Recent studies have shown that some digenean trematodes previously identified as single species due to the lack of distinguishing morphological characteristics actually consist of a number of genetically distinct cryptic species. We obtained mitochondrial 16S and nuclear ITS1 sequences for the redial stages of Acanthoparyphium sp. and Curtuteria australis collected from snails and whelks at various locations around Otago Peninsula, New Zealand. These two echinostomes are well-known host manipulators whose impact extends to the entire intertidal community. Using phylogenetic analyses, we found that Acanthoparyphium sp. is actually composed of at least 4 genetically distinct species, and that a cryptic species of Curtuteria occurs in addition to C. australis. Molecular data obtained for metacercariae dissected from cockle second intermediate hosts matched sequences obtained for Acanthoparyphium sp. A and C. australis rediae, respectively, but no other species. The various cryptic species of both Acanthoparyphium and Curtuteria also showed an extremely localized pattern of distribution: some species were either absent or very rare in Otago Harbour, but reached far higher prevalence in nearby sheltered inlets. This small-scale spatial segregation is unexpected as shorebird definitive hosts can disperse trematode eggs across wide geographical areas, which should result in a homogeneous mixing of the species on small geographical scales. Possible explanations for this spatial segregation of the species include sampling artefacts, local adaptation by first intermediate hosts, environmental conditions, and site fidelity of the definitive hosts.

Before the discovery of Toxoplasma gondii as a coccidium of the cat in 1970, cat and dog coccidia were classified in the genus Isospora and considered of little clinical or zoonotic significance. Since 1970, several new (Hammondia sp., Neospora sp.) and previously described species, including Sarcocystis, Besnoitia, and Cryptosporidium have been found as coccidians of cats and dogs with clinical and zoonotic significance. In the present paper I review salient features of the evolution of cat and dog coccidia.

Changes in the cardiac β-adrenergic system in early stages of Trypanosoma cruzi infection have been described. Here, we studied an early (135 days post-infection–p.i.) and a late stage (365 days p.i.) of the cardiac chronic form of the experimental infection (Tulahuen or SGO-Z12 strains), determining plasma epinephrine and norepinephrine levels, β-receptor density, affinity and function, cardiac cAMP concentration and phosphodiesterase activity, cardiac contractility, and the presence of β-receptor autoantibodies. Tulahuen-infected mice presented lower epinephrine and norepinephrine levels; lower β-receptor affinity and density; a diminished norepinephrine response and higher cAMP levels in the early stage, and a basal contractility similar to non-infected controls in the early and augmented in the late stage. The Tulahuen strain induced autoantibodies with weak β-receptor interaction. SGO-Z12-infected mice presented lower norepinephrine levels and epinephrine levels that diminished with the evolution of the infection; lower β-receptor affinity and an increased density; unchanged epinephrine and norepinephrine response in the early and a diminished response in the late stage; higher cAMP levels and unchanged basal contractility. The SGO-Z12 isolate induced β-receptor autoantibodies with strong interaction with the β-receptors. None of the antibodies, however, acted a as β-receptor agonist. The present results demonstrate that this system is seriously compromised in the cardiac chronic stage of T. cruzi infection.

Phosphoarginine is a cell energy buffer molecule synthesized by the enzyme arginine kinase. In Trypanosoma cruzi, the aetiological agent of Chagas' disease, 2 different isoforms were identified by data mining, but only 1 was expressed during the parasite life cycle. The digitonin extraction pattern of arginine kinase differed from those obtained for reservosomes, glycosomes and mitochondrial markers, and similar to the cytosolic marker. Immunofluorescence analysis revealed that although arginine kinase is localized mainly in unknown punctuated structures and also in the cytosol, it did not co-localize with any of the subcelular markers. This punctuated pattern has previously been observed in many cytosolic proteins of trypanosomatids. The knowledge of the subcellular localization of phosphagen kinases is a crucial issue to understand their physiological role in protozoan parasites.

