Past and more recent research has examined the ultrastructure, metabolism, cell biology, genomics and post-genomics of schistosome schistosomula. These areas are considered and discussed in this review with particular emphasis on (1) the early migration phases through the host, (2) interaction of the host immune response with the parasite surface, (3) glucose uptake mechanisms, and (4) defining the transcriptional profiles of lung-stage schistosomula compared with other developmental stages using microarrays. The microarray profiling studies suggest caution is required when considering the use of schistosomes obtained by in vitro means for molecular or biochemical studies.

Two experiments studied the effects of dietary chicory against gastrointestinal nematodes in cattle. In Experiment (Exp.) 1, stabled calves were fed chicory silage (CHI1; n = 9) or ryegrass/clover hay (CTL1; n = 6) with balanced protein/energy intakes between groups. After 16 days, all calves received 10 000 Ostertagia ostertagi and 66 000 Cooperia oncophora third-stage larvae (L3) [day (D) 0 post-infection (p.i.)]. In Exp. 2, calves were assigned to pure chicory (CHI2; n=10) or ryegrass/clover (CTL2; n = 10) pastures. After 7 days, animals received 20 000 O. ostertagi L3/calf (D0 p.i.) and were moved regularly preventing pasture-borne infections. Due to poor regrowth of the chicory pasture, CHI2 was supplemented with chicory silage. At D40 p.i. (Exp. 1) and D35 p.i. (Exp. 2) calves were slaughtered for worm recovery. In Exp.1, fecal egg counts (FEC) were similar between groups. However, O. ostertagi counts were significantly reduced in CHI1 by 60% (geometric mean; P < 0·01), whereas C. oncophora burdens were unaffected (P = 0·12). In Exp. 2, FEC were markedly lowered in CHI2 from D22 p.i onwards (P < 0·01). Ostertagia ostertagi adult burdens were significantly reduced in CHI2 by 66% (P < 0·001). Sesquiterpene lactones were identified only in chicory (fresh/silage). Chicory shows promise as an anti-Ostertagia feed for cattle and further studies should investigate its on-farm use.

The ultrastructure of the parenchyma and interstitial material and the interrelations between them are described.

The interstitial material, composed of a granular matrix containing fibres, is shown to ramify as a network between parenchymal cells and around organ systems. It is postulated that this structure is a ‘skeleton’.

In certain localized areas the interstitial material between parenchymal cells is absent and at these points adjacent cells are united by attachment plaques (desmosomes) without tonofibrils.

The possible functions of the parenchyma are considered and it is suggested that these cells are responsible not only for secreting the interstitial material, but also store glycogen and act, in the absence of a circulatory system, as a transport system for metabolites and excretory products.

During the early stages of infections of mice with Fasciola hepatica (6–11 days) the young flukes feed almost exclusively on hepatic cells which the oral sucker and the pharynx have broken down into a kind of homogenate containing Kupffer cells, invading leucocytes and some erythrocytes. As the flukes increase in size liver damage also increases in amount because of the larger burrows which are made. In some instances this does not adversely affect the host but in many infections excessive liver damage produces critical conditions which threaten the life of the host and its parasites. A comparison of the lesions produced in infections lasting 17–25 days with lesions produced after only 6–7 days has shown that the former, unlike the latter, are not due entirely to the feeding activities of the fluke. In short-term infections the inflammatory reaction produces the characteristic effects which are concerned with the healing of fluke tracts, but in older infections this reaction appears to be much more violent and tremendous leucocytic infiltrations break down apparently normal hepatic parenchyma and convert the terminal part of the burrow into a pool containing enormous numbers of invading leucocytes, broken hepatic cells and blood. These are the conditions which prevail at the onset of the critical period, when flukes have their growth inhibited as if by nutritional deficiencies. Some hosts are able to survive the critical period and nurture well-grown flukes for long periods, and may be able to obviate the critical conditions. It is suggested that the excessive damage which occurs in many instances during the critical period is not due to the feeding activities of the larger flukes but is a consequence of less restrained or even unrestrained inflammatory reactions which may lead to more serious pathogenic effects bordering on malignancy. This may be related to differences in the time spent by flukes in the hepatic parenchyma, early entry into the biliary system obviating these effects, late entry facilitating them.

