Vitellogenin synthesis by the fat body has been monitored using in vitro culture and immunoprecipitation. This system was found to be efficient for measuring vitellogenin production in both non-infected Tenebrio molitor and those infected with Hymenolepis diminuta. In fat bodies from infected beetles, vitellogenin production was decreased by up to 75% (day 24 post-infection) and, at all times investigated, vitellogenin synthesis was significantly below control levels (days 3–30 post-infection). Incubating fat bodies from control insects with isolated metacestodes indicated that this may be a direct effect by the parasite which is developmental stage-specific. Stage II, but not stage III–IV, nor heat-killed parasites could bring about this decrease in vitellogenin. In addition, these effects may be density dependent within the range of 2–20 parasites per fat body; only 2 metacestodes were necessary to cause a significant decrease. Since metacestodes do not take up vitellogenin, nor limit the amount of [14C] leucine available to the fat body for vitellogenin production, it is conceivable that the parasite produces a potent inhibitor of vitellogenin synthesis, or a molecule which induces cells within the fat body to do so.

The schistosome intermediate snail host, Bulinus truncatus (Mollusca: Planorbidae), has two reproductive (phally) morphs. Both aphallics and euphallics can self-fertilize, but aphallics cannot donate sperm because they do not develop a functional penis and prostate. This study investigated the interactions between phally and fitness consequences of Schistosoma haematobium infection in B. truncatus. Snails which developed patent infections produced 26% fewer eggs than controls and 35% fewer eggs than exposed snails which did not develop infections. This reduction was due to a lower lifetime production of egg masses and a smaller mean number of eggs/mass in infected snails relative to control or exposed snails. However, there was no evidence of increased mortality in infected snails. Contrary to reports of fecundity compensation in other intermediate host snails, egg production post-exposure during the pre-patent period did not increase relative to that of controls in either infected or exposed snails. Phally did not influence susceptibility to infection or length of the prepatent period. Furthermore, lifetime egg, egg mass and hatchling production, as well as mean eggs/mass and number of hatchlings reaching maturity, did not differ significantly between aphallics and euphallics within control or exposed experimental groups. However, within the infected group euphallics produced 38% fewer eggs, smaller egg masses, and fewer hatchlings reaching maturity than aphallics, supporting the prediction of a cost to the growth and maintenance of a full male tract. This cost was detectable only when snails were under the stress of infection. The proportion of euphallic offspring produced did not differ across experimental groups. We discuss these results in light of alternative host strategies to minimize fitness costs of infection.

The germinal layer of sterile 9-month-old murine peritoneal cysts of Echinococcus granulosus equinus shows interrelated variation in depth, tissue integrity, metabolic reserves and the number of autophagic lamellar bodies present. These features are similar in large and medium-sized cysts from the same host, whether occurring singly or within cyst masses. Deep germinal layers (> 16 μm) are lipid- and glycogen-rich and possess numerous autophagic vacuoles with 6 nm period lamellar stacks asymmetrically disposed peripherally; shallow layers (< 12 μm), with indications of degeneration, have depleted metabolic reserves and fewer lamellar bodies. These bodies are formed by smooth endoplasmic reticulum encirclement of small glycogen masses followed by further sequestration, and eventually definition of glycogen particles may be lost. Autophagy of mitochondria and cytoplasmic vesicles also occurs. The presence of lysosomal enzymes within the layer suggests autolysosomal compartmentalization of excess substrate and effete material. Mucopolysaccharide bodies, containing material similar to that exocytosed to form the laminated layer matrix, occur and are formed from fusion and autophagy of Golgi-derived vesicles. These bodies may also develop peripheral 6 nm period lamellar stacks, but of limited depth. Mucopolysaccharide bodies are the dominant feature of the germinal layer of very small cyst-mass cysts in which laminated layer production is considered to be arrested. They thus represent a repository for the unreleased mucopolysaccharide material.

