Removal of parasite free-living stages by predators has previously been suggested an important factor controlling parasite transmission in aquatic habitats. Experimental studies of zooplankton predation on macroparasite larvae are, however, scarce. We tested whether trematode cercariae, which are often numerous in shallow waters, are suitable prey for syntopic zooplankters. Feeding rates and survival of freshwater cyclopoids (Megacyclops viridis, Macrocyclops distinctus), calanoids (Arctodiaptomus paulseni), cladocerans (Sida crystallina) and rotifers Asplanchna spp., fed with cercariae of Diplostomum pseudospathaceum, a common fish trematode, were studied. In additional long-term experiments, we studied reproduction of cyclopoids fed with cercariae. All tested zooplankton species consumed cercariae. The highest feeding rates were observed for cyclopoids (33 ± 12 cercariae ind−1 h−1), which actively reproduced (up to one egg clutch day−1) when fed ad libitum with cercariae. Their reproductive characteristics did not change significantly with time, indicating that cercariae supported cyclopoids’ dietary needs. Mortality of rotifers and cladocerans was high (25–28% individuals) when exposed to cercariae in contrast to cyclopoids and calanoids (<2%). Cercariae clogged the filtration apparatus of cladocerans and caused internal injuries in predatory rotifers, which ingested cercariae. Observed trophic links between common freshwater zooplankters and cercariae may significantly influence food webs and parasite transmission in lentic ecosystems.

This study assessed the anthelmintic activity of plant-derived compounds against gastrointestinal nematodes of goats using the egg hatch and larval motility assays. The compounds tested were saponins (digitonin and aescin) and their respective sapogenins (aglycones), hecogenin acetate and flavonoids (catechin, hesperidin, isocordoin and a mixture of isocordoin and cordoin). Additionally, cytotoxicity of active substances was analysed on Vero cell through 3-4,5-dimethylthiazol-2-yl,2,5diphenyltetrazolium bromide (MTT) and propidium iodide (PI) tests. Significant reduction on the egg hatching (P < 0.05) was seen only in the treatments with aescin (99%/EC50 = 0.67 mg mL−1) and digitonin (45%). The compounds that reduced the larval motility (P < 0.05) were digitonin (EC50 = 0.03 mg mL−1 and EC90 = 0.49 mg mL−1) and the hecogenin acetate (75%). The other sapogenins showed low anthelmintic activity. All the flavonoids showed low ovicidal (4–12%) and larvicidal (10–19%) effects. The aescin and digitonin showed low toxicity in PI test (viable cells >90%). Nevertheless, higher cytotoxicity was observed in the MTT assay, with IC50 of 0.20 mg mL−1 (aescin) and 0.0074 mg mL−1 (digitonin). Aescin and digitonin have a pronounced in vitro anthelmintic effect and the glycone portion of these saponins plays an important role in this activity.

Human anti-A and anti-B and pig anti-A agglutinins were neutralized by Ascaris lumbricoides materials.

The infection of pigs with A. lumbricoides stimulated the production of anti-A agglutinin but this agglutinin appeared to have no protective action.

Oesophagostomum dentatum infection in pigs did not affect the anti-A agglutinin levels.

Experimental infection of adult Drymaplaneta variegata Shelford, 1909 (Blattodea) with known numbers of eggs of Protrellus dixoni Zervos, 1987 (Nematoda: Thelastomatidae) showed that each infrapopulation was regulated by a density-dependent and sex-dependent reduction in infection intensity with infrapopulation age. This reduction was not equal in initial speed or intensity between the sexes (reduction in number of males was faster) and led to infrapopulations with never more than a single adult male, 1–8 (usually 1–3) adult females and 0–28 juvenile females. In structure, these laboratory-produced infrapopulations resembled those in field-collected hosts. Parasite-mediated chemical interference competition is suggested as the cause of infrapopulation regulation. Per capita egg production was greater in uncrowded worms which suggests that self-regulation benefits those nematodes that survive competition. Unmated females produced male offspring only (probably by arrhenotokous parthenogenesis). Only females that occurred with a male produced females although some also produced males; such females may avoid insemination or prevent fertilization of some or all eggs. Female offspring probably result from amphimixis.

