Atsuo Sato

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.

The presence of Angiostrongylus cantonensis in Viti Levu, Fiji

Wild rats and molluscs were examined for Angiostrongylus cantonensis infection on Viti Levu, Fiji. A. cantonensis were recovered from 29.6% (16/54) of Rattus rattus and 59.5% (25/42) of R. exulans. A. cantonensis-like larval nematodes were found in all of four slugs, Laevicaulis alte, and ten of 20 unidentified land snails. The larvae developed to adult A. cantonensis in the pulmonary arteries of laboratory rats 40 to 42 days after ingestion. This is the first record of A. cantonensis in Fiji.

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.

Observations on the transmission of Angiostrongylus cantonensis from snail to rodent

A survey of Angiostrongylus cantonensis was carried out to investigate the mode of transmission from mollusc to rat in a fixed study area of Yoron Island from 1979 to 1982. Rattus rattus was found to be infected with a small number of worms in spite of heavy infection with third-stage larvae in Achatina fulica and an abundance of this snail in the area. Natural infection and/or susceptibility with A. cantonensis were confirmed in three small snail species. Bradybaena circulus, Fruticicola despecta and Luchuena reticulata. Young A. fulica was found to be infected with fewer third-stage larvae than mature A. fulica. It was concluded that molluscs which were infected with a small number of third-stage larvae of A. cantonensis play an important role in maintaining the life cycle of A. cantonensis. The percentage of rat stomachs containing mollusc tissue was relatively low, and the incidence and infection was low in rats. Infection with A. cantonensis did not occur very often in R. rattus in nature.

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.

Effects of infection with Angiostrongylus cantonensis on the circulating haemocyte population and the haematopoietic organ of the host snail M-line Biomphalaria glabrata.

The number of circulating haemocytes, the size of the haematopoietic organ, and the size of haemocyte capsules around the parasite were studied in M-line Biomphalaria glabrata snails exposed to 100 or 400 first-stage larvae of Angiostrongylus cantonensis. The number of haemocytes in exposed snails increased significantly at 1 day post-exposure, decreased to control value, and then increased again. The decrease in number of circulating haemocytes is probably due to the removal of cells from the circulation to participate in encapsulation of larvae. The majority of circulating haemocytes in M-line B. glabrata are fully-spread granulocytes, which increase significantly in number in snails following exposure to A. cantonensis larvae. However, populations of partially-spread granulocytes, round cells, hyalinocytes and miscellaneous haemocytes were relatively constant. The size of capsules around the parasite increased during the 42-day interval of the experiment. The haematopoietic organ increased in size in response to infection.