Avian Influenza: Fact Sheet

Cause:

• Type A influenza viruses (many subtypes and continual evolution by genetic drift and shifts)
• Accumulation of mutations and mixing of genes between viruses can move virus from low pathogenicity to high pathogenicity

Species Affected:

• Many bird species (more than 60 species of reports of domestic, wild, captive and experimental birds are taken into account)
• Influenza viruses in wild birds historically has had low pathogenicity for other species
• Most often found in migratory waterfowl, especially juvenile mallard ducks

Source:

• Inapparent low pathogenicity avian influenza viruses circulate in healthy wild birds
• Once low pathogenicity wild bird avian influenza viruses mixes in flocks of domestic poultry, the virus has the potential to change to a highly pathogenic form, capable of killing chickens, wild birds and potentially infecting humans

Transmission:

• Fecal-oral transmission in wild bird populations
• Birds maintain the virus in these populations
• Potential for respiratory transmission

Distribution:

• Avian influenza viruses with low pathogenicity occur in wild bird populations throughout the world
• Highly pathogenic H5N1 avian influenza virus is currently found in poultry and some wild birds in Asia, Europe, and Africa

Field Signs:

• Sub-clinical infections
• Prior to the emergence of H5N1 Highly Pathogenic Avian Influenza virus, the only documented avian influenza mortality event in wild birds was in common terns in South Africa in 1961

Diagnosis:

• No gross lesions in wild birds infected by traditional avian influenza viruses
  
• Definitive diagnosis made by virus isolation from cloacal swabs and histopathology confirming cause of mortality
• Serology testing for antibody used to determine exposure

Prevention and Control:

• No effective control for wild bird species
• Domestic Poultry Operations Prevention Measures:
1. Prevent virus entry into flocks as first line of defense
2. Minimize contact between domestic poultry and wild birds
3. Good biosecurity and hygiene
4. Vaccination
• Domestic Poultry Operations Control Measures:
1. Depopulation
   
2. Proper clean-up of all dead poultry and disinfection of cage equipment
3. Quarantine of affected regions
4. Stop illegal movement and smuggling of birds

Human Heath Concerns:

• At the time of publication of the Field Manual of Wildlife Diseases (U.S.G.S), 1999: 'the strains that infect wild birds do not infect humans'. Since the late 1990s, unique related avian influenza viruses have circulated in domestic poultry in Asia. These viruses have infected and caused mortality in humans, wild birds and other species in close contact with infected poultry.
• No known human infection from avian influenza virus of a wild bird origin

Domestic Animal Health Concerns:

• Domestic poultry are at risk for disease.