The ultrastructure of the macrogamete and developing oocyst of Eimeria maxima (Weybridge strain) was examined in the intestinal cells of chicks fed 3 different anticoccidial drugs. Amprolium at 125 p.p.m., arprinocid at 35 p.p.m. and dinitolmide at 250 p.p.m. caused considerable morphological abnormality and incomplete development of the wall-forming bodies of Type 2 (WFB II), which did not appear able to participate in oocyst wall formation. The wall-forming bodies of Type 1 (WFB I) were able in each case to participate in oocyst wall formation although amprolium and dinitolmide produced morphological abnormalities in them. In birds medicated with dinitolmide, the outer layer of the oocyst wall was formed initially at opposite poles of the macrogame tes rather than as a uniform layer. Other abnormalities resulting from drug treatment are reported and some evidence that intravacuolar tubules may be formed by the parasite pellicle is presented.

An in vitro system is described in which over 85% of a population of Leishmania mexicana mexicana amastigotes transforms to promastigotes within 48 h. The differentiation process involves 3 morphologically and biochemically distinct intermediates, including a division stage. Cell division is shown to be necessary for complete development to promastigotes. Foetal calf serum (FCS) has been found to be an essential component of the medium for high percentage transformation to be achieved. One of the important components of the FCS has been identified as non-esterified fatty acids, and these support a relatively high percentage of amastigotes through transformation in the absence of FCS, possibly due to their use as energy substrates. Only small numbers of amastigotes transform to promastigotes if glucose or amino acids are the only energy substrates available. Transformation is inhibited by a number of metabolic inhibitors including anti-leishmanial and other anti-protozoal drugs. The stage at which inhibition is apparent varies with the inhibitor. It is suggested that the system described for the transformation in vitro of L. m. mexicana amastigotes to promastigotes may be the best method available at present for studying the metabolism and drug sensitivity of amastigotes free from possible interference by host macrophage components.

Hymenolepis citelli caused a marked mortality in Tribolium confusum during the first 14 days of infection. The mortality was higher when the beetles were starved for 6 days immediately prior to infection (73–93%) than when they were starved for 1 day (51%). Regardless of the starvation time, the majority of beetle deaths occurred between days 8 and 11 post-infection (p.i.) and the precise survival time for individuals tended to vary inversely with the number of parasites they contained. With few exceptions beetles that survived until day 15 p.i., when the experiments were terminated, contained 14 or fewer cysticercoids, whereas those that died on or before day 14 p.i. contained 20 or more parasites. Mortality was equally high in both sexes but the mean survival time was significantly shorter for female beetles (8·8 days) than for males (9·6 days). Also, parasite development rate varied with the sex of the host. When parasite populations recovered from beetles that died on the same day were compared, the degree of development attained by those from males was significantly higher than in the populations grown in female hosts. The line of H. citelli used in these experiments has been maintained in the laboratory for the past 5 years. The results obtained with the current generation of this line were compared with those obtained with it 2 years earlier (approximately 16 generations ago). Mortality was lower with the current generation (67%) than with the earlier generation (93%). However, with the latter generation, the mean parasite population size in beetles that survived to day 15 p.i. was significantly higher (14·1 cysticercoids/beetle) than in those infected with the recent generation (7·3–7·9) cysticercoids/beetle). These findings suggest that relatively high selection pressures have been applied by T. confusum to H. citelli, thereby reducing the number of parasite lines with high infectivity and consequently improving host survivorship. The host also responded to artificial, directed selection for reduced cysticercoid number (heritability estimates of 0·30 ± 0·12 and 0·26 ± 0·12) and increased survival (heritability estimates of 0·28 ± 0·12 and 0·15 ± 0·083). The realized heritability was 0·37 for cysticercoid number and 0·17 for increased survival.

The anticoccidial effect of narasin against Eimeria flavescens, E. intestinalis, E. magna, E. perforans and E. stiedai was tested in experimentally infected rabbits. The drug was highly effective in reducing oocyst output and in preventing clinical signs. Maximum activity as measured by oocyst discharge was achieved with feed levels from 12 to 24 p.p.m.; there was no influence on oocyst sporulation. Optimal weight gain and food consumption were obtained with levels between 8 and 12 p.p.m.; at higher levels there was an adverse effect on growth, food intake, relative liver and heart weights and on serum potassium and glucose.

