The influence of subcutaneous infection with protoscoleces of Echinococcus granulosus on the distribution of lymphocyte subsets in draining lymph nodes has been evaluated by immunocytochemical labelling of lymphocyte surface antigens. These studies reveal marked expansion of paracortical Thy-1 +, Lyt-1 + cells and moderate proliferation of surface immunoglobulin-bearing B-cells immediately after infection. The Lyt-1 +:Lyt-2 + ratio decreases rapidly during the first 21 days post-infection and remains below unity until at least 12 weeks post-infection due to severe depletion of Lyt-1 + cells in draining lymph nodes and a significant increase in the percentage of Lyt-2 + cells. The potential role of these Lyt-1 ∓, 2 + (putative T-suppressor) cells in regulation of the anti-parasite immune response and mediation of generalized immunosuppression is discussed in the light of evidence of inhibition of anti-parasite immunity in infected mice.

1. “Trichomonas” keilini n.sp. has three anterior flagella, and a short undulating membrane, whose bordering flagellum does not become free. The flagella arise from an anterior blepharoplast. There is a single nucleus, anteriorly placed, and a mouth, but no basal fibre to the undulating membrane. An axostyle may be present or absent, but when present it is siderophilic. The method of multiplication of “T.” keilini is similar to that of T. hominis and T. batrachorum.

2. “T.” keilini was found in water from a pond in Lincolnshire.

3. It has been cultivated in serum-saline media, in hay infusion, and in pond or rain water with boiled wheat grains, from 4 to 31° C.

4. Cysts have never been found.

I should like to record my gratitude to Prof. Keilin, F.R.S., who gave me the sample of water in which I first saw the organism, and who gave me encouragement throughout this study; and to Mr Clifford Dobell, F.R.S., for the gift of the macaque-human strain of Trichomonas and for so kindly reading through and criticising this manuscript.

Young white mice were infected with different doses of eggs or cysticercoids of Hymenolepis nana and the subsequent faecal egg output was measured over a 3-day period. This was then correlated with worm numbers, determined after killing the hosts. The longest worm in each infection was measured and it was shown that crowding decreased the linear dimensions, number of eggs per proglottis and rate of proglottis production of these worms, but that their shape was not affected.

The relation between total egg output and worm numbers was complex. In both egg-derived and cysticercoid-derived infections the egg production rose to a peak, fell and then levelled off to a constant rate with increasing worm numbers. Cysticercoid-derived worms were larger than egg-derived worms, but produced approximately the same number of eggs per unit of biomass. The differences in the egg output curves for the two types of infection were interpreted as being due to their size difference; this in turn may be a consequence of the host immunological response.

The completed life-cycle of Cyclospora talpae, an extra-intestinal coccidian (Apicomplexa) of the liver of the mole (Talpa europaea). is reported. Oocysts sporulated within 12–14 days at room temperature (20–22 °C). Both macro- and micro-gametocytes developed independently within the nucleus of epithelial cells lining the bile duct as demonstrated by both light and electron microscopy. Merogony was seen in the mononuclear cells in the capillary sinusoids of the liver. Merozoites showed the typical ultrastructural features of the Apicomplexa. The life-cycle of C. talpae and the ultra-structure of the gametogonic and merogonic stages are reported; the ultrastructure of the merozoites is reported as the first description of this stage for the genus Cyclospora.

A study was made of some of the factors which affect the growth of Plasmodium knowlesi in blood diluted in the Harvard medium. Some slight enhancement of growth and re-invasion of new host cells was obtained when P. knowlesi was incubated in low oxygen tensions. Some growth but no re-invasion was obtained under anaerobic conditions. High oxygen tensions were also inhibitory.

The lipids present in the plasma are important for the growth of P. knowlesi in vitro. Stearic acid and cholesterol are required by the parasite but do not account for all the growth promoting properties of plasma. A requirement for vitamin B12 was also demonstrated.

I should like to thank Dr F. Hawking and Dr J. Williamson for their advice and for reading through the manuscript, Mr T. J. Scott-Finnigan for technical assistance, Dr K. Mervyn (Glaxo Research Ltd.) for samples of vitamin B12 analogues and the Hachmeister Company (Pittsburgh) for a sample of TEM 4T. This work received financial assistance from the World Health Organization.

