Survival curves for cercariae of Schistosoma mansoni maintained at different temperatures were determined. Between 15 and 35 °C the curves were of reverse sigmoid form and the probit transformation gave a statistically good fit. The slope of the regression lines fitted to the probit transformations increased exponentially as the temperature rose. Above 35 °C heat intolerance became important and increased exponentially as the temperature rose. Below 15 °C, cold intolerance caused an initial high level of mortality followed by an extended period with insignificant mortality. The glycogen content of whole cercariae and separated cercarial bodies and tails was measured during ageing. The glycogen content of whole cercariae declined exponentially during ageing. This was a product of exponential decreases in the glycogen content of both the body and the tail of the organism. The cercarial tail was shown to contain slightly over half of the total glycogen content. The rate of glycogen use was higher in the tail than in the body. A computer simulation model was used to demonstrate that the observed exponential use of glycogen could generate survival curves similar to those observed experimentally.

The behaviour of oncomiracidia of the monogenean skin parasite Entobdella soleae, after hatching without chemical stimulation, has been studied in vertical, 4 cm high chambers illuminated from above. Most freshly hatched larvae are photo-positive and swim to the top of the vessel, where they remain actively swimming. Occasionally larvae become photo-negative and make a brief excursion to the bottom of the vessel. As the larvae grow older, these photo-negative excursions become more frequent and larvae spend progressively longer in the photo-negative phase of behaviour, but, even after many hours, photo-positive vertical excursions are still occurring. If this pattern of alternating photo-positive and photo-negative vertical movements occurs in the natural environment, these vertical movements, coupled with horizontal transport of larvae by water currents, would provide a search pattern for the host, the diurnally-inactive, bottom-living flatfish Solea solea. When eggs are stimulated to hatch in the chambers with urea, large numbers of larvae emerge within a few min, and it was observed that during the period of about 30 min after stimulation, many larvae are photo-negative. When eggs on the sea bottom are stimulated to hatch by mucus or urine from a nearby host, such behaviour would greatly enhance chances of contact with the fish. When eggs are stimulated to hatch by means of urea in the absence of light, there is evidence that the oncomiracidia are geo-negative. It has been shown that larvae are able to extricate themselves in total darkness from sediment containing buried eggs and that, in an experimental situation illuminated only by an infra-red beam, larvae readily attach themselves to the lower skin of soles within 2 min of hatching. There is evidence that, in aquaria, some invasion of the host takes place from below.

By transferring Schistosoma mansoni (12 to 14-day-old worms) from one host into the peritoneal cavity of a host of a different species, it was possible to demonstrate that worms grown in rats, hamsters, Mastomys natalensis and Cebus monkeys were rejected by recipient animals previously immunized against red blood cells of the donor hosts. These results suggest that host-like antigens are acquired by S. mansoni in all hosts. The transfer of worms into the peritoneal cavity has proved to be a simple and convenient method for studying the presence of host antigens in S. mansoni.

The surface morphology of schistosomula extracted from the skin, lungs and hepatic portal system (hps) of mice was investigated from Days 0 to 18 post-infection. Skin schistosomula and newly arrived schistosomula from the hps were of similar dimensions but were morphologically distinct. Lung schistosomula were considerably elongated with an estimated 53% increase in surface area compared to skin schistosomula. The pitted tegument of lung schistosomula was formed into ridges and troughs. These were compressed together in contracted individuals recovered from the hps on Day 10. The annular ridges were cross-linked by longitudinal septae which possibly prevent further elongation of the body. A regression of the spines between the mouth and the ventral sucker was observed in Day 2 skin schistosomula. In lung schistosomula only the spines at the anterior and posterior of the body remained. New spines were formed after the schistosomula reached the hps. It is suggested that the spines in the mid-region of the body are selectively disassembled and that their loss facilitates migration along the lumina of capillaries with the residual spines acting as anterior and posterior anchors. The mouth opening was enlarged in schistosomula from the hps recovered from Day 10 onwards. Skin schistosomula lost the cercarial apical tegumentary ridges between 24 and 48 h after penetration but a spineless protrusible area remained. After arrival in the hps this area became integrated into the anterior surface as the oral sucker developed around the sub-terminal mouth. The cercarial ciliated papillae were lost on penetration. The migrating schistosomulum had few visible sensory papillae but following arrival in the hps new papillae were observed.

The reproduction and survival of the ectoparasitic digenean Transversotrema patialense on the fish host Brachydanio rerio are shown to be temperature-dependent. Survival is reduced by any deviation from an optimum temperature of approximately 23°C. With increasing temperature the rate of egg production per surviving fluke rises progressively faster to a higher peak up to 29°C but falls to zero by 35°C. The span of egg production varies closely with the life-span of the parasite at each temperature. The optimum temperature for the total number of eggs produced by each cohort of parasites is also 23°C. This number is a function of both adult parasite survival and the rate of egg output.

