Predictive action tracking without motor experience in 8-month-old infants.

A popular idea in cognitive neuroscience is that to predict others' actions, observers need to map those actions onto their own motor repertoire. If this is true, infants with a relatively limited motor repertoire should be unable to predict actions with which they have no previous motor experience. We investigated this idea by presenting pre-walking infants with videos of upright and inverted stepping actions that were briefly occluded from view, followed by either a correct (time-coherent) or an incorrect (time-incoherent) continuation of the action (Experiment 1). Pre-walking infants looked significantly longer to the still frame after the incorrect compared to the correct continuations of the upright, but not the inverted stepping actions. This demonstrates that motor experience is not necessary for predictive tracking of action kinematics. In a follow-up study (Experiment 2), we investigated sensorimotor cortex activation as a neural indication of predictive action tracking in another group of pre-walking infants. Infants showed significantly more sensorimotor cortex activation during the occlusion of the upright stepping actions that the infants in Experiment 1 could predictively track, than during the occlusion of the inverted stepping actions that the infants in Experiment 1 could not predictively track. Taken together, these findings are inconsistent with the idea that motor experience is necessary for the predictive tracking of action kinematics, and suggest that infants may be able to use their extensive experience with observing others' actions to generate real-time action predictions.

A two-lab direct replication attempt of Southgate, Senju and Csibra (2007).

The study by Southgate et al. (2007 Psychol. Sci. 18, 587-592. (doi:10.1111/j.1467-9280.2007.01944.x)) has been widely cited as evidence for false-belief attribution in young children. Recent replication attempts of this paradigm have yielded mixed results: several studies did not replicate the original findings, raising doubts about the suitability of the paradigm to assess non-verbal action prediction and Theory of Mind. In a preregistered collaborative study including two of the original authors, we tested one hundred and sixty 24- to 26-month-olds across two locations using the original stimuli, procedure and analyses as closely as possible. We found no evidence for action anticipation: only roughly half of the infants looked to the location of an agent's impending action when action prediction did not require taking into account the agent's beliefs and a similar number when the agent held a false-belief. These results and other non-replications suggest that this paradigm does not reliably elicit action prediction and thus cannot assess false-belief understanding in 2-year-olds. While the present results do not support any claim regarding the presence or absence of Theory of Mind in infants, we conclude that an important piece of evidence that has to date supported arguments for the existence of this competence can no longer serve that function.

Low genetic diversity in a snail intermediate host (Biomphalaria pfeifferi Krass, 1848) and schistosomiasis transmission in the Senegal River Basin.

Population genetic perturbations of intermediate hosts, often a consequence of human pressure on environmental resources, can precipitate unexpectedly severe disease outbreaks. Such disturbances are set to become increasingly common following range changes concomitant with climate shifts, dwindling natural resources and major infrastructure changes such as hydroprojects. Construction of the Diama dam in the Senegal River Basin (SRB) reduced river salinity, enabling the freshwater snail intermediate host Biomphalaria pfeifferi to rapidly expand its distribution. A serious public health problem ensued, with an epidemic of intestinal schistosomiasis occurring in the previously schistosome-free Richard-Toll region within 2 years. The current study aimed to assess the population variability of B. pfeifferi in the SRB, and speculate upon its subsequent impact on host-parasite interactions following such engineered ecological change. Genetic variation at nine polymorphic microsatellite loci revealed little population differentiation in SRB snails compared with those from natural habitats in Zimbabwe, where Schistosoma mansoni transmission is much lower. 'Open' SRB habitats are associated with greater water contact, smaller population sizes and less genetic diversity, with sites downstream of Richard-Toll showing greater inter- and intrapopulation variation, concomitant with less frequent human contact. These observations may be explained by rapid expansion into pristine habitat selecting for high fecundity genotypes at the expense of schistosome resistance, presenting S. mansoni with genetically homogenous highly fecund susceptible populations around the focal point, promoting development of a highly compatible host-parasite relationship. Longitudinal study of such systems may prove important in predicting public health risks engendered by future environmental engineering projects.

