Infectious coryza: Overview of the disease and new diagnostic options

Infectious coryza is a well-recognized and commonly encountered upper respi ratory tract disease of chickens that is caused by the bacterium Haemophilu s paragallinarum. The occurrence of recent outbreaks in North America has e mphasized that the disease can be significant in meat chickens as well as l ayer chickens. In developing countries, coryza is commonly complicated by t he presence of a range of other infections, resulting in severe disease and significant economic losses. Unusual forms of the disease, involving arthr itis and septicemia, again associated with the presence of other pathogens, have been found in South America. Newly recognized bacteria such as Ornith obacterium rhinotracheale and phenotypic variant forms of both H. paragalli narum and close relatives (variant in that they no longer require V-factor for growth in vitro) have increased the difficulty associated with diagnosi ng the disease. There have been suggestions in both South America and South Africa that new serovars or serovar variants, associated with unusual clin ical manifestations and causing vaccine failures, are emerging. Definitive evidence to confirm or deny the role of these "variants" in vaccine failure s is currently not available. A new DNA-based diagnostic technique, involvi ng PCR, has been recently described and will greatly assist in the diagnosi s of infectious coryza.