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Influenza A (H7N7) virus

H7N7 is a subtype of Influenzavirus A, a genus of Orthomyxovirus, the viruses responsible for influenza. Highly pathogenic strains (HPAI) and low pathogenic strains (LPAI) exist. H7N7 can infect humans, birds, pigs, seals, and horses in the wild; and has infected mice in laboratory studies. This unusual zoonotic potential represents a pandemic threat.

In 2003 in the Netherlands 89 people were confirmed to have the H7N7 influenza virus infection following an outbreak in poultry on several farms. One death was recorded. Antibodies were found in over half of 500 people tested according to the final official report by the Dutch government:
"As at least 50% of the people exposed to infected poultry had H7 antibodies detectable with the modified assay, it was estimated that avian influenza A/H7N7 virus infection occurred in at least 1000, and perhaps as many as 2000 people. The seroprevalence of H7 antibodies in people without contact with infected poultry, but with close household contact to an infected poultry worker, was 59%. This suggests that the population at risk for avian influenza was not limited to those with direct contact to infected poultry, and that person to person transmission may have occurred on a large scale. Final analysis of Dutch avian influenza outbreaks reveals much higher levels of transmission to humans than previously thought."

In August 2006, low pathogenic (LP) H7N7 was found during routine testing at a poultry farm in Voorthuizen in the central Netherlands. As a precautionary measure, 25,000 chickens were culled from Voorthuizen and surrounding farms.

In June 2008, high pathogenic (HP) H7N7 was confirmed on a 25,000-bird laying unit at Shenington, England; probably derived from a pre-existing low pathogenic variety. "Increased mortality (2.5 per cent in one shed) and a drop in egg production had been recorded two weeks before birds started dying in large numbers on June 2, leading to the diagnosis of HP H7N7 on June 4."

In October 2009, high pathogenic (HP) H7N7 was confirmed on a farm in Almoguera, Guadalajara, Spain. Hong Kong announced that it would suspend the import of poultry from Spain.