Evidence for the presence of 11 intestinal parasites in pre-school children from 4 rural villages in Ghana was obtained from an examination of stool samples. Striking differences were detected between the prevalence of some of the 6 common infections in the 4 villages. The prevalance of Ascaris lumbricoides varied from about 76% in one village (Oshiyie, coastal savanna) to apparently 0% in another (Akuma, forest zone). No differences in prevalence for any infection were observed to be sex dependent. Investigation of the relationship between age of the children and prevalance showed that the degree of prevalence of both A. lumbricoides and Trichuris trichiura had essentially levelled off by the time the children were 4 years old. There was no evidence to suggest that the prevalence of either Entamoeba sp. or spp. or hookworm was approaching a maximum value, even in the oldest children. These trends applied across the villages regardless of the differences in prevalence values for the infections. On average, the children of Oshiyie were found to harbour twice as many infections as the children of the other villages. The investigation of the prevalence data revealed evidence of associations between pairs of infections, particularly those involving hookworm and T. trichiura.

A variety of morphological forms developed during monophasic culture of ruptured brood capsules of equine Echinococcus granulosus. Attached to some protoscoleces were small posterior bladders, with a surface ultrastructure of truncated microtriches, and these never developed a laminated layer. In contrast, small free vesicles of similar size and ultrastructure, but devoid of an attached protoscolex, produced a layer by 20–30 days. The surface ultrastructure of both these forms is similar to that of the protoscolex attachment stalk and the brood capsule lining, and posterior bladders and small free vesicles are considered to be derived from portions of the stalk±part of the brood capsule lining retained at protoscolex release. Also present were large vesicles interpreted from their size and surface anatomy as ruptured, everted brood capsules. When devoid of attached protosoleces these formed cysts each with a laminated layer, whereas similar vesicles with several attached protoscoleces did not develop a layer, or only very occasionally after 70 or more days. In contrast, a few large vesicles with a single attached protoscolex produced a laminated layer. The possibility that protoscolex attachment to stalk remnants or brood capsules inhibits the cystic development of these structures is discussed.

Mating was observed in populations of Gyrodactylus turnbulli from guppies. Copulation took place between older (post-1st birth) flukes and resulted in the insemination of spermatozoa into the seminal receptacle. New-born flukes, and flukes which had only recently given birth for the first time (in which the penis was absent or developing), were never inseminated. Flukes were promiscuous, copulating with several partners in succession. The occurrence of mating was related to the size, age and crowding of the G. turnbulli population, taking place most frequently when the parasites were most densely crowded upon the peduncle of the fish on days 5 and 6 of the infection. Maximum population size was positively correlated with the number of flukes initiating an infection. As a result, mating began earlier, and continued for longer in populations founded by several parasites rather than those begun by single flukes. These observations are discussed with respect to the population biology of G. turnbulli: it is likely that sexual and asexual reproduction alternate, with sex being important only during phases of epidemic population growth. The significance of sex in gyrodactylids is discussed, and the potential importance of continuous sexual reproduction in G. turnbulli infections on cultivated guppies is noted.

1. The oxidation-reduction potential in cultures of E. histolytica has been studied. It was found that a close relation exists between the potential in the culture and the growth, encystation, and excystation of E. histolytica. The small differences observed in different cultures indicate the reproducibility of the potentials and the reliability of the potential condition in explaining these biological activities of the amoebae in culture.

2. The best growth of trophozoites was observed at potentials between −350 and −425mV., less at potentials between −275 and −350mV., still less at between −200 and −275mV. At potentials between −150 and −200mV. a bare increase in number of trophozoites was noticed. Between potentials of −50 and −150mV. no increase of growth was observed. Trophozoites were found dead in 12 hr. or more at potentials between −50 and +50mV., and died and disintegrated in a couple of hours between potentials of +100 and +200mV.

3. The life span of a culture of E. histolytica was also found to be related to the potential condition. The longer the potential in the culture remains below −150mV., the longer the culture remains positive.

4. Excystation of E. histolytica, no matter in what media, took place only at potentials of −115mV. or lower.

5. Mass encystation of E. histolytica was induced in cultures in which a ‘sharp rise of potential’ occurred after a greatly increased rate of multiplication of trophozoites after 22–24 hr. of incubation. Maturation of cysts occurred during this period of ‘sharp rise of potentials’. If the potential went down shortly after its sharp rise, the cysts failed to become mature and disappeared in about 12 hr.

