The newly formed egg-shell from eggs in the proximal part of the uterus of Paraplerurus sauridae is colourless and transparent, whereas the shell from eggs in the distal uterus is golden yellow in colour. Histochemical tests reveal the presence of phenol, protein and phenolase in the freshly formed egg-shell. The egg-shell from eggs in the distal uterus shows the property of sclerotin. Histochemical reactions, chromatography and spectrum analysis reveal the presence of a dityrosyl linkage in the egg-shell. The nature of the protein component in the egg-shell is discussed.

The epidermis of Diplectanum aequans has, in general, been found to be similar to the epidermis of other monogeneans, consisting of a syncytial outer epidermis and sunken sub-epidermal nucleated regions. However, the epidermis of D. aequans differs from that of other monogeneans in 3 respects. These are, the presence of large areas of granular cytoplasm within the outer epidermis, the presence of myofibres invaginating into the epidermal matrix and, in the posterior regions of the epidermis, the presence of epidermal scales. These scales occur within the epidermal cytoplasm, beneath the outer membrane, and are composed of moderately electron-dense material. Also present beneath the outer membrane in the more anterior regions of the epidermis are small scale-like sclerites of a similar electron density to the epidermal scales.

Acid phosphatase activity was demonstrated in the intact blood nematodes, Dirofilaria immitis and Angiostrongylus cantonensis. Biochemical studies on acid phosphatase, using intact females and whole worm, body-wall and visceral homogenates were undertaken to clarify the characteristics and the distribution of the enzyme. In D. immitis, high acid phosphatase activity was observed at pH 3·8–5·8 and in A. cantonensis, at pH 4·5–6·0. Molybdate, fluoride, copper and zinc ions and L(+)-tartrate were effective inhibitors of the enzymes of both parasites while cobalt and magnesium ions and D(−)-tartrate had no noticeable effect on the activity. When the effect of substrate concentration on the phosphatase activity was studied, kinetic curves of Michaelis–Menten type were obtained with the 2 species of intact worms as well as their homogenates. The reproductive organs and body wall of D. immitis showed high total acid phosphatase activity. In A. cantonensis, the majority of the enzyme was localized in the body wall. The activity of intact A. cantonensis expressed as μg Pi/h/mg dry weight decreased with increase in mean worm weight. The characteristics of the acid phosphatase of the 2 nematodes are compared with those of other parasitic helminths and of acid phosphatase of mammalian origin. The localization of the phosphatase responsible for the hydrolysis of the external substrate has been discussed for D. immitis and A. cantonensis based on results of the kinetics and distribution of the enzyme.

In undernourished rats infected with Nippostrongylus brasiliensis partial villus atrophy was observed in large areas of the anterior and posterior regions of the intestine. In addition, the following changes in structure were observed; some areas of the intestine contained misshapen villi which lacked microvilli on the lateral surfaces; cell-like bodies devoid of microvilli appeared to be budded off from the sides and tips of some malformed villi and there appeared to be extensive leakage of blood constituents into the lumen of the intestine. Morphological changes were present up to day 24 of the infection when the experiment was terminated. The possible consequences of the extensive breakdown of villus structure are discussed.

In female NIH strain mice, expulsion of a primary infection of the nematode Trichinella spiralis began on day 8 and was virtually complete by day 14 of infection. In secondary and tertiary infections, the number of larvae which established in the intestine was normal, but expulsion began on day 6 and was complete on day 10. In a primary infection the shedding of larvae by female worms began on day 5, reached its peak on days 6–7, began to decrease on day 8 and was minimal by day 10. In secondary and tertiary infections fecundity was depressed. The depression of fecundity occurred slightly in advance of worm loss. During the stable phase of infection, T. spiralis occurred in the anterior half of the small intestine. During expulsion, living worms were found increasingly in more posterior parts of the gut but their fecundity did not vary with position. After direct inoculation into the posterior ileum, adult and larval T. spiralis remained in the posterior half of the small intestine. In this position, larvae established in normal numbers, grew and reproduced normally. Therefore, any part of the small intestine was a suitable site for T. spiralis and expulsion is not merely due to a change in the position of the worms.

Interactions between infections of Trichinella spiralis and Nippostrongylus brasiliensis were studied in the NIH strain of mouse which is known to react strongly to T. spiralis. The course of N. brasiliensis infection in this strain of mouse is described and expulsion is shown to be accelerated in immunized mice and inhibited in cortisone-treated mice. There was no evidence of inter-specific competition between the two species of worm in concurrent infections; the number and location of adults of both species were normal and T. spiralis was able to grow and reproduce normally. No evidence was found of direct immunological cross-reaction between N. brasiliensis and T. spiralis as assessed by the kinetics of adult worm numbers on heterologous challenge of immunized mice 90 days after the initiation of the last of 3 immunizing infections. Interaction was observed only when the timing of concurrent infections was such that one species was established in the intestine immediately before the beginning of expulsion of the second species. Interaction was manifested as a premature loss of worms and, in addition, as impairment of growth and fecundity of T. spiralis. These effects on T. spiralis were similar to those observed as a consequence of a specific immune response to T. spiralis. The rapidity of appearance of these effects and the lack of direct cross-immunity between the two species of worm suggest that the events involved in interaction were non-specific in action and possibly due to environmental changes in the gut caused by the immune response. These non-specific effects are therefore analogous, but not necessarily homologous, to the expulsion of these parasites in single species infections.

