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Understanding
Influenza
Nick Dorko of Aviagen urges producers to srengthen biosecurity
practices to prevent the introduction of high path avian
influenza into their flocks.
Avian Influenza is a respiratory illness associated with
infection by influenza virus Type A. Severe infection is
systemic. Influenza is caused by a family of viruses and can
infect a variety of species including humans, pigs and
poultry. Two proteins on the surface of the virus, called
Haemagglutinin(H) and Neuraminidase(N) vary between the
different flu viruses. Among the influenza type A virus
there are 15H and 9N subtypes, resulting in 15x9 different
combinations.
 The
different combinations of H and N alter the viruses' ability
to cause infection. Most outbreaks of human flu are an H1N1,
H1N2 and H3N2 and are distinct from Avian Influenza which is
usually H5, H7 or H9.
What is Avian Influenza?
Avian influenza (AI) viruses are a group of viruses that can
infect many species of birds. Some AI viruses can cause
catastrophic mortality in poultry, with up to 100% mortality
within 5 days. This is now usually referred to as high path
avian influenza (HPAI) but names used in the past include
Fowl Pest, Fowl Plague and Avian Flu etc. Mortality can be
up to 100% in chickens and turkeys. HPAI in Chickens has
only been caused by H5 and H7 types of Avian Influenza virus
(AIV). Low path (LPAI) are virus infections in poultry that
are not apparent or have mild effects (egg drops, kidney
failure or respiratory disease are typical) and are caused
by H7 (for example Connecticut last year), H5, H9 (currently
from the Middle East to Japan) and other types (H1 in
turkeys and swine in Northern Ireland).
How is AI transmitted?
The virus is excreted from the respiratory system and faeces
of infected birds. This excretion can be in enormous
quantities.Where does the primary source infection of AI
into domestic poultry come from?
As a group the reservoir for these viruses is waterfowl and
other migratory birds and in fact these infections cause
very little effect in these birds or domestic ducks. The
infection in these birds is usually LPAI. However the LPAI
then gets into commercial poultry, usually free range birds,
or through contamination of water supplies to intensive
poultry. The LPAI causes few clinical signs in poultry, but
will sometimes act synergistically with other pathogens to
cause disease. However, some LPAI H5 or H7 viruses mutate
and can become HPAI. They then become highly virulent and
highly infectious with massive excretion.
Once infection is in domestic poultry and has mutated to
HPAI, there is enormous excretion of the virus and usually
very rapid spread by people, vehicles and equipment.
Infected faeces are usually the carrier.
There is no vertical infection – but surface contamination
of eggs with infected faeces does pose a risk.
How easy is it to kill the virus?
Avian influenza is a fragile virus but can survive in cold
moist conditions for some weeks and in contaminated surface
water and lakes for months in colder climates. Wetting,
drying, detergents and even simple soap will effectively
inactivate the virus on cleaned surfaces. Using a
combination of detergents and disinfectants is the most
effective procedure. When using combinations of products
make sure they are compatible. However, carcasses, litter
and wild birds pose special problems.
Chlorination of water will quickly kill the virus.
Wild birds?
The most common route of infection from wild birds is
through them contaminating drinking water or through direct
contact with free range poultry. Chlorination of drinking
water will very effectively kill the AI virus. Wild birds
must be discouraged by preventing access to feed etc. If
there is HPAI in a region, then keeping free range birds
indoors should be considered.
In warm climates cool pads are used to control house
temperature. The cool pad water reservoir must be
effectively bird proofed, otherwise carrier wild birds
bathing or drinking from these reservoirs will shed the
virus into the water. The virus will then gain access to the
house as the water is pumped to the cool pad system.
How does AI move?
The movement of people and equipment mechanically carrying
the virus is by far the greatest threat to the industry. The
list is long and includes feed delivery vehicles, egg
vehicles, egg flats, farm workers, catching teams, etc. An
infected flock will excrete enormous quantities of the virus
and will very easily contaminate vehicles, people and
clothing that enter the farm. In addition, there will be a
plume of windborne infection which may pose a risk for up to
3 kms depending on the number of birds, severity of
infection and climatic conditions.
Prevention
If there is suspicion of AI on a farm, then the farm must be
quarantined and all direct and indirect contact with other
poultry farms prevented.
Routine precautions
Clean laundered clothes should be worn to farms. Vehicles
that have been to AI areas or transported people who have
been should not be used to go to "clean" farms. The
exclusion of people that have flu-like symptoms would be
prudent.
International status of AI
HPAI is an Office International Epizootic (OIE) List A
disease and is defined as occurring when certain criteria
are met. Another List A disease of poultry is Newcastle
disease. All countries in the OIE have agreed to rapidly
tell the OIE, and therefore all other member countries, when
List A diseases occur. This is to prevent the spread of List
A diseases by movement of birds.
