The fine structure of the oncosphere of Hymenolepis nana has been investigated by transmission and scanning electron microscopy, together with light microscope observations of JB–4 embedded material. The outer surface of the oncosphere is covered by an epithelial layer, termed the embryonic epithelium. Cell types present within the oncosphere include the penetration gland cell, oncoblast, or hook-forming cells, nerve cells, muscle cells (both somatic and hook), and undifferentiated ‘stem’ cells. The penetration gland is a large, U-shaped structure, situated in the anterior region of the oncosphere, and filled with secretory granules of 2 distinct morphological types. Histochemically, the secretory material yields reactions characteristic of an acid mucopolysaccharide. A proteinaceous-substance and small amounts of glycogen are also present. Up to 4 pairs of ducts from the penetration gland have been observed. They pass through the basal lamina and the epithelial layer to open against the polar filament layer at the anterior end of the oncosphere. Nerve cells are described in a cestode oncosphere for the first time. The cells are paraldehyde-fuchsin-positive and show a high level of secretory activity, as evidenced by the large numbers of dense-cored vesicles produced by the Golgi apparatus in the perikarya; consequently, they are tentatively regarded as possible neurosecretory cells. The vesicles are transported down the axon to be stored in specialized swollen axon terminals, which form definite junctions with the muscle cells.

The Bd37gene encoding for a glycosyl-phosphatidyl-inositol anchored protein of Babesia divergens displays genetic polymorphisms among isolates. Five major polymorphic groups (clades) were shown by PCR-RFLP among different B. divergens isolates. Each group has been characterized according to a reference Bd37 gene (Rouen87, W8843, Y5, 6303E and 1705B). Recombinant (GST fusion) protein (Bd37r) expressed from the Bd37 gene, was used as antigen in a saponin-based formulation and was able to protect gerbils, after 2 injections at low dose vaccine concentration (1 μg per dose), against a virulent challenge with the B. divergens Rouen87 isolate. In spite of polymorphism of Bd37 gene, Bd37r induced complete immunoprotection against challenges with each of the 5 reference isolate groups defined by PCR-RFLP.

A detailed study of the structure of the tegument of D. phoxini has been carried out using probe and transmission electron microscope. The distribution of spines and sense organs on the forebody has been described, as well as the nature of the lappets in the everted and retracted state. The adhesive organ exhibits two different surfaces which also differ from the surface of the rest of the body. The use of the ‘Stereoscan’ has confirmed and extended the concept of surface specialization based on transmission studies.

The effects of sex, age of the human host, patency of asexual and sexual stages and seasonality on infectiousness of Plasmodium falciparum to mosquitoes were investigated in a rural village in southern Tanzania between 1992 and 1994. Villagers from randomized subgroups of households were surveyed for malaria parasites. Gametocyte and trophozoite prevalences were age dependent and fluctuated without any clear pattern of seasonality. A sample of 107 participants, selected to include an excess of gametocyte carriers, slept under bednets with holes cut into the sides for 3 weeks. A total of 3837 Anopheles gambiae s.l. and 5403 A. funestus recovered from these bednets, was examined for all oocysts 5–7 days after feeding or for oocysts less than 17·5 µn in diameter 2–3 days after feeding. Additional blood slides from participants were taken twice weekly. The 5–7 day oocyst rates were 12·1% in A. gambiae s.l. and 10·9% in A. funestus and 2–3 day rates were 3·6 and 4·9%, respectively. The higher rates using the former method were attributed to previous infection. There were strong correlations in the levels of infection in both vectors when they fed on the same hosts. However, patent gametocytaemia was only weakly associated with the development of oocysts in the mosquito. Infectiousness was not related to host age, sex, or the season.

After hamsters have been infected with Dipetalonema viteae for about 4 months, microfilariae disappear from the circulation but the adult worms remain alive and active. Such hamsters are said to harbour a ‘latent’ infection. Additional adult worms implanted into such hamsters produce no microfilariae, but adult worms recovered from hamsters with latent infections resume microfilariae production when surgically transplanted into new hosts. In vitro, worms from hamsters with latent infections renewed microfilariae production in the presence of serum from uninfected but not infected hamsters. Serum from infected animals had a marked suppressive effect on the microfilariae production of adult worms implanted into passively immunized hamsters. This suggests that microfilarial release is regulated by a serum factor. Microfilarial production in in vitro and in vivo experiments was more strongly inhibited by serum taken from hamsters with latent infections and hamsters infected for only 30 days (pre-patent) than by serum taken 90 days after infection (whilst microfilariae were in the circulation of the serum donors). A cytotoxic effect of sera from infected hamsters on the microfilariae could not be demonstrated.