Angiostrongylus vasorum is a nematode parasite of sylvan and domestic species of the family Canidae. It has a broad but patchy distribution worldwide, and there is evidence for geographical spread and increasing incidence of infection in recent years. While historically Angiostrongylus-like nematodes identified in dogs and foxes have been described as A. vasorum in Europe and Angiocaulus raillieti in South America, more recent taxonomic revision has amalgamated these into a single species, A. vasorum. Here we report, for the first time, the molecular characterization of isolates of A. vasorum from Germany, Portugal, Denmark and the United Kingdom on the basis of the mitochondrial COI gene and the second ribosomal internal transcribed spacer. When compared with isolates from Brazil, sequence analysis revealed 2 distinct genotypes. Estimated rates of evolution based on COI sequences for both nematode and host are consistent with the hypothesis that the presence of A. vasorum in South America is a result of an ancient evolutionary event. Angiostrongylus vasorum in South America potentially represents a separate species to that observed in Europe.

The development and survival of larvae of Nematodirus filicollis, an important nematode parasite of ruminants, were extensively investigated in the laboratory for the first time, using eggs harvested from sheep grazing in the UK in winter. Third-stage larvae (L3s) developed within the eggs between 12 and 25°C, with the proportion of eggs developing successfully being highest at the upper end of this range. Eggs required chilling below 10°C before being able to hatch at all, and maximum hatch was observed only following chilling to 4°C. Hatching occurred above 6°C, and peaked at 13°C, with the proportion of eggs hatching decreasing to 17–20°C, which appears to form an upper threshold temperature for hatching. When fully developed eggs were placed at 11–13°C, L3 emerged very rapidly with hatching being completed within 6 days. Mortality of emerged L3s increased with temperature, particularly above 20°C. For this parasite, given the low minimum hatching thresholds and the rapid emergence of L3, the existence of an upper hatching threshold is likely to have limited impact on patterns of larval availability on pasture. The strict requirement for chilling is surprising, being at odds with both previous observations and the wide geographical distribution of this species. It is possible that the proportion of eggs requiring chilling is an adaptable trait, enabling early infection of naïve hosts in the face of competition from N. battus, yet also persistence in regions that do not provide good conditions for the chilling of eggs. Further study of selectable variation in this trait could help us to understand the contrasting geographical ranges and disease patterns within the genus, and how different species might respond to climate change.

Schistosoma haematobium is refractory to praziquantel (PZQ) during the prepatent period of infection. A hypothesis based on this observation is that in areas where S. haematobium transmission is seasonal, the outcome of chemotherapy depends on the timing of the treatment relative to the annual transmission pattern. To examine this hypothesis, a study was carried out in southern Mozambique. Following demonstration of seasonal transmission, PZQ was administered separately to two cohorts of S. haematobium-infected schoolchildren in (1) the high and (2) the low transmission seasons and followed up after two months when levels of infection and intensities were measured. The prevalence of infection decreased from 54·2% and 51·7% in cohorts 1 and 2 to 30·3% and 1·8%, respectively. The geometric mean intensity of infection decreased from 23·3 eggs/10 ml of urine at baseline to 15·6 eggs/10 ml of urine in cohort 1 (treated during high transmission season), and from 23·5 eggs/10 ml urine to 7·3 eggs/10 ml of urine in cohort 2 (treated during low transmission season). The observed cure rates in cohorts 1 and 2 were 69·7% and 98·2%, respectively. Differences in infection between the cohorts in terms of cure rate and level of infection two months post-treatment were statistically significant and indicate that in areas with a seasonal transmission pattern, the effect of PZQ can be enhanced if treatment takes place during the low transmission season. We conclude that appropriately timed PZQ administration will increase the impact of schistosomiasis control programmes.

