An experimental study of hatching in the oxyurid nematode Aspiculuris tetraptera indicates that the major factors in the initiation of hatching are the pH and temperature of the environment and that the process is aerobic. Carbon dioxide and reducing agents do not appear to be as important factors in the hatching of eggs of this nematode as they are in the hatching of eggs of ascarids. It is suggested that the physiology of hatching in ascarids is not necessarily the typical nematode pattern.

My grateful thanks are due to Dr P. Tate, Director of the Molteno Institute, and to Dr D. L. Lee for their encouragement and very helpful discussions on various aspects of this study.

A female-specific sequence was isolated from a cDNA library of Schistosoma mansoni and further characterizedSequences reported here are available from DDBJ/EMBL/GenBank under the Accession number Z27402.. Expression of the corresponding gene (p19) depends on pairing with a male. In situ hybridization and immunohistology experiments revealed exclusive expression of the gene in the cells of the vitellarium, suggesting a function in egg formation. In addition, experimental evidence for cross-linking of the protein under oxidative conditions supports the assumption that the p19 gene may code for an egg-shell precursor protein.

A description is given of the morphology and behaviour of the oncomiracidium of the monogenean D. sagittata. The larva has many features in common with the oncomiracidium of Diplozoon paradoxum but its development is less precocious than the latter. Suggestions are made as to the possible relationships of a pair of degenerate hooks on the haptor.

Female mice survived longer than male mice when infected with 400 eggs but not when infected with 100 eggs of Amplicaecum robertsi.

The larvae grew to greater lengths in young than in older mice; smaller worm burdens were also found in the older animals.

The growth of the larva was associated with the total worm burden of the host. As the worm burdens, of 40-day-old female mice, increased up to 281 individuals the length of the larvae attained after 14 days decreased; when the larval population increased above this number the lengths of the worms also increased.

These crowding effects are discussed in relation to competition for nutrients, immunological suppression of larval growth and to the ability of large larval populations to swamp the resistance mechanisms of the host. It is suggested that the increased growth of the larvae in large populations is due to their ability to break down the liver of the infected host more efficiently than small populations. However, this eventually leads to the deaths of the host through total liver breakdown.

This work was done during the tenure of a Senior Research Fellowship from the Wool Research Board of Australia. My best thanks are due to Mr J. James for his assistance with the statistics, to Professor J. F. A. Sprent for his help and advice and to Mr C. Wilkinson for his assistance.

During the past summer numerous inquiries were received by Professor Elford, Dominion Poultry Husbandman, Experimental Farm, Ottawa, with regard to an apparently infectious disease appearing among ducks. So frequent and insistent were the appeals for aid in this connection that the co-operation of the Health of Animals Branch was requested. This resulted in an investigation being undertaken to ascertain the clinical nature of the disease; to demonstrate, if possible, the cause; and also institute measures for its prevention.

The mouse major histocompatibility complex (MHC) class I sequence was detected in 8-week-old Schistosoma mansoni by in situ polymerase chain reaction (in situ PCR). The signals to the mouse class I MHC sequence were observed in the nuclei of the mesenchymal and reproductive cells of S. mansoni. Signals were also observed in the cytoplasm of the tegumental tubercles. This finding suggested the possibility of MHC gene transfer from the host to schistosomes. Furthermore, the class I MHC sequence was detected in the DNA extracted from the cercariae of S. mansoni by nested PCR. Neither the nucleotide sequence of class I MHC detected in adult worm DNA nor that of class I MHC detected in the host (mouse) DNA was identical with that of class I MHC detected in the cercarial DNA. From the data we assumed that S. mansoni may have retained their own mouse class I MHC sequence in their genome throughout their life-cycle.

