Infectious Bronchitis (IB) is a highly contagious infection of the upper respiratory tract caused by an avian coronavirus. The virus has been found in pheasants and peafowl but causes disease in chickens. The virus is worldwide with many types, some types are widespread and others more regional. It can quickly mutate so there may be several types in a region.
It is spread through respiratory droplets in the air and through faeces. The incubation period is about one to three days and the highest level of transmission can last three to five days. Morbidity, which is the condition of suffering from a disease in non-vaccinated flocks, is 100% but it usually has a low mortality rate of about 5%. However, some types of IB can cause a kidney infection leading to death, raising the mortality rate to about 60%.
It is present worldwide and as it mutates very quickly there may be several types present at any one time. It’s passed from bird to bird so it thrives in conditions where they are housed close together. The infection is spread through the air via respiratory discharges and also through faeces. This means it spreads rapidly where there is a high bird density.
The clinical signs of Infectious Bronchitis can vary depending on the age of the chicken. In young birds the signs are coughing, gasping, sneezing and nasal discharge. In general they will be depressed and have reduced weight gain and feed consumption. In adult layers and breeders after the respiratory signs they’ll show a drop in egg production with deformed shells and internal changes, affecting the hatchability rate. It can take eight weeks for egg production to return to normal.
There are several serology tests that can confirm the presence of the disease. In post mortem examination of young chicks a yellow cheesy plug at the tracheal bifurcation is an indicator. In older birds mucus and redness in the trachea, exudate in the air sacs and changes in the oviduct are signs of infection.
Treatment and control
There is no treatment for Infectious Bronchitis. Vaccination is the best protection from this virus. However, there are many distinct types of the virus so a strain-specific vaccine is required but these do not cross protect. As the virus is spread through the air, housing birds in a spacious well ventilated environment will help. Also maintaining robust biosecurity measures as well as cleaning and disinfecting hatches will also help limit the spread of disease.
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