Analysis of egg and worm counts of Ascaris recorded at various intervals following a mass anthelmintic treatment programme in a South Indian fishing community is presented. Three indices of infection in the community are compared, namely the prevalence and intensity of egg output (at 2, 6 and 11 months following treatment) and the number of worms expelled following an 11 month period of reinfection. Detailed examination of these measurements revealed significant associations with patient sex and age. The age-prevalence profile of Ascaris infection changed little over time (except immediately following treatment) with the peak prevalence found in the 5–9 year age group. Although 85% of both males and females harboured Ascaris initially, the prevalence following 11 months reinfection was decreased, due to a significantly lower proportion of males being reinfected. By the 11th month of reinfection, the age-intensity profiles of egg output were similar to those observed at initial treatment in the older age groups (10 years and above) and in male children (< 10 years). However, a dramatic increase in the egg output of female children, greatly exceeding the initial mean, was observed within a 6 month period of reinfection. The intensity of egg output did not accurately reflect the abundance of Ascaris recovered via drug-induced expulsion following an 11 month period of reinfection. Although the egg output attained preintervention levels, the average worm intensity reached only half the initial value. The trends in the sex- and age-intensity profiles were consistent at the two sampling dates and showed similar patterns to the egg output curves. The relevance of the results to helminth control and the monitoring of reinfection is discussed.

A 3-step procedure for cloning Theileria parva parasites was developed. The first step involved the in vitro infection of a fixed number of bovine lymphocytes with titrated sporozoites. The cell lines obtained from infections initiated using sporozoite/lymphocyte ratios below 1:100 were then selected for cloning as these contained schizont-infected cells, each of which was derived from infection with a single sporozoite. In the second step, these cell lines were cloned by limiting dilution. As sporozoites infect lymphocytes and transform to induce clonal multiplication, this step produced infected cell lines containing both cloned parasites and cloned lymphocytes. In the third step, the cloned cell lines were used to infect cattle and isolation of the parasite in ticks was made during piroplasm parasitaemia. Finally, sporozoites were harvested from infected ticks and used for further characterization. Sporozoites derived from cloned cell lines of T. parva Muguga, Marikebuni, Boleni, Uganda and buffalo-derived 7014 were characterized using monoclonal antibody profiles, DNA restriction fragment length polymorphism detected using repetitive and telomeric probes, in vivo infectivity and, in one case, cross-immunity studies. Additionally, several distinct schizont-infected lymphocyte clones were isolated from the Muguga, Mariakani and buffalo-derived 7014 stocks. The combined results of the characterization revealed that the cloning procedure selected clones of T. parva from the parental stocks which were known to contain a mixture of genetically different parasite populations. The cloning method and the clones generated will be of value in studies of the biology of the parasite and in elucidating the strain specificity of immune responses in cattle.

1. The nomenclature and host specificity of Toxascaris leonina is reviewed and the conclusion reached that this parasite occurs in a wide range of feline and canine hosts. Notice is given of application to the International Commission on Zoological Nomenclature, for the suppression of Ascaris leptoptera Rudolphi 1809 and A. microptera Rudolphi, 1819, which appear to be senior synonyms of Toxascaris leonina. The synonyms and hosts of T. leonina are tabulated.

2. The distribution and growth of the larvae of T. leonina in experimentally infected mice, cats, and dogs is reported. A feline and a canine strain were used for these infections and infection of cats and dogs was produced both by feeding the eggs containing second-stage larvae and by feeding mouse tissues containing third-stage larvae.

Programmes to control Ascaris lumbricoides, Trichuris trichiura and hookworm infections have often been targeted at each infection separately, but the advent of benign and broad-spectrum anthelmintics suggests that combined control ma be feasible. The extent to which the infections co-occur in communities will determine the need for, and potential benefits of, such a combined approach. This paper examines the comparative distribution of the three geohelminths in different geographical areas and shows that A. lumbricoides and T. trichiura have closely related distributions, while hookworm infection is largely independent of the other two. These results indicate that many communities are at risk of disease from infection by more than one species of helminth. The similar distributions and epidemiological characteristics of A. lumbricoides and T. trichiura suggest that simultaneous control of these two parasites by the same strategy would be feasible and highly beneficial to communities. Multiple species control strategies which aim to control hookworm infection may require a more complicated protocol with more precise locality targeting.

