By Lingying Zhao
While we are still in the COVID-19 pandemic, a “bird flu” outbreak caused by Avian Influenza (AI) virus started initially among wild birds and then domestic poultry in February of this year. The AI viruses have two strains: low-pathogenic (LPAI) or high-pathogenic strains (HPAI). HPAI strains are highly infectious, result in high mortality rate of birds, and can spread rapidly. The strains currently spread in the U.S. are HPAI. So far, the HPAI outbreak has affected 372 flocks of 40.09 million birds in 36 states. Once the HPAI is detected on a farm, all of the birds need to be depopulated. One farm in Iowa had nulled more than 5M birds after detection of the HPAI virus. HPAI outbreak have resulted in significant economic losses and is trigging concerns of animal health, food safety, and human health. Vaccine is under development, even though significant challenges still exist for development of vaccine effectively targeting the incoming HPAI strains. Biosecurity control is crucial, current USDA biosecurity measures cannot effectively stop transmission of the HPAI virus.
For effective controls of HPAI, let’s first review the scientific facts related to the HPAI virus. First, HPAI viruses like cool and moist conditions, especially with presence of organic materials. The World Organization for Animal Health (OIE) has demonstrated AI viruses can live for extended periods in water, dry and wet feces, and soil at ambient temperatures. Conversely, hot and dry conditions can quickly inactivate AI viruses.
HPAI viruses spread through direct contact among birds, indirect contact through a contaminated environment, such as equipment, clothes and shoes, animal bedding, manure, water, feed, farm equipment.
Based on the above understandings, the following biosecurity measures and engineering control strategies are suggested by USDA Animal and Plant Health Inspection Service (APHIS) to prevent and control HPAI spread in poultry production.
Current USDA APHIS’s biosecurity measures include structural biosecurity and operational biosecurity. Structural biosecurity measures use physical construction and maintenance to prevent wildlife access to the poultry facilities, water surfaces, and land surfaces via a series of specific strategies (https://www.aphis.usda.gov/animal_health/downloads/animal_diseases/ai/hpaifactsheet_wildlife-biosecurity.pdf).
Operational measures implement practices and policies, such as preventing contact with wild birds, reducing visitors, washing hands before and after contact with birds, providing disposable boot covers and/or disinfectant footbaths for workers and visitors, changing clothes before entering and exiting poultry facilities; cleaning and disinfecting tools or equipment before moving them to a new poultry facility, looking for signs of illness, and reporting sick birds (https://agri.ohio.gov/divisions/animal-health/resources/02.25.2022HPAIUpdate).
Once infected, depopulation will be implemented in a short period. Thorough cleaning of the animal facilities to remove any biomaterials out of the poultry facilities is crucial. During dry and/or wet cleaning, precautions are needed to not aerosolize the virus.
Then heat poultry houses to raise room temperature to 100- to 120-degree F for 7 days with at least three consecutive days to eliminate virus from the infected animal facilities.
Drying and heating are effective to destroy/eliminate the virus. Finally, proper
disposal of poultry litter and/or manure through composting process is also crucial to prevent spread of the virus.
One important virus transmission path, that has been overlooked, is the airborne transmission of the virus. Like COVID-19, the HPAI viruses can also be airborne that transmit by droplets and/or dust particles generated through bird flapping wings, scratching surfaces, shaking head, and dropping manure by infected wild birds or infected domestic birds in poultry facilities. The virus attached to droplets or dust particles can be transported over long distances and stay alive for long periods of time depending on the initial velocities and sizes of the droplets or dust particles, and the ambient environmental conditions (airflow speed, air temperature, and relative humidity).
Most large layer operations use enclosed buildings with automatic environmental control systems. It is hard for domesticated birds to have direct contact with wild birds. However, many incidences of HPAI infections had happened in the past four months in fully enclosed poultry facilities with modern environmental control systems. After the USDA APHIS’s biosecurity measures are fully implemented, the only virus transmission path left is airborne transmission of the HPAI through dust laden air stream passing through the air inlets of the buildings. This hypothesis may explain the reason for the fact that in this year, the infection occurred sporadically on farms with no links between the infected farms. During a meeting of United Egg Producers (UEP), some farmers also thought their layer houses are infected by dust laden inlet air stream and requested air cleaning and disinfection technologies to be developed. UEP also advises farmers to avoid creating dust around the farm and louvers on exhaust fans and air inlets of barns.
The Air Quality and Bioenvironmental Engineering Lab at The Ohio State University (OSU) has been conducting research to optimize electrostatic precipitation-based technologies to control duct emissions in commercial poultry facilities over the past five years. We have developed electrostatic precipitators and electrostatic spray scrubbers to mitigate dust emission from manure-belt layer houses. An interesting side effect of the electrostatic precipitation dust control technologies is their varied capacities for pathogen control. We are proposing research projects to the USDA Sustainable Agricultural Systems Grant program to further optimize the electrostatic precipitation technologies for HPAI virus deactivation, especially at the air inlets of the poultry building to protect the layer facilities from virus infection during the HPAI outbreak. More and more frequent outbreaks of HPAI and other airborne diseases demand new pathogen control methods to be developed to better protect the economic interests of poultry facilities and the health of birds.
In summary, High Pathogenicity Avian Influenza (HPAI) virus has had two major outbreaks in the United States in the last decade alone. These outbreaks have caused the depopulation of tens of millions of birds and costed the poultry industries billions of dollars. HPAI viruses like cool and moist conditions and could be potentially airborne. Current USDA APHIS’s biosecurity measures cannot stop the spread of HPAI effectively. We may have overlooked one important virus transmission path, airborne transmission. Many incidences of the current on-farm infections indicate the possibility of airborne transmission of HPAI. OSU is proposing research to the USDA Sustainable Agricultural Systems Grant program to optimize electrostatic precipitation technologies for airborne HPAI pathogen control.
Lingying Zhao, Professor and Extension Agricultural Engineer, can be reached at firstname.lastname@example.org. This column is provided by the OSU Department of Food, Agricultural and Biological Engineering.