The cellular reactions to the migration of challenge schistosomula of Schistosoma mansoni through the cheek pouch skin in Chinese hamsters immunized 20 weeks previously via the abdomen has been investigated at the ultrastructural level. The composition of the leucocytic infiltrate into the dermis and epidermis changed with time after infection. At 24 and 48 h the infiltrate was composed mainly of neutrophils and mononuclear cells. At 72 h fewer neutrophils but more eosinophils were present. The interaction of the leucocytes with the challenge schistosomula is described. Degranulation of eosinophils at the cell-parasite interface has been observed. Despite the fact that approximately 30% of 48 h schistosomula and 50% of 72 h schistosomula examined had adherent leucocytes only a few of the parasites exhibited signs of damage, consisting of tegumental vacuolation and changes in the electron opacity of the tegumental cytoplasm. There was no strong evidence of increased attrition of challenge schistosomula in the cheek pouch skin relative to the primary infection, although some dead challenge parasites were observed. It is concluded that a substantial proportion of the attrition of challenge infections in the Chinese hamster occurs at a post-dermal location.

The outer tegument membranes of Schistosoma mansoni schistosomula have been removed by mechanical disruption in a hypotonic salt solution and partially purified by differential and sucrose density gradient centrifugation. Fractionation was monitored by measuring increase in specific activity of bound [125I] wheat-germ agglutinin (WGA), alkaline phosphatase and calcium-stimulated ATPase. Two-dimensional IEF/SDS polyacrylamide gel electrophoresis was used to analyse the peptide composition of the isolated membranes and to compare and contrast with lactoperoxidase/glucose oxidase surface labelled peptides. At least 35 surface-labelled peptides were resolved on the two-dimensional maps: all were also present in the membrane material recovered from the sucrose gradient. Western blot analysis demonstrated a marked heterogeneity in the antibody response of infected human patients to individual membrane antigens. The antigenic profile of membranes isolated from cercariae, 18 and 96 h schistosomula were compared using Western blots: some minor differences were observed between the three preparations.

Immunity to Hymenolepis nana was adoptively transferred to recipient mice of 4 strains using mesenteric lymph node cells (MLNC), spleen cells (SC), and/or serum taken from infected donor mice. Donor cells capable of transferring immunity appeared in the mesenteric lymph nodes and spleen at an early stage (5 days) after infection. Immunity was most effectively transferred with MLNC and immune serum did not enhance this effect. It is suggested that effective immunity to H. nana involves both antibody and T cell-mediated inflammatory events.

The ultrastructure of the tegument of Schistosoma haematobium was examined using scanning and transmission electron microscopy. The surface of the male worm is characterized by numerous raised tubercles bearing apically directed spines. The female in contrast to the male is cylindrical and relatively smooth. Details of oral and ventral suckers are given. The use of uranyl acetate as a tertiary fixative and en bloc stain has revealed the heptalaminate nature of the outer membrane. Tegumental mitochondria are shown to be morphologically more complex than those of S. mansoni. Spherical and elliptical inclusion bodies are also described. The ultrastructure of the oesophageal tegument of S. haematobium is described for the first time and corresponds with earlier observations of S. mansoni.

The tegument of adult Schistosoma mekongi has been studied by both scanning and transmission electron microscopy. The gross surface topography of the parasite resembles that of S. japonicum, in that branched ridges, microvilli and sensory papillae predominate; such characteristics distinguish these two species from the non-oriental schistosomes. A unique feature of S. mekongi, however, is the numerous pleomorphic protruberances which are concentrated particularly on the middle three-fourths of the body surface. Transmission electron microscopy has revealed that these protruberances enclose bundles of microfilaments which appear to insert into the tegumental outer membrane. The microfilaments are suggested to have a supportive or stabilizing function, and may compensate for the absence of more typical crystalline spines. The tegumental outer membrane is typically heptalaminate in section, while the basal membrane infoldings are surrounded by concentrations of mitochondria. Three types of tegumental inclusion bodies have been recognized. Discoid bodies and membraneous bodies are morphologically identical to those described in all other schistosome species, except that the latter inclusions have been seen connected to each other and to the tegumental outer membrane by unique channels lined with trilaminate membrane. The third inclusion takes the form of spherical, lucent vesicles containing membrane fragments; these may represent the remains of spent membraneous bodies.

