Highly Pathogenic Avian Influenza: What Does it Mean for City Dwellers? Back »

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The emergence of highly pathogenic avian influenza (HPAI) in the spring of 2015 was devastating for many large turkey and egg layer farms, but the virus also affected smaller “household” flocks. City dwellers are increasingly turning to backyard poultry flocks for food as well as for the enjoyment of raising these animals. These producers, as well as other citizens who enjoy songbirds, gardening, and other activities in their urban backyards, have found themselves needing to bone up on this devastating disease. While the spring 2015 outbreaks have subsided, there is considerable worry about a reemergence of the virus in the fall. What should urban citizens know about highly pathogenic avian influenza?

What do we know – and what’s left to learn - about these highly pathogenic avian influenza viruses?

  1. They’re different from human influenza viruses. The influenza viruses prevalent during “cold and flu” season almost exclusively affect people and not other animal species. Similarly, these HPAI viruses exclusively affect birds. They have not caused illness in people – even those with close contact with a lot of affected birds.
  2. They’re especially severe for some – but not all – birds. The term “highly pathogenic” refers to strains of avian influenza that can cause severe and rapid illness and death in affected poultry. Of all the bird species studied, mallard ducks were found to carry the virus in large amounts while not becoming ill themselves. They (and likely other waterfowl as well) spread the virus through their droppings (influenza viruses in waterfowl tend to affect the digestive tract rather than the respiratory tract). Turkeys appear to be more severely affected than chickens. For these particular HPAI viruses, the role of other birds has not been well-studied. Songbirds and other non-waterfowl bird species are rarely carriers of avian influenza viruses in general, but have been implicated in the transmission of some strains of the virus.
  3. Wild game birds such as pheasants have been shown to be susceptible to HPAI and have been affected in at least one backyard poultry outbreak. To date, however, no infections or death losses have been detected in wild pheasants. It is not known if wild upland game birds are more resistant to HPAI, or whether they simply do not contract enough of the virus to cause illness and spread it to other pheasants.
  4. How the virus was carried to large turkey and chicken barns is still being studied. Because of the timing of the outbreaks and the ability for waterfowl to carry and spread large amounts of the virus, it’s generally accepted that those birds carried the virus in during their migration in the spring – or possibly last fall (there is evidence that the virus could survive up to months in the right weather conditions). Farms situated closer to water ponds and cornfields, where migratory birds spend time, tended to be more likely to succumb to an outbreak, especially after windy weather that could have blown contaminated material into barns.

The potential for avian influenza virus to come to town

Because of the presumed role that waterfowl play in HPAI transmission, anywhere wild ducks and geese congregate could be a potential source for the virus, shed in the birds’ droppings. This could include small lakes and ponds in urban parks, retention ponds, or housing developments adjacent to wetlands.

Citizens should keep in mind that these viruses have no effect on people, other animals, or the safety of food. A backyard playing host to children, pets, songbirds, and gardens will be unaffected – even if the virus somehow gets dropped or blown into that space.

A backyard playing host to chickens, ducks, or other domestic poultry is another story, however. Backyard poultry flocks have not been spared by HPAI outbreaks, and infections of poultry within city limits are possible – and more likely if the yard is near a site where wild ducks and geese spend time.

Protection for the backyard flock

Backyard poultry should be excluded as thoroughly as possible from contact with wild waterfowl. They should not be allowed access to nearby ponds or water sources that may have been contaminated by wild waterfowl species. If backyard flocks are housed near these areas, it may be prudent to provide a solid barrier between the poultry and the adjacent wetland, to prevent contaminated dust, snow, or plant material from blowing into the housing area.

Even if birds are physically kept away from these potential sources of HPAI, the virus can still enter their yard if people, vehicles, pets, or other animals are allowed to track in contaminated material from outside. Wheels, shoes, boots, and paws can all transport HPAI from one place to another if steps aren’t taken to clean and disinfect (or exclude) these materials.

All backyard flock owners should follow appropriate biosecurity measures. Examples of these rules, which are meant to exclude new potentially hazardous germs from entering a population of animals, can be found a the USDA Biosecurity For Birds website. If any unexplained death loss or illness occurs, a veterinarian should be contacted immediately.


We are learning more about the HPAI viruses that recently devastated poultry operations throughout the Midwest. But more remains to be learned. In addition, influenza viruses are notorious for changing. For these reasons, it’s important for all of us to keep abreast of current information regarding this pathogen, especially as wild bird migration commences this fall and next spring.

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