Hosts face mortality from parasitic and environmental stressors, but interactions of parasitism with other stressors are not well understood, particularly for long-lived hosts. We monitored survival of flour beetles (Tribolium confusum) in a longitudinal design incorporating cestode (Hymenolepis diminuta) infection, starvation and exposure to the pesticide diatomaceous earth (DE). We found that cestode cysticercoids exhibit increasing morphological damage and decreasing ability to excyst over time, but were never eliminated from the host. In the presence of even mild environmental stressors, host lifespan was reduced sufficiently that extensive degradation of cysticercoids was never realized. Median host lifespan was 200 days in the absence of stressors, and 3–197 days with parasitism, starvation and/or DE. Early survival of parasitized hosts was higher relative to controls in the presence of intermediate concentrations of DE, but reduced under all other conditions tested. Parasitism increased host mortality in the presence of other stressors at times when parasitism alone did not cause mortality, consistent with an interpretation of synergy. Environmental stressors modified the parasite numbers needed to reveal intensity-dependent host mortality, but only rarely masked intensity dependence. The longitudinal approach produced observations that would have been overlooked or misinterpreted if survival had only been monitored at a single time point.

A partial cDNA sequence was obtained from the human blood fluke, Schistosoma mansoni using a signal sequence trap approach. The full-length cDNA was cloned and termed Sm-7TM. The corresponding open reading frame had 7 membrane spanning domains and shared identity with a small, novel group of seven transmembrane (7TM) receptors from vertebrates and invertebrates, including the human ee3 receptor – a heptahelical protein implicated in neuronal signalling. Phylogenetic analysis of this novel family showed that the Sm-7TM ORF formed a clade with exclusively invertebrate sequences. Based on topology modelling with ee3, Sm-7TM was predicted to possess an intracellular C-terminal tail, which was expressed as a soluble thioredoxin fusion protein (Sm-7TMC) in Escherichia coli and purified using metal ion-affinity chromatography. A polyclonal antiserum against this domain was used to detect Sm-7TM in detergent-soluble parasite extracts and to immunolocalize the receptor to the tegument of adult S. mansoni.

Seasonal life cycle of body cavity dwelling (BCD) Philometra ovata (Nematoda: Philometridae) has been reported in southern and central European countries, but its swim bladder dwelling (SBD) stage and northern populations have remained unstudied. In this study, we investigated the seasonal life cycle and infection ecology of P. ovata in both swim bladder and body cavity in the European minnow (Phoxinus phoxinus) in Finland. The larval P. ovata infected the swim bladder of minnows mainly in August. Female SBD P. ovata emigrated to body cavity mostly in September, grew to their full size by the end of the next June, and evacuated from minnows in July. In addition, female SBD P. ovata retarding their development and staying in swim bladder were found commonly in minnows, thus the mean monthly prevalence (6·7 ± 3·9%) and mean intensity (1·4 ± 0·8) of BCD P. ovata was lower than that of SBD P. ovata (37·8 ± 15·1% and 2·0 ± 1·5, respectively). Finally, despite the large size of BCD individuals, infection of P. ovata did not impair body condition and relative gonad size of minnows, but increased the mortality and caused physical damages in their hosts during the evacuation period.

Testosterone is involved in the development and expression of physiological, morphological and behavioural traits. High levels are often associated with high infection risk and/or intensity, suggesting a trade-off between sexual traits and immunity. Classically invoked mechanisms are immunological or behavioural, i.e., testosterone increases susceptibility or resistance to parasites via an impact on immunity or modulates behaviours involved in parasite transmission. However, studies report contrasted patterns. Given its modes of action and the diversity of host-parasite interactions, testosterone should not act similarly on all interactions. To reduce host and context diversity, we studied 3 viruses in the same cat population: the aggressively transmitted Feline Immunodeficiency virus (FIV), and the Feline Calicivirus (FCV) and Herpesvirus (FHV) both transmitted during friendly contacts. Testosterone had a strong effect on the probability of being positive to FIV whereas its effect was significantly weaker on FCV and FHV. These findings demonstrate that testosterone can be differentially associated with parasites of the same type (viruses). The difference we observed was consistent with a behavioural-mediated effect (increased aggressiveness), supporting the idea that the testosterone effect on infection risk is at least partially driven by behavioural mechanisms in our system. Further investigations (e.g., individual immunity measures) are required to confirm this hypothesis.

Eimeria cernae is recorded for the first time in England and the life-cycle is described in experimentally infected bank-voles (Clethrionomys glareolus). The pre-patent period was 6 days and the patent period was 4–6 days. Oocysts were ellipsoidal in shape and measured 20·2 × 15·9 μm. Sporocysts, measuring 11·5 μm long and 6·8 μm wide, possessed a small stieda body and contained a mass of granular sporocyst residuum. The endogenous stages developed in the epithelial cells of the colon and rectum. Three generations of schizonts were found. The lst-generation schizont seen at 48 h post-infection (p.i.) contained up to 8 merozoites, the 2nd-generation schizont seen at 72 h p.i. had a mean number of 16 (12–20) merozoites and the 3rd-generation schizont at 96 h p.i. had a mean of 18 (14–21) merozoites. Gamogonic stages were present from 96 to 120 h p.i. in the rectum only.

