Michael D. Ruff

Phylogenetic relationships among eight Eimeria species infecting domestic fowl inferred using complete small subunit ribosomal DNA sequences

Complete 18S ribosomal RNA gene sequences were determined for 8 Eimeria species of chickens and for Eimeria bovis of cattle. Sequences were aligned with each other and with sequences from 2 Sarcocystis spp., Toxoplasma gondii, Neospora caninum, and 4 Cryptosporidium spp. Aligned sequences were analyzed by maximum parsimony to infer evolutionary relationships among the avian Eimeria species. Eimecia bovis was found to be the sister taxon to the 8 Eimeria species infecting chickens. Within the avian Eimeria species, E. necatrix and E. tenella were sister taxa: this clade attached basally to the other chicken coccidia. The remaining Eimeria spp. formed 3 clades that correlated with similarities based on oocyst size and shape. Eimeria mitis and Eimeria mivati (small, near spherical oocysts) formed the next most basal clade followed by a clade comprising Eimeria praecox. Eimeria maxima, and Eimeria brumetti (large, oval oocysts), which was the sister group to Eimeria acervulina (small, oval oocysts). The 4 clades of avian Eimeria species were strongly supported in a bootstrap analysis. Basal rooting of E. necatrix and E. tenella between E. bovis and the remaining Eimeria species and the apparent absence of coccidia that infect the ceca of jungle fowl all suggest that E. necatrix and E. tenella may have arisen from a host switch, perhaps from the North American turkey, Meleagris gallopavo.

Comparison of Disease Susceptibility and Subclass-Specific Antibody Response in SC and FP Chickens Experimentally Inoculated with Eimeria tenella, E. acervulina, or E. maxima

Susceptibility to disease and the subclass-specific antibody response to Eimeria tenella, E. acervulina, and E. maxima were compared in two inbred strains of chickens, FP (B15B21) and SC (B2B2). FP strain was more susceptible to coccidiosis than SC chickens based on oocyst production, lesion score, and clinical signs. FP chickens infected with E. tenella had more severe cecal lesions and a significantly lower hematocrit level than SC chickens. FP chickens infected with E. acervulina excreted five times as many oocysts at 6 days postinfection as SC and showed a 71% reduction in plasma carotenoid level compared with controls (56% reduction in SC chickens). Body-weight change did not correlate with other signs of disease. Both SC and FP chickens produced high levels of serum IgM and IgG and biliary IgA. Although SC chickens had a slightly higher antibody response than FP chickens at 7 days postinoculation, both strains maintained high levels of IgM, IgG, and IgA for a prolonged period post primary inoculation. Although SC and FP chickens show different disease susceptibility to coccidiosis, they demonstrate similar antibody response.

In Vivo Role of Tumor Necrosis-Like Factor in Eimeria tenella Infection

The effect of tumor necrosis-like factor (TNLF) on the pathogenesis of coccidiosis was investigated. Injection of crude chicken TNLF enhanced the weight loss caused by Eimeria tenella infection. Rabbit polyclonal antibody against recombinant human tumor necrosis factor-alpha (rhTNF) partially restored E. tenella-induced weight loss in SC chickens, but not in TK chickens. However, injection of chickens with chicken TNLF, rhTNF, and rabbit serum against rhTNF had no significant effect on cecal lesions. Both SC and TK chickens produced circulating TNLF following primary, but not secondary infection, and SC chickens showed higher level of TNLF production than TK chickens. Peripheral blood leukocyte-derived macrophages from SC and TK chickens produced a significant amount of TNLF compared to the preinfection condition when cocultured with sporozoites. In general, macrophages from SC chickens produced higher levels of TNLF than those from TK chickens. No significant difference was observed between primary and secondary infection. These results suggest that the excessive TNF production may be involved in weight loss caused by E. tenella infection in SC chickens.

Effects of Eimeria brunetti on intestinal pH in conventional and gnotobiotic chickens.

White Leghorn cockerels, 2-4 weeks of age, inoculated with sporulated oocysts of Eimeria brunetti had a lower mean pH in the middle and lower small intestine than did uninoculated controls by 5-9 days post-inoculation. No effect of the infection on pH was seen in the upper intestine while pH in the gizzard and caeca was occasionally higher than in controls. Magnitude of pH. decrease did not correlate with increases in oocyst dosage and severity of infection as measured by lesion score. Studies with germ-free (GF) and gnotobiotic chicks showed that host bacterial flora was essential for a pH decrease in the middle and lower small intestine with E. brunetti infection. Inoculation of GF birds with Lactobacillus acidophilus or L. acidophilus plus Streptococcus faecalis, in addition to E. brunetti resulted in some decrease in pH.

Effects of Turkey coccidiosis on intestinal pH

Broad Breasted White turkey poults (toms) infected with either Eimeria meleagrimitis or E. gallopavonis had significantly more acidic intestinal contents at 6 days postinoculation (PI) than did uninoculated controls. E. meleagrimitis caused lower pH values in both the duodenum and jejunum, the primary areas of parasitism, but not in the ileum or caeca. E. gallopavonis, which infects the ileum, reduced pH only in that region. The caecal coccidium of turkeys, E. adenoeides, did not significantly alter pH in any of the four regions (duodenum, jejunum, ileum, and caeca) examined. A mixed E. meleagrimitis and E. adenoeides inoculum significantly decreased pH values in the duodenum and jejunum 4, 6 and 8 days PI. Heavily infected poults had significantly lower pH values in the ileum, and higher values in the caeca as compared to uninoculated controls.