Identification and Characterization of Eimeria tenella Microneme Protein (EtMIC8)

Microneme proteins (MICs) of Eimeria tenella play key roles in motility, migration, attachment, and invasion processes. More than 20 apicomplexan parasite's MICs have been identified, with nine Eimeria MICs being reported. In this study, a novel E. tenella MIC was identified, and its gene structural features, developmental expression levels, localization, role in adhesion and invasion, and immunogenicity were studied. The results showed that the open reading frame was 1,650 bp, encoding 550 amino acids. It contains a signal sequence, a transmembrane region, four low-complexity boxes, and five epidermal growth factor-like domains (EGF). Subcellular localization revealed its distribution on the membrane surface of the parasite. These characteristics are consistent with the common features of MICs and are named EtMIC8. Anti-EtMIC8 antibodies recognized a specific binding of about 100 kDa in E. tenella, which was twice as large as the prokaryotic expression (about 50 kDa), suggesting that MIC8 may exist naturally as a dimer. EtMIC8 was expressed at higher levels in sporozoites (3.08-fold) and merozoites (2.1-fold) than in sporulated oocysts. The attachment assays using a yeast surface display of MIC8 and its different domains showed that the adherence rates of EtMIC8 to host cells were significantly higher than those of the control (3.17-fold), which was the full contribution of EGF, but neither was alone. Anti-EtMIC8 antibodies significantly reduced the invasion rate of sporozoites into host cells compared to those of the control (P < 0.01). Recombinant EtMIC8-EGF peptides could provide moderate protective efficacy (anticoccidial index [ACI]: 169.7), induce humoral responses, and upregulate CD3+CD8+ lymphocyte cells.

Cloning and characterization of three Eimeria tenella lipid phosphate phosphatases

Although lipid phosphate phosphatases (LPPs) play an important role in cellular signaling in addition to lipid biosynthesis, little is thus far known about parasite LPPs. In this study, we characterized three Eimeria tenella cDNA clones encoding LPP named EtLPP1, EtLPP2 and EtLPP3. Key structural features previously described in LPPs, including the three conserved domains proposed as catalytic sites, a single conserved N-glycosylation site, and putative transmembrane domains were discovered in the three resulting EtLPP amino acid sequences. Expression of His6-tagged EtLPP1, -2, and -3 in HEK293 cells produced immunoreactive proteins with variable molecular sizes, suggesting the presence of multiple forms of each of the three EtLPPs. The two faster-migrating protein bands below each of the three EtLPP proteins were found to be very similar to the porcine 35-kDa LPP enzyme in their molecular size and the extent of their N-glycosylation, suggesting that the three EtLPPs are partially N-glycosylated. Kinetic analyses of the activity of the three enzymes against PA, LPA, C1P and S1P showed that Km values for each of the substrates were (in μM) 284, 46, 28, and 22 for EtLPP1; 369, 179, 237, and 52 for EtLPP2; and 355, 83, and 260 for EtLPP3. However, EtLPP3 showed negligible activity on S1P. These results confirmed that the three EtLPPs have broad substrate specificity. The results also indicated that despite structural similarities, the three EtLPPs may play distinct functions through their different models of substrate preference. Furthermore, particularly high expression levels of the three EtLPP genes were detected in the sporozoite stage of the E. tenella life cycle (p<0.001), suggesting that their encoded proteins might play an important biological function in the sporozoite stage.

Identification and characterization of Eimeria tenella apical membrane antigen-1 (AMA1)

Apical membrane antigen-1 (AMA1) is a micronemal protein of apicomplexan parasites that appears to be essential during the invasion of host cells. In this study, a full-length cDNA of AMA1 was identified from Eimeria tenella (Et) using expressed sequence tag and the rapid amplification of cDNA ends technique. EtAMA1 had an open reading frame of 1608 bp encoding a protein of 535 amino acids. Quantitative real-time PCR analysis revealed that EtAMA1 was expressed at higher levels in sporozoites than in the other developmental stages (unsporulated oocysts, sporulated oocysts and second-generation merozoites). The ectodomain sequence was expressed as recombinant EtAMA1 (rEtAMA1) and rabbit polyclonal antibodies raised against the rEtAMA1 recognized a 58-kDa native parasite protein by Western Blotting and had a potent inhibitory effect on parasite invasion, decreasing it by approximately 70%. Immunofluorescence analysis and immunohistochemistry analysis showed EtAMA1 might play an important role in sporozoite invasion and development.

Eimeripain, a cathepsin B-like cysteine protease, expressed throughout sporulation of the apicomplexan parasite Eimeria tenella

The invasion and replication of Eimeria tenella in the chicken intestine is responsible for avian coccidiosis, a disease that has major economic impacts on poultry industries worldwide. E. tenella is transmitted to naïve animals via shed unsporulated oocysts that need contact with air and humidity to form the infectious sporulated oocysts, which contain the first invasive form of the parasite, the sporozoite. Cysteine proteases (CPs) are major virulence factors expressed by protozoa. In this study, we show that E. tenella expresses five transcriptionally regulated genes encoding one cathepsin L, one cathepsin B and three cathepsin Cs. Biot-LC-LVG-CHN₂, a cystatin derived probe, tagged eight polypeptides in unsporulated oocysts but only one in sporulated oocysts. CP-dependant activities were found against the fluorescent substrates, Z-FR-AMC and Z-LR-AMC, throughout the sporulation process. These activities corresponded to a cathepsin B-like enzyme since they were inhibited by CA-074, a specific cathepsin B inhibitor. A 3D model of the catalytic domain of the cathepsin B-like protease, based on its sequence homology with human cathepsin B, further confirmed its classification as a papain-like protease with similar characteristics to toxopain-1 from the related apicomplexan parasite, Toxoplasma gondii; we have, therefore, named the E. tenella cathepsin B, eimeripain. Following stable transfection of E. tenella sporozoites with a plasmid allowing the expression of eimeripain fused to the fluorescent protein mCherry, we demonstrated that eimeripain is detected throughout sporulation and has a punctate distribution in the bodies of extra- and intracellular parasites. Furthermore, CA-074 Me, the membrane-permeable derivative of CA-074, impairs invasion of epithelial MDBK cells by E. tenella sporozoites. This study represents the first characterization of CPs expressed by a parasite from the Eimeria genus. Moreover, it emphasizes the role of CPs in transmission and dissemination of exogenous stages of apicomplexan parasites.

Eimeria tenella: genomic organization and expression of an 89kDa cyclophilin

Though parasite cyclophilins are promising new drug targets, Eimeria tenella cyclophilins have not been characterized yet. Here, we describe an 89kDa cyclophilin, designated EtCYP89. It is expressed throughout the developmental cycle of E. tenella, both in the intracellular stages in chicken and in extracellular sporulated oocysts and sporozoites. The EtCYP89 protein contains two Ser-rich domains in its NH2-terminus separated by a His-rich stretch. WD40 repeats are localized in the central part of the protein followed by a cyclophilin domain at the COOH-terminus. Both protein and genomic organization of EtCyp89 are conserved in comparison with its ortholog TgCyp81.6 in Toxoplasma gondii, except for the absence of a Ser- and His-rich NH2-terminus in TgCYP81.6. In particular, those 13 residues are conserved which are responsible for binding the anti-coccidial drug cyclosporine A.