The recent development of genetic methods allows the delineation of species boundaries, especially in organisms where morphological characters are not reliable to differentiate species. However, few empirical studies have used these tools to delineate species among parasitic metazoans. Here we investigate the species boundaries of Clinostomum, a cosmopolitan trematode genus with complex life cycle. We sequenced a mitochondrial [cytochrome c oxidase subunit I (COI)] gene for multiple individuals (adults and metacercariae) from Middle-America. Bayesian phylogenetic analysis of the COI uncovered five reciprocally monophyletic clades. COI sequences were then explored using the Automatic Barcode Gap Discovery to identify putative species; this species delimitation method recognized six species. A subsample was sequenced for a nuclear gene (ITS1, 5·8S, ITS2), and a concatenated phylogenetic analysis was performed through Bayesian inference. The species delimitation of Middle-American Clinostomum was finally validated using a multispecies coalescent analysis (species tree). In total, five putative species are recognized among our samples. Mapping the second intermediate hosts (fish) onto the species tree suggests that metacercariae of these five species exhibit some level of host specificity towards their fish intermediate host (at the family level), irrespective of geographical distribution.

Some Kudoa species display variations in the number of polar capsules in spores within an individual pseudocyst. Nonetheless, there is usually a dominant morphotype which forms a significant element of diagnosis. In 2007, a Kudoa isolate from whiting (spores with 5 (dominant) or 6 (minor) polar capsules) was characterized by Burger et al. (2007) as being 100% identical in SSU rDNA to Kudoa yasunagai (spores with 7 polar capsules) from a halibut, despite its obvious morphological differences. The authors hypothesized that either SSU rDNA had reached its level of resolution or that the genetic identity revealed conspecificity. To further investigate these hypotheses, SSU and LSU rDNA sequence data were coupled with principal components, correlation, and regression analyses of morphometric data from different kudoid isolates that infect brain tissue to determine the relationships between spore morphotypes and different kudoid isolates. The trends in morphometrics between the spores of particular isolates were so similar that it was concluded that the molecular results did indicate conspecificity rather than SSU reaching its level of resolution. This phenotypic influence on a significant diagnostic character within the Kudoidae has a major impact on the diagnosis of this, and potentially other, pathogenic species.

Schistosomiasis is a health problem in Brazil and the role of rodents in maintaining the schistosome life-cycle requires further clarification. The influence of Schistosoma mansoni on a population of Nectomys squamipes was studied by capture-recapture (1st phase, from June 1991 to November 1995) and removal (2nd phase, from April 1997 to March 1999) studies at Sumidouro, Rio de Janeiro, Brazil. During both phases coproscopic examinations were performed. At the 2nd phase the rodents were perfused and worms were counted. The population dynamics of parasites was studied. During the 1st phase, female reproductive parameters, longevity, recruitment and survivorship rates and migration patterns were studied in relation to schistosome prevalence. Water contamination (source of miracidia), abundance intermediate host and rodent migration were related to prevalence. The N. squamipes population was not obviously influenced by the infection, as shown by the high number of reproductive infected females, high longevity of infected individuals and the absence of a relationship between recruitment or survivorship rates and the intensity of schistosome infection. The data indicate that N. squamipes can increase transmission of S. mansoni in endemic areas and carry it to non-infected areas. Furthermore, this rodent can be used as an indicator of a transmission focus.

Recent work has highlighted and enumerated the economic annual losses due to Neospora caninum abortions worldwide, which should provide strong motivation for the control of bovine neosporosis. However, with the recent withdrawal from sale of the only commercially available vaccine, control options for N. caninum have become more restricted. While researchers continue to work on developing alternative efficacious vaccines, what are the control options presently available for the cattle industries? At the practical level, recommendations for ‘Test-and-cull’, or ‘not breeding from seropositive dams’ stand diametrically opposed to alternative options put forward that suggest a primary producer is better advised to keep those cows in the herd that are already seropositive, i.e. assumed to be chronically infected, and indeed those that have already aborted once. Treatment with a coccidiostat has been recommended as the only economically viable option, yet no such treatment has gained official, regulatory approval. Dogs are central to the life cycle of N. caninum and have repeatedly been associated with infection and abortions in cattle by epidemiological studies. Knowledge and understanding of that pivotal role should be able to be put to use in control programmes. The present review canvasses the relevant literature for evidence for control options for N. caninum (some of them proven, many not) and assesses them in the light of the authors’ knowledge and experience with control of N. caninum.

