Ponazuril inhibits the development of Eimeria vermiformis in experimentally infected outbred Swiss mice.

We evaluated a 15% paste formulation of ponazuril in outbred Swiss mice that were experimentally infected with Eimeria vermiformis. Thirty, 8-week-old female mice (approximately 20 g) were placed in one group of 10 mice and one group of 20 mice. Mice in both groups were gavaged with approximately 5,000 sporulated oocysts of E. vermiformis on day 0. Mice in group 2 (n=10) were treated orally on days 3 and 4 with ponazuril (suspended in 30% propylene glycol) at the rate of 20 mg/kg. Mice in group 1 (n=20) were gavaged with a similar volume of 30% propylene glycol. Rates of oocyst passage (oocysts/g feces) were determined on day 10 (peak patency) for treated and nontreated mice using a fecal aliquot oocyst counting technique. Oocysts were not observed in the feces of treated mice using the aliquot technique. Control mice passaged oocysts at a geometric mean rate of >104,000 oocysts/g feces. Control mice also produced significantly less feces on day 10. These results indicate that ponazuril is effective against E. vermiformis under the conditions utilized in this study, and that the E. vermiformis mouse model could be useful in predicting the efficacy of new anticoccidial drugs.

Major histocompatibility complex class I- and II-deficient knock-out mice are resistant to primary but susceptible to secondary Eimeria papillata infections.

Two distinct mechanisms seem to function in reducing oocyst output during Eimeria papillata infections in mice. For naive mice, immunity was afforded by a T-cell-independent gamma-interferon (IFN-gamma) response mediated by natural killer (NK) cells. On reinfection, resistance was associated with T-cells and, to a lesser extent, perforin. To determine if antigen presentation with major histocompatibility complex (MHC) molecules was required to control oocyst production by NK cells during primary infection or by T-cells during secondary infection, mutant mice that lacked H2-IAbeta(b) (Abeta(b)-/-) or beta2-microglobulin (beta2m-/-) were used. Since MHC molecules are required for the maturation of alphabeta T-cells, Abeta(b)-/- and beta2m-/- mutant mice are also deficient in functional alphabeta+CD4+ or alphabeta+CD8+ T-cells, respectively. As compared with wild-type control mice, oocyst output by mutant mice was not significantly affected during primary infection, suggesting that the ability of NK cells to control parasite replication is not dependent on the expression of MHC molecules. On reinfection, differences were observed for mutant mice as compared with controls. Abeta(b)-/- mice were found to be more susceptible than beta2m-/- mice, suggesting that the alphabeta+CD4+ T-cell subset plays a greater role in resistance to reinfection than does the alphabeta+CD8+ T-cell subset. The mechanism of resistance depends on the immune status of the host and requires the coordinated interaction of both alphabeta+ T-cell subsets for optimal parasite control during subsequent infections.

Cellular dynamics and cytokine responses in BALB/c mice infected with Eimeria papillata during primary and secondary infections.

BALB/c mice were infected with the intestinal intracellular parasite Eimeria papillata to characterize lymphocyte responses and cytokine profiles throughout primary and secondary infections. Lymphocytes from the mesenteric lymph node (MLN) and the gastrointestinal tract (GIT) of infected mice were phenotypically analyzed using flow cytometry and immunofluorescence microscopy, respectively. Lymphocytes isolated from the MLN during primary infections of BALB/c mice with E. papillata do not proliferate, compared to day 0 uninfected controls, when stimulated in vitro with conconavalin A and express TH2-type cytokines (interleukin [IL]-4 and IL-10) on day 3 PI followed by the release of TH1-type cytokines (IL-2 and interferon-gamma) during patency. In the small intestine, significantly more T cells and their subsets were observed during primary infection. During secondary infections, IL-2 was the only 1 of the 4 cytokines that was expressed earlier and at higher levels in the MLN when compared to primary infections. In the small intestine, significantly more alphabeta+ and CD8+ T lymphocytes were observed in mice during secondary infection. Oocyst antigens did not induce cellular proliferation at any time point during primary or secondary infections. We conclude that primary oral infection of BALB/c mice with E. papillata is associated with localized immunosuppression that may be mediated, in part, by early TH2-type cytokines. Immunity to secondary infection may be mediated by intestinal alphabeta+ CD8+ T lymphocytes through an IL-2-dependent mechanism.

Comparison of four murine Eimeria species in immunocompetent and immunodeficient mice.