The infectivity of Heterorhabditis megidis infective juveniles (IJs) increases during storage in water. We investigated whether this change can be related to other features of the IJs' behaviour. IJs were stored in water for 4 weeks at 20 °C, and the following parameters were assessed at intervals: infectivity for Galleria mellonella, dispersal in sand, host-finding on agar, and the percentage of IJs active in water. In addition, the behaviour of the IJs in water was described using 7 categories. Immediately after emerging from the host cadaver, IJs were highly active (99% of IJs in water were active and 65% displayed ‘waving’, the normal method of forward movement). Maximum responsiveness to host volatiles in an agar plate assay was recorded on day 2 (69% of IJs moved from the point of application and 44% of all IJs in the agar arena moved towards a host) and maximum dispersal in sand (5·8 cm) on day 0. These tendencies declined gradually with age, while infectivity underwent a significant increase from 11 nematodes per insect on day 0 to 38 nematodes per insect on day 9. Three phases could be distinguished in the behaviour of H. megidis IJs: an initial dispersal phase, during which infectivity was low; an infective phase, during which dispersal tendency was declining, and a third phase during which all behaviours (dispersal, infectivity and activity) were declining. Over the 4-week storage period, infectivity of H. megidis IJs was correlated (R2 = 0·83) with the percentage time IJs engaged in ‘head thrusting’ (a behaviour that resembles penetration). There is no evidence that the observed increase in infectivity of H. megidis strain UK211 could be accounted for by a generally greater level of motor activity, nor by an increase in responsiveness to volatile host cues, and it is suggested that it is due to an increased tendency to attempt penetration.

Our knowledge of this interesting group of mites has been built up by the writings of some twenty-two acarologists, of different nationalities, whose papers are published in some four or five languages and have appeared in thirty to forty journals.

Methods for screening compounds against Eimeria tenella in cell culture and in the chicken are described. An analysis for incidence of anticoccidial activity and host cell toxicity has been made of 11550 compounds screened in vitro, and some correlation of activity in vitro and in vivo has been attempted. The results show that screening compounds in tissue (cell) culture is not a satisfactory or reliable alternative to screening in chickens, although in vitro studies undoubtedly have a part to play in the evaluation of an active drug.

A Batch of twenty-nine larvae of Stegomyia scutellaris Walker, were collected on 24 July 1920 from an old earthenware pot found in a Malay's garden. It was at once seen, even with the unaided eye, that many, some considerably paler than others, were characterised by a pearly-white opalescence of the tracheal gills at the hinder end of the body.

Uncertainty and disagreement still exist among protozoologists regarding the proper name of the trichomonad flagellate which is commonly found in the human mouth and generally called “Trichomonas buccalis”. The nomenclature of this organism undoubtedly presents several awkward problems; but I believe all of them can be solved simply and satisfactorily if we merely read aright the description recorded by its discoverer, and consequently recognize the validity of his original specific name.

The durations of the various phases of the life-history of the ixodid tick H. anatolicum anatolicum are described with particular reference to the modifying influence of temperature and relative humidity. An increase in the ambient temperature was found to decrease the length of the feeding, preoviposition, oviposition, larval and nymphal moulting periods and the egg-incubation period. The effect of change in relative humidity was less marked, the only significant effect being on the oviposition period which was protracted when the relative humidity was increased.

Daily percentage water loss and longevity were found to be more or less inversely proportional. Thus at high temperatures and low relative humidities a large percentage of water was lost daily with consequent reduced life span.

I wish to thank Dr R. P. Chaudhuri for providing me with the specimens of H. anatolicum anatolicum from which the culture was started, and Professor D. R. Arthur for his advice and assistance. I am also grateful to the Science Research Council for the provision of a research grant.

