NAD (V‐factor)‐independent and typicalHaemophilus paragallinaruminfection in commercial chickens: A five year field study

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Abstract
An unusual bacterium causing respiratory disease in chickens emerged in South Africa in February 1989. The disease resembled infectious coryza but the organism differed from typical Haemophilus paragallinarum especially in that it did not require V‐factor for growth. It has been termed an NAD‐independent H. paragallinarum. A study of avian haemophili isolated from diseased chickens in Kwazulu‐Natal over the past five years revealed the presence of typical H. paragallinarum, NAD‐independent H. paragallinarum and H. avium (now transferred to the genus Pasteurella). Before the end of 1989 the NAD‐independent H. paragallinarum had become the predominate isolate and thereafter was isolated from commercial chickens in other regions of South Africa. The disease affected all strains of chickens in an overall age range of 14 days to 64 weeks. The organism was responsible for upper respiratory disease of broilers and layers and implicated in lower respiratory disease of broilers. It was commonly isolated from diseased adult birds previously vaccinated against typical H. paragallinarum. Broilers were most commonly infected from 3 weeks of age and layers within the placement to peak production period. Whole cell protein profiles of NAD‐independent H. paragallinarum isolates from five different commercial poultry units were identical but differed from that of a typical isolate.