A rapid method is described for preparing and staining salivary glands of Rhipicephalus appendiculatus ticks infected with Theileria parva. The technique, involving the use of a modified methyl green pyronin stain, minimizes the risk of losing material and allows examination of stained glands within minutes of preparation. The technique was applied in a series of studies in which ticks were either infected with T. parva under different conditions, or maturation of parasites in adult ticks was stimulated by different means. When nymphal ticks were fed on the ears of cattle the subsequent infection rate of the adult ticks showed no correlation with the parasitaemia of the cattle at the time of nymphal engorgement. There was no difference in infection rates between adult ticks in which parasite maturation had been stimulated either by incubation at 37 °C or by feeding on rabbits. However, parasite maturation took about 1 day longer in incubated ticks than in rabbit-fed ticks. Female ticks were consistently more highly infected than males, both in terms of the percentage of ticks infected and the mean number of infected acini/tick. Ticks were infected with T. parva by injection of nymphs with parasitaemic bovine blood, but the resultant adult infection was lower than that in ticks which had been infected naturally by feeding on cattle.

Investigations of nematode hatching have concentrated on the parasitic forms, especially on synchronization between host and parasite life-cycles which, in some species, is so close that the parasite is dependent on the host for the hatching stimulus. Research into nematode hatching reflects the artificial separations created throughout nematology by defining research groups and their activities in terms of the host; consequently, useful comparisons between hatching of plant and animal parasitic nematodes have been few. With the increasing use by geneticists of nematodes as model animals and the interest in them by neuro-physiologists, molecular biologists and others, we hope that such distinctions will be lessened.

NADPH diaphorase has recently been discovered to be responsible for neuronal nitric oxide (NO) synthase activity in mammals. It thus serves as a histochemical marker for the localization of NO synthase in the nervous system. The histochemical technique was used to map out potential NO-producing neurones in the nervous system of the parasitic nematode, Ascaris suum. Positive staining for NADPH diaphorase was present in various parts of the central nervous system, in particular within selective cell bodies and fibres in the ventral ganglion, the retrovesicular ganglion, ventral and dorsal cords and sublateral lines. Intense staining was also present in the motorneurone commissures, indicating a potential role for NO as a neurotransmitter at the neuromuscular junction. NADPH disphorase-positive neurones were not confined to the central nervous system. Selective staining was also present in the enteric nervous system, in particular the pharynx and in the peripheral nervous system innervating the sensory organs.

Nine attempts to infect kittens directly with E. histolytica macacorurn by means of amoebae (per anum) or cysts (per os) in the faeces of 2 M. sinicus (Polo and Susanna) and 1 M. rhesus (Jacko), were wholly unsuccessful. Four similar experiments with cysts (per os) from another M. sinicus (Bonar) gave 2 positive (Kittens 28 and 31) and 2 negative results.

Attempts to transmit strains of E. histolytica macacorum from one species of Macacus to another have been uniformly successful.

A strain (D.) of E. histolytica, derived from a man suffering from acute amoebic dysentery, has been cultivated in vitro continuously for 5½ years.

(i) The fact has been confirmed that strains of E. histolytica which, when newly isolated, are infective for kittens, may lose this infectivity after continued cultivation in vitro.

