“Tick paralysis” occurs in British Columbia and affects man, sheep, and probably other animals. The disease is caused by the bites of Dermacentor venustus Banks. It is usually of short duration, is benign in character, but occasionally it persists for long periods, and may terminate fatally. From an economic point of view, the disease is of some importance to the sheep industry. The causative agent has not been discovered, and the disease has not been reproduced by inoculation. The most likely hypothesis is that the tick injects a toxin which gives rise to symptoms appearing coincidentally with the complete engorgement of the tick. In three consecutive cases, experimentally produced by me in lambs, paralysis occurred six to seven days after the ticks were put on. In no case did I fail to produce paralysis through the agency of the tick bites. It has been proved that D. venustus usually bites sheep along the back-bone; possibly the point of attachment may have some bearing on the symptoms or severity of the case. It is probable that other species of ticks may produce a similar disease. No larvae or nymphs were encountered on sheep, and I have no records of their attacking man in British Columbia.

The changes in the percentage chemical composition of both complete strobilae, and of the immature, mature, and gravid regions of the strobila of Hymenolepis diminuta have been studied during development of the worms from 5 to 16 days postinfection. The chemical components that have been evaluated are non-protein nitrogen, protein nitrogen, ribonucleic acid, deoxyribonucleic acid, lyo-glycogen, desmo-glycogen and total lipid.

While the nitrogen, RNA and DNA fractions, expressed as μg/mg of worm dry weight, all decreased markedly with increasing worm age and size, the carbohydrate and lipid fractions increased over the same period of development.

In worms up to 7 days old there is a high non-protein nitrogen value, high RNA and DNA fractions, the lyo-glycogen component of the total carbohydrate is very large, but the amount of carbohydrate expressed as a percentage of dry weight is low. These values are associated with the very high rate of metabolism of the young worms. From 7 to 16 days postinfection the rate of growth slows considerably, which is reflected in the corresponding decreases in the non-protein nitrogen, RNA and DNA fractions, and the increase in the total carbohydrate percentage.

The changes in the chemical composition along a complete strobila complement the morphological evidence as the emphasis switches from segmentation to tissue differentiation and organ maturation.

The changes with age in the percentage composition of the same region of the strobila show that neither the complete worms nor the different regions of a strobila are static in terms of their chemical components, but are changing systems which may be correlated with the ontogenetic development and migrational behaviour of the worms.

The processes which govern the age structure of Fasciola hepatica populations in sheep were investigated by means of a simple mathematical model. The mortality of the metacercariae on the pasture was shown to be a factor of major importance. The mortality rate depends on the micro-climate that prevails at the pasture surface, and thus the age distribution curve of a population of flukes is also determined in part by the weather. This has important implications for the chemotherapy of fascioliasis: flukicides are not equally effective over the whole range of age-classes of parasite and so the factors which govern the age distribution curve of the parasite population within individual hosts ultimately determine the efficiency of chemotherapy.

A microsporidium, isolated from echinostome and strigeid larval trematodes in Lymnaea peregra, is described as a new species Unikaryon slaptonleyi sp.nov. The nuclei isolated at all stages of development, the disporoblastic sporogony and development in contact with host cell cytoplasm are used to assign the species to the genus Unikaryon. The absence of a vacuolar membrane to isolate the meronts and stages of sporulation from the host cell cytoplasm differentiates this genus from Encephalitozoon. Spores are uninucleate, have 17–21 turns of the polar filament coil and measure 5·0 × 2·8/μm fresh. U. slaptonleyi was isolated from rediae and metacercariae of Echinoparyphium recurvatum and sporo-cysts and cercariae of an unidentified strigeid trematode in L. peregra. It was transmitted in the laboratory to unidentified echinostomes in L. peregra and to unidentified strigeids in Planorbis planorbis by feeding the spores to field-collected snails from which cercariae were already emerging. In these natural and experimental hyperinfections the snail tissues were lightly infected but, in the helminths, much of the parenchyma and germinal tissue was destroyed, so that few cercariae were released and most of those were distorted. Similar heavy infections were produced in Fasciola hepatica in Lymnaea truncatula, when spores were fed to the snails 14 days after miracidial penetration, but even high doses (106 spores/snail) produced only light infections in Schistosoma mansoni in Biomphalaria glabrata, in only 2 out of 9 snails. No infections were obtained in larvae producing xiphidiocercariae in P. planorbis although echinostomes became infected under the same conditions. Of a number of aquatic and terrestrial arthropods tested for susceptibility by feeding or by inoculation of spores into the haemocoele, only Pieris brassicae became infected. In a small proportion of pupae surviving from larvae which had been inoculated with spores at 3rd or 4th instar, there was clear evidence of spore replication.