In animals immunized by extracts of adult worms or microfilariae, microfilaraemia was considerably reduced. In contrast, animals immunized repeatedly with the extract from small numbers of microfilariae during the pre-patent phase of an infection had an enhanced microfilaraemia. Adult worm numbers were not affected by immunization except in animals given extract from a single female worm which harboured fewer worms than controls.

The midgut epithelium of Glossina morsitans centralis, G. austeni, G. pallidipes, G. palpalis palpalis, G. p. gambiensis, G. fuscipes fuscipes, G. tachinoides and G. brevipalpis from ILRAD-bred colonies was examined, by electron microscopy, for the presence and distribution of Rickettsia-like organisms (RLOs). RLOs were present in the midgut epithelial cells of all non-teneral tsetse. In G. m. centralis, G. pallidipes and, to a much lesser extent, G. brevipalpis, RLOs were numerous and were present in all the specimens examined. RLOs were present in fewer numbers in the epithelial cells of tenerals of these three tsetse species. In contrast, RLOs occurred in very much lower numbers within the midgut cells of nonteneral G. austeni, G. p. palpalis, G. p. gambiensis, G. f. fuscipes and G. tachinoides; were not seen in every specimen, and were rarely observed in the midgut cells of teneral tsetse. The RLOs were typical rod-shaped bacteria with an inner and outer membrane, which occurred free within the host cell cytoplasm and appeared to cause no obvious pathology. The micro-organisms divided by binary fission and at least two distinct morphological forms plus a range of intermediate forms were seen in the midgut cells. A comparison of the presence and numbers of RLOs within the midgut cells and the midgut infection rates of both Trypanosoma congolense and T. b. brucei, both between Glossina species and also within the same stock of tsetse, clearly indicates that the ability of trypanosomes to establish and develop to mature infections is unlikely to be correlated solely with the presence of RLOs within the tsetse midgut.

Ascaris suum possesses a large number of FMRFamide-related peptides (FaRPs) of which KNEFIRFamide (AF1), KHEYLRFamide (AF2) and KSAYMRFamide (AF8/PF3) have been shown to modulate the intrinsic, rhythmic activity of the vagina vera of A. suum in vitro. In the present study, the effects of the nematode FaRPs, SDPNFLRFamide (PF1), SADPNFLREamide (PF2) and KPNFIRFamide (PF4) (from Panagrellus redivivus) and AVPGVLRFamide (AF3) and GDVPGVLRFamide (AF4) (from A. suum) on the in vitro activity of the vagina vera were examined. The effects of each of the peptides were qualitatively and quantitatively distinct. All 3 FaRPs from P. redivivus were inhibitory, causing a cessation of contractions. PF2 was 3 times more potent than PF1, with a threshold of 1 nM. Although PF4 was the least potent (threshold, 10 nM), its effects at [ges ]10 nM were quantitatively the greatest. Both AF3 and AF4 (1 μM) induced complex, multiphasic responses consisting of an initial contraction and spastic paralysis followed by a return of contractile activity of increased amplitude. AF3 was 3 times more potent than AF4. The effects of these peptides had some similarities to those observed on A. suum somatic body wall muscle in vitro, with PF1, PF2 and PF4 being inhibitory and AF3 and AF4 being excitatory.

In this paper the dynamics and control of nematode parasites of farmed ruminants are discussed via a qualitative analysis of a differential equation model. To achieve this a quantity, ‘the basic reproduction quotient’ (Q0), whose definition coincides with previous definitions of R0 for macroparasites, but extends to models with periodic time-varying transition rates between parasite stages or management interventions, is introduced. This quantity has the usual threshold property: if Q0 is less than one the parasite population cannot maintain itself in the host population, and in the long term becomes extinct; but if Q0 is greater than one the parasite can invade the host population. An alternative quantity, R(E), that is often easier to calculate is also introduced, and shown to have the same threshold property. The use of these two quantities in analysing models for the dynamics of nematodes in complex situations is then demonstrated, with reference to the dynamics of mixed parasite species in one host; the effects of breeding host animals for resistance to parasitism; and the development of parasite strains that are resistant to chemotherapy. Five examples are discussed using parameters for the dynamics of nematode infections in sheep, and some statements on control policies are derived.