All mammalian-parasitic stages of a range of nematode species investigated (Brugia pahangi, Acanthocheilonema viteae, Strongyloides ratti, Nippostrongylus brasiliensis, Trichinella spiralis and Ostertagia ostertagi) labelled in a surface-restricted manner with the fluorescent lipid analogues 5-N-(octadecanoyl)aminofluorescein (AF18) or nitrobenzoxadiazole-cholesterol (NBD-chol), but failed to bind other similar probes. In contrast, the surfaces of the ‘pre-parasitic’ infective stages of these species had affinity for neither AF18 nor NBD-chol. This exclusion of lipid analogues changed rapidly upon exposure of the larvae to tissue culture conditions which mimic the mammalian tissue environment (e.g. RPMI 1640/37°C) such that the above probes could then insert into the surface layer of the larvae. The dauer larva of Caenorhabditis elegans also excluded the probes, but became permissive to labelling upon stimulation to emerge from the dauer state. The time taken for the surface transformation to occur ranged from less than 10 min in the vector-borne parasites to approximately 5 h in those which enter by the oral route, with direct skin-penetrators occupying an intermediate position. In all cases, the alteration proceeded too rapidly for it to have been associated with a moult. Fluorescence Recovery After Photobleaching (FRAP) studies of A. viteae larvae showed that approximately 50% of the AF18 probe was free to diffuse within the plane of the surface immediately after transformation. This is only a transitory state because AF18 was found to be highly restricted in its lateral diffusion on the surface of adult parasites. In the larvae of S. ratti, the change in affinity for AF18 was accompanied by the rapid shedding of an otherwise stable surface coat of polyanionic material, here visualized by labelling with fluorescein-conjugated cationized ferritin. Incubation of larvae in lipid-rich host serum during the induction of transformation inhibited subsequent labelling with AF 18. This possibly reflects competition for insertion sites and an in vivo propensity towards the acquisition of host lipid by invading parasites.

Some factors affecting the suceptibility of chick embryos to E. tenella infection have been examined. An incubation temperature of 41 °C was found to be more suitable for the development of the parasite than 38 or 39 °C. At the higher temperature development of schizonts was more rapid and mortality caused by the parasite occurred earlier and was substantially greater. Mortality, caused by E. tenella, was dose related and doses between 15000 and 45000 sporozoites produced 100 % mortality in embryos incubated at 41 °C.

There were differences in the susceptibility of three strains of W.L. embryos to E. tenella infection; ‘S’ strain W.L. embryos were more susceptible than either ‘C’ or ‘K’ strains. However, the susceptibility was not evident in hatched chickens of the ‘S’ strain.

Two laboratory strains of E. tenella (‘W’, ‘H’) were shown to produce different mortality levels in embryos; the ‘W’ strain was markedly more virulent, perhaps because schizonts of the 2nd generation matured more rapidly in both embryos and chickens inoculated with this strain of E. tenella.

I wish to thank Dr R. K. Cole of Cornell University for making three strains of W.L. embryos available to me for this work. I also wish to thank the Governing Body of the Houghton Poultry Research Station; the Agricultural Research Council and the Avian Diseases Department of Cornell University for making it possible for me to undertake a substantial part of this work at that University in 1968. Grateful thanks are due to Dr P. P. Levine, D. L'Amoreaux and M. S. Shirley for their help at various stages of the work.

Thirty-two isolates from man in known areas of Gambian trypanosomiasis, in the Sudan, Kenya, Zaire, Nigeria, Ivory Coast, Burkina Faso, Liberia and Senegal, were examined by isoenzyme electrophoresis of 11 enzymes. Comparisons were also made with our previously published results on 23 other stocks of similar origins, which had been examined in the same manner. All those stocks of low initial virulence to laboratory rodents, which thus conform to the accepted view of the behaviour of Trypanosoma brucei gambiense can be identified by characteristic combinations of enzyme patterns, especially certain aminotransferase markers. A limited study of superoxide dismutase polymorphism suggested a further marker of value. The isolates of high initial virulence to rodents, which are thus behaviourally akin to T. b. rhodesiense, did not share these characteristics. We conclude that there exists a homogeneous group of trypanosomes of wide dispersion throughout tropical Africa, characterized by certain isoenzyme combinations and low initial virulence to rodents, which corresponds to the classical concept of T. b. gambiense. The features of limited antigenic repertoire, high resistance to normal human serum and restriction fragment length polymorphisms of the genes for certain variant surface glycoproteins also appear to be characteristic of this group.

