The possibility that much of the spatial and temporal variation in helminth communities in freshwater fish can be explained in terms of metapopulation theory was tested by examining helminth component communities of eels sampled from 3 localities in the River Exe and 5 of its tributaries on 2 occasions at an interval of 3 years. Four specific predictions of metapopulation theory in relation to community dynamics were tested. The prediction that parasite species could be recognized as common and rare and that this was sensitive to scale was met. The prediction that core species would be more widely distributed and have a higher dispersal ability was met only in part. The prediction that similarity between communities would increase with connectivity and decrease with distance apart was not met. The final prediction that species would go locally extinct and be replaced by rescue effects was not met. There was evidence of local extinctions; not of eel specialists but of species using other fish species as their principal definitive hosts. Eel helminth communities were heavily dominated by 3 species of eel specialists which were relatively stable and responsible for most of the similarity and its changes in space and time. It was concluded that metapopulation theory did not provide a very satisfactory explanation for the changes in the helminth communities in eels and reasons for this included the inherent difficulty of applying metapopulation theory to parasites and the fact that the helminth communities in eels in the River Exe were atypical in being dominated by eel specialists.

The genetic programmes associated with the sexual biology of dioecious schistosomes remain a critically important but significantly understudied area of parasitology. Throughout the last four decades, progress has been slow in describing the gross antigenic and proteomic differences linked to sexually mature schistosomes and in characterizing some of the sex-associated transcripts and regulatory mechanisms induced during developmental maturation. These investigations have been severely hindered by the lack of complete EST/genomic information, as well as corresponding post- and functional-genomic tools for studying these pathogenic parasites. As near complete transcriptomes for Schistosoma japonicum and S. mansoni have recently been reported, and both DNA microarrays and post-transcriptional gene silencing have been applied to schistosomes, the tools and techniques for the high-throughput identification and characterization of transcripts involved in conjugal biology are now readily available. Here, an historical review is presented that summarizes some of the most significant findings associated with schistosome sex and sexual maturation during the last several decades. Following this discussion is a current overview of some modern day genomic approaches used to study schistosomes, which illustrates how major advances in the field of conjugal biology will be achieved.

The specific objectives of this study were to elucidate metal toxicity to hatching, survival and avoidance behaviour of Schistosoma mansoni miracidia. The toxicity of cadmium, zinc, and cadmium/zinc mixtures at concentrations ranging from 10000 to 10μg/l was investigated. Metal mixture toxicity investigation was undertaken with equal concentrations of the metals. The hatching of miracidia from eggs was inhibited by concentrations of 1000–10000μg/l of single metals. Metal mixtures had no effect on egg hatching. Survival of miracidia was reduced by increasing metal concentration except at concentrations of 10μg/l for single metal toxicity where survival was increased above the control. Miracidia demonstrated a rapid avoidance behaviour when briefly exposed to heavy metals. The mechanisms of metal toxicity to miracidia are briefly discussed.

Chagas disease is a public health problem, affecting about 7 million people worldwide. Benznidazole (BZN) is the main treatment option, but it has limited effectiveness and can cause severe adverse effects. Drug delivery through nanoparticles has attracted the interest of the scientific community aiming to improve therapeutic options. The aim of this study was to evaluate the cytotoxicity of benznidazole-loaded calcium carbonate nanoparticles (BZN@CaCO3) on Trypanosoma cruzi strain Y. It was observed that BZN@CaCO3 was able to reduce the viability of epimastigote, trypomastigote and amastigote forms of T. cruzi with greater potency when compared with BZN. The amount of BZN necessary to obtain the same effect was up to 25 times smaller when loaded with CaCO3 nanoparticles. Also, it was observed that BZN@CaCO3 enhanced the selectivity index. Furthermore, the cell-death mechanism induced by both BZN and BZN@CaCO3 was evaluated, indicating that both substances caused necrosis and changed mitochondrial membrane potential.

