Patterns of nematode fecundity were investigated for infections of the caecal worm Heterakis gallinarum in the ring-necked pheasant (Phasianus colchicus). Worm length was a good predictor of parasite fecundity. After controlling for worm length no other factors, including parasite intensity, were related to worm fecundity. Density dependence in worm size was detected in natural infections at parasite intensities above a threshold of 96 worms (worm size decreased with increasing parasite intensity). However, below this threshold, worm size actually decreased with decreasing parasite intensity (inverse density dependence). The interaction between density dependence and inverse density dependence in regulating the development and subsequent fecundity of H. gallinarum worms in ring-necked pheasants was demonstrated in an infection experiment. Density dependence was observed in the stunted growth of worms in heavily infected hosts, relative to worms in lightly infected hosts. Inverse density dependence in worm size was the common pattern across hosts by the end of the experiment, when parasite intensities were below the density dependence threshold. This is the first study to document both density dependence and inverse density dependence in parasite fecundity in the same host–helminth system.

Ecdysteroids (moulting hormones), juvenoids and neuropeptides in ticks are reviewed but, by far, the emphasis is on the former since this class of hormones has been the subject of most investigations. In immature stages of ticks, ecdysteroids have been shown to regulate moulting and to terminate larval diapause. Although there is a paucity of information on the molecular action of ecdysteroids in ticks, their action appears to be via a heterodimeric ecdysone/ultraspiracle receptor, as in insects. The role of ecdysteroids in sperm maturation in adult males is considered. In females, ecdysteroids function in the regulation of salivary glands, of production of sex pheromones and of oogenesis and oviposition. There is evidence for ecdysteroid production in the integument and pathways of hormone inactivation are similar to those in insects. Ecdysteroids also function in embryogenesis. Although evidence for the occurrence and functioning of juvenile hormones in ticks has been contradictory, in recent thorough work it has not been possible to detect known juvenile hormones in ticks, nor to demonstrate effects of extracts on insects. Factors (neuropeptides) from the synganglion affect physiological processes and limited immunocytochemical studies are reviewed. Sigificantly, a G-protein-coupled receptor has been cloned, expressed, and specifically responds to myokinins.

Benzimidazole (BZ) resistance is widespread and appears to be readily selected in a variety of nematode parasites of animals. There have been reports of a lack of efficacy of BZ anthelmintics against soil transmitted nematode parasites of humans. However, resistance to BZs in nematodes of humans has not been confirmed. It is difficult to perform tests to confirm anthelmintic resistance in humans for a variety of technical and ethical reasons. The use of anthelmintic drugs for the control of helminth parasites in people is increasing massively as a result of numerous programmes to control gastrointestinal nematode parasites in children, the Global Program for the Elimination of Lymphatic Filariasis and other programmes. Many of these programmes are dependent on BZ anthelmintics and this will increase the pressure for resistance development to BZ anthelmintics in nematode parasites of people. We need to perform monitoring for anthelmintic resistance in these programmes and we need new tools to make that monitoring sensitive, inexpensive and practical. There is a real need for DNA-based markers for BZ resistance in nematode parasites of humans. We have a reasonable understanding of the molecular mechanisms and genetics of BZ resistance in some nematode parasites of animals and similar mechanisms are likely to prevail in nematodes of humans. Based on the likelihood that similar single nucleotide polymorphisms (SNPs) will be involved in BZ resistance in human, as in animal nematode parasites, rapid SNP assays have been developed for possible BZ resistance development in Wuchereria bancrofti.