The metabolites of 5-hydroxytryptamine (5-HT, serotonin) namely, L-tryptophan, 5-hydroxytryptophan, 5-hydroxyindole acetic acid and 5-hydroxytryptophol were measured in perfused tissue and whole worms from adult female Ascaris suum using reversed-phase liquid chromatography with electrochemical detection. The intracellular levels of each metabolite were quantitated in response to several physiological effectors but only Ltryptophan (TRP) caused dose-dependent changes in these metabolites. Serotonin itself could also be absorbed by perfused A. suum muscle and intestinal tissue. When live A. suum were tied at the anterior and posterior regions to restrict TRP absorption by the intestine, TRP was absorbed through the cuticle and converted into 5-HT by the muscle tissue. In untied live parasites TRP absorption was observed in both muscle and intestinal tissue. Collectively, the data indicated that 5-HT may be either absorbed directly or synthesized de novo from absorbed TRP in the isolated tissue of A. suum. The 5-HT, in the live adult female A. suum, can be synthesized de novo from TRP, or 5-HT can be absorbed from the environment both through the cuticle and by the intestine of living parasites. Data also indicated that there was preferential sequestering of 5-HT and the metabolites of 5-HT in the anterior tissues of the worms.

We used selection to test for a genetic component to the pattern of emergence of infective juveniles from the host cadaver in the entomopathogenic nematode, Steinernema glaseri (Steiner), and whether other traits would respond to selection on this major and complex life-history character. We selected for early (‘ fast’) and late (‘ slow’) emerging lines by perpetuating nematodes that emerged on the first and after the seventh day of emergence respectively. After 12 cycles of selection, the pattern for the slow line but not the fast line differed significantly from the base population. Cumulative emergence for the slow line was less than the base population from Days 4 to 14 of the 18-day emergence period. The maximum difference occurred on the fourth day when 72·6% of emergence was complete for the base population but only 55·4% for the slow line. Decreases in infective juvenile size over the emergence period were consistent with the change in emergence pattern, but variation in sex ratios was not. No differences in infectivity were found. These results indicate that the emergence pattern has a genetic component, and that genetic variability for this trait occurs in natural populations. Furthermore, the asymmetric response to selection suggests that our field population is under strong selection for a highly skewed early emergence.

This investigation compared the effect of two common types of diet on worm burdens and faecal egg counts of pigs inoculated with Ascaris suum and Oesophagostomum dentatum. The diets were both considered nutritionally sufficient for pigs of this age, and gave high and comparable growth rates. Pigs were inoculated with both worm species at 14 weeks of age and slaughtered 3 or 12 weeks later. At 3 weeks, A. suum larvae were numerous in the small intestine of pigs fed ground barley plus protein supplement, but were not detected from pigs fed a commercial full-constituent pelleted feed. At 12 weeks, however, average adult worm burdens were low and similar in both groups. At both slaughter times, O. dentatum worm burdens were significantly higher in pigs fed barley plus protein than in pigs given commercial feed, particularly for female worms, and the commercial diet led to worms being located further along the large intestine, and to reduced worm fecundity. The chemical composition of large intestinal contents differed significantly between pigs fed the two diets.

High molecular weight proteinases of Trichomonas vaginalis (with apparent Mr values 142 and > 220 kDa) and Tritrichomonas mobilensis (Mr 67, 86, 104 and 120 kDa), optimally active at pH 8, were analysed in gelatin-containing polyacrylamide gels. All of these proteinases were resistant to serine-, aspartic- as well as cysteine proteinase inhibitors. Both proteolytic bands in T. vaginalis and two proteinases in T. mobilensis (67 and 104 kDa) were inhibited by EDTA and EGTA suggesting that they belong to the metallo-proteinase class. The 67 kDa proteinase of T. mobilensis was inhibited also by o-phenanthroline. The other two bands of T. mobilensis (86, 120 kDa) were not classified to any proteinase group since they appeared to be resistant to the chelating agents tested in this study.