A population approach was employed to study the effects of a bopyrid isopod, Aporobopyrus muguensis, on the growth and reproduction of its anomuran host, Pachycheles rudis. Indirect evidence, provided by the size-specific prevalence pattern, and direct evidence, provided by laboratory moult frequencies and moult-stage data, indicated that the frequency of moulting was reduced among parasitized crabs. Moult increments of parasitized crabs were less than those of non-parasitized crabs. Although parasitized female P. rudis were able to reproduce, their fecundity was substantially reduced. Parasitized female hosts appeared to be delayed in their attainment of sexual maturity. Once mature, these crabs produced significantly smaller size-specific clutches than those produced by non-parasitized female crabs. Because fecundity increases with size in P. rudis, the slower growth rates of parasitized female hosts may further limit their fecundity. Potential mechanisms by which A. muguensis limits the growth and reproduction of P. rudis are discussed.

Several years have elapsed since the publication by Johnson et al. (1989) of the cloning of a recombinant antigen from the cestode parasite Taenia ovis which stimulated high levels of protective immunity in sheep. A great deal of subsequent research and development was necessary to bring the fledgling vaccine to the point of being a registered commercial product. The results of these subsequent studies are dealt with briefly in this paper, including the results of field trials. The T. ovis vaccine was registered by the New Zealand Animal Remedies Board in February 1994. Where then is the commercial product ? This paper gives a background to market problems which have emerged through the politics (and realities) of the NZ T. ovis control campaign. It serves as notice that the best science dedicated to producing vaccines or products for parasitic, or other, diseases often faces significant hurdles in the real world of commerce and politics.

A temporal study of the effects on the tegument of Schistosoma mansoni adult worm following in vivo praziquantel and oxamniquine treatment was performed. Drug-induced damage to the tegument, exposure of surface antigens and attachment of host antibody occurred rapidly, within 1 h, following praziquantel treatment. Oxamniquine-treated worms required 4–8 days for these effects to be apparent. The 2 drugs differed in the degree and sites of damage on the worm surface. The administration of 2 different polyspecific rabbit sera with drug significantly increased the efficacy of praziquantel when administered with the drug, but not when given 6–9 days after drug treatment. In contrast, only 1 serum was synergistic with oxamniquine when administered with drug and both sera were synergistic when given 6–9 days after drug treatment. The effect of immune killing of drug-treated worms is discussed.

The technique of Random Amplified Polymorphic DNA (RAPD) PCR has been used to detect DNA polymorphisms among Toxoplasma gondii strains. Seven arbitrary oligonucleotides (10-mer) were used as primers to amplify total genomic DNAs and significant genetic heterogeneity was detected among 11 T gondii strains with different virulence for mice. The polymorphisms observed allowed relationship dendrograms of T. gondii strains to be constructed by PHYLIP and PAUP analyses. The genetic relationships of the T. gondii strains generated by 2 analyses using completely different assumptions were similar. Both analyses revealed 2 groups of T. gondii strains, one formed by the 6 virulent strains and the other formed by the 5 avirulent strains. This suggests that the genus Toxoplasma may actually contain 2 groups, correlated with their virulence, which have probably evolved independently following their initial separation. Significant polymorphisms were also detected between 2 different laboratory stocks of the T. gondii RH strain.

Relatively little is known of the way in which the populations of monogenean parasites are related to the behaviour and physiology of their hosts or how such populations vary in composition over the year. Bychowsky (1957, trans. Hargis, 1961, p. 108) has described the results of studies upon six different fish hosts and parasites, while Llewellyn (1962) has studied two other species of Monogenea living on one host species. In all these investigations, the various ecological factors which influence the life cycles of the parasites have been determined.

Dogiel, Petrushevski & Polyanski (1961, p. 14) referred to a previous population study of Discocotyle sagittata on a host Coregonus lavaretus in Lake Ladoga, Russia. The parasite was said to breed in July and August, while in September broods of young and old parasites overlapped. The large individuals disappeared in October and November and this ‘death of the older generation’ was taken to indicate that the parasites had a life span of only one year.

