Blastocrithidia familiaris were found to be parasitic in the midgut, ileum and rectum of Lygaeus pandurus. The host—parasite relationship is described. Attachment of parasites in the midgut and ileum occurs by interdigitation of expanded flagella over and between the microvilli. No attachment to microvilli was observed where extracellular membranes form well-organized layers which lie parallel to the gut wall and completely separate the microvilli border from the lumen. The extracellular membranes originate from delamination of the outer unit membrane of microvilli which consists of a double plasma membrane. The function of the extracellular membrane layers and their possible role as a peritrophic membrane in preventing parasite attachment is discussed in relation to previous studies on midgut cells in Hemiptera with a similar apical coat on midgut microvilli. In the rectum, parasites attach to the cuticle of the gland cells and not to the rest of the rectal wall. Attachment to the cuticle occurs by the formation of hemidesmosomes. A comparison of the relationship of B. familiaris and its host to previous ultrastructural studies of associations between kinetoplastid flagellates and their respective hosts is discussed.

Computer-aided reconstruction from serial sections has been used to analyse the 3-dimensional structure of entire amastigotes of Leishmania mexicana mexicana and to determine the number, arrangement and volume of each organelle. In two reconstructions, the lysosome-like ‘megasomes’ were the most numerous organelle, there being 34 in one amastigote, and they comprised as much as 15% of the total cell volume. In contrast, as few as 9 glycosomes were present, accounting for less than 1% of the cell volume. The unitary nature of the mitochondrion was confirmed and its complex basket-like structure was revealed. The spatial arrangement of the cell organelles is here displayed in stereo-pairs.

The effects of parasitization by Hyposoter exiguae on the nutritional physiology of Trichoplusia ni were influenced by the dietary sucrose level. The results confirmed that host nutrition plays a significant role in the manifestation of parasitic infection during the insect parasite-host association. Increased dietary sucrose level resulted in an increase in haemolymph trehalose concentration in both control and parasitized insects, but the increase was greater in the latter group. However, when the sucrose level was increased without energetic compensation and the dietary casein level was maintained constant, the haemolymph trehalose concentration was affected very little in unparasitized individuals but was markedly elevated in parasitized hosts. This result suggests that the de novo synthesis of carbohydrate in parasitized T. ni may not be regulated by dietary sugar intake.

The nuclear DNAs of 71 trypanosome stocks from different African countries, representative of the three Trypanosoma brucei subspecies, and one T. evansi stock, have been analysed by the combined use of restriction endonuclease digestion, gel electrophoresis and molecular hybridization with both trypanosome surface-antigen-specific and undefined genomic DNA probes. In contrast with T. brucei brucei and T. brucei rhodesiense stocks, all the T. b. gambiense stocks are characterized by a conserved, specific DNA band pattern, regardless of the probe. This allows T. b. gambiense to be non-ambiguously identified. On the contrary, T. b. brucei and T. b. rhodesiense, which could not be discriminated by the same criteria, both yield highly variable DNA band patterns. Our data confirm that domestic animals like pig, dog and sheep constitute a potential reservoir for T. b. gambiense. Using a numerical analysis of the DNA hybridization patterns we have measured the degree of similarity between the 72 trypanosome stocks. This investigation shows that all T. b. gambiense stocks are included in the same homogeneous population, while the stocks from the two other subspecies seem to be distributed in several heterogeneous groups, some of these showing correlation with the geographical origin of the trypanosomes. It is concluded that (i) T. b. gambiense stands out as a real subspecies that has undergone a distinct evolution relative to the ‘non-gambiense’ group, (ii) the alleged T. b. rhodesiense subspecies does not fit with any of the groups evidenced by our cladistic analysis and hence does not appear as a distinct subspecies and (iii) ‘non-gambiense’ trypanosomes are probably evolving much more rapidly than T. b. gambiense. Different aspects of trypanosome relationships and evolution are discussed.

The sequence of appearance of specific lytic activity against more than 20 variable antigen types (VATs) of Trypanosoma vivax in the serum of 27 animals belonging to 5 species has been examined. For each host species there was a characteristic course of infection, with differences in height and duration of parasitaemia and in pathogenicity. The sequence of antigenic variation was similar in all host species, with some VATs consistently eliciting response more rapidly than others. The predominant group, comprising VATs which apparently developed within the first 3 weeks, varied in size according to the total number of trypanosomes in the bloodstream within that period, suggesting there is a spectrum, rather than discrete groupings, in the hierarchy of VAT expression. There was very little evidence for differences in appearance of VATs between host species; the only clear example was one VAT which apparently did not develop in one host species. The sequence of antigenic variation in T. vivax seems to be determined by the parasite rather than the host species.