Serine protease activity in developmental stages of Eimeria tenella

A number of complex processes are involved in Eimeria spp. survival, including control of sporulation, intracellular invasion, evasion of host immune responses, successful reproduction, and nutrition. Proteases have been implicated in many of these processes, but the occurrence and functions of serine proteases have not been characterized. Bioinformatic analysis suggests that the Eimeria tenella genome contains several serine proteases that lack homology to trypsin. Using RT-PCR, a gene encoding a subtilisin-like and a rhomboid protease-like serine protease was shown to be developmentally regulated, both being poorly expressed in sporozoites (SZ) and merozoites (MZ). Casein substrate gel electrophoresis of oocyst extracts during sporulation demonstrated bands of proteolytic activity with relative molecular weights (Mr) of 18, 25, and 45 kDa that were eliminated by coincubation with serine protease inhibitors. A protease with Mr of 25 kDa was purified from extracts of unsporulated oocysts by a combination of affinity and anion exchange chromatography. Extracts of SZ contained only a single band of inhibitor-sensitive proteolytic activity at 25 kDa, while the pattern of proteases from extracts of MZ was similar to that of oocysts except for the occurrence of a 90 kDa protease, resistant to protease inhibitors. Excretory-secretory products (ESP) from MZ contained AEBSF (4-[2-Aminoethyl] benzenesulphonyl fluoride)-sensitive protease activity with a specific activity about 10 times greater than that observed in MZ extracts. No protease activity was observed in the ESP from SZ. Pretreatment of SZ with AEBSF significantly reduced SZ invasion and the release of the microneme protein, MIC2. The current results suggest that serine proteases are present in all the developmental stages examined.

The methylerythritol phosphate pathway for isoprenoid biosynthesis in coccidia: presence and sensitivity to fosmidomycin

The apicoplast is a recently discovered, plastid-like organelle present in most apicomplexa. The methylerythritol phosphate (MEP) pathway involved in isoprenoid biosynthesis is one of the metabolic pathways associated with the apicoplast, and is a new promising therapeutic target in Plasmodium falciparum. Here, we check the presence of isoprenoid genes in four coccidian parasites according to genome database searches. Cryptosporidium parvum and C. hominis, which have no plastid genome, lack the MEP pathway. In contrast, gene expression studies suggest that this metabolic pathway is present in several development stages of Eimeria tenella and in tachyzoites of Toxoplasma gondii. We studied the potential of fosmidomycin, an antimalarial drug blocking the MEP pathway, to inhibit E. tenella and T. gondii growth in vitro. The drug was poorly effective even at high concentrations. Thus, both fosmidomycin sensitivity and isoprenoid metabolism differs substantially between apicomplexan species.

Maternal immunization by egg propagated gametocyte vaccine to control Eimeria tenella infections in newly hatched chicks

The present paper reports the ability of egg-propagated gametocyte vaccine to induce protective immunity against Eimeria tenella infections in offspring chicks. For this purpose, breeding hens were immunized with adjuvanted gametocyte vaccine orally, being the best vaccine in our previous studies. Eggs collected 2 weeks after the boosting dose were allowed to hatch. Upon challenge with sporulated oocysts of E. tenella (local isolates) to 7-day-old chicks from immunized hens showed more than 70% reduction in oocyst production compared with chicks from control hens. Furthermore, no mortality was recorded in immunized chickens, while four out of five control chickens died due to coccidiosis. These results suggested that maternal immunization with egg-propagated gametocyte vaccine can control E. tenella infections in offspring chicks.

Immunogenic characterization of egg-adapted gametocytes of Eimera tenella

Egg-adapted gametocytes of Eimeria (E.) tenella (local isolates) were subjected to sodium dodecyl sulphate polyacrylimide gel electrophoresis under reducing conditions to fractionate the proteins. Immunogenicity of the gametocytes was detected by modified counter immunoelectrophoresis (MCIE) using convalescent sera from the outbreak cases of coccidiosis. Gametocytes of all the three isolates of E. tenella showed similar protein bands of molecular weights of 48.43, 27.20, 25.75, 22.57, and 12.92 kDa. MCIE recognized three precipitation bands with convalescent sera in comparison with the control. Results suggested that some of the 48.43-, 27.20-, 25.75-, 22.57-, and 12.92-kDa antigen(s) exist as soluble proteins in the parasite, which gave protection in our previous experiments against coccidiosis. Further studies on the biochemical characterization of the egg-adapted gametocyte antigen(s) and its role in E. tenella oocyst wall formation is underway.

Eimeria tenella: further studies on the development of the oocyst

AIM

The present study investigated the processes of macrogametogenesis and oocyst formation of Eimeria tenella (Xiamen strain), including the formation of wall-forming body1 (WFB1) and wall-forming body 2 (WFB2), the club-shape body and the origin of the residual body during the transformation from a macrogamete to an oocyst.

METHOD

Transmission electron microscopy was used to follow ultrastructural changes of the organelles during parasite development. Frozen section techniques and special staining were used to determine the chemical composition of the club-shape body.

RESULTS

Electron lighter WFB1 appeared earlier than the electron denser WFB2 during the process of cyst wall formation. WFB2 appeared to play a key role in cyst wall formation, whereas WFB1 may have a limited role in the wall-forming process. When two last generation merozoites entered the same host cell simultaneously, one of them grew well, but the other one was developmentally retarded, and became a residual body. Our study indicates that the content of the club-shape body are lipoidal in nature, not amyolpectin as suggested previously, because they stained black by Sudan black-B.

CONCLUSIONS

During of macrogametogenesis and oocyst formation of E. tenella (Xiamen strain), WFB2 plays a major role in cyst wall formation. The residual bodies come from the undeveloped macrogametes. The club-body is lipoid; and lipometabolism is important energy resource in E. tenella development.

Some observations on the adaptation of Eimeria tenella (local isolates) sporozoites on chicken embryos through chorioallantoic membrane

Eimeria (E.) tenella (local isolate) sporozoites were adapted on the chorioallantoic membrane (CAM) of 10-12 days chicken embryos and completed its life cycle in 6~7 days at 39℃ and 70 per cent humidity. Only 23 embryos (4.6%) were found dead from 1~4 day post inoculation of sporozoites with mild lesions on CAM with no gametocytes but few sporozoites in chorioallantoic fluid (CAF). On 5~7 day post inoculation, 432 embryos (86.4%) were found dead with severe haemorrhages on CAM and CAF contained uncountable number of gametocytes. After seven days post inoculation, 45 embryos (9%) were found to be alive. Some oocysts were also detected in the CAF on 6~7 days post inoculation. In the histological sections of the CAM, there were abundant small dark colored rounded bodies of gametes; distributed extensively in tissues of CAM on 5~7 days post inoculation of sporozoites. In some cases, cluster of small mature and immature relatively large bodies were seen in increasing numbers on 5~6 days post inoculation.