Hosts are typically simultaneously co-infected by a variety of microparasites (e.g. viruses and bacteria) and macroparasites (e.g. parasitic helminths). However, the population dynamical consequences of such co-infections and the implications for the effectiveness of imposed control programmes have yet to be fully realised. Mathematical models may provide an important framework for exploring such issues and have proved invaluable in helping to understand the factors affecting the epidemiology of single parasitic infections. Here the first population dynamic model of microparasite-macroparasite co-infection is presented and used to explore how co-infection alters the predictions of the existing single-species models. It is shown that incorporating an additional parasite species into existing models can greatly stabilise them, due to the combined density-dependent impacts on the host population, but co-infection can also restrict the region of parameter space where each species could persist alone. Overall it is concluded that the dynamic feedback between host, microparasite and macroparasite means that it is difficult to appreciate the factors affecting parasite persistence and predict the effectiveness of control by just studying one component in isolation.

For hundreds of years, the unmanaged Soay sheep population on St Kilda has survived despite enduring presumably deleterious co-infections of helminth, protozoan and arthropod parasites and intermittent periods of starvation. Important parasite taxa in young Soay sheep are strongyles (Trichostrongylus axei, Trichostrongylus vitrinus and Teladorsagia circumcincta), coccidia (11 Eimeria species) and keds (Melophagus ovinus) and in older animals, Teladorsagia circumcincta. In this research, associations between the intensity of different parasite taxa were investigated. Secondly, the intensities of different parasite taxa were tested for associations with variation in host weight, which is itself a determinant of over-winter survival in the host population. In lambs, the intensity of strongyle eggs was positively correlated with that of Nematodirus spp. eggs, while in yearlings and adults strongyle eggs and coccidia oocysts were positively correlated. In lambs and yearlings, of the parasite taxa tested, only strongyle eggs were significantly and negatively associated with host weight. However, in adult hosts, strongyles and coccidia were independently and negatively associated with host weight. These results are consistent with the idea that strongyles and coccidia are exerting independent selection on Soay sheep.

The trypanosomes cause two neglected tropical diseases, Chagas disease in the Americas and African trypanosomiasis in sub-Saharan Africa. Over recent years a raft of molecular tools have been developed enabling the genetic dissection of many aspects of trypanosome biology, including the mechanisms underlying resistance to some of the current clinical and veterinary drugs. This has led to the identification and characterization of key resistance determinants, including transporters for the anti-Trypanosoma brucei drugs, melarsoprol, pentamidine and eflornithine, and the activator of nifurtimox-benznidazole, the anti-Trypanosoma cruzi drugs. More recently, advances in sequencing technology, combined with the development of RNA interference libraries in the clinically relevant bloodstream form of T. brucei have led to an exponential increase in the number of proteins known to interact either directly or indirectly with the anti-trypanosomal drugs. In this review, we discuss these findings and the technological developments that are set to further revolutionise our understanding of drug-trypanosome interactions. The new knowledge gained should inform the development of novel interventions against the devastating diseases caused by these parasites.

Parasite life-history traits should reflect past environmental and host-related selective pressures acting to produce strategies that maximize transmission success. The evolution of adult body size and egg production in 804 species of trematode parasites was investigated using independent contrasts derived from a phylogeny of trematodes. Contrasts in trematode body size were positively correlated with contrasts in egg size, and almost significantly correlated with contrasts in numbers of uterine eggs. After controlling for body size, no relationship existed between egg size and egg numbers, suggesting that there is no trade-off between the two components of egg production. Average host body mass and latitude of the sampling site did not correlate with either trematode body size or egg size. Contrasts between trematode taxa exploiting ectotherm hosts and their sister taxa exploiting endotherms showed no consistent difference in either body size or egg size. The effect of other variables on trematode life-histories, such as the nature of the habitat in which eggs are released, the site of attachment within the host's body, or the number of hosts involved in the life-cycle, could not be evaluated statistically. The similarity in life-history traits among members of given clades suggests that phylogenetic constraints may have acted to limit or mask any adaptive changes expected from changes in host-related or environmental conditions.