The reproductive duct of the male blood fluke Schistosoma mansoni is relatively short and undulating, extending from the most posterior testis to the beginning of the gynecophoric canal. The reproductive duct may be divided into 3 main regions which differ in ultrastructure; the vas efferens/deferens, the seminal vesicle and the cirrus tube. The epithelium of the vas efferens/deferens consists of a single layer of elongate cells with abundant convoluted lamellae on their apical surfaces. The wall of the seminal vesicle and the cirrus tube are tegumentary in nature. The basic similarities in structure of the surface tegument, the seminal vesicle and the cirrus tube suggest a common embryological origin. The presence of complex lamellae on the luminal surface suggests that the vas efferens and deferens have secretory and possibly nutritive functions apart from temporarily storing developing germ cells. The primary function of the seminal vesicle appears to be that of sperm storage; while the cirrus tube with its complex infolded wall is extensible for insemination. The presence of abundant concentrically distributed sensory papillae around the male genital pore may assist in the pairing of males and females.

Mice given primary infections of Schistosoma mansoni by percutaneous or subcutaneous routes were found to acquire a higher degree of resistance against homologous challenge after 7–8 weeks than mice infected intraperitoneally. Mice infected by the intraperitoneal route tended to have smaller worm burdens than those infected with the same number of cercariae by the other two routes and this may, in part, have contributed to the relative lack of efficacy of intraperitoneal infections in inducing resistance to re-infection. The same degree of resistance was acquired after primary percutaneous infection irrespective of whether it was administered in 3 equivalent weekly doses, or the same total number of cercariae was administered as a single infection. The same degree of resistance was also observed when a percutaneous challenge was administered on the same or a different skin site to that which received the percutaneous primary infection. The degree of resistance to re-infection acquired after a percutaneous primary infection correlated well with the size of the primary worm burden and the number of eggs in the intestine and liver, but did not correlate with the number of eggs in the lungs.

Chicken macrophages, obtained by cultivation of blood monocytes, were infected with epimastigote and bloodstream trypomastigotes of the Y and the CL strains of Trypanosoma cruzi. The percentage of infected cells and the mean number of parasites per cell were determined after 2, 6, 12 and 24 h of parasite–cell contact. After 6 h of contact about 80% and 40% of the macrophages were infected by trypomastigotes of the Y and CL strains respectively. After longer periods of contact almost all macrophages were infected by Y trypomastigotes while only about 60% were infected by those of the CL strain. After 2 h of contact almost all macrophages were infected by CL epimastigotes while only about 50% were infected by Y epimastigotes. After 6 h of contact almost all macrophages were infected by epimastigotes of both strains. These results are discussed taking into consideration differences between parasites of the two strains and between the two developmental stages of the T. cruzi life-cycle.

The egg-shell of Hammerschmidtiella diesingi and Aspiculuris tetraptera reduces the rate of water loss from the egg when exposed to desiccation. Staining of the enclosed larva by acid fuchsin and the collapse of eggs exposed to desiccation indicate that the permeability barrier is heat labile. This suggests that the lipid layer is the main permeability barrie of the shell. The complex structure of the uterine layers has a similar morphology to the respiratory structures of the chorion of some insect eggs. Reflections from the shell, the rate of embryonic development under various conditions and the penetration of lead ions indicate that the shell does not trap a layer of air when immersed in water and the uterine layers cannot, therefore, function as a plastron network. Calculations indicate that if diffusion is limited to the pores in the external uterine layer, the area available for gaseous exchange is reduced by 85·5% in H. diesingi, 95·6% in A. tetraptera and 96·8% in Syphacia obvelata. It is suggested that the uterine layers of oxyurid egg-shells function in a similar fashion to the pores in bird egg-shells and the aeropyles in the chorion of insect egg-shells which do not possess plastron networks. These structures reduce water loss from the egg whilst ensuring an adequate supply of oxygen for embryonic development.

Lambs given 60000 third-stage larvae of Nematodirus battus were killed on days 16, 20, 22, 24 and 32 of the infection and the duodenal mucosa was examined by scanning electron microscopy (SEM). On day 16 of the infection the villi were long and finger-like and, although goblet cells were visible, the surface of the villi was not extensively folded, as is the surface of villi of uninfected control animals. By day 20 of the infection the villi had been reduced to flattened, plate-like structures or had formed low, irregular-shaped ridges. On this day of the infection the nematodes appeared to be enclosed by mucus-like material. As the infection progressed the intestinal damage was repaired, so that, by day 24 of the infection, the surface of the intestine was covered by short, smooth, finger-like projections and, by day 32 of the infection, the morphology of the intestine was somewhat similar to that of the control lamb. The possible role of villus atrophy and of mucus in the rejection of N. battus from the intestine is discussed.

