Isoenzyme analysis was conducted on the tachyzoite stage of 35 Toxoplasma gondii isolates. Fifteen enzyme systems were studied after isoelectrofocusing of tachyzoite extracts in polyacrylamide or agarose gels. Six enzyme systems showed variable electrophoretic patterns: aspartate aminotransferase (EC 2.6.1.1), glutathione reductase (EC 1.6.4.2), glucose phosphate isomerase (EC 5.3.1.9), amylase (EC 3.2.1.1), acid phosphatase (EC 3.1.3.2), and propionyl esterase. Their combination allows the description of 5 zymodemes among the 35 T. gondii isolates. Zymodeme 1 involves 6 isolates that are highly pathogenic to mice and for which oocysts could not be obtained. Isolates belonging to zymodemes 2, 3, and 4 are less pathogenic to mice and produced oocysts. Zymodeme 5 involves only 1 isolate, which was highly pathogenic to mice.

In an attempt to obtain the continuous development of Hammondia hammondi in vitro, culture of the parasite was performed in 3 cell lines. Although organisms were present in culture fluids of feline kidney cells (CRFK) for as long as 3 mo, continuous culture was not possible. However, for the first time, cysts of H. hammondi were observed in cell culture from day 6 after inoculation of sporozoites. Ultrastructure of the H. hammondi cysts was similar to that observed for in vitro-obtained Toxoplasma gondii cysts. Feeding a cat with these in vitro-developed cysts resulted in oocyst shedding 5 days after ingestion.

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The genetic polymorphism of Toxoplasma gondii was evaluated for 14 strains by isoenzyme and DNA analysis. The 14 strains belonged to 5 different zymodemes defined by the variable patterns of 6 enzyme systems. A restriction-fragment-length polymorphism analysis was carried out with two endonucleases (Sal I and Pst I) and two repetitive probes (TGR1E and TGR6). This kind of repetitive probe allowed an individual identification of strain, with 13 schizodemes being observed among 14 strains. Only two strains were found to be totally identical when DNA and isoenzyme characters were considered. The numerical taxonomy methods applied to the results obtained for both types of characters allowed determination of linkage groups. Strain clustering obtained by numerical analysis of DNA characters alone is similar to the clustering obtained by analysis of isoenzyme and DNA characters together. A relationship was observed between the defined groups and virulence in Swiss mice.

RÉSUME. Cinq espèces de limnées : Lymnaea glabra, L. palustris, L. peregra, L. stagnalis, L. truncatula, ont été testées sur leur participation en tant qu'hôtes intermédiaires dans le cycle évolutif de Fasriola hepatica. Les jeunes sont nés au laboratoire à 23° C et ont été exposés chacun à trois miracidiums juste après leur naissance (entre 1 et 24 heures de vie). Au 30e jour post-exposition, le taux d'infestation varie de 15,8 % à 64,5 % selon l'espèce. La hauteur de la coquille des limnées à infestation évolutive est plus réduite que celle des individus à infestation abortive ou des témoins, ceci pour les cinq espèces. Le nombre moyen de cercaires émises par les limnées à infestation évolutive est faible : de 12,2 à 18,4 cercaires par mollusque. Les cercaires ont été émises en une seule journée par 114 limnées, en deux jours par 41 limnées et sur une période de 3 à 31 jours pour les 54 autres limnées. Nous n'avons pas observé de rythme net dans la production des cercaires chez ces mollusques. La viabilité des métacercaires fournies par les diverses espèces de limnées en expérience a été testée chez le cobaye. Les infestations se sont toutes révélées positives. La signification de ces observations est discutée. Experimental data on the infection of very young snails of five lymnaeid snails by Fasciola hepatica L. SUMMARY. The ability of five lymnaeid species (Lymnaea glabra, L. palustris, L. peregra, L. stagnalis, L. truncatula) to act as intermediate hosts of Fasciola hepatica was investigated under controlled conditions. Each snail born in the laboraratory (at 23° C) was infected when 1-24-hours-old, using 3 miracidia of F. hepatica. The percentage of infected snails ranged from 15.8% to 64.5% on day 30 post-exposure. The shell height of snails with evolutive infection was significantly reduced than the shell height of snails with abortive infection or controls. The mean number of cercariae produced by the snails with evolutive infection was low: from 12.2 to 18.4 cercariae per snail. The length of the shedding period was one day for 114 snails, two days for 41 snails and 3-31 days for the 54 other snails. We did not observe a distinct rythm in cercarial production of these snails. All infections of guinea-pigs with these metacercariae were positive. The significance of these observations is discussed. 1 Ce travail a été présenté dans le cadre d'une thèse de Doctorat en Médecine (Busson, 1981). Accepté le 5 avril 1982.

Isoenzyme analysis using isoelectrofocusing in polyacrylamide gels was used to distinguish Hammondia hammondi and Toxoplasma gondii sporozoites. Five enzyme systems were studied: aconitase (EC 4.2.1.3), aspartate aminotransferase (EC 2.6.1.1), glucose phosphate isomerase (EC 5.3.1.9), lactate dehydrogenase (EC 1.1.1.27), and phosphoglucomutase (EC 2.7.5.1). Three stocks of T. gondii belonging to 3 zymodemes were compared to 1 stock of H. hammondi. Hammondia hammondi differed from T. gondii at all 5 loci analyzed. This was observed for all 3 zymodemes of T. gondii. These results indicated clear genetic differences between the 2 species.

Toxoplasma gondii: Ultrastructure of cyst-like forms observed in human fibroblasts cell culture.SUMMARY. A strain of Toxoplasma gondii, non pathogenic to mice (Prugniaud strain) produced cyst-like stages when inoculated in human fibroblast culture. An ultrastructural study was performed in order to compare these cyst-like forms to brain cysts of the same strain and to intracellular clusters of tachyzoites observed in mice TG 180 sar coma cells.Electron microscopy confirmed the similarities between brain cysts and cysts obtained in vitro.

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