Praziquantel: its use in control of schistosomiasis in sub-Saharan Africa and current research needs.

Treatment with praziquantel (PZQ) has become virtually the sole basis of schistosomiasis control in sub-Saharan Africa and elsewhere, and the drug is reviewed here in the context of the increasing rate that it is being used for this purpose. Attention is drawn to our relative lack of knowledge about the mechanisms of action of PZQ at the molecular level, the need for more work to be done on schistosome isolates that have been collected recently from endemic areas rather than those maintained in laboratory conditions for long periods, and our reliance for experimental work mainly on Schistosoma mansoni, little work having been done on S. haematobium. There is no evidence that resistance to PZQ has been induced in African schistosomes as a result of its large-scale use on that continent to date, but there is also no assurance that PZQ and/or schistosomes are in any way unique and that resistant organisms will not be selected as a result of widespread drug usage. The failure of PZQ to produce complete cures in populations given a routine treatment should therefore solicit considerable concern. With few alternatives to PZQ currently available and/or on the horizon, methods to monitor drug-susceptibility in African schistosomes need to be devised and used to help ensure that this drug remains effective for as long a time as possible.

Recent studies on the reproductive biology of the schistosomes and their relevance to speciation in the Digenea.

The members of the family Schistosomatidae, dioecious Digenea, are discussed with regard to their distribution, intermediate and definitive host-parasite relationships. The biological species concept is considered together with the difficulties of its application to Schistosoma spp. and the Digenea. The correlation between pairing of adult schistosomes, physical and sexual development and the maintenance of reproductive potential is emphasised. Development of the female reproductive system does not depend upon species-specific pairing. In some combinations, e.g., Schistosoma haematobium/Schistosoma intercalatum and Schistosoma bovis/Schistosoma curassoni, a specific mate choice system apparently does not exist, whereas it does in other combinations, e.g., Schistosoma mansoni/Schistosoma intercalatum. In mixed infections change of mate may occur and when the opportunity arises heterospecific pairs of worms will change partners to conspecific pairs. Interspecific pairing in adult schistosomes will lead to either hybridisation or parthenogenesis. Yet the majority of schistosomes that inhabit the same definitive host maintain their genetic identity: specific mate recognition, site selection within the host and heterologous immunity have been suggested as isolating mechanisms. Experimental intraspecific crosses have enabled evaluation of the degree to which some populations separated and became reproductively isolated through pre-mating isolating mechanisms, indicative of incipient speciation, e.g., the Lower Guinea and Zaire strains of S. intercalatum. The occurrence and significance of parthenogenesis in schistosomes and other species of Digenea are discussed. The consequences of interspecific mating interactions in schistosomes with regard to parasite epidemiology, interspecific competition and genetic heterogeneity are debated. Geographical isolation and host specificity represent important pre-zygotic isolating mechanisms. It is suggested that site selection within the host and heterologous immunity may both reduce interspecific genetic interchange when digenean parasites utilise the same definitive host.

A phylogenetic analysis of Schistosoma haematobium group species based on randomly amplified polymorphic DNA.

Randomly amplified polymorphic DNA (RAPD) profiles were produced using four oligonucleotide primers with genomic DNA from 15 isolates of schistosome. Both inter- and intraspecific variation were noted. Intraspecific variation was greater for two species of the S. haematobium group (S. haematobium and S. intercalatum) than for S. mansoni. The inferred phylogeny placed S. curassoni and S. bovis as sister groups to S. mansoni-S. rodhaini group. S. mattheei and S. leiperi formed a separate lineage. The results confirm that RAPD profiles may be used for both strain and species differentiation and for the generation of phylogenetic trees.

In vitro responses of praziquantel-resistant and -susceptible Schistosoma mansoni to praziquantel.

