Can animals shed the virus before clinical signs are observed?
"Shedding," as it applies to viruses, means that the animal's secretions and/or droppings contain viral particles that may infect other animals or people. Some animals (i.e., growing poultry) rapidly show clinical signs of disease and simultaneously shed virus.
Other animals, including some species of waterfowl, may appear clinically healthy, but are shedding the virus, which is the reason that surveillance of waterfowl for early detection of influenza viruses along the major flyways is an important measure to prevent outbreaks of disease in commercial poultry.
The incubation period is the time that passes between when the bird first gets infected and the appearance of clinical signs of disease. The incubation and shedding periods for avian influenza virus in many species are not known.