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The Biology of Avian Influenza
Q. What is avian influenza?
A. Avian influenza (AI)--the bird flu--is a virus that infects wild
birds (such as ducks, gulls, and shorebirds) and domestic poultry
(such as chickens, turkeys, ducks, and geese). There is flu for birds
just as there is for humans and, as with people, some forms of the flu
are worse than others.
AI viruses are classified by a combination of two groups of
proteins: the hemagglutinin or H proteins, of which there are 16
(H1-H16), and neuraminidase or N proteins, of which there are 9
(N1-N9). Based upon these two groups of proteins, there are 144
different characterizations of the virus.
AI strains also are divided into two groups based upon the ability
of the virus to produce disease in poultry: low pathogenic avian
influenza (LPAI) and highly pathogenic avian influenza (HPAI).
LPAI, or "low path" avian influenza, naturally occurs in
wild birds and can spread to domestic birds. In most cases it causes
no signs of infection or only minor symptoms in birds. These strains
of the virus pose little threat to human health. LPAI H5 and H7
strains have the potential to mutate into HPAI and are therefore
closely monitored.
HPAI, or "high path" avian influenza, is often fatal in
chickens and turkeys. HPAI spreads more rapidly than LPAI and has a
higher death rate in birds. HPAI H5N1 is the type rapidly spreading in
some parts of the world.
Q. How does the avian influenza virus spread in birds?
A. Avian influenza is primarily spread by direct contact between
healthy birds and infected birds, and through indirect contact with
contaminated equipment and materials. The virus is excreted through
the feces of infected birds and through secretions from the nose,
mouth and eyes.
Contact with infected fecal material is the most common of
bird–to–bird transmission. Wild ducks often introduce low
pathogenic avian influenza into domestic flocks raised on range or in
open flight pens through fecal contamination. Within a poultry house,
transfer of the highly pathogenic avian influenza virus between birds
also can occur via airborne secretions. The spread of avian influenza
between poultry premises almost always follows the movement of
contaminated people and equipment. Avian influenza also can be found
on the outer surfaces of egg shells. Transfer of eggs is a potential
means of transmission. Airborne transmission of virus from farm to
farm is highly unlikely under usual circumstances.
Q. What are the signs of illness of birds infected with avian
influenza?
A. Low pathogenic avian influenza signs are typically mild.
Infected birds typically show signs of decreased food consumption,
respiratory signs (coughing and sneezing) and decreased egg
production. Birds that are infected with highly pathogenic avian
influenza are more severely ill and could exhibit one or more of the
following clinical signs: sudden death; lack of energy and appetite;
decreased egg production; soft–shelled or misshapen eggs; swelling;
purple discoloration; nasal discharge; coughing, sneezing; lack of
coordination and diarrhea.
Q. Is it possible for a low pathogenic avian influenza strain to
become highly pathogenic?
A. Some low pathogenic subtypes have the capacity to mutate into
more virulent strains. While low pathogenic avian influenza is
considered lower risk, low pathogenic strains of the virus – the H5
and H7 strains – can mutate into highly pathogenic forms.
History of Avian Influenza in the United States
Q. Does highly pathogenic H5N1 avian influenza currently exist
in the United States? Has it ever occurred in this country?
A. Incidents of low pathogenic avian influenza are commonly
detected in domestic poultry flocks. Low pathogenic avian influenza
does not pose a serious threat to human health.
There is no evidence that any highly pathogenic avian influenza
currently exists in the United States. Historically, there have been
three highly pathogenic avian influenza outbreaks in poultry in this
country--in 1924, 1983 and 2004. No significant human illness resulted
from these outbreaks.
The 1924 H7 HPAI outbreak was detected in and contained to East
Coast live bird markets.
The 1983-84 H5N2 HPAI bird outbreaks resulted in the destruction of
approximately 17 million chickens, turkeys, and guinea fowl in the
northeastern United States to contain and eradicate the disease.
In 2004, USDA confirmed an H5N2 HPAI outbreak in chickens in the
southern United States. The disease was quickly eradicated thanks to
close coordination and cooperation between USDA, state, local, and
industry leaders. Because of the quick response, the disease was
limited to one flock.
