Identifying data gaps in bird flu host dynamics to help conserve vulnerable species
Johanna Harvey,
an assistant professor of wildlife disease wildlife ecology at the University
of Rhode Island, has described bird flu in public presentations as a quiet
virus with loud consequences.
Now she’s published a new paper in Wildlife Monographs,
describing how circulating avian influenza viruses (HPAIV) show an expanded set
of susceptible hosts, including many migratory wild birds, and higher
transmission rates. In the paper, Harvey examines data gaps in avian influenza
host dynamics to prioritize wildlife conservation — and protect human health.
Johanna Harvey’s new paper in Wildlife Monographs describes
how circulating avian influenza viruses show an expanded set of susceptible
hosts and higher transmission rates.
The flagship wildlife science journal publishes only a small number of papers annually, presenting a thorough, book-length analysis on a particular wildlife topic. The journal is now offering a foundational, go-to reference on avian flu with input from Harvey, an evolutionary ecologist, in collaboration with Jennifer Mullinax at the University of Maryland.
They are examining how risk factors relate to biological
traits to begin disentangling their interactions.
The magnitude and spread of HPAIV animal transmission have
introduced a novel stressor to bird species already facing severe population
declines due to the cumulative effects of climate change, habitat loss and
degradation, food stress, contaminant exposure, and other pathogens. This
represents a conservation crisis for wild birds, particularly the waterbirds
and raptors most impacted by HPAIV mortality.
Harvey and Mullinax have compiled an updated primer
describing host-virus interactions in wild birds, showing how seasonal
patterns, migration, and species interactions are shaping transmission dynamics
across diverse landscapes.
Migration matters
Prior to the early 2000’s, HPAIV outbreaks in wild birds
were rare — largely contained to domestic birds. After wild birds began getting
infected and dying in Eurasia in 2005, HPAIV transmission and detection in wild
birds started to increase globally, due to birds’ migratory flyways. However,
long-term virus spread among wild birds was still rare until the clade H5N1
caused more problematic spread via migration.
The H5N1 virus was first identified in wild hosts during
outbreaks in 2002, affecting wild species such as waterfowl, egrets, herons,
and gulls, and even flamingos. The detection of HPAI H5 in wild bird species
marked a pivotal moment, drawing attention to the potential for global spread
through seasonal migration.
Bird flu has continued to evolve, spreading to other
continents and arriving in North America in 2014. In the U.S., the H5 virus
caused an outbreak primarily impacting poultry and also some wild birds. This
virus was seemingly eradicated via culling of infected poultry and was not
detected again in wild birds. During its first half decade, HPAI transmission
in the U.S. increased by 297%, infecting an increasingly broad range of host
species.
A highly pathogenic virus was not seen again in the U.S.
until 2021 with the incursion of the H5N1 into North America via Newfoundland,
Canada. Wild birds began to be affected by HPAIV beginning with a highly
pathogenic H5N1 virus lineage A/Goose/Guangdong/1/96 (Gs/GD), first isolated in
a domestic goose in China in 1996. Descendents of this virus strain became more
adapted to wild birds and this current global H5 is a descendant from that
Gs/GD virus.
This current wave of transmission has already caused close
to 10,000 occurrences in wild birds, impacting 255 total avian species.
Harvey’s research shows that the circulating dominant strain possesses an
elevated ability to infect hosts, casting another shadow over an already grim
situation.
In the paper, Harvey describes how the newest circulating
virus’ spread and persistence in the U.S. is closely linked to its expanding
host range, host demographics, and birds’ seasonal behaviors.
Peaks in virus activity also coincide with periods of
immunological naivety as young birds enter the population. Nestlings have
partially developed immune systems, and receive protection from maternal
antibodies. Their immunity develops for several weeks post-hatching, creating a
window of heightened susceptibility coinciding with pre-migration staging.
It appears that transmission is strongly biased toward
introduction into domestic birds from wild birds, with relatively few spillover
events from domestic poultry into wild populations.
Vulnerable wild species
Harvey’s paper identifies a few well-known wild bird
species, such as house sparrows, mallard ducks, and trumpeter swans, as
particularly susceptible to viral infection. The study also indicates that
Canada geese and some swans have the potential to be supermover / superspreader
hosts.
Early HPAIV surveillance work also established waterbirds as
a primary source of HPAIV, capable of spreading the virus to others.
Some seagulls have recently been identified as key players
in HPAIV transmission, with the initial 2021 incursion of HPAIV into North
America resulting from a migratory gull. These species may act as biological
bridges between continents, with the virus spreading rapidly through waterfowl
and seabird colonies after the initial incursion. Transmission generally occurs
when species become infected through shared water habitats.
Many marine and coastal birds breed in dense colonies that
can facilitate rapid transmission. Raptors and scavenging birds may experience
increased exposure risks. Infection exposure and susceptibility is also
influenced by flock foraging and the bird trait of gregariousness — generally a
positive except when it comes to bird flu transmission. Gulls have been shown
to contribute to rapid transoceanic spread of HPAIV H5, while wild ducks
facilitate swift regional dispersal and geographic expansion.
Luckily, Harvey says that the beachgoing public can still
enjoy their time by the shore as the summer season commences. “As beach traffic
picks up in the heat of summer, virus prevalence and transmission seems to be
reduced,” she said.
In cases where humans are regularly interacting with
superspreaders or supershedders — either for research, work activities, or
randomly occupying the same space — it may be necessary to adjust, limit, or
cease human activities which contribute to HPAIV spread. For example, food
piles and feeders may artificially increase the density of animals at a
location and facilitate transmission for certain high abundance species such as
geese (home bird feeders are not likely to cause HPAIV spread, Harvey said).
By reviewing and analyzing this considerable amount of data,
Harvey hopes to provide direction for future research to inform efforts on
mitigating HPAIV impacts on wild birds by providing practical insights for
policymakers, public health officials, and wildlife management authorities.
She also says that communicating these bird flu findings
with the public can help guide management and decision-making.
Support for this study was provided by the U.S.
Geological Survey and National Science Foundation.
