This paper describes further characteristics of the immunization of sheep against schistosomes using live, irradiated schistosomula. Sheep immunized with a non-virulent strain of Schistosoma mattheei were protected against a more virulent strain of the same species for over a year. As there was no evidence that the irradiated parasites were able to persist this long, it was concluded that the vaccine had induced a sterile resistance. Heterologous vaccination, using irradiated S. mattheei schistosomula to immunize against S. bovis or irradiated S. mansoni schistosomula to immunize against S. mattheei, failed to induce any protection.

Effects of thermal effluent on the incidence and abundance of gill and intestinal metazoan parasites of the black bullhead, Ictalurus melas, were investigated. A total of 472 bullheads from a thermal outfall area and an unaltered area of Lake Monona, Dane County, Wisconsin were examined. All parasites underwent a seasonal cycle in abundance with peak infections occurring in summer, except for the acanthocephalan, Pomphorhynchus bulbocolli, which underwent a seasonal cycle in abundance in the reference area but not in the outfall area. Thermal effluent had little effect on the incidence of the parasites. Differences in abundance between the outfall and reference areas were observed for all parasites but these differences were not always consistent nor statistically significant. P. bulbocolli was more abundant in the reference area than in the outfall area in summer (P ≤ 0·05). The monogenean, Cleidodiscus sp. was more abundant in the reference area than in the outfall area in August (P ≤ 0·05). The infections of the gill copepod, Achtheres ambloplitis, were higher in the reference area than in the outfall area in spring, June, August, and September (P ≤ 0·05). Availability of infective larvae and variability in host feeding patterns were suggested as the controlling factors of the patterns of abundance observed.

The effect was compared in CBA mice of adding Corynebacterium parvum, saponin, and Bordetella pertussis to living or killed Trypanosoma cruzi (Y strain) epimastigote vaccines on the induction of protective immunity against subcutaneous (s.c.) challenge with blood trypomastigotes. The addition of C. parvum to a low dose of T. cruzi vaccine, which alone was non-protective, generated a greater degree of protection than did saponin or B. pertussis. C. parvum alone increased resistance to infection to a variable and usually weak extent. The addition of C. parvum to larger doses of T. cruzi vaccine, which were themselves sufficient to elicit some degree of protection, improved resistance when the challenge was given 1 or 12 weeks after immunization, but lowered it at 3 weeks. It is concluded that the comparative efficacy of adjuvants for T. cruzi vaccines needs to be assessed on 3 parameters: (1) the dose of antigen, (2) the dose of adjuvant and (3) the time interval between immunization and challenge.

Two experiments were carried out in which calves reared parasite-free were infected with a single dose of 3rd-stage larvae of Cooperia oncophora. In the first experiment the calves received 20000 or 200000 infective larvae and they were autopsied 28 or 56 days after the infection. In the second experiment the doses were the same but the animals were killed 14, 84 or 140 days after infection. If a dose of 20000 was given, clinical signs were never observed, while at a dose level of 200000 the weight gain was less on 56 and 84 days after the infection compared with the low-infected groups or the control animals. After 140 days the differences in weight gain were compensated. Faecal egg output was higher in the 200000 groups only in the first period of patency, thereafter the calves in the 20000 groups produced more. No obvious differences between the two infection levels were observed with regard to the haematological data. In the low-infected groups worm counts were only slightly lower when the results after 28 days were compared with those after 56 days. Also, the worm numbers after 14 days were almost equal to those after 84 days, while at 140 days 1 animal still had the same number, the other one had lost its worm burden. In the high-infected groups the worm loss was much quicker. After 28 days a great part of the population had already been lost. Obviously, at the 200000 level the reaction of the host against the parasite was much stronger. Adult worms were expelled at a higher rate than early 4th-larval stages. In the first experiment worm measurements revealed differences between the length of females, males and spicules of males, these being significantly longer in the low-infected groups. Analysis of the distribution of worms over the small intestine showed that in the low-infected groups worms were mainly restricted to the first 6 metres. In the high-infected groups the worm population was distributed more evenly over the whole small intestine.

The uptake of bloodstream forms of Trypanosoma cruzi, Y and CL stocks, by mouse peritoneal macrophages and their intracellular differentiation and multiplication has been compared in vitro. After 48 h the number of macrophages showing intracellular amastigote forms was higher when the Y stock was used. The number of parasitized cells increased with the time of contact between parasites and macrophages. Prior treatment of the parasites with anti-T. cruzi antibodies and/or complement increased the number of infected macrophages, but did not interfere with their subsequent differentiation within the macrophages. The number of parasitized cells was greater when macrophages were obtained from mice previously treated with lipopolysaccharide, peptone or thioglycollate. Uptake was not appreciably affected when macrophages were pre-treated with trypsin or anti-macrophage serum, or when the parasites and macrophages were incubated in the presence of cytochalasin B. In the same experimental conditions, epimastigotes of T. cruzi were not able to differentiate into amastigotes. Their uptake was potentiated by previous treatment with specific antibodies and/or complement and was blocked by cytochalasin B. These results confirm that epimastigotes derived from T. cruzi cultures are phagocytosed and suggest that bloodstream forms penetrate actively into macrophages.

