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Updated: Mar 6, 2026
Nucleofection and In Vivo Propagation of Chicken Eimeria Parasites
Published on: February 14, 2020
Differences in fecundity of Eimeria maxima strains exhibiting different levels of pathogenicity in its avian host
Mark C Jenkins1, J P Dubey1, Katarzyna Miska1
1Animal Parasitic Diseases Laboratory, Agricultural Research Service, United States Department of Agriculture, Beltsville, MD 20705, USA.
Abstract:
Eimeria maxima is one of the most pathogenic species of avian coccidia, yet it is unknown why different E. maxima strains differ in the pathogenic effects they cause in chickens. The purpose of this study was to determine if a more pathogenic E. maxima strain (APU1) was also more fecund than a less pathogenic E. maxima strain (APU2). At identical doses, E. maxima APU1 always produces greater intestinal lesions and lower weight gain compared to E. maxima APU2. Using a dose response study, median and mean intestinal lesion scores in E. maxima APU1-infected chickens were greater by a score of 1-1.5 compared to chickens infected with E. maxima APU2. Likewise, weight gain depression in E. maxima APU1-infected chickens was 20-25% greater (equivalent to 110-130g body weight) than in E. maxima APU2-infected chickens. In order to understand the underlying cause of these observed clinical effects, 120 broiler chicks (5 oocyst levels, 6 replicates/level) were inoculated with various doses of E. maxima APU1 or APU2 oocysts. The dynamics of oocyst shedding was investigated by collecting fecal material every 12h from 114 to 210h post-inoculation (p.i.) and every 24h thereafter from 210 to 306h, and then processed for measuring E. maxima oocyst output. Oocysts were first observed at 138h p.i., and time of peak oocyst production was nearly identical for both E. maxima APU1 and APU2 around 150-162h. Total oocyst production was 1.1-2.6 fold higher at all dose levels for E. maxima APU1 compared to E. maxima APU2, being significantly higher (P<0.05) at the log 1.5 dose level. Other groups of chickens were infected with higher doses of E. maxima APU1 or APU2 oocysts, and intestinal lesions were assessed by histology at 72, 96, 120, and 144h p.i. Although schizonts, gamonts, and oocysts were observed at expected time-points, no obvious differences were noted in lesions induced by the two E. maxima strains. This study showed that the greater fecundity of E. maxima APU1 compared to E. maxima APU2 explains in part the observed differences in pathogenicity of the two E. maxima strains, but that other factors may contribute to differences in observed clinical effects.
Insights
A more pathogenic strain of Eimeria maxima (APU1) showed higher oocyst production in chickens compared to a less pathogenic strain (APU2). This increased fecundity partially explains the greater pathogenicity of Eimeria maxima APU1.
Area of Science:
- Avian Health
- Parasitology
- Veterinary Medicine
Background:
- Eimeria maxima is a significant cause of avian coccidiosis.
- Variations in pathogenicity among Eimeria maxima strains are not well understood.
- Understanding strain-specific differences is crucial for effective disease management.
Purpose of the Study:
- To investigate if a more pathogenic Eimeria maxima strain (APU1) exhibits higher fecundity than a less pathogenic strain (APU2).
- To correlate oocyst production with observed clinical effects like intestinal lesions and weight gain depression.
Main Methods:
- Broiler chicks were inoculated with varying doses of Eimeria maxima APU1 or APU2.
- Oocyst shedding dynamics were monitored through fecal sample analysis at multiple time points post-inoculation.
- Intestinal lesion scoring and histological assessments were performed.
Main Results:
- Eimeria maxima APU1 consistently induced greater intestinal lesions and weight gain depression compared to E. maxima APU2 at identical doses.
- Total oocyst production was 1.1–2.6 fold higher for E. maxima APU1 across all tested doses.
- Peak oocyst shedding occurred around 150–162 hours post-inoculation for both strains, with no significant difference in timing.
Conclusions:
- The increased fecundity of Eimeria maxima APU1 is a contributing factor to its higher pathogenicity in chickens.
- While fecundity plays a role, other unidentified factors likely influence the observed clinical differences between E. maxima strains.
