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Highly Pathogenic Avian Influenza
Veterinary Services
March 2004
A Threat to U.S. Poultry
Worldwide, there are many strains of avian influenza (AI) virus that
can cause varying amounts of clinical illness in poultry. AI viruses
can infect chickens, turkeys, pheasants, quail, ducks, geese, and guinea
fowl, as well as a wide variety of other birds. Migratory waterfowl
have proved to be the natural reservoir for this disease.
AI viruses can be classified into low pathogenic (LPAI) and highly
pathogenic (HPAI) forms based on the severity of the illness they cause.
Most AI virus strains are LPAI and typically cause little or no clinical
signs in infected birds. However, some LPAI virus strains are capable
of mutating under field conditions into HPAI viruses.
HPAI is an extremely infectious and fatal form of the disease for chickens.
The U.S. Department of Agriculture's (USDA) Animal and Plant Health
Inspection Service (APHIS) works to keep HPAI from becoming established
in the U.S. poultry population. HPAI can strike poultry quickly without
any infection warning signs. Once established, the disease can spread
rapidly from flock to flock. It is essential for the U.S. poultry industry
to be alert to this disease threat.
Clinical Signs
Birds affected with HPAI may show one or more of the following signs:
- Sudden death without clinical signs
- Lack of energy and appetite
- Decreased egg production
- Soft–shelled or misshapen eggs
- Swelling of the head, eyelids, comb, wattles, and hocks
- Purple discoloration of the wattles, combs, and legs
- Nasal discharge
- Coughing, sneezing
- Incoordination
- Diarrhea
Economic Impact of an HPAI Outbreak
A major outbreak of HPAI would be costly to the poultry industry, consumers,
and taxpayers. Eradication of an HPAI outbreak that occurred during
1983 and 1984 in the northeastern United States resulted in the destruction
of more than 17 million birds at a cost of nearly $65 million. This
outbreak also caused retail egg prices to increase by more than 30 percent.
Introduction and Spread of HPAI Virus
Exposure of poultry to migratory waterfowl and the international movement
of poultry, poultry equipment, and people pose risks for introducing
HPAI into U.S. poultry. Once introduced, the disease can be spread from
bird to bird by direct contact. HPAI viruses can also be spread by manure,
equipment, vehicles, egg flats, crates, and people whose clothing or
shoes have come in contact with the virus. HPAI viruses can remain viable
at moderate temperatures for long periods in the environment and can
survive indefinitely in frozen material. One gram of contaminated manure
can contain enough virus to infect 1 million birds.
Potential Threat to Human Health
In some instances, strains of HPAI viruses can be infectious to people.
Human infections with the avian influenza viruses under natural conditions
have been documented in recent years. The H5N1 strain, isolated in Hong
Kong in 1997, was highly pathogenic for chickens and caused a limited
outbreak in 18 people. Six of these individuals died. Since mid–December
2003, a growing number of Asian countries have reported outbreaks of
HPAI in chickens and ducks. The rapid spread of HPAI, with outbreaks
occurring at the same time, is historically unprecedented and of growing
concern for human health as well as for animal health.
According to the World Health Organization (WHO), particularly alarming
is the HPAI strain of most of these outbreaks—H5N1—which
has jumped the species barrier causing severe disease, with high mortality
in humans. For this reason, poultry personnel and avian health care
specialists should wear adequate personal protective equipment, such
as boots, coveralls, gloves, face masks, and headgear, and follow appropriate
sanitary and disinfectant procedures when on premises known or suspected
to be infected with HPAI.
Of greater concern to WHO is the possibility that the present situation,
if the virus acquires human influenza genes, can give rise to human–to–human
transmission and possibly another influenza pandemic in people.
Trade Restrictions
Because many Asian countries are not considered free of another contagious
poultry disease, exotic Newcastle disease (END), the United States restricts
imports of poultry and poultry products from all Asian countries. Therefore
live birds, poultry and hatching eggs would be quarantined for 30 days,
and would be tested for END and AI while in quarantine.
Regulations require that poultry meat be cooked or processed in a manner
that would ensure that the virus be inactivated if it were present.
Additionally, poultry meat is not imported from Asia because USDA’s
Food Safety and Inspection Service (FSIS) has not approved Asia’s
poultry meat processing plants. However, poultry meat extract (i.e.,
instant soup and chicken noodle soup) can be imported as these contain
less than 2 percent meat and are not subject to FSIS regulations. The
National Center for Import/Export (NCIE) issues import permits for these
extracts requiring government certification of cooking at boiling temperature
or at least cooked to 72 C internal temperature. When a product reaches
this internal temperature the END and HPAI viruses are considered inactivated.
