Analysis: Avian flu risk is greater downwind, APHIS says

Epidemiological studies show avian influenza is likely to beairborne, and poultry farms downwind of infected premises are at greater risk ofthe disease.

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Your avian flu risk mitigation check plan should include five things to help ward off the highly pathogenic avian influenza (HPAI) disease in poultry flocks.

The chief epidemiologist at the U.S. Department of Agriculture's (USDA) Animal and Plant Health and Inspection Service (APHIS) named five risk factors that should be checked in every poultry operation. Attending to these risk factors could help avoid an HPAI disease outbreak.

Speaking at the International Conference on Avian Influenza and Poultry Trade, Dr. Brian McCluskey flagged the risk factors based on the epidemiological investigations ongoing in farms that have contracted highly pathogenic avian influenza.

One surprising factor – airborne transmission of highly pathogenic avian influenza – involves a poultry farm’s location and may be more difficult to mitigate, short of filtering incoming air in the poultry house.

Plume modeling studies show increased downwind risk

Preliminary data from epidemiological models show that farms downwind of infected farms may be five to six times more likely to become infected with avian influenza. In other words, it appears that airborne transmission of the disease occurs.

“The data from the modeling studies allow us to answer the question of whether it is more risky to be inside a wind plume. The first modeling done shows that premises inside a plume are five to six more times likely to become infected than farms outside the plume. It certainly looks like airborne transmission might be happening,“ McCluskey said.

Wind plumes are polygons of 0.01 daily probability of transmission and 0.05 daily probability of transmission around infected premises. They were generated at various wind speeds using wind modeling and the exponential dose response model. The wind model estimates the concentrations from a point source given dispersion and particle settling processes. The potential exposure period assumed to be 14 days prior to clinical signs.

Four more factors for HPAI risk mitigation

McCluskey shared other risk mitigation factors identified in APHIS’ investigations of the HPAI outbreaks in 2015:  

  1. Sharing farm equipment between premises and poultry barns  is a leading culprit in spreading avian influenza in the outbreaks that have plagued the U.S. poultry industry in 2015. Even where attempts are made to clean and disinfect equipment, this factor is suspected of transmitting the disease.
  2. An audited biosecurity plan should be in place.  Having a biosecurity policy or manual on the premises means nothing if the plan is not followed. The plan should be followed at all times. If adherence to the plan is not routinely checked, the plan is suspect. Consider adopting third-party biosecurity audits.
  3. Are your poultry houses bird-proofed?  McCluskey said 62 percent houses in one series of outbreak investigations were bird-proof. Wild birds were observed in just about all the other houses. Small perching birds like sparrows and starlings can move the virus from one poultry operation to another.
  4. Vehicles moving on and off the poultry farm are a risk factor.  Feed truck network analysis is being done to determine if feed trucks might be moving the virus around, but vehicular movement poses risk. McCluskey said investment in equipment/facilities for the washing/spraying of vehicles moving on and off every farm will be worthy of consideration.

On-farm sampling for avian flu risk continuing

On-farm sampling for the avian influenza virus is being conducted by APHIS inside and outside turkey barns. The sampling, which supports the wind modeling studies, is done inside the houses, and at distances of 5 meters, 70 to 150 meters, and 500 to 1,000 meters.

“Virus is being pushed outside the barns, and this may be contaminating environments where people, trucks, birds, rodents move it to other barns,” he said.

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