Living Schistosoma mansoni of various developmental stages were studied with respect to their ability to activate the complement system in sera of humans, mice and rats. Immunofluorescence assays demonstrated that binding of human C3 occurred on fresh schistosomula as well as on schistosomula prepared from mouse lymph-nodes or lungs and on adult schistosomes. However, rodent C3 was deposited only on fresh schistosomula. Deposition of human C3 on the worms' surface required activation of the complement system. The alternative pathway was shown to be involved in deposition of human C3 on schistosomes of all ages, whereas activation of the classical pathway was demonstrable only with fresh schistosomula. Immunoelectrophoretic studies demonstrated a dose-dependent cleavage of human C3 and conversion of factor B by living adult schistosomes. The results demonstrate that the ability of living schistosomes to activate complement in vitro is dependent not only on their developmental stage but also on the species of the serum.

A statistically derived disease reaction index based on parasitological, clinical and haematological measurements observed in 309 5 to 8-month-old Boran cattle following laboratory challenge with Theileria parva is described. Principal component analysis was applied to 13 measures including first appearance of schizonts, first appearance of piroplasms and first occurrence of pyrexia, together with the duration and severity of these symptoms, and white blood cell count. The first principal component, which was based on approximately equal contributions of the 13 variables, provided the definition for the disease reaction index, defined on a scale of 0–10. As well as providing a more objective measure of the severity of the reaction, the continuous nature of the index score enables more powerful statistical analysis of the data compared with that which has been previously possible through clinically derived categories of non-, mild, moderate and severe reactions.

Varying degrees of naturally occurring immunoglobulin (Ig) M antibodies to Toxoplasma gondii were observed in almost all of adult Japanese populations negative for IgG antibodies as determined by an enzyme-linked immunosorbent assay (ELISA). The antibody activity was reduced by absorption of sera with Toxoplasma soluble antigen or by 2-mercapto-ethanol treatment of the IgM fraction after sucrose density gradient centrifugation. Umbilical cord sera had almost no detectable IgM antibodies, and the ELISA value in infants increased with age until 1 year. Most paired sera collected from adults at a 1-year interval showed constant IgM antibody levels, suggesting retention of natural IgM antibodies throughout their lives without changing ELISA values of ≥ 0·1/year. Polar staining was observed in immunofluorescent studies for 14 serum samples with natural IgM antibody levels of ≥ 0·5, while samples obtained from a pregnant woman with natural IgM antibody levels of ≥ 0·9 reacted to the whole organism as was observed in positive sera of acute patients. Western blotting analysis revealed that natural IgM antibodies were directed to multiple antigen molecules. The band pattern differed slightly from one serum to another, but almost consistent patterns were observed in sera sequentially obtained from an adult over 4 years.

Biochemical characterization of 137 Leishmania braziliensis isolates from South and Central America, and from selected endemic foci in Bolivia, Brazil and Colombia, performed by isoenzymatic electrophoresis using 10 enzymatic systems, showed a high enzymatic polymorphism (44 zymodemes obtained) based on the variation of a small number of enzymes. Cladistic analysis showed close links between the zymodemes within the L. braziliensis s.s. cluster. The position of 2 Colombian zymodemes obtained (MON*204 and MON*205) justify the inclusion of L. peruviana within the L. braziliensiscluster.