The thermal preferences of two strains of the snail Biomphalaria glabrata, one resistant to, and one susceptible to, the parasite Schistosoma mansoni were determined in an aquatic thermal gradient. Snails were tested without exposure to the parasite, and 2 h and 5 weeks after exposure to trematode miracidia. The mean temperature selected by susceptible strain snails 2 h post-exposure tended to be lower than that of unexposed controls, although this was not statistically significant. In this strain, at 5 weeks post-exposure, the preferred temperature dropped by 1.9±0.5°C. The resistant strain displayed a significant drop of 1.8±0.6°C 2 h post-exposure. These results are consistent with the hypothesis that a drop in mean temperatures selected by snails is due to altered levels of endogenous cytokines such as IL-1 or TNF in association with parasite activation of the snail internal defense system.

Light and transmission electron microscopy revealed pericytes of brain capillaries of moles (Talpa europaea L., 1758) as parasitized intracellularly. These host cells were enlarged and of globular or ellipsoid shape, and incorporated a cell-within-cell sequence of primary, secondary and, rarely found, tertiary developmental stages of an eukaryotic organism. Other stages like spores were not discovered either in brain or in other organs. Due to the vertebrate host, and the parasitic cells showing the enveloped state this parasite can be classified as belonging to the Myxozoa rather than Paramyxea. Since spores, which would allow an exact identification of the parasite, could not be detected and mammals are very unusual hosts for Myxozoa, the parasite was designated a myxozoan-like organism.

Angiostrongylus cantonensis (rat lungworm), a parasitic nematode, is expanding its distribution. Human infection, known as angiostrongyliasis, may manifest as eosinophilic meningitis, an emerging infectious disease. The range and incidence of this disease are expanding throughout the tropics and subtropics. Recently, the Hawaiian Islands have experienced an increase in reported cases. This study addresses factors affecting the parasite's distribution and projects its potential future distribution, using Hawaii as a model for its global expansion. Specimens of 37 snail species from the Hawaiian Islands were screened for the parasite using PCR. It was present on five of the six largest islands. The data were used to generate habitat suitability models for A. cantonensis, based on temperature and precipitation, to predict its potential further spread within the archipelago. The best current climate model predicted suitable habitat on all islands, with greater suitability in regions with higher precipitation and temperatures. Projections under climate change (to 2100) indicated increased suitability in regions with estimated increased precipitation and temperatures, suitable habitat occurring increasingly at higher elevations. Analogously, climate change could facilitate the spread of A. cantonensis from its current tropical/subtropical range into more temperate regions of the world, as is beginning to be seen in the continental USA.

The structure and staining properties of the epithelium of the midgut in Unionicola intermedia are described. Intracellular non-specific esterase, acid and alkaline phosphatase are present and confined to vacuoles. Extracellular enzymes are absent. Nymphal and adult stages of U. intermedia feed principally on the haemocytes (= amoebocytes) and mucus of their molluscan host, Anodonta anatina. Feulgen-positive material recorded from the lumen and midgut cells of the mites is believed to be derived from the nucleated haemocytes and to undergo intracellular digestion in the midgut cells. Starved mites show steadily decreasing amounts of Feulgen-positive material in the vacuoles. Haemocytes are present in large numbers below the site of attachment of the mites, their presence represents an inflammatory response, and the mite feeds on the products of this response. Large amounts of bound iron are present in the midgut cells but the origin and role of this is unknown.

