Avian influenza (aka AI,
avian flu, bird flu, fowl plague) is a contagious virus that expresses
itself through a variety of subtypes. Each is characterized by its proteins
and ability to produce disease, or pathogenicity. By way of different
protein combinations, there are potentially 144 versions. Most are referred
to as low pathogenic (LPAI), causing minimal to no clinical signs, while
others as highly pathogenic (HPAI), killing 90 to 100 percent of infected
birds. The Asian subtype HPAI H5N1 dominated headlines five years ago when
it spread through eight Asian countries and more than 100 million birds
were culled or died. Outbreaks are ongoing and, to date, 60 countries have
reported its presence and over 250 million poultry and 256 humans have
died. This subtype has not made it to the United States, but other subtypes
are here and something for poultry farmers to keep in mind.
|Photos courtesy of USDA/APHIS File Photo.
|Birds with AI may exhibit a purple discoloration
of wattles, combs and legs.
Waterfowl, shorebirds, terns and gulls are natural
reservoirs for AI, carrying the virus in their intestines. An infected bird
excretes the virus through its feces, and it is not uncommon for wild ducks
to transmit LPAI to pastured poultry flocks when range is shared. Migratory
birds are only one route for transmission, though. The smuggling of birds
and poultry products is considered the primary means of transmission in
other parts of the world and U.S. officials are regularly intercepting
shipments of eggs, feet and birds from Asian countries. Humans and poultry
equipment traveling to and from infected areas are also a potential route
for transmission, along with newly acquired birds from not-so-trustworthy
sources. Once a bird comes into contact with the virus, it spreads via
nose, mouth and eye secretions. Flocks raised indoors can even transfer the
virus by way of airborne secretions.
Detection of a low pathogenic subtype can be tricky,
as its presence isn’t always evident to the naked eye, and when it is
evident, signs are typically mild: a drop in the consumption of food and
egg production and coughing and wheezing. Keep in mind that we’re
talking about a flu virus and, just like with humans, some varieties can
pack a wallop while others tread lightly on the system. Birds infected with
a highly pathogenic subtype will show a lack of energy and appetite;
decreased egg production; soft-shelled or misshapen eggs; swelling on the
head, eyelids, comb, wattle and hocks; purple discoloration of the wattles,
combs and legs; nasal discharge, coughing and sneezing; lack of
coordination; and diarrhea.
In the interests of healthy poultry, it’s
important that we not let AI slip off our radar screen. It is also in the
interests of human health, as research has shown that certain low
pathogenic subtypes have the potential to mutate into highly pathogenic
subtypes. There is a strong species barrier (i.e., the virus does not
easily jump from birds to humans), but pigs, horses, cats, ferrets and
marine mammals have been shown to carry it. And, this is where it gets
interesting: pigs can carry both human and avian flu strains and there is
considerable concern that the two could combine and reassort to produce a
strain capable of human-to-human transmission. It is in a virus’
nature to evolve over time, and influenza viruses mutate at a relatively
high rate. Good for the virus, not so good for humans who want to control
To maintain a species barrier and keep your birds
healthy, there are preventative measures you can take to minimize the risk
of exposure. Vaccines are not considered effective in preventing poultry
disease, cleanliness is. Keep a clean operation, and that includes you.
Wash your hands before and after working with your birds. If you visit
another farm or go to a live bird market or show, clean and disinfect your
clothes, shoes, hands and equipment when you get home. A solution of equal
parts bleach and water is an adequate disinfectant. There are also a number
of products you can buy to do the job. If other farmers visit, restrict
access to your facilities or offer them clean boots and coveralls. Remove
dirt, litter, manure and other organic materials from poultry house
surfaces and wash and disinfect regularly, including cages, tools, feeders
and waterers. Keep in mind that, unless covered with polyurethane, wood
surfaces are nearly impossible to sterilize. Clean and disinfect any
poultry equipment you borrow or that is returned to you—better yet,
do not borrow or lend equipment.
|Swelling of the head, eyelids, wattles
and hocks is a sign of AI.
The AI infection rate in migratory waterfowl is about
1 percent, and that number rises in late summer and early fall. If you let
your birds range, do not let them coexist with wild ducks or geese or use
any water source that the fowl could have contaminated. If a pond is your
water source, disinfect that water before giving it to your birds. Ask your
veterinarian for safe methods. When acquiring birds, get them from a
reputable source that practices good disease control and keep these birds
separate from the rest of the flock for 30 days. If you’ve shown
birds at a fair, isolate them for at least two weeks after the show.
Although Northeastern states have been clamping down on live bird markets
and requiring the testing of flocks destined for them, you can never be too
safe. Do not bring live birds back from these markets. Lastly, properly
dispose of dead birds.
If you think your birds are showing signs of the flu,
report it. Call the USDA Veterinary Services at 866-536-7593 or contact
your state or local veterinarian. Cooperative extension agents are also
good, knowledgeable people to turn to if you have questions or concerns. If
you’re interested in reading more about avian influenza, visit the
USDA’s avian influenza Web site, www.usda.gov/birdflu, or the USDA APHIS backyard biosecurity Web site, www.aphis.usda.gov/vs/birdbiosecurity. I also encourage you to do an Internet search to learn about
ongoing surveillance efforts in your state.
The author, a brand new contributor to Farming, is a biologist who
lives and farms in Vermont’s Northeast Kingdom.