The H5N1 strain of bird flu has been spreading among wild birds and poultry globally for more than two years.
But scientists are on alert for changes in H5N1 which could signal the virus is adapting to spread easily among humans amid reports of human cases and spread among cattle in the US too.
"The H5N1 virus is constantly evolving and could potentially become easily transmissible from person to person," the World Health Organization's (WHO) website states.
"If this occurs, it could be the start of a new influenza pandemic, as was the case with the 1918 and 2009 H1N1 pandemics."
Last week, New Zealand public health experts, via a Public Health Communication Centre briefing, said recent developments underscored the urgent need for pandemic preparedness efforts "to the evolving threat" posed by H5N1.
The authors - Michael Baker, John D. Potter, Nigel French, Jemma L. Geoghegan, Nick Wilson, Oz Mansoor, Sue Huang and Richard Webby - said New Zealanded needed to update its national pandemic plan, effective public health and social measures, and timely access to testing, vaccines, antivirals, and infection prevention equipment.
"We need to make sure our pandemic preparedness is up to scratch and ready for emerging threats such as H5N1. Careful reviewing of our pandemic plan, as well as cross-agency practice exercises will give us a better chance of preventing and minimising the impact of pandemics in Aotearoa," Prof Baker said.
A 'One Health' approach to surveillance and response was key to identifying and swiftly responding to potential outbreaks, the authors said.
"We need to use this opportunity now as we never know the timing of the next pandemic," Prof Baker said.
"These capabilities are a good investment as they also help New Zealand prevent and manage the infections we already have, which is a further benefit."
"The increasing host range of the virus, potential spread among mammals and between a mammal and a human, its wide geographical spread, and the unprecedented scale of the outbreaks in birds raise concerns about the pandemic potential of HPAI A(H5N1)," an article on medical journal The Lancet stated.
Distinguished Professor of infectious disease epidemiology and public health Nigel French, of Massey University, said they also backed the 'one health' approach, given the strain's effects on animals and the potential for it to infect humans.
"Aotearoa's Health agencies, the Ministry for Primary Industries, the Department of Conservation, iwi, community groups and the farming sector are working together to ensure any incursion of bird flu is detected early and an appropriate response instigated.
"This includes the H5N1 strain of global concern, and all other avian influenza viruses, including H7N3. The public are also encouraged to help with surveillance by familiarising themselves with the signs to look out for, particularly in wildlife, and what to do to report anything that looks suspicious of bird flu. Comprehensive information on what to look for and how to respond is here."
From 2003 to 1 April 2024, a total of 889 cases and 463 deaths caused by H5N1 have been reported worldwide from 23 countries, according to WHO.
The United Nations agency said there was a risk for sporadic infections in mammals and humans due to exposure to infected animals or contaminated environments, and so further human cases were not unexpected.
Recent developments in the bird flu outbreak
The US Department of Agriculture is ordering dairy producers to test cows that produce milk for infections from highly pathogenic avian influenza (HPAI H5N1) before the animals are transported to a different state following the discovery of the virus in samples of pasteurized milk taken by the Food and Drug Administration.
The H5N1 outbreak has spread to dairy cattle in nine states, including Michigan and Texas where two farm workers were found to be infected.
However, the US Centers for Disease Control and Prevention (CDC) said the risk to the general public remained low and it had not seen evidence of human to human transmission of bird flu, Reuters reported.
US officials had thought the outbreak was recent, but a recent study found bird flu was likely circulating on a limited basis as far back as late 2023..
The study said it believed wild birds transmitted the virus to cattle, which then expanded when the cows were shipped to other states.
On Wednesday, Australia confirmed its first human case of the bird flu after a child returning from overseas tested positive for the H5N1 strain.
Meanwhile, another strain of the virus, H7N3, was found on an egg farm in the Australian state of Victoria.
"This is the second time an outbreak of a strain of avian influenza has emerged in Australian egg producers in the last few years, the last being an outbreak of H7N7 in 2020," Prof French said.
"The human case in Australia was a traveller from a country where H5N1 is circulating. No other cases have been identified through contact tracing, and although they developed severe symptoms, they have since recovered. This is a common scenario for human cases of bird flu - sporadic, severe infections with no evidence of sustained transmission."
The WHO's advice on recent US cases stated "enhanced surveillance in potentially exposed human populations becomes necessary" where there is exposure to an outbreak or a confirmed human infection.
"Should infected individuals from affected areas travel internationally, their infection may be detected in another country during travel or after arrival. If this were to occur, further community-level spread is considered unlikely as this virus has not acquired the ability to transmit easily among humans."
New Zealand's situation
There are no known outbreaks in animals - or human cases - in New Zealand so far.
H5N1 is among the notifiable infectious diseases, meaning health professionals are required to report to the local Medical Officer of Health if they find a suspected or confirmed case.
Prof French is also the chief science adviser at Te Niwha - an infectious disease research platform - which is funding a University of Otago and Environmental Science and Research project to develop monitoring for bird flu in wildlife.
"The Department of Conservation is trialling vaccination of endangered taonga wild birds."
In March, the Ministry for Primary Industries and Department of Conservation said they were preparing a contingency plan for an inevitable "tsunami" of bird flu coming to New Zealand.
"Biosecurity New Zealand has systems in place to prevent HPAI entering New Zealand through human activity and to ensure early detection if it does arrive," the Department of Conservation's website stated.
How is H5N1 spreading?
It remains unclear how the virus is spreading, but there is evidence of wild bird-to-cow, cow-to-cow, cow-to-poultry, and one case of cow-to-human transmission. There is no evidence of human-to-human transmission, US officials reiterated.
Because of the heavy viral load in milk and mammary glands, scientists suspect the virus is being spread to animals during the milking process, either through contact with infected equipment or with virus that becomes aerosolised during cleaning procedures.
It remains unclear whether the virus can spread through respiratory droplets that infect the airway, as flu viruses typically spread in humans.
A nasal swab from the Michigan worker tested negative for influenza in a state lab. But an eye swab from the patient was shipped to CDC and tested positive for the H5N1 virus, the CDC said, indicating it may have been transmitted in that way.
- Reuters / RNZ