Heat shock proteins (HSPs) were documented for the first time in both somatic extracts and excretory/secretory (ES) products of the infective-stage larvae of Trichinella spiralis and T. pseudospiralis. Larvae recovered from muscles of infected mice were heat shocked at 37, 40, 43 and 45 °C in RPMI 1640 medium containing L-[35S]methionine. Somatic extracts and ES products of heat-shocked worms were then analysed by SDS-PAGE, autoradiography and laser densitometry. Prominent bands of HSPs were observed at 43 °C which is the optimal heat shock temperature. The major HSPs in somatic extracts of T. spiralis were 20, 47, 50, 70, 80 and 86 kDa. When the temperature was increased from 37 to 43 °C, the greatest increase in absorbance was observed in HSPs 70 and 86. In vitro translation of mRNA in a nuclease-treated rabbit reticulocyte lysate system showed an increase in the synthesis of the 80 kDa protein. This suggests that the production of HSP 80 is regulated at the transcriptional level. The major HSPs in the ES products were 11, 45, 53 and 64 kDa. In T. pseudospiralis, the major HSPs in the somatic extracts were 20, 26, 31, 50, 53, 70, 80 and 86 kDa, and in the ES products, 11, 35, 37, 41 and 64 kDa.

The ultrastructural changes accompanying oocyte differentiation in the ovaries of the monogeneans, Diclidophora merlangi, Diplozoon paradoxum and Calicotyle kröyeri have been described. In each case, oogenesis in the ovary proceeds as far as meiotic prophase in the primary oocyte. A three-stage sequence of development based on oocyte morphology is proposed: (1) Oogonia and early, immature primary oocytes are typically undifferentiated, with chromatin-laden nuclei occupying most of the cell volume. The cytoplasm contains small clumps of mitochrondria and unattached ribosomal aggregates. There is evidence of mitosis and, in later stages, meiotic prophase is indicated by the appearance of nuclear synaptonemal complexes. (2) Maturing primary oocytes are characterized by increased nucleolar volume associated with the production of RNA for export to the cytoplasm. An organized GER and Golgi apparatus are established and involved in the synthesis and packaging of membrane-limited cortical granules. Annulate lamellae and nucleolus-like bodies appear in the cytoplasm and, with development, the cells increase in size and, peripherally, become interdigitated. (3) Mature primary oocytes represent a resting phase when cellular activity is minimal. Golgi disappear and the ER fragments or becomes reduced in dimensions. Mitochondria and free ribo-somes are numerous and cortical granules move to the cell periphery. The cells separate and, when mature, are released from the ovary. There are minor species differences in oocyte ultrastructure and development.

It has been shown that in intact cercariae of Schistosoma mansoni in water, both head and tail had an identical, aerobic energy metabolism. As long as the environment was water, glucose was mainly degraded to carbon dioxide by both head and tail whether or not these two were still connected to each other. Transfer of intact cercariae into a simple salt medium supplemented with glucose resulted in a very rapid transition towards a more anaerobic energy metabolism: the production of lactate and pyruvate increased, whereas the production of carbon dioxide remained more or less constant. A concomitant rise in temperature to 37°C was not essential for this biochemical transition, but made it more pronounced. Experiments on isolated cercarial bodies and tails in a transforming medium demonstrated that the tails oxidized glucose to carbon dioxide, whereas bodies produced mainly pyruvate and lactate. The results showed that the metabolic transition towards a more anaerobic energy metabolism occurred only in the head and not in the tail of the cercariae. Loss of the tail was shown not to be a pre-requisite for this transition, nor did it by itself trigger a metabolic switch in the resulting cercarial body.

Cercaria patialensis Soparkar, 1924, emerging from the snail Melanoides tuberculatus (Müller) has been encountered at Waltair. The cercariae begin to emerge from the snail at dusk and continue to do so during the period of darkness.

Stages resembling the adult but without the development of eggs have been encountered in nature on the fresh water fishes Panchax panchax (Ham. & Buch.) and Esomus danricus (Bleeker). These stages have also been raised experimentally by exposing P. panchax, E. danricus and fingerlings of Catla catla Ham. & Buch. to the cercariae.

The cercaria is referable to the genus Transversotrema Witenberg, 1944.

It is suggested that there may not be a metacercarial stage in the life-cycle of Transversotrema spp.

A strain of Trypanosoma avium isolated from Corvus frugilegus in England was readily cultivated in vitro in diphasic blood agar, or blood nutrient agar, media at 28 °C.