We report the results of experimental studies of the generation of age-prevalence curves for Schistosoma mansoni infections in laboratory populations of Biomphalaria glabrata. Within snail populations of varying sizes and age structures, the net force of infection is shown to be linearly dependent on the rate at which miracidia are introduced into the aquatic habitat of the host. For individual snails, the per capita force of infection is shown to be related to snail age and size, and the death rate of shedding snails is demonstrated to be dependent on the period of time during which a snail has been releasing cercariae. Both factors are important determinants of the proportion of infected snails within populations of hosts and may generate convex age-prevalence curves. Comparisons of snail abundance in populations either exposed, or not exposed, to infection suggest that S. mansoni can act to significantly depress the population growth of its intermediate host. Mathematical models are developed, encorporating the age structure of snail populations, to aid in the interpretation of experimental results.

Adult Onchocerca volvulus worms obtained by enzyme digestion from nodules of infected Mexicans were radio-isotope labelled by the chloramine-T or Bolton–Hunter methods. No antigenic determinants were detected in extracts of worms labelled by the chloramine-T method but 3 antigens were detected in extracts of the Bolton–Hunter labelled worms. Two were present in such small amounts that it was impractical to investigate them further, but a major component of mol. wt 20 kDa was purified by gel filtration and used in a serological survey of inhabitants of villages in Southern Mexico. Using the 20 kDa antigen, which is superficially located on both sexes of O. volvulus, sera from both non-endemic and endemic regions were analysed by radio-immunoprecipitation of this antigen. In Southern Mexico, the average sensitivity of the test was 92%, and the specificity 98%. Whilst the 20 kDa antigen did not detect antibodies in the sera of Trinidadians infected with Wuncheria bancrofti or Mansonella ozzardi, this antigen detected high levels of antibodies in Indians exposed to W. bancrofti.

The morphology of the post-hatch moulting and developmental sequence of an amphimictic population of Rotylenchulus reniformis has been examined in living and fixed material. Under suitable conditions of temperature and in a moist environment the 2nd-stage larva (L2) undergoes a series of 3 moults and developmental changes which result in the formation of males and immature females. After hatching and prior to the start of the first of these moults (the second moult), there is a pre-moult period, usually of 3–5 days duration. The morphology of the entire moulting and developmental sequences, from L2 to just after the final moult, has been followed in single living specimens of a parasitic nematode using differential interference contrast optics, and sections cut through different stages have been observed under the transmission electron microscope. These moulting sequences (at 24 °C) take place at similar times in developing males and females. The second moult takes place on the second day after commencement of moulting, the third on the third or fourth days and the fourth and final moult on the sixth or seventh days, followed by further development over several days to give rise to the adult male and the immature female. The ultrastructure associated with some of the more obvious of these developmental changes is described and includes the morphology of the head region and cuticles of L2, L4, adult males and immature females, the oesophageal glands of the immature female and the copulatory spicules and spermatozoa of the male.

A stereological study was undertaken on the length, diameter and numbers of microtriches and on the structural and functional amplification factors of the adult cestodes, Hymenolepis diminuta, Hymenolepis nana, Eubothrium crassium, Proteocephalus pollanicoli, the plerocercoid of Schistocephalus solidus and the cysticercus of Taenia crassiceps. The study showed wide variations in these stereological parameters between species, stages and regionally in the same species. A comparison of the present results with previous studies has shown a large measure of agreement but some differences are evident and possible explanations of these differences are proposed.

