Filariasis in Poultry

Microfilariae are commonly found in the blood of some wild bird species. In poultry, however, they are rare to absent, except in Southeast Asia, where subclinical infections in chickens and domestic waterfowl occur.

The prevalence of microfilariae in wild birds generally varies from 3% to 6%; however, it can be as high as 20% in some species, such as ptarmigan, swans, and geese. The prevalence of microfilariae in pet birds has changed. Before 1992, when importing psittacines into the US was legal, it was not unusual to observe microfilariae in the peripheral blood of imported birds, especially imported cockatoos. Now that psittacines are no longer imported into the US but are bred domestically, it is unusual to see microfilariae in their blood in the US.

Avian filarioid nematodes are classified in the family Onchocercidae, in the superfamily Filarioidea, with 16 genera. All have an indirect life cycle, and bloodsucking insects (eg, lice, mosquitoes, midges) serve as intermediate hosts. Adult nematodes mature in body cavities, including the eye and ventricles of the brain, respiratory system, cardiovascular system, and connective tissues; some produce characteristic subcutaneous nodules.

Microfilariae can be numerous in circulation, especially in the skin vasculature. Microfilariae can be observed in blood smears. However, a buffy coat smear obtained from a microhematocrit tube is a more sensitive diagnostic method. Increased numbers of microfilariae have been reported in stressed individuals; however, they rarely cause clinical signs or death.

Possible exceptions in domesticated birds include the infection of emus with Chandlerella quiscali (a common filarid of the brain in free-living grackles) and the infection of geese and swans with Sarconema eurycera (syn Splendidofilaria eurycera).

Emus infected with C quiscali show signs of CNS disease (eg, torticollis, ataxia), and they have encephalitis with necrosis and C quiscali adults in lesions. C quiscali apparently does not produce microfilariae in emus.

Adults of S eurycera are found in the epicardium and myocardium of infected birds and can cause myocardial injury and inflammation.

Treatment with ivermectin, fenbendazole, or levamisole, along with surgical removal of adult parasites, has been used to treat filarial infections in birds. Local guidelines must be followed for appropriate withdrawal and residue avoidance times.