Evidence has been adduced that the surface antigens of Trypanosoma brucei subgroup are a group of glycoproteins having D-galactose, D-mannose and D-glucosamine as monosaccharide components.

There was considerable variation in the number of antigen components, and their relative amounts, as revealed by isoelectric focusing on polyacrylamide gel. The relevance of these variations to the adaptation theory of antigenic variation in trypanosomes is discussed.

The activity of 12 anticoccidial drugs against an embryo-adapted strain of Eimeria tenella has been investigated. After seven and five serial passages respectively, in the presence of drug, resistance was developed to methyl benzoquate and buquinolate. A strain of E. tenella made resistant by exposure to drugs in chickens was resistant to the same drugs when evaluated in infections of chick embryos. This relatively simple technique would appear to offer advantages over existing methods for the study of drug resistance.

The range of fish hosts parasitized by Diplostomum spathaceum was assessed. Natural and experimental levels of infection were compared between host species. The accumulation of eye flukes with age was established in one host – Rutilus rutilus. Development of metacarcariae in lenses of naturally infected Gasterosteus aculeatus throughout the year was compared with that of experimentally infected South African clawed toads, Xenopus laevis, maintained at various temperatures (5–30 °C). The importance of temperature changes to this part of the life-cycle of the parasite is discussed.

Lambs were infected at daily intervals from 3 weeks of age with increasing doses of infective larvae of Trichostrongylus colubriformis, according to an exponential infection schedule designed to simulate the pattern of infection experienced by grazing lambs during the spring and early summer in Britain. The faecal egg counts and the worm burdens in the lambs followed a similar exponential trend for 12 weeks after initial infection.

The T. colubriformis burdens in these lambs appeared to be cumulative during the first 12 weeks, after which the animals developed a resistance to further reinfection, which was very strong by 16 weeks after initial infection. However, even lambs which were refractory to new infection continued to harbour large numbers of adult worms, which caused clinical disease in most of the lambs.

There was no evidence to suggest that either a turnover of the worm burden, inhibition of larval development or the sudden loss of established parasites played any major role in the regulation of the burdens of T. colubriformis in these young lambs.

The removal of the established burden 16 weeks after initial infection in one lamb appeared to result in a partial loss of resistance to a challenge infection given 10 days later.

Three groups of lambs, aged 3, 5 and 6 months respectively, were infected daily with 5000 infective larvae of Trichostrongylus colubriformis for periods of 15–20 weeks. Some of the lambs also received a single challenge infection at the end of week 16. The course of the infections was monitored by means of faecal egg counts, measurement of live-weight gains and regular post mortem worm counts.

There was an initial rapid increase in egg counts soon after patency, which was followed by an exponential fall in the counts in most lambs. This fall seemed to precede the expulsion of worms by a few weeks and was associated with reduced fecundity in the female worms. Furthermore, although the trend of the egg counts of some lambs suggested that a self-cure reaction had taken place, in a number of these lambs the low faecal egg counts did not reflect the size of their worm burden.

Heavy worm burdens were usually associated with clinical symptoms of trichostrongylosis, including anorexia, diarrhoea and loss of weight. As the lambs developed resistance to reinfection and expelled their worm burden a rapid clinical recovery occurred, except in a few lambs which appeared to have suffered irreversible damage from the earlier heavy worm burden.

The worm burden in most lambs appeared to be cumulative during the first 4–8 weeks before they developed a strong resistance to reinfection. There was considerable loss of the adult worm burden by 8–15 weeks after initial infection and some evidence of stunting in the remaining parasites.

The immunological control of T. colubriformis infections in these lambs was achieved by means of the development of resistance to reinfection, inhibition of the ovulation of the female worms, stunting of adult worms and expulsion of adult worms by resistant lambs. These may be separate immune phenomena requiring different thresholds of parasitic material in individual animals, depending on their age, the rate and duration of infection and their innate ability to develop resistance to the parasite.

Normal mouse erythrocytes and erythrocytes containing Plasmodium berghei were incubated for 1 h in a medium containing either adenosine, guanosine, cytidine or thymidine labelled with 14C or 3H. The purine nucleosides, adenosine and guanosine, but not the pyrimidine nucleosides, cytidine and thymidine, were incorporated into the nucleic acid of the parasite–host cell complex. The concentration achieved by all four nucleosides in both normal and parasitized cells was at least as high as that in the suspending medium, showing that not only purines but also pyrimidines enter the parasitized erythrocyte.