Schistosomula, surface labelled with trinitrophenyl (TNP) target antigens were tested for their susceptibility to killing by humoral- or cell-mediated anti-TNP effector mechanisms in vivo. It was found that mice passively immunized with anti-TNP serum effectively rejected an intravenous (i.v.) challenge infection with TNP-labelled schistosomula. In contrast, mice which demonstrated a strong TNP-specific, delayed hypersensitivity response to the haptenated larvae as evidenced by ear swelling, were unable to eliminate the same challenge infection. Significant passive immunization against TNP-labelled schistosomula was shown to require microlitre quantities of anti-TNP serum and could be conferred with an IgG fraction purified from the serum. The role of cells in the antibody-dependent rejection of TNP-labelled schistosomula was investigated using histopathological methods. In passively immunized mice, haptenated larvae elicited neutrophil-enriched focal reactions in the lungs and showed evidence of degeneration as early as 2 h after injection. These cellular reactions were not observed in recipients which had received prior whole-body irradiation. Nevertheless, by 24 h TNP-labelled larvae were found to have been killed in the lungs of the irradiated mice despite the absence of significant cellular attack. The above observations suggest that the antibody-dependent destruction of haptenated schistosomula results from two overlapping responses, an early response mediated by radio-sensitive cells and a second, radio-resistant response manifesting its effects at later time points. Since mice genetically deficient in the fifth component of complement fail to develop the later response, it probably reflects the effect of the lytic pathway of complement on the parasite.

Mice experimentally infected with the hydatid parasite Echinococcus granulosus (secondary echinococcosis), were used as spleen cell donors for hybridoma production. Two hybridomas were produced which secreted antibody with anti-E. granulosus cyst fluid (EgCF) activity. Radio-immunoassays comparing the binding of these hybridoma-derived antibodies to E. granulosus versus several other antigen preparations from sheep parasites showed that the antibodies had a high degree of specificity for the hydatid parasite. However, using a panel of clinically defined sheep sera in a competitive radio-immunoassay, the binding of the hybridoma-derived antibodies to EgCF was inhibited strongly by sera from sheep infected with the common parasites Fasciola hepatica and Taenia hydatigena. When the hybridoma-derived antibodies were conjugated to CNBr-activated Sepharose and the crude EgCF applied to the affinity column, the ‘run through’ antigen preparation showed a significant increase in specificity for experimental E. granulosus infection. A useful means of applying the hybridoma technology in the development of new immunodiagnostic reagents may be to select those murine hybridomas which produce high-affinity, cross-reacting antibodies and to use these antibodies in the processing of homologous antigen by affinity chromatography.

The prevalence of Taenia saginata (Cestoda) among 146 predominantly Pokot tribesmen in western Kenya was studied in an attempt to assess the reliability of detecting infections by faecal examinations. Firstly, a single faecal sample was microscopically examined after being processed by a standard ether sedimentation technique. Secondly, all subjects were treated with niclosamide and a purgative and the tapeworms were recovered. In this way the efficiency of diagnosing infections by faecal examinations was estimated. T. saginata eggs were found in the faeces of 68% of the men who were eventually found to be infected. Information was collected by interview from all subjects about whether they were or ever had been infected with tapeworms and about the form of treatment previously sought or taken. Eleven out of 25 men were apparently unaware of their tapeworm infections while no evidence of infection was found among 10 of the 24 reportedly infected men. A change in the pattern of treatment for tapeworms was reported which may have resulted in a recent decline in the prevalence of infection.

A simple, quick and reproducible method consisting of density-gradient centrifugation of homogenized infected mouse brain tissue on Percoll is described for the isolation and purification of cysts of Isospora (Toxoplasma) gondii. A 100% recovery of cysts, with 74·2% in a single fraction with a specific gravity of 1·056, was obtained by overlaying homogenates of infected mouse brains on a pre-formed Percoll gradient and centrifugation at low g forces. With this procedure recovery was independent of the age of the cysts. Titration of purified cystozoites showed there to be no loss of infectivity.

A passive transfer system, dependent upon hyperimmune rat serum, was used to study in vivo protective humoral immunity to Schistosoma mansoni infection in Fischer rats. Infected recipients of hyperimmune serum exhibited a significant reduction (51%) in the number of recovered adult schistosomes relative to infected recipients of normal rat serum. Furthermore, schistosomula were equally sensitive to the effects of hyperimmune serum injected up to and including 7 days post-infection, a phenomenon which was termed ‘extended sensitivity’. Schistosomula were beginning to lose sensitivity to the effects of hyperimmune serum by the 8th day post-infection and were completely refractile by the 9th day. In addition, it was demonstrated that parasite elimination occurred after the lung stage. Some protection was also observed when hyperimmune rat serum was transferred to mice as late as 5 days post-infection.

