Hosts

More avian influenza viruses have been isolated from ducks than any other species although most free-flying birds may also be infected including shorebirds, gulls and other seabirds. Waterfowl are more resistant to avian influenza than are domestic poultry. Viruses that cause no obvious disease in waterfowl can be highly pathogenic (rapidly fatal) in domestic poultry. Among domestic poultry species, turkeys are more commonly infected than are chickens.

Transmission

Waterfowl act as a reservoir of avian influenza virus by carrying the virus in their intestinal tract and shedding it in their feces. Avian influenza viruses are spread to susceptible birds through inhalation of influenza particles in nasal and respiratory secretions and from contact with the feces of infected birds.

Signs of disease

Signs of avian influenza are extremely variable. In some flocks the only evidence of the infection is seroconversion i.e., the birds develop a detectable antibody titer to AI. AI can also be manifest as respiratory, enteric, reproductive or nervous system disease. Decreased food consumption and drops in egg production are among some of the earliest and most predictable signs of disease.

Signs including coughing, sneezing, ruffled feathers, swollen heads, nervous signs like depression, and diarrhea may occur together or singly. In some cases, birds die rapidly without clinical signs of disease.

Prevention and control

Wild birds and their excreta should be considered a major source of avian influenza. Preventing direct contact with free-flying birds and protecting domestic poultry from contact with the feces of wild birds is an important way to prevent avian influenza.

Live bird markets have been an important source of avian influenza, especially on the East coast of the U.S. It is important to avoid live markets, educate employees about the dangers posed by these markets, and prevent the spread of disease from these markets to your flock by preventing any contact.

Infected birds shed virus in saliva, nasal secretions and feces in the first two weeks of infection. Four weeks after infection, virus can no longer be detected. Hence, prevention is best accomplished by preventing contact between newly infected and susceptible birds. Biosecurity is a first line of defense (see Biosecurity for Poultry Flocks, J. Jeffrey, UC Davis Extension Poultry Veterinarian. Avian influenza can be spread from infected birds through the transfer of feces especially on contaminated equipment and clothing. Controlling the traffic between infected and uninfected birds is essential.
Cleaning and disinfection

Influenza viruses are very sensitive to most detergents and disinfectants. They are readily inactivated by heating and drying. However, flu viruses are well-protected from inactivation by organic material and infectious virus can be recovered from manure for up to 105 days. Complete removal of all organic material is part of any effective disinfection procedure.

Contaminated houses are heated for several days to inactivate virus. Organic material is removed followed by complete cleaning and disinfection of all surfaces. Contaminated litter and manure is problematic and should be composted or buried to ensure that it does not spread infectious virus.

Frequently asked questions

1. Are the flu viruses of human and birds the same?

In most cases, the influenza viruses that infect birds do not infect humans and vice versa. However, in Hong Kong in 1997, a unique avian influenza virus infected both chickens and humans. This is the only time an avian influenza virus has ever been transmitted directly from birds to humans. This appears to have been a totally unique occurrence. The World Health Organization continuously monitors human influenza viruses isolated from cases all over the world. No avian viruses have been found infecting humans since 1997.

2. What are the risks of getting avian influenza from waterfowl?

Avian influenza virus infections are widespread in wild birds, especially ducks. Migrating waterfowl are a significant source of avian influenza viruses especially in the major flyways. Turkeys on open ranges in Minnesota, a state in the major flyway for migrating ducks, frequently experience avian influenza problems. But the prevalence of avian influenza in turkeys has been high in some years and minimal in others. The reason why influenza viruses come and go is not known. The risk to susceptible birds from contact with waterfowl must be considered very high although it may vary from year to year for unknown reasons.

3. Why can't I prevent infection by vaccinating my flocks?

Vaccines effectively prevent clinical signs of influenza infections in many species including poultry. However, the vaccines are not cross-protective for the 15 virus subtypes that can infect poultry. Since there is no way to predict which type will infect a flock, vaccines are generally not practical to prevent infections.

4. What should I do if I suspect avian influenza in my birds?

You should contact your veterinarian if you observe any of the signs of avian influenza, especially if they are accompanied by a drop in feed consumption and/or a significant drop in egg production. Because the signs of avian influenza are so variable, it is important to get the help of an expert for diagnosis.

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