Ternidens deminutus (Strongylida) is a parasitic nematode infecting non-human and human primates in parts of Africa, Asia and the Pacific islands. The present study genetically characterized T. deminutus and defined genetic markers in nuclear ribosomal DNA (rDNA) as a basis for developing molecular-diagnostic tools. The sequences of the second internal transcribed spacer (ITS-2) of rDNA were determined for adult specimens of T. deminutus (Nematoda: Strongylida: Oesophagostominae) from the Olive baboon and the Mona monkey.Nucleotide sequence data used in this paper are available in the EMBL, GenBank and DDJB databases under the Accession nos. AJ888729, AJ888730, AF136576, Y10789, Y10790, Y11733, Y11735, Y11736, AJ001594, AJ001599, AJ006149 and AJ006150. The former 2 sequences represent original data reported in this paper. The length and G+C content of the ITS-2 sequences was 216 bp and ~43%, respectively. While there was no sequence variation among individual T. deminutus specimens from the baboon, 6 (2·8%) nucleotide differences were detected in the ITS-2 between the parasite from baboon and that of the Mona monkey, which is similar to the difference (3·2%) between 2 other species of Oesophagostominae (Oesophagostomum bifurcum and O. stephanostomum) from non-human primates, suggesting significant population variation or the existence of cryptic (i.e. hidden) species within T. deminutus. Pairwise comparisons of the ITS-2 sequences of the 2 operational taxonomic units of T. deminutus with previously published ITS-2 sequences for selected members of the subfamilies Oesophagostominae and Chabertiinae indicated that species from primates (including those representing the subgenera Conoweberia and Ihleia) are closely related, in accordance with previous morphological studies. The sequence differences (27–48·3%) in the ITS-2 between the 2 taxonomic units of T. deminutus and hookworms (superfamily Ancylostomatoidea) enabled their identification and delineation by polymerase chain reaction (PCR)-based mutation scanning. The genetic markers in the ITS-2 provide a foundation for improved, PCR-based diagnosis of T. deminutus infections and for investigating the life-cycle, transmission patterns and ecology of this parasite.

Babesia divergens was cultivated in RPMI 1640 (25 mM HEPES) supplemented with 10% human serum (RPMI-10% HS) with a high percentage of parasitized erythrocytes (PPE) ([ges ]40%). Standardization of in vitro tests, purification of exoantigens, biochemical studies and the safety of the culture handler motivated the development of a serum-free defined medium. Removal of serum greatly reduced the PPE but, after a period of adaptation, the culture was continuous and the parasite was able to develop a 3% routine PPE. Addition of vitamins or reduced glutathione in basal medium (RPMI) did not improve the PPE. The supplementation of basal medium with lipidic carrier (Albumax I or bovine serum albumin–Cohn's fraction V) promoted the growth of B. divergens with high PPE (>30%) close to those obtained in RPMI–10% HS. Neither protein nor lipid fractions alone were able to restore the growth of B. divergens. Nevertheless, the whole lipid fraction from serum or Albumax I added to delipidated albumin partially restored the growth (7% PPE), indicating that the presentation of specific lipids by a carrier is crucial for the parasite. All the data indicate that Albumax I can replace human serum offering the advantages of safety, standardization for chemosensitivity tests, and exoantigen purification.

A second species of the genus Endorchis is described—E. mandubé; also new species of the rare genera Monticellia, Amphoteromorphus and Nomimoscolex, viz. Monticellia piracatinga, M. rugosa, Amphoteromorphus parkarmoo, Nomimoscolex piracatinga and N. kaparari.

A new genus Manaosia is created to contain the anomalous species M. braço de moça. Proteocephalus lenha becomes Nomimoscolex lenha.

The species Spatulifer surubim, originally described by me as Peltidocotyle rugosa and later referred to the Amphilaphorchidinae, is now regarded as a species of the Monticelliinae.

The eight known species of the Monticelliinae are all referred to the single genus Monticellia, since, differences in vitellaria distribution not corresponding to differences of scolex form, the only alternative is to create an unnecessary number of genera. The genera Goezeella Fuhrmann and Spatulifer Woodland are thus regarded as superfluous.

“Ephedrocephalus” lobosus is removed from the Ephedrocephalinae (which retains its single species E. microcephalus) and, with the two species of “Amphilaphorchis” recently described by me, is placed in Fuhrmann's genus Rudolphiella, now re-established, in the subfamily Rudolphiellinae, thus replacing the Amphilaphorchidinae.

The complete list of known subfamilies, genera and species of the Proteocephalidae described from the Amazon, amended in accordance with the above conclusions, has been published in my last paper on the subject (Woodland, 1935).

Large numbers of electron-dense bodies, 700–1900 Å in diameter, usually seen each with its own limiting membrane, were found in axons of the ventral nerve of infective juveniles of H. contortus. Axons containing these granules merged, without limiting membranes, with a ‘light’, diffusely granular region, about 1·5–2 μm3. The ‘light’ area also merged without boundaries with the underlying cuticle which was different from the surrounding cuticle. This modified cuticle, of which the anterior border lies about 1·3 μm from the posterior edge of the excretory pore, extends slightly beyond the ‘light’ area. Otherwise it is a useful topographical marker for the extent of the ‘light’ area.