This paper describes the distribution of Ascaris suum in experimentally and naturally infected pigs, and offers a comparison with A. lumbricoides infections in humans. In the first study, worms were recovered post-mortem from a group of 38 pigs that had been trickle inoculated with 10000 infective A. suum eggs twice weekly for 12 weeks. In the second study, worms were collected from a group of 49 pigs that had been kept on a pasture contaminated with infective A. suum eggs for 10 weeks, after which they received treatment with an anthelmintic; they then were turned out on the same pasture for a second 10-week period before slaughter. The worm burdens of the naturally infected pigs were recorded both at treatment and post-mortem. Mean worm counts were similar at all occasions but the prevalence of infection was higher in the trickle infected and naturally reinfected pigs. Furthermore, the prevalence in naturally infected pigs increased significantly over the study period. Worm burden distributions in all groups were heavily overdispersed, but the distribution patterns differed significantly between groups: lower exposure (initial natural infection) gave a low prevalence and an almost uniform distribution of worm burdens among infected hosts. Continued or higher exposure (trickle and natural reinfection) resulted in increased prevalence and a reduction in the proportion of hosts with increasing worm load. A positive correlation was found between initial and reinfection worm burdens in the naturally infected pig population, suggesting that individual pigs are predisposed to a high or low intensity of infection. The prevalence and intensity as well as the distribution observed for A. suum infection in pigs were comparable to those reported for A. lumbricoides in endemic areas, and there is evidence for predisposition to A. suum in pigs, with an estimated correlation coefficient similar to that found in humans. It is concluded that A. suum infections in pigs are a suitable model to study the population dynamics of A. lumbricoides in human populations.

A holotrichous ciliate found repeatedly in very large numbers in the body cavity of larval midges (Chironomus plumosus) from Paris and Berlin areas is described as a new species of the genus Tetrahymena, named T. chironomi sp.nov. It appears to represent a true example of facultative parasitism, since parasites released from the host survive in laboratory cultures, and free-living ciliates believed identical have been isolated from fresh-water sources in nature. Over a 3-month period more than 2000 larvae, principally fourth-instar stages, were examined; about 9 % of these were found to be infected with ciliates.

T. chironomi is the thirteenth species to be added to the growing holotrich hymenostome genus Tetrahymena. It is taxonomically distinguishable from other members of the genus on the basis of a combination of characteristics related to its morphology and bionomics. It is one of the smallest species, has 24–27 ciliary meridians and a relatively large, spherical micronucleus, does not exhibit dimorphism or cystic stages in its life cycle, and does not possess a caudal cilium.

Eimerian oocysts were found in 98% of 422 faeces samples from goats in SE England. It was found that 74% of the samples contained thousands or tens of thousands of oocysts/g. Kids less than 1 year old had higher oocyst counts than yearling or adult goats. Nine species of Eimeria were identified, and 65% of the samples contained 3–5 species. The most prevalent species were E. arloingi (94%), E. hirci (69%), E. christenseni (64%) and E. caprina (55%). E. ninakohlyakimovae (48%), E. alijevi (42%) and E. apsheronica (23%) were common, and E. joichijevi (8%) and E. caprovina (4%) were comparatively rare. Developmental stages of E. caprina destroyed the crypt epithelium in the mucosa of the large intestine, causing severe haemorrhagic enteritis similar to that produced by E. ninakohlyakimovae. The literature on Eimeria species in sheep and goats is reviewed and, on the grounds of priority, E. bakuensis is the correct name for E. ovina in sheep.

Dogs infected with Angiostrongylus vasorum, a potentially lethal parasite parasitizing the heart and pulmonary arteries, may present severe respiratory, haematological and neurological signs. In this first large-scale seroepidemiological survey, 4003 sera originating from Germany and 4030 from the UK were tested by an ELISA for the detection of circulating antigen of A. vasorum, and by a separate ELISA detecting specific antibodies. In Germany, where mainly western federal states were sampled, 0·3% (n = 13, CI: 0·2–0·6%) of dogs were positive in both ELISAs, whereas in total 0·5% (n = 20, CI: 0·3–0·8%) were antigen-positive and 2·25% (n = 90, CI: 1·8–2·8%) were positive for specific antibodies. Regions with antigen- and antibody-positive animals were overlapping. In the UK, where mainly the south of the country was sampled, 0·97% (n = 39, CI: 0·7–1·3%) of dogs were antigen- and antibody positive. In total, 1·32% (n = 53, CI: 1·0–1·7%) were antigen-positive, and 3·2% (n = 129, CI: 2·7–3·8%) were positive for specific antibodies, again in overlapping regions. These results confirm the occurrence of A. vasorum in a random dog population originating from large parts of the countries investigated. The use of the tests alone or in combination was considered as a function of their sensitivities and specificities, in order to guide efficient clinical and epidemiological application.