The variable antigen repertoire expressed by metacyclic Trypanosoma brucei rhodesiense is not influenced by the anamnestic expression whereby the variable antigen type (VAT) ingested by a tsetse fly is present at high levels in early bloodstream populations of fly-infected mice. This has been demonstrated by feeding to Glossina morsitans a trypanosome line expressing a VAT which is normally a component of the metacyclic repertoire. The VAT did not constitute a significantly increased proportion of the resultant metacyclic population which would have occurred had anamnestic expression and metacyclic expression been linked. Five other metacyclic VATs were also present at control levels. We conclude that the mechanisms of expression of VATs in the fly and in the mammal are independently controlled.

Coated metacyclics of Trypanosoma vivax exist in the hypopharynges of infected tsetse flies and are extruded in low numbers when the flies are induced to probe onto warm slides or into medium. After extensive searching of T. vivax-infected proboscides, and resort to a process for the examination of single, extruded, metacyclic trypanosomes, electron micro scopic evidence is presented that, contrary to an earlier report, metacyclic T. vivaxacquire a surface coat before contact with the mammalian host. Since T. vivax exhibits antigenic variation, the role of the surface coat in this species is likely to be functionally equivalent to the surface coat of the other tsetse-transmitted trypanosome species, T. brucei and T. congolense.

Autoradiography of compressed mouse tissues has been used to estimate the numbers of Se-labelled schistosomula present in different mouse organs. Day 7 parasites extracted from the lungs of donor mice were delivered by injection to the lungs, systemic organs and liver of recipient mice as a discrete pulse. The numbers detected in various locations with time post-injection were then used to analyse the dynamics of intravascular migration. Approximately 98% of cercaria-associated label was lost during the first 14 days of parasite life, two-thirds of this in the first 7 h post-infection. Nevertheless, 99–113% of schistosomula could be detected 30 min post-injection into the locations chosen. The efficiency of the parasite delivery system was 95%. The time required for the number of foci in the lungs to decline to 50%, after injection of parasites via the femoral vein, was 55 h. Adjustment of this data to allow for parasites returning to the lungs after passage round the systemic vasculature gave a value of 30–35 h for the true mean time of lung transit. The distribution of parasites to systemic organs after their exit from the lungs was proportional to the fractional distribution of cardiac output. The probability (P) of a schistosomulum being distributed to splanchnic beds was estimated at 0·32 and its P of being trapped in the hepatic portal distributaries within the liver as 0·72–0·86. On this basis, the entire hepatic portal population of adult schistosomes would be recruited during 2–3 circuits of parasites around the pulmonary-systemic vasculature. The mean transit time of schistosomula through intestinal capillaries was 6·5 h whilst that through other systemic organs combined (muscles, kidneys, brain, etc) was 16 h, considerably more rapid than lung transit. The time taken for schistosomula to pass between organs, in arterial and venous blood, was shown to be less than 30 min in both cases (probably much less).

The migration of the schistosomula of Schistosoma mansoni labelled with [75Se] has been followed from the skin to the hepatic portal system. Parasites were detected in all mouse tissues by compressed organ autoradiography. Two separate experiments were performed to track parasites in normal mice, and in mice previously vaccinated with irradiated cercariae. In normal mice, the profile of numbers of autoradiographic foci detected in the skin, lungs, systemic and splanchnic organs was described with time post-infection. The distribution of parasites to systemic organs, following exit from the lungs, paralleled the fractional distribution of cardiac output. Accumulation of schistosomula in the hepatic portal system was complete by day 21 post-infection. Only 2–3 passes of parasites around the vascular system would be required to produce the hepatic portal population. No significant decline in total foci was detected in the first 12 days post-infection. The majority of parasite elimination appeared to occur in the lungs as late as day 21, with lesser proportions in the systemic organs and skin infection site. The pattern of migration in vaccinated mice was similar to that in normal animals. One difference observed was the longer duration of stay in the skin; however, the majority of parasites eventually reached the lungs. The systemic phase of migration occurred on a reduced scale, as did accumulation of parasites in the hepatic portal system. The decline in total foci in vaccinated mice commenced approximately 7 days earlier than in normal mice and proceeded to a lower end-point. Again the majority of parasite elimination appeared to occur in the lungs with lesser proportions in the systemic organs and skin infection site. It is suggested that resistance to reinfection in vaccinated mice has two additive components which combine to retard the migration of schistosomula within the vasculature, preventing them from reaching the hepatic portal system.