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.

After 24 h desiccation at 28–29 °C and approximately 50 % relative humidity about 70 % of B. microplus larvae drank sufficient solution containing 1·5 mCi of 32P per ml for their movements on the host to be followed with a portable G-M counter. Reduced viability of the labelled ticks could not be detected when they were kept for 24 h on the host and either allowed to feed or prevented from doing so. When feeding was continued for 72 h or when larvae were incubated for 3–4 weeks, adverse effects were found, the severity of which could not be directly related to the amount of 32P label. Desiccation, handling of larvae and exposure to radiation in the drinking solution may have contributed to their reduced viability.

Since resistance to the tick is manifest within the first 24 h after infestation labelled larvae could be used to compare development on different hosts during this time. Even after feeding for 72 h, larvae were more adversely affected by host resistance than by labelling damage.

We would like to thank Mr C. A. Schuntner for helpful advice and Mrs J.Galligan for technical assistance. The financial support of the Australian Meat Research Committee is gratefully acknowledged. Messrs D. Hancox and S. R.Henderson assisted with some of the experiments.

The pattern of DNA synthesis in chicken kidney (CK) cells parasitized by Eimeria tenella was altered; a 2-fold increase in the uptake of [3H]-thymidine occurred in these cells compared with that shown by the controls. This difference was significantly different at 16 h post-inoculation (p.i.) and reached a peak at 20 h p.i. Non-parasitized cells in co-culture with parasitized cells showed a level of incorporation intermediate between that of the parasitized and non-parasitized mono- cultures. It was shown that this stimulation was due to a factor released into the medium by the parasite or the parasitized cell. A possible course of events leading to induced and prolonged DNA synthesis by the host cell and the significance of this change in the life-cycle of the parasite is discussed.

1. It has been observed that the larvae of four species of chironomid midges invade and destroy the contents of the egg masses of Bulinus (Physopsis) globosus in Amani lake, Tanganyika.

2. There was no indication that this type of predation exercised any restraint on the density of adult snails.

Ultrastructural changes associated with exsheathment of the infective juveniles of Haemonchus contortus are described. Hyaline ring formation occurs associated with annulations 10 and 20 and consists of the dissolution of the basal zone and the inner electron-dense layer resulting in the rupture of the sheath. These changes are consistent with the action of a protease-exsheathing enzyme. There is a significant reduction associated with exsheathment in the size of the excretory cells and the number of excretory granules contained within them. No changes in the oesophagus were observed associated with exsheathment. These, and the observations of earlier workers, suggest that it is the excretory cells and not the oesophagus which are the source of exsheathing fluid during exsheathment.

The post-cercarial development of G. crumenifer (Creplin) has been experimentally elucidated.

Gyraulus convexiusculus (Hutton) serves as the intermediate host under natural conditions.

The adult stage of the fluke was raised experimentally in ruminants, the time taken by the parasite to attain maturity being 118 days in the kid and 114 in the buffalo calf.

Cercaria chungathi Peter & Srivastava, 1955, has been established to be the larva of Gastrothylax crumenifer. The cercaria, the redial parthenita and the metacercaria have been described.

The authors are grateful to the Director, Indian Veterinary Research Institute, for his keen interest in these studies.

The nematodes described below were collected by M. L. Emanuel from two specimens of the pouched mouse, at Innisfail, North Queensland. They were very kindly sent to the author by Dr M. J. Mackerras of the Queensland Institute of Medical Research. Both species of parasite were present in both host animals. Trichostrongyles have not previously been described from phascogales but a metastrongyle, two spirurids, and a rictulariid, are listed by Dr Mackerras in her check-list of parasites of Australian mammals (Mackerras, 1958). To these may now be added the present records, the details of which are as follows: Phascogale flavipes (Waterhouse, 1838). Innisfail, Queensland. Nicollina phascogale sp.nov., Tetrabothriostrongylus mackerrasae gen.nov., sp.nov.

Infective 3rd-stage larvae of three species of marine ascaridoid nematodes, Pseudoterranova (= Phocanema = Porrocaecum = Terranova) decipiens, Anisakis simplex and Phocascaris/Contracaecum sp. were cultured in vitro in 0·9% saline or Medium 199 at 37°C beneath an atmosphere of either air or 95% air:5% CO2 All three species responded to culture at 37°C by producing a new cuticle. The majority of P. decipiens completed ecdysis under all the culture conditions employed. Ecdysis in A. simplex was stimulated by a high concentration of CO2; this effect was particularly noticeable in saline cultures. Both A. simplex and Phocascaris/Contracaecum sp. developed more effectively in a nutrient medium than in saline.

