Systematic Veterinary Virology

PATHOGENESIS

• Host affected
  • Many avian species are affected by AI. Certain subtypes of virus may infection predominantly in any one of the species of birds. AI has been reported in chickens, turkeys, ducks, waterfowls, gulls, shorebirds etc.
• Transmission
  • Migratory waterfowl, sea birds, or shore birds are considered responsible for introducing the virus into poultry. Waterfowl serve as reservoir for AIV.
  • Virus is found in large quantities in faeces and respiratory secretions of infected birds. The virus spreads to susceptible birds through inhalation of influenza particles in nasal and respiratory secretions and from contact with the faeces of infected birds. 
  • Once introduced into a flock, the virus spreads from flock to flock by the movement of infected birds, contaminated equipment, egg flats, feed trucks, and service crews etc. The infection spreads through shared and contaminated drinking water.
  • Airborne transmission may occur if birds are in close proximity and with appropriate air movement. Vertical transmission is not completely established. There is also no vector involvement in the transmission of infection.
• Incubation period
  • The incubation period is usually 3 to 7 days, depending upon the subtype of virus, the species, and age of the bird.
• Morbidity and mortality
  • Morbidity and mortality rates are upto 100 percent within 2 to 12 days after the first signs of illness in HPAI.