Antioxidant status during the course of Eimeria tenella infection in broiler chickens

The antioxidant status of broiler chickens (Cobb 500 hybrids) infected with Eimeria tenella was monitored by determining blood plasma malondialdehyde (MDA), superoxide dismutase (SOD) and catalase (CAT). The results of the experiment showed an increase in MDA - a marker of radical-induced damage of E. tenella-infected birds, compared to healthy chickens (3.01 micro mol/L vs. 2.55 micro mol/L, P<0.05). Correspondingly, a decreased SOD activity was observed in infected birds compared to controls (2429.0 U/g Hb vs. 3044.6 U/g Hb, P<0.05). Furthermore, CAT activity in infected birds was higher than in healthy ones (2242.2 U/g Hb vs. 1367.0 U/g Hb, P<0.001). The observed enzyme changes suggest an impaired antioxidant status of chickens during the course of an E. tenella infection and the occurrence of oxidative stress following infection. Alterations in the caecum, oocyst production, weight gain and feed conversion ratio were indicative of a severe infection involving pathogenic oxidative stress and impaired ecological oxidative balance.

De novo ribosome biosynthesis is transcriptionally regulated in Eimeria tenella, dependent on its life cycle stage

Protozoan parasites go through various developmental stages during their parasitic life, which requires the expression of different genes. To identify stage specific gene products in Eimeria tenella, a differential screening was performed comparing the intracellular schizont stage with the extracellular oocyst stage. De novo transcripts of 18S-5.8S-26S rRNA transcription units and of two ribosomal proteins (RPL5 and RPL23) were specifically identified in schizonts and were undetectable in oocysts. The stage specific transcription of pre-rRNAs (prior to processing) was confirmed with Northern blot analysis. Since the E. tenella genome contains a repeated gene cluster with an estimated 140 large rRNA transcription units, they all might be similarly regulated. Specific expression of RPL5 and RPL23 in E. tenella schizonts was also confirmed by Northern blotting. Furthermore, an analysis of the E. tenella EST database with 26,705 ESTs showed that 9.5% of all merozoite ESTs and only 0.2% of the sporozoite ESTs encoded ribosomal proteins (RPs). These ESTs encoded 69 different RPs, suggesting that most and possibly all RPs are differentially transcribed in E. tenella. Analysis of EST data from other Coccidia, such as Toxoplasma gondii, indicated a similar stage dependent transcription of RP genes. We conclude that ribosome biosynthesis is transcriptionally regulated in E. tenella and other Coccidia, such that rapidly growing parasite stages utilize much of their resources to de novo biosynthesis of ribosomes, and that "dormant" oocyst stages do not synthesize new ribosomes. The 50- to 100-fold reduction in transcription of RPs together with the reduced rRNA transcription prevents that unnecessary new ribosomes are synthesized in oocysts.

In vitro inhibition of Eimeria tenella invasion by indigenous chicken Lactobacillus species

The aim of this study was to determine the effects of indigenous chicken Lactobacillus species isolates from different parts of the gastrointestinal tract on Eimeria tenella invasion in vitro and to characterise the nature of inhibition, if any. The effects of competitive exclusion, steric interference and bacterial extracellular factors on E. tenella invasion were examined in an MDBK cell model. Several Lactobacillus species were initially isolated from chickens and identified by biochemical characteristics and 16S-rRNA. All Lactobacillus species isolates tested, significantly inhibited E. tenella invasion. Steric interference did not affect parasite invasion. Extracellular metabolic factors secreted by Lactobacillus species isolates into the surrounding media were shown to inhibit parasite invasion and these factors appeared to be heat stable. These results show that the natural microflora of poultry can provide a source of E. tenella-inhibiting Lactobacillus species in vitro, and thus may contribute to the control of Eimeria infection.

Eimeria tenella sporozoites and merozoites differentially express glycosylphosphatidylinositol-anchored variant surface proteins

Little is known about glycosylphosphatidylinositol (GPI)-linked surface proteins in the coccidian parasite Eimeria tenella. Examination of 28,550 EST sequences from the sporozoite and second merozoite developmental stages of the parasite led to the identification of 37 potential GPI-linked variant surface proteins, termed EtSAGs. Analysis of the complete nucleotide sequences of 23 EtSAG genes separated them into two multi-gene families. All the predicted EtSAG proteins (which vary in length from 228 to 271 residues) have an N-terminal hydrophobic signal peptide, a C-terminal hydrophobic GPI signal-anchor peptide and an extracellular domain organised around six cysteine residues, the positions of which are conserved within each family. Using specific antibodies against a small number of recombinant-expressed EtSAGs, the surface localisation and GPI-anchorage of members of both families was confirmed experimentally. Expression of EtSAGs is differentially regulated between the oocyst/sporozoite and second generation merozoite stages, with only one expressed specifically in the sporozoite, a small number expressed in both stages and the majority expressed specifically in the second generation merozoite. Preliminary data support a model in which multiple variant surface antigens are co-expressed on individual parasites, rather than a model of antigenic switching. The biological role(s) of EtSAGs and the effect(s) that expression of a complex repertoire of variant surface antigens by the second generation merozoite has on host adapted immunity are unknown.

Comparative development of Eimeria tenella (Apicomplexa) in host cells in vitro

Attempts to propagate Eimeria tenella in cell culture over the years have met with limited success. The host cell type is an important parameter in such cultures. This study assessed the ability of different host cell lines to support E. tenella infection in vitro. The initial development in cell lines and the effects of incubation at 37 degrees C and 41 degrees C on the host-parasite relationship was investigated. Eleven cell lines were seeded into 96 well plates and incubated at 37 degrees C in 5% CO(2) to reach confluency. Sporozoites of E. tenella were inoculated into wells and allowed to invade at 37 degrees C and 41 degrees C. Intracellular parasite development was quantified using (3)H-uracil incorporation. All cell lines facilitated parasite invasion and development. The MDBK cell line supported the highest degree of E. tenella development. A time-course study was undertaken to look at this host cell-parasite relationship during infection.

Gene discovery in Eimeria tenella by immunoscreening cDNA expression libraries of sporozoites and schizonts with chicken intestinal antibodies

Specific antibodies were produced ex vivo from intestinal culture of Eimeria tenella infected chickens. The specificity of these intestinal antibodies was tested against different parasite stages. These antibodies were used to immunoscreen first generation schizont and sporozoite cDNA libraries permitting the identification of new E. tenella antigens. We obtained a total of 119 cDNA clones which were subjected to sequence analysis. The sequences coding for the proteins inducing local immune responses were compared with nucleotide or protein databases and with expressed sequence tags (ESTs) databases. We identified new Eimeria genes coding for heat shock proteins, a ribosomal protein, a pyruvate kinase and a pyridoxine kinase. Specific features of other sequences are discussed.

Effect of dietary supplementation with oregano essential oil on performance of broilers after experimental infection with Eimeria tenella

A study was carried out to examine the effect of dietary supplementation of oregano essential oil on performance of broiler chickens experimentally infected with Eimeria tenella at 14 days of age. A total of 120 day-old Cobb-500 chicks separated into 4 equal groups with three replicates each, were used in this study. Two groups, one infected with 5 x 10(4) sporulated oocysts of E. tenella and the other not, were given a basal diet and served as controls. The other two groups also infected with E. tenella were administered diets supplemented with oregano essential oil at a level of 300 mg/kg, or with the anticoccidial lasalocid at 75 mg/kg. Following this infection, survival rate, bloody diarrhoea and oocysts excretion as well as lesion score were determined. Throughout the experimental period of 42 days, body weight gain and feed intake were recorded weekly, and feed conversion ratios were calculated. Two weeks after the infection with E. tenella supplementation with dietary oregano oil resulted in body weight gains and feed conversion ratios not differing from the non-infected group, but higher than those of the infected control group and lower than those of the lasalocid group. These parameters correspond with the extent of bloody diarrhoea, survival rate, lesion score and oocyst numbers and indicated that oregano essential oil exerted an anticoccidial effect against E. tenella, which was, however, lower than that exhibited by lasalocid.