The epidemiology of trypanosome infections of Glossina pallidipes was studied at a riverine site in the Zambezi Valley, Zimbabwe for a period of 13 months. Over 9000 flies were captured using a single trap. These flies were dissected, screened for trypanosome infection, sexed, and aged using both wing fray and (for females) ovarian category indices. Midgut infections were identified to species using recently developed DNA probes. The overall prevalence of mature infections was 5·5%, comprising 3·1% Trypanosoma vivax-type and 2·4% T. congolense-type (which included very low prevalences of T. brucei, T. simiae and another Nannomonas species). The prevalence of infection increased with age. For T. vivax-type infections in flies aged by ovarian category this relationship could be described by a simple ‘catalytic’ model assuming a constant per capita rate of infection. For T. congolense-type infections this model tended to over-estimate prevalence in older age classes, implying that the rate of infection decreases with age, and/or that infected flies have higher mortality rates, and/or that a significant fraction of the population is resistant to infection. Prevalences of infection also varied between months. This variation was more marked for T. vivax-type infections and was negatively correlated with both temperature and rainfall. The shape of the age-prevalence relationship, however, did not vary significantly between months. These observations are not fully explained by variation in the age-structure of the tsetse population and are consistent with temporal variation in the rate of infection (rather than in the trypanosome developmental period or in effects of infection on fly mortality). Possible causes of this variation are discussed.

A size selected genomic DNA library was constructed using DNA extracted from Taenia saginata. The DNA was digested using the restriction enzyme EcoR1 under star conditions and the 2–4 kbase fraction, selected following sucrose density-gradient separation, was cloned in the bacteriophage λgt 10. A panel of cestode DNAs including Taenia saginata, Taenia solium, Taenia taeniaeformis, Taenia crassiceps, Echinococcus granulosus and DNAs of bovine, porcine and human origin were used in conjunction with hybridization analysis to identify two recombinant bacteriophages. The first probe, designated HDP1, reacted specifically with T. saginata DNA. The second, designated HDP2, reacted with DNA from both T. saginata and T. solium but not the other DNA samples and thus provided a general reagent for positive identification of fragments of Taenia spp. proglottides of human faecal origin. If used in conjunction the two DNA probes allow positive identification of T. saginata. In the clinical situation it is important to be able to distinguish T. saginata and T. solium infections and DNA probes such as these may be useful in such differentiation.

The New Zealand cockle Austrovenus stutchburyi, whose foot is commonly infected by the digenean trematode Curtuteria australis (Echinostomatidae), is often found heavily infected and unable to burrow on the sediment surface of tidal flats. This has been interpreted as a Curtuteria-manipulation with the purpose of increasing the transmission of the parasite to shorebirds acting as final hosts. Using a field-experimental approach the alternative hypothesis was tested, that surface-dwelling cockles, caught on the surface for other reasons than parasites, accumulate larval C. australis at a higher rate than buried cockles. During the 3-month experiment, larval trematodes accumulated with a rate of approximately 0·5 metacercariae/day in both surface and buried cockles. The result strengthens the manipulation hypothesis indirectly by rejecting the alternative hypothesis. The metacercariae were unevenly distributed along the cockle-foot, with about 4 times as many cysts being found in the tip than in either the mid or hind part of the foot. In light of existing knowledge of the burrowing behaviour and apparatus in bivalves, and a negative relationship between foot mobility and infection intensity, it is suggested that C. australis manipulates its host through a mechanical obstruction of foot muscles and the dynamic hydrostatic skeleton, both necessary for successful burrowing.

The uptake of Wuchereria bancrofti microfilariae (Mf) by Culex quinquefasciatus and their development in relation to human Mf density were quantified by allowing a total of 1096 wild mosquitoes to feed on 13 volunteers sleeping under partially open bed-nets. For each volunteer, each hour between 18.00 and 06.00 h the Mf density in finger-prick blood was determined and engorged mosquitoes collected. Each hourly collection of mosquitoes was kept separately. Half of them was dissected within 18 h post-feeding for the presence of ingested Mf, the other half was reared for 12 days to allow for the development of L3 larvae. About 20% of the latter mosquitoes died during these 12 days and these harboured significantly more larvae than the surviving ones, which could be an indication of excess-mortality among heavily infected mosquitoes. Assuming that variability in Mf uptake and in the number of developed L3 larvae can be described by a negative binomial distribution, a maximum-likelihood procedure was applied to estimate the relationship between human Mf density and both the arithmetic mean Mf uptake and L3 development. Both were adequately described by a saturating hyperbolic function that significantly differed from linearity. The saturation level for Mf was estimated at 29 (CI: 20–54) and for L3 larvae at 6·6 (CI: 4·3–17·0). Next, the L3 yield was related to Mf uptake indicating that the W. bancrofti–C. quinquefasciatus complex shows ‘limitation’, i.e. a decreasing yield for an increasing uptake. Both the number of Mf ingested and the number of L3 larvae developing per mosquito were found to be highly aggregated, with the level of aggregation decreasing in a non-linear way with human Mf density.

