Cercariae develop from individual germinal cells occurring freely within the posterior body cavity of rediae. Individual germinal cells give rise to a germinal ball which becomes enveloped by increasing numbers of cytoplasmic extensions originating from specialized parenchyma-like cells, termed nursc cells. Up to eight cytoplasmic layers of nurse cells invest larger germinal balls. These layers may provide mechanical support for developing embryos and/or play a role in the provision of nutrients to them. The cercarial tegument develops from superficially located somatic cells in the germinal ball. Cytoplasmic extensions of presumptive tegumental cells fuse laterally to form a syncytial layer beneath the encapsulating nurse cell layers. As the cercarial tegument differentiates further, the cytoplasm of the nurse cell layers becomes vacuolated and ultimately these layers degenerate. The surface tegumental syncytia of intra-redial cercariae and newly released extra-redial cercariae are nucleated. Separate subtegumental perikarya develop with further differentiation of extra-redial cercariae.

Lymnaea truncatula, 4 mm in height, were subjected to infection by a single miracidium of Fasciola gigantica, then raised at 23°C until day 60 of the experiment. Histological study of these snails demonstrated a mean redial burden of 34 parasites at day 60, of which one third were degenerating forms. The mean number of living independent rediae did not exceed 5 for the first and second generations. Conversely, in subsequent generations there were as many as 18 rediae per snail at day 60. The first living redia of the first generation in particular gave rise to daughter rediae. Mature rediae appeared at day 35 and especially concerned the first and second generations at day 60. The authors conclude that development of the first and second redial generations occurs during the same period, and that the forms of the first cohort of the second generation are produced from the first redia of the first generation which originated from the sporocyst.

The host-parasite relationships of a Schistosoma haematobium isolate, originating from Niger, and the white mouse are described. Swiss OF1 albino mice were exposed individually to 200 cercariae and worms were recovered 9, 12, 16 and 20 weeks post infection. The mean worm returns ranged between 10·54 and 13·5% and did not alter significantly between 9 and 20 weeks post infection. The sex ratio of worms was always in favour of males; from 7·9:1 at 9 weeks after infection it decreased regularly to 3·28:1 at 20 weeks. Male worms reached a mean length of 8·72 mm at 20 weeks. From the 12th week post infection, a high number of eggs was found in the liver and gut. At 20 weeks, eggs were also found in the bladder. Viable eggs and infective miracidia were obtained. The infection of Bulinus truncatus from Niger succeeded with a mean rate of 61% after the first passage through mice. The isolate of S. haematobium was maintained in the laboratory during 3 successive passages through mice. These entirely new results are very probably linked to genetic characteristics peculiar to the S. haematobium populations from Niger.

Exposure of Biomphalaria alexandrina to sublethal concentrations (0·125, 0·25 and 0·05 ppm) of the organophosporous insecticide, chlorpyrifos (Dursban), induced a reduction in egg production and egg hatchability. Exposure of Schistosoma mansoni miracidia to the insecticide (60 min, 0·05 ppm) prior to infection of B. alexandrina did not affect the subsequent production of cercariae. However, exposure of S. mansoni—infected snails to the insecticide until day 55, from day 20 to day 62 and from day 35 to 62 following infection resulted in blockage of cercarial shedding. cercarial shedding commenced in some snails when the treatement stopped. Exposure to the insecticide in concentrations of 0·125 and 0·25 ppm during the first 20 days following infection did not affect the subsequent production of cercariae, but exposure to 0·5 ppm during the first 20 days affected markedly the production of cercariae due to a high snail mortality. The findings indicate that the cercaria is the target stage for the activity of chlorpyrifos on the intramolluscan larval development. It is suggested that S. mansoni cercarial production in B. alexandrina may he a useful system for monitoring the effect of low concentrations of pesticides on the aquatic environment, and that the ability by chemical means to interrupt the cercarial production might be a useful tool in further analyses of important aspects of the snail/parasite relationship.

The effects of crowding on growth, reproduction, rate of recovery and site of infection of Philophthalmus nocturnus were investigated by infecting various groups of day-old chicks with 25, 50,75, or 100 excysted metacercariae and examining them at 10 or 25 days post-infection. Considerable reduction in the body length and the size of the gonads was noticed in flukes grown under crowded conditions. Crowding also caused some change in the habitat of flukes, but had no effect on their rate of recovery. Very few flukes reached the ovigerous stage under overcrowded conditions and none reached the embryonated larval stage.