Identification and quantification of granulocytes in caecal mucosa and submucosa of chickens experimentally infected with Eimeria tenella and Salmonella enteritidis

1. Poultry granulocytes are not clearly distinguished from each other with haematoxylin-eosin (HE) stain; thus, histochemical techniques must be used. Three experiments were carried out using 4-week-old Leghorn chickens. 2. Three, 80-chicken groups were orally infected with (1) 10(8) colony forming units (CFUs) Salmonella enteritidis, or (2) 10(4) Eimeria tenella oocysts, or (3) 10(8) CFUs S. enteritidis + 10(4) E. tenella oocysts. Ten chickens from each group were euthanased and caecum samples obtained. Caecum samples were fixed in 10% formalin (buffered, pH 7.4) at 4, 8, 12 h, 1, 3, 5, 7, and 14 d post-inoculation (PI). 3. Samples were stained using three different staining techniques: HE for the identification of heterophils and eosinophils, Ziehl-Neelsen for mast cells, and p-phenilenediamine dihydrochloride plus pyrocatechol (PPD + PC) for eosinophils. 4. Birds from Experiment 1 showed no changes in the numbers of granulocytes. Birds from Experiments 2 and 3 showed higher numbers of heterophils in caecal mucosa and submucosa separately, on d 5 and 7. In Experiment 3, a decrease was observed in submucosal mast cells on d 3. Chickens from Experiments 2 and 3 showed increased numbers of mucosal mast cells between d 7 and 14. 5. PPD + PC positively stained eosinophils, but not heterophils. 6. Numbers of heterophils and mast cells were increased during the acute inflammatory process caused by E. tenella. Therefore, mast cells could play a role as primary inflammatory cells. Eosinophils seem not to be part of the inflammatory process caused by E. tenella.

Comparative EST analyses provide insights into gene expression in two asexual developmental stages of Eimeria tenella

The protozoan parasite Eimeria tenella has a complex life cycle that includes two major asexual developmental stages, the merozoite and the sporozoite. The expressed sequence tag (EST) approach has been previously used to study gene expression of merozoites. We report here the generation and analysis of 556 ESTs from sporozoites. Comparative analyses of the two datasets reveal a number of transcripts that are preferentially expressed in a specific stage, including previously uncharacterised sequences. The data presented indicate the invaluable potential of the comparative EST analysis for providing information on gene expression patterns in the different developmental stages of E. tenella.

Clinicomorphological studies in chicks fed ochratoxin A while simultaneously developing coccidiosis

The progression of coccidiosis and the resultant mortality were followed in chicks fed a OTA-contaminated diet. More complex and rapid progress of coccidiosis occurred in OTA-treated chicks than in chicks fed a OTA-free diet. The concentration of total protein in the serum was significantly decreased in the chicks in the OTA-treated group, whereas this was significantly increased in chicks infected with Eimeria tenella, irrespective of additional treatment with OTA. The serum glucose concentration was significantly increased in all the chicks exposed to OTA and/or suffering from coccidiosis, as was serum retention of uric acid in all groups, most notably in those consuming OTA. OTA induced degenerative changes in, and an increase in the weight of the kidneys, liver, heart and ventriculum; there was depletion of lymphoid tissue and a decrease in the lymphoid organs' weight and body weight. Coccidiosis induced only a slight growth depression and a slight increase in the relative weight of the kidneys and liver. The intensity of the clinical signs, the impairment of kidney function, macroscopic and histopathological changes, deviations in the weight of some organs and general depression in growth were greater when chicks infected with E. tenella were also given OTA.

Development and application of a standardized assay for chemical disinfection of coccidia oocysts

The development and application of a standardized model for testing of anticoccidial disinfectants are described. Due to its economic impact, tenacity of oocysts, and reproducibility of the course of infection Eimeria tenella has been chosen as test organism. Oocysts of the Houghton strain were more susceptible to disinfection with 4% TP4 (Preventol) than oocysts of a field isolate (FI 292/1) as determined by sporulation inhibition and lysis. Scoring of intestinal lesions and of oocyst numbers in mucosal scrapings in chicken infected with various doses of oocysts were found unsuitable for assessment of disinfectants. Because strain differences were observed only Houghton strain oocysts were applied for further testing. Guidelines for standardized in vivo testing of disinfectants have been stipulated by the German Veterinary Society (DVG) on the basis of these studies. When applied for testing of Neopredisan (NP) in two separate laboratories similar results were obtained. Inhibitory activity (IA; proportion of inactivated oocysts) of 92.9 and 90.6% were calculated for 3% NP and of 95.2 and 96.8% for 4% NP after treatment with the disinfectant over 120 min. According to the guidelines IA of at least 95% is required for certification of sufficient disinfecting efficacy by the DVG.

Study of resistance against some ionophores in Eimeria tenella field isolates

Three Eimeria tenella field isolates from Gurgaon district of Haryana (north India) were studied in a battery test for evaluating drug resistance against two currently used ionophores; maduramicin (5ppm) and salinomycin (60ppm). Broiler birds (Ross strain) were infected with 10(5) sporulated oocysts each at the age of 2 weeks and prophylactic medication commenced 2 days prior to infection. Drug resistance was assessed by calculating the global index for individual ionophore compounds based on weight gain, feed conversion ratio, oocyst index, lesion score and mortality. Present studies revealed no resistance of the ionophores in any of the field isolates. Both the drugs showed varying degree of efficacy, e.g. maduramicin exhibited limited efficacy against all the three field isolates, whereas salinomycin showed limited efficacy against Gurgaon isolate (GrI)-I, good efficacy against GrI-II and partial resistance against GrI-III.

Nitrophenide (Megasul) blocks Eimeria tenella development by inhibiting the mannitol cycle enzyme mannitol-1-phosphate dehydrogenase

Unsporulated oocysts of the protozoan parasite Eimeria tenella contain high levels of mannitol, which is thought to be the principal energy source for the process of sporulation. Biosynthesis and utilization of this sugar alcohol occurs via a metabolic pathway known as the mannitol cycle. Here, results are presented that suggest that 3-nitrophenyl disulfide (nitrophenide, Megasul), an anticoccidial drug commercially used in the 1950s, inhibits mannitol-1-phosphate dehydrogenase (M1PDH), which catalyzes the committed enzymatic step in the mannitol cycle. Treatment of E. tenella-infected chickens with nitrophenide resulted in a 90% reduction in oocyst shedding. The remaining oocysts displayed significant morphological abnormalities and were largely incapable of further development. Nitrophenide treatment did not affect parasite asexual reproduction, suggesting specificity for the sexual stage of the life cycle. Isolated oocysts from chickens treated with nitrophenide exhibited a dose-dependent reduction in mannitol, suggesting in vivo inhibition of parasite mannitol biosynthesis. Nitrophenide-mediated inhibition of MIPDH was observed in vitro using purified native enzyme. Moreover, MIPDH activity immunoprecipitated from E. tenella-infected cecal tissues was significantly lower in nitrophenide-treated compared with untreated chickens. Western blot analysis and immunohistochemistry showed that parasites from nitrophenide-treated and untreated chickens contained similar enzyme levels. These data suggest that nitrophenide blocks parasite development at the sexual stages by targeting M1PDH. Thus, targeting of the mannitol cycle with drugs could provide an avenue for controlling the spread of E. tenella in commercial production facilities by preventing oocyst shedding.

