Two additional wild birds have been found to be infected with highly pathogenic avian influenza (HPAI) A(H5N1) virus in South and North Carolina, the United States Department of Agriculture's (USDA) Animal and Plant Health Inspection Service (APHIS) announced on Tuesday.
The two birds were found to be infected just days after a wild American wigeon was found to be infected with the virus in Colleton County, South Carolina, the first case of Eurasian H5 avian influenza in the US since 2016. Other variants of the bird flu have been detected in the US in recent years.
APHIS added that it expects to find further cases among wild birds and advised people to avoid having direct contact with wild birds. The service urged farmers and hunters to practice good biosecurity to prevent the spread of the virus.
The USDA added that the US Centers for Disease Control and Prevention (CDC) still considers the risk to the general public from the variant to be low. No human infections from the variant have occurred in the US.
In the UK, one person was infected with the H5N1 variant earlier this month and has since recovered without experiencing severe illness. The patient had close contact with ducks.
In China, a spike in the number of human infections caused by the H5N6 subvariant of the bird flu has been recorded in the past year. One new case of human infection was reported to the World Health Organization (WHO) between January 14 to 20.
According to the WHO, the rise in H5N6 cases may reflect the continued circulation of the virus in birds and enhanced surveillance due to the COVID-19 pandemic. The WHO added that the zoonotic threat remains elevated due to the spread of the viruses among birds, but that the overall pandemic risk associated with the strain of bird flu has not significantly changed.
The increase in human infections caused by the H5N6 subtype of avian influenza is causing concern among experts, who say that a previously circulating strain appears to have changed and could be more infectious to people.
"The increase in human cases in China this year is of concern. It's a virus that causes high mortality," said Thijs Kuiken, professor of comparative pathology at Erasmus University Medical Centre in Rotterdam, to Reuters in October.
A large number of bird flu outbreaks have been reported throughout Europe, Africa and Asia in recent weeks, mostly due to the H5N1 subtype, which comes from the H5 lineage, according to the World Organization for Animal Health.
Over a million birds were found to be infected with the variant in Israel in recent months, although Israel's Agriculture Ministry declared in recent weeks that the outbreak is now under control.
The OIE has urged countries to increase surveillance for HPAI outbreaks, as the virus has been reported in over 40 countries since July.
The H5N1, H5N3, H5N4, H5N5, H5N6 and H5N8 subtypes of HPAI are circulating in bird and poultry populations across the globe, sparking concern at OIE which called this an “unprecedented genetic variability of subtypes... creating an epidemiologically challenging landscape.”
Earlier this month, OIE Director General Monique Eloit told Reuters that "this time the situation is more difficult and more risky because we see more variants emerge, which make them harder to follow."
"Eventually the risk is that it mutates or that it mixes with a human flu virus that can be transmitted between humans then suddenly it takes on a new dimension," she added.
Germany’s Federal Research Institute for Animal Health, the Friedrich Loeffler Institute, told the German Deutsche Presse-Agentur (DPA) that Europe is experiencing its “strongest avian flu epidemic ever.”
The institute added that “there is no end in sight” as the virus spreads throughout the continent and around the world, with new cases reported on a daily basis.