Artificial selection for improved productivity may reduce an animal's ability to cope with pathogens. Here, we used Roslin mice, uniquely divergently selected for high (ROH) and low (ROL) body weight, to assess interactive effects of differing growth potential and protein nutrition on host resilience and resistance. In a 2×2×6 factorial design, ROH and ROL mice were either sham-infected or infected with 250 L3Heligmosomoides bakeri and fed diets with 30, 80, 130, 180, 230 and 280 g crude protein per kg. The infected ROL-30 treatment resulted in clinical disease and was discontinued. In the remaining ROL mice, infection and feeding treatments did not affect growth but infection reduced weight gain in ROH-30, ROH-80 and ROH-130 mice. Although infection resulted in temporarily reduced food intake (anorexia) in both mouse lines, mean food intake over the whole experiment was reduced in ROH mice only. ROH mice excreted more worm eggs and had higher worm burdens, with relatively fewer female worms, than ROL mice. However, these resistance traits were not sensitive to dietary protein. These results support the view that selection for high growth may reduce the ability to cope with pathogens, and that improved protein nutrition may to some extent ameliorate this penalty.

The population dynamics of Trichuris suis in pigs was studied during long-term experimental infections. Twenty-three 10-week-old pigs were inoculated with 5 T. suis eggs/kg/day. Seven, 8, and 8 pigs were necropsied at weeks 4, 8, and 14 post-start of infection (p.i.), respectively. The median numbers of worms in the colon were 538 (min–max: 277–618), 332 (14–1140) and 0 (0–4) at 4, 8, and 14 weeks p.i. respectively, suggesting an increased aggregation of the worms with time and acquisition of nearly sterile immunity. The serum levels of T. suis specific antibodies (IgG1, IgG2 and IgA) peaked at week 8 p.i. By week 14 p.i. the IgG2 and IgA antibody levels remained significantly elevated above the level of week 0. The population dynamics of T. suis trickle infections in pigs is discussed with focus on interpretation of diagnostic and epidemiological data of pigs, the use of pigs as a model for human Trichuris trichiura infections and the novel approach of using T. suis eggs in the treatment of patients with inflammatory bowel disease.

Ticks are blood-feeding arthropods widely distributed in the world and vectors of several diseases. As haematophagy demands evasion strategies and repeatedly infested hosts develop protective immune responses, we investigated the mechanisms of the Rhipicephalus (Boophilus) microplus saliva anti-haemostatic activity and the possible relationship between the acquired natural anti-tick host resistance and anti-haemostatic action. For this purpose, we studied the effects of R. microplus saliva on different pathways of haemostasis and tested whether repeated infested bovine sera (RIBS) are able to abolish salivary anti-haemostatic activities. R. microplus saliva (i) displays inhibitory activity upon collagen-induced platelet aggregation; (ii) inhibits the induction of endothelial pro-coagulant state; and (iii) reduces thrombogenesis in vivo. RIBS were shown to be able to partially block the delay of coagulation and the anti-thrombotic effect of saliva, and to totally abolish the modulation of endothelium activation. Conversely, RIBS has no effect on the inhibition of platelet aggregation. These results show, for the first time, the neutralization ability of sera from acquired resistance hosts against tick anti-haemostatics. Moreover, this is the first report of a haematophagous parasite able to modulate endothelial cell pro-coagulant state, and addresses the presence of anti-platelet and anti-thrombotic activity in R. microplus saliva.

Control programmes generally use a school-based strategy of mass drug administration to reduce morbidity of schistosomiasis and soil-transmitted helminthiasis (STH) in school-aged populations. The success of school-based programmes depends on treatment coverage. The community-directed treatment (ComDT) approach has been implemented in the control of onchocerciasis and lymphatic filariasis in Africa and improves treatment coverage. This study compared the treatment coverage between the ComDT approach and the school-based treatment approach, where non-enrolled school-aged children were invited for treatment, in the control of schistosomiasis and STH among enrolled and non-enrolled school-aged children. Coverage during the first treatment round among enrolled children was similar for the two approaches (ComDT: 80·3% versus school: 82·1%, P=0·072). However, for the non-enrolled children the ComDT approach achieved a significantly higher coverage than the school-based approach (80·0 versus 59·2%, P<0·001). Similar treatment coverage levels were attained at the second treatment round. Again, equal levels of treatment coverage were found between the two approaches for the enrolled school-aged children, while the ComDT approach achieved a significantly higher coverage in the non-enrolled children. The results of this study showed that the ComDT approach can obtain significantly higher treatment coverage among the non-enrolled school-aged children compared to the school-based treatment approach for the control of schistosomiasis and STH.