The haemocytes of Gammarus, which are part of the environment of P. minutes, have been found to react by encapsulation, against a variety of foreign bodies, wounded tissues and interspecific transplants. Cuticular wounds appear to present the most urgent stimulus to the haemocytes. The haemocytic reaction is not suppressed by X-irradiation. Differences in haemolymph salt concentration between G. pulex and G. duebeni do not appear to be responsible for the failure of transplants of tissue from G. pulex to G. duebeni. It is concluded that the haemocytic reaction of Gammarus is very similar in response and nature to that of insects.

Healthy P. minutus does not stimulate the haemocytic reactions of its hosts, but wounded or damaged parasites are encapsulated. The capsule of connective tissue, which surrounds the parasite during its development in the haemocoele of the intermediate host, appears to be essential for the parasite's survival.

I am most grateful to Dr P. Tate for helpful discussions, and Dr George Salt, F.R.S., for his advice and criticism of the manuscript. I also wish to thank Drs H. Laser and B. E. B. Moseley for irradiating the amphipods for me.

This paper reports the comparative antimalarial efficacy of intravenous artelinate and artesunate in rats. Prior to efficacy experiments, a Plasmodium berghei–Sprague-Dawley rat model of malaria was developed, in which the clearance effects of intravenous drugs could be readily compared. In efficacy experiments, groups of P. berghei-infected rats were given 3 daily intravenous treatments of artelinate or artesunate at molar equivalent dose rates (total of 0–191·2 μmoles/kg). Artelinate was superior to artesunate in terms of clearance (100% clearance dose of 95·6 μmoles/kg (40 mg/kg) versus 191·2 μmoles/kg for AS (73·4 mg/kg)) and parasite clearance time (1·7±0·5 days for AL versus 2·7±0·5 days for AS at a dose rate of 191·2 μmoles/kg, P<0·01). No frank clinical toxicity was observed, though both artesunate and artelinate induced dose-related vascular necrosis at the site of injection. The necrosis was less severe and reversible when the drugs were administered via femoral, rather than tail/foot veins. The data suggest that the P. berghei–7-week-old Sprague-Dawley rat model of malaria is reproducible and useful for assessing the efficacy of antimalarials and that artelinate is at least as potent, and safe, as artesunate, the leading clinical treatment for severe malaria.

The metacercarial cyst wall of Bucephaloides gracilescens is bilayered. It comprises an inner granular layer of pepsin-resistant carbohydrate and protein material secreted by the parasite, and an outer fibrous and cellular capsule susceptible to pepsin digestion and elaborated by the host. The capsule of cysts from the orbits and nasal regions of the whiting host are substantially thicker than those from the cranial cavity. Cells in the outer portion of the capsule resemble fibrocytes engaged in the synthesis and secretion of collagen; collagen fibres form a loose meshwork in the intercellular space. The cells incorporated [3H]proline in vitro, but not [3H]tyrosine. The cells of the inner portion of the capsule are closely packed and possess pyknotic nuclei; desmosomes and cytofilaments are numerous and probably impart strength and elasticity, respectively, to the cyst wall. Host cells are necrotic at the interface with the inner cyst wall, possibly due to compression or isolation from oxygen and nutrients. Differences in the levels of incorporation of trace-labelled substrates by encysted metacercariae were related to the site of infection and to the thickness and permeability of the cyst wall.

