Submitted to: WATT Poultry USA
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 15, 2003
Publication Date: N/A
Interpretive Summary: One of the obstacles facing the poultry industry in the near future is the insistence by regulatory agencies and consumer groups to reduce the use of antibiotics in poultry feed. Anticipating these new regulations, the poultry industry is examining alternatives to drugs, such as ionophores, for controlling avian coccidiosis. One alternative that has gained limited popularity is the use of live oocyst vaccines whereby chickens are inoculated at hatch with low doses of virulent or attenuated Eimeria oocysts. The difficulty with this approach is that one species of Eimeria, namely E. maxima, shows appreciable immunovariability such that one strain of E. maxima will not protect against another strain. In an effort to determine the mechanism driving this immunovariability, experiments were conducted where chickens were immunized by oral inoculation with one strain of E. maxima oocysts and then challenged with the same or a different strain. These experiments showed that two parameters of coccidiosis, weight gain and production of oocysts, were useful in identifying cross-protective strains, while another parameter, lesion scoring, was not useful. These results indicate that poultry producers and vaccine manufacturers should be mindful of immunovariability and which parameter is used to determine whether one strain will protect against another.
Technical Abstract: The purpose of this study was to compare three different strains of Eimeria maxima to determine if immunization with one strain conferred protection against the others. Chickens (7-day-old, 10 per group) were immunized by oral 'trickle' infection with one of three strains of E. maxima oocysts (designated strains A, B, or C) and then challenged with either a homologous or heterologous strains at 4 weeks of age. The experiment was terminated 1 week after challenge infection and intestinal lesion scores, weight gain, and oocyst output was measured. As indicated by weight gain and oocyst production, chickens immunized with strain A or B oocysts were protected against strain A and B challenge, but not against strain C challenge infection. In contrast, chickens were completely protected against intestinal lesions after challenge with any of the 3 E. maxima strains. Also, immunization with strain C oocysts protected against strain A, B, or C challenge as measured by weight gain, lesion scores, or oocyst output. These results indicate that cross-protection between strains depends on the primary immunization. Also, weight gain and oocyst output appear to be sensitive parameters for cross-protection, while lesion scores are insensitive measures.