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 Post subject: Avian Influenza
PostPosted: Fri Apr 05, 2013 12:39 am 
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Wise Wyandotte
Wise Wyandotte

Joined: Fri Feb 15, 2008 11:58 am
Posts: 4234
Location: Plainland, SEQ
AVIAN INFLUENZA (FOWL PLAGUE)

Also called:
AI, European fowl pest, Fowl plague

Incidence:
- worldwide in domestic and wild birds of all ages, but serious outbreaks are rare

System/Organ affected:
- primarily respiratory, sometimes involves digestive and nervous systems

Incubation period:
- a few hours to 3 days

Progression:
- severity of the disease depends on the strain of the virus
- acute, spreads rapidly, runs through flock in 1 to 3 days

Symptoms:
- sudden death without signs or
- severe depression
- droopiness
- coughing, sneezing, rattling
- watery eyes
- huddling, ruffled feathers
- loss of appetite, weight loss
- reduced fertility, increased broodiness
- sudden drop in egg production, eggs with soft or no shells
- skin hemorrhages, sometimes bloody nasal discharge
- fever
- greenish diarrhea
- darkened head, comb, wattles and or swollen eyes, comb and wattles
- sometimes twisted neck, loss of coordination, paralysis of legs or wings
- swollen hock joints, purplish shanks, rapid deaths

Percentage affected:
- 100 percent

Mortality:
- 0 to 100 percent, usually low
- the highly virulent form causes very high mortality and is a notifiable disease.


Resembles:
- mild form: infectious bronchitis, chlamydiosis, chronic respiratory disease, Newcastle disease

Diagnosis:
- symptoms (high rate of rapid deaths), confirmed by laboratory identification of virus

Cause:
- several strains of type A influenza orthomyxoviruses, some mild, some lethal, that affect a wide variety of bird species but do not survive long in the environment
- infection often in combination with a bacterial or mycoplasmal disease

Transmission:
- highly contagious
- contact with infected birds (either domestic or wild) and their body discharges, especially droppings
- spreads through improper disposal of infected birds and their manure, on contaminated equipment and the feet of insects, rodents and humans

Prevention:
- do not visit flocks or let people visit your flock if an outbreak occurs in your area
- keep chickens away from water frequented by wild waterfowl

Treatment:
- no vaccine and not treatment
- mild form: antibiotics to prevent secondary bacterial or mycoplasmal infections
- survivors are immune for several months but are carriers
- severe form: this is a reportable disease

Human health risk:
- type A influenza viruses have the potential for causing infection in humans and other mammals

References:
http://poultryworld.tripod.com/dis_dir.htm
http://www.sp.uconn.edu/~mdarre/CPA/news.html
http://fowlfacts.proboards.com


Further reading:
Avian Influenza -Understanding Influenza

http://www.aviagen.com

Nick Dorko of Aviagen urges producers to strengthen 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 airborne infection which may pose a risk for up to 3 km 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.

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
- 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.
- fSeek 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
• http://www.phls.org.uk/topics_az/influenza/flufaq.htm
• http://www.aphis.usda.gov/lpa/pubs/fsheet_faq_notice/fsfaqnot_animalhealth.html

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