Prevalence and abundance of Cryptosporodium parvum and Giardia spp. were studied in 3 species of rodents from forests and abandoned agricultural fields in N.E. Poland (Clethrionomys glareolus n = 459; Microtus arvalis n = 274; Apodemus flavicollis n = 209). Overall prevalence was consistently higher in the voles compared with A. flavicollis (70·6, 73·0 and 27·8% respectively for C. parvum and 93·9, 96·3 and 48·3% respectively for Giardia spp.). Prevalence and abundance of infection also varied markedly across 3 years with 1998 being a year of higher prevalence and abundance with both species. Fewer older animals (especially C. glareolus and M. arvalis) carried infection with C. parvum and infections in these animals were relatively milder. Although seasonal differences were significant, no consistent pattern of changes was apparent. Host sex did not influence prevalence or abundance of infection with C. parvum, but made a small contribution to a 4-way interaction (in 5-way ANOVA) with other factors in the case of Giardia spp. The 2 species co-occurred significantly and in animals carrying both parasites there was a highly significant positive correlation between abundance of infection with each, even with between-year, seasonal, host age, sex and species differences taken into account. Quantitative associations were confined to the 2 vole species in the study. These results are discussed in relation to the importance of wild rodents as reservoir hosts and sources of infection for local human communities.

Here we examined whether the recent dramatic decline in malaria transmission in Sri Lanka led to a major bottleneck in the local Plasmodium vivax population, with a substantial decrease in the effective population size. To this end, we typed 14 highly polymorphic microsatellite markers in 185 P. vivax patient isolates collected from 13 districts in Sri Lanka over a period of 5 years (2003–2007). Overall, we found a high degree of polymorphism, with 184 unique haplotypes (12–46 alleles per locus) and average genetic diversity (expected heterozygosity) of 0·8744. Almost 69% (n = 127) isolates had multiple-clone infections (MCI). Significant spatial and temporal differentiation (FST = 0·04–0·25; P⩽0·0009) between populations was observed. The effective population size was relatively high but showed a decline from 2003–4 to 2006–7 periods (estimated as 45 661 to 22 896 or 10 513 to 7057, depending on the underlying model used). We used three approaches – namely, mode-shift in allele frequency distribution, detection of heterozygote excess and the M-ratio statistics – to test for evidence of a recent population bottleneck but only the low values of M-ratio statistics (ranging between 0·15–0·33, mean 0·26) were suggestive of such a bottleneck. The persistence of high genetic diversity and high proportion of MCI, with little change in effective population size, despite the collapse in demographic population size of P. vivax in Sri Lanka indicates the importance of maintaining stringent control and surveillance measures to prevent resurgence.

We have recently proposed revival of the name Entamoeba nuttalliCastellani, 1908 for a virulent amoeba (P19-061405 strain) isolated from a rhesus monkey (Macaca mulatta) and located phylogenetically between E. histolytica and E. dispar. In this study, E. nuttalli was isolated from feces of captive Japanese macaques (M. fuscata) in an open-air corral in Japan. The sequence of the 18S rRNA gene in the isolates differed from the P19-061405 strain in 2 nucleotide positions, but was identical to the EHMfas1 strain isolated previously from a cynomolgus monkey (M. fascicularis). One of the E. nuttalli isolates from Japanese macaques, named the NASA6 strain, was axenized and cloned. In isoenzyme analysis, the mobilities of hexokinase and phosphate glucose isomerase in the NASA6 strain were identical to those in the P19-061405 and EHMfas1 strains, but the mobility of phosphoglucomutase was different. These results were supported by gene analyses of these enzymes. Inoculation of NASA6 strain trophozoites into the liver of hamsters led to formation of an amoebic liver abscess. The liver lesions were characterized by extensive necrosis associated with inflammatory reactions. These results demonstrate that the NASA6 strain is potentially virulent and that E. nuttalli should be recognized as a common parasite in macaques.