Avian Influenza and USDA's Role in Protecting the United States
Q. What is USDA doing to prevent the introduction of HPAI into
the United States?
A: USDA recognizes that highly pathogenic avian influenza poses a
significant threat to animal health and has the potential to threaten
human health. Accordingly, USDA has safeguards in place to protect
against the introduction of highly pathogenic avian influenza into the
United States. USDA maintains trade restrictions on the importation of
poultry and poultry products from countries and/or regions where there
have been confirmed outbreaks of highly pathogenic H5N1 avian
influenza in commercial or traditionally-raised poultry.
Surveillance: USDA works with Federal and State partners and
industry to monitor U.S. bird populations. Surveillance is conducted
in four key areas: live bird markets, commercial flocks, backyard
flocks, and migratory bird populations. Extensive testing occurs in
live bird markets and commercial flocks. Additionally, birds that show
signs of illness are tested.
Through a backyard flock biosecurity program, USDA encourages
backyard and small poultry producers to strengthen biosecurity
practices in order to prevent the introduction of AI into their
flocks. Biosecurity refers to practical management practices that help
to prevent diseases.
USDA recognizes that prevention is only one part of a comprehensive
strategy and therefore continues to work closely with its Federal,
State, and Tribal partners and industry stakeholders to have effective
and coordinated emergency response plans at the ready should an
outbreak of highly pathogenic avian influenza occur in the United
States.
Q. Is USDA doing any work globally?
A. USDA works closely with international organizations like the
World Organization for Animal Health (OIE), the United Nations' Food
and Agriculture Organization (FAO), and World Health Organization
(WHO) to assist highly pathogenic H5N1 avian influenza-affected
countries and other neighboring Asian-Pacific countries with disease
prevention, management, and eradication activities. By helping these
countries prepare for, manage, or eradicate highly pathogenic H5N1
avian influenza outbreaks, USDA can help stop the spread of this virus
at its source - overseas.
Some efforts include:
 | Training sessions for veterinarians and poultry disease experts
from H5N1-affected and at-risk countries to teach testing
protocols.
| Professional expertise and funding to help launch the FAO-OIE
Crisis Management Center in Rome, to respond rapidly and
effectively to avian influenza outbreaks in poultry worldwide.
| Assistance to highly pathogenic H5N1-affected countries,
including laboratory equipment, reagents, and sample shipping
containers to bolster AI testing and diagnostic programs.
| In collaboration with FAO and OIE, USDA has deployed expert
scientists, veterinarians, and animal health emergency managers to
highly pathogenic H5N1-affected countries to test and diagnose
avian influenza; advise on surveillance and vaccination programs
to protect poultry; and advise on emergency contingency plans. |
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Q. If there was an outbreak of avian influenza in the United
States, what would USDA do?
A. USDA works closely with its Federal, State, and tribal partners,
as well as industry stakeholders, to coordinate emergency response to
animal disease outbreaks, including AI.
USDA provides expertise, funding, and support personnel to States
when low pathogenic avian influenza is detected. Close attention is
paid to low pathogenic avian influenza H5 and H7 strains, because of
their potential to mutate into highly pathogenic avian influenza. When
highly pathogenic avian influenza is detected, USDA and State
personnel are primary responders because of the rapid spread and high
death rate among poultry.
In the event of a highly pathogenic avian influenza outbreak in the
United States, USDA would work with States and industry to respond
quickly and decisively following these five basic steps:
| Quarantine – restrict movement of poultry and poultry-moving
equipment into and out of the control area;
| Eradicate – humanely euthanize;
| Monitor region – broad area of testing;
| Disinfect – kills virus; and
| Test – confirm that the poultry farm is AI virus-free. |
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USDA also maintains a bank of AI vaccine that could be used to
protect healthy birds outside a control area, if necessary.
USDA and State veterinarians are specially trained to diagnose
foreign animal diseases, such as avian influenza and regularly conduct
field investigations of suspicious disease conditions. This monitoring
is assisted by university personnel, State animal health officials,
USDA–accredited veterinarians, and members of the industry who
report suspicious cases. USDA and State animal health officials work
cooperatively with the poultry industry to conduct surveillance at
breeding flocks, slaughter plants, live–bird markets, livestock
auctions, and poultry dealers.
