A strain of bird flu, H7N3, has been found in Victoria, with one retroactive case in a child returning from overseas and active infections reported at a poultry farm.
Experts say that while it is reassuringly not the problematic H5N1 strain which is circulating globally, the new outbreak of the H7 virus serves as a reminder about the need for vigilance regarding avian influenza and the need to report sick or dying birds to the appropriate authorities.
Avian influenza has been at the centre of an alarming outbreak discovered in US cattle-herds, where milk from infected udders has been identified as the pathway that led to the subsequent infection and death of farm cats housed at these locations.
Agriculture Victoria confirmed this week that preliminary tests detected the presence of bird flu, noting that the property has been placed into quarantine with samples sent to the Australian Centre for Disease Preparedness for further investigation.
It has since been confirmed that it is the H7N3 strain, which has previously caused a small number of outbreaks between 2012-2020 in NSW and Victoria, which were successfully contained.
Professor Adrian Esterman, the Chair of Biostatistics at the University of South Australia, said it was different to the H5N1 strain that had been devastating domestic and wild birds around the world.
“The H5N1 bird flu is highly pathogenic for birds, and for the small number of humans infected, the case fatality rate has been high. The current H5N1 outbreak was first detected in Europe in 2020. It has affected a wider range of bird species than previous outbreaks and has led to significant losses in both wild bird populations and poultry flocks worldwide and it is highly likely that it will eventually be detected in Australia.”
Dr Vinod Balasubramaniam, a virologist at the Jeffrey Cheah School of Medicine & Health Sciences at Monash University in Malaysia, said the H7N3 subtype was mainly known for its impact on domestic poultry, particularly chickens, turkeys, and ducks.
“Originating from wild birds, especially waterfowl, which act as natural reservoirs, the virus often circulates asymptomatically in these populations,” he said. “However, when transmitted to domestic poultry, particularly in densely populated environments like poultry farms, it can spark widespread outbreaks.
“Transmission occurs through various routes, including direct contact between infected and susceptible birds, contamination of surfaces and equipment, and the dispersal of infectious aerosols within confined spaces.
“Despite its primarily avian focus, H7N3 possesses zoonotic potential, albeit limited. Human infections are rare and typically result from close contact with infected birds or contaminated environments.”
Dr Balasubramaniam said documented human cases of H7N3 infection served as important markers of its zoonotic capacity.
“Instances such as those recorded in British Columbia, Canada, in 2004, and Jalisco, Mexico, in 2012, underscore the importance of surveillance and rapid response measures,” he said.
“While human cases have generally resulted in mild symptoms and full recovery, the potential for severe outcomes cannot be discounted, particularly in vulnerable populations.”