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.

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 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.

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 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.

Excretory/secretory (ES) antigens were obtained by culturing pre-encysted Trichinella spiralis larvae which were recovered from muscles of experimentally infected mice 14–15 days postinfection. Analyses of these antigens (PEL ES) with immunoblotting, SDS-PAGE and Triple Antibody ELISA showed that they yielded a low sensitivity and specificity when tested antisera against the common nematodes of Chinese pigs. As compared to ES antigens from encysted larvae. PEL ES also contained more low molecular mass proteins.

Seven geographically varied isolates of Strongyloides ratti were cloned. Each clone was examined for the degree of homogonic development of the free-living generation and by enzyme electrophoresis. Considerable variation was found between the clones in the degree of development that was homogonic. In Contrast, the clones were indistinguishable by enzyme electrophoresis.

The life cycle of Gnathostoma nipponicum was examined by field survey and by experimental infection of animals with the larvae. Naturally infected larval G. nipponicum were found in loaches, catfish, and snakes. Experimentally, loaches, killifishes, frogs, salamanders, mice, and rats were successfully infected with the early third-stage larvae of G. nipponicum obtained from copepods (the first intermediate host), whereas snakes, quails, and weasels were not. Frogs, snakes, quails, and rats were experimentally infected with the advanced third-stage larvae (AdL3) from loaches. These results reveal that some species of fishes, amphibians and mammals can act as the second intermediate host and that some species of reptiles, birds and mammals can act as a paratenic host. The life cycle was completed in weasels, the definitive host, which were infected with AdL3 from loaches and started to evacuate eggs of G. nipponicum in faeces on days 65–90 postinfection.

A previously reported cDNA clone encoding 34 kDa antigenic polypeptide of Dirofilaria immitis (λ cD34) was studied to elucidate the mechanism of stage-specific gene expression. The 34 kDa polypeptide was a larva-specific antigen and the mRNA was detectable in microfilariae but not in adult worms and eggs. The λ cD34 gene was not sex linked and was contained in the genome of D. immitis at each stage. The stage-specific expression of the developmentally regulated gene in D. immitis may be controlled primarily at the mRNA level.

Sterols in the digestive gland-gonad (DGG) complex of Biomphalaria glabrata (Gastropoda) infected with patent larval stages of Echinostoma caproni (Trematoda) versus uninfected control snails were studied by gas-liquid chromatography. The major sterol present in both populations was cholesterol, 59% in the infected snails and 51% in the controls. Infected snails contained the same phytosterols as the controls—desmosterol, campesterol, stigmasterol, and beta-sitosterol–but the percent composition was reduced. The reduction was significant for both campesterol and stigmasterol.

Gnathostoma spinigerum was found in gastric nodules in 4·1% of 2940 dogs surveyed in northeastern Thailand. The prevalence and worm burden of G. spinigerum exhibited a seasonal fluctuation. The parasites were more abundant in the rainy season and the early winter (August–December) than in the summer (April–March). Most parasites were sexually mature between August and December while immature worms were observed during March and April. The distribution of gnathostomes within the sampled dogs was highly dispersed and few animals were found to harbour more than five worms.

Sera of 699 individuals, aged between 5–24 years, from the Irbid area. Jordan, were tested for Toxocara canis antibodies using an ELISA-IgG test. Crude prevalence was 10·9% (76 of 699) but age-adjusted prevalence was 14·3%. The highest prevalence was observed in females aged 5–9 years. 23·3% (7 of 30). and males of 15–19 years of age. 19·5% (16 of 82). The lowest prevalence was observed in females aged 20–25 years. 5·2% (8 of 155). Significant differences (P<0·05) between the prevalences of the toxocaral antibodies in males and females were observed in the age groups 5–9, 15–19 and 20–24 years. The trend of prevalence in relation to age was different according to sex.