Freshly excysted Fasciola hepatica possess an outer glycocalyx which stimulates an antibody response in cattle infected with F. hepatica metacercariae. Sera from animals receiving either a single or a double infection were examined for levels of IgM, IgG1 and IgG2 specific for the outer glycocalyx of intact live juvenile F. hepatica. High levels of specific IgG1 were found to predominate. Using positive sera in an indirect fluorescent antibody assay, the bovine immunoglobulins labelled the outer glycocalyx in a characteristic reticulated pattern. On incubation at 37 °C this pattern rapidly broke up into discrete clumps and progressed until the entire antibody–outer glycocalyx complex was shed. The shedding phenomenon was shown to be continuous and, by using preparations of Fab fragments, was not due to the bivalent binding of the sensitizing antibody.

Neither phosphagens nor phosphagen phosphotransferase activity could be detected in Fasciola hepatica, Hymenolepis diminuta, Moniezia expansa or in the plerocercoids of Ligula intestinalis. The plerocercoids of Schistocephalus solidus, however, possess an active taurocyamine phosphotransferase, although it too contains no detectable phosphagens. The taurocyamine phosphotransferase of S. solidus has an absolute requirement for a divalent metal ion and ATP could not be replaced by ITP, GTP, CTP, or UTP as the phosphate donor. The role of phosphagens in helminths is discussed.

Adult Ostertagia circumcincta from freshly killed sheep were incubated at 39 °C in a medium containing inorganic salts, antibiotics and D-[U-14C] glucose. The worms appeared healthy even after incubation for as long as 72 h. All the radioactivity was recovered either within the worms or in the incubation vessel in the form of metabolic products or unmetabolized glucose. Incubations were carried out at low oxygen tension except for those in which CO2 was measured. These were either aerobic or anaerobic. In terms of both quantity and radioactivity the main metabolic products of glucose were CO2, propan-1-ol, acetate and propionate. Smaller amounts of ethanol, lactate and succinate were formed. The results are compared with those found for the similar nematode Haemonchus contortus.

The daily food intake and related changes in body weight were measured in young rats which were fed on synthetic diets containing 1% (3 experiments), 2% (4 experiments) and 20% (1 experiment) casein respectively. Some rats were infected with Nippostrongylus brasiliensis and allowed to feed ad libitum, some remained uninfected and were allowed to feed ad libitum while others, which were matched by initial weight with rats from the infected group, remained uninfected and were given only the same amount of food as that consumed during the previous 24 h by their infected partners. No significant differences were detected between the rats before the start of the infection. Thereafter, the food intake of the infected undernourished rats was usually found to be significantly lower and the loss of body weight significantly greater than those of the uninfected rats. In infection periods of relatively long duration, the pair-fed uninfected rats did not lose as much weight as their infected partners even though their food intake (1% and 2% casein) was the same. Although the food intake, and consequently the weight, of infected rats fed on the diet containing 20% casein were significantly less than in their uninfected partners, no significant differences were observed between the weights of the infected and pair-fed rats fed on this diet.

On day 10 of a primary infection of Trichinella spiralis in NIH mice, when adult worms were in the process of being expelled, their fecundity was markedly depressed. Upon transplantation to new host mice, the worms were able to establish successfully in their usual position in the anterior small intestine, even if originally recovered from the large intestine of mice expelling their worms, and these worms fully recovered their fecundity after 7 days in recipients. On day 5 of secondary and tertiary infections, immediately before loss of worms began, the adult worms were stunted and had a depressed fecundity. However, such worms, when transplanted, were able to establish in normal numbers and in a normal position in the intestine of recipient mice. Additionally, these worms were found to have developed a fecundity, and grown to a length, comparable to that of normal worms, but slightly less than that of control worms transplanted from day 7 of a primary infection, after 7 days in a new host. Electron microscopy showed that worms taken at the time of expulsion in primary and tertiary infections showed structural abnormalities, including large quantities of lipid in intestinal cells and somatic musculature and decreased quantities of stored glycogen. Upon transplantation to new host mice, these worms were found to have recovered a normal ultrastructural appearance within 7 days, although there was still evidence of a slightly elevated lipid and depressed glycogen content. It is concluded that immune expulsion of T. spiralis from mice does not involve irreversible damage to the worms.

Mono-metacercarial infections of Echinostoma revolutum in the domestic chick yielded 14- or 15-day-old worms that produced viable eggs, indicating that this species can self-fertilize under conditions which preclude cross-fertilization. In multiple infection studies, chicks were fed either 5 or 10 cysts and each infected chick contained 2–7 worms at necropsy 14 or 15 days later. Worms from multiple infections were mainly paired or clustered and they tended to locate more posteriorly in the intestine than single worms. Length measurements of single and multiple worms were similar. Both the number of eggs and the percentage of hatched eggs were considerably greater in multiple than in single infections.

