As summer
evening fades to night in Atlantic Canada, a few
dark-brown ducks are dabbling for vegetation and
insects in a marsh. As they feed, the wary birds
are poised to escape danger by diving underwater
or by a quick, nearly-vertical flight. They are
American black ducks and their watchful habits
protect them from predators. But there are clever
hunters of a different sort in the marsh tonight:
scientists, who are trapping birds as part of
Canada's Inter-Agency Wild Bird Influenza Survey.
From May to October, wildlife
researchers in six regions across Canada and in
Iceland will target about 12 000 healthy wild
birds to be tested for avian influenza viruses.
Testing will also occur for wild birds found dead
in Canada. Most birds in the survey are young
mallard ducks; some 500 American black ducks will
be included in Atlantic Canada.
Surveyed birds are safely trapped
and, after putting up with a swab to collect fluid
samples for testing, resume their usual activities
unharmed. The samples that field scientists collect
across the country are sent for analysis to a
network of six diagnostic laboratories which have
science capacity in influenza virology.
This surveillance is part of
Canada's response to the virus known as Asian
H5N1 – often called "bird flu" – which
has never been found in North America. Testing
transatlantic migrants along the eastern Arctic
and in Iceland is considered a first line of defence
in maintaining vigilance for its possible arrival.
The Canadian Cooperative Wildlife Health Centre
coordinates the Canadian component of the survey.
Environment Canada's Canadian Wildlife Service
is a major participant, as are provincial natural
resources agencies. In the United States, the
U.S. Fish & Wildlife Service also conducts
widespread surveys along the west coast.
In North America, harmless strains
of native avian influenza commonly circulate in
wild birds. Last year more than 4000 birds – mainly
waterfowl – were tested across Canada. About 35
per cent of the birds tested carried avian influenza
viruses that were neither disease-causing nor
closely related to Asian H5N1, as researchers
expected.
The complex world of
the flu
Year after year, people on every
continent cope with influenza. Known as the flu,
the common respiratory illness is caused by human
influenza viruses. Wild birds cope with flu viruses
too but they carry different viral strains which
seldom make them ill. The avian influenza viruses
can move from wild to domestic birds but it is
rare for the virus to move to humans or other
mammals. Rarer still is the movement of the virus
from a bird to a human and then on to another
human.
Some subtypes – including Asian
H5N1 – are highly pathogenic, meaning that they
are likely to cause severe illness.
The first human death from Asian
H5N1 occurred nearly a decade ago and there have
been less than 250 human deaths world-wide from
the illness. It is possible that future genetic
changes to bird flu could allow the virus to move
more easily from person to person, no longer needing
an avian source. But this alteration has not happened
anywhere in the world to date.
Meanwhile, the virus has spread
among birds – from Asia to Europe, Africa and
some Middle Eastern countries. It has become established
in the poultry flocks of Asia and areas of northern
Africa. The global trade in domestic birds is
expected to be the chief risk for transmission
of bird flu to other parts of the world. Both
legal and illegal trade channels are difficult
to secure because of their volume. Illegal trade,
naturally, may pose the most serious risk.
If Asian H5N1 infiltrated North
American bird populations, it could have implications
for the health of wild bird populations. The stakes
are higher for the domestic poultry industry because
the arrival of contagious disease in intense farming
regions, such as British Columbia's Lower Fraser
Valley, is generally met with lethal culls to
protect neighbouring flocks – and the health of
human workers.
It is imperative to remain vigilant
and understand avian influenza viruses and their
behaviour. If the virus does appear in North America,
however it arrives, it must be detected quickly
and any outbreak of disease among birds must be
contained. Central to making this happen is building
on the current knowledge and capacity to manage
this relatively new viral strain.
Nation-wide survey results will
build a year-over-year understanding of the incidence
rates of avian influenza viruses and create a
current inventory of the viruses that exist in
the birds, while keeping watch for the emergence
of new disease.
That is the kind of vigilance
that the wary American black duck would understand.
