Freshly isolated oocysts were sporulated at 29°C with constant aeration. Minimum sporulation time was determined by dosing the developing oocysts at intervals of 1 h to successive groups of chickens to assess the first occurrence of infective forms. Microscopic analysis of the sporulating oocysts allowed calculation of the time required for 50% of the oocysts to complete the process. This was considered to be the most accurate determination and the most useful for comparative purposes. For 7 species of coccidia in the fowl, the 50% sporulation times were as follows: Eimeria acervulina 11·4 h; E. brunetti 38·3 h; E. maxima 38·1 h; E. mivati 19·0 h; E. necatrix 19·7 h; E. praecox 24·8 h; E. tenella 21·2 h.

The serial passage of 3 strains of Eimeria from the chicken in embryonating turkey embryos is reported here. All 3 strains increased their reproduction in turkey embryos; reproduction being equal to or better than the same lines maintained in chicken embryos. Pathogenicity and immunogenicity trials conducted in chickens using these 3 strains of Eimeria showed that all 3 turkey embryo-adapted lines were significantly less pathogenic than the parent lines. Only 1 of the lines (E. tenella (PS) turkey embryo-adapted) maintained its immunogenic potential

The proteins in the soluble and membrane fractions of Plasmodium lophurae, separated by SDS-PAGE and stained with Coomassie blue, were distinct from one another and different from the soluble and membrane proteins of the host cell, the duckling erythrocyte. Pulse-labelling of malaria-infected red cells containing schizonts or trophozoites with [14C]isoleucine, followed by parasite isolation, SDS-PAGE and autoradiography, showed a pattern of incorporation into soluble proteins identical to the banding pattern of gels stained with Coomassie blue. On autoradiograms, the banding patterns of the membrane proteins of trophozoites and schizonts labelled with [14C]isoleucine were similar. No qualitative differences in the soluble proteins of trophozoites and schizonts were apparent when isoleucine was used as the radiotracer; however, the banding pattern of membrane and soluble proteins labelled with [14C]isoleucine were distinct from each other. The banding pattern of soluble proteins, after staining with Coomassie blue, was distinctly different from the array of bands seen after autoradiography of parasites derived from infected cells pulse-labelled with [14C]histidine. Only small amounts of contaminating haemoglobin in the soluble protein fraction of parasites were labelled with histidine; the membrane fraction, on the other hand, had high incorporation into a single 43 kDalton band, the histidine-rich protein. No band differences, either in the membrane or soluble fractions, were observed in autoradiograms after pulse-labelling trophozoites and schizonts with [14C]histidine. The most consistent and distinct differences in protein synthesis were seen in P. lophurae pulse-labelled with [14C]proline. Autoradiograms of both soluble and membrane fractions showed the presence of bands unique to the trophozoite and schizont–stage-specific proteins.

Six samples of rodent blood infected with malaria parasites were isolated from Cameroon. Of these, 2 contained mixed infections of Plasmodium vinckei and P. yoelii, 3 contained P. vinckei alone and 1 P. chabaudi alone. Each isolate was cloned and the resulting lines examined for morphology of blood and mosquito forms, and for electrophoretic variation in enzymes. The P. chabaudi and P. yoelii lines were morphologically and enzymically identical to isolates of the Central African Republic. Similarly, 1 P. vinckei line was identical to an isolate of the Central African Republic. The remaining 4 P. vinckei lines showed considerable variation, some enzymes being like those in isolates of surrounding regions, while others were unique to Cameroon.

The interactions in vivo between Plasmodium berghei sporozoites and Kupffer cells in rat livers were studied by transmission electron microscopy. By 10 and 15 min after inoculation, sporozoites were both free in the liver sinusoids and inside endocytotic vacuoles of the Kupffer cells. The latter cells were very active in phagocytosing sporozoites, bacteria and red blood cells. The sporozoites retained their integrity inside the endocytotic vacuoles and no signs of lysosomal digestion were observed. Sporozoites seen within endocytotic vacuoles 1 h after inoculation were still morphologically intact, although bristle-coated vesicles fused with the vacuole membrane. Evidence is presented which suggests that Kupffer cells transport sporozoites towards the space of Disse and adjacent hepatocytes. No sporozoites were seen to penetrate an endothelial cell or its narrow fenestrae. It is proposed that Kupffer cell passage, rather than gaps in the sinusoidal lining, represents the normal route that sporozoites take to circumvent the endothelial barrier. The localization of exo-erythrocytic forms was made easier by the use of Brown Norway rats in which many more parasites develop than in the Wistar rats. The distribution pattern of the parasites was found to be mainly around the ‘periportal’ zones of the acini of liver tissue.