Three groups of stocks of Trypanosoma brucei ssp, defined by the criteria of host, human serum resistance and place of isolation as T. b. gambiense, T. b. brucei (Nigeria) and T. b. brucei/rhodesiense (non-gambiense, Uganda) were screened for electrophoretic variation at 20 enzyme loci. One enzyme (Peptidase C) was found to differentiate all T. b. gambiense stocks from the other T. brucei stocks and, taken together with specific variants of 5 other enzymes, could be used to unambiguously define T. b. gambiense stocks. Using a population genetics approach, the frequencies of the different variants in the three groups of stocks were estimated and from them the average similarity and difference between groups were measured using the statistics of genetic identity (I) and genetic distance (D). These results show firstly, that T. b. gambiense is more different from the other two groups than they are from each other and, secondly, that the values of I and D obtained are consistent with T. b. gambiense constituting a sub- or sibling species of T. brucei. Three domestic animal isolates from Zaire and Cameroun were also screened for enzyme variation and two of these identified as T. b. gambiense, thereby establishing the existence of an animal reservoir host. In parallel, these stocks were tested for human serum resistance resulting in the same identification. Studies of the antigen repertoires and antigen gene structure were carried out by other workers on all the T. b. gambiense stocks reported here and the same conclusions reached as to the identification and ability to discriminate this subspecies from other groups of T. brucei stocks. The results presented here are discussed in relation to other published data on enzyme variation in T. brucei.

In PVG rats a single immunizing infection with Schistosoma mansoni cercariae exposed to 0, 5, 10 or 20 krad. gamma radiation failed to induce more than minimal resistance (17–29%) to challenge 4 weeks later, whereas 4 immunizations with 20 krad.-irradiated cercariae, over several months, induced substantial resistance (75%). In contrast, significant protection was induced in Fischer rats by a single immunization with unirradiated cercariae or cercariae irradiated with up to 80 krad. Comparable resistance was induced by unirradiated and by 2, 5 and 20 krad.-irradiated cercariae (67–74%) and lower levels by 10, 40 and 80 krad.-irradiated infections (57, 48 and 33%, respectively). Although the resistance induced by a single dose of 1000 20 krad.-irradiated cercariae could be boosted by a second (88%), further immunizations failed to enhance this resistance. Also, increasing the number of immunizing cercariae in single or multiple vaccinations from 1000 to 3000 failed to increase the resistance. While the resistance induced by 20 krad.-irradiated cercariae persisted undiminished for at least 25 weeks (67%), the resistance induced by normal cercariae declined to insignificant levels by 25 weeks (21%). Comparison of the migration and survival of unirradiated and of 20 and 40 krad.-irradiated cercariae revealed dramatic differences in their fate: parasites exposed to 40 krad. remained in the skin, while the majority of 20 krad.-irradiated parasites died in the lungs after a sojourn of at least 14 days. Thus, although skin schistosomula alone could induce significant protection, optimal resistance was induced only by parasites which migrated to the lungs or beyond. The immunizing potential of these older parasites was investigated by exposing rats to lung-and liver-stage larvae injected into the tail and mesenteric veins, respectively. Irradiated 4-day lung schistosomula induced comparable resistance (79%) to that induced by a complete unattenuated cercarial infection (78%), whereas less resistance was induced by irradiated and unirradiated 11-day-old liver worms (30 and 27%) and by 25-day-old pre-adult worms (48%).

A series of development stages (I–XI) have been devised to describe the development of the cyst wall of the metacestode of Hymenolepis diminuta. The cyst wall possesses tegumentary, muscular, fibrous and inner cyst tissues, the developmental rates and differentiation patterns of which are not identical. The tegumentary tissue differentiates posteriorly. Its microvillus-bearing distal cytoplasm remains simple until scolex retraction, after which rapid increase in depth followed by vacuolation occurs and basal membrane infoldings surround Phase 3 fibrogenesis fibrils. Senescence, which also affects the tegumentary cytons, then ensues. The muscle system development is posteriad and maturation, completed before scolex retraction, is followed by myocyton senescence. Posteriorly differentiated fibroblasts commence Phase 1 fibrogenesis after scolex retraction and the primary fibrous zone is fully established within approximately 6 days. Phase 2 and 3 fibrogenesis develop centrifugally, the fibrils of Phase 2 surrounding the tegumentary cytons and myocytons prior to their senescence, and those of Phase 3 lying more peripherally. The inner cyst tissue, established posteriorly, differentiates anteriorly, centripetally and early, the penultimate stage commencing just before scolex retraction, about 6 days after which the final maturation junctional complexes start development. Neither in vitro excystment nor infectivity of the definitive host can be satisfactorily achieved before the initial development of the primary fibrous zone. This may play a skeletal role during excystment, and is shown to be unaffected by the digestive enzymes which cause loss of cytoplasmic integrity in the outer regions of the cyst.