Products that contain eggs or egg products as an ingredient that are
in finished form and ready for commercial distribution, such as cake
mixes, bread mixes, drink mixes, do not require a veterinary import
permit. Finished products containing feathers and/or down imported ready
for retail sale/commercial distribution, such as mattresses, jackets,
pillows, do not require a veterinary import permit and are subject to
inspection at the port of entry to verify that the feathers and/or down
are clean, dry, and free from blood, skin, and manure.
Other poultry products may be imported for research or commercial purposes
depending upon the pre–importation processing protocols. These
poultry products require an import permit issued by NCIE.
Biosecurity Measures on the Farm
Poultry producers should strengthen biosecurity practices to prevent
the introduction of HPAI into their flocks. The following are some sound
biosecurity practices:
- Keep an "all–in, all–out" philosophy of flock
management.
- Protect poultry flocks from coming into contact with wild or migratory
birds. Keep poultry away from any source of water that may 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.
- Avoid visiting other poultry farms. If you do visit another farm
or live–bird market, change footwear and clothing before working
with your own flock.
- Do not bring birds from slaughter channels, especially live–bird
markets, back to the farm.
Biosecurity Measures at Live–bird Markets
To prevent a possible outbreak of HPAI, poultry producers and dealers
must also use biosecurity precautions at live–bird markets. Live–bird
markets operate in many major cities.
Avian influenza viruses can be introduced into these markets if they
receive infected birds or contaminated crates and trucks. Once the virus
is established in the market, the movement of birds, crates, or trucks
from a contaminated market can spread the virus to other farms and markets.
Therefore, the following protective measures should be taken at live–bird
markets to prevent the possible spread of disease:
- Use plastic instead of wooden crates for easier cleaning.
- Keep scales and floors clean of manure, feathers, and other debris.
- Clean and disinfect all equipment, crates, and vehicles before returning
them to the farm.
- Keep incoming poultry separate from unsold birds, especially if
birds are from different lots.
- Clean and disinfect the marketplace after every day of sale.
- Do not return unsold birds to the farm.
For more specific information about biosecurity and cleaning and disinfection
practices, contact your local APHIS' Veterinary Services (VS) office.
Disease Prevention Activities
To prevent HPAI from being introduced into the United States, USDA
requires that all imported birds (poultry, pet birds, birds exhibited
at zoos, and ratites) be quarantined and tested for this virus before
entering the country.
In addition to international import restrictions, APHIS and State veterinarians
specially trained to diagnose foreign animal diseases regularly conduct
field investigations of suspicious disease conditions. This surveillance
is assisted by university personnel, State animal health officials,
USDA–accredited veterinarians, and members of industry who report
suspicious cases.
Furthermore, APHIS 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.
If HPAI were detected in U.S. poultry, APHIS veterinarians would work
quickly with their State counterparts and the industry to implement
measures such as quarantine, control, and cleanup to prevent opportunities
for the virus to spread.
Report Suspicious Signs
If birds exhibit clinical signs of HPAI or may have been exposed to
birds with the disease, immediately notify Federal or State animal health
officials.
For more information about HPAI or biosecurity practices, contact:
USDA, APHIS, VS
Emergency Programs
4700 River Road, Unit 41
Riverdale, MD 20737–1231
Telephone (301) 734–8073
Fax (301) 734–7817
For public health information, contact the Centers for Disease Control
and Prevention in Atlanta, GA, at (404) 639-3311. For import information
contact APHIS, VS, NCIE at (301) 734–3277 or at the Web site www.aphis.usda.gov/vs/ncie/importing.htm.
Current information on animal diseases and suspected outbreaks is also
available on the Internet at http://www.aphis.usda.gov.
The U.S. Department of Agriculture (USDA) prohibits discrimination
in all its programs and activities on the basis of race, color, national
origin, sex, religion, age, disability, political beliefs, sexual orientation,
or marital or family status. (Not all prohibited bases apply to all
programs.) Persons with disabilities who require alternative means for
communication of program information (Braille, large print, audiotape,
etc.) should contact USDA's TARGET Center at (202) 720-2600 (voice and
TDD).
To file a complaint of discrimination, write USDA, Director, Office
of Civil Rights, Room 326–W, Whitten Building, 14th and Independence
Avenue, SW, Washington, DC 20250–9410 or call (202)720–5964
(voice and TDD). USDA is an equal opportunity provider and employer.
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