What is Influenza?

Avian influenza (AI) Type A viruses may cause infection in domestic poultry, wild birds, and those kept as pets or in zoos. AI viruses in domestic poultry are usually of low pathogenicity and cause infection with no symptoms, or infection where you will see either respiratory disease or a decrease in their production of eggs. There are a few AI viruses that are highly pathogenic that will result in more severe infections and have a high mortality rate; this has been called “fowl plague”. 

AI infections in wild birds usually don’t show symptoms. The viruses are a natural occurrence in wild aquatic birds and while they can be infected with the viruses in their intestines and respiratory tract, they usually do not show symptoms of illness. The avian influenza A viruses are extremely contagious among birds and can cause serious illness in a variety of domesticated birds.

Occurring as a low pathogenicity or high pathogenicity virus, avian influenza can lead to respiratory symptoms through systemic illness and death in infected birds.

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Symptoms of Influenza in Birds

In a low pathogenicity infection of AI you may notice:

  • Respiratory symptoms (sneezing, coughing, discharge from the nose and mouth, sinus swelling)
  • Sinusitis often occurs in domestic ducks, quail and turkeys
  • Respiratory tract lesions, along with congestion and swelling in the lungs and trachea

In a high pathogenicity infection of AI you may see:

  • Serious systemic disease
  • A high rate of death, especially in chickens and turkeys
  • In particularly severe cases there may be no clinical signs prior to death
  • In acute cases, the head, comb, wattle and snood may swell 
  • Greenish diarrhea
  • Hemorrhages in organs and muscles
  • Discharge from the nose or mouth that includes blood

Other symptoms that may be noticed are a significant loss in appetite where the bird eats less food, a decrease in egg production and apparent depression.

Types 

Viruses can either be low pathogenicity or high pathogenicity.

In viruses with a low pathogenicity, the bird will usually show respiratory symptoms. Sinusitis will often occur in domestic ducks, quail and turkeys. The death rate is typically low when it comes to infection with low pathogenicity viruses, with the exception of when there is a secondary infection occurring or if the condition is worsened as a result of stressors in the environment.

In high pathogenicity viruses, severe systemic disease will typically occur, regardless of whether there is any secondary infection occurring. Mortality can reach 100%. Should a bird survive a peracute infection, they may experience involvement of their central nervous system and you may notice they lack coordination, their wings droop or they are paralyzed. Microscopic lesions may be present, though their location and severity will vary.

AI viruses are divided into 16 hemagglutinin subtypes (H1-16) and 9 neuraminidase (N1-9) subtypes. These classifications are based on hemagglutinin inhibition and neuraminidase inhibition tests. The majority of AI viruses (H subtypes) are considered low pathogenicity. Some of the H5 viruses, and the H7 can be very pathogenic for chickens, turkeys and related birds. The high pathogenicity viruses result from a mutation of some of the H5 and H7 viruses that are low pathogenicity. 

Causes of Influenza in Birds

The cause of AI is a virus, called Orthomyxovirus Type A. Its ability to cause disease varies. Those that are highly pathogenic are typically of the H groups 5 and 7 when designated.

Birds that are infected can shed the virus in saliva, nasal discharge and their feces. Birds that are susceptible can become infected when coming into contact with the virus as it is shed, through ingesting or inhaling it. Infection is also possible through coming in contact with surfaces contaminated with the virus. The incubation period varies when it comes to these viruses. It can be a few days in a particular bird to about two weeks in the flock.

Diagnosis of Influenza in Birds

To diagnose AI, oropharyngeal and cloacal swabs may be used; the viruses of both low and high pathogenicity can be easily isolated from them. High pathogenicity viruses may also be isolated from internal organs. The virus can be identified through Agar Gel Immunodiffusion or other immunoassays. An influenza A-specific reverse transcriptase-PCR test can determine that viral RNA is present. 

A veterinarian will seek to determine that infection with a low pathogenicity virus is the reason for respiratory disease or a decrease in egg production as opposed to other conditions like:

  • Infectious bronchitis 
  • Infectious laryngotracheitis 
  • Low virulent Newcastle disease 
  • Bacterial disease like mycoplasmosis, infectious coryza or ornithobacteriosis 
  • Fungal disease like aspergillosis

When considering a possible high pathogenicity infection, a veterinarian will want to rule out:

  • Virulent Newcastle disease
  • Peracute septicemic fowl cholera
  • Heat exhaustion
  • Significant lack of water

Treatment of Influenza in Birds

While there is no efficacious treatment for AI, ensuring that the birds have good living conditions, proper nutrition and are given broad spectrum antibiotics should help minimize the losses that occur through secondary infection. Increasing environmental temperatures is also thought to be helpful. Flocks of birds that recover from AI do continue to shed the virus periodically.

To avoid transmission of the virus, any place where an infected bird or flock has been should be cleaned and disinfected once they are no longer present. Any litter or manure should be composted.

Recovery of Influenza in Birds

Vaccines are key in preventing birds from developing clinical signs of infection. It is thought that replication of the virus, as well as shedding of it from the respiratory and gastrointestinal tracts. will be decreased in birds that have received the vaccine.