A rapid method for the bulk isolation of purified Leishmania mexicana mexicana amastigotes from parasite-induced lesions in experimentally infected mice is described. The procedure includes purification steps based on differences in net cell charge, lysis susceptibility and buoyant density between parasite and host cells. Yields of up to 2 × 1010 untransformed amastigotes with minimal contamination with host cells and cell debris can be obtained. At least 90 % of the purified amastigotes are viable as judged by light and electron microscopy, the staining of their lysosomes with acridine orange, their ability to transform to promastigotes and their infectivity to macrophages in vivo and in vitro.

Schistosomula of Schistosoma mansoni, recovered either after penetration of cercariae through isolated rat skin or by mechanical transformation of cercariae, become fully resistant after 24–48 h of culture to damage by human blood eosinophils in the presence of human anti-schistosomular sera. Cultured schistosomula are also shown to lose their susceptibility to attack by human eosinophils in the presence of human complement. This resistance is related to the simultaneous reduction of the ability of human anti-schistosomular antibodies and human complement component C3 to bind to the surface of the cultured larvae. The development of insusceptibility to antibody, complement and eosinophil-mediated attack does not require the acquisition by the schistosomula of a protective coat of host or other macromolecules, since it is achieved in chemically defined culture medium free of serum and macromolecules. This supports the hypothesis that schistosomula undergo intrinsic changes which render them insusceptible to immune attack.

Three types of vaccine (1) a sonicated extract of killed larvae, (2) 5-fluorouracil-treated larvae and (3) 40 krad. X-irradiated larvae have been evaluated. Pups aged 3–4 months, weighing 2± 0·5 kg and free of natural hookworm infection were selected for experimental studies. The sonicated extract was given either in a single dose or as 2 doses at weekly intervals, whereas the 5-fluorouracil-treated and X-irradiated larvae were given in a single dose only. After completion of the vaccination schedule, the pups were challenged with filariform larvae and were sacrificed 3 weeks after challenge. Non-vaccinated pups and those vaccinated with a single dose of sonicated extract lost weight and had diarrhoea or dysentery after challenge. Furthermore, in non-vaccinated pups, haemoglobin levels fell and at autopsy the intestinal mucosa was found to be grossly congested and free blood was present in the lumen of the intestine. Such findings were not obtained in pups vaccinated with the other types of vaccines. The percentage of infective larvae which developed to the adult stage in non-vaccinated pups was 82·7 ± 9·53 compared with 45·1 ± 12·33, 30·1 ± 10·05, 20·6 ± 10·60 and 8·0 ± 7·46 %, respectively in pups vaccinated with a single dose of sonicated extract, double dose of sonicated extract, 5- fluorouracil-treated and 40 krad. X-irradiated larval vaccines. While the irradiated larval vaccine provided maximum protection against clinical ancylostomiasis, 2 doses of the sonicated larval vaccine could also afford almost equal protection to pups.

Antibodies to Toxocara were measured by enzyme-linked immunosorbent assay (ELISA) in sera of ascarid-free dogs which had been fed 0,100 or 10000 embryonated T. canis eggs. Dogs fed 10000 eggs developed higher titres than those given 100 eggs and larvae failed to complete their migration to the gut. In addition, in dogs given 100 eggs, there was a significant negative correlation between the number of worms in the gut and granulomatous foci in the lung. The data suggest that the ELISA is sensitive and specific for Toxocara infection in dogs.

Pasture plots in a warm coastal region were separately contaminated in the autumn, winter and spring with eggs of a coastal strain of Ostertagia ostertagi derived from dairy calves. At the same times, a parallel set of plots was contaminated by a strain transferred from within a beef cattle management system in a cooler tablelands region. A reciprocal transfer of the coastal strain was also made to the tablelands, where pasture plots were contaminated with eggs of both strains of O. ostertagi in winter. Successive groups of parasite-free calves were grazed on the plots for 10–14 days at 4-week intervals and then killed for worm counts 14 days after their removal from pasture. In both environments, irrespective of the season of pasture contamination, inhibition of development reached a maximum in spring and the two strains differed only in the proportion of the population inhibited, which was significantly greater for the table- lands strain. There was no strain difference for either numbers of infective larvae on pasture or total O. ostertagi numbers. This suggested that the difference between coastal and tablelands populations in the extent of inhibition is genetically determined. If an environmental stimulus was implicated in the spring occurrence of inhibition, the stimulus was provided equally in coastal and tablelands environments and it cannot be exposure to low temperatures.

