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PubMed2003

Description and classification of abnormal cercariae of Schistosoma mattheei and a method of concentration and collection.

Over a period of about 12 years, 30 abnormal Schistosoma mattheei cercariae were found among a total of approximately 2.8 million examined. Initially seven were recovered from about 1.02 million (0.0007%), which were examined individually while being counted with the aid of a stereoscopic microscope. Subsequently, on the strength of relatively high percentages of abnormal individuals recovered when counting cercariae that failed to penetrate into oxen, it appeared that the morphologically abnormal cercariae were unable to swim and would mostly sediment out of a suspension while most of the normal cercariae would remain swimming. This surmise is supported by recovery of 23 morphologically abnormal cercariae (0.001%) from about 1.8 million, by examining the sediment after the cercarial suspension had been left standing undisturbed in glass measuring cylinders. The abnormalities ranged from aberrant tails only (e.g. an underdeveloped tail, or different degrees of schism) or aberrant heads only, to abnormalities of both the heads and tails. A suggested schematic classification of abnormal cercariae is presented. A young, adult hamster was exposed to eight S. mattheei cercariae with complete schism of the shaft of the tail, by pipetting the cercariae onto the shaved abdominal skin of the anaesthetised animal. Two underdeveloped females were subsequently encountered in squash preparations of the liver when the hamster was killed for worm recovery 10 weeks after infection, thus showing that some of the abnormal cercariae were viable. A method is also described for killing and fixing cercariae while retaining some of the shining brilliance of live cercariae, without them becoming shrivelled, granular and semi-opaque, as occurs when cercariae die spontaneously or are killed with heat. This is apparently the first report of abnormal cercariae of S. mattheei. In addition, a method of concentrating abnormal cercariae after emergence from a snail, a schematic classification of abnormal cercariae and a method for killing and fixing cercariae while retaining much of the shiny brilliance of live cercariae are also reported for the first time as far as is known.

Animals↗
PubMedDate not supplied

[Respiration and motor activity of cercariae of three trematode species from the intertidal mollusc Littorina littorea L (Gastropoda) from the White sea].

The age dynamics in oxygen consumption of the cercariae Himasthla elongata, Cryptocotyle lingua and Cercaria parvicaudata (Renicola sp.) was studied using modified Winkler's method. It was detected that under stable temperature and water salinity conditions the rate of oxygen uptake depends directly on cercariae size. The highest intensity of energetic metabolism was recorded in the first few hours of cercariae life when their movement activity was maximal. The following reduction of oxygen consumption passed unequally in three cercariae species studied. Large, long-lived H. elongata cercariae after relatively short period of active swimming turn to crawling on the bottom. The rate of oxygen uptake in such cercariae was two times less than in free-swimming ones and remained approximately invariable up to the cercariae death. The smaller sized, short-lived Renicola sp. cercariae swim actively in the water and during this time the level of their energetic metabolism remains more or less stable. It decreased drastically after cercariae sinking to the bottom, after that they perished very soon. Also relatively small C. lingua cercariae alternate the active and passive phases of swimming. Thanks to that they consume the energetic resources economically and prolong their longevity. During free-swimming period the rate of oxygen uptake of C. lingua cercariae remains more or less stable. As in the case of Renicola sp. cercariae, it decreased drastically after the cercariae sinking to the bottom. Apparently such cercariae lose their ability to infect the second intermediate host (fish).

Animals↗
PubMed2003

Effects of temperature on survival, infectivity and in vitro encystment of the cercariae of Echinostoma caproni.

The effects of temperature on survival, infectivity and in vitro encystment of Echinostoma caproni cercariae in artificial spring water (ASW) were studied. Effects of aging cercariae in ASW at various temperatures showed that at 23 degrees C cercariae achieved 50% survival in 24 h, compared to 92 h at 12 degrees C. Cercariae aged in ASW at 28 and 37.5 degrees C showed 50% survival at 16 and 10 h, respectively. Cercariae aged at different temperatures for various times were used to infect juvenile Helisoma trivolvis (Colorado strain) snails maintained in ASW at 23 degrees C. Index of infectivity was based on counting encysted metacercariae in the snails at 8 to 12 h post-infection. Cercariae aged at 23, 28 and 37.5 degrees C showed 50% encystment at 6, 8 and 4 h, respectively. Cercariae aged at 4 degrees C showed 50% encystment in 10 h and cercariae aged at 12 degrees C showed 50% encystment beyond 16 h. Cercariae showed maximal longevity and infectivity in snails when aged at 12 degrees C in ASW. For E. caproni, as in other digeneans, the infective period of cercariae is markedly shorter than the maximal life-span at any given temperature. Studies on in vitro encystment of E. caproni cercariae in Locke's solution:ASW (1:1) showed that encystment was optimal at 23 degrees C (78% encystment) and that it declined to 44% at 28 degrees C and became almost nil (0.02%) at 12 or 37.5 degrees C.

Aging↗
PubMed2002

Life history and life cycles: production and behavior of trematode cercariae in relation to host exploitation and next-host characteristics.

