Investigators from the University of Arizona inoculated broiler chicks with mixtures of C. perfringens strains to explore the singlestrain dominance that has been observed in natural cases of NE.

In the first of two studies, birds received one NE strain known as JGS4143, PFGE pattern 8, as well as four strains that do not cause NE. Lesions typical of NE developed after inoculation. However, only the NE strain could be recovered through the first post-inoculation day, despite “intense” efforts to recover the other strains. Thereafter, previously undetected PFGE strains were found, and JGS4143 was undetectable.

Findings in a second study were similar. Birds were inoculated with five NE strains, including JGS4143, and developed NE lesions. Initially, only JGS4143 was recovered, but birds began to be repopulated with other NE strains that were not used for inoculation.

“All NE strains inhibited growth of normal flora, but normal flora strains did not but the other two were extremely pathogenic and were found in 77% and 25% of flocks. “Twenty years’ use of the same type of coccidiostat in the broiler industry may have contributed to the increased incidence of coccidiosis on Norwegian farms,” says Anita Haug, who performed the surveys as part of her doctoral thesis. The studies, conducted on broilers receiving in-feed narasin during 2000 to 2004, were published in the June 2008 issue of Avian Pathology and were the focus of a recent article on thepoultrysite.com. Although the total parasite load countrywide did not alter significantly during the study period, there were large regional differences in the numbers of infected flocks, the level of infection and the dominant coccidial species, Haug found. Parasite load alone was not a good measure of the economic significance of coccidial infection, but reduced production occurred when there were over 50,000 parasites per gram of feces and the pathogenic strains dominated. A corresponding level of infection with more benign coccidial strains did not have the same effect on production. The surveys were funded by the Research Council of Norway; Haug performed her work at the National Veterinary Institute in Oslo and the National Veterinary Institute at Uppsala, Sweden. She developed new test methods by simplifying traditional ones, and also developed a “robust, effective and sensitive” molecular-biological test. inhibit any NE strain,” write Angelique J. Barbara and colleagues about their study, published in em>Veterinary Microbiology 126 (2008) 37-382. In addition, there were two NE strains that inhibited each other and normal flora strains, but normal flora strains did not inhibit each other, showed the study, supported in part by Intervet/Schering-Plough Animal Health.

The inhibition of one NE strain by another may be due completely, or in part, to factors other than bacteriocins — proteins produced by the bacteria of one strain against those of a closely related strain. Those other factors might include superior adhesion characteristics, more rapid multiplication and production of specific toxins, the investigators say.

Improved understanding of how NE strains displace non-NE strains in the chicken gut could, in time, bring about a better understanding about the pathogenesis of NE and provide targets for managing the disease, Barbara and colleagues write.

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