Radio-immunoassay of plasma gastrin showed that hypergastrinaemia developed in sheep during experimental infections with Ostertagia circumcincta. Elevations of plasma gastrin occurred within 8 days of the first dose of infective larvae, with the most marked increase being after 11–20 days when adult worms would be expected to be present in the abomasum. Increases of plasma gastrin levels from 69·0 ± 7·6, 28·7 ± 5·3, 48·7 ± 5·9 and 60·6 ± 9·4 pg/ml before infection to maxima of 650, 230, 900 and 750 pg/ml respectively were recorded in 4 sheep infected for the first time. In 2 others which had been previously infected and then treated with anthelmintic, plasma gastrin rose from 16·0 ± 4·0 and 377 ± 87 pg/ml to maxima of 260 and 900 pg/ml at 24 and 29 days after re-infection, respectively. The cause of hypergastrinaemia has not been established. The elevation of abomasal pH which occurs in ostertagiasis may result in increased gastrin levels but is thought not to be the only cause since plasma gastrin increased before the abomasal pH rose and developed in sheep infected for a second time although their abomasal contents remained at pH 4·0 or lower. The presence of the parasite is critical for development of hypergastrinaemia as shown by return of the gastrin level to normal following therapy with an anthelmintic. It was shown that the parasites do not depend on the hypergastrinaemia since O. circumcincta became established in antrectomized sheep in which hypergastrinaemia did not develop.

The effect of repeated dehydration and hydration on the salt content of 2nd-stage larvae of Anguina tritici was studied. The sodium, potassium, magnesium and calcium contents of the larvae after subjection to varying periods of desiccation and rehydration were determined with atomic absorption spectrophotometry and flame photometry. External cation concentrations on the cuticle of the head, middle body and tail regions were determined semi-quantitatively with scanning electron microscopy in conjunction with X-ray analysis (EDAX). Salt concentrations decreased with each dehydration/rehydration cycle. The greatest loss occurred on revival from the first desiccation period. The results indicated that A. tritici was incapable of regulating it's internal sodium content during revival, but suggested a limited ability to control potassium, magnesium and calcium loss. Salt loss through the nematode cuticle was restricted to potassium and calcium during desiccation. The salt losses encountered are discussed in relation to nematode osmoregulation and to the survival of the nematode in the anhydrobiotic state.

Infective 3rd-stage larvae of Dictyocaulus viviparus were filmed whilst climbing sporangiophores of the coprophilous fungus, Pilobolus and invading sporangia in numbers up to about 50, shortly before the sporangia were explosively discharged. Like the sporangiophores of Pilobolus the nematodes reacted positively towards light. Robinson (1962) demonstrated the spectacular way in which D. viviparus can be dispersed by Pilobolus, although he saw the nematodes accumulating only on top of the sporangia. Hazards including desiccation would offset the advantage of dispersal unless protection is somehow provided. Free D. viviparus larvae are susceptible to desiccation and discharged sporangia appear to dry quickly, so what protection, if any, operates? Several other nematodes that are susceptible to desiccation survive because structures surrounding them dry quickly (for example, an ensheathing cuticle, egg-shell, gelatinous ‘egg-sac’ matrix) and in doing so form barriers which limit the rate of water loss from the nematode within. Such dried sporangia of Pilobolus could aid survival of the ensheathed D. viviparus larvae inside them by retarding desiccation of the nematodes, in much the same way that within cysts of Globodera and Heterodera spp. the cyst wall, egg matrix and outer eggs protect the inner eggs by reducing the rate, if not the extent, of water loss. The sporangium wall may also protect the nematodes from harmful ultraviolet irradiation and from being washed by rain into less advantageous situations.

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.