The resistance status of five praziquantel-susceptible and five praziquantel-resistant isolates was confirmed by chemotherapy in CD(1) mice with 3 x 200mg/kg micronised praziquantel. Micronised praziquantel had higher efficacy than two other praziquantel formulations (prepared without milling). The five resistant isolates were less responsive to praziquantel than the five susceptible isolates (59-74% reduction in worm burden in resistant isolates compared with 92-100% in susceptible isolates). Observations were made on the in vitro responses of different stages of 10 isolates to praziquantel. There were different in vitro responses to praziquantel at the egg, miracidial, cercarial and adult stages of Schistosoma mansoni between praziquantel-resistant and praziquantel-susceptible isolates. There were differences in the response of resistant and susceptible isolates following exposure of freshly hatched miracidia to 10(-6)M praziquantel for 1 min and observing the percent change in shape. Using this test it should be possible to determine whether failed therapy in patients infected with S. mansoni is due to the presence of praziquantel-resistant worms. Similarly, by exposing freshly shed cercariae to 4 x 10(-7)M praziquantel and observing the percent of tail shedding over 80 min it should be possible to monitor for the presence of praziquantel-resistant worms in snails collected in the field.

Evidence for the occurrence of Schistosoma intercalatum at Albert Nile in northern Uganda.

During a field investigation in Rhino Camp at Albert Nile in northern Uganda, 77.8% of 636 persons excreted Schistosoma mansoni ova that were detected by the Kato-Katz method. Six patients, 8-17 years of age, had terminally spined schistosome eggs in their stools. These findings were confirmed when preserved specimens were examined at the Institute of Medical Parasitology in Bonn using a concentration technique. The mean +/- SD length of 36 terminally spined eggs was 156 +/- 6 microns and the mean +/- SD width was 59 +/- 3.6 microns. Urine filtration in the study patients revealed no schistosome eggs in the urine. It is concluded that these findings provide evidence for the occurrence of S. intercalatum at Albert Nile in northern Uganda.

Enzyme analyses of Bulinus africanus group snails (Mollusca: Planorbidae) from Tanzania.

38 population samples of snails of the Bulinus africanus group, collected from three separate areas of Tanzania, have been examined. Enzymes in crude digestive gland extracts of individual snails have been analysed by isoelectric focusing in polyacrylamide gels. The enzymes studied were: malate dehydrogenase (MDH); phosphoglucomutase (PGM); glucosephosphate isomerase (GPI); acid phosphatase (AcP) and hydroxybutyrate dehydrogenase (HBDH). Samples of B. nasutus were clearly differentiated from other species and enzyme differences were apparent between samples from the lake and coastal areas. Similarly, although clear distinctions could not always be made, samples of B. africanus, B. globosus and B. ugandae were characterized by their enzyme types. Individual variation was detected within populations and the significance of enzyme polymorphisms in relation to identification has been considered. No correlation was found between snail enzyme type and susceptibility to Schistosoma haematobium or S. bovis.

Application of single strand conformational polymorphism (SSCP) analysis with fluorescent primers for differentiation of Schistosoma haematobium group species.

To assess the utility of single-stranded conformational polymorphism (SSCP) analysis for the differentiation of schistosomes, using methods adapted for a Perkin Elmer ABI Prism 377 automated sequencer, 3 isolates of Schistosoma haematobium, 2 of S. intercalatum and single isolates of S. curassoni and S. bovis were selected for study. Two fluorescently labelled, double-stranded polymerase chain reaction products, amplified from the mitochondrial cytochrome oxidase subunit 1 (CO1) gene and the nuclear ribosomal second internal transcribed spacer (ITS2), were generated from single male and female worms. Changes in electrophoretic mobility of fragments within an SSCP profile revealed variation at individual, isolate and species levels. The mutational basis between representative SSCP profiles was confirmed by direct sequencing, demonstrating that single point substitutions were detectable. SSCP analysis has considerable potential as an alternative molecular method of identification and characterization of schistosomes. More broadly, fluorescence-based SSCP analysis is applicable to almost any gene target from any species of parasite and is a powerful molecular tool for genetic profiling.

Schistosomiasis in the Republic of São Tomé and Principe: human studies.