Experiments were carried out to determine the susceptibility of mammalian cells to infection with different species of Theileria in vitro. Sporozoites of Theileria parva (parva), Theileria parva (lawrencei) and Theileria taurotragi were isolated from Rhipicephalus appendiculatus ticks by grinding infected ticks in medium, filtering the suspension and concentrating by centrifugation. The sporozoites were used in attempts to infect in vitro peripheral blood leucocytes harvested from 16 different mammalian species which included 12 species of Bovidae from 6 different sub-families. The technique was shown to be both sensitive and reproducible. The sporozoites of T. parva (parva) infected and transformed cells from 2 species of the sub-family Bovinae, the two cattle types and African buffalo. Theileria parva (lawrencei) infected and transformed cells from the two cattle types, African buffalo and Defassa waterbuck. Theileria taurotragi sporozoites infected in vitro cells from 11 different species of Bovidae which were members of 6 sub-families; Bovinae, Tragelaphinae, Reduncinae, Alcelaphinae, Antilopinae and Caprinae. Transformed lymphoblastoid cell lines were established from 7 of the species infected. Sporozoite attachment and infection was not observed with non-susceptible bovid host cells, nor were any of the non-bovid leucocytes infected by the parasites. The host range observed in this study corresponded to the known host range in vivo.

A 2 hectare paddock on the Muguga Estate, Kiambu District of Kenya (altitude 2100 m) free of Theileria parva-iniected ticks was seeded by applying Rhipicephalus appendiculatus nymphs to cattle infected with Theileria parva (Kiambu 4). It was estimated that over 50000 engorged nymphs fell onto the pasture from 4 cattle with high parasitaemias during the cold season (June). Samples of these ticks were placed in plastic cylinders under the vegetation in the paddock and sexual stages of T. parva were detected in gut lumen smears in these samples up to 21 days alter repletion. Zygotes were first observed to transform into kinetes on day 55 and parasites were first detected in salivary glands of adults on day 64. Moulting of the nymphs started on day 60 after repletion and was completed by day 87. Cattle introduced into the paddock showed their first infestation with adult R. appendiculatus on day 64 after repletion of the nymphs and the infestation level gradually increased. On day 76 after repletion, 17% of a sample of adult ticks infesting cattle showed salivary gland infections with T. parva and this increased to over 70% by day 150. From day 360 onwards, a decrease in both the percentage of ticks infected and the number of salivary gland acini infected/tick was noted. In addition, T. parva infections within the salivary glands required a longer period of feeding in the older ticks before they developed into sporozoites. Cycling of Theileria through ticks was prevented by the removal of female ticks before they completed repletion. Lethal challenge levels of T. parva for cattle existed in the paddock up to day 547 after repletion, after which introduced cattle showed no infection or only a sub-lethal infection. Cattle introduced into the paddock on day 808 after repletion showed no evidence of T. parva infection. The tick infestation of introduced cattle decreased markedly from day 368 and infestation had virtually ceased by day 808

Theileria annulata was transmitted transtadially by an Israeli strain of Hyalomma excavatum from larvae to nymphs and from nymphs to adults. However, the adults developing from larvae which engorged on infected calves and fed during the nymphal stage on non-infected calves, rabbits or gerbils (Meriones tristrami), did not transmit theileriosis. Suspensions of infected unfed nymphs or adults did not produce theileriosis but both nymphs and adults of the same batch became infective to cattle after 2 days of feeding. Suspensions of salivary glands or of whole ticks derived from infected adults that remained attached to rabbits for more than 7 days, were not infective to cattle.