The fine structure of the oncosphere of Hymenolepis nana has been investigated by transmission and scanning electron microscopy, together with light microscope observations of JB–4 embedded material. The outer surface of the oncosphere is covered by an epithelial layer, termed the embryonic epithelium. Cell types present within the oncosphere include the penetration gland cell, oncoblast, or hook-forming cells, nerve cells, muscle cells (both somatic and hook), and undifferentiated ‘stem’ cells. The penetration gland is a large, U-shaped structure, situated in the anterior region of the oncosphere, and filled with secretory granules of 2 distinct morphological types. Histochemically, the secretory material yields reactions characteristic of an acid mucopolysaccharide. A proteinaceous-substance and small amounts of glycogen are also present. Up to 4 pairs of ducts from the penetration gland have been observed. They pass through the basal lamina and the epithelial layer to open against the polar filament layer at the anterior end of the oncosphere. Nerve cells are described in a cestode oncosphere for the first time. The cells are paraldehyde-fuchsin-positive and show a high level of secretory activity, as evidenced by the large numbers of dense-cored vesicles produced by the Golgi apparatus in the perikarya; consequently, they are tentatively regarded as possible neurosecretory cells. The vesicles are transported down the axon to be stored in specialized swollen axon terminals, which form definite junctions with the muscle cells.

In this study we examined the influence of salinity and temperature on egg development and miracidial emergence of the digenean, Himasthla militaris. In the range 2·1 to 34‰ salinity the eggs developed normally (i.e. no significant difference in the percentage embryonation), and miracidial emergence was only markedly inhibited in water with a salinity of 34‰. At 12 °C embryonation ceased; at 20 and 30 °C egg development as well as miracidial emergence occurred, but at 20 °C both processes progressed at a slower rate than at 30 °C.

Coxal secretion of adult female Ornithodoros erraticus was found to contain a sex pheromone that induces in males of this species a mating response towards nymphs smeared with this secretion. Heterospecific coxal fluid from O. tholozani and O. moubata also elicited a mating response from O. erraticus males. Adult O. erraticus females did not evoke courting behaviour when immobilized or killed, but normal mating behaviour was regained when the immobilized females were freed – proving that both pheromone and recognition of a behavioural pattern are essential components of mating behaviour. Secretion of the sex pheromone appears by the 4th day after a blood meal and accumulates with time, thus increasing the number of attempted matings.

Irradiation doses of 800 rad. or less had no detectable effect on the subsequent development of unfed nymphal Rhipicephalus appendiculatus ticks. Doses of 1600 rad. or above impaired feeding and moulting and delayed the subsequent development of unfed nymphs. At 6400 rad. no ticks completed their moult. Unfed nymphal R. appendiculatus irradiated at 0, 400, 800 and 1600 rad. were applied to 3 cattle infected with T. parva (Kiambu 4). The Theileria infections in the salivary glands of the resultant adult ticks were assessed and it was found that irradiation doses of 800 rad. or less had little effect on the Theileria infections, but an–irradiation dose of 1600 rad. greatly reduced the level of infection. The numbers of salivary gland acini in ticks of this group were reduced but the percentage of infected acini was similar.

A new form of parasitic copepod, Coelotrophus nudus gen. et sp. nov., is described based on the specimens recovered from the coelomic cavity of a species of Sipuncula, Phascolosoma scolops (Selenka and Be Man), at Sado Island in the Sea of Japan. The new genus is distinguishable from its closest allies, Akessonia, Siphonobius and Staurosoma, in the complete absence of appendages in the female and the absence of a mouth in both female and male. The incidence of infection is fairly high (34·1%) in this population of P. scolops at Sado Island. Histological studies of the gonads and microscopical examinations of the coelomic fluid of P. scolops collected monthly from April through December, 1979 have revealed that the presence of C. nudus causes sterility in its host. Some infected P. scolops also showed a marked decrease in the number of corpuscles in the coelomic fluid.

Parasitologists are fond of alluding to the possible antiquity of their chosen group. They may even place the origin in a specific period of geological time and trace its co-evolution, or lack thereof, with the hosts. These speculations usually make only passing comments on the actual fossil record, but a critical examination suggests that this area can throw much light on both the origins and evolution of parasitism. This review is concerned primarily with the fossil record and its immediate implications. It does not appraise parasite evolution in the light of evidence from sources, often of excellent quality, such as comparative anatomy and physiology or ecology. As some parasitologists may not be entirely familiar with the geological column and time scale, Table 1 depicts these and indicates some records of parasitism mentioned here, together with the major events in this history of life.