Hisatake Nojima

Schistosoma mansoni and Schistosoma haematobium: Emergence of schistosome cercariae from snails with darkness and illumination

Abstract Biomphalaria glabrata and Bulinus globosus were infected with Schistosoma mansoni and Schistosoma haematobium , respectively, and the effect of different illumination conditions at 25 C on cercarial output was observed for 4 days. In both species, a dark period of 10–14 hr on Day 2 of the observation period resulted in an emergence pattern on Day 3 similar to the regular pattern recorded for Day 1. Total cercarial output on Day 3 was within 30% of the control (Day 1) output. A dark period of between 0 and 8 hr resulted in suppression of cercarial emergence and in abolishment of the regular hourly emergence pattern on Day 3. A dark period of 16–20 hr resulted in an emergence pattern with two peaks, the first occurred at Hour 1, and the other at Hour 5 of the subsequent light period. Interjection of a 1-hr dark period during the light period of Day 3, following short (2–8 hr) exposure to dark on the preceding day, produced an increase in cercarial shedding of S. mansoni immediately after restitution of the light conditions. On the other hand, in S. haematobium , cercarial output was stimulated during the interposed dark period itself.

Transmammary transmission ofStrongyloides ratti

The rate of transmammary transmission ofStrongyloides ratti was examined in albino rats in terms of the route of subcutaneous (s.c.) migration from the infection site (the skin) to the cranium. Inoculation sites nearer the cranium resulted in less frequent transmammary infection. The maximum number of adult worms was recovered from the sucklings when the mother was inoculated in her hindquarter and sucklings were allowed to feed for 30–36 h after inoculation (AI). Few worms were recovered from sucklings when they were allowed to nurse during periods of<24 h AI or>42 h AI. In lactating mothers, larval infection of the mammary glands was commonly observed, and these larvae showed an increased esophagus length. In nonlactating mothers, most larvae completed their migration to the cranium within 36 h AI.

THE EMERGENCE OF SCHISTOSOMA JAPONICUM CERCARIAE FROM ONCOMELANIA QUADRASI

The release of Schistosoma japonicum cercariae from Leytean Oncomelania quadrasi snails was observed under laboratory conditions. Two patterns of emergence were noted. The initial, nonperiodic emergence occurred immediately after submerging the snails in water and was followed by a periodic, diurnal emergence which peaked in the afternoon. The daily cercarial output of the periodic emergence appeared to be affected by exogenous light intensity. Furthermore, there was a cessation or reduction in cercarial output every 3rd or 4th day.

THE EFFECTS OF SINGLE AND REPEATED INOCULATIONS OF VARIOUS LARVAL DOSES ON STRONGYLOIDES RATTI BURDEN AND DISTRIBUTION IN RATS

The changes in worm burden, distribution, length, and fecundity after and during single and repeated inoculations of 10, 50, or 500 larvae of Strongyloides ratti were examined in rats. Worm burden after a single inoculation of a higher larval dose reduced rapidly. Repeated inoculations of lower larval doses at weekly intervals led to a delayed peak and slower reduction of worm burden; the repeated inoculations of 10 larvae did not induce worm expulsion for at least 7 wk. In repeated inoculations at 3-wk intervals, a primary inoculation of 500 larvae induced strong resistance to reinfection at week 3, whereas no resistance was induced until week 6 in rats receiving repeated inoculations of 10 or 50 larvae. Similar dose-dependent reductions in worm length and fecundity were observed in single and repeated inoculations, and the reductions began earlier than worm expulsion. Intestinal migration of worms from the upper small intestine to the large intestine was observed during the course of single and repeated inoculations. Earlier and clearer migration was observed in rats receiving higher doses. These findings indicate that in S. ratti infection, the changes of worm burden, distribution, length, and fecundity are dependent on the inoculated larval dose.

Serial implantations of larval Schistosoma mansoni from infected to uninfected snails.

The long-term maintenance of Schistosoma mansoni in intermediate snail hosts is described. Snails were infected with one or five miracidia to obtain the initial parasitized liver tissue. The serial implantations were conducted. When the materials for serial implantation were obtained 20 to 60 days after the hosts had begun to release cercariae, the proportion of snails becoming infected was higher than when materials obtained earlier were used. It made no difference whether the initial infection was with one or five miracidia. Our findings suggest the possibility of cloning of unisexual infections in experimental infections.

Incidence of Centrocestus formosanus infection in snails.

fluent monolayers of host cells that had been thoroughly rinsed for several hours with serumfree medium. Each monolayer was then covered with a 12-mm-diameter circular coverslip and examined by phase-contrast microscopy. We observed many of the sporozoites undergoing active motility on the surface of both HepG2 and WI38 cells; this was manifested as rapid circular gliding, probing of the cell surface by one end of the sporozoite, attached waving, and an unusual snakelike flexion of the sporozoite body into hairpin turns. We speculate that the reason sporozoites are motile and nominally invasive when in contact with WI38 cells is that these cells, even after thorough rinsings in serum-free medium, probably still have some serum proteins, such as albumin, bound to their surface. Because HepG2 cells are known to synthesize and secrete many serum proteins, including albumin (Knowles et al., 1980, Science 209: 497-499), this would provide an even greater induction of sporozoite motility and invasiveness than the residual serum bound to washed WI38 cells. This would explain the better relative success sporozoites have in invading washed HepG2 cells than WI38 cells. Alternatively, sporozoite motility may have been induced by a nonalbumin factor secreted by, or associated with the surface of, these cell lines. Regardless of the identity of the motility-inducing factor, the important point is that sporozoites settling on the surface of cultured cells incubated in the absence of serum are motile. Thus, these results are still compatible with our motility-invasiveness hypothesis. This study was supported by the U.S. National Institutes of Health through Research Grant AI 09560 and NIAID Training Grant NIH AI T32AI-07180-06AI.