In some Biomphalaria glabrata–Schistosoma mansoni combinations snails are susceptible to infection as juveniles, but have variable susceptibility as adults. These snails become non-susceptible at the onset of egg-laying and typically revert to susceptibility in old age. Certain stocks of B. glabrata have the capacity to form amoebocytic accumulations in the atrium, and this ability is under genetic control. The atrial amoebocytic accumulations are transitory, typically appearing at onset of egg-laying and disappearing after a few months. A snail stock which has genetic tendencies for both adult variable susceptibility and atrial amoebocytic accumulations was studied. An association between the time of occurrence of adult non-susceptibility and atrial accumulation is revealed as snails never became infected with S. mansoni when amoebocytic accumulations were present. Developing parasites, however, were not necessarily encapsulated and destroyed by amoebocytes. Some sporocysts were able to delay development until the amoebocytic accumulations disappeared. The timing of atrial amoebocytic accumulations and resulting transient non-susceptibility in this host-parasite combination could influence snail population dynamics.

Flubendazole or thiabendazole were administered orally to mice harbouring larvae of Angiostrongylus cantonensis, Trichinella spiralis, Diphyllobothrium erinacei or Hymenolepis nana 5–10, 28–33 and 21–26 and 1–6 days post-infection respectively. All the mice infected with A. cantonensis were completely cured after treatment with flubendazole at 5 mg/kg/day for 6 days. No noticeable damage was found in the cerebral hemispheres of the mice treated with flubendazole and examined under a dissecting microscope. On the other hand, larvae were found in or on the cerebral hemispheres showing obvious haemorrhage in the control mice. The mice treated with flubendazole gained weight while the control mice lost weight. No larvicidal effect of thiabendazole on A. cantonensis was found at a dose of 10 mg/kg/day for 6 days. The mean reduction of larval T. spiralis in mice treated with flubendazole at 5, 50 and 100 mg/kg/day for 6 days was 64, 100 and 99% respectively. In comparison, thiabendazole showed no efficacy against T. spiralis larvae at 50 or 100 mg/kg/day. Mice harbouring plerocercoids of D. erinacei or H. nana larvae were not cured with either flubendazole or thiabendazole at 50 or 100 mg/kg/day for 6 days.

We examined a host-finding factor of the monogenean Heterobothrium okamotoi oncomiracidia to develop an alternative prophylaxis. H. okamotoi oncomiracidia attached preferentially to gill filaments and skin mucus from the tiger puffer Takifugu rubripes compared with corresponding material from other tested fishes (amber jack Seriola dumerili, red sea bream Pagrus major, Japanese flounder Paralichthys olivaceus and spotted halibut Verasper variegatus). The body mucus pH of the tiger puffer was 6·40±0·09 (mean±S.D.), whereas that for the other tested fishes was 7·2–7·4. To find if this difference in pH could account for the specific targeting of tiger puffer by H. okamotoi oncomiracidia, the attachment response of the oncomiracidia to pieces of agar buffered at various pH between 6·0 and 7·4 was examined. The number of attaching oncomiracidia was maximal at pH 6·4. We produced gynogenetic tiger puffers from a single female. These gynogenetic individuals showed a variety of body mucus pH and they were exposed to the oncomiracidia. Thirteen days after exposure, more young H. okamotoi were found on the gills of gynogenetic tiger puffer with mucus at pH 6·3–6·6, than on gills of fish with mucus at pH 6·0–6·3 and 6·6–7·2. H. okamotoi exploits the body mucus pH to identify the host. The simplicity of pH as a lure may lead to development of a simple and economical method to control H. okamotoi outbreaks.

Ticks and tick-borne pathogens can have considerable impacts on the health of livestock, wildlife and people. Knowledge of tick–host preferences is necessary for both tick and pathogen control. Ticks were historically considered as specialist parasites, but the range of sampled host species has been limited, infestation intensity has not been included in prior analyses, and phylogenetic distances between hosts have not been previously considered. We used a large dataset of 35 604 individual collections and two host-specificity indices to assess the specificity of 61 South African tick species, as well as distinctions between adult and juvenile ticks, for 95 mammalian hosts. When accounting for host phylogeny, most adult and juvenile ticks behaved as generalists, with juveniles being significantly more generalist than adults. When we included the intensity of tick infestation, ticks exhibited a wider diversity of specificity in all life stages. Our results show that ticks of mammals in South Africa tend to behave largely as generalists and that adult ticks are more host-specific. More generally, our analysis shows that the incorporation of life-stage differences, infestation intensity and phylogenetic distances between hosts, as well as the use of more than one specificity index, can all contribute to a deeper understanding of host–parasite interactions.

