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Mild strains of avian influenza may present no symptoms or will cause sick birds and low levels of mortality. Moderate drops in egg production or increased numbers of poor egg shells are additional symptoms in laying hen flocks. These symptoms can easily be confused with other small flock diseases such as Infectious Laryngotracheitis, Fowl Cholera or Infectious Bronchitis. Mortality can range from 0% to 20% over a period of several days to weeks. In flocks with other health problems such as worms or respiratory infections, half or more of the birds may die.
Strains that have mutated to a deadly form of avian influenza are obvious. It is not unusual for a deadly strain to kill half of your chickens or turkeys in 24 hours. In laying hen flocks, a dramatic drop in egg production is often the first sign. Chickens and turkeys may display respiratory or nervous signs or die suddenly without first appearing sick. Your ducks and geese may show little or no signs of illness with any form of avian influenza infection and often none will die.
Only submitting your birds to a veterinarian will tell you if the mortality or egg production problem on your farm is being caused by avian influenza. The signs of the disease vary too much from flock to flock for you to be able to make a home diagnosis.
In North America there are two major reservoirs or sources of avian influenza:
Unlike the strains of avian influenza native to North America, the Asian H5N1 strain can arrive in a form ready to kill chickens, turkeys and other gallinaceous birds. It does not need to cycle in a large flock of poultry before gaining the ability to kill large numbers of birds. This strain of virus can jump from wild waterfowl to your small flock of poultry and start to rapidly kill your birds immediately. This virus has spread from southeast Asia to Russia, Europe, Africa and the Middle East but has not yet been identified in North America.
The Asian H5N1 strain of avian influenza is a significant concern because it has demonstrated a very limited ability to infect people. If this strain mutates to a form that can readily infection people, the human health consequences could be severe.
Strains of avian influenza that have mutated into forms that kill large numbers of poultry can readily infect and kill chickens, turkeys, quail, guinea fowl, pheasants, pea fowl, and partridges. Some pet birds such as parrots and finches can also be very susceptible to the virus. There are contradictory reports as to whether wild sparrows or starlings will become sick or shed any virus. Wild and domestic geese may show some signs of illness such as difficulty walking and some deaths may occur. Ducks are highly resistant and will normally appear healthy if infected - although some cases of sick ducks have been observed with the Asian strain of the virus. Pigeons appear to resist most strains of the virus although some mortality due to the Asian strain has been reported. With the Asian strain of avian influenza, deaths have occurred in swans and a variety of other wild waterfowl.
For information on bird flu and people, read, "Avian Influenza," in the Q & A section of the Manitoba Health webpage on Pandemic Influenza. To find this and other avian influenza documents, visit www.gov.mb.ca/pandemic .
None of the human cases of "bird flu" reported world-wide have been associated with properly cooked eating chicken or eggs. Health Canada does recommend properly handling and cooking of eggs and poultry as a routine precaution (http://www.hc-sc.gc.ca/fn-an/securit/animal/avia-poul/index_e.html).
Dr. Wayne Tomlinson
Manitoba Agriculture, Food and Rural Initiatives