This is due to wild birds, who are migrating for the winter, spreading the disease as they travel.
The disease is spread from bird to bird, by direct contact or through contaminated body fluids and faeces.
Bird keepers should note that it can also be spread by contaminated feed and water or by dirty vehicles, clothing and footwear.
There are two types of avian influenza; Highly-pathogenic avian influenza (HPAI) is the more serious type and often fatal. This strain has been reported in Great Britain.
The main signs of HPAI, given by the Department for Environment, Food and Rural Affairs and the Animal and Plant Health Agency are:
- Sudden and rapid increase in the number of birds found dead;
- Several birds affected in the same shed or air space;
- Swollen head;
- Closed and excessively watery eyes;
- Lethargy and depression;
- Recumbency and unresponsiveness;
- Incoordination and loss of balance;
- Head and body tremoring;
- Drooping of the wings and/or dragging of legs;
- Twisting of the head and neck;
- Swelling and blue discolouration of comb and wattles;
- Haemorrhages on shanks of the legs and under the skin of the neck;
- Loss of appetite or marked decrease in feed consumption;
- Sudden increase or decrease in water consumption;
- Respiratory distress such as gaping (mouth breathing), nasal snicking (coughing sound), sneezing, gurgling or rattling;
- Fever or noticeable increase in body temperature;
- Discoloured or loose watery droppings;
- Cessation or marked reduction in egg production.
Clinical signs can vary from species to species. Ducks and geese for example, may show minimal clinical signs.
The second strain, low pathogenic avian influenza (LPAI) is less serious. It also shows more vague clinical signs.
This strain can cause minor breathing problems and a reduction of egg production, but affected birds will not always show clear signs of infection.
LPAI can be more serious if a bird already has another illness.
Anyone who keeps poultry is urged to keep a close watch for signs of the disease and to contact their vet promptly should they have any concerns.