Megatrypanum trypanosomes have been isolated from a number of different European Cervidae, but on the basis of morphology it has not been possible to define the species to which these isolates belong. We isolated Trypanosoma (Megatrypanum) theileri from 10 cattle, and Megatrypanum trypanosomes from 11 fallow deer (Cervus dama), 9 red deer (Cervus elaphus), and 4 roe deer (Capreolus capreolus) by blood culture on a biphasic medium (NNN agar slopes). Trypanosomes were propagated in Schneider's Drosophila medium and characterized by isoenzyme analysis and molecular karyotyping. Isocitrate dehydrogenase and phosphoglucomutase were visualized after starch gel electrophoresis of trypanosome lysates. By cluster analysis of this data all isolates from deer were clearly separated from the T. (M.) theileri isolates from cattle. Isolates from roe deer were different not only from T. (M.) theileri but also from the other deer isolates. Isolates from fallow deer and red deer were grouped together. Thus, there are probably at least two different species of Megatrypanum trypanosomes in the three Cervidae. One parasitizing roe deer, the other, apparently less host specific species, infecting red deer and fallow deer. Separation of the chromosomes of Megatrypanum trypanosomes by pulsed-field gradient gel electrophoresis (PFGE) showed that each isolate contained a large number (> 18) of chromosomes ranging in size from 300 to > 2200 kb. The molecular karyotypes were similar for all isolates, although no isolate was identical to another.

Cyclin-dependent kinases (CDKs) are essential for the regulation of the eukaryotic cell cycle. A number of chemicals, which selectively inhibit the CDK activities, have been synthesized for the development of anti-cancer drugs. This report describes the inhibitory effect of purine derivatives known to be CDK inhibitors on the asexual growth of Babesia bovis. The 4 compounds, roscovitine, purvalanol A, CGP74514A, and CDK2 Inhibitor II, showed significantly suppressive effects on the in vitro growth of B. bovis. Three (roscovitine, purvalanol A, and CDK2 Inhibitor II) showed an inhibitory effect on the early stages of intraerythrocytic development of B. bovis. CGP74514A (CDK1-specific inhibitor) blocked the erythrocyte invasion by merozoites. Our data suggest the chemotherapeutic potential of the CDK inhibitors for babesiosis, and the target molecules of the compounds would participate in the process of successful erythrocyte invasion or intraerythrocytic development of B. bovis.

Offspring size and performance in invertebrates often decrease with maternal age or as a response to seasonal environment. In viviparous ectoparasites maternal provision may wholly determine offspring performance outside the host. The viviparous deer ked (Lipoptena cervi), an ectoparasite of cervids, breeds from autumn to spring. We reared deer ked pupae through the reproductive period to investigate whether offspring size and performance vary according to maternal age and offspring environment. We expected that, in autumn, young females would produce the largest offspring to ensure that early-born pupae would survive a long period of winter diapause, and that offspring size would decrease with maternal age and decreasing diapause length. Diapause was associated with a significant weight loss, which reduced survival through post-diapause development. It was thus surprising that the early-born offspring were the smallest, and that size and survival (eventually) increased towards the spring. The variability among offspring in the length of off-host period seems to be an important component of life-history evolution in this ectoparasite, and should be studied further. Unexpected seasonal variation in the offspring size of this blood-feeding ectoparasite may result from changes in female resources due to weakening host condition as the winter progresses.

The genus Clavella Oken, 1815, comprises parasitic Copepods belonging to the family Lernaeopodidae. The object of this paper is to dwell upon the following characteristics of the genus:

Members of the genus Clavella are pre-eminently parasitic on Gadoid fishes. (Four British species not occurring on Gadoids have already been removed to other genera; one doubtful species will probably have to follow, and I am suggesting the removal of two more.)