The only schistosome species found in stool specimens in the local population of the republic of São Tomé is Schistosoma intercalatum. An initial survey of schoolchildren showed an overall prevalence of 10.9%, with some schools reaching 29%. No S. haematobium egg was found in 782 urine specimens from the local population, although some were seen in the urine of Angolan soldiers stationed near the capital city. One village in the endemic area, San Marçal, had an S. intercalatum prevalence of 43%, with 14 persons > 40 years of age harbouring severe infections. The transmission area is restricted to the north-east of the main island, where 5 foci apparently account for most of the infections. Seven cases recorded from Principe may be explained by the fact that the children were attending school at São Tomé. Women carrying out domestic activities are more at risk of contracting the infection because of longer periods of water contact than men. The morbidity produced by the infection is restricted to splenomegaly and blood in the stools. High prevalences have been found of Ascaris lumbricoides and Trichuris trichiura, and hookworm and Stronglyloides stercoralis were also observed. Praziquantel was well tolerated and appears to be a good tool for control purposes, although reinfection in the transmission area apparently occurs rapidly. Control strategies based on chemotherapy should take into account an older age group as well as the schoolchildren. Focal mollusciciding and the introduction of washing facilities may also have a role to play in control. The possible recent introduction of the infection to the island is discussed.

Epidemiological and genetic observations on human schistosomiasis in Kinshasa, Zaire.

A survey for Schistosoma intercalatum conducted in Kinshasa, Zaire, in September 1994 revealed a prevalence of 3.6% (n = 167). Three isolates of schistosomes were made by exposing Bulinus wrighti to miracidia hatched from eggs collected from 2 infected children. Characterization of the isolates by biochemical (isoenzymes of phosphoglucomutase), molecular (restriction fragment length polymorphism and randomly amplified polymorphic deoxyribonucleic acid analysis) and morphological (egg measurements) techniques confirmed the existence of an autochthonous transmission focus of S. intercalatum in Kinshasa. The study also provided evidence of the occurrence of natural hybridization between S. intercalatum and S. haematobium. No potential snail host for either species was found in the 2 rivers examined. Apart from Bu. globosus from Zambia and Bu. wrighti, snail infection experiments showed an incompatible relationship between the parasite isolates and snails belonging to the Bu. forskalii group, the Bu. iruncatus/Bu. tropicus complex, and the Bu. africanus group.

Schistosomiasis in the Republic of São Tomé and Principe: characterization of Schistosoma intercalatum.

This paper reports the morphological and biochemical characterization of the species of Schistosoma infecting humans in the Republic of São Tomé and Principe. The eggs are typical in shape and size of S. intercalatum, measuring on average between 174.5 microns and 189.1 microns. The eggs are voided in the faeces and not the urine of infected people. The parasite experimentally develops in several different species of Bulinus belonging to the B. forskalii group, including B. forskalii, with a minimum prepatent period of 25 d, and also in snails of the B. reticulatus group (B. wrighti); it is incompatible with snails of the B. africanus and B. truncatus/B. tropicus complex. A survey of 5 different habitats at intervals of 2 weeks over a period of one year showed that populations of B. forskalii increased during the dry period of June, July and August in 1988, and in 3 of the habitats snails were present throughout the year. Hence transmission may take place in these habitats throughout the year. Preliminary evidence suggests that water velocity is a limiting factor confining Bulinus to the north-east of the island where the terrain is less mountainous. Development of schistosomes from São Tomé was followed in experimentally infected hamsters. The cross-over point (the point at which the paired male and female worms are of the same average length) occurred at about 49 d after infection: eggs were first seen in the uteri of the female worms 48 d after infection. The parasite from São Tomé developed in sheep and produced viable eggs.(ABSTRACT TRUNCATED AT 250 WORDS)

Schistosomiasis in Dogon country, Mali: identification and prevalence of the species responsible for infection in the local community.