Life history trade-offs affect trematode parasites reproducing inside their 1st intermediate hosts. Within the constraint of the effect on host survival, parasite production of cercariae is subject to a size-numbers trade-off. Within each cercaria, resources must be partitioned between host-seeking and subsequent developmental functions. Three species of microphallid trematodes with the same 1st intermediate host (the gastropod Littorina saxatilis) were investigated. Maritrema arenaria periodically released many small cercariae. Microphallus similis released fewer, 15% larger, cercariae without periodicity. Microphallus similis cercariae were strong swimmers, moving toward the dark and downward in turbulent water, whereas Ma. arenaria cercariae remained suspended. Maritrema arenaria cercariae, although smaller in body and tail size, were produced at an average daily volume nearly twice that of M. similis. These differences are interpreted as transmission adaptations related to mobility and predictability of the 2nd intermediate host. Microphallus similis, with a mobile and less predictable crab host, adopted a 'bethedging' prolonged production of fewer cercariae by less intensive host exploitation, each cercaria having a high allocation to host-seeking behavior. Maritrema arenaria, with predictable sessile barnacle hosts, produced less mobile but potentially longer-lived cercariae in larger numbers. Microphallus piriformes metacercariae remain in the gastropod host. The number of M. piriformes metacercariae increased in larger hosts. The 3 species differed in the number of sporocysts and (meta)cercariae per sporocyst within the gastropod but not in the within-host volume of parasites. Variation in host exploitation and life history appeared adaptive for transmission to the next host.

Animals↗
PubMed2004

[Preliminary study on the ecology of Trichobilharzia cercariae in the Huaihe river system].

OBJECTIVE: To investigate the ecological habit and characteristics of Trichobilharzia cercariae in the Huaihe river system. METHODS: During June of 2002-May of 2003, Radix auricularia snails were collected monthly in Yaohe Fishery of the branch of the Huaihe River. The cercariae, released from the positive snails and collected by Shade Drop Bottle, were examined by direct press. Ducklings were infected by cercariae with different ages and examined for the infection by miracidia hatching method. RESULTS: The results showed a typical seasonal fluctuation in infection rate of the snails, i.e. the cercariae detection rate was 0.81% in July, 0.65% in June, 0.07%-0.26% in April, May, August, September and October respectively, with a significant difference (chi2 = 26.73, P < 0.01). The release of cercariae from the snails showed a diurnal pattern in the natural conditions, with a significant peak between 8:00-12:00. It was proven that the main factors affecting the emerging of cercariae were temperature and light. The cercariae showed positively phototaxis. It was also showed that 50% mortality of the newly released cercariae between 18-25 degrees C occurred at 41 h, and all cercariae died within 52 h. The infectivity of cercariae was age-dependent. Under 18-25 degrees C, the highest infectivity was found at 0.5-8 h after emergence, then declined steadily to negative by 40 h post-emergence. CONCLUSION: The ecological characteristics of Trichobilharzia cercariae have been preliminarily verified in the Huaihe river system.

Animals↗
PubMed1984

Immunization of rats against Schistosoma mansoni using irradiated cercariae, lung schistosomula and liver-stage worms.

In PVG rats a single immunizing infection with Schistosoma mansoni cercariae exposed to 0, 5, 10 or 20 krad. gamma radiation failed to induce more than minimal resistance (17-29%) to challenge 4 weeks later, whereas 4 immunizations with 20 krad.-irradiated cercariae, over several months, induced substantial resistance (75%). In contrast, significant protection was induced in Fischer rats by a single immunization with unirradiated cercariae or cercariae irradiated with up to 80 krad. Comparable resistance was induced by unirradiated and by 2, 5 and 20 krad.-irradiated cercariae (67-74%) and lower levels by 10, 40 and 80 krad.-irradiated infections (57, 48 and 33%, respectively). Although the resistance induced by a single dose of 1000 20 krad.-irradiated cercariae could be boosted by a second (88%), further immunizations failed to enhance this resistance. Also, increasing the number of immunizing cercariae in single or multiple vaccinations from 1000 to 3000 failed to increase the resistance. While the resistance induced by 20 krad.-irradiated cercariae persisted undiminished for at least 25 weeks (67%), the resistance induced by normal cercariae declined to insignificant levels by 25 weeks (21%). Comparison of the migration and survival of unirradiated and of 20 and 40 krad.-irradiated cercariae revealed dramatic differences in their fate: parasites exposed to 40 krad. remained in the skin, while the majority of 20 krad.-irradiated parasites died in the lungs after a sojourn of at least 14 days. Thus, although skin schistosomula alone could induce significant protection, optimal resistance was induced only by parasites which migrated to the lungs or beyond. The immunizing potential of these older parasites was investigated by exposing rats to lung- and liver-stage larvae injected into the tail and mesenteric veins, respectively. Irradiated 4-day lung schistosomula induced comparable resistance (79%) to that induced by a complete unattenuated cercarial infection (78%), whereas less resistance was induced by irradiated and unirradiated 11-day-old liver worms (30 and 27%) and by 25-day-old pre-adult worms (48%).

Animals↗