The succinate dehydrogenase of adult Fasciola hepatica was found to exist in active and inactive forms. The enzyme was inactivated by 1 μM oxaloacetate and activated by incubation with compounds which bind to the active site (succinate, fumarate, malonate) or by incubation with anions and certain nucleotides. The activation of the enzyme by succinate followed first-order kinetics. The extent of activation of F. hepatica succinate dehydrogenase depended on the nature and concentration of the activator and on the pH. The rate of activation of the enzyme depended on the temperature. In contrast, the fumarate reductase activity of F. hepatica was not activated by incubation with substrate or anions and was not inhibited by oxaloacetate (100 μM). The significance of these results in the regulation of the tricarboxylic acid cycle in parasitic helminths is discussed.

Draft genome sequences for Schistosoma japonicum and S. mansoni are now available. The schistosome genome encodes ∼13 000 protein-encoding genes for which the functions of few are well understood. Nonetheless, the new genes represent potential intervention targets, and molecular tools are being developed to determine their importance. Over the past 15 years, noteworthy progress has been achieved towards development of tools for gene manipulation and transgenesis of schistosomes. A brief history of genetic manipulation is presented, along with a review of the field with emphasis on reports of integration of transgenes into schistosome chromosomes.

Head lice transmit to new hosts when people lean their heads together. Humans frequently touch their heads to express friendship or love, while this behaviour is absent in apes. We hypothesize that this behaviour was adaptive because it enabled people to acquire head lice infestations as early as possible to provoke an immune response effective against both head lice and body lice throughout the subsequent periods of their life. This cross-immunity could provide some defence against the body-louse-borne lethal diseases like epidemic typhus, trench fever, relapsing fever and the classical plague. Thus the human ‘touching heads’ behaviour probably acts as an inherent and unconscious ‘vaccination’ against body lice to reduce the threat exposed by the pathogens they may transmit. Recently, the eradication of body-louse-borne diseases rendered the transmission of head lice a maladaptive, though still widespread, behaviour in developed societies.

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.

Three groups of chickens were fed small numbers of ova (3, 5 or 9 ova per bird) of Heterakis gallinarum in a quantitative study of the transovarial transmission of Parahistomonas wenrichi by the nematode. Subsequent incidence rates of Parahistomonas infections in recipient birds were analysed according to the methods of Chiang & Reeves (1962). The results indicated that at least 25 % of Heterakis ova, passed in the faeces of birds with concomitant Parahistomonas infection, carried the protozoon. The appearance of Parahistomonas in a bird which retained all its challenge nematodes indicated that the protozoon can be released by living worms. Data on the pre-patent periods of Parahistomonas infections are consistent with a hypothesis that the protozoon is typically released at the time of the final (fourth) moult of the nematode.

The flagellate to be described in this paper was found in the faeces of a native of the Bahamas who was admitted to the Seamen's Hospital, Albert Dock, in October, 1909. In the course of the examination of the perfectly fresh material it was noticed that numerous flagellates were swimming about. They were taken to be Trichomonas but on closer examination they were seen to differ markedly from these. In the character of their movements there was little to distinguish them from Trichomonas except that the undulating membrane so characteristic of this genus appeared to be absent. The body is pear shaped and there are three long flagella directed forwards from the blunt end of the body. By the lashing of these three flagella the animal is drawn along with the blunt end in advance and at the same time revolves upon its longitudinal axis. A very characteristic feature is the presence of a very large cytostome extending from the base of the three flagella towards the posterior end of the body for about one half to two thirds of its length. The movements of the animals were at first so violent that great difficulty was experienced in making out the details of the anatomy, but as the faeces cooled their activities began to abate. It was then seen that the flagella was as long or longer than the body and that the large cytostome was arranged in a slightly spiral manner: that is to say it did not run directly parallel to the longitudinal axis of the body.