Abstract. We have cloned from Schistosoma haematobium genome a repeated sequence, the DraI repeated sequence, which consists of tandemly arranged 121-bp-long units and which is highly abundant (ϳ 15% of the S. haematobium genome). By these features, the DraI repeat is similar to the Sm1-7 sequence of Schistosoma mansoni previously described by us. However, their nucleotide sequences are profoundly different. Polymerase chain reaction (PCR) primers were designed on the basis of the DraI sequence information and were used in a PCR assay by which as little as 10 fg of schistosomal DNA as well as individual cercariae were detected. The DraI repeat cross-hybridized with DNA from Schistosoma bovis, Schistosoma magrebowiei, Schistosoma mattheei, Schistosoma curassoni, and Schistosoma intercalatum, but not with DNA from S. mansoni nor from Trichobilharzia ocellata and Echinostoma sp. A potential value of this PCR assay is suggested for monitoring free-living cercariae and infected snails only in bodies free of cross-hybridizing species.

Abstract. In the present study, we adapted a polymerase chain reaction (PCR) assay, previously shown by us to be very sensitive for detecting cercariae in water, for the sensitive detection of Schistosoma mansoni DNA in infected snails from early prepatency. Polymerase chain reaction primers were designed based on the 121-basepair highly repeated sequence we previously identified in the genome of S. mansoni. The DNA was prepared from the snails by a simple alkaline extraction procedure, and the PCR assay enabled a clear differentiation between infected and normal snails. Infected snails were detected as early as one day after penetration of a single miracidium. The high sensitivity of the test enabled identification of a single infected snail even when its DNA was pooled with material from up to 99 uninfected snails, thus demonstrating the possibility of mass diagnosis in pools of snails. The assay has the potential for large-scale determination of prepatent infection prevalence in snails, thus offering new possibilities for the evaluation of schistosomiasis transmission and for schistosomiais control, as discussed.Schistosomiasis, is caused in humans by three main species of blood flukes (Schistosoma mansoni, S. haematobium, and S. japonicum) and is transmitted by freshwater snails. It continues to plague many developing countries in the tropics 1 with an estimated 200 million infected people worldwide.Freshwater snails, intermediate hosts of schistosomes, become infected by larvae (miracidia) released from schistosome eggs that reach the water with excreta. After several weeks of asexual multiplication within the snail's tissues, larvae infective to humans by active penetration through the skin (cercariae), are released into the water. Snail infection and contact patterns of humans with water infested with cercariae are important factors in the transmission of schistosomiasis, and risk of infection is normally estimated by detecting infected intermediate hosts in sites where humans come in contact with water. 2 Infection rates in field populations of snails are routinely determined by searching for cercariae shed from snails with patent infection. 3 In contrast, prepatent infections, which can constitute a significant proportion of infected snails populations, 4 are not determined routinely because of a lack of a suitable method. Microscopic examination of crushed snails in search of developing cercariae and intramolluscan-multiplying larvae (the sporocysts) 5 is sometimes used for this purpose but is highly inaccurate at early prepatency, and unsuitable for routine large-scale screening of snail populations. 4 Another approach is to examine nonshedding field snails maintained for several weeks in the laboratory for protracted shedding. However, this method is time-consuming, it cannot be done routinely on a large scale, and it can be highly inaccurate if snails mortality is high. The omission of data on prepatent infections leaves out important information for the evaluation and mathematical modeling of trans...

Fasciolosis is a re-emerging parasitic disease that affects an increasing number of people in developing countries. The most severe endemic affects the Bolivian Altiplano, where the liver fluke (Fasciola hepatica) and its hermaphroditic snail host, Lymnaea truncatula, have been introduced from Europe. To achieve a better understanding of the epidemiological situation and the consequences of the colonization event of this invasive species, genetic analysis of Bolivian snail populations was needed. Here we compare the genetic diversity and population structure of snail samples from the Bolivian Altiplano with samples from the Old World at six polymorphic microsatellite loci. Whereas some variability exists in the snail populations from the Old World, we observe only a single genotype of L. truncatula in the Bolivian Altiplano. We discuss the possible explanations for such a reduction in genetic variability, and, given the high natural parasitism pressures exerted on the snail populations, we discuss the relevance of this result for host-parasite interactions.