Typically, the planned response to these diseases is
slaughter of infected flocks (with or without compensation)
and rigorous monitoring, tracing and control of flocks that
could be infected. This includes the movement of personnel
and disposal of potentially infected materials. This needs
to be done on an industry-wide (meat, layer, turkey, poultry
products and other birds) and backyard-poultry wide basis in
an area which is why the Government veterinary services are
the best placed to do this.
What about vaccination?
Vaccination has to be specific for the H type, e.g. to
protect against an H5 infection, a H5 vaccine needs to be
used. Vaccines usually consist of killed virus plus adjuvant
but there have been live pox vaccines, with Influenza
antigens genetically engineered into them, used in Mexico.
Vaccination makes diagnosis more difficult because birds
become seropositive. Some new serological tests can tell the
difference between a vaccinated bird and an infected bird.
There are no current vaccines that protect against all
possible AI types and vaccination has not been popular with
official veterinarians.
But in the face of an outbreak vaccination with a specific H
type can be used to ring-vaccinate round the outbreak and
may be an effective control, if combined with excellent
biosecurity and a properly coordinated eradication of all
infected flocks. Vaccination has been used successfully
especially against LPAI infections, for example in turkeys
in Minnesota and in Italy.
As outbreaks become too large for veterinarians and the
industry to handle, vaccination becomes a more attractive
option, even at the expense of losing the ability to export.
Government action needs to be swift and decisive to minimize
the spread of the virus.
What risk is posed by poultry products?
Live birds and hatching eggs present a risk, and can be
contaminated before clinical signs are seen in the source
flock. Cooked chicken products represent no risk, provided
normal precautions are taken to prevent recontamination
after cooking.
Status of the Aviagen flocks?
All of our flocks are negative for AI. The programmes, both
in the UK and the USA, are closely monitored by official
government veterinarians. Currently, these flocks
contribute to over 1000 export orders annually and are
therefore subject to a very high level of scrutiny. At the
moment, DEFRA in the UK and the USDA in the USA certify
our flocks as negative, based on substantial testing. We
maintain protection against AI, and a range of other
diseases, through our high levels of biosecurity and the
advantage of no local AI challenges.
What should you do if AI is suspected?
If AI is suspected the following guidelines should be
followed:
• Immediately quarantine the flock and any recent contact
flocks.
• Contact the official government veterinarians and company
veterinarians and arrange for samples to be sent to an
International reference lab. For example. Avian Virology,
VLA, Weybridge, New Haw, Addlestone, Surrey, KT15 3NB,
ENGLAND - phone +44 1932 357736.
• Remember that with acute infection there will be mortality
before seroconversion and samples have to go for virus
isolation or PCR to confirm diagnosis. International
reference laboratories such as Weybridge are also potential
sources of antigens for HI testing.
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 lend or borrow equipment or vehicles to or from
other farms.
• Make sure plastic egg flats are properly washed and
disinfected before accepting on your farm. Do not re-use
fiber egg flats or any other packing materials.
• 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
Influenza in huumans?
There have been some rare exceptions with H5 viruses causing
serious infections in a very small number of susceptible
humans who have been in very close contact with infected
poultry. These infections have not been able to transfer
efficiently between humans and are far less infectious to
people than other human influenzas.
What precautions should people take?
• People are the number one source for the spread of AI.
Employees, farm workers and visitors should have no contact
with other poultry farms, poultry shows, live bird markets
or backyard birds.
• Avoid contact with birds with AI; wear clean protective
clothing and a face mask.
• Ensure good personnel hygiene with regular washing of
hands, particularly before handling food.
• Seek medical advice on flu vaccination and the use of the
antiviral drugs that can control influenza infection.
Conjunctivitis is the most common, though infrequent, sign
of AI infection in people.
If, despite the above, a person has conjunctivitis, flu-like
or respiratory symptoms within 7 days of contact with
poultry then seek medical advice and explain the entire
situation.
References
• World Poultry November 2000 Special Avian Influenza.
Elsevier.
• The Definition of Avian Influenza (The use of vaccination
against Avian Influenza) Scientific Committee on Animal
Health and Animal Welfare. Sanco/B3/AH/R17/2000.
• Proceedings of the Fifth International Symposium on Avian
Influenza. Special Issue of Avian Diseases. The American
Association of Avian Pathologists. 2003 (Also
available in CD).
• Orthomyxoviridae – Avian Influenza by Dennis Alexander. In
Poultry Diseases. 5th Edition.
• Influenza by David E. Swayne and David A. Halvorson in:
Diseases of Poultry. 11th Edition. Y.M. Saif and editors...
2003
• Highly pathogenic Avian Influenza by David E. Swayne and
David. L. Suarez in: Diseases of Poultry: World Trade and
Health Implications. Rev. sci. tech.Epiz., vol 19 (2) 2000
• www.phls.org.uk/topics_az/influenza/flufaq.htm
• www.aphis.usda.gov/lpa/pubs/fsheet_faq_notice/fsfaqnot_
animalhealth.html
For further information please contact your local Aviagen
representative.
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