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Animal Health at the Crossroads: Preventing, Detecting, and Diagnosing Animal Diseases
TABLE 3-2 Timeline of Key Influenza Events
Fowl plague (FP) was described as a serious disease in chickens in Italy.
Spanish flu (influenza A) pandemic claimed 20 to 50 million lives worldwide in less than a year and ranks among the worst disasters in human history. In the United States alone, an estimated 1 in 4 people became ill and 675,000 people died (Crosby, 1989). Recent studies now suggest this historic pandemic was associated with interspecies transmission of an avian influenza virus (Hampton, 2004; Stevens et al., 2004).
Fowl plague virus was determined to be one of the influenza viruses.
Outbreak of avian influenza virus H5N2 in poultry in the Northeast United States. It initially caused low mortality, but within 6 months had mutated to a highly pathogenic virus causing nearly 90 percent mortality. The outbreak cost over $65 million and resulted in the destruction of 17 million birds.
An avian influenza virus H5N2, identified as “low pathogenecity” in Mexico, mutated to a highly pathogenic form and continued to spread until 1995. In 1999, an Italian H7N1 virus had a similar pattern of mutation over a 9-month period and was not controlled until 2001. The 2001 Italian losses are estimated at 13 million birds.
The first documented AI infection of humans occurred in Hong Kong when the H5N1 strain caused severe respiratory disease in 18 humans, of whom 6 died. Extensive investigation determined that close contact with live infected poultry was the source of the human infection. Studies at the genetic level further determined that the virus had jumped directly from birds to humans but had only very limited human-to-human spread.
concern because it mutates rapidly and has a documented propensity to acquire genes from viruses infecting other animal species (WHO, 2004). The majority of avian influenza viruses have low pathogenicity, typically causing little or no clinical disease in infected birds, particularly migratory waterfowl, which serve as a reservoir of the virus. The highly pathogenic strains may be associated with mortality close to 100 percent (Easterday et al., 1997; WHO, 2004). The highly pathogenic influenza virus subtypes can cause significant economic losses to poultry, impinge on international trade, and, if transmitted to humans, pose public health risks with the potential to initiate deadly human influenza pandemics. The virus is additionally considered a potential biothreat agent based on its abil-