The in vitro interaction between rat peritoneal macrophages and Dipetalonema viteae microfilariae in the presence of amicrofilaraemic rat immune serum was studied by transmission electron microscopy. The probable sequence of events leading to the killing of D. viteae microfilaria by macrophages is as follows. (a) Rat peritoneal macrophages in the presence of amicrofilaraemic rat immune serum adhere to the parasite surface, (b) the macrophages extend their pseudopodia around the parasite, (c) the ‘lysosome-like’ granules discharge their contents on to the parasite surface, (d) the lytic activity of these products begins at the parasite surface and (e) subsequent breaking of the microfilarial cuticle occurs, exposing the parasite intracellular material.

Variant antigenic types (VATs) represented in a total of 47 first relapse populations of 6 clones of Trypanosoma brucei LUMP 227 were identified by immunofluorescent staining of living trypanosomes, using antiserum raised against purified surface antigens. The relative growth rates of these 6 clones were measured both individually and when grown together in a mixed population, and were found to be different under these two sets of conditions. A pattern emerged in the VATs represented in relapses of each clone, with some types being expressed more frequently than others and certain VATs being only very rarely expressed. It is suggested that new VATs are expressed according to a statistically definable order of priority which is different for each parent VAT, and that some VATs may be able to change to certain others only after passing through an intermediate VAT. The order of priority of appearance of VATs does not appear to correlate with growth rate measured either in individual clones or when clones are grown in a mixed population.

Two stocks of Trypanosoma congolense were established in culture at 28 °C using trypanosomes from the proboscides of infective Glossina morsitans. Successful primary cultures were initiated by placing an infected tsetse proboscis beside a bovine dermal collagen explant in Eagle's minimum essential medium supplemented with foetal calf serum. The trypanosomes multiplied rapidly in the medium and also gradually formed an adherent layer on the plastic surface of the culture vessel. Three primary cultures produced organisms infective for mice from 14, 20 and 35 days after initiation and thereafter continuously until days 76, 76 and 52 when they were discarded. Four attempts to initiate infective cultures using infected tsetse proboscides in medium without dermal explants were unsuccessful. When trypanosomes from primary cultures were placed in culture medium with proboscides from uninfected tsetse flies, the parasites multiplied, formed an adherent layer in the culture flasks and were seen in the proboscides within 24 h. A line of 1 stock was serially sub-passaged in this way 4 times during a period of 215 days. Infectivity titrations in mice indicated that primary and sub-passaged cultures each contained similar numbers of infective organisms. Another line of the same stock was also sub-passaged 4 times in medium alone over a period of 186 days. These sub-cultures again retained infectivity for mice, but titrations showed a decrease in infective organism production in the 4th sub-culture. Primary and sub-passaged cultures all included a variety of morphologically different developmental forms of T. congolense, closely resembling those described in the labrum and hypopharynx of Glossina by previous workers. Short metacyclic-like trypanosomes and organisms with proteinaceous surface coats were present in infective cultures. Cultures were successfully re-established after cryopreservation at −196 °C and retained the ability to produce infective organisms.

Ouabain applied to adult male Schistosoma mansoni causes a large, non-reversible tension increase of the parasite's musculature and elimination of spontaneous contractions. The tension increase and the time-course of tension development caused by ouabain are dose dependent with significant effects obtained at 3 × 10−6m. Digoxin and digoxigenin act in a similar manner with a relative potency of ouabain ≃ digoxin > digoxigenin. Lowered temperature as well as substitution of Li+ for Na+ increases muscle tension. The membrane potential recorded from the ventral tegument is also affected by treatments which interact with Na+–K+ transport systems. Ouabain (0·1 mm) causes a rapid depolarization without a significant effect on membrane resistance. The tegument is depolarized by temperatures below 30 °C. The effect of temperature is readily reversible and the temperature sensitivity is eliminated by pretreatment with ouabain. Substitution of Li+ for Na+ also causes a depolarization of the tegument. Tracer experiments show both an increase in Na+ and a decrease in K+ in the parasite within 10 min after treatment with ouabain (1 × 10−5m). Decreasing temperature of the bathing medium also causes an accumulation of Na+ as well as a decrease in the animals. The above results indicate a significant role for active Na+–K+ transport in muscle contraction and in maintenance of the tegumental membrane potential. The data also suggest that the Na+–K+ transport in S. mansoni may be electrogenic.