Larvae of a species of Proteocephalus were observed in the intestines of larvae of Sialis lutaria (Insecta: Megaloptera) in a single locality at prevalence levels of up to 40% and over a period of three years. The cestodes were plerocerciform in character and up to 3 mm in length, having undergone some growth and development in the insect. Comparison of scolex morphology with that of adult Proteocephalus spp. obtained from fish in the same river suggests the most likely identity of the parasite is P. filicollis. Support for this suggestion came from the recovery of two parasites from experimentally infected sticklebacks, Gasterosteus aculeatus. This is the first record of a proteocephalid larvae from an insect, and so also from S. lutaria, and of a proteocephalid using a second, additional invertebrate host. The use of S. lutaria is so far known only from this one locality and may reflect the peculiar, but continuing, ecological conditions there, but it is suggested that the ability to use S. lutaria as an additional host may be associated particularly, though not exclusively, with parasites of sticklebacks.

In the Attaouia area, the density of Bulinus truncatus (Audouin, 1827), was monitored monthly for a period of one year in correlation with weather variations. Snails were active throughout the year and particularly abundant at the end of spring and summer. Two snail generations were found to overlap. The infection rate of B. truncatus reached a maximum of 3·5% in the summer when human water contact was frequent. A selective survey conducted in the village of Lamyayha showed that the prevalence of infection with S. haematobium among the local population was 21·2% who were passing from 10 to 80 eggs per 10 ml of urine.

The morphology of the tegument in the redia of Paramphistomum epiclitum (Digenea: Paramphistomidae) resembles that shown by most larval and adult digeneans; an outer surface syncytium is in continuity with the cytoplasm of in-sunken, nucleated cytons. Although tegumental cytons usually contain a single nucleus, some display up to six nuclei. The tegumental syncytium lining the pharynx of P. epiclitum rediae lack underlying cytons. The apical membrane of the tegument is elaborated by folds and microvilli, which presumably facilitate uptake of nutrients and/or exchange of ions involved in osmoregulation. A single type of secretory body, resulting from the fusion of smaller vesicles produced at Golgi complexes in the cytons, occurs throughout the tegument. Uniciliate sensory receptors occur in the surface syncytium particularly around the oral opening.

Haematuria and proteinuria as detected by chemical reagent strips correlated moderately (r=0·7) with prevalence and intensity of infection with Schistosoma haematobium in an area of Anambra State, Nigeria. Differences attributable to age and sex were also reflected in a similar pattern, all peaks occurring in the 5–14 year age group. The differences observed with varying levels of intensity and haematuria at both 10 and 50 erythrocytes/μl (p<0·001) and proteinuria at 0·3 g/dl (p<0·01) were statistically significant. At a proteinuria level of 1 g/dl, the observed differences were however not statistically significant (p>0·5). The percentage of specimens from children (1–14 years) positive for S. haematobium eggs and with at least traces of haematuria and proteinuria (63·4% and 95%, respectively) was higher than in adults (33·3% and 80·2%, respectively). All individuals with more than 50 eggs/10 ml of urine were correctly identified using both indices either separately or in combination. For egg counts of less than 50 egg/10 ml of urine, false diagnosis occurred in only 5% of all specimens examined. The sensitivity and specificity of haematuria and proteinuria at trace quantities was very high, hut haematuria had a higher predictive value for a positive test (PvPt) and was considered the overall better indicator. A combination of both indices did not significantly increase the PvPt. When trace haematuria and moderate proteinuria were combined, both the sensitivity, specificity and PvPt were all above 90%, giving the best overall values in all the combinations made.

In an environment seriously impaired by human interference (draining the reservoir), ecological relationships in a community of copepods and their impact on the transmission of the tapeworm Proteocephalus neglectus La Rue. 1911 were studied. The impairment of the environment resulted in changes in the species composition of the copepod community and in the increased diversity of the copepod species, as well as in a multiple inversion of the dominant and subdominant relationships of the two most numerous copepod species (Cyclops vicinus and Eudiaptomus zachariasi). The structure of the developmental stages of the copepod community, the seasonal dynamics of the number of copepods and the abundance of P. neglectus procercoids have changed. The predominant species in the copepod community and the most susceptible intermediate host of P. neglectus (C. vicinus) was not infected. The infection of copepods decreased by 95% and that of the definitive hosts (Oncorhynchus mykiss) by 97·5% compared with the index values recorded in the previous year.

Experimental infection of Echinoparyphium recurvatum von Linstow (Digenea: Echinostomatidae) cercariae in the snail second intermediate host Lymnaea peregra Müller shows that metacercarial encystment takes place on the lining of the mantle cavity, pericardial cavity and kidney lumen, with the mantle cavity the most preferred site. All three sites are accessible via the body openings. The metacercariae appear to be more susceptible to encapsulation in the visceral mass than in the cavity of the mantle, pericardium and the lumen of the kidney.

Restriction fragment length polymorphisms (RFLPs) of ribosomal DNA (rDNA) were compared between Diphyllobothrium latum and D. nihonkaiense using seven kinds of restriction endonucleases. No intra-specific variation in restriction fragment profiles was shown within both species of Diphyllobothrium. Digestion of the genomic DNA with three endonucleases, Smal, Hinfl and Hhal, provided one or two different bands between two species, although the hybridization patterns generated with the others, Hindlll, Xbal, Styl and Haelll, were the same in both. RFLPs in the digested profiles with Smal, Hinfl and Hhal could be used as species-specific markers even if only fragments of strobilae with morphological similarity were available. Other cestodes, Spirometra erinacei and Taenia saginata, used as controls showed quite different restriction fragment patterns with all the enzymes used.

