Avian Influenza

The first report on the isolation of the influenza virus from turkeys with respiratory signs was in the 1960s in the United States. Since then, several outbreaks caused by low-pathogenic (LP) and highly pathogenic avian influenza (HPAI) subtypes, that is, H1, H3, H5, H6, H7, and H9, have been observed in many countries worldwide. Differences in susceptibilities between turkeys and chickens have been identified. It was found that H7N2 was more infectious for turkeys than chickens. Sinusitis is a common sign in turkeys infected with LPAI. In addition, turkeys play an important role in the evolution of avian influenza viruses for several reasons: (i) Turkeys have both avian- and human-type receptors, making them highly probable mixing vessels for avian influenza viruses. Both avian-type and human-type receptors are expressed in the nasal cavity, lung, kidney, esophagus, and intestine. (ii) Turkey breeders especially can also be infected with swine influenza viruses such as H1N1, H1N2, and H3N2, causing a severe drop in egg production and severe economic losses as well as increasing the probability of reassortments and virus evolution in turkey hosts. (iii) Interspecies transmission of swine influenza viruses to turkeys is common. Interspecies transmission between ducks to turkeys has been reported but less frequently. Mixing different poultry species and outdoor rearing could favor the adaptation of LPAI viruses and pose a serious health risk.