6. Trophozoites and cysts observed in cultures with very low potentials (below −300mV.) and a rapid multiplication were definitely smaller than those in cultures having higher potentials and trophozoites multiplied slowly.

7. In cultures of amoebae in which mass encystation failed to occur, or mass encystation occurred but cysts failed to become mature, some success was observed in a few trials by artificially creating the ‘sharp rise of potential’ by oxygenation.

8. The pH values noticed in cultures at times of encystation ranged from 6.4 to 6.8. This pH range was a little lower than that observed previously. Mass encystation failed to occur at the change in potential if the pH was 7.2 or higher.

9. It is felt that the process of encystation requires, at least, two extrinsic and one intrinsic factors. The first two are the potential change from more favourable to less favourable conditions and the pH. The last one is the tendency to encyst possessed by the amoebae.

10. The low potential condition in a culture of E. histolytica was found chiefly provided by the activity of the accompanying bacteria. It is, therefore, felt that the indispensability of a bacterial flora for cultivation of amoebae may be explained, partly if not entirely, by the potential relation. To verify this statement, it is hoped to propagate E. histolytica in cultures in which a strongly reducing condition is provided without the presence of bacteria.

The author wishes to acknowledge the kindness of Dr David Weinman of this department in making many invaluable corrections of this manuscript, and he is very grateful to Mrs Elizabeth B. Keller and Mrs Wanda Reed for their help in preparing the graphs accompanying it.

Naturally occurring immunoglobulin M antibodies to Toxoplasma gondii in human sera were examined for their ability to enhance toxoplasmacidal activities of human neutrophils to show a role of natural antibodies in immunity to the early stage of Toxoplasma infection in humans. Neutrophils were mixed with tachyzoites at a ratio of 1:5 in the presence or absence of antibodies and were cultured for 1–18 h for microscopical examination. The count of tachyzoites phagocytosed in 200 neutrophils within 1 h was significantly higher in the presence of sera with natural IgM antibody levels of > 0.8 than those of < 0.1, with 2.4- to 2.9-fold differences (P < 0.02). The total tachyzoite counts at 18 h decreased to 26–39% of those at 1 h in the presence of natural IgM antibody levels of > 0.8 (P < 0.01), while the counts at 1 h consistently increased by 18 h in the absence of natural IgM antibodies. These results indicate that relatively high levels of natural IgM antibodies enhanced phagocytic and microbicidal activities of neutrophils against Toxoplasma. The enhancement was dose dependent, and was also weaker than that obtained with the same dilution of sera from individuals with chronic or acute infections. Live and dead tachyzoite counts in infected neutrophils suggested a quicker effect of natural IgM antibodies than IgG antibodies elicited by infection.

One diphyllidean and five tetraphyllidean cestodes from Australian elasmobranchs are described and figured. Echinobothrium heroniensis sp.nov., from Himantura granulata (Macleay, 1883) possesses two groups each of 42 apical hooks, eight rows each of 25 hooks on the cephalic peduncle and ten testes in each proglottid. In Anthobothrium sexorchidum sp.nov. from T. lymna (Forskal, 1775) there are only six testes and the bothridium is irregularly divided into a number of shallow areolae while in Rhinebothrium himanturi sp.nov. from Himantura granulata there are 22 proglottids, 52 loculi and 19–20 testes. Comments are made on the taxonomy of Rhinebothrium sp., Spiniloculus mavensis and Yorkeria parva. The value of some helminths, especially cestodes from elasmobranchs, as an aid to the study of the taxonomy, biology and zoogeography of their hosts is briefly discussed with reference to some previous papers on this topic. Previous work on the cestodes of Australasian marine fishes is summarized briefly.

To combat schistosomiasis, the World Health Organization (WHO) recommends that infection levels are determined prior to designing and implementing control programmes, as the treatment regimens depend on the population infection prevalence. However, the sensitivity of the parasitological infection diagnostic method is less reliable when infection levels are low. The aim of this study was to compare levels of Schistosoma haematobium infection obtained by the parasitological method vs serological technique. Infection levels in preschool and primary school-aged children and their implications for control programmes were also investigated. Infection prevalence based on serology was significantly higher compared with that based on parasitology for both age groups. The difference between infection levels obtained using the two methods increased with age. Consequentially, in line with the WHO guidelines, the serological method suggested a more frequent treatment regimen for this population compared with that implied by the parasitological method. These findings highlighted the presence of infection in children aged ⩽5 years, further reiterating the need for their inclusion in control programmes. Furthermore, this study demonstrated the importance of using sensitive diagnostic methods as this has implications on the required intervention controls for the population.

