Avian influenza, commonly known as “bird flu”, is a highly contagious viral disease affecting several species of birds. There are two main types of avian influenza viruses that cause disease in poultry – low pathogenic avian influenza (LPAI) and highly pathogenic avian influenza (HPAI). HPAI viruses are extremely virulent, often fatal to chickens and turkeys, and can spread rapidly through flocks.
When an outbreak of HPAI occurs on a poultry farm, emergency measures are implemented to contain and eradicate the disease. A key part of controlling avian flu outbreaks is establishing a control zone around infected premises. This article will provide an overview of avian influenza control zones, including:
What is a control zone?
How big are control zones?
What measures are implemented in a control zone?
How long do control zones last?
Conclusion
What is a control zone?
A control zone, also known as a movement restriction zone, refers to an area surrounding an infected poultry farm where disease control measures are established to prevent further spread of avian influenza. The boundaries of the control zone are based on epidemiological factors concerning the outbreak.
Within the control zone, movement restrictions and biosecurity protocols are put in place. These aim to control the disease by limiting the spread of potentially infected poultry, equipment, and personnel.
Control zones provide a detailed focus area for disease surveillance, cleaning and disinfection, and tracing of contacts. They enable veterinary authorities to implement tightened biosecurity and conduct extensive testing around infected premises to ensure no further spread has occurred.
Establishing control zones is an important strategy mandated by the World Organisation for Animal Health (OIE) in responding to significant animal disease outbreaks. Most countries have regulations allowing control zones to be declared rapidly around infected premises during avian influenza outbreaks.
How big are control zones?
The size of an avian influenza control zone can vary depending on the epidemiology of the outbreak, density of poultry farms, and geographical factors. Control zones are typically measured in kilometers starting from the infected farm(s).
According to the United States Department of Agriculture (USDA), a minimum control zone extends outward at least 3 km (1.9 miles) from the perimeters of the quarantined infected premises.
However, many control zones are much larger than this minimum size. For example, during the 2014-2015 HPAI outbreak in the U.S. Midwest, control zones covered between 6.2-10 km (4-6 miles) around infected farms.
The larger the control zone, the more poultry farms fall within the restricted area. But larger zones may be necessary to control spread based on features like proximity of farms, connections between premises, and movements of workers and equipment.
The following table provides some examples of avian influenza control zone sizes from around the world:
Country | Control Zone Size |
---|---|
United States | Minimum 3km (1.9 miles) |
United Kingdom | Minimum 3km, up to 10km based on risk assessment |
Netherlands | Minimum 1km, often 3-10km |
Canada | Minimum of 3km, up to 12km |
Australia | Minimum 10km |
As shown, control zone sizes vary but are typically between 3-10km around infected premises. Larger zones over 10km may be established in areas with high farm density. The boundaries are determined by animal health authorities based on the specific situation.
What measures are implemented in a control zone?
Once a control zone is established, strict biosecurity protocols and movement restrictions come into force to contain the disease. Some of the key measures include:
Movement restrictions
– Poultry and egg movements within, into, and out of the control zone are banned. Exceptions may be permitted under license for slaughter or disposal only.
– Movements of poultry equipment, vehicles, and non-essential personnel are prohibited.
– Movements of other livestock, animal feed, bedding, and supplies are tightly controlled.
Increased monitoring and testing
– Extensive avian influenza testing required on all poultry farms within the control zone, regardless of clinical signs.
– Daily monitoring and recording of bird health status and mortality.
– Testing of wild birds in the control zone area.
Biosecurity requirements
– All poultry must be housed or kept separate from wild birds.
– Strict biosecurity protocols enforced for all entries, exits, sanitation, and personnel protection.
– Vehicles and equipment must be thoroughly cleaned and disinfected when entering or leaving farms.
– Poultry litter, manure, and waste tightly controlled.
Continued surveillance
– Public awareness campaigns on biosecurity.
– Tracing and sampling of all dangerous contacts.
– Ongoing reassessment of control zone boundaries and restrictions.
These measures aim to thoroughly contain and eliminate the virus within the high risk control zone area.
How long do control zones last?
Avian influenza control zones remain in place until the outbreak is deemed resolved and the risk of further spread is minimized. This means control zone restrictions can sometimes last for several months.
The World Organisation for Animal Health (OIE) provides guidelines that a control zone should be maintained for a minimum of 21 days after preliminary cleaning and disinfection of the infected premises.
However, the zone is typically maintained much longer – usually until the following conditions are met:
– No further cases detected within 42 days (twice the maximum incubation period of avian influenza in birds).
– All poultry farms within the control zone test negative for the virus.
– Trace-back and trace-forward of all potentially infected contacts show no further spread.
– Thorough cleaning, disinfection, and surveillance have been completed on all at-risk premises.
– The risk assessment indicates infected wildlife pose no further threat.
The control zone is then lifted in phases, with the highest risk areas closest to the infected premises continuing restrictions until the very end.
Some particularly extensive avian influenza outbreaks can result in control zones in place for 6 months or longer before authorities feel the risk has diminished enough to lift restrictions. However, most control zones last approximately 1-3 months from the initial detection before stepwise relaxation of measures can begin. The prolonged restrictions and work involved highlights how seriously veterinary services take controlling avian influenza outbreaks.
Conclusion
Avian influenza control zones are critical disease containment measures implemented around infected poultry facilities. A control zone establishes strict movement restrictions and biosecurity protocols for a designated area surrounding the outbreak. This prevents further spread of infection via birds, people, equipment, vehicles or other materials. While initial control zones are often at least 3km, larger zones may be required based on the disease epidemiology and characteristics in the region. Within the control area, extensive surveillance, testing, monitoring, cleaning and disinfection take place until the disease risk is reduced. Although economically and logistically challenging, control zones have proven a necessary strategy in controlling avian influenza and preventing a wider scale epidemic. While control zones typically last for several months, the long duration is vital to ensure no vestiges of the virus remain to potentially re-ignite the outbreak.