The prevalence of schistosomiasis amongst the Dogon people in 4 villages and one school of the Bankass district of Mali was determined during 2 surveys in 1992; 1398 urine and 1199 stool samples were examined. The most common schistosome was Schistosoma haematobium, with an overall prevalence of 51.3%; S. mansoni had a prevalence of 12%. No S. intercalatum egg was seen in the stools. Biomphalaria pfeifferi and Bulinus truncatus were found in pools at the base of the Dogon cliffs; Bulinus forskalii was found in smaller numbers in brick pits. Two isolates from urine samples of children were identified as S. haematobium in the laboratory using an alpha-glycerophosphate marker, restriction enzyme analysis of ribosomal deoxyribonucleic acid (rDNA) and random amplification of polymorphic DNA. The isolates did not develop in Bulinus forskalii or B. crystallinus of the B. forskalii group. Some evidence for past hybridization of S. haematobium and S. intercalatum is provided by the enzyme and rDNA results as well as the positive Ziehl-Neelsen staining of polymorphic eggs in urine samples. The findings are discussed in relation to the published observations concerning schistosomiasis in travellers returning from this region of Mali.

Royal Society of Tropical Medicine and Hygiene meeting at Manson House, London, 18 May 1995. The epidemiology of human schistosomiasis in the Senegal river basin.

Extensive water development has taken place in the north of Senegal over the last decade, resulting in a large increase in the amount of fresh water for irrigation. The objectives of the present study were to determine the prevalence and intensity of Schistosoma mansoni and S. haematobium in the Senegal river basin (SRB), and to ascertain the distribution of the snail species acting as intermediate hosts for both species of schistosomes. The schistosomiasis survey started in January 1994 and was completed in March 1995. Compared to studies before the construction of the Diama dam, there was a significant increase in both the prevalence and intensity of urinary and intestinal schistosomiasis in the human population in parts of the SRB. From the 9014 people who were registered from 180 villages and 4 towns (10 districts), 7750 were examined. S. mansoni was found in the lower valley (lower delta-Senegal river, lower delta-Lampsar river, upper delta, and diéré) but not in the middle valley. The mean prevalence ranged from 4.4% in the lower delta-Senegal River to 71.8% in the zone of Lac de Guiers, where prevalence and intensity of infection were higher on the eastern side of the lake (81.3% with a mean number of 2088 eggs/g of faeces) compared with the western side (50.3% with a mean 1111 eggs/g). S. haematobium was recorded throughout the area of study, ranging from a mean prevalence of 0.37% in diére (lower valley) to 41.5% in the lower valley (Lampsar river), where the mean egg count was 313/10 mL of urine. Physical and chemical changes to the environment have favoured the spread and increase in the populations of freshwater snails. The only snail involved in the transmission of S. mansoni was Biomphalaria pfeifferi. Five species of bulinid snails were present--Bulinus globosus, Bu. umbilicatus, Bu. senegalensis, Bu. forskalii and Bu. truncatus--but only the first 3 species were involved in the transmission of S. haematobium in the lower and middle valleys.

The epidemiology of human and animal schistosomiasis in the Senegal River Basin.

The results of four field surveys in Senegal are reported. 1. A snail survey in various parts of the Senegal River Basin, including the Senegal River, temporary rain-fed pools, swamps, irrigation canals and drains, ricefields and Lac de Guier was carried out. Three species of snails were commonly found: Bulinus guernei was the most common, occurring in permanent habitats, Bulinus senegalensis occurring in laterite pools in the eastern part of the Middle Valley, and also in the ricefields of Guédé Chantier and Lampsar; B. forskalii was found in small numbers in Lac de Guier and Richard Toll. Three B. guernei were found to be naturally infected with S. bovis. Neither B. jousseaumei, B. globosus nor B. umbilicatus were found in our surveys. 2. A survey for urinary schistosomiasis was carried out in 100 villages (walo, near the Senegal River) and 11 villages (diéré, away from the river) by delivering questionnaires in schools and by direct examinations of haematuria samples. The prevalence of haematuria varied between 0 and 33%. Generally, walos showed low rates of haematuria with the exception of Lampsar and Guédé Chantier, and diérés showed higher rates of haematuria. 3. Examination of 400 cattle at the abattoir St. Louis, revealed a prevalence of 80% of schistosome infection. Two species were present, S. bovis and less commonly S. curassoni. Sometimes high worm burdens were seen, but lesions appeared to be minimal because of high ratio of male to female worms. 4. Examinations of 5722 sheep and 1752 goats in the abattoir, Dakar revealed an overall prevalence of 2.1%. Of the infected animals, 97.3% were infected with S. curassoni and 2.7% with S. curasonni and S. bovis. Laboratory snail infection experiments showed that S. curassoni is marginally compatible with B. senegalensis, but incompatible with B. guernei.