Two species of Eimeria isolated from jungle fowl of Malaysia were examined in infections of chickens. Eimeria diminuta reproduced well in the embryo CAM and caused severe infection of the lower small intestine and caeca of chickens, but did not develop in the duodenum. It reproduced well in chickens and severely affected their body weight gain. The endogenous stages and oocysts were similar to E. acervulina var. mivati and cross-protection tests with this parasite and E. acervulina confirmed the close relationship between them. It is suggested that the parasite should be referred to as E. acervulina var. diminuta.

The oocysts of another species examined (E. indentata) were similar to E. maxima: the parasite reproduced well in chickens, was pathogenic and showed marked cross-protection against two strains of E. maxima isolated in Britain. The name E. maxima var. indentata is suggested for this parasite.

When low immunizing doses of two strains of E. maxima isolated and maintained in Britain were given, they did not completely cross-protect against re-infection with the heterologous strain.

Acquired immunity to Schistosoma mansoni in the rat can be assayed by the recovery of a proportion of the schistosomula of a challenge infection from the lungs 5 days after the challenge has been given. The recoveries from immune rats, which are significantly less than those from control animals, demonstrate that a proportion of a challenge infection is killed in the lungs or at an earlier point in the pathway of migration.

Immunity in the Sprague–Dawley rat can first be shown by the lung recovery technique 3 weeks after an immunizing exposure of 500 cercariae. Immunity reaches a peak between weeks 6 and 7 but then declines to zero by week 12. The PVG inbred Hooded rat shows a similar but delayed development and decline of immunity. When the lung recovery technique shows immunity to be declining, hepatic perfusion demonstrates that immunity to reinfection is partially retained, indicating that at this stage the challenge is killed after the first 5 days.

Re-exposure of rats in which immunity has declined induces an anamnestic lung recovery response. There appears to be a relationship between spontaneous cure and the decline of immunity. A factor in the serum of infected rats which kills young schistosomula in culture develops in parallel with immunity, but high titres of this factor are maintained during the decline of immunity.

The ectoparasitic copepod Lepeophtheirus pectoralis exhibited a regular annual cycle of abundance on its hosts. Both the incidence and intensity of infection were greatest in August or September and both declined over winter to their minimum values in April. Very similar cycles were observed in both 1972 and 1973. Analysis of the age structure of the parasite population showed that the increase in abundance coincided with the onset of the breeding season. Although females always outnumbered males the sex ratio approached unity during the breeding season, which extended from May to October. Copulating pairs were most commonly observed during this period.

There was a marked bimodal peak of egg production each year, with the first mode occurring around May and the second mode around August or September. This pattern was produced by a system of alternation of generations operating within the parasite population, with a summer type generation (distinguishable by its rapid maturation rate and reduced longevity) alternating with an overwintering type of generation.

The numerical relationships between a population of Lepeophtheirus pectoralis and its host population (plaice) have been described. There was no significant difference between infection levels in male and female plaice. In most of the monthly samples (75%) there was no significant relationship between host length and either the incidence or intensity of infection. The samples in which significant positive correlations occurred were usually taken within the period November to April. It is probable that the immigration of smaller fish, with lower levels of infection, from shallower water produces this effect.

The parasite population was found to have an overdispersed distribution (variance > mean) within its habitat, the host population. The frequency distributions of numbers of parasites per fish were calculated and the negative binomial distribution was fitted to these. The fit was good in 22 of the 24 samples and the value of k, the exponent, was found to be directly related to the mean density of the parasite population. Iwao's (1970) method of dispersion analysis indicated that the observed negative binomial was generated by a model of randomly distributed clumps or colonies of individuals. A possible mechanism of producing this pattern was proposed based on evidence from studies of mortality in the parasite population (which indicated that all-or-none type mortality operates on the clumps at certain periods during the year), the infection process (which demonstrated that a single wave of infection produces an overdispersed spatial distribution) and the examination of parasites from individual fish (which displayed a clumping of parasites at certain stages rather than an even spread over the range of possible stages). The mechanism proposed is that the adaptations for host location of the infective copepodid stage tend to produce aggregations of these larvae in favourable areas of a heterogeneous habitat. Fish moving randomly into these areas will tend to be infected by more than one larva (a clump of larvae) at any one time when available for infection. The fish can be regarded as equivalent to random samples of the free larval population and the aggregated distribution of the parasite population on its hosts is therefore directly related to the aggregated distribution of the free-swimming infective larvae.