No differences in susceptibility or parasite distribution of avirulent Toxoplasma was observed between biotin-, pantothenic acid-, nicotinic acid-, riboflavin- and heat-labile vitamins-deficient chicks and their controls. Ordinary diet supplemented with cod-liver oil did not have any effect either. Avirulent Toxoplasma were readily isolated from the brains of all the animals at the end of 1 month.

We are grateful to Professor P. C. C. Garnham for his interest.

The capillariid nematodes present in passeriform hosts collected in Taiwan are recorded and described. Two new species are established, Capillaria parusi sp.n. from Parus monticolus insperatus and Sitta europaea formosana, and C. madseni sp.n. from Corvus macrorhynchus colonorum, and their affinities are discussed. Capillaria tridens, C. longifila and C. contorta are recorded from a number of new hosts.

The growth of an axenic strain of Entamoeba invadens in two media (Trypticase–liver broth and Trypticase–Panmede) is compared with that of a monobacterial strain in diphasic medium supplemented with starch. The axenic strain multiplied more slowly, and produced lower yields of amoebae than the monobacterial strain.

Amoebae multiplied more rapidly and produced higher yields in Trypticase–liver broth than in Trypticase–Panmede.

The effect of certain variations in the basic Trypticase–Panmede medium was investigated. Serum stimulated the growth of the axenic strain in Trypticase–Panmede, so that although the initial multiplication rate was not increased, the maximum yields of amoebae were increased to levels that varied according to the concentration of the serum.

The multiplication of the axenic amoebae was depressed by procedures which probably aerated the medium.

I thank Dr L. S. Diamond for axenic strain NIH:200 of E. histolytica, and Professor E. Meerovitch for axenic strain PZ of E. invadens. I am much indebted to Dr P. Whittlestone, of the Department of Animal Pathology, Cambridge, who examined cultures of strain N for the presence of mycoplasmata. The work was carried out while the author was a member of the scientific staff, Medical Research Council.

We report the discovery of a biological rhythm in the reproductive behaviour of the tick Bothriocroton hydrosauri that was absent in Amblyomma limbatum, a species that occurs on the same species of reptile host. Female B. hydrosauri mated in autumn or winter delayed oviposition until the following spring, while there was no diapause in conspecific females mated in spring or early summer. Initiation of ovipositional diapause in ticks is usually related to photoperiodic stimuli, but this was not the case for B. hydrosauri. The sinusoidal pattern in pre-oviposition times of B. hydrosauri females mated in different months in the laboratory suggests an internal seasonal time-keeping mechanism. We hypothesize that hormones imbibed by females during their bloodmeal may provide environmental cues associated with the induction of diapause. Irrespective of the mechanism underlying the rhythm, diapause by B. hydrosauri females mated during autumn or winter is of adaptive advantage because it synchronizes oviposition with favourable environmental conditions for egg hatching and increases the chance of larvae finding a host. The lack of a similar biological rhythm in A. limbatum may be a reflection of the different environmental conditions this species experiences throughout most of its range as compared with B. hydrosauri.

Theileria parva is an intracellular protozoan parasite transmitted by ticks that causes a fatal lymphoproliferative disease of cattle known as East Coast Fever. Vaccination against the disease currently relies on inoculation of the infective sporozoite stage of the parasite and simultaneous treatment with long-acting formulations of oxytetracycline. Sporozoites are maintained as frozen stabilates of triturated infected ticks and the method requires accurate titration of stabilates to determine appropriate dose rates. Titration has traditionally been undertaken in cattle and requires large numbers of animals because of individual variation in susceptibility to infection. An alternative tissue culture-based method is laborious and time consuming. We have developed a flow cytometric method for quantifying the infectivity of sporozoite stabilates in vitro based on the detection of intracellular parasite antigen. The method allows clear identification of parasitized cells with a high degree of sensitivity and specificity. Analysis of infected cells between 48 and 72 h post-infection clearly defines the potential transforming capability of different stabilates.

Giardia lamblia is one of the most prevalent parasites of mankind and is estimated to cause over 200 million infections per year. To screen chemical libraries for compounds that perturb trophozoite proliferation we adapted a conventional culture method to 384-well plates and identified numerous inhibitors. Here we used a modified assay to screen for compounds that promote trophozoite multiplication. Trophozoite growth was reduced by dilution of the culture medium and the growth period was extended to screen 2 compound libraries comprising 1500 compounds. A total of 4 agonists of trophozoite multiplication were identified. In the presence of one of these compounds, strychnine, enhanced growth was accompanied by unusual trophozoite morphology characterized by dividing trophozoites displaying more than the 2 nuclei per cell which are normally observed. The other agonists, although belonging to 2 distinct chemical groups, are known to affect isoprenylation, indicating a link between protein or lipid isoprenylation and growth in culture. Although inhibitors of isoprenylation are known to antagonize proliferation of mammalian cells, an agonistic effect of isoprenylation modulators has to our knowledge not been described previously. These observations illustrate the power of chemical genetics for identifying pathways controlling specific traits in G. lamblia.