AVIAN INFLUENZA (AI)
This disease (also referred to as Bird Flu Virus) is infectious in birds and is caused by various strains of avian influenza virus. Some are present in wild bird populations without leading to disease. However, those that infect domestic poultry can cause severe disease.
Epidemiology and Aetiology
Avian Influenza (AI) viruses are member of the family Orthomyxoviridae. It is in the genus influenza A.
AI can take two forms, a mild form referred to as low pathogenicity avian influenza (LPAI) and a more severe form called highly pathogenic avian influenza (HPAI or H5N1. The latter form is characterised by sudden onset, severe illness and rapid death, with a mortality that can approach 100%.
It is often difficult to identify the source of the infection in domestic poultry. However, it is believed that most infection starts from direct or indirect contact of poultry with water birds. The virus is spread from infected birds through their saliva, nasal secretions and faeces. Poultry can be infected by coming into contact with contaminated surfaces such as dirt or cages and materials such as water and feed.
Clinical Signs
Infection causes a wide spectrum of symptoms in birds, ranging from mild illness (low pathogenic form) to a highly contagious and rapidly fatal disease resulting in severe epidemics.
They will vary depending on many factors such as the age and species of the affected poultry, general husbandry practices and the pathogenicity of the strain of influenza virus.
Some clinical signs include:
- Soft-shelled eggs
- Sudden reduction in egg production
- Ruffled feathers
- Depression and lethargy
- Unusual head or neck posture
- Loss of appetite, reluctance to drink
- Cyanosis (Purple-blue colouring) of wattles and comb
- Oedema and swelling of the head, wattle, comb and hocks
- Diarrhoea
- Discharge from nostrils (tinged with blood)
- Lack of coordination
- Respiratory distress
- Increase in death rate within a flock.
Pathogenesis and Lesions
Lesions will vary depending on the pathogenicity of the virus, the age of the bird and the type of poultry. They can include swelling of the face and the beak region. Once you have removed the skin from the carcass you might find a clear-coloured fluid in the subcutaneous tissue.
Blood vessels will usually be engorged with the virus.
There may be signs of haemorrhage in the trachea, proventriculus, beneath the lining of the gizzard and throughout the intestines.
Swelling and haemorrhages may also be found in the muscle along the breast bone, in the heart, gizzard and abdominal fat.
Young broilers may display signs of dehydration, but with lesions either less pronounced or absent.
Specimen Collection
The specimens required will depend on the regulations of the country you are in. Usually two throat (oropharyngeal) swabs are required. Other specimens may include:
- Nasal swab or wash
- Tracheal aspirate
- Other respiratory specimens such as Bronchoalveolar lavage (BAL) fluid and pleural fluid0
Other specimens may be required depending on the observed clinical signs.
Diagnosis
Diagnosis is made following display of clinical symptoms in flocks along with positive specimen results.
Differential Diagnosis
Infections in birds can lead to a variety of clinical signs that can vary according to the host, strain of virus and the hosts’ immune status, presence of any secondary exacerbating organisms and environmental conditions. AI clinical signs are similar to those of other avian diseases. It can sometimes be confused with
- Infectious bronchitis
- Infectious laryngotracheitis
- Cholera
- and Newcastle Disease
Treatment
There is currently no effective treatment of AI in poultry once clinical signs of the disease appear. However, good husbandry and nutrition as well as the use of broad spectrum antibiotics may reduce losses due to secondary infection.
Following a viral outbreak, all buildings should be thoroughly disinfected and the infected flock removed. There should be a waiting period of 7 days before repopulation with birds following removal of the infected population.
Prevention and control
Some countries have encouraged vaccination programs along with strict quarantine rules to control mild forms of the disease in commercial poultry flocks. Where there have been serious outbreaks, strict quarantine and destruction of the population of infected flock is the most effective control measure. The success of these programs relies on the support of the poultry and associated industries. Relevant authorities should also be notified of any outbreaks.