In the male reproductive system of Nematodirus battus the spermatogonia and spermatocytes are arranged upon a central rachis and the spermatocytes are characterized by the presence of cup-shaped membranous organelles which are formed in association with Golgi complexes and granular endoplasmic reticulum. Spermatozoa of N. battus in the male nematode have an electron-dense, conical tail-like region which contains the nuclear material and an elongate cytoplasmic region which contains the cell organelles. In the uterus of the female, however, the cytoplasmic region of the spermatozoon has an amoeboid appearance and in the seminal receptacle the cytoplasmic region is dome-shaped and many of the membranous organelles have connexions with the outer membrane of the spermatozoa. Movement was not observed in spermatozoa released from the seminal vesicle of the male worm.

Oocyst wall formation in Eimeria maxima was studied during the macrogamete stage in intestinal cells of the chick and in unsporulated oocysts isolated from faeces. The outer of the 2 membranes bounding the mature macrogamete separated from the surface but remained as a veil surrounding the developing oocyst throughout the whole intracellular process. Wall-forming bodies Type I were initially applied to the limiting membrane of the zygote cytoplasm; a layer of material similar to their contents was then formed around the zygote. As this occurred a new double membrane was formed surrounding the oocyst cytoplasm. The outer wall layer was initially homogenous in appearance but later developed into 2 zones, an outer amorphous region and an inner osmiophilic region. The inner layer of the oocyst wall was formed from the contents of the wallforming bodies Type II which dispersed between the outer wall and the limiting membranes of the oocyst cytoplasm. There was evidence of an additional membrane formed external to the outer wall. The outer membranes were not present around the wall of oocysts passed in the faeces of chicks, but the same wall zonation was evident, although the inner osmiophilic zone of the outer wall layer was markedly thinner in comparison with the same zone seen in the tissues.

Uptake of radioactively labelled purine bases and nucleosides by suspensions of Trypanosoma brucei and Trypanosoma congolense in bicine buffer was determined at 37 °C. With T. brucei, the rate of uptake of adenosine was much greater than that of the other compounds tested, the uptake of which decreased in the order adenine, inosine, guanosine and hypoxanthine. With T. brucei, adenosine uptake increased with concentration in a manner suggesting two mechanisms, one with high and the other with low affinity for adenosine. The uptake of adenine increased with concentration only up to about 1·5 µM while the uptake of guanosine increased little with concentration and that of inosine and hypoxanthine not at all. In both species adenosine strongly inhibited the uptake of both of the other nucleosides and of both purine bases. In T. brucei, guanosine and inosine caused small increases in adenosine uptake which was, however, inhibited by them in T. congolense. In T. brucei, each of the purine bases adenine and hypoxanthine inhibited its own uptake maximally but that of each other less effectively. Hypoxanthine was more effective than adenine in inhibiting the uptake of the nucleosides guanosine and inosine, but neither base effected marked inhibition of adenosine uptake. The uptake of adenosine by T. brucei was inhibited by dipyridamole and its analogue, compound RA–233, strongly at 100µM and slightly at 10 µM. The other dipyridamole analogues, VK–744 and VK–774, were ineffective.

As the infection progresses in lambs, the developing germ cells of male Nematodirus battus become filled with lysosome-like bodies, electron-dense granules and membrane-bound vesicles, and the organization and division of the gametic nucleus appears to be altered. The epithelial cells of the reproductive tract are also damaged and the secretory-type globules produced by the cells of the vas deferens are denatured. These changes are compared with ultrastructural changes observed in other species of nematode affected by the immune response of their hosts.

Aromatic amino acids (phenylalanine, tryptophan and tyrosine) are absorbed by Hymenolepis diminuta through a combination of mediated (non-Na+-sensitive) transport and diffusion. All 3 amino acids are accumulated against an apparent concentration difference during a 30-min incubation of tapeworms in 0·1 mM 3H-labelled amino acid. Inhibitor studies demonstrate that phenylalanine, tryptophan and tyrosine are mutually competitive inhibitors of the uptake of each other, and the uptake of these amino acids is inhibited by aliphatic amino acids but not by basic or dicarboxylic amino acids. The D- and L-isomers of aromatic amino acids are equally effective in inhibiting aromatic amino acid uptake. The data indicate that at least 3 amino acid transport loci are involved in aromatic amino acid transport by H. diminuta.

