Differentiating vaccine-related fowl cholera from naturally occurring disease

Vaccine-related fowl cholera must be considered when flock mortality increases after use of a live vaccine product. All vaccines serotype as Heddleston 3,4, however this is also the most common serotype of outbreak isolates in broiler breeders and turkeys. Therefore, serotyping is not useful for diagnosing vaccine-related fowl cholera. This research was to produce a vaccine-specific test to differentiate vaccine-related disease from naturally occurring outbreaks. Results indicate that vaccine strains were commonly isolated from broiler breeders exhibiting signs of fowl cholera post vaccination, but some isolates exhibited only serotype 4 antigenicity. Studies of the serotype 3, 4 lipopolysaccharides were used to characterize the nature of the commercial vaccine preparations in an effort to explain varying virulence of the commercial preparations. These results suggest that vaccine-related disease may not be uncommon in broiler breeders and commercial vaccine preparations might have increased virulence do to unknown lipopolysaccharides structures.