Factors associated with immune-mediated protection against coccidial parasites were examined in a series of experiments utilizing immunocompromised scid/scid(SCID) and scid/scid.beige/beige(SCID/Bg) mice, as well as immunocompetent BALB/c mice. Number of oocysts produced per g feces each day and prepatent and patent periods were assessed for 4 eimerian parasites (Eimeria papillata, Eimeria vermiformis, Eimeria falciformis, and Eimeria ferrisi) using the 3 murine strains. The number of infections required to elicit a protective immune response was also determined for each coccidial species in BALB/c mice. We report the first description of patent infections in inbred immunocompetent and immunodeficient mice infected with E. papillata. Results indicate that during primary infections, parasite replication is under partial immunological control for all Eimeria species. However, the control is mechanistically different for E. papillata because the adaptive immune response does not contribute to the control of primary infections. Both coccidial species infecting intestinal villar epithelial cells (E. papillata and E. ferrisi) were affected by the beige mutation using parasite output as an indicator, whereas E. falciformis, which infects intestinal crypt cells, is not. BALB/c mice were more resistant to challenge infections with upper intestinal parasites (E. papillata and E. vermiformis) in comparison to challenge infections with lower intestinal and cecal parasites (E. falciformis and E. ferrisi).

Ultrastructural observations of host-cell invasion by sporozoites of Eimeria papillata in vivo.

Scanning and transmission electron microscopy were used to study the invasion of mouse small-intestinal epithelium by sporozoites of Eimeria papillata. Some mice received oocysts by gavage and others received either sporocysts or sporozoites by direct injection into the small intestine. The highest concentration of invaded cells were found in ligated intestinal tissues studied at 5-45 min after the inoculation of sporozoites. Sporozoites actively invaded anterior end first, which resulted in extensive damage to the host cell. Such cells showed disrupted microvilli; protuberances of cytoplasm into the lumen, apparently the result of a disrupted plasma membrane; vacuolization of the cytoplasm; and damage to the mitochondria. These damaged cells were rapidly vacated as the sporozoite moved laterally into one or more adjacent intact host cells without entering the lumen. It is suggested that the host cell initially entered from the lumen becomes so severely traumatized that the parasite of necessity enters an adjacent cell as a prelude to further development. Various aspects of host-cell invasion by coccidia and malarial parasites are reviewed.

Scanning and transmission electron microscopy of host cell pathology associated with penetration by Eimeria papillata sporozoites.

Scanning and electron microscopy was used to study the pathogenesis that occurred in mouse epithelial cells that had been penetrated by Eimeria papillata sporozoites. Optimal penetration of parasites injected into nonligated and ligated mouse intestine was found to occur at 4-15 min post-inoculation. During initial penetration, the parasite caused disruption of the microvilli of the intestinal cells, which led to detachment of the microvilli from the plasma membrane of the penetrated cell. Host cells penetrated by the parasite showed extensive destruction of the internal cellular organization together with blebbing of host-cell cytoplasm and release of internal organelles such as mitochondria. Ultimately, the penetrated cells completely broke down, leaving vacuolated areas next to ultrastructurally normal epithelial cells.

A scanning electron microscope study of the colon of the mouse (Mus musculus) infected with Eimeria ferrisi (Protozoa, Apicomplexa, Coccidia).

Micromorphological changes in the colon of mice infected with Eimeria ferrisi were studied by scanning electron microscopy. The damage observed consisted of swelling of epithelial cells, profound stretching of the host cell membranes, loss of microvilli and erosion of tissues. Mature meronts were visible at 3 days post-inoculation (PI) in localized areas of cellular rupturing. At 4-6 days PI, the cellular rupturing and epithelial disruption were more widespread, exposing intra- and extracellular meronts, merozoites, and sexual stages. Microgametes of E. ferrisi are equipped with 2 flagella. Even though large portions of the infected area become denuded of surface epithelium, recovery had begun by day 7 PI.

A freeze-fracture study of the host cell-parasite interface during and after invasion of cultured cells by cystozoites of Sarcocystis muris.

The parasite-host-cell interface of Sarcocystis muris in cell culture was studied by freeze-fracture electron microscopy. Cystozoites of S. muris have an intra membrane particle (IMP) density of 1347 ± 146 IMP/µm(2) on the P face and 638 ± 109 IMP/µm(2) on the E face. After exposure to trypsin during extraction from the cysts a reversal of IMP density to 820 ± 115 µm(2) on the P face and 1277 ± 140 µm(2) on the E face occurred. Invasion of S. muris cystozoites is followed by the enclosure of the parasite in a primary parasitophorous vacuole (PV 1), limited by a membrane which partly originates by invagination and inward expansion of the plasmalemma of the host cell. A decline of local densities of IMP on the P face of the infected host cell from 2557 ± 567 IMP/µm(2) to 417 ± 217 IMP/µm(2) in the membrane of PV 1 represents a significant decrease of protein elements. S. muris gamonts became translocated to a new vacuole (PV 2) 30 to 45 minutes after invasion. IMP reappeared on both fracture faces of the vacuole membrane. The rapid increase of IMP on the PV 2 membrane coincides with the release of large amounts of dense granule contents.