In both media, small trypanosomes appeared which morphologically resembled the metacyclic forms from the insect vector and which were infective to canaries. They were more numerous, and developed more regularly, in the medium with the nutrient agar base.

At 40–41 °C a few of these small trypanosomes apparently developed into large trypanosomes similar to, but not identical with, those seen in the blood of infected birds.

1. The life cycle of Gigantobilharzia huronensis Najim, 1950, was determined experimentally. The snail, Physa gyrina (Say), served as the intermediate host. The natural definitive hosts were goldfinches (Spinus tristis tristis) and the cardinals (Richmondena cardinalis). Chicks and canaries served as susceptible hosts in the laboratory

2. The shortest time recorded for the hatching of eggs in water is about 20 min. Cercariae were liberated from the snail as early as 24 days after exposure. Eggs were found in the faeces of the definitive host 31 days after the first exposure to the cercariae.

3. Adult worms are elongate and filiform. Females are longer than males, and in both sexes the oral and ventral suckers are absent. The cuticle has no spines. A short gynaecophoric canal is present. Up to 300 testes are present in the male and the cirrus is spiny. Laurer's canal is present and vitelline follicles fill most of the body of the female. Eggs are spherical to very broadly ovoid in shape and averaged 93µ in length by 88µ in width. The uterus contains from one to several eggs at a time, and the genital pore is located shortly posterior to the mouth opening.

4. The miracidium has a peculiar wide gap between the second and third rows of epidermal plates. The body covering consists of twenty-two epidermal plates arranged in four rows of 6:9:4:3. The mother sporocyst has an elongate, sac-like body. A birth pore is present in the mature mother sporocysts. The daughter sporocyst also has an elongate body, but the anterior end is covered with spines. A birth pore is present in the mature daughter sporocysts.

5. The cercaria is an apharyngeal, furcocercous, brevifurcate, distome with pigmented eyespots; the body averaging 240µ in length by 72·5µ in width; the tail stem averaging 268·5µ in length by 30µ, in width; the furca averaging 146·8µ in length by 15µ in width. The furcae have fin folds. The body and tail are covered with spines. There are five pairs of penetration glands and an oral gland. The excretory system is usually 2[(2) + (2+1)]. The cercaria attaches to the surface film of the water with the body parallel to it and the tail hanging downward at different angles. The cercaria is a dermatitis producer in human skin.

1. The development of resistance to metachloridine (3-metanilamido-5-chloropyrimidine) was studied in two clones of Plasmodium gallinaceum derived from single erythrocytic parasites and maintained by serial inoculation in young chicks. Resistance developed with equal facility and similarly in the two clones.

2. In thirteen strains of these clones an enhancement of resistance was obtained after three to five courses of treatment, each of seven doses of metachloridine over a period of 3½ days.

3. The effect of the size of the inoculum (2·5 × 107–109 parasites), and of the dose of drug upon the rate of development of resistance was studied. Although the number of courses of treatment required to produce an enhancement of resistance was not always related to the size of the inoculum, with the largest inoculum an enhancement of resistance was observed after the minimum number of courses of treatment (three), whereas with the smallest inoculum no enhancement of resistance was obtained. The rate of the development of resistance did not appear to be related to the size of the dose of drug.

4. In some strains the increase in resistance was sudden, whereas in others it was more gradual. Resistance was retained when parasites of a newly resistant strain were transmitted through Aëdes aegypti or maintained for 43 days in the absence of the drug.

5. A comparison of the development of resistance in populations of normal parasites, and of populations composed of mixtures of known numbers of resistant and normal parasites, indicated that the pattern of the development of resistance in normal populations could be explained by the selections of mutations of a frequency of less than 1 in 5 × 107, or probably less than 1 in 109 parasites.

On the available data from south Wales and southeast England, the tick Ixodes hexagonus Leach has spring and autumn peaks of activity on hedgehogs, stoats and weasels.

One or more stages of this tick have been recorded on fifteen mammalian hosts. All stages have been collected from hedgehogs, stoats, foxes, polecats and ferrets. The weasel is probably the smallest habitual host. No specimens of I. hexagonus have been found on birds.