Growth of Hymenolepis nana in mice is analysed by identifying designated stages of proglottid maturation in the strobila, and by determining the numbers of proglottids between them and the posterior terminus of the worm, as a function of time after cysticercoid infection. The proglottid maturation rate was fairly constant between stage A (onset of the somatic primordium formation) and stage B (first appearance of sperms in the seminal vesicle), but gradually fell after stage B, during pre-patent development of the worm. The actual rate of proglottization during this period coincided well with that estimated from the number of proglottids between stages A and B on an assumption of a certain maturation rate. This procedure is extended to estimate the rates of proglottid formation and shedding during later development. It is deduced that the absolute rate of proglottization increases until day 12, gradually decreasing afterwards, and that from 2300 to 2800 proglottids are shed by day 20, until which from 4000 to 4500 proglottids have passed stage A. It is shown that the proportionate increase of the gravid region in older worms depends not only on a decrease in the rate of proglottization, but also on the prolonged period during which proglottids stay in the strobila.

In this study, we have developed a reliable radioimmunoassay (RIA) for Ascaris suum protein (Asp) and have measured the serum concentration of Asp in control subjects and in patients with helminthiasis and a variety of gastrointestinal diseases. The cross-reactivities of Asp antibody with other helminth worm antigens were also measured by RIA. Ascaris lumbricoides contained approximately the same amount of Asp antigenic substance as did Ascaris suum. Toxocara canis had a high concentration of a substance partially cross-reactive with Asp. Small amounts of substance cross-reacting with Asp were also exhibited by Anisakis larvae, Schistosoma japonicum and Taenia saginata. However, no cross-reactivities of Fasciola hepatica and Paragonimus westermani with Asp were observed in this study. Almost all the serum levels of Asp from normal control subjects were below the sensitivity of this RIA (10 ng/ml). High concentrations of Asp were observed in sera from patients with ascariasis (64.5±18.8 ng/ml: mean ± S.E.), anisakiasis (75.2±28.0 ng/ml), toxocariasis (78.4±31.3 ng/ml) and schistosomiasis japonica (14.3±3.4 ng/ml). Asp levels in sera from patients with other helminthiasis were not significantly high. From these findings, it was suggested that RIA for Asp may not be specific for diagnosis of ascariasis, but might be a suitable screening method for patients with some kinds of helminthiasis. Interestingly, high concentrations of Asp were also observed in sera from patients with ulcerative colitis (24.8±2.5 ng/ml) and Crohn's disease (19.8±5.2 ng/ml), but Asp levels from 7 other gastrointestinal diseases seemed not to be significantly high. These findings remain unexplained but may derive from cross-reactivities between helminthic and gut mucosal antigens.

The results of an epidemiological study involving the estimation of worm counts of gastro-intestinal nematodes of lambs, during the period December 1978 to November 1979, in the Baghdad area are reported. Ostertagia spp. and Trichostrongylus spp. were the most abundant nematodes in the weaned lambs used in this study. Ostertagia spp. infection was present throughout the period of observation, the level of infection being the highest during early summer (May–June). Trichostrongylus spp. infection, however, reached a peak during July–August. In the tracer lambs the maximum population of Ostertagia spp. was found during February–March, while that of Trichostrongylus spp. could be observed only after mid-June. Other nematodes encountered were Haemonchus contortus and Trichuris sp. but they were only present in small numbers. The proportion of inhibited larvae of Ostertagia spp. was markedly high during the dry summer months. Little inhibition was noticed during autumn and the early winter months. It appears that if the seasonal inhibition of Ostertagia spp. in Iraq is brought about by an environmental stimulus acting upon pre-parasitic larval stages, that stimulus cannot be chilling or falling temperatures, as observed in temperate northern zones.

The behaviour of mice exposed to graded doses of Trichinella spiralis larvae was monitored in an open-field situation. Ambulatory and exploratory activity declined significantly as the infections progressed, whereas the time spent inactive increased concomitantly. The advent of these behavioural changes coincided with the expected release of larvae by the adult worms and showed no clear signs of abating as late as 90 days post-inoculation. The levels of activity were negatively correlated with the inoculating dose. Such behavioural changes may render the host more vulnerable to predation and thus enhance parasite transmission.