Peritoneal leucocytosis, with an increased percentage of eosinophils, was found in mice which had been infected with Schistosoma mansoni for 7 weeks or longer. Specific IgG against worm and egg antigens increased in peritoneal fluids and their corresponding sera respectively 5 and 7 weeks after infection. An intraperitoneal challenge with schistosomula elicited neutrophilia in all mice regardless of immune status, as well as infiltration of eosinophils and macrophages in infected mice. The secondary eosinophilia occurred in mice previously infected for 1 week or longer, whereas the infiltration of macrophages occurred only after worms from the primary infection had started laying eggs. Unlike the eosinophilia the macrophage response required infection with bisexual populations of cercariae. Injection of previously infected mice with Escherichia, Trichinella or Toxocara failed to increase the proportions of eosinophils and macrophages. Schistosomula-induced eosinophilia could be elicited in passively sensitized mice. Intraperitoneal injection of PBS extract of adult worms elicited eosinophilia in infected mice and neutrophilia in normal mice. Two chromatographic fractions induced eosinophilia and the third only neutrophilia. The relevance of these observations to host response to S. mansoni infections is discussed.

A glycoprotein cross-reactive among Schistosoma mansoni, Trichinella spiralis and Fasciola hepatica was identified and characterized by use of monoclonal antibodies prepared against S. mansoni glycoproteins. Four monoclonal antibodies recognized the same antigen which was one of the major S. mansoni glycoproteins precipitated by sera of hosts infected with either S. mansoni or T. spiralis. This antigen was expressed in S. mansoni cercariae, adult male and female worms, and eggs, and in S. haematobium but not in S. japonicum. Radio-immunoprecipitation and partial proteolytic digest mapping showed that the monoclonal antibodies each recognized a unique epitope. These epitopes were heat labile, sensitive to chaotropic agents, but resistant to reduction and alkylation or digestion with glycosidases, indicating that the recognition sites were amino acids and not carbohydrates. Epitopes recognized by the four monoclonal antibodies were expressed in F. hepatica, whereas only two were expressed in T. spiralis. Analysis by immunofluorescence microscopy showed that the antigen was expressed in S. mansoni in the parenchymal tissue and on the surface of the dorsal tubercles; in mature F. hepatica in the parenchymal tissue, vitelline glands and eggs; in immature F. hepatica only in the parenchymal tissue and in larval T. spiralis in the hypodermis.

Protoscoleces of Echinococcus granulosus absorb the amino acids cycloleucine and α-aminoisobutyric acid (AIB) by a combination of mediated uptake and diffusion. After correcting for the latter, values for Kt and Vmax of 0·124 mM and 0·947 nmoles/mg protein/2 min for cycloleucine were calculated; corresponding values for AIB were 0·039 mM and 0·139 nmoles/mg protein/2 min. Both amino acids were accumulated against a concentration gradient and a comparison of Kt and Kt values determined in mutual inhibition experiments suggested that both cycloleucine and AIB share a common uptake locus (loci). Cycloleucine uptake was pH-dependent and could be inhibited by a variety of other amino acids. Neither D- nor L-proline inhibited cycloleucine absorption but D-methionine, D-alanine, D-leucine, D-valine and D-serine were much more effective inhibitors than their L-counterparts.

Acanthocephaloides geneticus sp.nov. is described from Arnoglossus laterna (Bothidae) from the Mediterranean littoral (Sète-France). The new species most closely resembles Acanthocephaloides propinquus (Dujardin, 1845) Meyer, 1932, whose type host is Gobius niger (Gobiidae). A genetic comparison of the parasites collected from these two Teleostean fishes has confirmed the value of morphological differences which seemed too slight to raise the populations to species status.

Testes in the male early acanthella of Moniliformis dubius are cellular. The testes in the middle and late acanthellae and cystacanth stage also contain individual cells but these are embedded in a compact supporting syncytium which also forms the boundary of the testis. The testes are embedded in the cytoplasmic wall of the ligament sac in the early acanthella but after this stage they become exposed in the cavity of the sac when the surfaces of the testes become covered by a surface coat. Certain cells adjacent to testes primordia in the early acanthella appeared to have formed rudiments of vasa efferentia in the middle acanthella.

Gametogenesis in Dirofilaria immitis has been studied principally by means of the aceto-orcein chromosomal squash technique, but with additional ultrastructural observations. A terminal germinative zone, in which a continuous and rapid division of germ cells occurs, has been identified in the gonoduct of both male and female worms. Approximately 20% of cells within these germinative zones were in arrested mitotic division following the incubation in vitro of excised gonads in 0·01% colchicine for 4 h. All primary spermatocytes within a 1–2 cm length of the testis proximal to the germinative zone were at the prophase of the 1st meiotic division. In the corresponding region of the ovary, the primary oocytes were similarly at the prophase of the 1st meiotic division in 75% of female worms examined but in the remaining 25% all primary oocytes possessed markedly less condensed, probably interphase nuclei. A possible hormonal control of the cyclical development of primary oocytes, but not primary spermatocytes in D. immitis is suggested. In most of the remaining length of the gonoducts beyond this region of cells at meiotic prophase, the chromatin material of both primary spermatocytes and oocytes is decondensed. Recondensation of chromosomes in the spermatocytes is observed just prior to entry into the seminal vesicle, where meiosis I is completed and meiosis II takes place. In the primary oocyte, completion of meiosis only occurs after fertilization within the seminal receptacle by an entire male gamete. Following the 2 meiotic divisions in the oocyte and subsequent extrusion of the 2 polar bodies, the haploid chromosome complement of the female unites with that of the male, re-establishing the diploid number of the zygote (2n = 10). Male chromosomes within the oocyte remain visible throughout late oogenesis and fusion occurs without the formation of pronuclei.