Adult Haemonchus contortus worms simultaneously excrete and fix CO2. Their initial content of CO2 was measured as 4·55 μmoles/100mg wet weight and their excretion rate in air as 1 μmole/100 mg wet weight/h for at least 4 h. When the worms were incubated either aerobically or anaerobically with 14CO2 most of the metabolized radioactivity was associated with propan-1-ol and propionate but small amounts were found in succinate and lactate. No radioactivity was associated with ethanol or acetate, two major catabolites of glucose. Stepwise degradation of the metabolized radioactive propanol and propionate showed that all the radioactivity in both compounds was associated with carbon atom no. 1. These results show that H. contortus has much in common with the anaerobic energy metabolism of Ascaris lumbricoides but they are not inconsistent with the utilization of the tricarboxylic acid cycle by the worm. H. contortus worms were found to metabolize their excretory products. When they were incubated with either [2,3-14C]succinate or [2-14C]acetate, 14CO2 was excreted under aerobic but not under anaerobic conditions. These results are consistent with a pathway similar to that used by Ascaris operating alone under anaerobic conditions and together with the tricarboxylic acid cycle under aerobic conditions.

Intraperitoneal injection of cercariae into pristane (2, 6, 10, 14 tetramethyl pentadecane)-primed Balb/c mice led to greatly diminished numbers of portal and peritoneal worms compared with untreated mice. Schistosomula taken from the peritoneal cavity of pristane-primed mice carried globules of pristane on their surfaces, were contracted and were permeable to Trypan blue. Pristane globules bound also to adult worms in vitro and in vivo causing rapid damage to the surface membrane. Hydrophobic compounds other than hydrocarbons either bound without causing gross damage, or did not bind to the adult worms. 51Cr release studies showed that pristane had no effect on the permeability of human erythrocytes, while causing significant release from both schistosomula and adult worms. The binding of hydrocarbon globules to a variety of other parasites did not occur. The binding of n-[1-14C]hexadecane to adult Schistosoma mansoni was significantly decreased by extraction of the parasite with organic solvents or treatment with staphylococcal δ toxin, which interacts with phospholipids in the membrane. Possible mechanisms of damage of the parasite by the hydrocarbons are discussed.

Incorporation of labelled amino acid into tegumental proteins and acquisition of protection by schistosomula against antibody-mediated killing in vitro were simultaneously stimulated by serum factors and inhibited by puromycin. Comparison of polyacrylamide gel electrophoresis patterns with fluorographic autoradiography indicates that the majority of proteins in the parasite tegument were labelled with the isotope after incubation for 3 h. No new, clearly defined band was observed in the autoradiography pattern. During this period a decreasing susceptibility of the schistosomula to antibody plus complement was observed. Quantitative fluorescence assay shows that schistosomula insensitive to antibody plus complement were still able to bind the same amount of antibody as the unprotected parasites. Pre-culture of schistosomula in the presence of inactivated normal rabbit serum also decreased the susceptibility of the parasites to the in vivo killing mechanism.

Amastigotes from Leishmania braziliensis and L. mexicana were isolated from cutaneous lesions in infected animals using the plant lectin Concanavalin A as a specific agglutination agent. Amastigotes were collected in preparations of up to 95% purity as determined by cell count. The parasites obtained by this method showed no apparent loss of viability as measured by growth rates and DNA replication, or pathogenicity as measured by routine passages in hamsters or mice.

Glycoproteins of Trypanosoma congolense have been detected on SDS-polyacrylamide gels using the Concanavalin A peroxidase technique. Using [35S]diazoniobenzenesulphonate as a marker for cell surface proteins it was possible to distinguish between internal glycoproteins and the surface coat proteins. On SDS-polyacrylamide gels Con A reacted with the surface coat proteins. Results obtained from Con A-induced agglutination of living trypanosomes indicated that sugars of the surface coat proteins were accessible to Con A. This was reinforced by the cytochemical visualization of Con A binding to the trypanosome surface. The results suggested that the surface coat protein contained α-linked d-mannosyl, d-glucosyl, or N-acetyl-d-glucosaminoyl residues, which are exposed exteriorly on the surface coat.

Cyclical transmission of different variable antigen types of Trypanosoma congolense STIB 228 resulted in the development of metacyclic trypanosome populations which were similar in their variable antigen composition as judged by immunofluorescence and neutralization assays. The variable antigen types present in the ingested bloodstream populations were not found in the metacyclic populations. The bloodstream populations which were obtained from cyclically infected, irradiated (900 rad.) mice contained variable antigen types which were not present in the corresponding metacyclic populations. When derivatives of 2 other stocks of T. congolense, isolated in a different area of Tanzania, underwent cyclical development in the tsetse fly, the metacyclic populations of each stock also had a characteristic variable antigen composition. The metacyclic populations of the 3 stocks were, however, completely dissimilar in variable antigen composition. Simultaneous infection of tsetse flies with a mixture of different stocks resulted in the concurrent production of metacyclic trypanosomes which contained the characteristic variable antigen types of each stock. The effect of cyclical transmission on the process of antigenic variation in T. congolense infections is therefore similar to that in T. brucei infections.

