Following a six-week hiatus, the H5N1 highly pathogenic avian influenza (HPAI) virus has been detected in another poultry flock in Japan.
According to the official notification to World Organisation for Animal Health (WOAH), testing positive for the virus was a flock of around 57,500 commercial birds at the end of April. The farm is in the city of Tomisato in Chiba. This prefecture is part of the Kanto region on the main island of Honshu, corresponding to the area of Greater Tokyo.
The latest outbreak affected laying hens, according to Japan’s agriculture ministry, and suspicions of an infection arose from a sudden increase in flock mortality.
This development brings the country’s total outbreaks in poultry this year to 11. Directly impacted have been around 808,000 poultry, based on WOAH notifications.
Of these, 10 outbreaks involved the H5N1 virus serotype, and were widely dispersed across five of Japan’s eight regions. Furthermore, in February, a broiler flock in the southwestern-most main island of Kyushu tested positive for the H5N5 variant.
Furthermore, around 150 Japanese wild birds have tested positive for HPAI since the start of the 2023-2024 winter.
During the season, most prevalent in the wild population has also been the H5N1 virus serotype, while a few cases have involved the H5N5 and H5N6 variants. The most recent cases reported to WOAH were identified at the end of March, and involved the H5N5 virus.
Further poultry outbreaks in Bulgaria, South Africa
Last week, presence of the H5N1 HPAI virus serotype was detected at two more farms in Bulgaria.
Based on WOAH reporting, these bring the nation’s total outbreaks so far in 2024 to 16, directly impacting more than 803,000 poultry.
Latest cases were at premises in the central province of Plovdiv, and in Haskovo in southern Bulgaria.
A further HPAI outbreak in South Africa has been reported retrospectively to WOAH by the national veterinary agency.
It also involved the H5N1 virus variant, which was detected at a farm in Mogale city in Gauteng province in October of last year.
Since April of 2023, 29 outbreaks linked to this virus in the country have been registered with WOAH.
Around the same time, the H7N6 serotype was detected for the first time among South African poultry, and it has since affected 116 of the nation’s farms.
Study: Avian flu virus spreads fast at live bird markets
While previous studies show the potential for avian influenza viruses to spread rapidly at live bird markets, new research by the One Health Poultry Hub of the Global Challenges Research Fund demonstrates just how quickly that can occur under practical conditions.
Authors report that the findings of the study will support future research into potential measures to control avian flu at such markets.
Among the scientific partners were the Royal Veterinary College (RVC) and University of Oxford in the United Kingdom. Together with scientists from China, Bangladesh and France, the group used biological data gathered from chickens at live markets. They combined this with computer modelling to calculate virus transmission rates.
Researchers selected the H9N2 virus variant for the study. It is classed as low-pathogenic for poultry so it results in low mortality, but infections lead to production losses. Furthermore, this serotype is seen as a potential pandemic threat for humans as its genetic material has been detected in emerging virus variants. The world’s first confirmed case of H9N2 infection in a person was recently recorded in Vietnam.
The latest study revealed that more than 90% of chickens that arrive at a bird market without having been exposed to the H9N2 virus will become infected within one day. Furthermore, the time between infection and becoming contagious can be as short as 5.5 hours, and 10% of chickens tested positive for this virus variant on arrival at the market.
According to RVC, a previous study had shown that as many as 20-30% of birds entering live bird markets in Bangladesh and Vietnam had already been exposed to the H9N2 virus.
View our continuing coverage of the global avian influenza situation.