Cryptosporidia are important protozoan parasites of vertebrates, and a number of species and genotypes, with different host ranges, have been described. In this study a protocol was established for the detection and the genetic characterization of Cryptosporidium spp. isolated from various types of surface waters (rivers, creeks, lakes, sewage plant in- and outlets and swimming pools) from the area between Zurich (Switzerland) and Munich (Germany). Cryptosporidium oocysts were isolated by continuous-flow-centrifugation and immunomagnetic separation (IMS). A novel nested PCR combined with direct sequencing of the amplicon which spans a variable region of the 18S rRNA allowed characterization of species and genotypes. Cryptosporidium spp. were detected in 23 of the 68 water samples investigated. Almost half of these isolates represent species and genotypes known to be pathogenic to man, namely C. parvum ‘bovine genotype’ (from 6 samples) and C. parvum ‘human genotype’ (4). Furthermore, we identified C. muris ‘genotype A’ (3), C. muris ‘genotype B’ (6), C. baileyi (1) as well as 3 novel Cryptosporidium genotypes. Our results confirm the ubiquitous presence of Cryptosporidium oocysts in surface waters. The detection of a variety of species and genotypes stresses the importance that molecular characterization is indispensable before drawing conclusions of medical or epidemiological significance.

Partial 28S ribosomal RNA (rRNA) gene sequences, including the variable domains D1, D2 and D3, were determined for representative species from the 4 Schistosoma species groups. On an alignment of 1345 bp from S. mansoni, S. haematobium, S. spindale and S. japonicum (with Heterobilharzia americana chosen as an outgroup), both maximum likelihood and maximum parsimony analyses provide a robust molecular phytogeny for the genus; ((((S. haematobium, S. spindale), S. mansoni), S. japonicum), H. americana). When analysed separately, both domain D1 and domain D2 yielded similarly informative data whereas D3 failed to resolve the phylogeny. These results confirm a phylogeny previously suggested by 18S rRNA gene sequences, corroborating the status of S. spindale as a sister taxon to S. haematobium, and demonstrate the utility of 28S rRNA gene sequence data for resolving phylogenies within the Schistosomatidae.

Note: nucleotide sequence data reported in this paper are available in the EMBL database under the accession numbers Z46503/04/05/06/21.

The intestinal nematode Heligmosomoides bakeri has undergone 2 name changes during the last 4 decades. Originally, the name conferred on the organism in the early 20th century was Nematospiroides dubius, but this was dropped in favour of Heligmosomoides polygyrus, and then more recently H. bakeri, to distinguish it from a closely related parasite commonly found in wood mice in Europe. H. bakeri typically causes long-lasting infections in mice and in this respect it has been an invaluable laboratory model of chronic intestinal nematode infections. Resistance to H. bakeri is a dominant trait and is controlled by genes both within and outside the MHC. More recently, a significant QTL has been identified on chromosome 1, although the identity of the underlying genes is not yet known. Other QTL for resistance traits and for the accompanying immune responses were also defined, indicating that resistance to H. bakeri is a highly polygenic phenomenon. Hence marker-assisted breeding programmes aiming to improve resistance to GI nematodes in breeds of domestic livestock will need to be highly selective, focussing on genes that confer the greatest proportion of overall genetic resistance, whilst leaving livestock well-equipped genetically to cope with other types of pathogens and preserving important production traits.