Man is an ‘accidental’ host and records of this tick on man in the London area are given. From the present information it seems that ill-effects following the bite of this parasite are rare. In built-up areas the probable sources of infestation are dogs, cats and hedgehogs. Air-raid shelters and similar constructions which have harboured these hosts at one time or another may provide a centre of infestation of man. Our observations indicate that the number of ticks in most hedgehogs' nests is not large. Nothing is known of the tick population in the habitats of other hosts. It is suggested tentatively that the ticks may drop off hedgehogs away from the nest and that after further development (i.e. hatching of eggs and metamorphoses of later stages) they are picked up by such animals as foxes, stoats, weasels.

The records of this tick in Britain are summarized and they indicate that I. hexagonus is a southern species.

Toxoplasma gondii and Sarcocystis neurona are protozoan parasites with terrestrial definitive hosts, and both pathogens can cause fatal disease in a wide range of marine animals. Close monitoring of threatened southern sea otters (Enhydra lutris nereis) in California allowed for the diagnosis of dual transplacental transmission of T. gondii and S. neurona in a wild female otter that was chronically infected with both parasites. Congenital infection resulted in late-term abortion due to disseminated toxoplasmosis. Toxoplasma gondii and S. neurona DNA was amplified from placental tissue culture, as well as from fetal lung tissue. Molecular characterization of T. gondii revealed a Type X genotype in isolates derived from placenta and fetal brain, as well as in all tested fetal organs (brain, lung, spleen, liver and thymus). This report provides the first evidence for transplacental transmission of T. gondii in a chronically infected wild sea otter, and the first molecular and immunohistochemical confirmation of concurrent transplacental transmission of T. gondii and S. neurona in any species. Repeated fetal and/or neonatal losses in the sea otter dam also suggested that T. gondii has the potential to reduce fecundity in chronically infected marine mammals through parasite recrudescence and repeated fetal infection.

Psoroptic sheep scab and psoroptic otoacariasis of domestic rabbits occur in the same geographical regions of Switzerland. To address the question as to whether Psoroptes mites are naturally transmitted between sheep and rabbits, we determined the sequences of the rDNA second internal transcribed spacer (ITS-2) from psoroptic mites from sheep (5 field isolates from Switzerland and 2 laboratory isolates from Ireland and the UK) and from rabbits (8 field isolates from Switzerland). The ITS-2 sequences for all Psoroptes mites originating from sheep were identical and differed at 1 nucleotide position from all the sequences of the rabbit-derived isolates. A statistically significant difference between a rabbit-derived isolate and isolates originating from sheep was also obtained by morphometric analysis of the lengths of the outer opisthosomal setae. For comparative purposes, the ITS-2 sequences from Chorioptes and Sarcoptes collected in Switzerland were also determined. No intraspecies variation was found in 6 sarcoptic isolates from red foxes, with a sequence identity of 41% as compared to Psoroptes. The ITS-2 sequences of 3 chorioptic isolates differed by 24–29% from the Psoroptes sequence. Identical sequences were found for the Chorioptes isolates from sheep and a camel, which differed by 18% from the sequence of an isolate from a cow. These genetic data of psoroptic mites originating from sheep and rabbits from the same geographical area suggest the existence of epidemiologically separated populations.

Biological invasions expose parasites to new invasive hosts in addition to their local hosts. However, local parasites are often less successful in infecting and exploiting their new hosts. This may have major consequences for the competitive ability of hosts, and finally on the fate of the parasite-host community. In Burgundy (Eastern France), the acanthocephalan parasite, Pomphorhynchus laevis, infects 2 amphipod species living in sympatry: the native Gammarus pulex and the invasive Gammarus roeseli. While P. laevis affects the behaviour and the immunity of G. pulex, G. roeseli seems unaffected by the infection. In this study, we examined in detail the ability of the parasite to affect the immune system and resource storage of both gammarid species. We found that the infection was associated with a general decrease of the prophenoloxidase activity, haemocyte density, resistance to an artificial bacterial infection and level of sugar reserves in G. pulex, but not in G. roeseli. These results demonstrate a differential ability of P. laevis to exploit its local and its invasive gammarid hosts. Potential mechanisms of these differential physiological alterations and their potential consequences on the coexistence of both gammarid species in sympatry are discussed.