When applied to hermaphrodite organisms, the local mate competition hypothesis predicts an increase of the ratio of sperm to ova produced as the number of mates increases. Here we test this prediction using a hermaphroditic platyhelminth parasite (trematode), Echinostoma caproni. This worm inhabits the small intestine of vertebrates, inevitably inducing the formation of highly subdivided populations, a condition known to promote local mate competition. Moreover this echinostome exhibits an unrestricted mating pattern involving both selfing and outcrossing as well as multiple fertilizations. We quantified the investment in reproductive organs by estimations of testes, cirrus sac, ovary, and egg size and fecundity when echinostomes were isolated alone, in pairs, or in groups of 20 worms. Adult body size was also recorded as a covariate. When mating group size increases (singles, pairs, or groups) we observed a significant increase in resource allocation to male function in addition to a significant decrease in ovary size. Smaller ovaries do not seem to affect egg size, but do result in a reduction in fecundity. Finally, our results are in accordance with the expected theoretical relationship between male allocation and the number of potential mates given local mate competition.

SummaryHot water extracts of Rheum palmatum and Rheum dentatus (from China) showed molluscicidal activity against the snails Oncomelania hupensis, Biomphalaria glabrata and Bulinus globosus, which are vectors of Schistosoma japonicum, S. mansoni and S. haematobium, respectively. Activity was correlated with anthraquinones which were identified by HPLC: rhein and chrysophanol-anthron were most active (>50% dead snails after 2 days in a 0.03% solution). Molluscicidal activity was intermediate with Rheum-emodin and physcion and was not detectable with cinnamic acid or Aloe-emodin. The snail O. hupensis tended to be more sensitive for several compounds than B. glabrata. Extracts of Jatropha curcas seeds (from Mali) showed molluscicidal activity against both B. glabrata and O. hupensis, the latter being the more sensitive snail. The activity was associated with phorbol esters extracted from Jatropha oil. Of the pure phorbol esters tested, 4 -phorbol-13-decanoate killed both snail species at a concentration of 0.001% (10 p.p.m). As Jatropha is locally grown in Mali for other purposes, it might potentially be exploited for schistosomiasis control.

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Abstract. A sensitive and specific detection of cercariae of human schistosomes is required for better definition of risk of infection. In the present study, we have developed a polymerase chain reaction (PCR) assay for the detection of cercariae of Schistosoma mansoni in water. A simple DNA preparation was adapted for this purpose, and PCR primers were designed based on the 121-basepair highly repeated sequence we previously identified in the genome of S. mansoni. The PCR assay detected as little as 10 Ϫ6 ng of S. mansoni DNA, and the high sensitivity enabled the detection of a single cercaria. For trapping of cercariae we adapted a filtration apparatus previously used for separating schistosome eggs from turbid enzymatic digests of tissues. A single cercaria could be detected in repeated tests of water filtrates. Since the target DNA is tandemly arranged, a ladder pattern of the PCR products was demonstrated. A direct relationship was demonstrated between the number of ladder bands of the amplification products, and DNA concentration or number of cercariae. The feasibility of semiquantitation of schistosome larvae in natural water was thus suggested. The potential of the procedures described here for epidemiologic studies is discussed.Schistosomiasis, a water-borne disease caused by blood flukes, continues to plague many developing countries in the tropics, 1 with an estimated 200 million people infected worldwide by Schistosoma mansoni, S. haematobium, and S. japonicum, the main schistosome species of humans. Humans become infected by contact with water infested with schistosome infective larvae, the cercariae, which are capable of actively penetrating the skin. Cercariae are released into the water by certain aquatic snails, intermediate hosts of schistosomes, in which the parasite undergoes asexual larval multiplication. Snails, in turn, become infected by miracidia, larvae released from schistosome eggs reaching water with human excreta.Human infection by schistosomes frequently occurs in stable foci, 2,3 and is dependent on snail infection and contact patterns of humans with water infested with cercariae. 4 The risk of infection in these transmission sites may be routinely estimated by detecting infected snails capable of shedding cercariae. 5 However, since seasonal fluctuations exist in snail population densities, infection rates, and cercarial output, 2,6,7 information on both snail infection and presence and distribution of cercariae is required for evaluating the risk of infection. 4,8 Information on presence of cercariae in water is particularly important when only one of many snails is infected yet capable of shedding enough cercariae to maintain high endemicity. 9 Such a situation may occur in the case of residual transmission following intensive control, or during the initial stages of emerging transmission in newly contaminated water bodies.Schistosome cercariae are difficult to recover for identification in natural water bodies. The use of sentinel mice for this purpose 4,8 is inaccurate, time-...