A modification of the controlled test is described. This is designed to assess the value of a drug against immature as well as against the adult stages of the gastrointestinal nematodes of sheep. The use of faecal egg-count data in the assessment of anthelmintic activity is compared with the critical and controlled tests and the comparative value of all three types of test is discussed.

Parasite diversity is hypothesized to act on host life-history traits through investment in immunity. In order to incorporate the diversity of the parasite community that an individual host or a host species may face, two indices can be used: Taxonomic Species Richness and Taxonomic Entropy, where the taxonomic information is incorporated with the taxonomic weight. We tested whether these indices correlate with several morphological traits potentially implicated in immune defence and in reproduction, using data on gastrointestinal helminths and their rodent hosts sampled in Southeast Asia. We found no relationship between parasite diversity indices and either spleen mass or testes size at the intraspecific level, i.e. at the level of individuals. At the interspecific level, we found no relationship between the parasite diversity indices and testes size. However, we found that female spleen mass is significantly influenced by the specific species richness of parasites, whereas male spleen mass is influenced by individual mean parasite diversity indices. We concluded that female spleen mass may have evolved in response to gastrointestinal helminth pressure acting at species levels, while in males, the individual spleen mass could be constrained by other factors, such as the blood storage function of the spleen.

Adult Hymenolepis diminuta were tested for their ability to transport colloids under in vitro and in vivo conditions. The tracers employed included colloidal thorium dioxide (Thorotrast), carbon (Pelikan Ink), ferritin and the 14C-labelled protein fraction from Chlorella vulgaris. Though certain of these tracers were adsorbed to the external surface of the tegument plasmalemma, no evidence for the assimilation of any of these colloids was obtained in the present study. Further, significant differences in size and structure between the granular inclusions reported earlier by Rothman (1967) as assimilated colloids and the particles present in the respective colloidal suspensions were noted. Results of this investigation are interpreted as rendering untenable previous conclusions concerning transmembranosis of colloids by tapeworms.

The cellular responses in regional lymphoid organs of C57B1/6 mice were examined, following protective immunization with 20 krad.-irradiated cercariae of S. mansoni. Marked changes in total cell number were observed, with peak increases of 13·5-fold in the skin-draining (axillary) lymph nodes and 6·9-fold in the lung-draining (mediastinal) lymph nodes. In contrast, cellular responses were small in the spleen and undetectable in the brachial lymph nodes. The temporal pattern of responses was coincident with the kinetics of parasite migration, events in the mediastinal lymph node being apparent only after day 7. Phenotypic analysis of the cellular changes revealed an increase both in T lymphocytes and, to a greater extent, in B lymphocytes. The changes in Thyl+ cells comprised an increase in both L3T4+ and Lyt2+ populations. A comparison of mice exposed to non-immunizing parasites (normal or 80 krad.-irradiated cercariae) with protected animals, revealed smaller and more transient cellular changes in the axillary lymph nodes of the former. We suggest that the successful immunization of mice with attenuated parasites depends upon the prolonged priming of lymphocytes within the lymph nodes draining the skin-exposure site and that the persistence of 20 krad.-irradiated parasites within these nodes provides the requisite stimulus.

Human Oesophagostomum infections are locally common in northern Ghana. The present study describes the results of a cross-sectional survey involving 1011 subjects, selected by a compound-based random sampling method from 1227 compounds in 24 villages. Selected persons were examined by both Kato and coproculture methods. Hookworm-like eggs, representing ova of Oesophagostomum bifurcum and hookworm were detected in 87·5% of the Kato smears. The geometric mean egg count of the infected subjects was 1018. Upon coproculture, third-stage larvae of O. bifurcum and hookworm were detected in 53·0% and 86·9% of subjects respectively. Oesophagostomum infections were clustered but no clear explanation for aggregation of infections could be found as yet. Subjects infected with hookworm had a 5-fold higher risk of being infected with O. bifurcum. Infection rates in adult women were higher than in adult men. No association was found with family size, level of hygiene or with the presence of animals in the compounds. Representatives of the Bimoba-tribe were significantly more infected than those of the other tribes. It appears, however, that this tribal association is a geographical phenomenon: Bimoba are mostly living in villages with the highest infection rates.