Using groups of 4 baboons (Papio anubis), 21·0% of a trickle exposure of 480 Schistosoma mansoni cercariae/baboon (10/week for 48 weeks) were recovered as adult worms (Group A) compared with 72·6% from a single massive exposure of 2500 cercariae/baboon (Group C). Group B, exposed first to the trickle and then to the massive exposure simultaneously with Groups A and C, yielded a worm recovery of 54% which was slightly but significantly less than Group C. The trickle infection apparently induced a substantial resistance to light re-exposure, but only a partial, although significant, resistance to a massive re-exposure. In Group B, however, there was a marked reduction in the degree of gross pathology, despite high tissue egg production by the mature challenge worms. The parasitological results, in terms of resistance to reinfection by and development of pathology to a trickle infection, are not materially different from those obtained in studies using conventional heavy primary and challenge exposures with S. mansoni. The significance of these findings is discussed in relation to the epidemiology of human schistosomiasis mansoni in which heavy exposures are believed to be the exception rather than the rule.

A monoclonal antibody (OW-IGO) raised against purified excysted oocysts of Cryptosporidium parvum reacted in an immunofluorescence assay with the oocyst wall. The corresponding antigen was localized by immunoelectron microscopy in fibrillous material present in the parasitophorous vacuole of developing macrogametes and in the wall of both single and double layered sporulating oocysts. Gold particles were also detected over electron-lucent vesicles of the macrogametes by immunoelectron microscopy. On Western blotting of C. parvum oocyst extracts, major bands at 250 and 40 kDa and several minor components were recognized by Mab OW-IGO. Almost complete abolition of Western blot reactivity occurred after periodate oxidation of oocyst antigen, suggesting that monoclonal antibody OW-IGO reacts with a carbohydrate epitope. Taken together, our results suggest that a fibrillous glycoproteinic material is released in the parasitophorous vacuole from electron-lucent vesicles during gametogenesis, and later condensed in the oocyst wall.

1. Serial sections were examined of thoraces of a selected strain of Aedes aegypti infected with either Brugia pahangi or subperiodic B. malayi and of wild-caught Mansonia uniformis infected with the latter parasite.

2. A few badly damaged flight muscle fibres are seen in the early stages of infection but many more fibres are destroyed at the time when the mature filarial larvae leave the muscle and enter the haemocoel. In the intervening period, when the larvae are growing within the muscle fibres, only minor damage develops, affecting nuclei and/or mitochondria. The nature of such minor damage and the mechanism of complete muscle breakdown differs in the two species of mosquitoes.

3. It was concluded that the muscle damage was sufficiently severe to explain the significant mortality often observed among experimentally infected mosquitoes at the time when the mature filarial larvae enter the haemocoel.

I am very grateful to Dr W. W. Macdonald, of the Liverpool School of Tropical Medicine, who supplied the Aedes aegypti mosquitoes and who has given invaluable help and advice throughout this study. Mr Cheong Weng Hooi and his colleagues in Kuala Lumpur kindly supplied, and partly processed, the Mansonia uniformis mosquitoes. Miss M. A. Johnson assisted with the care of the A. aegypti colony and Mrs J. Oliver helped with some of the histological work.

Extensive cross-reactions have been found between cultural forms of trypanosomes of the ‘brucei’ group by the agglutination reaction. The antigen (or antigens) responsible for agglutination are apparently specific to the ‘brucei’ group of trypanosomes. These antigens are also quite stable to the presence of specific antiserum in contrast to the serotype of the blood trypanosomes which are known to be altered in the presence of specific antiserum.

The presence of living tapeworm increases the rate of hydrolysis of starch by α-amylase in vitro. This effect indicates that ‘membrane digestion’ may be one function of the tegument of tapeworms. The effect varies with the surface area and region of the tapeworm. Fixed tapeworm pieces do not enhance starch hydrolysis. The results may provide evidence both for and against the current explanations of membrane digestion. Some possible mechanisms involved in membrane digestion in tapeworms are considered. The importance of membrane digestion in the physiology of gut parasites and the possibility of its wide occurrence are discussed.