The transmission of Hammondia heydorni among sheep, goats, cattle, dogs and coyotes is described. Oocysts of H. heydorni, obtained from dog faeces by feeding naturally infected goat meat, were fed to an experimental goat. After 312 days tissues from this animal were fed to 2 dogs. One dog, which received goat muscle, shed oocysts, whereas the other dog which received brain, spleen, kidneys, lungs and liver did not. Oocysts from the dog fed goat muscle were fed to an experimental sheep. After 73 days sheep tissues were fed to a dog and a coyote, both of which shed oocysts 5–8 days later. A second isolate of H. heydorni was obtained by feeding naturally infected beef to a coyote. These oocysts were fed to a single goat and sheep and after 71 days, muscle from these 2 animals was fed to 2 dogs and 2 coyotes, all of which shed oocysts 5–8 days later. None of the animals inoculated with H. heydorni became ill and no Hammondia-like organisms were found in tissue sections from the herbivores. Another dog shed H. heydorni-like occysts between 7 and 10 days after ingesting naturally infected muscles from a moose. These results indicate that H. heydorni infects goats, sheep, moose and coyotes in addition to cattle and dogs.

The adenine nucleotide content and adenylate energy charge of Nematospiroides dubius from laboratory mice and of Trichostrongylus colubriformis from lambs has been measured. Administration of the anthelmintic, levamisole, to infected hosts resulted in only a slight fall in the adenylate energy charge of N. dubius over a 3-h period but there was a greater fall in the adenylate energy charge of T. colubriformis during this period. In neither case did the energy charge fall quickly, nor did it fall to the low levels which would be expected if the levamisole were inhibiting synthesis of ATP. The changes in energy charge of the nematodes which occurred following administration of levamisole to their hosts was of the order which can be satisfactorily explained by changes in the environment of the nematodes, such as reduced oxygen tension. It is concluded that the maintenance of levamisole-induced paralysis of these two species of trichostrongyle in vivo does not rely on the inhibition of fumarate reductase.

An experimental study of the effects of parasitism by H. diminuta on the intermediate host, Tribolium confusum, is described. No density- dependent constraints on parasite establishment within individual hosts are evident, although a reduction in cysticercoid size at high parasite burdens is demonstrated. The relationship between parasite burden, host mortality and host fecundity is investigated. Host mortality is linearly related to parasite burden, whereas the relationship between parasite burden and host fecundity is non-linear. There is no difference in viability between eggs from infected and uninfected females. The generative causes of these effects are not investigated experimentally, although it is postulated that survival is related to the degree of damage to the midgut wall caused by parasite penetration, and fecundity to the biomass of parasites harboured by the host. The significance of these effects is discussed in relation to the overall dynamics of the host-parasite association.

The sexual cycle of Theileria taurotragi was identified in the gut lumen of replete Rhipicephalus appendiculatus nymphs maintained at 28°C which had fed on eland with rising parasitaemias. Macro- and microgametes developed from ring-form piroplasms within 24 h after repletion. The microgamonts were elongate with 2 or more lateral projections. The nuclei of the microgamonts divided into 4 and the microgamonts differentiated into 4 thread-like microgametes each with a central nucleus. Round macrogametes developed at the same time and stages indicative of the fusion of the macro- and microgametes were observed after 48 h. The resultant zygotes were detected in the gut wall cells by day 4, many being rounded and vacuolated with a peripheral nucleus. By day 7 the zygote cytoplasm became dense and they lay in clusters still within the cells. Binucleate zygotes were observed at this stage. The zygotes increased in size and by day 12 began to transform into kinetes by invagination. By the time the nymphs moulted into adults (about day 14), the kinete straightened to a broad anterior end and a tapering posterior with a mean length of 22·1 μm. Kinetes were detected in the haemolymph by day 16. By day 20 the kinetes had penetrated the salivary gland acinar cells where they underwent schizogony until the infected acinar cells were filled with multinucleated sporoblasts. The nuclei of the infected acinar cells became greatly enlarged soon after penetration of the kinete. Division of the sporoblast nuclei was stimulated by feeding of the adult ticks. From the 2nd day of attachment of the ticks to rabbits the sporoblasts underwent a process of schizogony to produce cytomeres. Each nucleus of the cytomere divided to produce several small nuclei which differentiated into uninucleated sporozoites.

Strains of Babesia divergens of human and bovine origin were isolated from the same locality in Scotland. A morphometric comparison was then made between Babesia divergens parasites in blood smears made from groups of 3 splenectomized calves reacting to the inoculation of these strains. The various forms taken by the parasites of each strain were seen to be divisible into 7 categories and representatives of each category were found for each strain. More amoeboid forms were found in blood smears from calves infected with the strain of bovine origin but otherwise the frequencies of occurrence of different forms coincided. The dimensions of 3 forms of the parasites of each strain were compared and theparasites of human origin were found to be significantly larger. The reactions of the groups of calves to inoculation of the 2 strains of B. divergens were seen to be very similar, although inoculation of the bovine strain had a slightly greater effect on the animals' haematology as indicated by an increase in erythrocyte mean corpuscular volume.