The successful cellular immune response of larvae of D. melanogaster against A. tabida is characterized by an increase in the number of blood cells, a premature transformation of spherical plasmatocytes to flattened, disc-shaped lamellocytes, and the lysis of crystal cells. The plasmatocytes and transformed lamellocytes rapidly aggregate around the eggs of the parasite to form a cellular capsule, while the lysing crystal cells release substances causing the melanization of the capsule. The early appearance of large numbers of transformed blood cells in the haemolymph prior to their involvement in capsule formation suggests that transformation is independent of cell contact with the parasite and may be due instead to biochemical stimuli emitted from the parasite and/or by hormonal changes. Quantitative blood cell studies of hosts exhibiting no encapsulation and melanization response indicate that successfully developing parasites are recognized by the immune system but are able sufficiently to block the blood cell transformation and thus prevent capsule formation.

Cercaria vaullegeardi develops in daughter sporocysts within the digestive gland of the prosobranch Gibbula umbilicalis. On emergence into the host mantle cavity the cercarial body retracts into the cystophorous tail, the ‘encysted’ cercaria being then shed into the sea. The encysted cercaria is described at the ultrastructural level for the first time and developmental stages are redescribed. The cercarial body has no penetration or cystogenous glands: a single type of sub-tegumental secretory cell produces vesicles containing neutral mucopolysaccharides which pass into the tegument at encystment. The immotile cystophorous tail consists essentially of a fibrous caudal cyst and 8 appendages including a delivery tube. Scanning electron micrographs show the surface of tegumental membranes enveloping the caudal cyst to be covered with a honeycomb pattern of indentations derived from electron-lucent vesicles produced by the caudal gland. The fibrous-walled delivery tube comprises proximal and distal sections and a modified terminal end-piece.

A new microsporidian parasite of a freshwater cladoceran from southern Sweden is described using light and electron microscopical methods. Development comprises 2 merogonial sequences, the first resulting in a cluster of 8 merozoites, the second in a chain of 4 merozoites. Each secondary merozoite develops into a sporont which divides into 2 sporoblasts, each of which develops into a spore. The spores are broadly oval and in fresh smears measure about 6 μm in length, with a single nucleus and a posterosome. The polar filament is about 40 μm long, of even thickness throughout, and appears as 15—18 coils in a single layer. The anchoring disc is small and the polaroplast is composed of 2 lamellar parts. Outside the plasma membrane of the sporont a 5-layered, electron-dense substance is produced, which further differentiates into endo- and exospore, an electron-dense substance occurring patchily on the exospore and a pansporoblast membrane. During development the sporoblasts and the young spores are connected by a dense substance. Mature spores appear single or paired. The pansporoblast membrane is composed of 2 structurally different layers, namely a thin outer, single membrane and an inner layer composed of tubular structures. It is connected to the spore coat by patches of the dense substance. The new microsporidium is considered to belong to a new genus of the family Telomyxidae, and its systematic relationship with this and the related family Tuzetiidae is discussed. A survey of microsporidia from Cladocera is included.

Large inocula of dividing form-enriched Trypanosoma musculi parasites, harvested from the peritoneal cavity of infected CBA mice, were given intravenously to mice at various times during the infection. Mice infected for 10 or 15 days (including T cell-deprived, infected mice) eliminated dividing parasites from the blood within a few min, whereas those at earlier stages (1 or 5 days) were less efficient. The initial control of T. musculi parasitaemia thus appears to be due to a trypanocidal mechanism rather than reproduction-inhibiting factor (ablastin).

Trypomastigotes of Trypanosoma dionisii, a stercorarian trypanosome from bats, are effectively killed by neutrophils from human peripheral blood but are less sensitive to the cytotoxic action of human monocytes. The mechanism of killing appears to involve peroxidase and hydrogen peroxide. Trypomastigotes are as effective as epimastigotes in inducing the formation of hydrogen peroxide by effector cells. They are, however, less sensitive than epimastigotes to the cytotoxic effect of peroxidase and hydrogen peroxide. They are therefore susceptible to the high concentrations of peroxidase found in the phagosome of the neutrophil, but resist the lower levels encountered in monocytes.

The inoculative mechanism whereby cystophorous cercariae infect the copepod 2nd intermediate host is described for the first time in Cercaria vaullegeardi. Experimental infections of the harpacticoid copepod Tigriopus brevicornis are recorded and the infection process is related to the ultrastructure of the cercaria and to the feeding mechanics of harpacticoids. The cystophorous tail of C. vaullegeardi is shown to be a device whose shape and construction ensure that the cercarial body is neither damaged by copepod mouthparts nor swallowed, but reaches the host haemocoel during the initial stages of feeding. The cystophorous tail consists essentially of a caudal cyst, into which the cercarial body retracts at encystment, and various appendages including a delivery tube. The infection mechanism is triggered when the copepod mandibles bite the narrow posterior caudal cyst beak, when the delivery tube everts into the mouth and penetrates the dorsal mid-gut wall. The cercarial body, lubricated by tegumental secretions, passes simultaneously through the delivery tube and is inoculated into the host haemocoel.