We wish to thank Dr J. Llewellyn for his criticism and advice during the preparation of this manuscript and for providing rats and mice infected with Hymenolepis. We also thank Dr R. A. Thornhill for examining some tapeworm tissue under the electron microscope; also Mr A. Wilson of the Meat Inspection Department of the Birmingham Meat Market for his unfailing co-operation.

Neospora caninum tachyzoites attenuated through passage in tissue culture were tested for their ability to induce protective immunity against a lethal challenge dose of parasites. Balb/c mice were each inoculated with either 1×106 live virulent tachyzoites (Group 1) or 1×106 live attenuated tachyzoites (Group 2), while (Group 3) received a control inoculum. All mice were each challenged 28 days later with 5×106 virulent parasites. Histopathological lesions in the brains including necrosis and microgliosis were observed following post-mortem on day 28 post-challenge (p.c.) in 71% of Group 1 and 56% of Group 2. Immunohistochemistry (IHC) of these lesions showed tachyzoites and Neospora antigens to be associated with moderate brain lesions in 17% of Group 1, while in 11% of Group 2 N. caninum tissue cysts were detected, but these were not associated with lesions, Parasite DNA was detected by PCR in the brains of 86% of mice in Group 1 and 56% of mice in Group 2. Following challenge the mice in Group 3 showed high morbidity and 100% mortality within 17 days p.c. Positive IHC for N. caninum was seen in 88% of the Group 3 mice and parasite DNA was detected in all brain samples. This study shows that it is possible to protect against a lethal challenge of N. caninum through inoculation with attenuated or virulent tachyzoites. However, more severe pathology developed in mice initially inoculated with virulent parasites following a secondary challenge, compared to mice initially inoculated with attenuated parasites.

In Trypanosoma evansi infections changes in the haemogram are commonly observed, and the enzyme adenosine deaminase (ADA) plays an important role in the production and differentiation of blood cells. Thus, the aim of this study was to evaluate the activity of ADA in serum, erythrocytes and lymphocytes of rats infected with T. evansi compared to non-infected rats. Thirty adult rats were used, divided into 3 uniform groups. The animals in groups A and B were infected intraperitoneally with 2×106 trypomastigotes/rat. Rodents from group C (control group), were not-infected. Blood collection was performed on days 4 and 20 post-infection (p.i.) in order to obtain acute and chronic infection stages of disease. The blood was used to assess the activity of ADA. In the blood, reduced haematocrit and increased lymphocytes were correlated with ADA activity in erythrocytes and lymphocytes. We observed reduction of ADA activity in serum and erythrocytes in rats infected with T. evansi compared to non-infected rats (P<0·05). ADA activity in lymphocytes was decreased after 4 days, when the parasitaemia was high and increased after 20 days, when the number of circulating parasites was low. In conclusion, our results showed that the ADA activity was altered in serum, lymphocytes and erythrocytes of rats, concomitantly with haematological parameters, in experimental infection by T. evansi.

Complex life cycle helminths use their intermediate hosts as both a source of nutrients and as transportation. There is an assumed trade-off between these functions in that parasite growth may reduce host survival and thus transmission. The virulence of larval helminths can be assessed by experimentally increasing infection intensities and recording how parasite biomass and host mortality scale with intensity. I summarize the literature on these relationships in larval helminths and I provide an empirical example using the nematode Camallanus lacustris in its copepod first host. In all species studied thus far, including C. lacustris, overall parasite volume increases with intensity. Although a few studies observed host survival to decrease predictably with intensity, several studies found no intensity-dependent mortality or elevated mortality only at extreme intensities. For instance, no intensity-dependent mortality was observed in male copepods infected with C. lacustris, whereas female survival was reduced only at high intensities (>3) and only after worms were fully developed. These observations suggest that at low, natural intensity levels parasites do not exploit intermediate hosts as much as they presumably could and that increased growth would not obviously entail survival costs.