Eimeria tenella: hsp70 expression during sporogony

There is an increasing interest in identifying the parasite components involved in the maturation, development, and infectivity of intracellular protozoan parasites. In the present study, a heat shock protein (hsp) of the family of 70 kDa hsp (hsp70), which play important roles in the stage conversion and virulence of these parasites, was examined. Whereas hsp70 expression has been examined in Eimeria tenella within host tissues, in the present study, oocysts of E. tenella were used to investigate the expression of hsp70 during sporulation without interference from the host; hsp70 expression during excystation was induced by incubating sporulated oocysts under various experimental conditions to produce the stimuli necessary for sporozoites to become active and to excyst in vitro. Hsp70 was detected by immunohistochemical techniques; quantitative flow cytometric analysis was also been carried out using specific monoclonal antibodies against hsp70. Hsp70 was expressed during sporulation but was not found in sporulated oocysts after the completion of sporulation. Oocysts re-expressed hsp70 when excystation was induced. The presence of hsp70 prior to infection may preadapt the parasite for additional stress in the host and may be involved in the formation of sporozoites.

A novel method for counting eimerian oocysts at very low concentrations in aqueous suspensions

A novel method for counting eimerian oocysts in samples of drinking water has been developed to fulfil the need for monitoring the delivery of very low concentrations of live anticoccidial vaccines to poultry via pipeline nipple-drinker systems. Advantages of the method are the ease of sample collection and processing, high degrees of accuracy and precision, and a sensitivity of one oocyst ml(-1). Results of a validation test are presented, with a protocol for the method and notes on its use. The coefficient of variation (CoV) of 10 sets of oocyst counts with nominal means of 10 to 160 oocysts ml(-1)ranged from about 16 per cent down to 6 per cent. The recovery efficiency for all 100 validation counts averaged 100.2 per cent with a range of 70-130 per cent. A practical example of field use of the method is given, including a modification to decrease the time taken for counting. In this case, when oocysts were pumped around a pipeline circuit of 129 m for 2.5 hours, the CoV of a mean of 112 oocysts ml(-1)(n = 10) was 12.4 per cent.

Cell membrane labeling of Eimeria tenella sporozoites with the fluorescent dye PKH-67 GL for tracking parasite-host interactions

The fluorescent cell linker dye PKH-67 GL was used as a vital stain for sporozoites of Eimeria tenella for tests on viability, invasion of cultured primary chick kidney cells, flow cytometric analysis and fluorescence microscopy. The effect of PKH-67 GL on sporozoites was tested at a range of concentrations of dye and sporozoites. In flow cytometric analysis, 0.5-40x10(-6) M of PKH-67 GL labeled sporozoites to some degree, with the percentage of labeled sporozoites increasing with higher dye concentrations. The optimum concentration was 2x10(-6) M, allowing easy observation by fluorescence microscopy. Morphological changes in the sporozoite at concentrations greater than 5x10(-6) M were accompanied by loss of viability according to a propidium iodide inclusion assay. Sporozoite penetration of primary chick kidney cells was unaffected by the optimal level of 2x10(-6) M, allowing observation of intracellular activities. Overall, the cell linker dye greatly facilitated observation of E. tenella in vitro and in flow cytometric analysis.

Observation of sutures in the oocyst wall of Eimeria tenella (Apicomplexa)

Eimeria tenella is the causative agent of caecal coccidiosis in chicken. Infection of chicken is initiated by ingestion of sporulated oocysts. The oocyst wall has two typical layers: a smooth outer layer formed by wallforming body I (WF I) and an inner layer originating from WF II. We observed that the inner layer is circumscribed by a hitherto undocumented linear suture and propose its role in the process of infection.

Differential localisation of an Eimeria tenella aspartyl proteinase during the infection process

Aspartyl proteinases are essential for the survival of many pathogens. A single copy gene in species of Eimeria encodes an aspartyl proteinase, which we propose should be called eimepsin to conform to the commonly used names of this family of proteinases. An epitope map, constructed using BIAcore technology, confirmed the specificity of 14 mAbs for eimepsin and defined four antigenic domains, which were conserved between native and recombinant forms of eimepsin. In resting sporozoites, mAb defining antigenic domains I and II stained the refractile body organelles, whereas those defining antigenic domains III and IV stained cytoplasmic granules. During host cell invasion, the staining patterns of mAb defining antigenic domains I, III and IV changed dramatically with the apical tips of invading sporozoites becoming strongly stained. In contrast, mAb defining antigenic domain II continued to stain only the refractile bodies. During early schizogony, mAb to all four domains stained the single fused refractile body, but when schizonts matured, mAb to antigenic domains I, III and IV stained the apical tip of merozoites whereas those to antigenic domain II continued to follow the developmental redistribution of the refractile body. Irrespective of localisation, mAb to three antigenic domains recognised a polypeptide of 49 kDa, which from N-terminal sequencing corresponds to a mature form of eimepsin. Staining with fluorescent pepstatin localised a mature, active form of eimepsin to the refractile bodies of the sporozoite, schizont and first generation merozoite. It remains to be determined whether eimepsin has a catalytic function within the refractile body or whether the activated enzyme is stored in the refractile body so that it can be rapidly redistributed to the apical tip during parasite invasion.

Localization and immunogenicity of a low molecular weight antigen of Eimeria tenella

A low molecular weight (LMW) antigen recognized by a murine monoclonal antibody (C(3)4F(1)) was localized within endogenous stages of Eimeria tenella (USDA strain 80). Using indirect fluorescent antibody assay and immunoelectron microscopy, the LMW antigen was found in: sporozoites, first, second and third generation meronts, gamonts, unsporulated oocysts, and sporocysts. The antigen was observed in the cytoplasm and pellicle of the parasite, and in the parasitophorous vacuole, sporocyst walls and cytoplasm of infected host cells. The immunogenicity of this LMW antigen was assessed by antigen-specific serum antibody responses in chickens orally inoculated with live oocysts or injected intramuscularly with dead sporozoites. LMW antigen-specific serum antibodies were detected using Western blots of E. tenella sporozoites as early as 4 days after sporozoite injection and 6 days after oocyst inoculation. Unusually, the monoclonal antibody C(3)4F(1) reduced the binding of immune chicken serum to the antigen in a competitive antibody binding assay, but not the reverse, suggesting that there is a single, immunodominant epitope on this antigen.