Avian Influenza Testing and Diagnostics
Q. What kind of test is used to diagnose avian influenza in
birds?
A: Samples are usually taken by swabbing the mucus that coats the
throat of live birds, which does not harm the birds. With wild birds,
a fecal sample can be taken instead. These samples go into sealed
tubes and are taken to USDA-approved laboratories. The initial test is
a polymerase chain reaction (PCR) test. A PCR test is a rapid method
of identifying the virus, typically producing results within 3 hours.
If a sample from an area where avian influenza has not been previously
detected tests positive on a rapid test, a virus isolation
confirmatory test is performed. This test involves growing the sample
in embryonated chicken eggs, which then provides the material to allow
detailed identification of the strain of virus and whether it is
highly pathogenic or low pathogenic. The virus isolation test can take
7-10 days to produce results. All H5 and H7 isolations are confirmed
at the National Veterinary Services Laboratory at Ames, Iowa.
Protecting Birds from Avian Influenza
Q. I have a back yard flock. How can I protect them from avian
influenza?
A. USDA recommends that owners of backyard flocks follow these six
tips to prevent poultry disease:
| keep your distance (restrict access to your property and your
birds);
| keep it clean (clean and disinfect your clothes, shoes,
equipment, and hands);
| don't haul disease home (if you have been near other birds or
bird owners, clean and disinfect poultry cages and equipment
before going home);
| don't risk disease from your neighbor (do not borrow lawn and
garden equipment, tools, or poultry supplies from other bird
owners);
| know the warning signs (sudden increase in bird deaths,
sneezing, coughing, nasal discharge, watery or green diarrhea,
lack of energy, poor appetite, drop in egg production, swelling
around the eyes, neck, and head, and purple discoloration of
wattles, combs, and legs); and
| report sick birds (call your local or State veterinarian, or
USDA toll-free at 1-866-536-7593). |
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Q. What can poultry producers do to prevent an AI outbreak on
their farms?
A. Poultry producers should strengthen biosecurity practices to
prevent the introduction of AI into their flocks. The following are
some sound biosecurity practices:
| Keep an "all–in, all–out" philosophy of flock
management. Avoid skimming flocks—birds left behind are exposed
to work crews and equipment that could carry poultry disease
viruses. Process each lot of birds separately, and clean and
disinfect poultry houses between flocks.
| Protect poultry flocks from coming into contact with wild or
migratory birds. Keep poultry away from any source of water that
could have been contaminated by wild birds.
| Permit only essential workers and vehicles to enter the farm.
| Provide clean clothing and disinfection facilities for
employees.
| Thoroughly clean and disinfect equipment and vehicles (including
tires and undercarriage) entering and leaving the farm.
| Do not loan to, or borrow equipment or vehicles from, other
farms.
| Change footwear and clothing before working with your own flock
after visiting another farm or
| live–bird market or avoid visiting another bird farm if
possible.
| Do not bring birds from slaughter channels, especially those
from live–bird markets, back to the farm. |
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If avian influenza is detected, farms must be thoroughly cleaned
and disinfected. Avian influenza viruses are inactivated by heat and
drying and also these viruses are very sensitive to most disinfectants
and detergents. The area to be disinfected must be clear of organic
material, which greatly increases the resistance of avian influenza
virus' resistance to disinfection.
Q. What should producers do if their birds appear to have signs
of avian influenza?
A. If birds exhibit clinical signs of highly pathogenic avian
influenza or might have been exposed to birds with the disease,
producers or bird owners should immediately notify Federal or State
animal health officials. Information can be found at www.usda.gov/birdflu.
Food Safety and Avian Influenza
Q. Does proper food handling prevent avian influenza?
A. Avian influenza is not transmissible by eating properly prepared
poultry. If highly pathogenic avian influenza were detected in the
United States, the chance of infected poultry or eggs entering the
food chain would be extremely low because of the rapid onset of
symptoms in poultry as well as the safeguards in place, which include
testing of flocks, and Federal inspection programs.
USDA works to educate the public about safe food handling practices
in response to numerous questions from the public about the human risk
associated with avian influenza.
