H5N8 is a subtype of the influenza A virus (sometimes called bird flu) and is highly lethal to wild birds and poultry.[1] H5N8 is typically not associated with humans. However, seven people in Russia were found to be infected in 2021, becoming the first documented human cases.[2][3]
The H5N8 virus manifests itself in various ways, from asymptomatic and sub-clinical to highly lethal in some populations. Many of the findings in wild birds are based on the discovery of dead animals. Its intravenous pathogenicity index (IVPI) is greater than 1.2, giving it a mortality rate of at least 75 percent.[4]
Perhaps the most known outbreak of H5N8 occurred in Ireland in 1983. Poultry on two farms showed the usual symptoms, plus diarrhea, nervousness, and depression. Poultry farms within close proximity soon began to show signs of infection, as well, but no contact between the farms could be established. In the end, 8,000 turkeys, 28,020 chickens, and 270,000 ducks were culled. When investigated in the lab, clinical findings demonstrated that turkeys were the most susceptible to infection. The virus could not be clinically reproduced in ducks.[6]
An outbreak of H5N8 was reported in breeding ducks in North Jeolla Province, South Korea, on 18 January 2014. The virus spread in duck and chicken farms and at least 12 million poultry were culled.[7]
In the second half of 2016, an H5N8 outbreak was first reported in Europe, spreading to Asia by the end of the year.[citation needed]
On 27 October 2016, an H5N8 case was first reported in a wild swan in Hungary. Further reports were subsequently made from seven additional European countries. There were outbreaks in poultry and wild birds in Austria, Hungary, and Germany. There were reports of infection in wild birds only in Croatia, Denmark, Poland, and Switzerland.[citation needed]