Two groups of goldfish maintained at 20°C were experimentally infected with two different sized inocula of Trypanosoma danilewskyi. One group was inoculated with 380000 trypanosomes/fish and the other with 3800. Forty and 90% of the fish, respectively, survived. All surviving fish challenged 190 days post-infection were protected from re-infection. The plasma of these fish when inoculated into another group of fish also protected them from infection. Finally, trypanosomes incubated in vitro in immune plasma at 20°C for 2 h were not infective; however, incubations at 5°C or for 1 h were not as effective.

Tsetse flies (Glossina morsitans) were fed on the blood of mice containing any one of 5 variable antigen types (VATs) of Trypanosoma brucei AnTAR 1 serodeme. The VATs of the metacyclic trypanosomes subsequently detected in the flies' saliva probes were investigated using monospecific antisera to AnTAR 1 VATs in indirect immunofluorescence and trypanolysis reactions; these sera included 3 raised against AnTats 1.6, 1.30 and 1.45, previously identified as components of the metacyclic population (M-VATs), and against the 5 VATs originally ingested by the flies. The percentage of metacyclics reacting with a particular M-VAT antiserum remained more or less constant (AnTat 1.6, 6·0–8·3%; AnTat 1.30, 13·7–18·2%; AnTat 1.45, 2·0–8·0%), regardless of the age of the fly or the ingested VAT. As these 3 VATs accounted for no more than 30% of the metacyclic population, the existence of at least one more VAT is envisaged. The ingested VAT could not be detected among the AnTAR 1 metacyclic trypanosomes.

Studies on the nutrition and physiology of Trichomonas vaginalis have been hampered by the lack of a defined synthetic medium in which to grow the organism. New synthetic media free of ill-defined supplements and serum which support good growth of T. vaginalis have been developed in this study. The first successful approach to a defined medium resulted from the modification of the tissue-culture medium CMRL 1066. Essential modifications included (1) lowering the redox potential of the medium by adding high levels of ascorbate and (2) modifying the buffer system. Subsequently, CMRL 1066 was replaced by two new media DL7 and DL8 which have greater flexibility in their formulation and permit improved serum-free growth. Serum was replaced by bovine serum albumin and cholesterol, together with either a glyceryl fatty acid ester or a defined mixture of fatty acids. Preliminary nutritional studies using the new media have indicated a requirement for saturated and unsaturated fatty acids and a sterol.

The pathognomic, serologie and morphometric identity of a Babesia sp. recently isolated from sheep in Argyllshire was studied. Initially, problems were encountered due to the occurrence of Eperythrozoon ovis as a contaminant of the isolate and treatment with neoarsphenamine failed to remove it. Finally, a combination of oxytetracycline therapy and rapid passage allowed isolation of the Babesia sp. and its preservation in the form of a glycerolized, infected blood stabilate. Inoculation of the stabilate into splenectomized sheep produced a mild non-pyrogenic disease. Serologically the parasite was seen to have no affinity with either of the two Babesia recognized as parasitizing sheep, but some affinity with the cattle parasite B. divergens. Morphometrically it was seen to have affinity with the deer parasite B. capreoli and with the Babesia sp. isolated from red deer in Scotland, and the low number of budding forms of the parasite seen suggested that the parasite might be reproducing slowly in an alien host. It was concluded that the parasite was likely to be B. capreoli derived from red deer via the tick Ixodes ricinus.

Tsetse flies were infected with 5 different variable antigen types (VATs) or with a mixture of VATs of the AnTAR 1 serodeme of Trypanosoma brucei. Metacyclic forms from the salivary glands of infected flies were used to initiate infections in mice. Immunofluorescence and trypanolysis reactions employing 24 monospecific antisera were used to analyse the VATs present in the mice following cyclical transmission. Regardless of the VAT used to infect tsetse flies, the first VATs detectable in the bloodstream were those previously identified as metacyclic VATs (M-VATs). These were present until at least 5 days after infection, at which time lytic antibodies against at least 2 of the M-VATs were detectable in the blood of infected mice. In mice immunosuppressed by X-irradiation the M-VATs were detectable in the bloodstream for longer periods, but the percentage of the population labelled with anti-metacyclic sera showed a decrease on day 5 as in non-irradiated animals. The VAT ingested by the tsetse was always detectable early during the first parasitaemia following cyclical transmission and was usually the first VAT detected after the M-VATs. Neutralization of selected M-VATs before infecting mice resulted in elimination of the neutralized M-VAT from the first parasitaemia but had no effect on the expression of other VATs in the early infection.