A variant-specific surface antigen from a cloned population of Trypanosoma brucei S 42 has been isolated and partically characterized. [35S]L-methionine was found to be incorporated into this material by cells incubated in vitro in a chemically defined medium. Incorporation of [35S]L-methionine was inhibited by cycloheximide and puromycin at concentrations which are known to specifically inhibit protein synthesis in other systems. The rate of synthesis of the variant-specific antigen in vitro has been estimated to be about 8% of the rate in vivo. Newly synthesized [35S]L-methionine-labelled variant-specific antigen was incorporated into the surface coat.

1. Resistance to sulphanilamide, of a low order, has been developed in a strain of Plasmodium gallinaceum by the treatment of patent infections with the drug.

2. The sulphanilamide-resistant strain was resistant to paludrine over the whole range of doses tolerated by the host; it also proved to be resistant to sulphathiazole, sulphapyridine and sulpha-diazine, though the degree of resistance shown was much slighter than to paludrine.

3. Resistance to paludrine developed in the sulphanilamide-resistant strain before any resistance to sulphadiazine could be detected.

Previous studies have indicated that SAG1, the major surface molecule of the protozoan parasite Toxoplasma gondii, is an important attachment ligand for the host cell. However, the research data that supports this claim comes largely from studies investigating tachyzoite binding, and not SAG1 binding per se. In this study we successfully developed an in vitro attachment assay to directly evaluate the mechanism of SAG1-host cell binding. Competition experiments were then performed using SAG1 that had been pre-treated with the neoglycoprotein BSA-glucosamide or with antibody. Soluble BSA-glucosamide blocked SAG1 attachment to MDBK cells in a dose-dependent manner, implying that SAG1 binding is mediated, in part, via attachment to host cell surface glucosamine. Interestingly, pre-incubation of SAG1 in polyclonal sera from chronically infected mice failed to block binding. This challenges the assumption that anti-SAG1 antibodies block parasite attachment through the masking of SAG1 host cell binding domains. Taken together, this evidence presents new strategies for understanding SAG1-mediated attachment.

Two clones of East African Trypanosoma brucei, with distinct homozygous isoenzyme patterns for one of three enzymes examined, were cotransmitted through the tsetse fly vector Glossina morsitans centralis. Flies with mature infections were individually fed on mice and the subsequent bloodstream form populations analysed for the presence of hybrid trypanosomes by isoenzyme analysis. Several combinations have previously been detected using this approach (Schweizer, Tait & Jenni, 1988; Sternberg et al. 1989). Four clones were isolated from one of the hybrid-containing populations. They showed a hybrid phenotype, as would be expected for the F1 progeny in a diploid Mendelian system. The analysis of the progeny clones, using two gene probes which detect restriction fragment length polymorphisms between the two parental stocks, showed that alleles had segregated at each locus and given rise to three different non-parental combinations of alleles in the hybrid progeny. Characterization of the hybrid progeny clones by PFGE (pulsed field gradient gel electrophoresis) revealed that all progeny clones were recombinant for the intermediate size chromosomes. From the analysis of the segregation of the larger chromosomes, marked by P0K (phosphoglycerate kinase) and CP (cysteine protease) gene probes, it was inferred that the progeny clones did not result from a direct fusion of diploid cells. Results with the PGK probe fit into a classical system with meiosis and subsequent fusion of the nuclei to form diploid progeny. On the other hand, blots with the CP probe as well as some of the ethidium bromide stained PFGE gels revealed the existence of non-parental size chromosomes in some of the hybrid progeny. This phenomenon was observed previously (Gibson, 1989) and further investigation is required to elucidate the mechanism.