The recent implementation of mass drug administration (MDA) for control of uro-genital schistosomiasis has identified an urgent need for molecular markers to both directly monitor the impact of MDA, for example to distinguish re-infections from uncleared infections, as well as understand aspects of parasite reproduction and gene flow which might predict evolutionary change, such as the development and spread of drug resistance. We report the development of a novel microsatellite tool-kit allowing, for the first time, robust genetic analysis of individual S. haematobium larvae collected directly from infected human hosts. We genotyped the parasite populations of 47 children from 2 schools in the Ségou region of Mali, the first microsatellite study of this highly neglected parasite. There was only limited evidence of population subdivision between individual children or between the two schools, suggesting that few barriers to gene flow exist in this population. Complex relationships between parasite reproductive success, infection intensity and host age and gender were identified. Older children and boys harboured more diverse infections, as measured by the number of unique adult genotypes present. Individual parasite genotypes had variable reproductive success both across hosts, a pre-requisite for evolutionary selection, and, phenotypically, in hosts of different ages and genders. These data serve as a baseline against which to measure the effect of treatment on parasite population genetics in this region of Mali, and the tools developed are suitable to further investigate this important pathogen, and its close relatives, throughout their range.

In order to estimate the potential benefits of interventions against multiple geohelminth species in endemic areas, an improved understanding of the population biology of multiple infections is required. This paper presents a detailed analysis of the associations among Ascaris lumbricoides, Trichuris trichiura and hookworm infections in 1539 schoolchildren on Pemba Island, Tanzania, where 58% of the sampled children carried infections of all 3 parasites at the time of the study. Infection intensities of different species were positively correlated, and individuals with single-species infections had generally lower species-specific egg counts than individuals with multiple-species infections. There was no age- or sex-related clustering of infections. A weak clustering of intense infections among individuals with multiple-species infections was observed, which became more pronounced as the threshold defining an intense infection increased for each species. The results suggest that individuals with multiple species infections are likely to be at highest risk of geohelminth-related morbidity, not only because of the number of infections they harbour, but also because they generally carry heavier infections of each species.

1. Certain aspects of the general morphology of Polymorphus minutus are described together with a detailed description of the body wall.

2. An additional layer of the body wall, the epicuticle, has been demonstrated. It appears to consist of acid mucopolysaccharide and may have a function of protecting the parasite from the enzymes of its host.

3. A histochemical investigation has been made of the layers of the body wall and it is concluded that lipoprotein is one of the main structural components.

4. The distribution of the activity of the two enzymes, non-specific esterase and alkaline phosphatase, has been studied throughout the animal and the activity of a third enzyme, leucine aminopeptidase, has been detected in the body wall.

5. It is suggested that all the layers of the body wall, with the exception of the cuticle and epicuticle, are of metabolic importance. The striped layer may be connected with absorption and the felt and radial layers may be involved in the further metabolism of absorbed compounds.

6. The results obtained are used to formulate a possible structure of the surface of the parasite which would facilitate the absorption of nutrient substances through the body wall.

I am grateful to Dr P. Tate for advice and encouragement during this work, Dr R. J. Tatchell for helpful discussions, and Dr D. L. Lee for criticising the manuscript and Mr T. M. Warwick, Department of Zoology, University of Edinburgh for providing material.

Infectious agents have considerable potential to regulate or constrain the population growth of vertebrate hosts in natural habitats. A broad theoretical framework provides many insights into how the biology of the parasite and the demography of the host interact to determine this impact. It may manifest itself as a steady influence over time via stable endemic infection or in a recurrent epidemic fashion, sometimes with unpredictable intervals between epidemics depending on the generation time of the pathogen (time from infection to recovery or host death), its ability to induce lasting immunity and the population growth rate of the host species. Building on these notions, the paper focuses on recent work on the population dynamics of genetically variable pathogen populations and examines the factors that determine the evolution of virulence and the maintenance of genetic diversity in both host and pathogen. Recent research extends conventional theoretical templates to include population genetic elements and the within-host dynamics of the parasite and its interaction with the vertebrate immune system.