We studied the ‘crowding effect’ in Tribolium confusum infected with Hymenolepis diminuta. Manipulations included age and number of parasites, and diet, sex, age and number of exposures of hosts. Volume per parasite was unaffected until an intensity of at least 5–10 parasites per host, then declined approximately inversely as intensities increased. Parasite size was affected by host sex but not age or reproductive status. Host diet affected parasite size and the impact of crowding. Daily gain in parasite volume peaked partway through the developmental period and preceded the first evidence of a crowding effect. Parasites that established during a second exposure had a transient developmental delay but eventually grew as large or larger than parasites from a single exposure with the same total intensity. Parasites responded to crowding by differential allocation of resources. Cercomer volume decreased even with slight crowding, the capsule surrounding the scolex was not reduced until crowding became more severe, and scolex width was reduced only in the most extreme conditions. The data support the hypothesis that the crowding effect in this system is driven primarily by nutrient, rather than space limitations.

Infections by protozoan parasites, such as Plasmodium falciparum or Leishmania donovani, have a significant health, social and economic impact and threaten billions of people living in tropical and sub-tropical regions of developing countries worldwide. The increasing range of parasite strains resistant to frontline therapeutics makes the identification of novel drug targets and the development of corresponding inhibitors vital. Post-translational modifications (PTMs) are important modulators of biology and inhibition of protein lipidation has emerged as a promising therapeutic strategy for treatment of parasitic diseases. In this review we summarize the latest insights into protein lipidation in protozoan parasites. We discuss how recent chemical proteomic approaches have delivered the first global overviews of protein lipidation in these organisms, contributing to our understanding of the role of this PTM in critical metabolic and cellular functions. Additionally, we highlight the development of new small molecule inhibitors to target parasite acyl transferases.

A footpad assay was used to measure the DTH of mice to soluble worm antigens (SWAP), and to living day 7 lung schistosomula, following vaccination and challenge infections with Schistosoma mansoni. DTH to SWAP was first observed on day 10, and reached its maximum on day 17 post-vaccination. Treatment of mice with anti-CD4 antibody on the 3 days prior to footpad challenge completely abrogated this response. Reactivity to living parasites was of a lower order than that to SWAP; it also peaked earlier, on day 10 post-vaccination. By day 35, responsiveness to both sets of antigens had declined almost to control levels. There was no correlation between the level of DTH to living schistosomula, at any time, and the degree of resistance subsequently developed. Percutaneous challenge of vaccinated mice was followed by a resurgence of reactivity to SWAP. This secondary response occurred more rapidly than the primary response, peaking on day 7 post-challenge, and was of a similar magnitude. We were unable to detect a similar recall of DTH to living schistosomula, possibly because the assay was insufficiently sensitive. We conclude that the intensity and kinetics of DTH responsiveness are crucial features of the irradiated vaccine model, and suggest that further investigation of cell-mediated immune reactions, particularly those occurring in the lungs, is vital to a better understanding of events underlying the development and expression of immunity.

The effect of tumour necrosis factor-α on malaria-infected mice was studied. C57B1/6J mice infected with Plasmodium berghei K173 exhibited an increased sensitivity to exogenous TNF. Injection of 15 μg TNF was lethal to some of the animals when given 5–7 days after infection, while when given later on in the infection (i.e. days 8–10) amounts as low as 2·5 μg TNF appeared to be lethal in all mice. The pathology in infected mice treated with TNF resembled that found in the brains of infected mice dying with cerebral malaria. Infected mice treated with TNF, however, also developed severe pathological changes in other organs. On the contrary, treatment with sublethal amounts of TNF (1·0 μg or less) given on days 8 and 9 after infection, protected mice against the development of cerebral malaria. In addition, infected mice exhibited an enhanced sensitivity for treatment with lipopolysaccharide (LPS). Sublethal amounts of LPS, however, did not prevent mortality as in TNF-treated mice (LPS-treated mice died at about the same time as infected mice that developed cerebral malaria), but no cerebral haemorrhages were found in the majority of LPS treated, infected animals. Treatment with dexamethasone during infection protected mice against the development of cerebral malaria, but did not suppress their increased sensitivity to exogenous TNF. Treatment of mice with liposome-encapsulated dichloromethylene diphosphonate (lip-Cl2MDP), used to eliminate macrophages (an important source of TNF), prevented the development of cerebral malaria, but only when given before day 5 of infection. Mice protected by treatment with lip Cl2MDP, however, remained sensitive for LPS on the eighth day of infection.

