Eimeria separata: method for the excystation of sporozoites

Morphometric analysis of aerobic Eimeria bovis sporogony using live cell 3D holotomographic microscopy imaging

M onoxenous Eimeria species are widespread enteropathogenic apicomplexan protozoa with a high economic impact on livestock. In cattle, tenacious oocysts shed by E. bovis-infected animals are ubiquitously found and making infection of calves almost inevitable. To become infectious oocysts, exogenous oxygen-dependent E. bovis sporogony must occur leading to the formation of sporulated oocysts containing four sporocysts each harboring two sporozoites. Investigations on sporogony by live cell imaging techniques of ruminant Eimeria species are still absent in literature as commonly used fluorescent dyes do not penetrate resistant oocyst bi-layered wall. Sporogonial oocysts were daily analyzed by a 3D Cell Explorer Nanolive microscope to explore ongoing aerobic-dependent sporogony as close as possible to an in vivo situation. Subsequently, 3D holotomographic images of sporulating E. bovis oocysts were digitally stained based on refractive indices (RI) of oocyst bi-layered wall and sub-compartments of circumplasm using STEVE software (Nanolive), and the cellular morphometric parameters were obtained. Overall, three different E. bovis sporogony phases, each of them divided into two sub-phases, were documented: (i) sporoblast/sporont transformation into sporogonial stages, (ii) cytokinesis followed by nuclear division, and finally (iii) formation of four sporocysts with two fully developed sporozoites. Approximately 60% of sporulating E. bovis oocysts accomplished aerobic sporogony in a synchronized manner. E. bovis sporogony was delayed (i.e., 6 days) when compared to an in vivo situation where 2–3 days are required but under optimal environmental conditions. Live cell 3D holotomography analysis might facilitate the evaluation of either novel disinfectants- or anti-coccidial drug-derived effects on ruminant/avian Eimeria sporogony in vitro as discrimination of sporogony degrees based on compactness, and dry mass was here successfully achieved. Main changes were observed in the oocyst area, perimeter, compactness, extent, and granularity suggesting those parameters as an efficient tool for a fast evaluation of the sporulation degree.

Ruminant Coccidiosis

Ruminant coccidiosis, caused by Eimeria species, is a significant and widespread enteric disease in young livestock worldwide. High morbidities and significant mortalities may be observed. For disease diagnosis, fecal samples from clinically ill animals should be analyzed for both, identity (ie, pathogenicity) of Eimeria species and excreted oocyst amount. To prevent coccidiosis-related economic losses, management measures to reduce infection pressure and improve general animal health are crucial. Anticoccidial drugs are widely used to control clinical and subclinical disease. Treatment is most efficient when applied prophylactically or metaphylactically. To avoid development of parasite drug resistance, drugs should be used sustainably.

Optimized excystation protocol for ruminant Eimeria bovis- and Eimeria arloingi-sporulated oocysts and first 3D holotomographic microscopy analysis of differing sporozoite egress

Successful excystation of sporulated Eimeria spp. oocysts is an important step to acquire large numbers of viable sporozoites for molecular, biochemical, immunological and in vitro experiments for detailed studies on complex host cell-parasite interactions. An improved method for excystation of sporulated oocysts and collection of infective E. bovis- and E. arloingi-sporozoites is here described. Eimeria spp. oocysts were treated for at least 20 h with sterile 0.02 M _L-cysteine HCl/0.2 M NaHCO₃ solution at 37 °C in 100% CO₂ atmosphere. The last oocyst treatment was performed with a 0.4% trypsin 8% sterile bovine bile excystation solution, which disrupted oocyst walls with consequent activation of sporozoites within oocyst circumplasm, thereby releasing up to 90% of sporozoites in approximately 2 h of incubation (37 °C) with a 1:3 (oocysts:sporozoites) ratio. Free-released sporozoites were filtered in order to remove rests of oocysts, sporocysts and non-sporulated oocysts. Furthermore, live cell imaging 3D holotomographic microscopy (Nanolive®) analysis allowed visualization of differing sporozoite egress strategies. Sporozoites of both species were up to 99% viable, highly motile, capable of active host cell invasion and further development into trophozoite- as well as macroment-development in primary bovine umbilical vein endothelial cells (BUVEC). Sporozoites obtained by this new excystation protocol were cleaner at the time point of exposure of BUVEC monolayers and thus benefiting from the non-activation status of these highly immunocompetent cells through debris. Alongside, this protocol improved former described methods by being is less expensive, faster, accessible for all labs with minimum equipment, and without requirement of neither expensive buffer solutions nor sophisticated instruments such as ultracentrifuges.