Light and electron microscope study of Sarcocystis sp. from the fallow deer (Cervus dama).

By means of light and electron microscopy a study was made of Sarcocystis sp. from 11 fallow deer (Cervus dama). Cysts of Sarcocystis sp. were found in the tongue and abdominal muscle of 3 of 11 deer from forests near Bonn (FRG). These measured 212-560 micron in length and 54-120 micron in width and contained metrocytes and merozoites. The cyst wall, which had narrow band-like protrusions, is compared with other Sarcocystis sp. from Cervidae.

Cellular pathology in mouse embryonic brain cells following in vitro penetration by sporozoites of Eimeria papillata.

The pathology that occurs in mouse embryonic brain ( MEB ) cells that have been penetrated by sporozoites of Eimeria papillata was studied by light and electron microscopy. At the light microscopy level the greatest number of intracellular parasites was seen at 15 and 45 min postinoculation (PI). The monolayer of MEB cells had begun to round up by 45 min PI, and by 60 min PI most of the cells were stripped from the coverslip. Little ultrastructural damage was seen in MEB cells just penetrated by the parasites at 15 min PI, and no host cell membrane was seen around the sporozoites that had just entered the cells. Flexing and bending of the sporozoites within the MEB cell caused vacuolization of cell cytoplasm and in some cases rupture of host cell membrane. Sporozoites leaving the host cells at 15 min PI caused a rupture of the host cell membrane at the apical end of the parasite, and both host cell membrane and cytoplasm were attached to the surface of the parasite. MEB cells still attached to coverslips at 45 min PI demonstrated complete degeneration.

Ultrastructure of Sarcocystis sp. from the muscle of a white-tailed deer (Odocoileus virginianus).

Sarcocystis sp. from the muscle of naturally infected white-tailed deer (Odocoileus virginianus) was examined by transmission electron microscopy. The primary cyst wall forms regularly spaced protrusions filled with electron-lucent ground substance; no fibrils are present in the protrusions. The cysts are divided by septa into compartments containing typical coccidian metrocytes and merozoites. Taxonomy of the protozoon from the white-tailed deer-dog is discussed.

Fine structure of the oocyst wall and excystation of Eimeria procyonis from the American raccoon (Procyon lotor).

Oocysts of Eimeria procyonis, from the American raccoon (procyon lotor), were broken, added to a cell suspension, fixed in Karnovsky's fluid, and studied with the electron microscope. The oocyst wall has three layers: a thin electron-dense inner layer (8-15 nm), an electron-lucent middle layer (25-35 nm), and a thick outer layer (120-140 nm). The outer layer has an electron-dense inner portion and an electron-lucent outer portion that contains membrane-bound vesicles. When exposed to a trypsin-sodium taurocholate fluid, sporozoites excysted from most sporocysts which were 35-43 months old, but not from sporocysts that looked normal and were 106 months old. Excysted sporozoites measured 13-16 x 3-4 (mean 14.3 x 3.2) micrometer, usually had two refractile bodies, and had a nucleus with a prominent nucleolus.

Ultastructural studies of Sarcocystis sp. from the camel (Camelus dromedarius) in Egypt.

By means of electron microscopy a study has been made on Sarcocystis from 29 camels (Camelus dromedarius) in Egypt. In oesophagus and diaphragm muscles sarcocysts have been observed. The micromorphology of metrocytes, merozoites as well as of the cyst wall has been described.

Clinical and histologic observations of actively induced resistance to Eimeria ferrisi Levine and Ivens, 1965 (Protozoa: Eimeriidae) in the mouse (Mus musculus).

Actively induced resistance to Eimeria ferrisi was studied clinically and histologically in Mus musculus. Results indicated that a partial resistance to challenge was obtained. Initially infected animals had severe symptoms of coccidiosis but the symptoms diminished as the infections progressed. Previously infected mice had only slight symptoms of infection when challenged. Challenge doses produced severe coccidiosis in the non-immune controls although none died. Six mice died at peak patency during the immunizing inoculations. Histologic examination indicated that parasite numbers were reduced in resistant animals. The reduction appeared greatest during late sexual development. Tissues from resistant animals showed little evidence of damage and appeared to contain an increased amount of lymphoid tissue. Tissues from non-immunized mice killed after challenge were heavily infected and contained extruded blood, mucous, and cellular debris in the gut lumen. Considerable destruction of host epithelial cells occurred. The observations are discussed and compared to other coccidial immunity studies.