The use of parasites as biological tags allowed the identification of 3 stocks of Argentinean sandperch, Pseudopercis semifasciata (Cuvier), in the Argentine Sea. A total of 100 specimens caught in 3 zones: Villa Gesell (37°15′S, 57°23′W; n=20), Miramar (38°03′S, 57°30′W–38°44′S, 58°44′W; n=30) and Península Valdes (42°00′–42°45′S; n=50), were examined and 28 parasite species were found, 15 of them being new host records. Both univariate and multivariate analyses identified discrete stocks in each zone. The observed differences were not related to the host size or sex. Each locality was characterized by its own indicator species. Villa Gesell was typified by unidentified cestode plerocercoids, Corynosoma cetaceum and Hysterothylacium sp., Miramar by Heterosentis sp. and Pseudoterranova sp. and Península Valdes by A. simplex s.l. Fishes from both northern localities shared gnathiid pranizae, Corynosoma australe and Grillotia sp. as indicators, whereas Miramar and Península Valdes shared only Trifur tortuosus. The most distant localities showed no indicator species in common. Discriminant analyses of parasite assemblages agreed with populational comparisons in identifying the same set of biological tags, whereas some differences in the identity of indicator species were obtained by similarity analysis. However, the 3 approaches were congruent in identifying Grillotia sp., C. australe and C. cetaceum as indicators of northern localities, and A. simplex s.l. as related to Patagonian waters. Differences among zones could be enhanced by the sedentary habits, limited dispersal and high site fidelity of P. semifasciata, and their spawning in rocky outcrops, which are isolated environments.

Parasitism is often a source of variation in host's fitness components. Understanding and estimating its relative importance for fitness components of hosts is fundamental from physiological, ecological and evolutionary perspectives. Host-parasite studies have often reported parasite-induced reduction of host fecundity, whereas the effect of parasitism on host survival has been largely neglected. Here, we experimentally investigated the effect of infestation by rat fleas (Nosopsyllus fasciatus) on the life span of wild-derived male common voles (Microtus arvalis) bred in captivity. We found that the mean life span of parasitized voles was reduced by 36% compared to control voles. Parasitized voles had a smaller body size, but a relatively larger heart and spleen than control voles. These results indicate an effect of flea infestation on host life span and our findings strongly suggest that ectoparasites should be taken into account in the studies of host population dynamics.

Eimeria spp. are the causative agents of coccidiosis, a major disease affecting many intensively-reared livestock, especially poultry. The chicken is host to 7 species of Eimeria that develop within intestinal epithelial cells and produce varying degrees of morbidity and mortality. Control of coccidiosis by the poultry industry is dominated by prophylactic chemotherapy but drug resistance is a serious problem. Strongly protective but species-specific immunity can be induced in chickens by infection with any of the Eimeria spp. At the Institute of Animal Health in Houghton, UK in the 1980s we showed that all 7 Eimeria spp. could be stably attenuated by serial passage in chickens of the earliest oocysts produced (i.e. the first parasites to complete their endogenous development) and this process resulted in the depletion of asexual development. Despite being highly attenuated, the precocious lines retained their immunizing capacity. Subsequent work led to the commercial introduction of the first live attenuated vaccine, Paracox®, that has now been in use for 20 years. As much work still remains to be done before the development of recombinant vaccines becomes a reality, it is likely that reliance upon live, attenuated vaccines will increase in years to come.