Observations on natural and experimental interactions between Schistosoma bovis and S. curassoni from West Africa.

Surveys of 332 naturally infected bovines at eight abattoirs in Senegal, The Gambia and Mali were carried out to determine the prevalence of infection with Schistosoma bovis and S. curassoni and to pinpoint areas where the distribution of the species overlap. S. bovis was the commonest schistosome of cattle in Senegal and Mali being found in animals at seven abattoirs, the highest prevalence of 85.1% occurred at Mopti in Mali. S. bovis was the only bovine schistosome observed in The Gambia. S. curassoni was isolated from a cow at Bamako and shown to have similar glucose-6-phosphate dehydrogenase, phosphoglucomutase and acid phosphatase profiles to those described for a Senegalese isolate. Evidence of interaction of S. bovis with S. curassoni was found in cattle from Senegal, at Tambacounda and Kolda, and from Mali, at Bamako and Mopti. A mixed experimental infection of both species in a sheep showed the lack of any specific mate recognition system: identification of the worms was facilitated by analysis of acid phosphatase by isoelectric focusing in polyacrylamide gels. Viable hybrid parasites were produced in the laboratory and were maintained up until the F4 generation. Comparisons of egg morphology, surface structure of adult male worms and enzyme profiles have been made between experimental hybrid lines and field isolates. Possible mechanisms maintaining species integrity are discussed.

Schistosoma mattheei infections in cattle: changes associated with season and age.

The Schistosoma mattheei egg output was monitored in 31 cattle over a 18-month period on a dairy farm near Lusaka (Zambia). The animals were kept on pasture with free access to two streams which were suitable for the intermediate host, Bulinus globosus. Individual faecal egg excretion reached an average peak of 130 eggs per gram, around 9 months after birth and decreased markedly before the age of 18 months. Average counts declined significantly with age, down to less than five eggs per gram in adult cows. A seasonal increase in B. globosus snails and S. mattheei transmission during the rainy season had no effect on the egg output of animals older than 18 months. Two calves and two adult cows were necropsied to compare fluke and tissue egg counts in young and old infections. There was a marked decline in tissue egg accumulation in older cows, in spite of an increase in the numbers of adult female flukes, as compared with young animals. A shift of egg accumulation from the large intestine towards the liver was also observed as infection progressed. It is concluded from the results of faecal egg counts that cattle reared under conditions of continuous challenge develop acquired resistance to S. mattheei infection within the first year following primary infection. Comparison of fluke and tissue egg counts in farm animals of different ages suggests the acquisition of an anti-fecundity effect as infection progresses.

Pathology of natural infections of Schistosoma spindale Montgomery, 1906, in cattle.

The pathology of natural Schistosoma spindale infections in cattle in Sri Lanka was studied. Hepatic lesions were moderate with periportal cell infiltration and periportal epithelioid cell granulomas within perilobular zones. Submucosal and mucosal granulomas accompanied by cellular changes were present in the small and large intestine. Two unusual observations included the migration of an adult worm from the mesenteric veins to the mucosa of the small intestine in one bull and the presence of epithelioid cell granulomas containing slender living eggs in the urinary bladder of one animal. Intensities of infections, histopathological changes and immunological responses are discussed and comparison is made with other schistosome species.