Athymic mice (BALB/c nu/nu/Ola/Hsd) were experimentally infected intraperitoneally with Nosema corneum spores. Infection was monitored in the first and second weeks post-infection. The liver, spleen, kidney, intestine, lung, heart, brain and eye were collected. Quantification of infection in each organ using three different techniques gave approximately the same pattern of infection. Infection increased with time. Histological observations were made on the sites of infection in each organ. All organs were infected, the liver being the most heavily infected. The eye was infected in the retina in contrast to the cornea which was the site of infection in the original host. The present study of N. corneum in athymic mice has shown that this system could also be used to study host-parasite relationships and serve as a model for testing therapeutic agents. Previously the only microsporidian serving as a suitable model for human microsporidiosis was Encephalitozoon cuniculi.

Schistocephalus plerocercoids in the weight range 2–200mg F.W. recovered from the perivisceral cavity of Gasterosteus aculeatus were cultured in various media. In a medium composed of 25% horse serum, 0·5% yeast extract, 0·65% glucose and Hanks's saline at pH 7·1, 21°C, 95% air +5% CO2, dry weight increases of up to 500% were recorded in 8 days. The specific growth rate of large plerocercoids was only one-tenth of the rate observed in small plerocercoids. A plerocercoid of double the weight of another had approximately half the specific growth rate.

Worms after 8 days cultivation were found to have only slightly higher than normal glycogen and water content, and to be able to mature when heated to 40°C. However, the rate of growth slowed to zero by the 24th day in culture at 21°C. Electron microscopic examination showed a ‘deposit’ formed over the microvilli, thin at 8 days but dense after 21 days.

The in vivo glycogen and water content of plerocercoids from 3–300 mg F.W. was determined. Glycogen rose from 24% in plerocercoids of 10mg F. W. to 50–55% in plerocercoids over 80mg F. W. The water content was found to mimic precisely this change, falling from 82% to a plateau of 67–69%.

We wish to thank Professor Gareth Owen for permission to use the photograph shown in the Plate and for his help while using the electron microscope. It is also a pleasure to thank Miss Patricia Grant for her technical assistance.

This study describes experiments which demonstrate the presence of a parasite-induced or derived factor in the haemocoel of Onchocerca lienalis-infected simuliids. Haemolymph, when transferred from previously infected donor flies to previously untreated recipient flies, using fine glass needles, confers protection against a subsequent challenge to the recipients. In three trials using Simulium ornatum sl. or S. linealum, significant levels of protection in ‘immunized’ compared to ‘challenge control’ groups were achieved (84% and 81% with S. ornatum sl. and 85% with S. lineaturm). This is despite the fact that the worm burdens of the infected donor groups in the three trials were very different (means of 33·1 and 3·4 larvae/fly with S. ornatum sl. and 1·6 larvae/fly with S. linealum). The use of sham-operated and bentonite-inoculated control groups demonstrate that this effect is not merely a non-specific reaction to trauma, but is probably parasitic in its derivation. The use of double infections separated by 4 days shows that the donor flies have themselves probably acquired resistance to O. lienalis. Frequency distributions of O. lienalis burdens in individual flies show that there is a shift froni a normal to a skew distribution when comparing ‘challenge control’ flies with ‘immunized’. This possible acquired resistance could have important implications in the transmission of forest and savanna human onchocerciasis by the Simulium damnosum complex.

There is histochemical evidence for the presence of calcium, glycogen, simple proteins and alkaline phosphatase in the calcareous corpuscles occurring in the parenchyma of Taenia saginata. A distinct Feulgen-positive reaction is seen in most of these corpuscles. The material yielding this positive reaction is apparently derived from the nucleus of certain mesenchymal cells from which these corpuscles supposedly originate. In some corpuscles, which are probably at the early stage of formation, the nucleus of such a mesenchymal cell is clearly seen adhering to the surface of the corpuscle. The identity of the nucleus of such cells is apparently lost in the fully formed corpuscle. Each corpuscle has a concentric appearance and is probably formed in successive layers.

In India larvae of several species of Anopheles(Culicidae, Nematocera, Diptera) are parasitised by two species of fungi which form numerous large-sized spores in the host. These fungi occur in the haemocele of the Anopheles larva, and in heavily infected larvae the fungus can be seen to fill the entire haemocele from the thorax to the last segment of the abdomen. In many instances mycelia and spores occur even within the head of the insect. The fungi were not observed to invade the anal gills of the larva (except in a solitary instance in which spores occurred within the deteriorating anal gills).

