The surface architecture of adult male Schistosoma mansoni was explored using a range of lectins with differing carbohydrate specificities. Highest specific binding was achieved with concanavalin A and the agglutinin of molecular weight 60000 from Ricinus communis; the binding of wheat germ agglutinin was mostly non-specific. Small amounts of peanut agglutinin and soybean agglutinin binding were observed and the binding of these lectins was increased by pre-treating the parasite with neuraminidase. The fucose binding protein of Lotus tetragonolobus failed to bind. These results indicate that mannose and/or glucose, galactose, N-acetyl-glucosamine, N-acetyl-galactosamine and sialic acid are exposed on the surface of the adult male schistosome.

The frequency distribution of an ectoparasitic mite, Gammaridacarus orchestoideae, on its amphipod host, Orchestoidea corniculata, was found to differ significantly from random for all monthly samples taken between October 1977 and October 1978. The negative binomial distribution provided a good fit to these aggregated distributions. The degree of aggregation was negatively correlated with the prevalence of infestation. Prevalence and intensity were highest in the winter, when the degree of aggregation was lowest, and vice-versa in the late summer. This seasonal pattern can be explained through changes in size and density of the host population, which are associated with changes in the size of the habitat of the hosts. Within each sample the host population was highly heterogeneous with regard to infestation by mites. Females carried heavier loads of mites than did males. Both prevalence and intensity were low in the post-moult stages of the moult cycle. Reproductive females showed lower prevalence and intensity of infestation than did either non-reproductive females or males. Analysis of the regression analysis of ‘mean crowding’ on mean density also indicated that aggregation stemmed from a non-random distribution of individual parasites, rather than from clumping of the infective stages of the parasite. Heterogeneity of the host population is suggested as an important cause of the aggregated distribution of the parasite population.

The truncated negative binomial distribution is used to demonstrate water mite-induced mortality in a field population of the mosquito host Anopheles crucians. Consistent changes in the parameters of this distribution and in the number of hosts expected in higher mite load classes as truncation is applied to successively lower mite load classes suggest that many heavily parasitized individuals were missing from field samples. These changes are not observed in distributions derived from an association between parasitic larvae of another water mite, Hydrachna conjecta, and the insect Sigara ornata, which is apparently immune to this parasite. Although the method discloses parasite-induced mortality that is non-linearly related to parasite load, it fails to reveal linear parasite-induced mortality in a hypothetical example.

A delayed gamma distribution satisfactorily described the distribution of times to hatching of Ostertagia circumcincta eggs incubated in 0·1% saline at temperatures between 6 and 20 °C. Below 6 °C hatching of eggs was extremely variable. The relationship between rates of development and temperature within the range 10 to 20 °C was more closely described by a non-linear function than a linear one. The non-linear function was incorporated into a temperature summation equation which satisfactorily predicted the hatching of eggs incubated under conditions of alternating temperatures.

Infection of intact (nu/+) or hypothymic (nu/nu) BALB/c mice with the lethal intra-erythrocytic parasite, Babesia rodhaini, induced several changes in the surface proteins of red cells from infected blood. Lactoperoxidase-catalysed radio-iodination was used to compare the surface proteins on normal mouse erythrocytes and the total red cells from infected blood at different levels of parasitaemia. At very low parasitaemia, when only 2·5% of the red cells contained parasites, we observed significant changes in the profile of radio-iodinated proteins separated by SDS-polyacrylamide gel electrophoresis. These changes included the appearance of a group of high molecular weight proteins, and a protein with an apparent molecular weight (Mr) of 60 000, both of which were absent from normal erythrocytes. The major labelled band on the erythrocyte surface (Mr 92 000) also appeared to be less heavily labelled during infection. The magnitude of these differences in surface proteins increased as the parasitaemia rose, until the new bands dominated the radioactivity profile with blood of greater than 50% parasitaemia. Several control experiments established that the radio-iodinated proteins were surface molecules on intact cells and that artifactual proteolysis did not contribute to the observed differences. The results suggest that changes in the surface proteins occur on all red cells in the blood of infected mice. The results of labelling the surface glycoproteins by oxidation with periodate or galactose oxidase, followed by NaB3H4 reduction, have varied with the isolate of B. rodhaini. With the isolate currently in use, no significant differences were observed in the labelled surface glycoproteins of normal erythrocytes and red cells from infected blood of high parasitaemia, whereas an earlier isolate exhibited a marked decrease of glycoprotein labelling of both infected and uninfected red cells.