A microneme protein from Eimeria tenella with homology to the Apple domains of coagulation factor XI and plasma pre-kallikrein

Microneme organelles are present in all apicomplexan protozoa and contain proteins that are critical for parasite motility and host cell invasion. One apicomplexan-wide family of microneme proteins has been identified with members that are characterised by the possession of thrombospondin type I repeats, conserved adhesive motifs which are implicated in binding to glycosaminoglycan chains. In this paper we describe a micronemal glycoprotein, EtMIC 5, from Eimeria tenella which contains eleven cysteine-rich motifs that have striking similarity to the adhesive Apple (A-) domains of blood coagulation factor XI and plasma pre-kallikrein. EtMIC 5 is confined to an intracellular location in resting sporozoites but is translocated to the parasite surface and secreted into the culture supernatant during parasite infection of MDBK cells. During intracellular replication, the protein is switched off in early schizogony and is then re-expressed within the apical tips of newly formed merozoites. A-domain sequences were also found in microneme proteins from Sarcocystis muris and Toxoplasma gondii and in a protein of unknown localisation from Eimeria acervulina. These studies suggest that A-domain containing proteins may comprise a novel apicomplexan-wide family of microneme adhesins.

Vaccination against Eimeria tenella infection using a fraction of E. tenella sporozoites selected by the capacity to activate T cells

At 8 days after a primary Eimeria tenella infection, a subset of T cells, of which the protective role is as yet unclear, circulates in the peripheral blood. In order to investigate this, the in vitro cellular responsiveness of these peripheral blood lymphocytes has been used as selection criterion to identify potentially protective E. tenella sporozoite antigens. The hydrophilic protein phase of purified E. tenella sporozoite homogenates obtained by Triton X-114 extraction was fractionated using preparative gel electrophoresis. Nine fractions, separated according to different molecular weight, were tested for their ability to stimulate T-cell responses. Both the proliferation of peripheral blood lymphocytes and the macrophage activating activity released in the culture supernatants were measured. On the basis of this responsiveness, four fractions were selected and used to vaccinate chickens. All vaccine preparations induced strong T-cell responses. One fraction immunised chickens against subsequent challenge infection, in that the caecal lesion scores were significantly lower as compared with that of the unvaccinated controls. This fraction contained hydrophilic polypeptides with a molecular mass that ranged from 26 to 30 kDa.

Biosynthesis and catabolism of mannitol is developmentally regulated in the protozoan parasite Eimeria tenella

The mannitol cycle is a metabolic branch of the glycolytic pathway found in Eimeria tenella. In this paper, we describe the biosynthesis and consumption of mannitol during parasite development. Low micromolar levels of mannitol were detected in all of the asexual stages and mannitol production increased sharply during the sexual phase of the life cycle. Unsporulated oocysts had high mannitol content (300 mM or 25% of the oocyst mass). Mannitol-1-phosphate dehydrogenase (M1PDH), the first committed step of the mannitol cycle, was also elevated in sexual stages and this coincides with mannitol levels. Approximately 90% of the mannitol present in unsporulated oocysts was consumed in the first 15 hr of sporulation, and levels continued to drop until the sporulation process was complete at approximately 35 hr. Thus, mannitol appears to be the "fuel" for sporulation during the vegetative stage of the parasite life cycle. Evaluation of oocyst extracts from 6 additional Eimeria species for mannitol content and the presence of M1PDH indicated that the mannitol cycle was broadly present in this genus. This finding combined with the lack of mannitol metabolism in higher eukaryotes makes this pathway an attractive chemotherapeutic target.

Mechanisms of the Eimeria tenella growth inhibitory activity induced by concanavalin A and reticuloendotheliosis virus supernatants with interferon gamma activity in chicken macrophages and fibroblasts

Pretreatment of chicken bone marrow macrophages and embryo fibroblasts with supernatants containing chicken interferon gamma (IFN-gamma) for 24 hr prior to inoculation inhibited intracellular Eimeria tenella replication, measured by [3H] uracil incorporation. The supernatants (Sns) were obtained from culture of lymphoblastoid cells transformed by a reticuloendotheliosis virus (REV) and chicken splenocytes stimulated with concanavalin A (Con A). The mechanisms of the E. tenella growth inhibitory activity induced by Sn REV and Sn Con A in chicken macrophages and fibroblasts were studied. Addition of oxygen scavengers (superoxide dismutase, D-mannitol, DABCO, benzoic acid, L-histidine hydrochloride) was able to overcome the inhibition of E. tenella replication after pretreatment with Sn REV or Sn Con A in macrophage cultures but not in fibroblast cultures. Nitric oxide (NO) synthesis was induced in macrophage culture treated with Sn REV or Sn Con A but not in fibroblast culture. Addition of NG monomethyl-L-arginine, an NO synthase inhibitor together with the supernatants was also able to overcome inhibition of E. tenella replication in macrophage culture. On the other hand, addition of L-tryptophan to Sn REV- or Sn Con A-treated fibroblasts was able to reverse the inhibitory effect on E. tenella replication. In conclusion, production of inorganic NO or toxic oxygen intermediates may be involved in the E. tenella growth inhibitory activity of chicken macrophages pretreated with supernatants containing an IFN-gamma activity, and cellular tryptophan depletion may be involved for chicken fibroblasts, thus matching the mechanisms of the IFN-gamma-induced growth inhibitory activity for protozoans in mammals.

Transient expression of beta-galactosidase in differentiating sporozoites of Eimeria tenella

A transient transfection system has been developed for a member of the Apicomplexa, Eimeria tenella, using beta-galactosidase (betagal) from Escherichia coli as the reporter enzyme. Successfully expressed constructs contained sequences of the E. tenella microneme gene Etmic-1 fused to the coding region of lacZ. Transfectants expressing betagal were able to invade host cells and proceed through part of the life-cycle, forming schizonts from which merozoites were released. This indicated that transfectants could differentiate at least to first generation schizonts. However, this differentiation was delayed compared with unelectroporated sporozoites by approximately 15 h. Some merozoites arising from transfected sporozoites also expressed betagal. These results are encouraging for the development of a stable transfection system for E. tenella, using betagal as a reporter enzyme.

Inhibition of the development of Eimeria tenella in cultured bovine kidney cells by a soluble factor produced by peripheral blood lymphocytes from immune chickens

The intracellular development of Eimeria tenella sporozoites in in vitro cultured Madin-Darby Bovine Kidney (MDBK) cells was inhibited when parasite-infected MDBK cells were incubated with peripheral blood lymphocytes (PBL) from infected chickens. The inhibition mediated by PBL was quantified by [3H]uracil uptake and increased during the course of a series of oral infections of chickens with E. tenella. This was mirrored by the development of immunity in these birds, as assessed by counting the oocyst output following each re-infection. Similar levels of inhibition were observed using PBL from 3 inbred lines of chickens which differ in their relative susceptibility to infection with E. tenella, indicating that the genetic background of the host does not influence the production of this inhibitory activity. The inhibition could be transferred to freshly infected MDBK cells using supernatants prepared from parasite-infected monolayers incubated for 48 h with PBL from immune chickens. However, there was no inhibition using either supernatants from infected MDBK cells incubated with PBL from uninfected chickens, or supernatants from uninfected MDBK cells incubated with PBL from immune chickens. Experiments using Transwell plates showed that direct contact of PBL from immune birds with infected MDBK monolayers was not required to produce supernatants with inhibitory activity. Thus production of soluble inhibitory factor(s) by PBL from immune chickens can be specifically induced by soluble antigens present in the culture media of parasite-infected MDBK cells. These factors inhibit the intracellular development of sporozoites in in vitro culture.