The influence of nutrient level, temperature and larval density on the trapping of Heligmosomoides polygyrus L3 by the nematophagous fungi Arthrobotrys oligospora, Duddingtonia flagrans and Monacrosporium megalosporum were investigated by quantification of trapped nematodes. All 3 factors were found to have a significant effect on the number of larvae trapped by A. oligospora and M. megalosporum. Decreased nutrient concentrations resulted in increased trapping for these 2 fungi, but nutrient availability was not found to have a significant effect on trapping by D. flagrans. The 3 fungi were found to have similar responses to temperature, with peak trapping occurring at or near the optimum growth temperatures. Nematode trapping was found to be density dependent for all 3 fungi, with increased percentage trapping at increased larval densities. Comparison in a single experiment of the relative importance of these factors to each fungus showed that nutrient level was the main factor influencing trapping by A. oligospora, whereas D. flagrans and M. megalosporum were more dependent on larval density.

To examine how community-level genetic diversity of the malaria parasite Plasmodium vivax varies across time and space, we investigated the dynamics of parasite polymorphisms during the early phases of occupation of a frontier settlement in the Amazon Basin of Brazil. Microsatellite characterization of 84 isolates of P. vivax sampled over 3 years revealed a moderate-to-high genetic diversity (mean expected heterozygosity, 0·699), with a large proportion (78·5%) of multiple-clone infections (MCI), but also a strong multilocus linkage disequilibrium (LD) consistent with rare outcrossing. Little temporal and no spatial clustering was observed in the distribution of parasite haplotypes. A single microsatellite haplotype was shared by 3 parasites collected during an outbreak; all other 81 haplotypes were recovered only once. The lowest parasite diversity, with the smallest proportion of MCI and the strongest LD, was observed at the time of the outbreak, providing a clear example of epidemic population structure in a human pathogen. Population genetic parameters returned to pre-outbreak values during last 2 years of study, despite the concomitant decline in malaria incidence. We suggest that parasite genotyping can be useful for tracking the spread of new parasite strains associated with outbreaks in areas approaching malaria elimination.

The use of chimeric molecules fusing several antigenic determinants is a promising strategy for the development of low-cost, standardized and reliable kits to determine specific antibodies. In this study, we designed and assessed a novel recombinant chimera that complements the performance of our previously developed chimera, CP1 [FRA and SAPA antigens (Ags)], to diagnose chronic Chagas disease. The new chimeric protein, named CP3, is composed of MAP, TcD and TSSAII/V/VI antigenic determinants. We compared the performance of both chimeric Ags using a panel of 67 Trypanosoma cruzi-reactive sera and 67 non-reactive ones. The sensitivity of CP3 vs CP1 was 100 and 90.2%, and specificity was 92.5 and 100%, respectively. The mixture of CP1 + CP3 achieved 100% of sensitivity and specificity. More importantly, an additional subset of 17 sera from patients with discordant results of conventional serological methods was analysed; the CP1 + CP3 mixture allowed us to accurately classify 14 of them with respect to IIF, the usual technique used in most of the reference centres. These results show an improved performance of the CP1 + CP3 mixture in comparison with enzyme-linked immunosorbent assay and indirect haemagglutination commercial assays.

Transmission dynamics of the actinospore stage of Ceratomyxa shasta to the salmonid host were investigated under field and laboratory conditions. The number of parasites transmitted and the transmission rate were compared between 2 different exposure durations and also among different water velocities, by means of field exposures. Under laboratory conditions, the number of parasites transmitted and the transmission rates were compared across a broader range of water velocities and also at different water temperatures. Transmission rate was not constant over time as the number of parasites transmitted increased non-linearly between the 2 exposure durations. Transmission was also inversely related to water velocity and there was a threshold to transmission between 0·2–0·3 m s−1. Lastly, transmission rate increased with water temperature up to 18 °C then decreased at 23 °C. These experiments provide a range of values of transmission that will be incorporated into an epidemiological model to simulate the effectiveness of different management strategies. Additionally, these experiments provided novel information on the effects of environmental conditions (i.e. water velocity and water temperature) on the transmission dynamics between the salmonid host and the actinospore stage.