Lactating and nulliparous outbred Swiss (CF-1 strain) mice were infected at 12–16 weeks of age with Nippostrongylus brasiliensis or Trichinella spiralis. Lysophospholipase B levels in the intestinal tissue and faecal pellets were greatly depressed in infected lactating mice in contrast to infected nulliparous mice. Correlated with these depressions in lysophospholipase levels were markedly reduced numbers of bonemarrow eosinophils in infected lactating mice. Although the peak levels of lysophospholipase in the intestinal tissues occurred in both nulliparous and lactating mice by days 9 and 14 after infection with N. brasiliensis and T. spiralis, respectively, lactating mice had significantly lower lysophospholipase peak levels than nulliparous mice. The peak of luminal levels of the enzyme coincided with peak levels of the enzyme in the intestinal tissues and with theexpulsion of the majority of the worms from the small intestines of nulliparous mice. However, lactation delayed the temporal relation between the peak of lysophospholipase levels in the intestinal lumen and worm expulsion. These results suggest that lactation depressed the levels of the enzyme and interfered with its release into the intestinal lumen.

The surface proteins and glycoproteins of red cells from Plasmodium berghei-infected blood have been radio-isotope labelled and compared with those of normal mouse erythrocytes using the following protein labelling probes: lactoperoxidase-catalysed radio-iodination of tyrosyl residues, periodate oxidation and NaB3H4 reduction of sialic acid and oxidation of galactosyl/N-acetylgalactosaminyl residues by galactose oxidase with subsequent NaB3H4 reduction. During P. berghei infection, new tyrosyl-labelled proteins with apparent molecular weights (Mr) of 60000, 54000, 40000 and 27500 appeared on the surface of most, if not all, red cells in the blood. Purified multinucleate cells (mostly reticulocytes) differed only in that they also had a surface protein with Mr of 83000. However, this molecule is thought to be specific to mouse reticulocytes rather than derived from parasites. In contrast to the relatively minor changes detected with radio-iodination, striking changes in glycoprotein radio-isotope labelling resulted from infection. All of the red cells in infected blood of greater than 20% parasitaemia lost their periodate-sensitive glycoprotein sialic acid. With some samples there was little change in glycoprotein labelling by the galactose oxidase method, provided neuraminidase was also added. Modification of the exocyclic hydroxyls of sialic acid is postulated to account for this. Other blood samples exhibited a dramatic loss of galactose oxidase-dependent labelling. It is suggested that these observations may relate to the excessive red cell destruction of uninfected as well as infected cells which has been inferred in many haemosporidial infections, including malaria.

The development of the free-living stages of Ostertagia ostertagi incubated at constant temperatures from 5 to 27 °C and in dung pats in the field was observed. The death rates were adequately described by a single exponential function and the distribution of times for development by a delayed gamma density function. The times of appearance of selected development stages such as maximum numbers of embryonated eggs and half the maximum number of infective larvae, were highly dependent on temperature. The relationships between these times and temperature were adequately described by the Arrhenius equation. The parameters of this equation and mean hourly temperatures recorded in dung pats in the field were used to predict development times in the field. A comparison of predicted and observed times showed that an initial delay accounted for a large proportion of the time required for development in dung pats, particularly the embryonation of eggs. This delay was attributed to lack of aeration associated with high moisture content of the dung pat.

The structure of the intestine of adult Nematodirus battus is described. It is similar tothe intestine of some other trichostrongyles but with a few minor differences. Changes in the structure of the intestinal cells are described in N. battus taken from lambs during the later stages of an infection (days 20 to 32) with 60000 infected larvae. The mostnoticeable changes were a decrease in the amounts of glycogen and smooth endoplasmic reticulum, a reduction in the numbers of secretory-type granules and the appearance of vacuoles within the cells. Some of these vacuoles contained small crystals, and crystals, some of them large, were also found in the intestinal lumen. These changes, with the exception of the appearance of the crystals, are similar to changes described for Nippostrongylus brasiliensis affected by the immune response of the rat host, and it is concluded that the changes in N. battus could have been initiated by an immune response to this nematode in the lamb. Lambs given 2000 larvae of N. battus do not reject the nematodes in 32 days, and no changes were observed in the structure of these nematodes.

