, it is extremely important to install quarantine procedures when treating infected animals and consider these patients highly contagious. These precautions will help prevent other susceptible animals from becoming exposed. This is a very important protocol in hospital settings where thousands of animals come through every year.
CUTANEOUS FORM OR DRY POX CLINICAL SIGNS
The cutaneous form of AP is characterized by proliferative wart-like lesions on the unfeathered parts of the bird, such as the beak, eyelids, nostrils and the legs and feet. Clinical signs start as a red swelling that eventually cracks to become raised lesions. These lesions are usually self limiting and may persist from 1 week up to 4. In the last stages of development, lesions are very susceptible to trauma, resulting in hemorrhage and tissue death, thus permitting the entrance of opportunistic bacteria and fungi. In severe cases both skin and mucus membranes can be affected. Regression of the lesions generally occurs between 4 or 6 weeks after the first clinical signs appeared and correlates to the growing ability of the immune system to attack the virus. Once lesions begin to heal the abnormal epithelium will slough. Many birds recover with few or no permanent defects; however, young birds are usually more severely affected than adults. In some instances the lesions can cause permanent damage to the affected areas including blindness, beak malformations and loss of toes and feet. Following infection, lifelong immunity is thought to occur to that strain of virus.
Diagnosis is first suspected based on clinical signs but must be confirmed by microscopic examination of the affected tissue.
PREVENTION AND TREATMENT
Therapy is usually non-specific, meaning that the clinician must provide supportive care until the patient's immune system can respond to the infection. There is no "cure" for this disease. Supportive care consists of fluid therapy, balanced nutrition, decreasing stress levels, and pharmaceutical treatment for secondary bacterial or fungal infections. The lesions must be kept clean and disinfected, usually with an iodine-based solution. Other supportive treatments include Vitamins A and C which assist in skin repair, and other antiviral agents that work by boosting the patient's immune system. Although there is a vaccine for the chicken-pox strain, further investigation of the efficacy and benefits of this vaccine in raptors is needed. Prepared by Wildlife Center of Virginia Extern Dr. Ana Ródenas Martín