Recombinant cathepsin D aspartic protease of Schistosoma japonicum cleaved human IgG in vitro in a time and dose-dependent manner. Optimal cleavage was seen at pH 3·6–4·5; modest cleavage remained at pH 5·0, and no cleavage was detected above pH 5·0. Amino terminal sequencing of the major cleavage fragments of human IgG identified a Fab fragment from the VH1 domain, and 2 cleavage sites in the CH2 domain below the hinge region. The P1 and P1′ residues at the 2 CH2 cleavage sites were Phe254–Leu255 and Leu325–Thr326, indicating a preference by the schistosome protease for bulky hydrophobic residues flanking the scissile bond. No cleavage of the immunoglobulin light chain was detected. In addition, the recombinant schistosome protease indiscriminately degraded the human serum proteins complement C3 and serum albumin into numerous small fragments. These results demonstrate specific cleavage of human IgG by the recombinant schistosome aspartic protease, and highlight the broad range digestive specificity of the enzyme which may play a role in the degradation of host serum proteins ingested as part of the schistosome bloodmeal.

Protein tyrosine phosphatases (PTPases) have been described as virulence factors in different pathogenic microorganisms. The pathogenic process by Entamoeba histolytica is a multifactorial phenomenon that occurs in 3 steps: adhesion, cytolytic and cytotoxic effect, and phagocytosis. Lytic enzymes may participate during the second part of this process. In this work, we determined that purified membrane-bound acid phosphatase (MAP) from E. histolytica trophozoites has PTPase activity. The enzyme specifically dephosphorylated O-phospho-L-tyrosine at optimum pH of 5·0, with little activity towards O-phospho-L-serine, O-phospho-L-threonine, and ATP. It was inhibited by ammonium molybdate and sodium tungstate, and trifluoperazine did not show any effect. A monoclonal antibody against the catalytic domain of the human placental PTPase 1B, cross-reacted with a 55 kDa molecule present in the solubilized fraction. The interaction of the amoebic PTPase with HeLa cells resulted in the alteration of the cell actin cytoskeleton by disruption of the actin stress fibres.

Refer to the conclusions stated at the end of the foregoing sections on pp. 204, 206, 217–219 and the foregoing paragraph.

In chickens kidney-cell culture gametogony of E. tenella usually occurs in a limited number of selected cells in the form of nests of gametocytes. Some cells contain only macrogametocytes, others only microgametocytes and some cells contain both sexes together.Mixed nests of gametocytes are evidence for genetic sex determination.By using PAS staining the origin of macrogametocytes and microgametocytes can be retraced to the merozoites and schizonts of the last generation, which are differentiated by this technique.

Draft genome sequences for Schistosoma mansoni and Schistosoma japonicum are now available. However, the identity and importance of most schistosome genes have yet to be determined. Recently, progress has been made towards the genetic manipulation and transgenesis of schistosomes. Both loss-of-function and gain-of-function approaches appear to be feasible in schistosomes based on findings described in the past 5 years. This review focuses on reports of schistosome transgenesis, specifically those dealing with the transformation of schistosomes with exogenous mobile genetic elements and/or their endogenous relatives for the genetic manipulation of schistosomes. Transgenesis mediated by mobile genetic elements offers a potentially tractable route to introduce foreign genes to schistosomes, a means to determine the importance of schistosome genes, including those that could be targeted in novel interventions and the potential to undertake large-scale forward genetics by insertional mutagenesis.

The diversity and prevalence of malaria parasites of the genera Plasmodium and Haemoproteus were determined in the globally-threatened Aquatic Warbler Acrocephalus paludicola. Birds were sampled during migration in Portugal and at the wintering quarters in Senegal and parasites were detected using molecular methods. Only three generalist parasite lineages (Plasmodium) were found. There were no significant differences in the prevalence of parasites between sexes in Europe, but adults had higher prevalence than first-year birds, and birds in Europe had higher prevalence than those captured in Africa. When comparing with other Acrocephalus species and taking sample size into account, Aquatic Warblers had the lowest prevalence and, together with another threatened species, the Seychelles Warbler Acrocephalus sechellensis, the lowest diversity of malaria parasites. We hypothesize that the low diversity of parasites and absence of specialist lineages of Aquatic Warblers are caused by its small population size and fragmented distribution. Furthermore, Aquatic Warblers’ extreme habitat specialization may decrease their exposure to malaria parasites, but other explanations such as high mortality (which would constraint the sampling of infected birds) or, in contrast, very efficient immunological system in clearing the infections cannot be ruled out. This study contributes to explain variation in prevalence and diversity of malaria parasites among hosts.