The only relevant work available when the present study was commenced was the population study of the monogeneans Gastrocotyle trachuri and Pseudaxine trachuri by Llewellyn and as this concerned a marine host, it was of obvious interest to investigate the population dynamics of a parasite of a freshwater fish. Discocotyle sagittata was chosen because the biology of the British host, the brown trout (a different host from that in the Russian study of Discocotyle), has been intensively studied for many years. It was thought that this would be of advantage in attempting to relate any seasonal fluctuations in the parasite population to the biology of the host.

A descriptive analysis of observed water contact activities in seven Kenyan (Akamba) communities is presented. The patterns of contact with time of day, month of year, type of activity, degree of immersion, use of soap, use of ‘kithima’ and day of week are all considered, with particular attention given to how these vary with age and sex. It is noted that (a) patterns of contact vary dramatically between these culturally rather similar communities, (b) contact usually peaks in the second decade of life, (c) generally females, especially young women, spend more time at the water than males and (d) simple (unweighted) total observed duration of contact gives a relatively inflated estimate of exposure in adults, especially young women. The methodology of observation and data handling is described in some detail.

This study, based on correlative data, tests the hypothesis that infections with Eimeria spp. parasites exert a significant loss of fitness of bank voles (Clethrionomys glareolus) reflected in lower reproductive success and survival, declining host population densities and are associated positively with population size. The study was conducted in 20 mainland and 27 island populations in central Finland during May–September in 1999. Faecal samples showed that 28% of 767 individuals were infected with Eimeria spp. The presence of Eimeria parasites was higher in dense mainland populations than in sparsely populated islands. Eimerian infections increased during the course of the breeding season, probably as a result of the high infection rate of young individuals. Accordingly, the body masses of bank voles were negatively related to the presence of Eimeria spp. Reproductive output, as measured by the breeding probability of females and litter size, was not associated with the presence of eimerian infection. Interestingly, the body condition of the infected mothers appeared to be low. Moreover, mother's body condition was the single most important variable studied that showed a positive correlation to pup's body condition at birth. On small islands ([les ]3·2 ha) that were comprehensively trapped, the mean number of Eimeria spp. in the bank vole population was negatively related to density changes of the bank vole population during the study. Our data are consistent with the idea that infection with coccidian parasites may be one of the factors responsible for declining host populations in small, isolated populations.

Egg production by the freshwater gill monogenean Discocotyle sagittata infecting rainbow trout (Oncorhynchus mykiss) was monitored at 5, 13 and 18°C; eggs were incubated at 6, 10, 13, 15, 16, 18, 22 and 26°C and the hatching times determined. Mean per capita output at 13°C ranged from 0·8 eggs/worm/day (e/w/d) to 18·3 e/w/d for 25 hosts (burdens 1–17 worms/host). Average egg production rates for worms in single burdens varied from 3 e/d to 14·6 e/d at 13°C, mean 7·6 e/d (±0·63) (n=8). Egg production was temperature dependent, increasing from a mean of 1·5 e/w/d at 5°C to 12·0 e/w/d at 18°C. Developmental rate was also temperature dependent: larvae began hatching after 84 days at 6°C, 28 days at 13°C, and 20 days at 18°C. Eggs laid within the same 24 h period hatched over 3–7 days at 13–18°C; this range was extended at decreasing temperatures. Egg viability was generally high: between 13 and 18°C a mean of 92% of larvae successfully emerged. However, viability declined at the highest and lowest temperatures (23% hatching at 6°C, 55% at 8°C and 47% at 26°C). The implications for seasonal parasite transmission are discussed.

Hyperplasia of Paneth and intermediate cells is a recently described component of the response of the small intestine of mice to infection with the nematode Trichinella spiralis. To investigate whether this hyperplasia is parasite specific or represents a generic intestinal response to infection, mice were infected with T. spiralis, Nippostrongylus brasiliensis, Heligmosomoides polygyrus or Schistosoma mansoni and tissue samples taken at various time-points post-infection to determine Paneth and intermediate cell numbers. All infections induced Paneth and intermediate cell hyperplasia, but the patterns of response varied between the parasite species concerned, reflecting differences in their relationships with the host. Increases in the numbers of these cells appeared to correlate with known patterns of T-helper-2 immune responses.