Submitted to: Parasitology Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 5, 2005
Publication Date: June 10, 2005
Citation: Allen, P.C., Jenkins, M.C., Miska, K.B. 2005. Cross protection studies with eimeria maxima strains. Parasitology Research. 97:179-185
Interpretive Summary: Avian coccidiosis (caused by seven species of protozoa of the genus Eimeria ) is the most economically important parasitic disease of poultry world wide. Annual costs to the US broiler industry have been estimated to be about $460 million, attributed to necessary use of medicated feeds, as well as to mortality and morbidity that result in production losses. Traditionally used anticoccidial medications have become less effective because the parasites have developed resistance to these drugs. Since infection with Eimeria sp. can induce solid immunity, vaccination of flocks with live oocysts has become an increasingly viable and popular alternative method of coccidiosis control. However, this immunity is generally very species-specific. Therefore, most commercially available live vaccines contain combinations of several Eimeria species in order to present the widest range of immunizing antigens to the chickens. One of the species usually present in live vaccines is Eimeria maxima. Compared to other species, it is the most immunogenic. However, it also has been found to be highly immunovarient, so that in some instances flocks are not protected from strains that differ (for example from a different geographical origin) from the vaccine strain. Providing two strains of E. maxima in a vaccine is usually recommended. The nature of this immunovarience is not known, but immunovarient strains can be identified through cross-immune protection studies as described in this study. We have found that the fecundity, or reproductive ability of some E. maxima strains can also vary over time. This variation must be monitored carefully so that the fecundities of the strains being compared are as close as possible. This is because the host reaction to infection is generally proportional to the number of reproducing organisms present, generally represented by the intracellar stages. When fecundities are comparable, then differences in protective antigens among strains can be more easily identified.
The purpose of this study was to evaluate the level of cross immune protection afforded by oral infection of chickens with four strains of Eimeria maxima. Immunizations were initiated by loe dose gavages of sporulated oocysts to day-old male broiler chicks under conditions that allowed parasite recycling through the chickens. After 2 weeks on litter and 1 week in suspended gaces chicks were challenged with homologous and heterologous E. maxima strains. Effectiveness of immunization was measured using a protective index calculated from weight gain, gross lesion score, plasma carotenoids and plasma NO2- + NO3- data. An initial cross immunity study among Strains A, B, C, and D showed that immunization with Strain A afforded no cross protection against heterologous strains. The lack of cross protection appeared to be correlated with parasite fecundity. Following several passages in non-immune chickens, the fecundity of Strain A was increased to the level of Strain C. Furthermore, both strains were mutually cross protective. This study indicates that parasite fecundity is important inn providing good immune stimulation, and should be careful monitored when characterization of unique immuni potentials of Eimeria strains is undertaken.