This review addresses the potential use of neuropeptide receptors for the discovery of anthelmintic agents, and particularly for the identification of non-peptide ligands. It outlines which nematode neuropeptides are known and have been characterized, the published information on drug discovery around these targets, information about existing high- and low-throughput screening systems and finally the likely safety of neuropeptide mimetics.

In an attempt to induce passive protection in lambs against Taenia ovis larvae that would last for the 15–20 weeks from birth to slaughter as fat lambs, one group of ewes was immunized by a series of injections of 2000, 4000, 8000, 16000 and 32000 activated oncospheres of Taenia ovis prior to parturition. Another group of ewes was not immunized. All ewes had previously grazed pasture lightly infected with T. ovis eggs. Most lambs from non-immunized ewes developed cysts after oral infection with T. ovis eggs. However, no lambs from immunized ewes developed cysts up to and including 6 weeks after birth. Between 8 and 16 weeks after birth a proportion of lambs were found to be susceptible to infection. By 18 weeks after birth all lambs were apparently susceptible. The 99% confidence band for the mean duration of demonstrable complement-fixing antibody titres was 6·2–7·8 weeks for lambs from immunized ewes. The persistence of maternal protective antibody in some lambs could possibly preclude successful active immunization of all lambs against T. ovis larvae before 18 weeks of age.

Adult desert locusts were experimentally infected with a dose of 50 M. nigrescens ova and larval nematodes removed 14, 17, 21 and 24 days afterwards for in vitro radiotracer studies. These nematodes were incubated under controlled conditions either in a nutrient medium or in insect saline, which contained the appropriate 14C or 3H-labelled radioisotope. The rate of incorporation of the radioisotope into the proteins of the nematode was measured.

The rate of incorporation of 14C-leucine into proteins was greatest for the 17- day-old larvae and this accorded with the in vivo growth pattern of the nematode. This isotope was incorporated less rapidly into proteins by the 14-, 21 and 24-day- old larvae, which synthesized proteins at approximately the same rates as each other. A non-linear rate of incorporation was manifest for each of the larval stages.

Total dry weight and protein determinations showed that the nematode synthesizes relatively large quantities of non-proteinaceous reserves during the third week of infection, whilst proteins are preferentially synthesized between the 21st and 24th days of infection.

The 17-day-old nematode larvae were able to incorporate six 14C-amino acids into proteins to varying degrees. Leucine was incorporated most effectively into nematode proteins, whilst glutamic acid was the least incorporated of the six amino acids.

These nematode larvae could not effectively metabolize the 3H-dipeptide histidyl-leucine and incorporate its component amino acid residues into proteins. Similarly, a preparation of 3H-haemolymph proteins were not significantly metabolised and incorporated into proteins by the nematode. However, the nematode metabolized and incorporated an exogenous source of 14C-glucose into proteins at relatively high levels.

Incorporation of 14C-luecine into proteins was seven times more rapid for nematodes incubated in buffered insect saline than for those incubated in a more complete nutrient medium.

The dietary requirements of the nematode for protein synthesis were discussed in relation to their associated effects upon the host metabolism and an active transport of dietary amino acids into the nematode was postulated.

We wish to thank Dr H. L. Speer and Dr K. K. Nair for their helpful suggestions regarding radioisotope techniques. Thanks are also due to the National Research Council of Canada for providing financial assistance (Grant No. A4679).

When mice were irradiated immediately before infection with Trichinella spiralis there was a profound and long-lasting interference with their ability to expel adult worms from the intestine. Irradiation given after the fifth day of infection was progressively less effective in this respect. The ability to expel worms was not restored when mesenteric lymph node cells (MLNC) were transferred (a) on the day of infection in mice irradiated one day previously, or (b) on day 7 of an infection in mice irradiated on day 6, even though the MLNC transferred immunity to intact recipients. Transfer of bone marrow (BM) alone was also without effect. However, worm explusion was restored if, following irradiation and injection of BM, 10 days were allowed for BM differentiation before transfer of MLNC. This restoration was effective even after lethal levels of irradiation and was clearly dependent upon a donor-derived BM component cooperating with, or responding to, the activity of the transferred MLNC. The possibility that the BM component is non-lymphoid in nature is discussed.