This study aimed to develop and test the in vitro and in vivo effectiveness of diminazene aceturate encapsulated into liposomes (L-DMZ) on Trypanosoma evansi. To validate the in vitro tests with L-DMZ, the efficacy of a commercial formulation of diminazene aceturate (C-DMZ) was also assessed. The tests were carried out in culture medium for T. evansi, at concentrations of 0·25, 0·5, 1, 2 and 3 μg mL−1 of L-DMZ and C-DMZ. A dose-dependent effect was observed for both formulations (L-DMZ and C-DMZ), with the highest dose-dependent mortality of trypomastigotes being observed at 1 and 3 h after the onset of tests with L-DMZ. The results of in vivo tests showed the same effects in the animals treated with L-DMZ and C-DMZ in single doses of 3·5 mg kg−1 and for 5 consecutive days (3·5 mg kg−1 day−1). It was possible to conclude that T. evansi showed greater in vitro susceptibility to L-DMZ when compared with C-DMZ. In vivo tests suggest that treatment with the L-DMZ and C-DMZ showed similar efficacy in vivo. The potential of the formulation developed in this study was clearly demonstrated, as it increased the efficacy of the treatment against trypanosomosis, but more studies are needed to increase the effectiveness in vivo.

1. Entamoeba histolytica Schaudinn (vel E. dysenteriae Councilman and Lafleur), the human dysentery amoeba, is a collective species. It comprises a number of distinct races, strains, or pure lines, distinguishable from one another by the size of the cysts which they produce.

2. How many such distinct races exist is still undetermined; but we have demonstrated the existence of at least five.

3. There is no evidence that the different races differ in their geographical distribution, or in any character save size.

4. These races remain constant in character within a given host; and the dimensions of the cysts are not determined by the action of the host upon the parasite, since two different races may coexist side by side in the same host.

5. Different values for the dimensions of the cysts are obtained when these are measured in different media. Taking the measurements of living cysts suspended in physiological saline solution as representing the true value, we find that the dimensions of cysts in iodine solution are approximately the same; but that cysts which have been suitably fixed, stained, and mounted in balsam, have undergone an apparent reduction of approximately 10% from the true diameter.

6. The most suitable fixative for E. histolytica cysts we have found to be a modification of Schaudinn's fluid. (Saturated aqueous solution of corrosive sublimate, two parts; absolute alcohol, one part; glacial acetic acid, 4–5%.) Cysts fixed in this fluid undergo no measurable shrinkage or swelling in the process.

7. The apparent loss of size observed in cysts which have been fixed, stained, and mounted in balsam, is due chiefly to the invisibility of the cyst wall in the mounting medium.

8. It follows from what has been said above (5 and 6) that to obtain an approximately true value for the dimensions of the living cysts from measurements made upon those suitably fixed, stained, and mounted in balsam, these measurements should be multiplied by the factor

9. We find no evidence of the existence of a sexual dimorphism in the cysts belonging to a single race, such as has been described by Mathis and Mercier.

10. Since cysts of E. histolytica may be found with all diameters from about 5μ. to about 20μ—a range overlapping or covering the dimensions of the cysts of the two common harmless intestinal amoebae of man (E. coli and E. nana) and of other cysts and cyst-like bodies occurring in human faeces—it is of considerable practical importance to recognize and distinguish the diverse races of E. histolytica which differ from one another in the dimensions of the cysts which they produce.