Epidemiology of Infectious Bronchitis (IB)

The infectious bronchitis virus (IBV) is distributed worldwide. It is generally accepted that chickens are the most important natural hosts of IB; all ages of chickens can be infected. IBV, or closely related coronaviruses have also been isolated from other species such as turkeys, pheasants, quail and partridges.

Several different serotypes can co-circulate in the same area at the same time. Some are found worldwide, but others have a more restricted geographical spread. For example, some are found only in Europe; others only in the USA.

The most severe clinical signs are seen in chickens younger than 6 weeks of age. The morbidity rate is extremely high and the mortality rate is dependent on the age of the chickens when infected, and the presence of secondary invading organisms such as E. coli.

Coronaviruses in other avian species

Although IB mainly affects chickens, coronaviruses of other avian species are now recognized, sometimes associated with disease, sometimes not. Molecular analysis of isolates from turkeys and pheasants show that they are as closely related to IBV as different IBV strains are to each other. This suggests IBV may infect some other avian species. However coronaviruses from, for example pigeons, may be sufficiently different to suggest they may be a different species of coronavirus.