Excystation of Eimeria acervulina, E. maxima, and E. tenella differs in response to trypsin and chymotrypsin and the presence of reducing agents DTT and TCEP

Release of sporozoites from Eimeria oocysts/sporocysts is an essential step in the intracellular development of the parasite in its host. Little is known about this process except that elevated temperature (∼ 40 °C) plus trypsin and bile salts are required for sporozoite to escape from sporocysts. In this study, it was found that adding a reducing agent, either dithiothreitol (DTT) or Tris(2-carboxyethyl)phosphine hydrochloride (TCEP), increased the lifespan of sporozoites released from Eimeria maxima. While the addition of DTT or TCEP affected the apparent molecular weight of trypsin, it did not interfere with excystation of E. maxima, but rather had a positive effect on the number of viable sporozoites present after release. This effect was time-dependent in that the number of intact sporozoites at 15 and 30 min after excystation was similar between untreated and DTT- or TCEP-treated sporocysts. However, by 45-60 min, virtually no sporozoites were observed in excystation fluid not containing DTT or TCEP. Of interest is that this effect appeared to be Eimeria species-dependent. Eimeria acervulina and E. tenella sporozoites remained viable for at least 60 min after excystation in the absence of DTT or TCEP. The effect of DTT and TCEP on chymotrypsin was also studied with all 3 Eimeria species because there is some evidence that chymotrypsin is an effective excystation enzyme. Indeed, E. maxima sporozoites excysting from sporocysts with chymotrypsin in the presence of DTT or TCEP remained viable for at least 60 min after release, unlike excystation done in the absence of these reducing agents. Chymotrypsin was capable of excysting E. acervulina in the presence or absence of DTT or TCEP. Of interest, is that chymotrypsin was ineffective in the excystation of E. tenella. These findings suggest that trypsin and chymotrypsin have differential effects on sporozoite excystation and that reducing agents may alter sites on the enzyme that affect sporozoite viability, but not release from sporocysts.

Dual RNA-seq reveals no plastic transcriptional response of the coccidian parasite Eimeria falciformis to host immune defenses

Background

Parasites can either respond to differences in immune defenses that exist between individual hosts plastically or, alternatively, follow a genetically canalized (“hard wired”) program of infection. Assuming that large-scale functional plasticity would be discernible in the parasite transcriptome we have performed a dual RNA-seq study of the lifecycle of Eimeria falciformis using infected mice with different immune status as models for coccidian infections.

Results

We compared parasite and host transcriptomes (dual transcriptome) between naïve and challenge infected mice, as well as between immune competent and immune deficient ones. Mice with different immune competence show transcriptional differences as well as differences in parasite reproduction (oocyst shedding). Broad gene categories represented by differently abundant host genes indicate enrichments for immune reaction and tissue repair functions. More specifically, TGF-beta, EGF, TNF and IL-1 and IL-6 are examples of functional annotations represented differently depending on host immune status. Much in contrast, parasite transcriptomes were neither different between Coccidia isolated from immune competent and immune deficient mice, nor between those harvested from naïve and challenge infected mice. Instead, parasite transcriptomes have distinct profiles early and late in infection, characterized largely by biosynthesis or motility associated functional gene groups, respectively. Extracellular sporozoite and oocyst stages showed distinct transcriptional profiles and sporozoite transcriptomes were found enriched for species specific genes and likely pathogenicity factors.

Conclusion

We propose that the niche and host-specific parasite E. falciformis uses a genetically canalized program of infection. This program is likely fixed in an evolutionary process rather than employing phenotypic plasticity to interact with its host. This in turn might limit the potential of the parasite to adapt to new host species or niches, forcing it to coevolve with its host.

Electronic supplementary material

The online version of this article (10.1186/s12864-017-4095-6) contains supplementary material, which is available to authorized users.

Effects of different sizes of glass beads on the release of sporocysts from Eimeria tenella oocysts

The oocyst wall is severed by means of mechanical injury or chemical agents. This study reports the percentage of in vitro sporocyst release following mechanical shaking in the presence of varying sizes of glass beads. Glass beads measured 0.5, 1, and 3 mm in diameter and were shaken with the oocysts for different times ranging from 5 sec to 5 min. Approximately 80% of sporocysts were released with 5 min of shaking in the presence of 3 mm glass beads, as well as 30 sec with 0.5 mm beads and 1 mm glass beads. The release of sporocysts of E. tenella was most efficient using 1 mm glass beads and treatment times of 30 sec to 1 min. Therefore, the use of 1 mm glass beads with 30 sec to 1 min of agitation is recommended in order to maximize sporocyst release and recovery and to improve the yield of viable sporozoites for use in biochemical, tissue culture, and immunological applications of coccidia.

Lymphocyte subpopulations in the caecum mucosa of rats after infections with Eimeria separata: early responses in naive and immune animals to primary and challenge infections

This study aimed to characterise the local (intestinal) immune response of rats after primary and challenge infections with Eimeria separata. Naive rats and rats which had been immunised by two moderate infections were exposed to a heavy infection with 100000 oocysts per animal. Necropsies were performed 0, 24 and 48 h after infection and lymphocyte subpopulations were microscopically quantified in the caecum mucosa after marking by immunohistological techniques. There was no difference between naive and immune rats concerning the number of CD45R(+) (B) cells, whereas significantly more CD3(+) (T) cells were found in the caecum wall of the immune rats. CD4(+) T cells predominated in animals after primary infection, whereas CD8(+) T cells represented the major T-cell subset in challenged rats. The proportion of TCRgammadelta(+) T cells did not differ in the mucosa between the groups examined, whereas challenged rats showed significantly increased numbers of TCRalphabeta(+) T cells in the caecum wall when compared with animals after a primary infection. Thus, CD4(+) T cells may be particularly involved in the immune response to a primary infection of rats with E. separata whereas immunity to a challenge infection seems to be mediated predominantly by CD8(+) and TCRalphabeta(+) T cells.