The arrival of bird flu virus H5N1 in Australia has sent shockwaves around the world, marking the end of a continent once considered free from this highly pathogenic virus. The discovery of H5N1 in Western Australia's Cape Le Grand national park raises concerns about the potential for human transmission and food safety, prompting renewed discussions globally.
While experts stress that the risk to humans remains low, it is essential to understand how this virus spreads. The H5N1 strain is primarily an avian pathogen, meaning it does not easily jump from birds to humans or spread between people. According to NHS data, since late 2020, over 100 human H5N1 cases have been reported worldwide, mainly in the US and Cambodia. Historically, the fatality rate for those infected has been high, although recent US cases have shown a lower mortality rate, with two deaths among 71 reported infections.
The current H5N1 clade 2.3.4.4b originated in 2020 and has rapidly spread across the globe, infecting a wider range of bird species, including seabirds like skuas. Wild birds are typically the carriers, which can then infect domestic poultry, cattle, or other animals. In poultry, the virus is highly pathogenic, often leading to the culling of infected flocks to prevent further spread.
Humans usually contract H5N1 through close and unprotected contact with severely ill or dead infected birds or animals. Symptoms can range from eye redness (conjunctivitis) to more general flu-like symptoms such as fever, sore throat, cough, runny nose, body aches, headaches, and fatigue. Less commonly, individuals may experience diarrhoea, nausea, or vomiting. Unlike birds, infected cattle may not show severe illness, with early signs in the US including changes in milk consistency and colour.
Regarding food safety, consumers can be reassured that chicken, eggs, and other poultry products are safe to eat as long as they are cooked thoroughly. Cooking effectively kills the virus, while pasteurisation processes eliminate it from milk, making commercial dairy products safe. The main risk from contaminated poultry products would be through handling them raw, a risk mitigated by standard food hygiene practices. Back-yard poultry owners are advised to report any sick or dead birds to authorities without touching them.
The US has experienced widespread H5N1 infections in dairy cattle and poultry, primarily with the same global strain. This spread was facilitated by the movement of infected cattle and contact between humans and infected animals, highlighting the importance of vigilant monitoring and swift action to prevent further transmission.