Changes in plasma glucose and lactate and glycogen stores of cardiac and voluntary muscle have been determined during the course of an infection by Eimeria tenella.

No hyperglycaemia resulted nor was there any significant change in the stores of hepatic glycogen during the period of observation.

There was a significant reduction in the plasma lactate concentration on the 1st and 2nd days after infection.

There was a transient increase in the stores of cardiac glycogen on the 5th day after infection.

Glycogen stores of voluntary muscle were significantly reduced on the 5th and 6th days after infection. It is thought that this depletion resulted from a reduction in muscular activity rather than from an impairment of glycogenesis.

In 1926 Bequaert wrote, “In the light of the theory of evolution, the various cases in which hemipterous insects, that are normally predaceous or even phytophagous, occasionally become blood-suckers are of considerable interest. They show that haematophagous habits may be readily and rather suddenly acquired by insects that have developed suitable piercing and sucking mouth-parts, without previous adaptation to a blood diet.” These remarks accompanied an annotated list of the species of Hemiptera known to bite man without provocation. In the list are included six species of Cimicids and eleven Reduviids (Triatoma and Rhodnius) which are apparently obligate blood-suckers of Vertebrates; and nine Reduviids, one Nabid, five Anthocorids, and two Lygaeids (Geocoris henoni Puton and G. scutellaris Puton) which are normally predaceous on other insects, whose haemolymph they suck, being thus obligate blood-suckers of Arthropoda. The case of Clerada apicicornis Sign. is obscure, though this species is probably normally predaceous on other insects. An Australian species (C. nidicola Bergr.) is an inquiline in the nests of “opossums” (phalangers).

In previous studies, we demonstrated that CRA and FRA recombinant proteins, used for diagnosis of Chagas' disease, elicited a humoral immune response in susceptible and resistant mice. To understand better the immune response to these proteins, we have evaluated, the cellular immune response in CRA- and in FRA-immunized BALB/c and C57BL/6 mice. A specific cellular lymphoproliferative response was observed in both strains of mice. Spleen cell cultures mainly from CRA-immunized C57BL/6 and FRA-immunized BALB/c mice produced high levels of IFN-γ, indicating the induction of a Type 1 immune response. Regarding the T cell subsets, CD4+ T cells were the major source of IFN-γ in CRA- and FRA-immunized mice. These results suggest that CRA and FRA are important immunogens in inducing a Type 1 immune response and that they may be considered as potential vaccine antigens.

The bird-infecting acanthocephalan Polymorphus minutus has been suggested to comprise different lineages or even cryptic species using different intermediate hosts. To clarify this open question, we investigated Polymorphus cf. minutus cystacanths originating from amphipod intermediate hosts from 27 sites in Germany and France. Parasites and hosts were identified using integrated datasets (COI and/or morphology for hosts and COI + ITS1-5.8S-ITS2 for parasites).

Mitochondrial and nuclear data (ITS1) strongly support the existence of three cryptic species in Polymorphus cf. minutus (type 1-3). These three types reveal a high degree of intermediate host specificity, with Polymorphus type 1 only encountered in Gammarus fossarum type B, Polymorphus type 2 in Echinogammarus sp. and Echinogammarus berilloni, and Polymorphus type 3 in Gammarus pulex and Gammarus roeselii. Our results point to a so far neglected cryptic diversity of the genus Polymorphus in Central Europe. Furthermore, Polymorphus type 2 is most likely a non-native parasite in Germany that co-invaded with E. berilloni from the Mediterranean area. Potentially, type 3 originates from South-East Europe and migrated to Germany by G. roeselii, where it might have captured G. pulex as an intermediate host. Therefore, our findings can be seen in the context of ecological globalization in terms of the anthropogenic displacement of intermediate hosts and its impact on the genetic divergence of the parasites.

