By Margaret A. Wissman, DVM, DABVP, Avian Practice
Q: Should I worry about pox in my pet birds?
A: Every spring, there are cases of pox in psittacine birds. This viral infection spreads via biting insects, such as mosquitoes, mites and other blood-sucking insects. It also spreads by direct contact with an infected bird; however, the virus cannot penetrate intact skin. It can enter the body only through a trauma to the skin (i.e. a cut or other open wound).
Prevention is the best defense for our pet birds against psittacine poxvirus.
Poxviruses are extremely stable in the environment; they survive outside of the host body on inanimate objects, such as perches, contaminated gloves and enclosures. The virus can be transmitted through one of these infected surfaces.
Many poxvirus strains occur worldwide. Infections were documented in free-ranging and captive populations of Passeriformes, Falconiformes, Columbiformes and Anseriformes.
Avipoxvirus is thought to be a variant of the original poxvirus. Although all avian poxviruses are similar, they do exhibit host specificity. For example, there is canary poxvirus, pigeon poxvirus, magpie poxvirus, Agapornis poxvirus, fowl poxvirus, quail poxvirus and psittacine poxvirus, each named based on the type of bird that it infects. Some strains infect only one species, while other strains can infect several species.
Poxviruses tend to cause the worst disease in the natural host. For example, a psittacine poxvirus isolate that is dangerous for Amazon parrots might cause only mild disease in chickens. In some cases, birds infected with one strain of virus will be protected from infection by another strain.
Lesions tend to vary depending on the species of bird and the time of year. Lesions occur most commonly during periods of high rainfall and therefore during times when mosquitoes are most prevalent.
Some pox lesions are readily visible. In the cutaneous form, lesions appear in the skin as discreet nodules on unfeathered skin (also called “dry” pox). With the “wet”or diphtheritic form, lesions usually occur on mucous membranes (mouth, trachea, esophagus). Diphtheritic lesions might occur in the hard palate, larynx, pharynx, bronchi, crop or conjunctiva. These appear as cheesy-looking lesions.
Many birds recover from the cutaneous form. The wet form, however, is much more dangerous, especially when secondary infections with bacteria or fungi invade the already debilitated bird.
Many believe some birds that survive pox develop persistent infections and intermittently shed the virus from the GI tract, skin or feathers. This could explain periodic outbreaks in aviary birds housed outdoors.
Diagnosis occurs in several ways. The virus may be isolated by growing it in cell culture; it can be demonstrated using electron microscopy; the microscope can be used to look for the presence of characteristic Bollinger bodies; or classic lesions can be found on biopsy and staining of the tissues.
There is no specific therapy for poxvirus infections. Treatment is supportive care only. Infected birds should be isolated.
Vaccination is the best way to prevent poxvirus infection in the species for which an effective vaccination is available. Vaccines are available for pigeons, chickens, turkeys, canaries, quail, waterfowl and falcons. If possible, prevent pet and breeder birds from having exposure to wild birds that might be carriers or ill with a poxvirus infection. Pox isn’t likely to go away. Prevention is your best bet.