Excystation of Eimeria bovis and Other Species of Bovine Coccidia*

Abstract

SYNOPSIS. Mechanically released sporocyts of Eimeria bovis, E. ellipsoidalis and E. auburnensis readily excysted when incubated in a mixture of trypsin, steapsin, and bovine bile. Excystation of intact E. bovis, E. ellipsoidalis and E. auburnensis oocysts occurred after pretreatment at 37°C in aqueous 0.02 M cysteine hydrochloride under an atmosphere of CO2‐air or CO2‐N2, followed by incubation in an enzyme‐bile mixture. Nine % of E. bovis oocysts were activated after 6 hr of incubation at 37 C in a mixture of 0.5% (w/v) trypsin, 0.5% (w/v) steapsin, and 5.0% (v/v) bile at pH 7.5 with 10 hr pretreatment under air and 20% CO2; with 30% CO2, 80% activation occurred; with 50% CO2, 91% of the oocysts were activated. At CO2 levels from 10 to 40%, pretreatment with CO2 and N2 yielded less activation than CO2 and air. Pretreatment with CO2‐N2 (50–50) for 2 hr resulted in 37% activation; for 6 hr, 60%; for 10 hr, 94%; and for 14 hr, 99%. After pretreatment under 50% CO2 for 10 hr, 95% excystation was obtained by incubation for 6 hr in 0.5% trypsin and 5.0% bile. Only 76 or 69% excystation occurred when 0.25% trypsin or 1.0% bile, respectively, was substituted. Addition of steapsin to this mixture caused little change in the results. In oocysts pretreated 14 to 21 hr with steapsin, 2% or less excystation occurred after 6 hr in a trysinbile or bile mixture. E. ellipsoidalis oocysts, pretreated for 10 hr under CO2‐N2 (50–50), underwent 61 and 80% excystation when incubated for 2 and 6 hr, respectively, in trypsin, steapsin, and bile. E. bovis oocysts enclosed in a dialysis bag inside an intestinal fistula became thinned or flattened at the micropyle after 24 hr, and excystation occurred when these oocysts were mixed with trypsin, steapsin, and bile and returned to the fistula for 4 hr. No excystation occurred when oocysts without added enzymes were left 48 hr in the fistula. Sporozoites escaped first from sporocysts and then from oocysts.

Ultrastructure of Cryptosporidium parvum Oocysts and Excysting Sporozoites as Revealed by High Resolution Scanning Electron Microscopy1

“…In most coccidian species examined to date, in vitro excystation may be elicited by exposure of oocysts to conditions simulating the gut environment of the host (i.e. host body temperature, COz, reducing conditions, trypsin, and bile salts) (6,7,9). Eimeriid coccidia, such as Eimeria and Zsospora, are characterized by oocysts possessing inner sporocysts, each of which contains infective sporozoites.…”

The Effects of Selected Gases on Excystation of Coccidian Oocysts

“…He stated that this action was enhanced by the addition of a reducing agent. Nyberg and Hammond (1964), Nyberg et al (1968), Hibbert and Hammond (1968), and Bunch and Nyberg (1970) each used reducing agents along with CO2 in their in vitro excystation experiments; however, the role of CO2 was emphasized with little importance attributed to the action of the reducing agent.…”

“…Previous investigations have shown that CO2 and a suitable reducing agent can change the oocyst wall permeability, allowing the entrance of trypsin and bile (Jackson, 1962;Nyberg and Hammond, 1964;Bunch and Nyberg, 1970). The mechanism of CO2 action, however, is not well understood.…”

The Activation of Infective Stages of Endoparasites of Vertebrates

“…arloingi and E. intricata from sheep (Jackson, 1962;Bunch & Nyberg, 1970), E . bovis, E. auburnensis and E. ellipsoidalis from cattle (Hibbert & Hammond, 1968;Nyberg & Hammond, 1964) and for E . tenella, E. necatrix and E. acervulina from poultry (Hibbert & Hammond, 1968;Nyberg, Bauer & Knapp, 1968;Bunch & Nyberg, 1970).…”

“…bovis (Fig. I) to stain more readily with toluidine blue (Nyberg & Hammond, 1964). Lotze & Leek (1960) concluded that the oocyst wall of three species of Eimeria from sheep (Table 2) must be conditioned by the primary stimulus, so that the activator(s) in the small intestine could rapidly penetrate to the sporozoites.…”