The binding of chloroquine to DNA isolated from P. knowlesi has been investigated. In the presence of increasing concentrations of malarial DNA, the absorption spectrum of chloroquine exhibited strong hypochromism in the range 325–350 nm, small red shifts of the absorption maxima and an isosbestic point at 300 nm. The fluorescence emission of the drug at 380 nm (excitation 330 nm) was quenched five-fold by malarial DNA. Chloroquine itself protected malarial DNA from thermal denaturation. These data are consistent with binding of the drug to malarial DNA as has been suggested from studies with DNA from bacteria and mammalian cells. The binding affinity for malarial DNA is of the same order as that for mammalian DNA.

The effect of chloroquine on the metabolism of P. knowlesi in culture was also investigated. There was a direct correlation between concentrations of drug which affect the morphology of parasites and those which affect markedly the incorporation of 3H-adenosine into DNA and RNA, 14C-isoleucine incorporation into protein and the formation of lactate as a result of respiration. However, all processes were inhibited to the same extent, indicating that binding to DNA is not the only action of the drug.

The mode of action of chloroquine and the question of resistance to it are discussed.

One of us (P. I. T.) received financial assistance from the World Health Organization. We thank Dr F. Hawking and Dr J. Williamson for many helpful discussions, Dr K. N. Brown for reading through the manuscript, and Miss Jane Dunnett, Mrs A. C. Gutteridge and Mr T. Scott-Finnigan for skilled technical assistance.

Adult Wuchereria bancrofti were recovered from infected Presbytis cristatus monkeys and radio-isotope labelled extrinsically with 125I and in vitro with [35S]methionine. 125I labelling of the surface of adult W. bancrofti permitted a comparison between the major surface antigens of this species and those from the related lymphatic filariae, Brugia malayi and B. pahangi. All species bear a prominent Mr 29 000 surface antigen but among the differences observed were the strongly labelled molecules with Mr 58 000 and 67 000 in W. bancrofti which are extremely faint in the Brugia species. The [35S]methionine label was effectively incorporated into somatic parasite proteins in vitro although it was not possible to identify any secreted proteins in this way. The antigenicity of these products was investigated using a variety of sera from homologous and heterologous infections and the immunoprecipitation patterns highlighted particular differences between somatic proteins of male and female worms. One secreted antigen was detected, however, by virtue of its phosphorylcholine epitopes, in the culture medium of mixed adult worms; medium from male W. bancrofti adults was negative although homogenates of either sex of adult W. bancrofti were strongly positive in the same system.

Entamoeba moshkovskii and Entamoeba dispar are microscopically indistinguishable from the pathogenic species Entamoeba histolytica. Although sporadic cases of human infection with E. moshkovskii have been reported, the amoeba is still considered primarily as a free-living amoeba. A cross-sectional study was carried out among Orang Asli communities in 3 different states of Peninsular Malaysia. Fecal samples were examined by formalin-ether sedimentation and trichrome staining techniques and then single-round PCR assay was used to detect E. moshkovskii. Out of 500 fecal samples examined microscopically, 93 (18·6%) samples were positive for E. histolytica/E. dispar/E. moshkovskii complex cysts and/or trophozoites. PCR products were detected in 106 fecal samples. E. moshkovskii isolates were detected in 13 (12·3%) fecal samples. Of the 13 E. moshkovskii-positive samples, 5 were of single isolation of E. moshkovskii, 6 were also positive for E. dispar, and only 2 samples were positive for E. dispar and E. histolytica. Moreover, 3 E. moshkovskii-positive samples were collected from symptomatic individuals while the remaining 10 samples were from asymptomatic subjects. This is the first report on the identification of E. moshkovskii in Malaysia. Further studies are needed to confirm the pathogenicity of E. moshkovskii infection and determine the epidemiology among Orang Asli communities in Malaysia.