Great confusion prevails in literature with regard to the various species of nematode worms inhabiting the air-passages and blood-vessels of whales, porpoises and dolphins. These worms form a group analogous, and, as we believe, very closely related to the genera Metastrongylus, Dictyocaulus, Synthetocaulus, and Haemostrongylus, which occur in similar situations in terrestrial mammals. The genera named are referred to the family Meta-strongylidae Leiper (1908), as restricted by the exclusion of the forms now included in the family Trichostrongylidae Leiper (1912). The forms found in Cetacea, of which the typical genus is Pseudalius, have been ranked first as a subfamily Pseudaliinae of “Strongylidae” by Railliet and Henry (1909) and later as a family Pseudaliidae of Strongyloidea by Railliet (1916).

Helminth parasitology is an important discipline, which poses often unique technical challenges. One challenge is that helminth parasites, particularly those in humans, are often difficult to obtain alive and in sufficient quantities for study; another is the challenge of studying these organisms in vitro – no helminth parasite life cycle has been fully recapitulated outside of a host. Arguably, the key issue retarding progress in helminth parasitology has been a lack of experimental tools and resources, certainly relative to the riches that have driven many parasitologists to adopt free-living model organisms as surrogate systems. In response to these needs, the past 10–12 years have seen the beginnings of helminth parasitology's journey into the ‘omics’ era, with the release of abundant sequencing resources, and the functional genomics tools with which to test biological hypotheses. To reflect this progress, the 2019 Autumn Symposium of the British Society for Parasitology was held in Queen's University Belfast on the topic of ‘post-genomic progress in helminth parasitology’. This issue presents examples of the current state of play in the field, while this editorial summarizes how genomic datasets and functional genomic tools have stimulated impressive recent progress in our understanding of parasite biology.

CBA/T6 strain mice infected with Plasmodium berghei ANKA develop cerebral symptoms and die, with mononuclear cell attachment to the cerebral microvascular endothelium, petechial haemorrhages and breakdown of the blood–brain barrier, some 6–7 days post-inoculation. The effects of dietary restriction on this process were examined. Mice were fed ab libitum (Group 1) or their food was restricted to produce body weight loss of 1·0–2·0 % (Group 2), 2·5–3·5 % (Group 3), 4·0–6·5 % (Group 4) or 7·0–9·5 % (Group 5) relative to Group 1. Dietary restriction reduced deaths caused by cerebral malaria from 100% in Group 1 to 47% (Group 2), 43% (Group 3), 10% (Group 4) and 53% (Group 5). Restriction of food intake had no effect on (1) the progression of parasitaemia in infected mice (2) changes in haematocrit, spleen weight, total lymph node cell number or (3) peritoneal exudate cell number in either malaria-infected or uninfected mice. P. berghei ANKA infection did not significantly affect the proportion of lymph node leucocytes that were Thy-1+T cells or CD8+T cells, but did lead to significant increases in the CD4+ and B cell populations. Dietary restriction alone increased the lymph node CD4+cell population but did not affect the increase in B cells in malaria-infected mice. P. berghei ANKA infection and dietary restriction together did not lead to increased CD4+cell numbers in lymph node leucocytes. The in vitro proliferative response of isolated lymph node cells to concanavalin A or phorbol myristate acetate plus ionomycin was measured and found to be identical in all treatment groups. Plasma levels of tumour necrosis factor (TNF) increased from undetectable in uninfected mice or P. berghei ANKA-infected mice on days 1–6 post-inoculation to 21 ± 2 ng/ml on day 7 when cerebral symptoms were at their height and death was imminent. This increase in plasma TNF was substantially inhibited in those mice subjected to regimes of dietary restriction. There was a good correlation (r2 = 0·73) between plasma TNF level and percentage mortality in the 5 treatment groups. The results indicate that dietary status is an important factor in the outcome of murine cerebral malaria and perhaps, by extrapolation, in the human disease.