Stages seen in the life-cycle of Diplocystis tipulae sp.nov. parasitic in Tipula paludosa Mg., included a structure that was probably a trophozoite within the midgut epithelium of one host larva and gamonts that developed on the midgut wall in the haemocoele of the larvae. Syzygy occurred, usually in pairs, when the gamonts were about 200–300 μm in diameter. Initially, syzygous gamonts were bilobed but they quickly became spherical and were enclosed by a fine membrane to form a gametocyst 450–550 μm in diameter. Early stages of gametogony were seen in one pupa; sporogony occurred in pupae and adults. The mean size of the round–oval oocysts was 7·14 × 6·26 μm. Individuals of Tipula oleracea L. are also susceptible to infection with D. tipulae. This gregarine is considered to be a new species, independent of the gregarines of the gut lumen.

The uptake in vitro of various substances by Brugia pahangi was investigated using infective larvae obtained from Aedes aegypti and worms removed from Meriones unguiculatus at 2, 3, 10, 20 and 90 days post-infection. Worms incubated in growth medium 199 containing 1% Trypan blue possessed demonstrable dye in the oral orifice, the anterior oesophageal lumen and the external openings of the vulva and the cloaca or anus but the dye was not found in the gut lumen even after incubation for 24 h. No uptake of ferritin particles into the intestine of the worms was found and no fluorescence could be demonstrated in the gut lumen of worms incubated in medium containing 50% (v/v) fluorescein isothiocyanate-conjugated calf serum for up to 24 h. Trypan blue uptake by the gut of Aspiculuris tetraptera was clearly observed after incubation for several hours. The uptake of D-glucose and L-leucine by B. pahangi was demonstrated using autoradiographic and scintillation counting techniques and incorporation into worm tissues was detected. Glucose was found to be readily incorporated in the apical, glycogen-rich areas of the myocytes of worms of all ages studied and in the uterine epithelium of the adult female. In contrast, a lower incorporation of D-glucose was found in the eggs, embryos and vas deferens and especially in the gut. The incorporation of L-leucine occurred throughout the tissue of the worms during a 30 mm incubation. Labelling was also located over the surface of the cuticle of the worms, when incubated for a period of 15 to 60 mm in L-[3H]leucine. Scintillation counting techniques demonstrated that there was no uptake of 14C-labelled L-glucose or sucrose by B. pahangi. The data presented on the uptake in vitro of nutrients or other compounds by infective larvae and adult stages of B. pahangi did not demonstrate an intestinal route of uptake but indicated that the transcuticular route of uptake may be employed.

An examination of 2 strains of Eimeria acervulina var. mivati (since 1973 E. mivati has been regarded as a variant of E. acervulina) showed that previous confusion over the taxonomic status of E. mivati arose because the investigations were done using laboratory cultures of E. mivati which were contaminated with E. acervulina.

Electrophoretic analyses of enzymes, host specificity and cross-immunity tests have revealed that:

(1) The 1971 Houghton strain of E. acervulina var. mivati was a mixture of 2 parasites. (a) Passage of this strain in embryonating eggs resulted in a selection against that parasite previously characterized as E. acervulina. (b) The parasite which did reproduce in eggs did not immunize chickens against subsequent challenge with E. acervulina. This parasite is most likely E. mivati. (c) E. mivati recovered from eggs did, however, immunize chickens against challenge with a new field strain which was morphologically identical to E. mivati and characterized by the same electrophoretic forms of 2 enzymes.

(2) A strain of E. acervulina var. mivati from the USA was also a mixture of E. acervulina and E. mivati.

Uptake by the tegument of metacercariae of Bucephalus haimeanus of both particulate material and small molecules in solution is demonstrated by the use of electron-dense tracers and autoradiographic techniques. Ruthenium red (RR) uptake involved pinocystosis and the formation of large, electron-lucent vesicles in the outer cytoplasmic tegument. RR lost its association with these vesicles and became freely dispersed within the cytoplasm as it passed through the outer cytoplasmic tegument, down the cytoplasmic bridges and into the tegumental cell bodies. Ferritin, iodinated insulin and iodinated human serum albumin were also located within the outer cytoplasmic tegument and ferritin collected beneath the inner plasma membrane of the outer cytoplasmic tegument. Horseradish peroxidase was not absorbed by the tegument although it bound strongly to the outer surface of the metacercariae. C-labelled glucose, phenylalanine, tryptophan and tyrosine were all detected in the outer cytoplasmic tegument.

In vitro variation of glycogen content under aerobic conditions was measured on fresh weight basis in 3 sheep nematodes inhabiting different niches; Haemonchus contortus, Oesophagostomum columbianum and Trichuris ovis. The parasites were separated into species and then sexes and starved for varying periods of time up to 24 h in glucose-free physiological saline. The differences between females and males and among the species with respect to glycogen content and its rate of change with time are discussed.

Eimeria maxima (Weybridge) and E. maxima (indentata) were distinguished by the electrophoretic mobility of phosphoglucomutase. This enzyme was used as a marker to detect the transfer of methyl benzoquate resistance between resistant and sensitive lines of these parasites.

Oocysts of Eimeria maxima inoculated into guinea fowl do not develop. Infection occurs when intestinal mucosa or liver tissue from guinea fowl given E. maxima is transferred to susceptible chickens. By transferring material at different times after inoculation, it was shown that most of the stages are lost between 6 and 12 h and few, if any, survive to 48 h.

Sporozoites of E. tenella had low infectivity after 48 h contact in vitro with peritoneal macrophages from guinea fowls and turkeys. Sporozoites of E. grenieri from the guinea fowl appeared to be destroyed within macrophages taken from chickens.