Current models of the regulation of host populations by parasite infection assume that death of a host results in death of all the parasites contained within or on the host. This assumption acts as a density-dependent constraint on parasite population growth and contributes to the stability of the interaction between host and parasite populations. The protozoan Ichthyophthirius multifiliis, a parasite of freshwater fish, is one of a number of pathogens in which the reproductive capacity of an individual is not entirely destroyed by the death of its host. The effect of host death on the reproductive potential of I. multifiliis was investigated with a series of short-term experiments examining (i) the relationship between parasite burden and host mortality, (ii) parasite survival on the host and (iii) the relationship between parasite age and the number of infective stages released/parasite. Results of a series of experimental epidemics in which host numbers were maintained constant showed large oscillations in parasite numbers. Deterministic models ignoring the age structure of the parasite population were unable to reproduce the behaviour observed in the experimental epidemics. Using the results of the short-term experiments, a difference equation model was developed. This model was able to qualitatively reproduce the observed epidemic behaviour.

Cultured metacyclic forms of Trypanosoma congolense display a characteristic repertoire of metacyclic variable antigen types (M-VATs) similar to that exhibited in vitro in the tsetse fly. There appeared to be no change in expression of M-VATs in cultures of two stocks of T. congolense even after several passages, cryopreservation or long-term cultivation in vitro. Metacyclic forms transformed into mammalian forms when transferred to cultures of bovine aorta endothelial cells and whilst one stock retained expression of M-VATs without change even after 4 months, the other stock underwent antigenic variation within 14 days of transfer. Analysis of the M-VAT composition of mammalian forms of this stock using monoclonal antibodies showed that although the proportion of mammalian forms expressing certain M-VATs declined considerably, trypanosomes expressing one M-VAT increased proportionally to comprise 50 % of the population. In contrast, only small changes were seen in antigen expression in cultures of metacyclic trypanosomes from which mammalian-form cultures were derived. It was possible to produce in vitro, loss and reacquisition of variable antigen surface coat, similar to the differentiation process occurring when bloodstream trypanosomes are ingested by the tsetse fly and eventually develop into metacyclic forms.

Almost 100% of 7- to 10-day-old Hymenolepis diminuta became established when surgically transplanted from donor mice into the duodenum of naive recipient mice. Transplanted tapeworms survived 8–12 days, by which time they had survived much longer in total than they would have done in the donor. Mice previously immunized by a primary infection rejected transplants within 4 days. Sub-lethal irradiation (550 rad) delayed rejection by immune mice but such mice still rejected worms much more quickly than did naive mice.

Surgery was shown to delay by 2–3 days the rejection of worms by naive mice, and the importance of circumventing surgery by administering the worms per os is emphasized.

Prospects for reconstituting irradiated immune mice are considered vis-à-vis work with nematodes, and the differences which, on present knowledge, appear to exist between nematode and cestode rejection are briefly discussed.

The primary trophozoites of Malpighamoeba locustae excyst in the crop and midgut of the Desert Locust (Schistocerca gregaria) and then penetrate the epithelial cells of the midgut and caeca where they grow and multiply slowly. After about 10–12 days they leave the gut epithelium passively when the cells in which they have grown degenerate and are extruded. From the lumen of the gut they make their way into the lumen of the Malpighian tubules where they feed upon the brush border as extracellular parasites. No primary or secondary trophozoites were found in the haemocoele of the host.

During the first few days in the Malpighian tubules the secondary trophozoites undergo a rapid series of divisions which enables them to double their numbers every 24 h so that by day 20–22 the lumen of the tubules is packed with cysts and trophozoites. The trophozoites phagocy-tose small pieces of brush border and numerous food vacuoles are present in their cytoplasm. The cytoplasm of the primary trophozoite contains the normal complement of cell organelles, a notable feature of which are the large, numerous mitochondria with their tubular cristae. When the trophozoites are ready to encyst they round up and begin to lay down a series of membranes which totally cover the trophozoite. Numerous storage granules are found in mature trophozoites which are about to encyst and these may be utilized in cyst wall production.