TOKYO: Japan's agriculture ministry has confirmed an outbreak of highly pathogenic avian influenza at a poultry farm in Hokkaido, marking the northern prefecture's fourth case and the country's 21st outbreak this season. 

The affected farm, located in the town of Abira, keeps about 190,000 chickens, the Ministry of Agriculture, Forestry and Fisheries said in a statement on Thursday.

Local authorities were notified by the farm on Wednesday. A rapid avian influenza test conducted the same day returned a positive result, which was confirmed by genetic testing the following day.

All chickens at the farm will be culled, incinerated, and buried to prevent further spread of the virus.

Japan's avian influenza season typically runs from autumn until the following spring, Xinhua news agency reported.

According to the World Health Organization, Avian influenza A(H5N1) is a subtype of influenza virus that infects birds and mammals, including humans in rare instances. The goose/Guangdong-lineage of H5N1 avian influenza viruses first emerged in 1996 and have been causing outbreaks in birds since then. Since 2020, a variant of these viruses belonging to the H5 clade 2.3.4.4b has led to an unprecedented number of deaths in wild birds and poultry in many countries in Africa, Asia and Europe. In 2021, the virus spread to North America, and in 2022, to Central and South America.

Infections in humans can cause severe disease with a high mortality rate. The human cases detected thus far are mostly linked to close contact with infected birds and other animals and contaminated environments. This virus does not appear to transmit easily from person to person, and sustained human-to-human transmission has not been reported.

The WHO highlights that although human cases are rare, the high fatality rate (over 50 per cent in reported cases since 2003) makes it a major concern.