This paper describes a modification of the model for the transmission of schistosomiasis proposed by Macdonald (1965), which allows the snail host-locating efficiency of the miracidium to be taken into account. The modified model allows for a choice of miracidia efficiency. If it is assumed that the miracidia are inefficient hunters then the resulting model is very sensitive to perturbations; relatively small changes in snail numbers not only cause appreciable changes in the percentage of snails infected but result in attainment of the threshold (the point at which schistosomiasis ceases to be endemic). If, however, the miracidia are efficient snail hunters then the model is much less sensitive to perturbations; here the percentage of snails infected is much less affected by changing snail numbers, and the threshold is much more difficult to reach by reducing snail numbers. It is argued that, on the whole, the empirical data give more support to the latter model, although there are some circumstances under which the former model might apply. However, even with these modifications it is considered that the Macdonald model does not provide a satisfactory explanation of field observations.

The variation in the development of the reproductive system of female Schistosoma mansoni from single sex infections is described. Vitelline cell development was assessed by staining for phenolic substances and the development of Mehlis' gland and the ovary by electron microscopy. Although there was considerable variation in the development of worms from individual mice harbouring infections of the same age, the mean values indicated that there was a low level of differentiation and turnover of vitelline cells in worms 30–200 days post-infection. The proportion of females which possessed mature vitelline cells showed a general increase with age. The ovary was always in an immature stage but the development of Mehlis' gland showed some variation. The results suggest that the stimulus given by the male to the female is not necessarily to initiate development of the reproductive system but to increase the rate of development of the vitelline gland and to co-ordinate the development of the entire reproductive system.

Studies on the multiple compact testes of Schistosoma mansoni have revealed 2 principal cell types: germinal and non-germinal cells. Two morphological forms representing different stages in the cytomorphosis of the sustentacular cells have been considered. The polymorphic sustentacular cells which are conspicuously stained with potassium permanganate contain abundant ribosomal endoplasmic reticulum, glycogen particles and ribosomal masses in comparison with the germinal component of the testes. Golgi complexes with associated secretory bodies and vacuoles are present in the cells. The cytoplasm of the sustentacular cells interdigitate between other cells in the testes. Based on their morphology, nutritive, supportive and phagocytic functions have been attributed to the sustentacular cells. The possible recycling of nutrients by the cells is discussed. It is suggested that the cells regulate the production of spermatozoa from a nutritive viewpoint and also that the translocation of nutrients from the parenchyma to the testes is facilitated by these cells whose cytoplasm extends directly adjacent to the basal lamina.

The structure and development of microgametocytes of Eimeria maxima from chicks killed during the 6th day of infection were examined using transmission and scanning electron microscopy. Initially, nucleoli disappear and the surface of the microgametocyte invaginates. This is followed by a condensation of the chromatin which then lies at the periphery of the nuclei. Concurrent with this, the flagella are formed and they project into the parasitophorous vacuole and internal invaginations. Eventually, the nuclei become more dense and are seen to protrude from the periphery of the gametocyte. The surface view of mature microgametocytes consists of a large number of closely packed flagella.

A rapid method is described for preparing and staining salivary glands of Rhipicephalus appendiculatus ticks infected with Theileria parva. The technique, involving the use of a modified methyl green pyronin stain, minimizes the risk of losing material and allows examination of stained glands within minutes of preparation. The technique was applied in a series of studies in which ticks were either infected with T. parva under different conditions, or maturation of parasites in adult ticks was stimulated by different means. When nymphal ticks were fed on the ears of cattle the subsequent infection rate of the adult ticks showed no correlation with the parasitaemia of the cattle at the time of nymphal engorgement. There was no difference in infection rates between adult ticks in which parasite maturation had been stimulated either by incubation at 37 °C or by feeding on rabbits. However, parasite maturation took about 1 day longer in incubated ticks than in rabbit-fed ticks. Female ticks were consistently more highly infected than males, both in terms of the percentage of ticks infected and the mean number of infected acini/tick. Ticks were infected with T. parva by injection of nymphs with parasitaemic bovine blood, but the resultant adult infection was lower than that in ticks which had been infected naturally by feeding on cattle.

The occurrence of 3 mites (Acari: Astigmata) is reported, from the Central African hedgehog Erinaceus albiventris Wagner, in the Nairobi area of Kenya. Notoedres oudemansi Fain (Sarcoptidae) showed sporadic incidence, affected males particularly and caused high mortality. A description of the male mite is given. Caparinia erinacei Fain (Psoroptidae) was found on 72% of animals on capture but showed very low pathogenicity. Rodentopus sciuri Fain (Hypoderidae) was found in the hair follicles of 46% of 43 animals examined; adverse effects were slight.