International Evidence on Avian Influenza and H7N6 in Aotearoa

Avian influenza

Avian influenza (also known as bird flu) is caused by influenza A viruses that naturally infect birds. There are many in circulation and many are not harmful to birds or humans. Avian influenza viruses are classed as ‘highly pathogenic’ when they cause severe disease, or more frequently, ‘low pathogenic’ when they cause no signs of infection or cause very mild infections in poultry.

Influenza viruses are named after specific virus parts (proteins) they have on their surface, called H and N proteins. These proteins can be present in many combinations, and they help the virus to get in and out of the cells in their host to cause infection and spread. These differences on the virus surface change which animals it can infect easily, and how the virus is affected by vaccines or natural immunity, as well as how easily it can spread beyond an initial infection.

International evidence on H7N6 – which was found on Aotearoa poultry farms

H7N6 viruses are usually low pathogenic influenza viruses and are commonly found circulating in wild birds around the world. As the H7N6 strain identified in Aotearoa New Zealand is very closely related to low pathogenic influenza found circulating in waterfowl (ducks and geese), experts think this particular H7N6 virus has mutated from a low pathogenic virus to become highly pathogenic.

There have been several other reports of H7N6 influenza viruses in other parts of the world. In May 2023, an H7N6 virus emerged in South Africa, which then spread to Mozambique and other parts of the African continent. Almost 7 million birds either died or were culled to control the spread across Africa. There were also a limited number of human infections, usually in poultry farmers due to the close contact they had with infected birds.

While avian viruses can be very contagious between birds, they are generally considered low risk to public health as many are low pathogenic strains and have adapted to spread between birds rather than humans. These viruses can sometimes spread to humans but have not yet adapted to spread easily between people.

Other H7Nx (where x is 2, 3, 7 and 9) have caused human infections that result in conjunctivitis and/or respiratory symptoms. Deaths have been reported from some human H7Nx infections including the H7N9 avian influenza virus that killed 616 people in China and had a case fatality rate of 39%.

An H7N3 virus was found in Australia earlier this year and great efforts went into containing the virus to prevent losses in the poultry industry as well as to prevent spillover to other animals and humans. This Australian H7 outbreak is now reported to be under control.

While avian influenza viruses can pose a risk to human health, the H7N6 virus is considered to be quite low risk as the strain detected here in Aotearoa is currently best adapted to spread between birds rather than infecting people.

How is the strain of H7N6 detected in Aotearoa New Zealand different from other strains overseas?

The genetic code of the H7N6 virus that was found in the Otago poultry farm shows it’s likely to have been a virus circulating here as a low pathogen influenza, that has mutated to become a H7N6 virus, rather than being closely linked to the highly pathogenic strain found in Australia some months ago. In this case, there is good evidence that free-range hens have been exposed to a low pathogenic H7N6 virus from wild waterfowl, which has changed to become highly pathogenic. This is the first time this type of event has been reported in Aotearoa.

What is the risk to human health from the H7N6 strain identified in Otago poultry farms in New Zealand?

The current risk to human health is low. Avian influenza strains occasionally infect humans, but they don’t spread easily from person to person without adapting further. Experts get much more concerned when these viruses spillover into mammals such as cows, and start spreading between them, as that gives the virus the chance to adapt to infecting and spreading between animals that are more like humans. It also gives the virus more chances to come into contact with humans that work with them, which could then spread on to the wider public.

How is H7N6 different to H5N1? What is the evidence from overseas on H5N1?

The differences between H7N6 and H5N1 are to do with the outer surface proteins of the virus and these differences affect how easily the virus can get in and out of the cells in our body to infect us and spread. Unlike the H5N1 virus that is spreading throughout other parts of the world, H7N6 influenza strains have been easily contained to date.

H5N1 is currently widespread across the globe and is mostly found in wild birds but has caused outbreaks in domestic animals. In other nations the Centre for Disease Control reports H5N1 spilling over to a range of other animals including cows, dolphins, foxes, cats, seals and mice. There have also been infections of humans, particularly those that work with poultry and cows.

H5N1 has not yet been detected in Aotearoa. However as migratory birds carry the virus across the globe, it is difficult to keep out forever, as we cannot control the migration of these birds that may bring it here.

There have been dozens of H5N1 human infections elsewhere in the world, and over time the virus may adapt to spread much more easily between people. This is how pandemics can start. So far this has not happened, but it is important to keep tracking bird flu around the world and be ready to respond if a pandemic influenza does arise.

While the current risk to human health is quite low, the more time the virus spends in other mammals, the more it adapts to spreading in animals like humans, so we need to make sure we are ready to respond if needed to protect lives.