Circulating antigen has been detected in the serum of rabbits experimentally infected with Taenia pisiformis. A rabbit antiserum against an antigen preparation derived from the in vitro maintenance of living metacestodes of T. pisiformis was used in a double-antibody enzyme-linked immunosorbent assay (ELISA). Antigen was detected in infected rabbit serum 48 h after infection and peak levels were recorded at 2 weeks post-infection or post-challenge. The pattern of circulating immune complex formation followed closely that of circulating antigen, and infected rabbit serum contained both anti-metacestode and anti-oncospheral antibodies. Serum antigen levels were just detectable (0·4–0·8 μg protein/ml) over the period (> 2 weeks post-infection) of peritoneal cyst development. The circulating antigen probably has antigenic determinants in common with the oncosphere, juvenile and mature metacestode stages. Possible reasons for the temporal variation in serum antigen levels are discussed.

In a series of in vitro experiments, adult male and female Moniliformis dubius were incubated at pH 6·88 and 37 °C for 3 h in a 2·5 mM solution of 18 amino acids. Fifteen of these were absorbed slightly from the medium, but L-serine was almost completely absorbed while the concentrations of glycine and alanine in the medium increased during the course of the incubation. By using L-[U-14C]serine, it was found that labelled ethanol and CO2 were the main end-products of metabolism excreted into the medium, with smaller amounts of labelled alanine, lactate and acetate. Small amounts of cystathionine with high specific radioactivity were found in extracts of the worms at the end of incubation, together with other radioactive metabolites including glucose, ethanol, lactate, succinate, malate, serine, glycine and alanine. Ammonia was found to be an excretory product of the amino acid metabolism of M. dubius. Possible metabolic pathways and suggestions for the significance of serine metabolism in this parasite are discussed.

The physiology of the neuromuscular systems in Hymenolepis diminuta and H. microstoma was studied in vitro using intact, adult worm and strips of worm body wall. Intact worms were insensitive to ionic changes in the in vitro buffering system. However, strips of body wall containing longitudinal muscles were extremely sensitive to ionic manipulation. In intact worms tension generated in the strobila had two components; small brief tension peaks up to 500 mg amplitude are superimposed on larger, longer peaks of up to 1200 mg amplitude. Removal of the scolex and neck region either failed to show significant changes in tension, or showed a reduction in amplitude but not of frequency. Muscle contraction of both H. diminuta and H. microsoma were qualitatively similar. In split-worm preparations the concentration of Ca2+ in the bathing solution significantly affected both spontaneous and evoked contractions in H. diminuta and H. microstoma; the addition of CaCl2 greatly reduced the amplitude and frequency of the contractions. The chloride salts of cobalt, barium, cadmium and manganese elicited prolonged contractions of the longitudinal musculature of both H. diminuta and H. microstoma. While CoCl2 was the most effective in stimulating muscle contraction, the magnitude of the response varied with the concentration of Ca2+ in the bath. The results indicate that peripheral inhibition is extremely important in cestode motor control and that extracellular calcium ions may regulate the peripheral inhibitory mechanisms.