It is considered that the ‘light’ region has a special role in the physiology of the cuticle.

I wish to thank Mrs M. Ross for expert technical assistance and Mr R. I. Sommerville for valuable advice. This work was supported by a U.S. Public Health Service Grant, AI 04093–05. The use of the Siemens electron microscope was made possible by a grant from the Australian Research Grants Committee. Financial help from Parke, Davis and Co. (Australia) is also gratefully acknowledged.

A fish-infecting Microsporidia Potaspora morhaphis n. gen., n. sp. found adherent to the wall of the coelomic cavity of the freshwater fish, Potamorhaphis guianensis, from lower Amazon River is described, based on light microscope and ultrastructural characteristics. This microsporidian forms whitish xenomas distinguished by the numerous filiform and anastomosed microvilli. The xenoma was completely filled by several developmental stages. In all of these stages, the nuclei are monokaryotic and develop in direct contact with host cell cytoplasm. The merogonial plasmodium divides by binary fission and the disporoblastic pyriform spores of sporont origin measure 2·8±0·3×1·5±0·2 μm. In mature spores the polar filament was arranged into 9–10 coils in 2 layers. The polaroplast had 2 distinct regions around the manubrium and an electron-dense globule was observed. The small subunit, intergenic space and partial large subunit rRNA gene were sequenced and maximum parsimony analysis placed the microsporidian described here in the clade that includes the genera Kabatana, Microgemma, Spraguea and Tetramicra. The ultrastructural morphology of the xenoma, and the developmental stages including the spores of this microsporidian parasite, as well as the phylogenetic analysis, suggest the erection of a new genus and species.

Studies of the use of parasites as biological tags for stock identification and to follow migrations of marine fish, mammals and invertebrates in European Atlantic waters are critically reviewed and evaluated. The region covered includes the North, Baltic, Barents and White Seas plus Icelandic waters, but excludes the Mediterranean and Black Seas. Each fish species or ecological group of species is treated separately. More parasite tag studies have been carried out on Atlantic herring Clupea harengus than on any other species, while cod Gadus morhua have also been the subject of many studies. Other species that have been the subjects of more than one study are: blue whiting Micromesistius poutassou, whiting Merlangius merlangus, haddock Melanogrammus aeglefinus, Norway pout Trisopterus esmarkii, horse mackerel Trachurus trachurus and mackerel Scomber scombrus. Other species are dealt with under the general headings redfishes, flatfish, tunas, anadromous fish, elasmobranchs, marine mammals and invertebrates. A final section highlights how parasites can be, and have been, misused as biological tags, and how this can be avoided. It also reviews recent developments in methodology and parasite genetics, considers the potential effects of climate change on the distributions of both hosts and parasites, and suggests host-parasite systems that should reward further research.

Parasites inflict fitness costs on their hosts, but often the exact reduction in fitness is not well understood. We investigated the influence of infection by the gregarine genus Monocystis sp. on growth and female investment (cocoon production) of its earthworm host, Lumbricus terrestris. Earthworms (n=81) were observed in a laboratory setting for 8 months, after which parasite load was determined. The results revealed a significant negative relationship between parasite load and growth, yet no association to cocoon production was found. Although the exact nature, strength, and evolutionary consequence of reduced growth are still unclear, the results are the first indication for a clear, albeit weak effect of Monocystis on host fitness.

Lyme disease is caused by bacteria of the Borrelia burgdorferi genospecies complex and transmitted by Ixodid ticks. In North America only one pathogenic genospecies occurs, in Europe there are several. According to the dilution effect hypothesis (DEH), formulated in North America, nymphal infection prevalence (NIP) decreases with increasing host diversity since host species differ in transmission potential. We analysed Borrelia infection in nymphs from 94 forest stands in Belgium, which are part of a diversification gradient with a supposedly related increasing host diversity: from pine stands without to oak stands with a shrub layer. We expected changing tree species and forest structure to increase host diversity and decrease NIP. In contrast with the DEH, NIP did not differ between different forest types. Genospecies diversity however, and presumably also host diversity, was higher in oak than in pine stands. Infected nymphs tended to harbour Borrelia afzelii infection more often in pine stands while Borrelia garinii and Borrelia burgdorferi ss. infection appeared to be more prevalent in oak stands. This has important health consequences, since the latter two cause more severe disease manifestations. We show that the DEH must be nuanced for Europe and should consider the response of multiple pathogenic genospecies.