Cercariae of Psilotrema oligoon and Notocotylus attenuatus encyst free to form multilayered, hemispherical cysts. The former consists of four layers in which the innermost (layer 4) is divided into two, chemically and structurally different, areas. Cysts of the latter have three layers in which the innermost (layer 3) is again divided into two chemically different parts. A third cyst, produced by the encystment of Cercaria tarda in the tissues of Limnophilus flavicornis, is spherical and contains three layers (of which the outermost was not studied).

All of the cysts studied contain a high proportion of protein, which in some layers occurs combined with carbohydrates. In both free-encysting species the two outer layers are produced by expansion of a non-cellular layer covering the integument and the innermost layer is produced by secretion of bâtonnets from a layer of cells lying beneath the body wall. Cysts of P. oligoon are divided into two separate parts, each having two layers, whereas those of N. attenuates consist of a single three-layered wall. The innermost layer in both consists of a protein with disulphide and sulphydryl linkages, and in the cyst of P. oligoon it has a circular ventral area containing carbohydrates. A similar carbohydrate-containing area occurs in the innermost layer of the cyst of N. attenuatus but as a ventro-lateral ring of material. The cyst of Cercaria tarda is also predominantly proteinaceous and stains intensely for RNA.

The study of Aptinothrips rufus made in 1930, in the vicinity of Edinburgh, revealed the presence of a nematode parasite in the insect which seemed worthy of investigation. Little is known of the parasites of Thysanoptera in general, and I can find no record of any parasite of Aptinothrips.

There is considerable confusion concerning Sarcocystis species in camels. Five species: Sarcocystis cameli, Sarcocystis ippeni, Sarcocystis camelicanis, Sarcocystis camelocanis and Sarcocystis miescheri were named with inadequate descriptions and no type specimens. Here, we review literature on sarcocystosis in camels worldwide and redescribe structure of S. cameli and S. ippeni sarcocysts by light- and transmission electron microscopy (LM and TEM). Eight sarcocysts from the oesophagi of two camels (Camelus dromedarius) from Egypt were studied. By LM, all sarcocysts were thin-walled with barely visible projections on the cyst walls. By TEM, two structurally distinct sarcocysts were recognized by unique villar protrusions (vp) not found in sarcocysts from any other host. Sarcocysts of S. cameli had vp of type 9j. The sarcocyst wall had upright slender vp, up to 3·0 µ m long and 0·5 µ m wide; the total thickness of the sarcocyst wall with ground substance (gs) layer was 3·5 µ m. On each vp, there were rows of knob-like protrusions that appeared to be interconnected. The vp had microtubules that originated at midpoint of the gs and continued up to the tip; microtubules were smooth, without any granules or dense areas. Bradyzoites were approximately 14–15 × 3–4 µ m in size with typical organelles. Sarcocystis ippeni sarcocysts had type 32 sarcocyst wall characterized by conical vp with an electron dense knob. The total thickness of the sarcocyst wall (from the base of gs to vp tip) was 2·3–3·0 µ m. The vp were up to 1·2 µ m wide at the base and 0·25 µ m at the tip. Microtubules in vp originated at midpoint of gs and continued up to tip; microtubules were criss-crossed, smooth and without granules or dense areas. Bradyzoites were 12·0–13·5 × 2·0–3·0 µ m in size. Sarcocystis camelicanis, S. camelocanis and S. miescheri are considered invalid.

The role of acquired immunity in lymphatic filariasis is uncertain. Assuming that immunity against new infections develops gradually with accumulated experience of infection, models predict a decline in prevalence after teenage or early adulthood. A strong indication for acquired immunity was found in longitudinal data from Pondicherry, India, where Mf prevalence was highest around the age of 20 and declined thereafter. We reviewed published studies from India and Subsaharan Africa to investigate whether their age-prevalence patterns support the models with acquired immunity. By comparing prevalence levels in 2 adult age groups we tested whether prevalence declined at older age. For India, comparison of age groups 20–39 and 40+ revealed a significant decline in only 6 out of 53 sites, whereas a significant increase occurred more often (10 sites). Comparison of older age groups provided no indication that a decline would start at a later age. Results from Africa were even more striking, with many more significant increases than declines, irrespective of the age groups compared. The occurrence of a decline was not related to the overall Mf prevalence and seems to be a chance finding. We conclude that there is no evidence of a general age-prevalence pattern that would correspond to the acquired immunity models. The Pondicherry study is an exceptional situation that may have guided us in the wrong direction.

