Information for vets about HPAI (bird flu)

High pathogenicity avian influenza (HPAI)

The H5N1 strain of high pathogenicity avian influenza (HPAI) has caused high numbers of deaths in poultry and wild birds overseas. It has also spilled over to mammals, including marine mammals, domestic animals, cattle and, in a small number of cases, humans.

New Zealand has never had a case of HPAI. The likelihood of HPAI H5N1 entering New Zealand on pathways that we manage is low. As information emerges about the distribution of the disease in Antarctica, there will be a better understanding about the likelihood of it reaching New Zealand through wild bird movements.

If HPAI arrives here, veterinarians will have an important role in providing evidence-based advice to your clients and communities.

We are actively monitoring disease spread, particularly towards the Ross Sea region in Antarctica and globally. As information emerges about the distribution of HPAI H5N1 in Antarctica, there will be a better understanding about the likelihood of it reaching New Zealand through wild bird movements.

Unlike most biosecurity threats, human introduction of HPAI H5N1 is not the major risk to New Zealand. The disease is currently spreading internationally in wild birds, which is the most plausible path by which it would reach New Zealand.

In other countries where this strain is present, human infection has been rare and generally found in people who have had a lot of contact with infected birds or other infected animals. For veterinarians working with birds and other animals, the risk of infection is low if the appropriate precautions are taken.

The current outbreak

Prior to 2020, the usual pattern of HPAI emergence was as a mutation of low pathogenicity avian influenza (LPAI) in chickens, associated with contact between waterfowl with LPAI and poultry.

In 2020 a strain of HPAI H5N1 emerged that was well adapted to persisting and spreading in wild bird species. This strain was also different because it established in wildlife population species other than waterfowl. This allowed it to spread across the Atlantic to the Americas and eventually to the Antarctic peninsula through movement of these new host species.

As this virus spread into new wildlife populations, the way it affected those populations was unpredictable. Some bird species experienced mass die offs, while others seemed unaffected and were able to spread the disease long distances.

Some mammal species that ate infected wild birds, or were in very close proximity with them, have become infected. Some mammal species, particularly seals, experienced high numbers of deaths.

In the US, HPAI H5N1 has been detected in dairy cattle. The United States Department of Agriculture (USDA) has identified spread between cows within the same herd, spread from cows to poultry, and cattle movement spread between farms/states. Some cows without clinical signs of disease have tested positive for HPAI.

Genomics of the recovered virus in dairy cattle in the US suggests that the infection was from a locally contained spillover event where birds infected cattle on a handful of farms in northern Texas. Spread on farm is likely through human-associated milking practices. Further spread between farms has occurred through the movement of infected cattle. A small number of dairy farm workers have been infected.

Be alert for signs in commercial and domestic poultry, and wildlife

Include avian influenza in your differential diagnosis list for any unusual disease outbreaks or mortality events.

Continue to apply robust PPE when working with sick or dying birds of any type. Before handling potentially infected animals, cover up as much as possible (disposable gloves, overalls, washable boots, P2/N95 mask, and eye protection).

Examine birds well away from other animals at the clinic, in an isolation facility or separate area that can be thoroughly cleaned and disinfected afterwards.

Avoid touching your face after contact with birds or surfaces that may be contaminated. Wash hands well and use appropriate disinfectants for both footbaths and environmental disinfection.

Disease manifestations in infected birds range from asymptomatic infection to respiratory, enteric, neurological and reproductive disease of varied severity, to acute or progressive severe systemic disease with very high mortality.

Infected wild birds may show a wide range of clinical signs, including:

incoordination, tremors, swimming in circles
twisted necks or other abnormal posture
inability to stand or fly
diarrhoea
coughing, sneezing or difficulty breathing
swelling around the head, neck and eyes
cloudiness or change in colour of the eyes
sudden death.

Should HPAI arrive in New Zealand, fomite transmission from people moving between farms is a risk pathway that is manageable and an important way of mitigating spread. Continue to encourage and practice stringent biosecurity measures when you are moving between farms.

Spillover to other species

If HPAI H5N1 is detected in New Zealand and becomes established in wild birds, small animal, mixed practice or production animal veterinarians need to be alert and on the lookout for spillover events to non-avian species. Overseas, infected mammals have included dairy cattle, goats, cats and dogs, as well as wildlife species.

As with the US example of a spillover event into a new species, the clinical presentation may not be typical for an influenza virus. Always consider having HPAI in your list of differential diagnosis, for something that you have not seen before.

Statement on the finding in cattle in the USA - World Organisation for Animal Health (WHO)