Avian influenza in poultry
Avian influenza is a viral disease affecting the respiratory, digestive and/or nervous system of many species of birds. Avian influenza virus infection can occur in most, if not all, species of birds, both domestic and wild. Influenza viruses vary widely in their ability to cause disease (pathogenicity) and their ability to spread among birds. Wild species of birds usually do not develop clinical disease, but some influenza viruses cause severe illness or death in chickens, turkeys and guinea fowl.
A highly pathogenic form of avian influenza was known as "fowl plague". It first appeared in Italy more than 100 years ago (around 1878). Pathogenic avian influenza was first recognized in the United States in 1924-25. It occurred again in 1929. It was eradicated both times.
A major epidemic of highly pathogenic avian influenza occurred in the northeastern United States in 1983-84. It took more than 2 years to eradicate, at a cost of more than 70 million dollars. Approximately 17 million birds had to be destroyed during the eradication effort.
The United States has not had a major outbreak of highly pathogenic avian influenza since 1986, although less pathogenic strains of avian influenza virus are present and have caused significant losses in the poultry industry. Another major outbreak of highly pathogenic avian influenza would be disastrous to the American poultry industry.
In 1996-97 a number of table-egg farms in Lancaster and Lebanon Counties, PA tested positive for H7N2 avian influenza. Thus far, the avian influenza virus which has been detected by serologic means and/or virus isolation has been characterized as nonpathogenic to chickens, but the outbreak has had devastating effects on the local poultry industry. Between the first week of December 1996 and June 6 1997 nine flocks were depopulated. The Pennsylvania Agricultural Department imposed a quarantine on a 75-square-mile area restricting movement of poultry or poultry products into or off of operations in the area of the quarantine.
The severity of the disease ranges from inapparent (mild) to rapidly fatal. Lethal strains of the virus can strike so quickly, particularly in young chickens, that there may be no clinical signs other than sudden death.