Effect of conditioned media from chicken and turkey intestinal cell cultures on invasion by sporozoites of three species of avian coccidia

The effect of conditioned media from cultures of turkey and chicken intestinal cells on cellular invasion by sporozoites of avian Eimeria species was examined in vitro. Media conditioned by the growth of cells from the ceca, mid-intestine (area of the yolk stalk diverticulum), and duodenal loop were examined for their ability to enhance invasion. Conditioned medium from cultures of turkey cecal cells significantly enhanced invasion by the turkey coccidia Eimeria adenoeides, by 2.4-fold, and E. meleagrimitis, by 2.2-fold, as compared with invasion in the presence of control medium. Conditioned medium from mid-intestinal cell cultures enhanced invasion by the two coccidial species by 2.0- and 2.1-fold, respectively. The enhancement occurred with conditioned media from early (1) as well as later (11) passages of cells. This suggests that the enhancing factor was produced by fibroblast-like cells, the predominant cell type at both early and late passages, and not by epithelial-like cells that had disappeared by the first or second passage. Additionally, conditioned media from cultures of chicken cecal and duodenal loop cells significantly enhanced invasion by the turkey cecal coccidium, E. adenoeides, (1.7- and 1.6-fold, respectively). This was less enhancement than was caused by the turkey cell conditioned media. Heat treatment (56 degrees C for 45 min) of conditioned media failed to alter the effect on invasion. Neither the turkey or chicken cecal cell media nor conditioned media from any other chicken intestinal cell cultures enhanced invasion by E. tenella, the chicken cecal coccidium. Although morphologically dissimilar when they were first plated, the gross appearance and growth of the turkey and chicken cells when conditioned media was collected was comparable.

Recombinant chicken interferon-gamma-mediated inhibition of Eimeria tenella development in vitro and reduction of oocyst production and body weight loss following Eimeria acervulina challenge infection

Recombinant chicken interferon-gamma (chIFN-gamma) was produced in CHO-K1 or Spodoptera frugiperda (SF9) insect cells by transfection with a pcDNA vector or recombinant baculovirus (SF9-interferon-gamma [IFN-gamma] carrying the chIFN-gamma gene. A rabbit antibody against a synthetic peptide corresponding to an immunogenic portion of chIFN-gamma recognized a 22-23-kDa band in SF9-IFN-gamma cell extracts by western blot analysis. Biological activity of recombinant chIFN-gamma was shown by its inhibition of vesicular stomatitis virus-induced cytotoxicity of chicken embryonic fibroblast cells in vitro. To investigate the role of chIFN-gamma during Eimeria infection, CHCC-OU2 chicken cells either pretreated with chIFN-gamma or stably transfected with the chIFN-gamma gene were infected with Eimeria tenella sporozoites. IFN-gamma demonstrated significant reductions in intracellular sporozoite development without affecting sporozoite invasion of host cells. Furthermore, chickens treated with recombinant chIFN-gamma showed decreased oocyst production and significant improvement in body weight gain following Eimeria acervulina challenge infection. These results provide the first direct evidence that chIFN-gamma exerts an inhibitory effect against Eimeria and provides a rational basis for use of this cytokine as a vaccine adjuvant against coccidiosis.

Inhibition of Eimeria tenella development in vitro mediated by chicken macrophages and fibroblasts treated with chicken cell supernatants with IFN-gamma activity

Pretreatment of chicken macrophages or fibroblasts with supernatants from concanavalin A-stimulated spleen cells or from the virus-transformed cell line reticuloendotheliovirus as source of interferon gamma (IFN-gamma) slows down subsequent sporozoite replication in the cells. To identify the presence of IFN-gamma, we combined four typical activities of IFN-gamma: inhibition of cytopathic effect of vesicular stomatitis virus on IFN-gamma-treated fibroblasts, cytostatic activity of IFN-gamma-activated macrophages, induction of major histocompatibility complex II antigen expression on IFN-gamma-activated fibroblasts and macrophages, and induction of nitrite production in macrophages. We have shown that chicken fibroblasts and macrophages possess a microbiostatic capacity once they are able to prevent the otherwise unchecked intracellular replication of Eimeria tenella following activation with culture supernatants identified as containing a strong IFN-gamma activity.

Immunohistochemical identification of the cells parasitized by second-generation schizonts of Eimeria tenella

Conflicting reports exist in the literature concerning the type of cells within the lamina propria of the ceca that harbor second-generation schizonts of Eimeria tenella. Most of the previous studies concerning these cells have been performed using routine light or electron microscopy. Consequently, difficulties are evident in precise definition of the type of these cells using normal morphological criteria, since growth of the schizonts of E. tenella alters the morphology of the parasitized cell, making it difficult to recognize the cell type. This has led us to investigate the possibility of precisely identifying the subepithelial cells that are parasitized by mature schizonts. For this purpose we used cytoskeletal markers, namely, keratin and vimentin intermediate filaments, which allow the discrimination between epithelial and mesenchymal cells. Localization of keratin and vimentin on frozen cecal sections was studied immunohistochemically using specific monoclonal antibodies. Sites of antigenicity were detected by the avidin-biotin complex (ABC) immunoperoxidase technique and visualized by the deposition of diaminobenzidine. The identity of the cells was confirmed by the immunodetection of keratin intermediate filaments in the cytoplasm of the cells. Immunoreactivity for vimentin was absent in the parasitized cells. Therefore, we conclude that the development of second-generation schizonts of E. tenella takes place in epithelial cells within the lamina propria, which are presumably crypt epithelial cells that leave the crypts and enter the lamina propria after infection by first-generation merozoites.

Comparison between effects of standard feed and whole wheat supplemented diet on experimental Eimeria tenella and Eimeria maxima infections in broiler chickens

The effects of experimental infections with Eimeria tenella (Experiment 1, n = 144) or E. maxima (Experiment 2, n = 216) in broiler chickens fed whole wheat, with or without access to grit, as compared to a standard pelleted feed were studied. Inclusion of whole wheat was gradually increased up to 30% at 3 weeks of age. Grit was given separately. The chickens were kept on litter in a parasite-free environment with free access to water and feed. At 3 weeks of age half the number of chickens were individually inoculated with 500 sporulated oocysts of E. tenella (Experiment 1) or 3,000 sporulated oocysts of Eimeria maxima (Experiment 2), and the remaining birds were kept separate as uninfected controls. Neither coccidiostats nor growth enhancers were used. Oocyst concentration was determined from each group separately. Intestinal lesions were scored on 6 birds per feed regime 7 d postinoculation, and on the remaining birds at slaughter. Diet had no significant effect or bird performance during infection. However, there was an indication that the E. maxima infection had more negative effect on weight gain in birds given standard feed than in those given whole wheat supplement, but the difference was not significant (p < 0.09). The number of oocysts shed or mean intestinal lesion scores did not differ between diets in either experiment. In both experiments, the number of Clostridium perfringens was higher in the caeca of inoculated birds, but there were no differences between diets.

Techniques for isolation and characterization of apical organelles from Eimeria tenella sporozoites

Apical organelles contain molecules that are of critical importance for the interaction of all apicomplexan parasites with their target host cells. Thus, there is considerable interest in characterizing and understanding the function of molecules that reside in these organelles. Large numbers of surface-sterilized oocysts of Eimeria tenella, an apicomplexan coccidian of the chicken, can be routinely obtained from the animal host, and invasive sporozoites, which contain abundant apical organelles, can be rapidly prepared from these oocysts in the laboratory. Thus, E. tenella is proving to be an amenable parasite for subcellular fractionation techniques that allow the direct isolation and characterization of apical organelles. In this paper, a series of protocols is described for the large-scale culture of E. tenella parasites, the preparation of invasive sporozoites, the isolation of apical organelles, and the use of in vitro culture for localization and functional studies.