For over 50 years it has been known that there are considerable differences in the severity and rate of progression of both Trypanosoma brucei rhodesiense and T. b. gambiense infection between individuals. Yet research into the factors, whether parasite or host, which control virulence in Human African trypanosomiasis is in its infancy. In this paper we review the clinical evidence for virulence variation and the epidemiological and experimental data that give clues as to the mechanisms involved. Evidence will be presented for both asymptomatic forms of T. b. gambiense infection and low virulence forms of T. b. rhodesiense infection in humans. While in both cases the mechanisms remain to be elucidated, the overall infection virulence phenotype is determined by both parasite and host genotype.

Echinococcus granulosus is the causative agent of cystic echinococcosis. The disease is a significant global public health concern and human infections are most commonly associated with E. granulosus sensu stricto (s. s.) genotype G1. The objectives of this study were to: (i) analyse the genetic variation and phylogeography of E. granulosus s. s. G1 in part of its main distribution range in Europe using 8274 bp of mtDNA; (ii) compare the results with those derived from previously used shorter mtDNA sequences and highlight the major differences. We sequenced a total of 91 E. granulosus s. s. G1 isolates from six different intermediate host species, including humans. The isolates originated from seven countries representing primarily Turkey, Italy and Spain. Few samples were also from Albania, Greece, Romania and from a patient originating from Algeria, but diagnosed in Finland. The analysed 91 sequences were divided into 83 haplotypes, revealing complex phylogeography and high genetic variation of E. granulosus s. s. G1 in Europe, particularly in the high-diversity domestication centre of western Asia. Comparisons with shorter mtDNA datasets revealed that 8274 bp sequences provided significantly higher phylogenetic resolution and thus more power to reveal the genetic relations between different haplotypes.

Histological investigations of the bile ducts of various hosts of F. hepatica during the early stages of infection, when the flukes are burrowing in the liver and have not yet reached the bile ducts, indicate that subtle changes are brought about, probably by chemical agencies and as a result of the inflammatory process, in the bile ducts of the hosts. The transitory appearance of minute cytoplasmic blebs at the free margins of the epithelial cells seems to inaugurate an intense hyperplasia of the epithelium with tubular ingrowths and adenomatous development of glandular tissue, and an associated fibrosis which produces a thick underlying layer of dense fibrous tissue. At the time of entry of the flukes into the biliary system the hyperplastic epithelium is intact, but soon the spines and suckers of the flukes abrade the superficial cells until this part of the duct is completely denuded. It is suggested that as a result of the inflammatory reaction, the fluke has been provided with a ‘pasture’ of hyperplastic epithelium and connective tissue on which it may continue to browse for considerable periods without necessarily affecting the host adversely. Tissue debris is found in the contents of the bile duct and similar homogenized materials occur in the caecal contents of the fluke. Previous researches have shown that the fluke will feed on various tissues, and it is suggested that this tissue-feeding habit persists during its life in the bile duct. These results agree with the findings of Müller (1923) but are at variance with the results obtained by other investigators, as is shown in discussion. The hyperplasia of the bile duct is not characteristic of fascioliasis, occurring also in clonorchiasis, opisthorchiasis and dicrocoeliasis, and in these and possibly other instances it is probably intimately connected with the nutrition of the flukes concerned.

Progress has been made in mapping and predicting the risk of schistosomiasis using Bayesian geostatistical inference. Applications primarily focused on risk profiling of prevalence rather than infection intensity, although the latter is particularly important for morbidity control. In this review, the underlying assumptions used in a study mapping Schistosoma mansoni infection intensity in East Africa are examined. We argue that the assumption of stationarity needs to be relaxed, and that the negative binomial assumption might result in misleading inference because of a high number of excess zeros (individuals without an infection). We developed a Bayesian geostatistical zero-inflated (ZI) regression model that assumes a non-stationary spatial process. Our model is validated with a high-quality georeferenced database from western Côte d'Ivoire, consisting of demographic, environmental, parasitological and socio-economic data. Nearly 40% of the 3818 participating schoolchildren were infected with S. mansoni, and the mean egg count among infected children was 162 eggs per gram of stool (EPG), ranging between 24 and 6768 EPG. Compared to a negative binomial and ZI Poisson and negative binomial models, the Bayesian non-stationary ZI negative binomial model showed a better fit to the data. We conclude that geostatistical ZI models produce more accurate maps of helminth infection intensity than the spatial negative binomial ones.

