Avian Influenza

Overview

Avian influenza (AI) is a highly contagious, reportable disease of chickens that is sporadically seen in backyard flocks. AI is caused by infection with type A influenza virus, which is a type of orthomyxovirus of the family Orthmyxoviridae. AI has a high pathogenicity (HPAI), and by H5 and H7 subtypes with low pathogenicity (H5/h7 LPAI).

AI has resulted in large economic losses in the worldwide poultry industry and is a continued threat to human health. AI viruses have been shown to naturally infect a wide variety of wild and domestic birds, especially free-living birds occupying aquatic habitats, such as waterfowl. Aquatic birds have been known to serve as a major reservoir of the influenza viruses, with the majority being low pathogenicity (low virulence) strains for chickens and turkeys.

Low pathogenicity avian influenza (LPAI) viruses cause the milder forms (mild respiratory signs) of avian influenza while highly pathogenic avian influenza (HPAI) viruses cause more severe forms (multi-systemic infections). Most birds infected with HPAI viruses do not survive but many infected with LPAI viruses can recover.

Clinical forms of AI range widely from low pathogenic (LPAI) to highly pathogenic (HPAI). Clinical signs can vary from a mild infection (chickens show loss of appetite, deceased egg production, mild respiratory disease, and diarrhea) for LPAI to severe respiratory, neurological, and gastrointestinal (GI) signs with HPAI (resulting in high mortality rates).

There is no specific treatment available for chickens with AI. The preferred method of diagnosis of AI in birds is through the use of rapid diagnostic methods, such as agar gel immunodiffusion (AGID) or rtPCR.

Transmission
AIV is transmitted through aerosol spread in the air, ingestion of influenza particles in nasal and respiratory secretions, fomites, or by direct contact with feces of infected birds.

Incubation Period
The incubation period is 3-5 days and is dependent on the dose of the virus, the route of exposure, the species exposed, and the ability to detect clinical signs.

Agent identification
Virus isolation is considered to be the "gold standard" in confirming that birds have been infected by the AI virus.