Echinococcus granulosus (sensu lato) is now recognized as an assemblage of cryptic species, which differ considerably in morphology, development, host specificity (including infectivity/pathogenicity for humans) and other aspects. One of these species, E. granulosus sensu stricto (s.s.), is now clearly identified as the principal agent causing cystic echinococcosis in humans. Previous studies of a small section of the cox1 and nadh1 genes identified two variants of E. granulosus s.s. to be present in Australia; however, no further work has been carried out to characterize the microdiversity of the parasite in its territory. We have analysed the sequence of the full length of the cox1 gene (1609 bp) from 37 isolates of E. granulosus from different hosts and geographic regions of Australia. The analysis shows that seven haplotypes of E. granulosus s.s. not previously described were found, together with five haplotypes known to be present in other parts of the world, including the haplotype EG01 which is widespread and present in all endemic regions. These data extend knowledge related to the geographical spread and host range of E. granulosus s.s. in a country such as Australia in which the parasite established around 200 years ago.

The range of water temperatures in which Perkinsus species can survive and proliferate remains ill-defined, particularly at lower temperatures. The in vitro viability, metabolic activity, and proliferation of 3 isolates each of P. marinus and P. olseni trophozoites at 28°C, and at 15 and 4°C, after transfer from 28°C, were compared. Both species showed declines in metabolic activity and proliferation from 28°C to 15°C. At 4°C, both species had viability after 30 days incubation time (P. marinus 49%, P. olseni 58%), but limited metabolic activity and no proliferation. Perkinsus marinus viability was further compared when transferred directly from 28°C, 18°C and progressively from 18°C (0·5°C/day) to 2, 4 and 6°C and maintained for up to 4 months. Viability was highest under progressive transfer (77% and 54% after 30 and 60 days exposure to test temperatures). The decrease in P. marinus viability at the lower temperatures in vitro only partially explains decreasing parasite infection intensities in eastern oysters in the colder months of the year. Moreover, the significant decrease in parasite infection intensities in late winter and early spring, as temperatures increase, is likely due to an active process of elimination by oyster host defences.

In this chapter, the contribution of molecular tools in understanding the aetiology and ecology of infectious diseases is examined in the context of molecular epidemiology (ME). ME is seen as providing the ‘tools’, both laboratory and analytical, which have predictive significance in epidemiological investigations of the causation of disease. A diversity of questions can be addressed with these tools which can conveniently be viewed as particular regions of DNA and grouped according to the different hierarchical levels of specificity by which infectious agents can be characterized. These groupings and the applications of the different molecular tools are described, and consideration given to the most appropriate methods of analysing data from ME investigations.

Myxobolus cerebralis is the causative agent of whirling disease that has significant economical and ecological impacts on trout populations. Although intensive studies have been conducted to understand its effects on and interactions with its fish host, only limited information is available about how and to what extent M. cerebralis affects its oligochaete host, Tubifex tubifex. We investigated the effects of M. cerebralis on survival, growth, reproduction, and feeding activity of T. tubifex. Mature, immature and juvenile worms were exposed to myxospores and their infection prevalence, mortality, sexual development, reproduction and spore production were compared with unexposed worms. The parasite affected neither survival nor growth but inhibited clitellar development and reduced cocoon production by over 80%. Numbers of actinospores released from mature worms were nearly 9-fold higher than that of immature worms. When non-clitellated infected worms were kept at 30°C for 4 days, spore release ceased and they re-developed a clitellum. These results suggest parasite-induced castration. Comparative monitoring of defecation rate revealed that M. cerebralis reduced feeding activity of T. tubifex by approximately 40%. Low energy intake and impaired energetic allocation may be the underlying mechanism behind reduced fecundity of infected T. tubifex.