Differential Diagnosis

A variety of conditions can present with head and wattle swelling in mature chickens -

1. Infectious Coryza - infection with Haemophilus paragallinarum

2. "Swollen Head Syndrome" which can be caused by Avian Pneumovirus (also known as Avain Rhinotracheitis Virus) infection or infection with other respiratory viruses such as Infectious Bronchitis, associated with secondary bacterial invasion.

3. Localized bacterial infection with staphylococci associated with physical injury of the skin or beak, or immunosuppression (occasionally associated with chronic or acute sulphonamide toxicity).

In the present case the serological examinations did not support the suspicion of a respiratory virus infection, and sulphonamide had not been used in the birds prior to the problem occurring. Macroscopic lesions of the respiratory tract and sinuses were not encountered, and this also helped eliminate the respiratory viroses and Coryza. The cannibalism encountered, especially in house 2, may have induced some lesions and increased the severity of others. However many of the birds with severe lesions did not appear to have damaged skin. The acute purulent lesions suggested a severe bacterial infection and the microscopic examination of smears and bacteriological examination confirmed that the lesions were associated with Pasteurella multocida

Diagnosis

Acute Localized Pasteurellosis. While there was serious mortality this seemed to be as a result of loss of mobility, and difficulty in feeding and drinking. Lesions typical of Acute Fowl Cholera were not encountered.