Parasite burden (by volume) was measured in female mice of three strains given single or concurrent infections of Mesocestoides corti and Taenia crassiceps. Significant suppression of T. crassiceps volume was observed over a range of M. corti inocula and occurred irrespective of whether M. corti was introduced before or after infection with T. crassiceps. Suppression of T. crassiceps volume was greatest with larger inocula of M. corti and with increased duration of M. corti infection. No significant difference was found in the intraperitoneal volume of M. corti from mice given single or simultaneous concurrent infections of M. corti and T. crassiceps. When M. corti were inoculated into mice with an established infection of T. crassiceps a significantly smaller volume of M. corti was retrieved at post-mortem from the peritoneal cavities of these mice, than from mice given just M. corti.

Evidence for the presence of 11 intestinal parasites in pre-school children from 4 rural villages in Ghana was obtained from an examination of stool samples. Striking differences were detected between the prevalence of some of the 6 common infections in the 4 villages. The prevalance of Ascaris lumbricoides varied from about 76% in one village (Oshiyie, coastal savanna) to apparently 0% in another (Akuma, forest zone). No differences in prevalence for any infection were observed to be sex dependent. Investigation of the relationship between age of the children and prevalance showed that the degree of prevalence of both A. lumbricoides and Trichuris trichiura had essentially levelled off by the time the children were 4 years old. There was no evidence to suggest that the prevalence of either Entamoeba sp. or spp. or hookworm was approaching a maximum value, even in the oldest children. These trends applied across the villages regardless of the differences in prevalence values for the infections. On average, the children of Oshiyie were found to harbour twice as many infections as the children of the other villages. The investigation of the prevalence data revealed evidence of associations between pairs of infections, particularly those involving hookworm and T. trichiura.

Investigations were carried out into the properties and localization of chitin synthase (EC 2.4.1.16) in connection with the formation of Ascaris suum egg-shells. The chitin synthase of eggs exhibited properties very similar to those found in other chitin-synthesizing organisms. It was stimulated by the presence of ATP, GlcNAc and Mg2+ with maximal activity at pH 7·0. In the phase of active chitin synthesis, during formation of the primary shell layers, chitin synthase was bound to the structures of the eggs. On completion of chitin synthesis in the eggs, the amount of the enzyme increased in the soluble fraction. Two forms of chitin synthase have been found in the eggs, namely an inactive (zymogenic) and an active form. Transformation of these two enzyme forms represents a key mechanism in the regulation of chitin synthesis in A. suum eggs.

The frequency distribution of parasites in hosts commonly follows a negative binomial or similar distribution. Under certain conditions the magnitude of parasite-associated host mortality can be estimated by comparing the tail of the observed distribution to that of the distribution predicted from the first few points of the data. For the technique to work the following assumptions need to be met: mortality in lightly infected fish must be rare; infection and consequent mortality occur only in fish younger than those sampled; and the frequency distribution of the parasite at the time of infection should conform to a known probability distribution. The method was applied to frequency distributions of blastocysts of Callitetra rhynchus gracilis in 898 Saurida tumbil (Bloch) and 5013 S. undosquamis (Richardson). Parasite-associated mortality in S. tumbil was calculated to be at least 11 % in males and 2% in females. For S. undosquamis, estimated mortality was about 5% in males and 3% in females. The numbers of parasites estimated to produce a 0·5 probability of death, the parasitological equivalent of an LD50 were 3·4 and 5·7 for S. tumbil males and females, and 18 and 3 for S. undosquamis males and females respectively.

The karyotype of Transversotrema patia1en consists of 10 pairs of chromosomes (2n = 20) of which 5 pairs are metacentrics and 5 pairs are submetacentrics. The chromosomes are large and range in size from 5 to 12 μm. The total chromosome length of the diploid complement is 16783 μm. Stages of spermatogenesis including the two gonial divisions and two reduction divisions leading to production of spermatozoa occur in cercarial embryos inside snail tissue, while the maturation divisions of the ovum occur in eggs freshly liberated by the fluke. The chiasma frequency is high, being 3888/cell and 388/bivalent. Cytological data indicate an independent phylogenetic status for the family Transversotrematidae.