Peripheral blood lymphocytes from Eimeria tenella infected chickens produce gamma-interferon after stimulation in vitro

Protective immunity to infection by Eimeria parasites has been demonstrated to be dependent on T-cell mediated immune responses and may be associated with the release of cytokines. We have previously shown that the proportion of CD8-expressing T-cells in the peripheral blood of chicken increases transiently at 8 days after a primary infection with Eimeria tenella oocysts. The increase in the CD8+ population coincided with an increased proliferative lymphocyte response upon stimulation with E. tenella sporozoite antigen in vitro. In this study, we further investigated the functional activity of these peripheral blood leucocytes (PBL) by determining both the potential to proliferative and to produce IFN upon stimulation with E. tenella sporozoite antigens and mitogens. Enhanced proliferative responses to parasite antigen were accompanied by reduced responses to T-cell mitogens around 1 week of infection. The IFN activity in the supernatants of the stimulated PBL was measured by the ability to inhibit Semliki Forest Virus (SFV) replication in chicken embryo fibroblasts (CEF) and to activate macrophages, as measured by nitric oxide production. At eight days after infection the highest levels of virus inhibition and NO-production were detected upon stimulation with both E. tenella sporozoite antigen and mitogen. A strong correlation between the individual data of the two methods was found at this timepoint indicating that the produced cytokine was indeed IFN-gamma. These results suggest that around eight days after a primary E. tenella infection a parasite specific T-cell subset with the capacity of produce IFN(-gamma) is circulating which would be involved in the induction of protective immunity against Eimeria tenella.

The effect of high n-3 fatty acids diets on the ultrastructural development of Eimeria tenella

A study of development of Eimeria tenella in chickens fed high n-3 fatty acids (n-3FA) diets showed ultrastructural degeneration of both asexual and sexual parasite stages. Abnormal shedding of asexual and sexual parasite developmental stages into the cecal lumen was also observed. Ultrastructural degeneration was characterized by cytoplasmic vacuolization, chromatin condensation within the nucleus, a lack of parasitophorous vacuole delineation, and, in some cases, a complete loss of parasite ultrastructural organization. The results of this study indicate that diets high in n-3FA may be useful in the control of avian coccidia.

Adapting Eimeria tenella to grow in primary chicken kidney cells following repeated passages between cell culture and chickens

The present study was undertaken to adapt a field isolate (F0) of Eimeria tenella to grow in primary chicken kidney cells (PCKCs) by selecting for characteristics of the parasite rather than modifying the culture and/or environmental conditions. Fourteen generations (F1 to F14) of E. tenella were produced following repeated passages between PCKCs and chickens. Although F1 yielded only a 28% increase in oocysts, in PCKCs compared with F0, F2 to F5 produced from 259% to 277% more oocysts, respectively. There was no significant increase in the percentage of oocysts produced in PCKCs by F6 to F14 compared with F5. Generations F1 to F14 demonstrated a greater propensity for multiple infections within the same host cell than did F0. For example, it was not uncommon to observe two, three, and occasionally four oocysts within a single PCKC. Chickens inoculated with F0 oocysts generally experienced greater pathogenesis by day 7 postinoculation than chickens inoculated with F14 oocysts as measured by decreased body weights, increased cecal lesions, and a higher mortality rate.

Eimeria tenella: genetic recombination of markers for precocious development and arprinocid resistance

A mating was made between two populations of Eimeria tenella possessing the complementary traits of normal development (virulence) + resistance to the anticoccidial drug arprinocid or precocious development (attenuation) + drug-sensitivity. A small number of "recombinant" oocysts was recovered. The inheritance of markers from both parents into 22 cloned lines derived from the recombinant oocysts was confirmed by analyses of restriction fragment length polymorphisms of four repetitive DNA sequences.

Eimeria tenella infections in chickens: aspects of host-parasite: interaction

Intestinal coccidiosis, caused by various species of Eimeria, has become an economically important disease of poultry and livestock throughout the world. Infection of chickens starts after ingestion of oocysts when sporozoites penetrate the epithelium of the villi. After passage through the lamina propria, they enter crypt epithelial cells where they undergo several rounds of asexual and sexual proliferation, thus forming merozoites and later, gametocytes. When macrogametes are fertilized by microgametes, oocysts are formed that are shed in the faeces. Nowadays, coccidiosis is prevented by anticoccidial drugs that are added to food, but the prolonged use of these drugs leads inevitably to the emergence of resistant Eimeria strains. During infection, there are three stages when the chicken immune system can inhibit parasitic development. The first is when the sporozoite searches for a site of penetration and binds to the epithelium. The second is when the sporozoite is in the villus epithelium amongst intra-epithelial leucocytes. The third is during its passage through the lamina propria to the crypt epithelium. To investigate this, the decisive factors in the induction and effector phase of immunity against coccidiosis have been investigated in situ. Our studies have revealed that three phenomena are responsible for immunity against Eimeria infections. First, the actual passage and presence of parasites in the lamina propria to induce immunity. Second, the sporozoite seems to be the most important parasite stage for immunity, and third, cytotoxic T cells are necessary to inhibit parasites.

Eimeria tenella: infection with a single sporocyst gives a clonal population

Two genetically defined parents of Eimeria tenella, each characterized by a selectable phenotype, were mated to provide "recombinant' oocysts for an analysis of the inheritance of DNA markers into the sporocyst stage of the life-cycle. A total of 23 populations was established from infection with a putative single sporocyst and their inheritance of DNA markers provided compelling evidence that the 2 sporozoites within each sporocyst are genetically identical. EAch of the 5 polymorphic DNA markers used segregated independently within the "recombinant' parasites and only 1 of the parental forms was inherited in 22 of the populations aimed to have been established from a single sporocyst.

In situ characterization of leucocyte subpopulations after infection with Eimeria tenella in chickens

We characterized the leucocyte subpopulations after infection with Eimeria tenella in both naive and immune chickens. Immunocytochemical staining was used to characterize the cells in situ, so that the interaction between host and parasite could be studied. More leucocytes were detected in the lamina propria of immune chickens, and leucocytes infiltrated the ceca more rapidly than in naive chickens, but the infiltration was less pronounced than in naive chickens. In naive chickens, most infiltrated leucocytes were macrophages and T cells. Two days after inoculation the number of CD4+ cells had increased greatly. In immune chickens, mainly T cells (CD4+ and CD8+) infiltrated the lamina propria, and in contrast to naive chickens, the number of CD8+ cells exceeded the number of CD4+ cells. Furthermore, we characterized which cells contained a parasite and which cells were detected next to the parasites, because these cells are probably involved in the arrested development of the parasites. In naive chickens, sporozoites were significantly more often located within or next to macrophages than in immune chickens. In immune chickens, sporozoites were significantly more often located within or next to CD3+, CD8+, and TCR2+ cells. In conclusion, the marked increase of CD4+ cells after primary infection suggests that these cells are involved in the induction of the immune response, whereas the increase of CD8+ cells after challenge infection suggests that these cells act as effector cells.