The molecular karyotypes of several different protozoan parasites show high intra-species variation, including different kinetoplastids such as Trypanosoma brucei, Trypanosoma cruzi and Leishmania ssp. In this study, the molecular karyotype of Trypanosoma rangeli was examined. To evaluate potential intra-species molecular karyotype variations, 16 different samples were studied by pulsed field gel electrophoresis (PFGE) followed by ethidium bromide staining and hybridizations with 6 different probes. The result showed that different T. rangeli populations are highly polymorphic regarding the molecular karyotype, and thus suggests that PFGE analysis can be used for classification of different T. rangeli isolates. In addition, the molecular karyotype of T. rangeli was compared to molecular karyotypes of other kinetoplastids, and was shown to be distinctly different from that of T. cruzi, but shows some similarities with the karyotype described for T. brucei. Among the probes used one was identified as highly polymorphic, and thus informative for studies of different T. rangeli populations, and another was useful for differentiation between T. rangeli and T. cruzi.

The perch was the principal host for the plerocercoid of Triaenophorus nodulosus in Llyn Tegid.

Three stages of plerocercoid development were recognized: non-encapsuled developing plerocercoids, encapsuled but living mature plerocercoids, and dead encapsuled degenerate plerocercoids.

The stomach contents of the perch were analysed and planktonic crustaceans were found to be a significant part of the food from May to December. No change in diet in relation to length was found.

The period of occurrence of developing plerocercoids in the perch livers was March to June. This in relation to other evidence was shown to indicate the period of infection of the perch by the procercoids.

The three stages of plerocercoid development recognized were found to occur simultaneously in a few perch, and thus may represent infections acquired over three successive seasons.

There was no seasonal periodicity of occurrence of the plerocercoids in the perch.

All the perch examined were more or less equally infected by plerocercoids. There was no tendency for older, longer perch to be more heavily infected.

One to five capsules, normally containing one plerocercoid each, occurred in the livers of the infected perch.

For the perch examined there was a dynamic equilibrium between establishment of procercoids from the copepod host, and loss of plerocercoids by degeneration within the perch.

The mature plerocercoids form the reservoir of infection for the definitive host of T. nodulosus, the pike.

The leucocyte responses in peripheral blood and pulmonary airways are described following vaccination of mice with radiation-attenuated parasites, and subsequent challenge with normal parasites. Percutaneous vaccination stimulated a large and sustained expansion of the circulating lymphocyte pool, more marked than after intradermal vaccination with lung schistosomula which induced comparable levels of resistance. Macrophages and lymphocytes infiltrated the pulmonary airways in response to vaccination by both routes, the lymphocytes being particularly abundant after intradermal vaccination. Exposure of mice to an equivalent number of normal cercariae induced an earlier lymphocytosis of short duration; far fewer macrophages and lymphocytes infiltrated the lungs than after vaccination. An intense but transient pulmonary eosinophilia peaked at 3 weeks after primary exposure to either normal or attenuated parasites. Percutaneous challenge of vaccinated mice elicited higher levels of circulating lymphocytes than challenge of unsensitized controls. However, whilst leucocyte numbers of all cell types were still elevated in the airways at challenge as a consequence of vaccination, no further cellular recruitment was observed coincident with parasite elimination. Our data are compatible with the hypothesis that the mechanism of immunity in once-vaccinated mice involves a T lymphocyte-macrophage interaction triggered by antigen release from lung schistosomula.