Plasmodium vinckei chabaudi (which has a 24 h cycle with high synchronicity) has a peak of schizogony in the early morning at about 02.00–04.00. This cycle is orientated to the cycle of the host (mouse or thamnomys). The male gametocytes become ripe for exflagellation in a well-marked wave from 22.00 to 08.00 with peak about 00.00–04.00. This timing presumably corresponds to the hours when the vector mosquitoes are most likely to suck blood, and it is adapted to facilitate transmission. The male gametocytes remain ripe for exflagellation for a mean period of about 6 h and then apparently degenerate.

The distribution of the integumentary papillae of the cercaria of Himasthla secunda has been studied by a variety of techniques. Structures stained by silver nitrate and visible under the light microscope correspond in their spatial distribution with papillae observed under the scanning electron microscope. The tegumentary papillae described with the light and scanning electron microscope are correlated with the specialized nerve endings in the tegument as seen in transmission electron microscopy. The ultrastructure of these papillae is examined by conventional transmission electron microscopy and the probability that these structures are sensory is discussed.

Freshly isolated pronephric leucocytes from roach, Rutilus rutilus and gudgeon, Gobio gobio were exposed to extracts of plerocercoids of Ligula intestinalis from these two cyprinid fish. Addition of the extracts or an increase in incubation temperature from 10 to 20 °C induced polarization of neutrophils and L1 granulocytes. Cells were transformed from their typical spherical shape to elongate forms possessing a ruffled leading edge. Extracts obtained from gudgeon-Ligula stimulated polarization of both roach and gudgeon leucocytes at 10 and 20 °C. In contrast, extracts from roach-Ligula, whilst having little effect at 10 °C, suppressed temperature-induced polarization of leucocytes at 20 °C. Addition of serum to all the essays enhanced polarization and abolished the roach-Ligula-induced suppression. It is suggested that leucocyte chemoattractants are present in Ligula from roach and gudgeon and only parasites from the former host contain an inhibitor of polarization. In addition, host-derived factors possibly complement, may be involved in leucocyte chemoattraction.

The fine structure of the envelopes surrounding hatched and unhatched oncospheres of Hymenolepis nana has been investigated by transmission and scanning electron microscopy (SEM), together with light microscope histochemical observations of JB-4 embedded material. The oncosphere is surrounded by 3 layers – the capsule, the outer envelope and the inner envelope, the latter giving rise to the embryophore and the ‘oncospheral membrane’. An additional layer – the polar filament layer – lies between the ‘oncospheral membrane’ and the oncosphere. Shell material is deposited on the capsule as a thin layer. It is secreted by the outer envelope, which degenerates once shell formation is complete. The uterus may also contribute to shell formation. The embryophore forms a thin, incomplete and peripheral layer within the inner envelope. In the basal region of this envelope, partial development of an ‘oncospheral membrane’ takes place, but it does not become detached as a separate layer. The polar filaments, which are characteristic of the oncosphere of H. nana, are derived from the epithelial covering of the oncosphere itself, which delaminates to form a separate polar filament layer. The filaments arise from knob-like projections at opposite poles of this layer. The design of the embryonic envelopes in H. nana show a number of modifications from the basic cyclophyllidean pattern, and these can be related to the demands of its ‘direct’ life-cycle.

Histological, histochemical and ultrastructural methods have been used to study the gut structure and digestive physiology in the parasitic nematode Cyathostomalari E. Banchard, 1849. The nematode is parasitic in the orbito-nasal sinuses of its host and feeds exclusively upon blood.

Three gland cells are present in the oesophagus, one in each sector. The two subventral gland ducts open into the lumen of the oesophagus at the level of the nerve ring, and the dorsal gland duct into the base of the buccal capsule. It is suggested that the latter gland may produce an anticoagulin, histolytic and/or haemolytic secretions, histochemically-inactive in situ. The intestine is syncytial, with no differentiation into secretory components, and its distal surface is provided with a prominent brush border of long microvilli.

A non-specific esterase, thought to originate in the oesophageal gland secretions, causes haemolysis of ingested erythrocytes. The major part of haemoglobin digestion is extracellular, partly by a process of contact digestion on the microvilli, initiated by the esterase, and the protein is then further broken down by an exopeptidase of the ‘leucine aminopeptidase’ type, and the products absorbed into the gastrodermis possibly with the aid of an acid phosphatase present on or in the microvilli. An insoluble iron-containing compound, which is not haematin, results from breakdown of the prosthetic group. A smaller proportion of haemoglobin is taken up by the gastrodermis and digested intracellularly by the action of lysosomal hydrolases. An endopeptidase and an acid phosphatase are present in the gastrodermis, possibly in sacs of GER which are suggested to be primary lysosomes and which fuse with the endocytosed heterophagosomes. The insoluble pigment haematin results from digestion within the heterolysosomes, and this gives rise to the iron-containing gastrodermal pigment granules. The products of extracellular digestion are absorbed by the gastrodermis where they are synthetized into lipid by a lipase, which probably resides in whorls of GER.