The larvae of Aspiculuris tetraptera were found in the mid-colon of mice within hours of infection. When the colon was divided into 10 equal sections the larvae were mainly found in sections 5, 6 and 7 during the first 6 days of the infection. The worms entered the crypts of Lieberkühn in this region on day 1 and remained there until day 4 or 5. After this time they left the crypts and returned to the lumen of the colon. On day 7 the worms emigrated anteriorly and thereafter were recovered only from the proximal region of the colon (sections 1–4), although in heavier infections a few larvae remained in the mid-colon.

The initial establishment site was the same in both Rattus norvegicus and in Apodemus sylvaticus, but an infection with A. tetraptera in the abnormal hosts, R. norvegicus and A. sylvaticus, was characterized by less than 7% of the inoculum becoming established, a slower rate of growth and a wider distribution centering around the preferred site. The small number of established larvae was lost from the rat before day 12 and from A. sylvaticus before day 8, whereas larvae persisted in laboratory mice for a longer period.

Young white mice were infected with different doses of eggs or cysticercoids of Hymenolepis nana and the subsequent faecal egg output was measured over a 3-day period. This was then correlated with worm numbers, determined after killing the hosts. The longest worm in each infection was measured and it was shown that crowding decreased the linear dimensions, number of eggs per proglottis and rate of proglottis production of these worms, but that their shape was not affected.

The relation between total egg output and worm numbers was complex. In both egg-derived and cysticercoid-derived infections the egg production rose to a peak, fell and then levelled off to a constant rate with increasing worm numbers. Cysticercoid-derived worms were larger than egg-derived worms, but produced approximately the same number of eggs per unit of biomass. The differences in the egg output curves for the two types of infection were interpreted as being due to their size difference; this in turn may be a consequence of the host immunological response.

Using biomedical techniques experimental determinations of the hydrostatic pressure in the pseudocoel of adult female Philonema oncorhynchi indicated that the rate of increase in pressure (dP/dT) and absolute pressure values (cm/H2O) shown by bursting worms in distilled water are correlated with the diameter of the nematode. At bursting pressures, wall tension in a wide size range of worms was virtually identical, indicating that the bursting process is independent of muscular contraction. That the generation of the hydrostatic pressure was an osmotic phenomenon was confirmed by measuring dP/dT in prelarvigerous and larvigerous female worms subjected to different concentrations of sodium chloride, ranging from 89 to 800 m-osmol/kg, and also to a variety of solutions of similar osmolarity (155–175 m-osmol/kg), e.g. magnesium sulphate, urea, potassium chloride, sodium chloride and sucrose. The overall rate of uptake was faster in the larger worms but, per unit surface area, small worms had an uptake rate three times that of the large individuals.

The prediction that the body wall of female P. oncorhynchi is permeable to ions such as Na+ was confirmed using radiolabelled 22Na and by bringing about changes in the osmolarity of worms subjected, for 5 min periods, to hyperosmotic solutions of sodium chloride and sucrose. The survival of P. oncorhynchi in the body cavity of sockeye salmon, Oncorhynchus nerka, is dependent upon the permeable nature of the body wall of P. oncorhynchi allowing the worm to function as an ‘osmometer', because as the anadromous O. nerka enters fresh water, the osmolarity of its blood plasma is known to decrease by about 15%. At the time of spawning in Cultus Lake, British Columbia, the body fluids of both female P. oncorhynchi and O. nerka are isosmotic, indicating that the worms are able to equilibrate to the above changes and at the same time preventing premature bursting in the body cavity of its host. However, osmotic invasion of water must occur far quicker than ionic exchange since complete release of larvae does take place when female worms pass out into the redd along with the eggs of the fish and burst.

By a variety of microscopical techniques, an initial survey has been made of the functional organization of ovarian balls from mature, inseminated female Moniliformis dubius and Polymorphus minutus. On the basis of evidence from observations made with the transmission electron microscope, we have concluded that the ovarian ball consists of three components; these are two separate, multinucleate syncytia and a cellular zone. The inner region is considered to be an oogonial syncytium from which the germ-line cells arise to form the cellular zone. The oogonial syncytium and the cellular elements are embedded in a supporting syncytium which also forms the boundary of the ovarian ball. Details of the ultrastructure of these components, observations on fertilization and a hypothesis to account for the main events occurring in an acanthocephalan ovarian ball are also presented.

Acanthocephalans are dioecious parasites which become sexually mature in the alimentary tract of vertebrates. After insemination, individual female worms begin to release embryonated eggs at rates which have been estimated to vary, on average, from 2000 per day in the case of Polymorphus minutus (Crompton & Whitfield, 1968) to 260000 per day in the case of Macracanthorhynchus hirudinaceus (Kates, 1944). Irrespective, however, of the species of acanthocephalan and the number of eggs produced, a most interesting mode of ovarian development and multiplication is believed to exist (see Bullock, 1969). Within the female worm, the primordial ovarian tissue gives rise to separate ovaries which are often termed ovarian balls. These in turn give rise to more ovarian balls and the process continues until large numbers have been formed. The ovarian balls of a mature female have no permanent attachment to the tissues of the worm. They are contained in the fluid of the body cavity either freely, or loosely constrained in large membranous chambers known as ligament sacs.