Lactoperoxidase-catalysed radio-iodination was used to compare the surface proteins on red cells from Plasmodium yoelii-infected and normal BALB/c mice. The profile of radio-iodinated proteins separated by SDS-polyacrylamide gel electrophoresis was different for infected blood of similar parasitaemia from mice inoculated with different doses of the parasite. Inoculation with the lower dose resulted in the appearance of a major radio-iodinated protein of apparent molecular weight (Mr) 76000 which was labelled to a similar extent on uninfected red cells from infected blood and purified multinucleate infected cells. Several minor radio-iodinated bands, with identical mobilities to the minor bands on normal BALB/c erythrocytes, were also present on red cells from this infected blood. In contrast, the higher inoculation dose produced changes in the minor labelled bands, and the band with Mr of 76000 was absent. In this case, the minor radio-iodinated proteins of the normal BALB/c erythrocyte (with Mr of 65000, 57000, 48000, 38000 and 32000) were replaced by a series of bands with Mr of 60000, 50000, 43000 and 28000 on both uninfected and infected red cells. These differences with inoculation dose may be related to the different duration of these infections, the development of anaemia and the extent of pathological changes at the erythrocyte surface. P. yoelii infection caused a marked loss in periodate-dependent labelling of sialoglycoproteins on most, if not all, red cells in infected blood. There was also a large decrease in galactose oxidase-dependent glycoprotein labelling with or without neuraminidase treatment. These changes in the carbohydrate groups on red cell membrane glycoproteins may be linked to the excessive loss of both uninfected and infected red cells during some malaria infections.

Eggs of Oesophagostomum dentatum in faeces deposited on grass plots from May to October developed into infective larvae. Warm wet weather facilitated development but weather conditions which caused the faeces to dry out rapidly resulted in a heavy mortality of eggs and pre-infective larvae. During the winter no development took place and the eggs died. In the early spring and late autumn a few eggs survived and developed into 1st-stage larvae but they died without developing further. In the laboratory no development took place at 4 °C but at temperatures ranging from 10 to 25 °C development into infective larvae was completed, the rate increasing as the temperature rose. Out-of-doors infective larvae survived in faeces and on herbage for 1 year under a wide range of climatic conditions including the exceptionally cold winter of 1978–79. In the laboratory, infective larvae suspended in water survived even longer at temperatures ranging from 4 to 27 °C. They were rapidly killed by continuous freezing and by desiccation when the relative humidity was less than 90%. The relationship between climatic conditions and the development and survival of the free-living stages is discussed.

An in vitro culture system incorporating a cell monolayer was used to induce most activated oncospheres of Taenia ovis to enter post-oncospheral development. Seven distinct developmental phases were recognized during the 23 days required for development to reach a stage similar to that achieved after 14 days in vivo. Secretions or tegumental substance were released during each developmental phase.

A simple in vitro technique was devised to culture chick embryos in Petri dishes from the 4th to the 21st day of incubation. Leucochloridiomorpha constantiae (Trematoda) metacercariae were placed either singly or multiply (5/embryo) on the chorio-allantois of in vitro grown embryos on day 7 and were removed on day 14. Growth and development studies were also made on worms grown singly or multiply (5/chick) in the bursa of Fabricius of the domestic chick. Worms grown singly or multiply in embryos were sexually mature, although eggs from these worms were abnormal when compared with eggs from worms recovered from chicks. The mean body area of worms from chicks was 2–3 times greater than that of worms from embryos. The mean body area of single worms from embryos was significantly larger than that of worms grown multiply in this site. However, the mean body area of multiple worms from the chick was significantly larger than that of single worms from this site. Worm pairs or clusters were seen in all embryos with the multiple infections.

Pathogenic effects caused by graded doses of recent isolates of Eimeria acervulina, E. mivati and a new isolate, thought at first to be E. mitis, were compared. Cross-immunity studies were conducted with 3 strains of E. acervulina and 2 strains of E. mivati, together with the new isolate. The results showed marked similarities between E. mivati and the new isolate and clear distinctions between these and E. acervulina. E. mivati produced scattered petechiae but did not form discrete lesions in the intestine comparable to those seen with E. acervulina. Endogenous stages of E. mivati were most numerous in the lower small intestine and proximal caeca. The ratio of villus height to total mucosal thickness in the lower intestine was reduced. Similar changes caused by E. acervulina were seen in the anterior intestine only.

Eimeria meleagrimitis oocysts were stored at 4, 22, 32 or 41·5 °C for up to 1 year. Decreases in amylopectin levels (measured as glucose) and viability (measured as oocyst production and mortality in turkeys) of the oocysts were generally related to the length of time in storage and the storage temperature. Oocysts assayed immediately after harvest contained 58·29 ± 0·75 μg of glucose/106 oocysts. When the oocysts were stored at 4 °C for 162 days, the amylopectin level decreased to 65% of the original level. In oocysts stored at 22, 32 and 41·5 °C, amylopectin declined to approximately 20% within 162, 76, and 41 days, respectively. Oocysts stored at 4 °C for 1 year produced more oocysts in turkeys than the original fresh isolate, but caused no mortality. Oocyst production from oocysts stored at 22 and 32°C decreased gradually until, after 9 and 7 months respectively, no patent infections were produced. Oocyst production from oocysts stored at 41·5 °C was markedly reduced within 1 month and was not detected after 4 months.