Infective metacyclic promastigote forms of Leishmania mexicana are introduced by the bite of sandfly vectors into their human hosts where they transform into the amastigote form. The kinetics of this process was examined in vitro in response to different combinations of temperature (26 °C or 32 °C), pH (7.2 or 5.5), and exposure to human serum. Little transformation occurred at 26 °C/pH 7.2, intermediate levels at 26 °C/pH 5.5 and 32 °C/ pH 7.2, and the greatest response at 32 °C/pH 5.5. Transformation was stimulated by exposure to normal human serum, but was markedly reduced when serum previously incubated at 56 °C for 1 h was used (complement heat-inactivated). This stimulatory effect was reproduced by exposure to a single purified component of human serum, C-reactive protein (CRP). Binding of CRP to the whole surface of L. mexicana metacyclic promastigotes, including the flagella, was demonstrated by an indirect fluorescent antibody test. The effect of purified CRP was dose dependent and occurred using normal serum concentrations. The stimulatory effect of whole serum was oblated by CRP depletion and restored by addition of purified CRP. The effects of cAMP analogues indicated that transformation could be mediated via an adenylate cyclase cascade.

The role of the essential nutrients, vitamins A,B (complex), C and E and iron, as prophylactic as well as supportive therapy in experimental visceral leishmaniasis (VL), was studied in hamsters. Prophylactic administration of vitamin C (50, 100 and 250 mg/kg) from day15 to day 0 (15 doses) significantly reduced the intake of Leishmania donovani in hamsters but had no therapeutic effect. In contrast, vitamins A,B complex and E and iron, whether used prophylactically or therapeutically, promoted parasite multiplication. The efficacy of sodium stibogluconate, a reference antileishmanial drug, was appreciably improved in animals administered prophylactically with vitamin C. However, supplementation of vitamin C during established infections resulted in reduced drug action. The results show that the prophylactic use of vitamin C may prevent the onset of leishmania infection and cautions against the indiscriminate use of nutrient supplements such as vitamin A, B complex, and E and iron in VL endemic areas.

In order to analyse the effect of hosts’ relationships and the helminthic load on the switching of parasites between native and introduced hosts, we sampled rodents belonging to two suborders from Central Chile. We compared the number of helminthic species shared between murids (introduced) and cricetid (native, same suborder) rodents to those shared between murids and hystricomorphs (native, different suborder), and we assessed the association between parasitic presence, abundance and geographical dispersion in source hosts to the presence and abundance in recipient hosts. Introduced rodent species shared more helminth species with cricetid rodents than with non-cricetids. Presence and abundance in recipient hosts was not associated with the prevalence and mean abundance in source hosts’ population. The mean abundance of parasites in source hosts throughout the territory and wider dispersion was positively associated with the likelihood of being shared with a recipient host. Closer relationships between native and introduced hosts and high parasitic abundance and dispersion could facilitate host switching of helminths between native and introduced rodents. This work provides the first documentation of the importance of parasitic abundance and dispersion on the switching of parasites between native and introduced hosts.

The glycolytic enzyme triosephosphate isomerase catalyses the isomerization between glyceraldehyde 3-phosphate and dihydroxyacetone phosphate. Here we report that Trichomonas vaginalis contains 2 fully functional tpi genes. Both genes are located in separated chromosomal context with different promoter regulatory elements and encode ORFs of 254 amino acids; the only differences between them are the character of 4 amino acids located in α-helices 1, 2 and 8. Semi-quantitative RT-PCR assays showed that tpi2 transcript is approximately 3·3-fold more abundant than tpi1. Using an anti-TvTIM2 polyclonal antibody it was demonstrated that TIM proteins have a cytoplasmic localization and both enzymes are able to complement an Escherichia coli strain carrying a deletion of its endogenous tpi gene. Both TIM proteins assemble as dimers and their secondary structure assessment is essentially identical to TIM from Saccharomyces cerevisiae. The kinetic catalytic constants of the recombinant enzymes using glyceraldehyde-3-phosphate as substrate are similar to the catalytic constants of TIMs from other organisms including parasitic protozoa. As T. vaginalis depends on glycolysis for ATP production, we speculate 2 possible reasons to maintain a duplicated tpi copy on its genome: an increase in gene dosage or an early event of neofunctionalization of TIM as a moonlighting protein.