Few investigations have been made into the structure and cytology of the ovarian balls of the Acanthocephala. Early observations on the histology of the germ-line constituents of ovarian balls were made by Hamann (1891), Kaiser (1893) and Meyer (1928), each of whom suggested that some of the developing oogonial stages were arranged in a syncytial manner. In a study of the embryology of P. minutus. Nicholas & Hynes (1963) interpreted preparations of ovarian balls, which had been subjected to the Feulgen reaction, as indicative of syncytial tissue in the central region of the ball. They also recorded their uncertainty about whether an ovarian ball has a bounding membrane or not. More recently, Robinson (1964, 1965) described mitotic and meiotic divisions in oogonia and oocytes from ovarian balls of Mac. hirudinaceus and Moniliformis dubius and Stranack (1972) included an electron micrograph of part of an ovarian ball of Pomphorhynchus laevis in a description of the nature of the egg envelopes of that species. In this paper, we present a general survey, based largely on evidence obtained with the electron microscope, of the functional organization of the ovarian balls of mature M. dubius and P. minutus.

Milk-borne infection is demonstrated for Strongyloides ratti in rats, accounting for 32% of the combined worm burden of non-immune mothers plus their offspring at a standard dose of 4000 L3. Migrating larvae are ‘switched’ to the mammary gland about 3 days prepartum in advance of the final events of lactogenesis in the host at 30 h prepartum. Larvae take between 24–48 h to reach the milk after injection.

The ‘take’ in lactating rats was half that in virgin controls and pregnant animals before day 3 prepartum, but this discrepancy was not made up by the number of worms in the litter, the combined figure for mothers and offspring still being only 75% of the potential judged by the controls.

Prenatal infection did not occur in these experiments, which involved carefully controlled cross-fostering between infected and uninfected mothers. Injections of larvae covered the period between 12 days to 20 h prepartum in different animals. This route is possible under other circumstances, although it is considered unlikely in non-immune females since there was no evidence of larval dormancy in maternal tissue.

The stimulus provided to cercariae by the skin fat of their definitive hosts is not the same for Schistosoma mansoni and Austrobilharzia terrigalensis. Cercariae of the former parasite are stimulated by unsaturated fatty acids, those of the latter by cholesterol.

A reinvestigation of the penetration stimulant factors present in crude egg lecithin, which contains both cholesterol and free fatty acids as impurities, has shown that the latter are responsible for the stimulus in S. mansoni. The phospholipid fraction is inactive as is pure cholesterol. A little excitation of cercariae is produced by the monoglyceride fraction. These results fully confirm earlier findings.

Of surface active agents other than lecithin, stimulatory activity was found only in one product which possessed carboxyl groups. Of the C18 acids examined, stearic (18:0) is inactive, oleic (18:1) slightly active, linoleic (18:2) and linolenic (18:3) acids highly active. Oleic acid was shown by GC-mass spectrometry to be the most abundant acid in crude egg lecithin and is probably the main penetration stimulus present.

Ward, P. F. V. The metabolism of glucose by Haemonchus contortus, in vitro.

Page 184, two lines from foot of page. For ‘glucose and on worms’ read ‘glucose and no worms’.

Lainson, R., Landau, Iréne and Shaw, J. J. (1974). Observations on nonpigmented haemosporidia of Brazilian lizards, including a new species of Saurocytozoon in Mabuya mabouya (Scincidae).

Due to postal delay in the receipt of corrected proofs of the above paper, the following errors have regrettably appeared in its publication and should be corrected as follows:

Page 215, lines 3 and 4 of the Summary, and page 216, line 10. The text should read ‘ …Garnia morula (Telford, 1970) Lainson, Landau & Shaw, 1971;… ’ and not ‘ …Garnia (Plasmodium) morula (Telford, 1970), Lainson, Landau & Shaw, 1971;…’

Page 220, lines 24 and 25 of the text should read ‘…Plasmodium tropiduri, P. diploglossi, a Plasmodium species close to P. diminutivum Telford 1973 a and Saurocytozoon’. Not ‘…P. diploglossi (a parasite close to P. diminutivum Telford 1973a) and Saurocytozoon’