Q. What does proper food handling mean?
A. Proper handling and cooking of poultry provides protection
against all avian influenza viruses, as it does against many viruses
and bacteria, including Salmonella and E.coli. Safe food handling and
preparation is important at all times. USDA continually reminds
consumers to practice safe food handling and preparation every day:
Cooking poultry, eggs, and other poultry products to the proper
temperature and preventing cross-contamination between raw and cooked
food is the key to safety. You should:
| Wash hands with warm water and soap for at least 20 seconds
before and after handling raw poultry and eggs;
| Prevent cross-contamination by keeping raw poultry and eggs away
from other foods;
| After cutting raw meat, wash cutting board, knife, and
countertops with hot, soapy water;
| Sanitize cutting boards by using a solution of 1 tablespoon
chlorine bleach in 1 gallon of water; and
| Use a food thermometer to ensure poultry has reached the safe
internal temperature of at least |
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165 °F to kill foodborne germs that might be present, including
the avian influenza viruses.
Avian Influenza and Human Health
Q. How can people become infected with avian influenza?
A. Although the highly pathogenic H5N1 avian influenza virus does
not usually infect people, more than 200 human cases have been
reported since 2004. Most people who have become sick or died from
highly pathogenic H5N1 have had extensive, direct contact with
infected poultry. Broad concerns about public health relate to the
potential for the virus to mutate, or change into a form that could
easily spread from person to person, a characteristic that could
result in a human influenza pandemic. There is no evidence that this
is occurring. Strains of avian influenza that have been detected in
U.S. poultry, including low pathogenic and highly pathogenic; have
caused no known human illnesses.
Avian Influenza and World Trade
Q. Could live poultry, poultry or poultry products come from a
country where there is highly pathogenic H5N1 avian influenza?
A. Poultry products imported into the U.S. must meet all safety
standards that are applied to foods produced in the United States.
No poultry or poultry products from countries and/or regions with
confirmed cases of highly pathogenic H5N1 avian influenza can be
imported into the United States. USDA regulations require that import
permits accompany properly sanitized poultry products, such as raw
feathers.
Q. Is avian influenza a reportable disease under international
trade guidelines?
A. Highly pathogenic avian influenza is considered a reportable
disease by the World Organization for Animal Health (OIE). OIE has
developed animal health standards that classify all H5 and H7 viruses
as reportable diseases.
Q. Does USDA maintain import restrictions?
A. USDA quarantines and tests live birds imported into the United
States to ensure that they do not have any foreign animal diseases
such as the highly pathogenic H5N1 avian influenza virus.
All imported live birds (except from Canada) must spend 30 days at
a USDA quarantine facility where they are tested for the avian
influenza virus before entering the country. Returning U.S.-origin pet
birds (except from Canada) also are tested and quarantined at a USDA
facility.
USDA maintains trade restrictions on the importation of poultry and
poultry products originating from countries and/or regions where the
highly pathogenic H5N1 avian influenza strain has been detected in
commercial or traditionally raised poultry (not wild birds). USDA
regulations require that import permits accompany properly sanitized
poultry products, such as raw feathers.
Additionally, USDA has increased its monitoring for illegally
smuggled poultry and poultry products through an anti-smuggling
program in coordination with the U.S. Department of Homeland Security
- Customs and Border Protection.
Q. How do I get more information about avian influenza?
USDA efforts to protect against and respond to bird flu:
www.usda.gov/birdflu
Report Sick Farm Birds: If your farm birds are sick or dying, call
USDA's Veterinary Services toll free at 1-866-536-7593, or your State
Veterinarian or local extension agent.
Report Dead Wild Birds: Dead wild birds can be reported to State or
Federal wildlife agencies. Information on how to make contact with
Wildlife officials in your State is available at www.usda.gov/birdflu
Safe Food Preparation: USDA Meat and Poultry Hotline -
1-888-MPHotline (1-888-674-6854), TTY: 1-800 256-7072 (available in
English and Spanish). Online answers are provided at www.fsis.usda.gov
by clicking on "Ask Karen."
Current Listing of Countries/Areas Affected with HPAI H5N1:
www.usda.gov/birdflu
U.S. Government efforts to protect human health:
www.pandemicflu.gov
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