Trichonema larvae are affected by light of visible wavelengths and there is a klinokinetic response to light intensity, the smallest rates of turning occurring in light of about 300 ft-c, and the rate of turning increasing with increased intensity (900 ft-c). In dim light the vertical migration of larval nematodes would be greatest, which explains in part the large recoveries from grass at dawn and dusk.

I thank Professor O. W. Richards, F.R.S., for permission to work at the Imperial College Field Station, and Professor B. G. Peters for help and advice. The work was financed by the Department of Scientific and Industrial Research.

The toxicity of cadmium, zinc and cadmium/zinc mixtures at concentrations ranging from 1000 to 50000μg/l were investigated against cercariae and metacercariae of Parorchis acanthus obtained from the dog whelk Nucella lapillus. Cercarial encystment at concentrations of 25000μg/l or higher was significantly impaired by all test metals; however, at lower concentrations only zinc demonstrated toxicity. Mixtures of cadmium and zinc had a synergistic effect compared with single metal toxicity but only at 50000μg/l. Excystment in vitro was only significantly affected by cercariae exposed to cadmium/zinc mixtures whilst encysting. Twenty-four h exposures of fully formed cysts had no effect on excystment in vitro. Effects on in vitro excystment rates over a 2h period demonstrated widespread effects for cercariae-exposed P. acanthus. No effects were evident on excystment rates of cyst-exposed parasites.

Distribution of Leptorhynchoides thecatus (Acanthocephala: Rhadinorhynchidae) among the pyloric caeca and the relationship between site and rate of maturation were studied in laboratory infectons of 10, 25 and 40 cystacanths fed to green sunfish, Lepomis cyanellus. After 1 week fish fed at each intensity had significantly different numbers of worms. By the 3rd week post-infection, parasites disappeared from the anterior portion of the intestine. At this time the mean numbers of worms recovered from 25 and 40-cystacanth infections were not significantly different. At the end of the 1st week, the area where caeca join the alimentary tract (between caecal area) and caeca numbered 6 and 7 contained significantly more worms than the other sites. By the 3rd week post-infection only caecum 7 contained significantly more worms, and at 5 weeks there was no significant difference between the number of worms present in any caecum or the between caecal area. Initially worms in the more intense infections matured more slowly, but by the 3rd week post-infection there was no significant difference in the states of maturity. The rate of maturation was not related to the site occupied.

Contrapsin, a serine protease inhibitor (serpin) present in mouse serum, was compared with that found in adult Schistosoma mansoni worm homogenates, which although immunologically identical to contrapsin in mouse serum, had a higher molecular weight in Western blotting. Immunolocalization studies demonstrated parasite-associated contrapsin on the surface and interstitial cells of adult male worms. After extraction of these parasites with Triton X-114, contrapsin was found in the aqueous phase of the detergent, suggesting it is unlikely to be an integral membrane protein. Treatment of adult worms with deoxycholate resulted in a change in the electrophoretic behaviour of worm-derived contrapsin. Parallel studies with trypsin suggested this was due to interaction of the serpin with a protease. Using porcine pancreatic trypsin as a model for a putative schistosome protease reacting with contrapsin, we have shown that trypsin, following complex formation with contrapsin, loses immunogenicity. Thus, when contrapsin–trypsin complexes were used as immunogen, the resulting antisera contained antibodies to contrapsin and contrapsin–trypsin complexes only, and none to native trypsin. Thus, epitopes characterizing native trypsin were presumably either masked following complex formation with contrapsin, or their processing and presentation to antigen presenting cells was suppressed, so that an antibody response was not mounted against them. These observations encourage speculation that S. mansoni may be elaborating an immune evasion strategy whereby immunologically sensitive proteases are first complexed with host serpins, which would render them immunogenically inert, and then cleared from the circulation by the host's reticulo-endothelial system. In this way the immune system would be unable to ‘see’ sensitive parasite proteases sufficiently to mount a response against the parasite.