Fifty day-old chicks were each infected with 10 excysted metaccreariae of Philophthalimus nocturnus Looss. 1907 around each orbit and growth, development and allometry were studied. The growth rate showed two phases over a period of 35 days, a limited lag phase lasting two days post-infection in which flukes did not exceed 440 μm in length, and a rapid phase during which growth was rapid and flukes reached a size of 3·008–3·504 mm on day 35. Five developmental stages were noticed during the course of development of the metacercaria to the egg-producing adult stage. Eggs appeared in the uterus on day 14 and oculate miracidia on day 25. The hindhody, testes and ovary showed positive allometric growth, the pharnyx less so, whereas negative allometric growth was shown by the forebody. Body width, oral sucker and ventral sucker were close to isometry, growing at the same rate as the body length.

The gene encoding an antigenic polypeptide of Anisakis simplex larvae was studied using recombinant DNA techniques. cDNA synthesized from poly(A)-rich mRNA from A. simplex larvae was ligated into phage vector λ gtll DNA and packaged in vitro. The phages were propagated on Escherichia coli and a λ gtll expression library was constructed. A cDNA clone encoding a 42 kDa antigenic polypeptide was selected by immunoscreening of the library and identified by the epitope selection method. A clone containing cDNA for a 42 kDa protein was isolated. The gene encoding this 42 kDa antigenic polypeptide was characterized by DNA and RNA blot analysis using the cDNA as a probe. The gene was transcribed to mRNA with approximately 1400 nucleotides and translated to 42 kDa polypeptide. The antigenic β-galactosidase fusion protein synthesized by bacteria had no cross-reactivity with other parasite-infected sera.

The ultrastructure of the spermatid and spermatozoon of Macracanthorhynchus hirudinaceus (Archiacanthocephala) was studied by means of transmission electron microscopy. The flagellum and nucleus in the spermatid gradually expanded simultaneously. The karyoplasm of the spermatid transformed into dense inclusions and a multibarrel structure, which were also found in the spermatozoan body. The multibarrel structure was located close to the flagellum and consisted of many irregular microtubes. The flagellum of the developing spermatozoon was observed in a concavity of the spermatid nucleus. The microtubule arrangement of the flagellum was ″9+2″. No mitochondria or acrosome were observed in spermatozoa.

The identity of Anisakis type II larvae with adult A. physeteris was confirmed by comparison of restriction fragment length polymorphisms (RFLPs) of 25S ribosomal DNA (rDNA). Patterns of RFLPs in larvae were almost identical with those in adult worms. Directly labelled 25S rDNA might serve as an appropriate probe with highly specific activity for examining RFLPs of larvae and adult worms.

The rediae of Fasciola hepatica were counted according to generation in adult and juvenile Lymnaea truncatula following single infection with Fasciola hepatica, double infection with F. hepatica and then Muellerius capillaris, or double infection with M. capillaris and F. hepatica. The rediae found in double infections were essentially first generation and an early cohort from the second generation. The following differences were observed in adult snails which underwent double infection when compared to corresponding single infections: i) dependent rediae were almost completely absent; ii) degenerating independent rediae were found in identical or decreased numbers; iii) living independent rediae of the first generation were decreased in number, while those of the second generation had variable decreased numbers. The results were similar in juvenile snails with double infections, except that the numbers of degenerating independent rediae were higher than those found in corresponding single infections and the numbers of rediae of the second generation were increased. The order of exposure in double infections had no influence on the number and maturation of fasciolid rediae.

The abundance of six species of trematodes: Aphanurus stossichi, Bacciger israelensis, Diphterostomum israelense, Plagioporus idoneus, Lepocreadium album and L. pegorchis, parasitic in the digestive tract of marine teleostei (Sparidae) collected near Jounieh (east Mediterranean), was analysed as a function of the host-size. In two parasite/host systems, infections were observed from the lowest size classes of the sample, with a clear tendency to an increase of abundance in older fish. In four others, parasites appear only above a rather high threshold class, young individuals never being infected. In the last three parasite/host systems, host invasion may occur early or late, but infection decreases above a well defined size class, old fishes rarely or never being infected. A given trematode species. when parasitizing several host species, shows similar abundance/host size relationships, e.g. P. idoneus in Diplodus vulgaris and Oblada melanura. When more than one species of trematode infects a single host species, curves can be markedly distinct; for instance, L. pegorchis was collected from Pagellus erythrinus below 15 cm. whereas D. israelense parasitized the same fish approximately above the same size. There is no evidence that such a replacement of one trematode by another in the course of host growth is a result of interspecific competition.