PHOTO: Ben Moreland/Unsplash

Is avian influenza a threat to Aotearoa? – Expert Reaction

The current international outbreak of avian flu is decimating wild birds, causing havoc for chicken farmers, and has even spilled over into several mammalian species – including our own. Could it come to NZ’s shores? And how worried should we be if it does?

Since 2021, the virus has gone gangbusters and made its way to almost every continent. However, human to human transmission of the virus has not been observed.

The SMC asked experts to comment on what this could mean for Aotearoa.

Associate Professor Jemma Geoghegan, Virologist, University of Otago, comments:

“Highly pathogenic avian influenza virus has spilled over to mammals including humans many times since it was first detected 20 years ago. Importantly there has, to date, been little evidence that the virus can spread between mammals. We are now diligently watching to see whether the virus will evolve the ability for mammalian transmission and how it might do that remains unknown. Irrespective of this, the virus is continuing to spread among birds and it has clearly evolved to spread more efficiently in avian hosts. There are now a number of studies to attempt to figure out the genetic changes that allowed this to occur.”

No conflicts of interest declared.

Dr Brett Gartrell, Professor of Wildlife Health, Wildbase, Tāwharau Ora, School of Veterinary Science, Massey University, New Zealand, comments:

“In the last two years (2021-2023) there has been an unprecedented mortality of wild birds throughout the Northern Hemisphere due to the avian influenza virus. During this period, over 400,000 dead birds have been recorded from over 2600 separate mortality clusters in wild bird populations, however, the actual number of birds affected is estimated to be much higher. Deaths due to this strain of the virus have been reported from almost every country in Europe, in North and South America and Northern Africa. Many bird species are affected, including seabirds, shorebirds and birds of prey. The virus has occasionally spilled over into mammals and has caused clusters of mortality in mink and sealions, and isolated deaths in bears, foxes and skunks. The virus responsible is a strain of Avian Influenza A(H5N1). The number of human infections with this strain of the virus is fortunately very low.

“Avian influenza viruses are a complex group of viruses that are of importance to bird and human health. Viruses evolve rapidly and this current strain of avian influenza is particularly concerning because it has high transmissibility, can infect hosts across species barriers, and is much more likely to cause severe disease and death in some wild bird species.

“If the H5N1 strain enters Aotearoa New Zealand the consequences for wild bird populations and poultry flocks may be severe. The Ministry for Primary Industries (MPI) has primary responsibility for exotic disease surveillance, investigation of unusual mortality clusters and the control of exotic disease incursions in animals and plants in Aotearoa New Zealand. MPI has a targeted surveillance programme where wild birds, particularly ducks, are screened for avian influenza viruses. Bird mortality events are also routinely reported and investigated by MPI’s incursion investigators.

“Our geographic isolation and strict biosecurity laws are barriers to this disease entering Aotearoa New Zealand. Although, our biosecurity laws currently prevent the importation of live birds, smuggling is a potential route for entry of the virus. Migratory shorebirds and seabirds are also possible vectors of the virus into the country. If the disease enters the country, it may move around the country in wild birds and traded poultry unless it is quickly eradicated. In a recent outbreak of a pathogenic avian influenza H7N7 strain in Australia, control and eradication were achieved by culling over 433,000 birds, including poultry, turkey, farmed emus, and pet birds. MPI would likely adopt a similar eradication strategy to prevent the virus from becoming established in New Zealand, however, it is not clear how this control strategy would be applied to wildlife populations. Early detection, reporting, containment and biosecurity measures will be important in trying to stamp out the disease to prevent further spread.”

No conflicts of interest declared

Dr Joan Ingram, Medical Advisor, IMAC, comments:

“Highly pathogenic avian influenza (HPAI) A(H5N1) virus has been circulating among birds and poultry in different parts of the world for many years and is continuing to evolve into different groups that are referred to as clades. The current clade of H5N1 virus, called clade, appears well-adapted to spread efficiently among wild birds and poultry in many regions of the world. For example, having been first identified in wild birds in the United States in January 2022 it has now been detected in wild birds in all 50 states and has caused bird outbreaks in 47 states affecting more than 58 million commercial poultry and backyard flocks. Fortunately, while the viruses are good at spreading between birds they do not readily transmit between people.

“Infections in humans generally result after close or prolonged contact with infected birds. The severity of illness can vary widely from no or mild symptoms to severe disease which can be fatal. Only seven human cases associated with poultry exposure during this outbreak have been reported globally since January 2022. A case has recently been reported from Cambodia. However, since 1997, over 880 human cases, nearly all from previously circulating H5N1 virus clades, have been reported from 21 countries with approximately 50% mortality, but very few cases have been identified worldwide since 2016. (See graph here.) Outbreaks have led to mass culling of domestic poultry on numerous occasions.

“As well as possible spread to humans H5N1 viruses may infect other animals such as wild or feral animals e.g., foxes; stray or domestic cats and dogs; domestic farm animals e.g., minks; zoo animals and marine mammals e.g. seals and sea lions.

“Migratory birds spread H5N1 viruses. For example, the virus was introduced into Senegal from Eurasia in late 2020. Migratory birds and sea mammals could potentially spread the virus to our shores and lead to spread within wild or domestic birds in New Zealand. This could have major implications for the affected species and potential for transmission to humans.

“The world is always concerned about another influenza pandemic and mutations and combinations of different influenza viruses including avian ones can lead to novel viruses which can become human adapted and have pandemic potential. Hence vigilance and monitoring of avian influenza types is important.”

No conflicts of interest declared.