The formation of the cyst wall surrounding Bucephalus haimeanus and the related changes in the parasite tegument during its metamorphosis from the cercarial to the metacercarial stage have been investigated by means of experimental infections in Gobiusculus flavescens. The initial fibrous cyst wall is formed from secretions produced by both the anterior gland cells and the tegument of the parasite. These secretions gradually become compacted against the surrounding hepatic cells until by the 20–30th day post-infection the 3-zoned inner layer, characteristic of the fully developed cyst wall, is formed. Hepatic cells immediately adjacent to this inner cyst wall layer are disrupted by the arrival of the metacercaria and form the middle vacuolated layer. As the metacercaria grows, the cyst increases in size causing still further hepatic cells to become flattened and incorporated into the cyst structure forming the outer nucleated layer. The structure of the cercarial tegument is described. Development of the metacercarial tegument is accomplished by the sequential movement of secretory vesicles from tegumental cell bodies into the outer cytoplasmic tegument. Vesicles of the types V. 1–5 are released from the outer cytoplasmic tegument, resulting in an almost complete breakdown of this layer prior to its replacement by the tegument of the fully developed metacercaria. The latter is characterized by the V. 6–9 type vesicles, dorso-ventrally flattened spines which terminate in 5–7 digits and by sensory cilia.

Sporozoites of Eimeria necatrix inoculated into the allantoic cavities of embryonating eggs completed their life-cycle in the chorio-allantoic membranes and produced fully viable oocysts. Subsequently, as a result of repeated passage in this host, an egg-adapted line was developed and was found to be markedly less pathogenic for chickens than the nonpassaged parent strain. Antigens capable of inducing protective immunity against challenge with low doses of the parent strain were retained, however, indicating a possible use for this egg-adapted (attenuated) line of E. necatrix in the immunization of comercially reared chickens.

A variety of measurements was made on small samples of schistosomula recovered from the skin, lungs and hepatic portal system of percutaneously infected mice, on the basis of which development could be divided into a migration and a growth phase. The density of schistosomula, estimated using a Ficoll gradient, was found not to vary significantly between Day 0 and Day 24 post-infection, having a mean value of 1·077. The reduced weight was measured by means of a Cartesian diver balance and used in conjunction with density to estimate the change in wet weight of schistosomula. Wet weight was found to decline slightly during the migration phase and to increase exponentially following arrival of schistosomula in the hepatic portal system. No change in nitrogen content was detected during migration but there was a rapid increase after arrival in the hepatic portal system. The rate of oxygen consumption, measured by Cartesian diver respirometer, declined significantly during migration and then increased exponentially after arrival of worms in the hepatic portal system. No change was detected in the lactic dehydrogenase activity of migrating worms but again, an exponential increase occurred after entry into the hepatic portal system. It was concluded that the migrating schistosomulum is in a semi-quiescent metabolic state, although it possesses the ability to take up nutrients and undergoes morphological changes. Growth is triggered by an unknown mechanism after arrival in the hepatic portal system. Examination of the various sets of data suggests that it is initiated between 10 and 11 days post-infection in the most advanced schistosomula.

The isolation of polysomes in bulk from bloodstream forms of Trypanosoma brucei is described. The polysomes are active in in vitro protein synthesis in the presence or absence of initiation inhibitors. Nascent variant surface antigen (VSA) has been detected on these polysomes using purified radio-iodinated antibody. EDTA-induced ribosomal sub-units and their large rRNA's are characterized. The 26S rRNA is nicked to produce 2 molecules which are both smaller than the 195 rRNA of the small sub-unit which is larger than that found in the majority of eukaryotic small sub-units.

The daughter sporocyst of Cercaria vaullegeardi has hitherto been regarded as occurring within the haemocoel of the digestive gland of Gibbula umbilicalis. A re-examination has shown that an important part of the sporocyst, previously overlooked, extends from the digestive gland, through the afferent renal vein, the right kidney haemocoel and the transverse pallial vessel into the blood channel within a gill filament, thus providing a means of exit from the host directly into the mantle cavity. The sporocyst is described at light and electron microscope levels, and the emergence of the cystophorous cercariae is discussed.