Anoplocephala perfoliata is the commonest tapeworm parasite of horses and is incriminated as a significant cause of clinical disease (e.g., ileocaecal intussusception, caeco-caecal intussusception and/or caecal perforation), particularly in horses chronically infected with large numbers of worms. The high prevalence (~20–80%) of the parasite in some countries suggests an increased risk of clinical cases. In spite of research, there is still a paucity of information regarding the pathogenesis of the disease, the epidemiology of the parasite in different geographical regions and there are significant limitations with the diagnosis of infection. The present article provides an account of the biology, epidemiology and pathogenic effects of A. perfoliata, the diagnosis of infection and treatment. It highlights some gaps in knowledge of the parasite and the disease it causes, and suggests opportunities for future research and prospects for improved diagnosis, prevention and control.

A benznidazole-resistant population of Trypanosoma cruzi, Y strain, was selected after 25 successive passages (8 months) in mice treated with a single high drug dose. Initially, the resistant parasites produced a low parasitaemia level and low mortality rate in infected mice. Thereafter, the parasitaemia level and mortality rate increased to the same value obtained for mice infected with the wild-type strain. Long-term treatment with benznidazole (100 mg/kg/day) cured 71–80% of mice infected with the wild-type strain. No cure was observed in mice infected with the selected resistant parasite population. Treatment with 500 mg/kg of benznidazole at peak parasitaemia cleared all blood parasites from mice infected with wild-type parasites. No effect on parasitaemia level was observed in mice infected with the selected parasites. Benznidazole-resistant parasites showed cross-resistance to different drugs. Contrary to wild type, all clones analysed from the resistant T. cruzi population were resistant to benznidazole. Without drug pressure the resistance phenotype of clones was far more stable than that presented by the resistant population. This work demonstrates, for the first time, the in vivo selection of a population and clones of T. cruzi resistant to benznidazole, and makes available an experimental model for the study of mechanisms of drug resistance in T. cruzi.

Lung-stage schistosomula are the target of protective immunity in mice vaccinated with attenuated cercariae of Schistosoma mansoni. Therefore, proteins present at this developmental stage, and in particular those which are secreted, are a potential source of novel vaccine candidates. However, little information is available about such molecules. Here we describe the cDNA clones identified by screening expression libraries with serum raised against proteins released by lung-stage schistosomula. In total, 11 different cDNA species were identified, 6 of which have been described previously in S. mansoni; these included fructose 1,6-bisphosphate aldolase and Sm21.7 which together accounted for two-thirds of all positive clones. Of the 5 newly described schistosome genes, 1 cDNA had a high degree of homology to the s5a subunit of 26S proteasomes, most significant being with the human protein. The remaining 4 clones showed no significant homologies to any genes sequenced previously. Fructose 1,6-bisphosphate aldolase, Sm21.7, the proteasome homologue and 1 unknown clone (A26) have been expressed in a bacterial expression system and serum produced against each recombinant protein. Immunolocalization showed fructose 1,6-bisphosphate aldolase, Sm21.7 and the proteasome homologue to be most abundant in muscle cells whilst clone A26 was distributed throughout many tissues, but was most abundant in the tegument. Analysis of the cellular immune responses of vaccinated mice showed 3 of the 4 expressed clones to be highly immunogenic, inducing the secretion of large quantities of the Th1-type cytokine interferon gamma.