Acquired resistance to Schistosoma japonicum was evident after the lung phase of migration of challenge schistosomula. ‘Trickle’ infections which gave similar primary worm burdens to single infections stimulated similar levels of resistance. There was a strong correlation between the size of the primary worm burden of individual mice and their ability to resist infection 8 weeks after exposure to S. japonicum. However, acquired resistance did not develop until 6 weeks, that is after the primary infection had become patent, and was maximal some 12 weeks after infection; thereafter resistance declined. The numbers of parasite eggs deposited in the tissues increased during acute infection (duration of 12 weeks or less) and tended to stabilize or decrease during chronic infection (longer than 12 weeks). There were good correlations between the resistance of mice to challenge and the numbers of eggs deposited in their livers, guts or lungs during acute infection, but these correlations were not evident during chronic infection. The inflammatory responses to tissue-bound eggs regress during chronic infection and this may influence the relationship between acquired resistance and egg burden. Comparable primary infections of S. japonicum or S. mansoni protected equally well against both heterologous and homologous challenges. However, unisexual infections of S. mansoni, which produced no overt pathology, failed to confer protection against a challenge of S. japonicum.

Intestinal and faecal IgA responses against different developmental stages of Nippostrongylus brasiliensis were studied in Hooded Lister rats vaccinated subcutaneously with infective larvae or intragastrically with 4th-stage larvae, adult nematodes, adult worm somatic and metabolic antigens. It was found that intragastric administration of L4 or adult worms produced as high resistance to challenge as normal infection. Oral vaccination with adult nematode excretory–secretory (ES) and somatic antigens produced 69 and 17% protection respectively. All vaccination regimes induced a considerable IgA response against somatic and metabolic antigens of the intestinal stages. However, no correlation could be seen between the IgA levels and degree of protection. Analysis of intestinal mucosal, intestinal contents and faecal IgA specific to larval or adult antigens suggests that the IgA is probably induced by antigen(s) common to all intestinal stages. Also secretory IgA responses against surface antigens of intestinal L4 did not show stage specificity, although this was detected in sera.

Male CD-1 mice inoculated by gavage with 400 larvae of Trichinella spiralis exhibited an increased latency of the wall-seeking response as well as a decline in running speed and the distance travelled to the first stop when compared with normal controls or animals inoculated with only 100 larvae. Doses of 200 larvae of this parasite affected running speed and distance travelled but not the advent of the running response. Such changes in behaviour may reduce the competitive fitness of the host and render it more susceptible to predation.

The skin phase of schistosomular migration was neither essential for the induction or expression of acquired resistance since mice given primary infections by the intraperitoneal route were as resistant to intra-peritoneal or percutaneous challenge as were mice given their primary infections percutaneously. Serum taken from resistant donors with acute or chronic infections conferred no ability to resist infection upon recipient mice. In two experiments mice that were deprived of their T-cells were as resistant to infection as intact mice and both types of host had comparable tissue egg loads and liver pathology. In a third experiment the immune-deprived mice had lower tissue egg counts than the intact mice and were less resistant to challenge. It is suggested that specific immune effector mechanisms may not be involved in acquired resistance to reinfection but rather that resistance is affected by the T-cell independent immunopathology induced by tissue-bound Schistosoma japonicum eggs.

An experiment was conducted to examine, under laboratory conditions, the pathophysiology of chronic ovine haemonchosis. In the present study, groups of Merino and Scottish Blackface lambs were maintained on a low plane of nutrition and infected with 50 Haemonchus contortus larvae/kg live weight. The parasitized lambs along with respective breed controls were examined over a 27-week period. In addition to the body weight, haematological and parasitological parameters, erythrokinetic, metabolic, digestibility and nitrogen balance studies were conducted in the early stages of the infection. The results demonstrated that a low level of infection with H. contortus in lambs on a poor plane of nutrition caused the development of a normochromic normocytic anaemia which was associated with a modest but significant increase in abomasal blood loss and slightly elevated erythropoiesis in both breeds relative to the controls. The level of anaemia, hypoproteinaemia and pathophysiological changes were more marked in the Merino lambs and they also had higher faecal egg counts than the Blackface lambs.