Avian Influenza: Always a Threat in the Fall

By Dr. F. Dustan Clark, Extension Poultry Veterinarian, University of Arkansas Cooperative Extension Service. He explains the background and history, virus description and disease symptoms, diagnosis and spread. He also gives tips on preventing disease exposure.
calendar icon 9 October 2002
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Background and History

Avian Influenza is a disease that can cause extremely high mortality in poultry. Outbreaks have cost the industry many millions to eradicate and the 1994-95 outbreak in Mexico that is still a problem in certain areas of that country. Costs can be devastating to producers since entire flocks can die in only a few hours after infection with a highly virulent strain of Avian Influenza. The costs associated with Avian Influenza outbreaks make it extremely important for the producer to be aware of the signs of the disease and take steps to prevent it.

The disease was first recognized in Italy in 1878 and was first reported in the United States in 1924 in New York City. An outbreak in Pennsylvania in 1983-84 was the most devastating disease outbreak in the recorded history of the U.S. poultry industry. It cost the industry an estimated $60 million to eradicate the disease and consumers about $349 million to replace the table eggs lost in the quarantine region.

Virus Description

The older literature called Avian Influenza 'Fowl Plague'. A virus called an orthomyxovirus causes Avian Influenza. The virus has two types of glycoproteins that project from the virus coat which may either protect the particle from destruction or allow it to adhere to a surface. These glycoproteins are called Haemagglutinin (H) and Neuraminidase (N). There are 15 different types of H glycoproteins and nine different types of N glycoproteins. These H and N glycoproteins are used by poultry health professionals to tell one Avian Influenza virus strain from other types, such as H5N2. The viruses are also designated as low pathogenic and high pathogenic based on their ability to cause death in susceptible chickens. Thus you can have a virus designated H5N2 that causes low mortality and is called a low pathogenic type or you could have an H5N2 that causes high mortality and as such is called a high pathogenic type. However, the virus can change from a low pathogenic type to a high pathogenic type without warning.

Disease Symptoms Diagnosis and Spread

Avian Influenza has an incubation period of 3-7 days depending on the virus dose, poultry species infected, route of exposure, and several other factors. The symptoms exhibited by an infected bird are variable and depend on the pathogenicity of the virus. Some of the possible symptoms are: depression, diarrhea, dehydration, appetite loss, weight loss, huddling, a drop in egg production and respiratory symptoms (cough, sneeze, sinusitis). The lesions that could be observed include: a bloody nasal discharge, facial swelling, blue discoloration of the face, subcutaneous hemorrhages, tracheal inflammation, nasal inflammation and hemorrhages on the shanks and in the proventriculus. There is no acceptable or practical treatment for poultry infected with high pathogenic Avian Influenza infected poultry.

Avian Influenza is diagnosed by blood testing and virus isolation. Blood testing is considerably more rapid and less expensive than virus isolation, but virus isolation is much more accurate than blood testing. Poultry found positive for the Avian Influenza virus are currently quarantined and destroyed to prevent spread to other flocks. Destruction of affected animals is the only viable method to control the spread of the disease.

The disease spreads from infected birds to non-infected birds via respiratory and gastrointestinal secretions. Susceptible birds can be exposed to respiratory or gastrointestinal secretions in numerous ways. Secretions can be spread on contaminated footwear, clothing, egg flats, equipment, cages, etc. In fact, Avian Influenza is most often spread from infected to noninfected flocks by people carrying the virus usually on their clothes or footwear. However, the virus can live for short periods on human skin or in human nasal passages. In addition, the virus can be shed by infected wild birds including migratory waterfowl (e.g. ducks and geese) or game birds, which show no clinical signs of the disease. The Avian Influenza virus has also been frequently isolated from clinically normal exotic birds. At moderate temperatures the virus can remain viable in organic materials for long periods of time and can survive indefinitely in frozen materials.

Steps to Prevent the Disease Exposure

  1. Keep 'No Visitors' and/or 'Restricted' signs posted at the road entrance of the farm.
  2. Do not allow visitors in the poultry houses or on the farm.
  3. All farm personnel should wear separate clothing (including shoes, boots, hats, gloves, etc.) on the farm. Clothes used on the farm should stay on the farm.
  4. Completely change all clothing after caring for the flock and wash hands and arms thoroughly before leaving the premises.
  5. Do not visit other poultry farms or flocks or have contact with any other species of birds.
  6. Keep all poultry houses securely locked. Lock all houses from the inside while working inside.
  7. All equipment, crates, coops, etc., must be thoroughly cleaned and disinfected before and after use.
  8. All essential visitors (owners, feed delivery personnel, poultry catchers and haulers, service men, etc.) are to wear protective outer clothing (coveralls), boots, and headgear prior to being allowed near the poultry flock or farm.
  9. Monitor all vehicles (service, feed delivery, poultry delivery or removal, etc.) entering the premises to determine if they have been properly cleaned and disinfected. This includes disinfection of the tires and vehicle undercarriage.
  10. Sick and dying birds should be submitted to a diagnostic laboratory for proper diagnosis of the problem. All commercial growers should contact their flock supervisor and follow their instructions.
  11. Dead birds are to be properly disposed of by burial, incineration or other approved method.
  12. Any person handling wild game (especially waterfowl) must completely change clothing and shower or bathe before entering the premises.
  13. Do not borrow equipment, vehicles, etc., from another poultry farm.
  14. Do not visit areas where Avian Influenza is a problem.
Dr F. Dustan Clark is Extension Poultry Veterinarian at University of Arkansas Cooperative Extension Service. This article was published in Avian Advice newsletter (Volume 2, Number 1; Fall 2000)

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