Groups of mice were exposed to multiple bites by tsetse flies (Glossina morsitans morsitans) infected with a clone of Trypanosoma congolense spread over a period of 8 days. The mice were subsequently treated with Berenil 10 days after the first fly bite as were uninfected control mice. The group of mice which received 12–15 infectious fly bites on two occasions, 21 days apart, were subsequently resistant to infection when re-challenged by flies infected with the same clone of T. congolense. These mice were also immune to challenge by flies infected with a different bloodstream variable antigen type derived from this same stock. The immunity was stock-specific and directed against the metacyclic forms of the parasite, but was short-lived.

The interaction between mouse peritoneal macrophages and ‘Y’ strain Trypanosoma cruzi bloodstream forms was studied at optical and electron microscopical levels. The method of marking lysosomes with Thorotrast, either before or after infection of cell monolayers with parasites, revealed that secondary lysosomes fused with phagosomes shortly after trypanosome interiorization. In spite of this, 24 h later most parasites were no longer in a vacuole but lay free within the host cell cytoplasm, multiplying actively. At this time, and up to shortly before 96 h when parasites escaped to the external milieu, most parasitized cells were not lethally injured, as revealed by the Trypan blue dye-exclusion test. Only when parasites were released into the external medium was this situation reversed and infected macrophages took up the dye.

LLC-MK2 cell monolayers infected with Trypanosoma cruzi were shown by immunofluorescence to present parasite antigens on the surface of both parasitized and non-parasitized cells after completion of the first intracellular cycle and rupture of infected cells. The cell-culture supernatant fluid at this stage, as well as the supernatant fluid of parasites left overnight in culture medium were concentrated and contained antigen capable of binding to uninfected cell monolayers. The origin of this antigen, as well as its eventual role in the pathogenesis of Chagas' disease, are discussed.

The use of human diploid cell lines of finite life for the in vitro production of Trypanosoma cruzi is described. Both MRC5 and WI38 cells release trypomastigotes with less than 5% amastigotes. This could form the basis for biochemical and immunological studies, which were previously limited by the problems of separating parasites from blood. By selecting the in vitro passage number of the parasite it is possible to select for either the broad or the slender forms of trypomastigotes, allowing comparative studies of these forms within a single strain of the parasite. It is also possible to isolate amastigotes by disrupting the cells before trypomastigotes appear, and separating them from cell debris with Metrizamide. It is shown that by incorporating [3H]uridine in the cell-culture medium, labelled trypomastigotes are obtained. The release of this label (putative RNA) provides a relatively simple isotopic assay for parasite death. Examples of this assay for testing drug toxicity and in immunological lysis are presented.

The morphology and development of Trypanosoma cobitis during its life-cycle in the blood of 6 species of River Lee fish, and also in its invertebrate vector, the fish leech Hemiclepsis marginata L., are described in detail.

A method has been devised to show that malaria parasites can be detected serologically in infected blood with a high degree of sensitivity. Using a murine malaria model, parasites were demonstrated in a solid-phase radio-immunoassay which measured antibody-binding inhibition. Lysed red blood cells (r.b.c.) were incubated with labelled specific antibody and were then reacted in antigen-coated tubes. The degree of inhibition of antibody binding in the tubes correlated with the level of parasitaemia in the test blood. Using homologous antisera the test detected infection at a level of 1 parasite/million r.b.c. The specificity of the method was shown by comparison of antibody-binding inhibition in normal and infected r.b.c. and in r.b.c. from non-infected mice with induced reticulocytosis. The sensitivity was shown in vitro in tests of serially diluted blood of high parasitaemia and in vivo for the detection of early infection. The presence of antibody in the test blood did not significantly affect the sensitivity of parasite detection.

Two new species of coccidia, Eimeria gourai sp. nov. from the Victoria crowned pigeon (Goura victoria Fraser) and Eimeria duculai sp.nov. from the Torres Strait imperial pigeon (Ducula spilorrhoa Gray) have been described. Eimeria gourai oocysts are spherical to sub-spherical in shape, measure 20·0 (19·0–22·0) × 20·0 (18·0–21·0) μm and are devoid of micropyle and oocyst residuum. Elongate sporocysts are 12·0 × 5·5 μm, and contain a granular residuum. Eimeria duculai oocysts are broadly ovoid with an inconspicuous micropyle at the narrower end. They are 28·0 (26·0–31·0) × 25·0 (23·0–27·0) μm in size, without residuum but with a membrane-bound polar granule. The elongate sporocysts are 15·5 × 7·2 μm, with prominent Stieda body and granular, membrane-bound residuum. The morphological characteristics of the known coccidian oocysts from birds of the avian order Columbiformes are reviewed.