This investigation was supported in part by Research Grant AI 06295 of the United States Public Health Service. The final manuscript was prepared during the tenure of a Postdoctoral Fellowship from the British Egg Marketing Board. I wish to extend my gratitude to Dr J. B. Jennings for advice and encouragement throughout this work.

An immunogold ultrastructural study was made of Cryptosporidium parvum-infected intestinal cells from SCID mice to locate parasite antigens recognized by monoclonal antibodies raised against sporozoite or oocyst wall antigens. The results suggested that these antigens were present in more than one life-cycle stage and demonstrated that the intracellular parasite modified the parasitophorous vacuole membrane and villous membrane surrounding the parasite. In an immuno-fluorescence antibody test monoclonal antibody (MAb) IB5 reacted with the oocyst wall, MAb 2C3 with the whole sporozoite and MAb 2B2 with the sporozoite surface. Western and dot-blot studies demonstrated that different carbohydrate epitopes were recognized by the respective sporozoite-reactive antibodies. In the ultrastructural examination MAb 1B5 reacted with macro- and microgametocytes as well as the oocyst wall. In the macrogametocyte MAb 1B5 recognized the large electron-dense bodies characteristic of this stage and, in some parasites, the parasitophorous vacuole and the parasite pellicle. The sporozoite-reactive MAbs were able to bind to all developmental stages. These antibodies recognized the parasite cytoplasm and, additionally, MAb 2B2 produced substantial labelling of the parasite membrane. Significantly, both these antibodies also detected antigen in the parasitophorous vacuole membrane and, to a lesser extent, the villous membrane surrounding the parasite.

In Part I the musculature of the internal organs of the male blow-fly, C. erythrocephala, testis, vas efferens, accessory gland, vas deferens, and ejaculatory sac and duct, is described, together with the movements observed in them and the passage of secretions down the system. It is suggested that the testicular and accessory gland secretions are ejaculated separately. The musculature, mechanics and co-ordinated movements of the external organs and associated structures are also described.

In Part II the generative organs of the female, except the ovaries, with special reference to their musculature and movements, and the musculature of the ovipositor are described and compared with those of M. domestica. It is suggested that the male accessory gland secretion is kept separate from the testicular secretion, the former passing into the lateral sacs of the female and the latter into the spermathecae.

In Part III the relation of the parts of the two sexes during coitus is discussed.

Clun forest sheep, worm-free from birth, were given a single dose of 20000 infective larvae of Haemonchus contortus. The total number of eggs/day in the faeces was recorded for 21 infections and data on population size, sex ratio and individual worm development were collected from 76 sheep. The female to male ratio was 1·28±0·07 (s.E.). The relation between increase in worm size and uterine egg content was linear. The number of eggs present in the uteri was found to be an accurate measure of eggs passed. It was shown that the daily faecal egg output is related to total parasite weight and is not a measure of the number of individuals present.

Eggs of three species of Diclidophora were incubated in alternating 12 h periods of light and darkness at 13°C. Eggs of D. merlangi collected at Arbroath hatched during the illumination period with most larvae being recovered in the first 4–6 h; some evidence of a seasonal difference in hatching of these eggs was found. Eggs of D. merlangi collected at Plymouth hatched with a peak of larval recovery in the 2 h period before the light came on. Eggs of D. luscae hatched over ‘dusk’ while those of D. denticulata hatched after the light was switched off. Neither mechanical disturbance nor the proximity of host tissue caused hatching in D. merlangi or D. luscae. Observations on the behaviour of the host fishes suggest that the hatching rhythms are adapted to specific host behaviour patterns.

Maximum levels of protective antibody activity were reached in the circulation of rats given a primary infection or one or two re-infections of Plasmodium berghei at the time the infection was finally eradicated. This association of maximum protective antibody activity with complete clearance of the parasite was also found in recipients of lymphoid cells from immune donor rats and suggests that a high level of protective antibody activity is one essential factor in complete elimination of the parasite.

Excellent technical assistance was given at different times by Mrs J. Page, Mr A. J. Edwards and Miss D. Leader.