A Cytological Study of the Sporozoites of Eimeria Caviae, a Coccidian Parasite of the Domestic Guinea Pig, Cavia Porcellus

Abstract

The problem. The present study was undertaken in order to provide information concerning the morphological and cytological characteristics of the sporozoites of Eimeria caviae, Sheather (1924), a coccidian parasite of guinea pigs. Observations concerning the prepatent and patent periods, the symptomatology and pathology, and the morphological features of the oocysts of this species are also reported. Procedure. Oocysts of Eimeria caviae, isolated from naturally infected guinea pigs, were excysted in vitro and the sporozoites studied in fresh and stained preparations. Fresh sporozoites were studied in the medium used for excystation, at room temperature, with the aid of a Zeiss RA and/or Zeiss photomicroscope equipped with achromatic objectives and bright field and phase contrast condensors. Smears for permanent preparations were made by smearing No. 1 cover slips with Meyer's adhesive and freshly excysted sporozoites. Sporozoites stained with the Giemsa method were fixed in methanol and those stained with Harris' hematoxylin and eosin were fixed in Zenker's fluid. Sporozoites stained with the periodic acid-Schiff (PAS) and the Feulgen methods were fixed in Bouin's fixative. Findings. Freshly excysted sporozoites were motile and exhibited flexion, probing, gliding and rotational movements. The sporozoites were curved in shape with the anterior end tapering to a point and the posterior end being more rounded and blunt. All sporozoites had one anterior and one posterior refractile body with a nucleus between these bodies. Staining reactions revealed refractile bodies, numerous granules distributed within the cytoplasm and a nucleus containing peripherally distributed chromatin; no nucleolus was observed. Sporulated oocysts were ellipsoidal and brownish-yellow in color. An oocyst residium was not observed. A cone-shaped Stieda body and membrane-bound sporocyst residium were present. The oocyst wall was smooth and consisted of two layers. The prepatent period of Eimeria caviae was found to range from 11 to 13 days; the patent period ranged from 7 to 13 days. Symptoms of infection in guinea pigs experimentally infected with E. caviae were loss of appetite, constipation, diarrhea, ruffled hair, and a "hunched" posture. Apathetic behavior was also a constant symptom. Conclusion. The cytological observations of the sporozoite of Eimeria caviae in the present study agree closely with those observed previously for this and other species. The prepatent and patent periods, symptomatology and pathology, and morphological features of the oocysts also agree with that information previously reported for this species. Recommendations. While information concerning the morphology of the sporozoites of Eimeria caviae is presented in the present study, many important problems concerning their mechanism of invasion of host cells, their excystation process, and the role they play in the immune response remain to be solved.