LONDON – Low pathogenic avian influenza (LPAI) H7N7 viruses mutated to highly pathogenic viruses in the most recent outbreak of avian influenza in the United Kingdom, the Department for Environment, Food and Rural Affairs reported. Defra reported the finding in a preliminary assessmentof an HPAI H7N7 outbreak in Germany.

Germany reported an outbreak of HPAI H7N7 at a farm in the northwest of the country on July 24. More than 10,000 laying hens were affected. Protection zones of 3 km and 10 km were implemented, and the birds were culled, Defra said. The farm is less than 1 km from another farm that reported an outbreak of LPAI H7N7 in June. But at that time, the newly-infected premises tested negative for LPAI H7N7.

The United Kingdom, Netherlands and Germany reported outbreaks of LPAI H7N7 in February, March and April, respectively. In July Stavely’s Eggs in Lancashire experienced an outbreak of highly pathogenic H7N7 among the company’s laying hens.

“Investigations into this outbreak revealed a mutation event occurred within the poultry premises, following an incursion of LPAI,” Defra said in its report. “The most likely source of infection was contact with wild birds, given the presence on the farm of nesting wild waterfowl and two ponds.”

Defra added that it’s no surprise that LPAI H7 was detected because the viruses are continually circulating in wild birds which presents a constant risk of infection into poultry raised for food. However, a “jump” from LPAI to HPAI viruses is rare, the agency noted.

“In the last 10 years, there have been only four such documented events of mutation from LPAI to HPAI occurring all within chicken layers in Europe: UK in 2008, Spain in 2009 (SCoFCAH, 2010), Italy in 2013 and UK in 2015; all involved H7N7,” Defra said in its report. “In the case of the UK mutation event in 2008, mallard ducks present at the premises and in contact with free range laying hens seemed to be the source for the LPAI incursion with subsequent mutation following sustained transmission within the flock.”

Defra went on to say that the mutation of LPAI strains to HPAI strains doesn’t present an increased risk to UK poultry farmers. The agency reminded poultry farmers to maintain high standards of biosecurity and to remain vigilant for any clinical signs of LPAI infection in their flocks.

“We are already on heightened risk level (albeit still low) for further incursions to occur in the UK poultry sector,” Defra said. “This has been in place since November 2014 when H5N8 HPAI was circulating in wild birds.”