Are Waterfowl Spreading Avian Flu?

This started out as a popularized review of an article about continental waterfowl movements spreading Avian Flu (H5N1). One week prior to publishing this on the Blood Origins website, a teenager in British Columbia was diagnosed with this dangerous disease, necessitating a broadening of the review. The following week a series of Canadian chicken farms were found infected with Avian Flu. Then 2 weeks later, a group of dairy workers showed evidence of H5N1 exposure causing worries about the safety of North America’s milk supply. It seems our understanding of the disease is unfolding faster than most can keep up with. As in Covid, zoonotic transmission (wild animal-to-human) cannot yet be clearly confirmed or ruled out but wildlife as disease reservoirs remains a large concern.

Article review and attached opinion by Lee Foote, PhD (Conservation Biology)

Recent work combining 15 million waterfowl GPS locations, exposure likelihood to Avian Flu (also called viral variant H5N1), and the movement of presumedly infected birds along their migratory paths has shown some predictability of when and where outbreaks will occur in domestic poultry farms. Lead study author Fiona McDuie and 32 additional authors (2024) published Mitigating risk: predicting H5N1 avian influenza spread with an empirical model of bird movement in the journal Transboundary and Emerging Diseases

At issue: Avian Flu is a highly pathogenic avian influenza virus (HPAIv), in a family of respiratory diseases spread by body fluids like blood, urine, saliva, and respiratory droplets similar to Covid transmission. Avian Flu affects over 83 million birds in North America [reviewer note: this updated to 105 million since publication] and results in tens of millions of poultry deaths in high-outbreak years. It is rarely contracted by humans but strikingly, kills between 1/3 and ½ of the people who show symptoms of being infected. It is not known how many people show no symptoms however, mutation dynamics that could increase transmission rates to humans.

Waterfowl are highly gregarious, long-lived, and long-distance migrators present in most of North America at least during migration, and because they harbor Avian Flu, they, appear to be a logical starting point to examine disease transmission risks.

Some Background:

Avian Flu was first detected in domestic birds (though true origins remain unknown) and then appears to have spread to wild species.
It has been detected in 511 species of birds thus far.
Avian Flu continues to mutate to become more virulent and lethal in wild birds along flyways and across the Atlantic as there is some migratory bird exchange with Europe and Asia.
Previously outbreaks diminished in waterfowl during summers but now Avian Flu appears to be both over-wintering and over-summering in dense nesting areas. Wildfowl appear to be both disease reservoirs and vectors (spreaders).
Waterfowl staging locations in Canada and breeding grounds of colonial arctic geese lead to the mixing of birds up and down all flyways which is a way the disease is widely distributed.

Using data to clarify the problem:

The authors used a series of waterfowl movement datasets including 15 million GPS data points on 1,300 migratory geese to both estimate their exposure to known Avian Flu occurrence at the county level and their subsequent movements in relation to Avian Flu outbreaks. They went further to check if these movements were specifically related to poultry farm outbreaks.

Poultry farms with infected waterfowl nearby were 2.2 times as likely to experience Avian Flu outbreaks as randomly selected poultry farms, so the model does seem to offer some broad predictive value.

Reviewer’s commentary (not from the article):

In the interim since publication, concern has emerged in the public press (10 November 2024) over a Washington State pig found infected with H5N1. The jump to mammals was predicted and swine are important amplifying and transformative carriers of viruses sometimes serving as a direct step to human infectivity.

In mid-November, Dr. Leana S. Wen, a health writer for the Washington Post, offered her four major concerns about Avian Flu.

Many human cases exist but are only found by accident while checking for other viral infections.
The gene sequencing of human cases suggests mutations to types more infectious to humans.
Many human cases have no farm animal exposure suggesting they caught it from another human or a pet.

The McDuie wildlife article only references “informing wildlife management” but informing is a prerequisite to acting including the use of hunting effort, hazing, precautions around backyard bird feeding near poultry, small poultry farmers, bird fanciers, or pigeon racers, pet stores, and habitat manipulation to reduce the concentrations of waterfowl in key staging areas. Some systematic sampling for baseline occurrence in hunters’ bags or wild flocks would improve tracking any disease resistance within waterfowl or possible population reductions of some flocks.

Whereas waterfowl are abundant and diverse, so are raptors (hawks, owls eagles, and vultures); another grouping of migratory birds susceptible to Avian Flu variants. Raptors all consume other birds which would likely increase their exposure risks. Carrion feeders, like the endangered California Condor, may also have higher exposure risks. Condor numbers hover around 300 individuals in the United States. Other rare birds such as Canada’s sage grouse, Trumpeter Swans, and Whooping Cranes occur near waterfowl concentrations on prairies and potholes which could lead to higher exposure risks. Rare species may be disproportionally de-populated.

Some have speculated that climate change that allows the distributional spread of skunks and raccoons, as well as omnivorous feral pigs, might amplify risks because they all readily consume sick birds and could play a role in bird-carnivore- livestock-human transmission.

Several hunting dogs have been affected by H5N1 though no symptoms were evident. House cats allowed to freely pursue birds also share increased risks of exposure, possibly increasing the [currently low] risk of transference to human owners.

From the Covid experience, we learned much about the waste of public resources over public hysteria and wild speculations posed as “truth”. Whether H5N1 reaches pandemic status or not will only become evident with time. We can, however, expect subsequent pandemics and careful examination of risks, possible transmission avenues, and the relative roles that humans, livestock, and wild animals play need to be disentangled so management can build barriers, prevention strategies, and cures.

Finally, although vaccinations are controversial and politically charged, the biology of viruses suggests reason to expect that partial protection from H5N1 may come from seasonal flu immunizations.