Trichinella spiralis infections influenced the establishment and maintenance of behavioural dominance among outbred male mice. Infected animals assumed a subordinate status when challenged by normal or more lightly infected conspecifics both in an unfamiliar test arena and in their established home cages. These effects were demonstrable during the acute and the chronic phases of infection. The significance of this phenomenon to the survival of the mouse host and the transmission of the parasite is discussed.

The tegument of the metacercaria of Gorgoderina vitelliloba contains S1, S2, S3 and S4 secretory bodies. Between the parenchymal cells 2 types of tegumental cyton occur. Type 1 contains S1 and S3 secretory bodies, whilst S2 and S4 bodies are limited to Type 2. Type 1 cytons and S1 secretory bodies disappear at excystment. Post-metacercariae contain a third type of tegumental cyton in which a new secretory body, S5, occurs. This cyton type disintegrates 1–5 days after infection. The maintenance and development of the outer anucleate layer after this period is the responsibility of Type 2 cytons. Type 2 cytons and S2 and S4 secretory bodies have also been found within the cercarial body. When juvenile flukes migrate from the kidney to the bladder of their frog definitive host 21 days after infection, the outer anucleate layer increases in electron density. Within the bladder, however, the tegument of the adult fluke appears normal. The distribution of mitochondria within the outer anucleate layer changes during the fluke's migration. The mitochondria, which have a random distribution in the metacercaria, are located adjacent to the outer and basal plasmalemmas in the early kidney stages. In late kidney stages and bladder stages mitochondria occur only against the former membrane. The mitochondria increase in size in the adult fluke.

A method of interrupting the life-cycle of the human blood fluke Schistosoma by increasing the proportion of genetically insusceptible intermediate host snails in natural populations was first proposed nearly 25 years ago. The method assumes that insusceptible snails will be at a selective advantage over susceptible snails when the schistosome parasite is present, and therefore natural selection will act to increase the proportion of alleles for insusceptibility. A major objection to the proposed technique is ‘If insusceptible snails are at a selective advantage, then why are they not predominant in natural populations that transmit disease?’ One explanation of this paradox is that insusceptibility may be associated with a disadvantageous character or a physiological defect. This study tests this hypothesis by measuring the relative reproductive success of susceptible and insusceptible snails under controlled conditions. Results indicate that insusceptible (unsuitable) snails are negatively affected in the presence of either susceptible snails or schistosome parasites. Furthermore, in the presence of both susceptible snails and schistosome parasites, insusceptible snails are selectively disadvantaged compared to susceptible snails. These results obtained under laboratory-controlled conditions suggest a plausible answer as to why insusceptible snails are not predominant in natural populations that transmit disease.

Rat peritoneal neutrophils adhere to schistosomula of Schistosoma mansoni in vitro in the presence of antibody, complement, or both. Ultrastructural studies have demonstrated that cell adherence is not intimate, and that electron-dense secretions are not liberated onto the parasite surface in the manner described for eosinophils. Cytochemical techniques confirm that peroxidase is confined within intracellularly located neutrophil secretion granules. The metabolic burst is shown to operate during Fc-mediated interactions, but since morphological damage depends upon the presence of complement in the system, toxic oxygen products would seem not to be involved in the initiation of surface perturbation. Complement-dependent, neutrophil-mediated schistosomular damage is characterized by vesiculation of the tegumental outer membrane, an increase in density of the tegumental cytoplasm and the eventual development of focal lesions. The cells migrate laterally to push aside damaged surface tissues and then adhere intimately to the exposed musculature. Damage appears earlier when both antibody and complement are present in the system, and this correlates with higher killing efficiency. The frequently observed association of contaminant eosinophils with areas of parasite damage indicates that eosinophils and neutrophils may cooperate to effect schistosomular killing. In the presence of antibody alone, attached neutrophils exhibit intense phagocytic activity towards the antigen-antibody complex formed at the parasite surface. This phenomenon may account for the eventual detachment of cells and lack of significant parasite damage recorded in this system