Avibacterium paragallinarum
Infectious coryza, caused by the bacterium Avibacterium paragallinarum (previously Haemophilus paragallinarum) , is a disease of poultry with the first serious outbreak in South Africa in 1968. Soon afterwards the disease spread to most large poultry production sites and established itself as the most common bacterial infection in layers. One of the main reasons for the very successful spread of A. paragallinarum is the fact that the chickens that recover from the infection become carriers and these chickens are often sold at point-of-lay, thus introducing the infection to new, clean sites. This disease causes severe reduction in egg production and is thus of significant financial importance to the poultry industry.
Infectious coryza causes an upper respiratory tract infection in poultry. This disease usually only shows mild clinical symptoms, but causes marked economic losses in many countries where egg production of between 10-40% may occur. The most prominent features of the disease include nasal discharge, facial oedema and conjunctivitis. Some infections may spread to the lower respiratory tract, resulting in rales. In most cases mortality is low, but morbidity is high resulting in decreased water and feed consumption.
There are different serovars of the bacterium and it was established that the incidence of these serovars has changed over the last thirty years. It has been shown that the incidence of serovar A-1 and C-2 has decreased while serovar C-3 has increased. (See scientific publications)
Changes in incidence of serovars
A new challenge model for infectious coryza has been established. By using this challenge model, the virulence of the different strains can be established. It is also possible to determine the efficacy of vaccines or treatments (See recent scientific publications).
Virulence of different serovars of A. paragallinarum
|