Molluscs in the transmission of human and veterinary helminthiasis

Fresh water gasteropods are intermediate hosts in the life cycle of numerous digeneans of medical and veterinary relevance, and of a few Protostrongylidae helminths. These molluscs harbour the larval development of parasites and their transmission to the final host, either directly or via another aquatic host, whether fish or crustacean. The behaviour of these molluscs plays a crucial role in the maintenance of schistosomiasis or distomatosis foci, knowing that the majority of these helminthiases are cosmopolitan zoonoses. Most of these parasitic diseases are cosmopolitan zoonoses. Although the specificity of the parasite towards its molluscan host is often high, incomplete larval development may occur in many molluscan species without transmission to mammals.Les mollusques gastéropodes d'eau douce interviennent comme hôtes intermédiaires indispensables dans le cycle de développement de nombreuses espèces de digènes d'intérêt médical et vétérinaire, et dans celui de quelques protostrongylidés. Ils assurent le développement larvaire de parasites et leur transmission à l'hôte définitif, de manière directe ou via un deuxième hôte aquatique, poisson ou crustacé. Le comportement des mollusques est déterminant dans le maintien des foyers de bilharziose ou de distomatose, sachant que la majorité de ces helminthoses sont des zoonoses cosmopolites. L'adaptation des espèces parasitaires aux mollusques hôtes est souvent assez étroite, même si un développement larvaire partiel des helminthes est possible chez de nombreuses espèces de mollusques, sans permettre la transmission aux mammifères

Fasciola hepatica: Variations in redial development and cercarial production in relation to the geographic origin of the parasite

Two hundred Galba truncatula, originating from a French population, were subjected to single-miracidium infections with an allopatric isolate (origin, Argentina) of Fasciola hepatica. The control group was constituted by 100 snails coming from the same population and exposed to sympatric miracidia of F. hepatica according to the same protocol. Snail samples were collected bimonthly from both groups between day 14 and day 112 p.e. (at 20 C) and snail dissections were performed to count free rediae, intraredial morulae and free cercariae. Third and fourth generation rediae were significantly more numerous in the allopatric group, while the number of first generation rediae was significantly lower. In the sympatric group, the decrease in the number of intraredial morulae in the first, second and third redial generations was significantly faster. Free cercariae within the snail body were significantly more numerous in the sympatric than in the allopatric groups, whatever the date of snail dissection. The changes in redial development and cercarial production noted in the Argentinean group might be due to the evolution of South American flukes in a divergent way after the introduction of foreign infected ruminants in this continent from the 15th century.Facultad de Ciencias Veterinaria

Fasciola hepatica: Variations in redial development and cercarial production in relation to the geographic origin of the parasite

Two hundred Galba truncatula, originating from a French population, were subjected to single-miracidium infections with an allopatric isolate (origin, Argentina) of Fasciola hepatica. The control group was constituted by 100 snails coming from the same population and exposed to sympatric miracidia of F. hepatica according to the same protocol. Snail samples were collected bimonthly from both groups between day 14 and day 112 p.e. (at 20 C) and snail dissections were performed to count free rediae, intraredial morulae and free cercariae. Third and fourth generation rediae were significantly more numerous in the allopatric group, while the number of first generation rediae was significantly lower. In the sympatric group, the decrease in the number of intraredial morulae in the first, second and third redial generations was significantly faster. Free cercariae within the snail body were significantly more numerous in the sympatric than in the allopatric groups, whatever the date of snail dissection. The changes in redial development and cercarial production noted in the Argentinean group might be due to the evolution of South American flukes in a divergent way after the introduction of foreign infected ruminants in this continent from the 15th century.Facultad de Ciencias Veterinaria

Human Paragonimiasis in Africa

An up-to-date review on human paragonimiasis in Africa was carried out to determine the current geographical distribution of human cases and analyze the animal reservoir, snails and crustaceans which intervene in the local life cycle of Paragonimus species. Two countries, i.e., Cameroon and Nigeria, were mainly affected by this disease, while the distribution of human cases in the other eight states of the intertropical zone was scattered. Infected patients were currently few in number and two Paragonimus species: P. africanus and P. uterobilateralis , were found. The animal reservoir is mainly constituted by crab-eating mammals. The identity of the host snail remains doubtful and was either a prosobranch, or a land snail. Seven crab species belonging to Callinectes, Liberonautes and Sudanonautes genera are able to harbour paragonimid metacercariae. Due to the current low prevalence of human paragonimiasis recorded in Africa and the high cost of wide-scale screenings for this disease, training of technicians in anti-tuberculosis centers would be the most realistic attitude to detect mycobacteria and/or Paragonimus eggs during the same sputum examination.Une revue sur la paragonimose en Afrique a \ue9t\ue9 r\ue9alis\ue9e pour d\ue9terminer la distribution g\ue9ographique actuelle des cas humains et analyser le r\ue9servoir animal, les mollusques et les crustac\ue9s qui interviennent dans le cycle local des esp\ue8ces de Paragonimus . Deux pays, \ue0 savoir le Cameroun et le Nigeria, sont principalement affect\ue9s par cette maladie tandis que la r\ue9partition des cas humains dans les huit autres \ue9tats de la zone intertropicale est dispers\ue9e. Les patients parasit\ue9s sont actuellement peu nombreux et deux esp\ue8ces de Paragonimus: P. africanus et P. uterobilateralis , ont \ue9t\ue9 identifi\ue9es. Le r\ue9servoir animal est principalement constitu\ue9 par des mammif\ue8res mangeurs de crabes. L\u2019identit\ue9 du mollusque h\uf4te reste douteuse et se rapporte \ue0 un prosobranche ou \ue0 un mollusque terrestre. Sept esp\ue8ces de crabes appartenant aux genres Callinectes, Liberonautes et Sudanonautes sont capables d\u2019h\ue9berger des m\ue9tacercaires de Paragonimus. En raison de la faible pr\ue9valence actuelle de la paragonimose humaine en Afrique et du co\ufbt \ue9lev\ue9 du d\ue9pistage \ue0 grande \ue9chelle pour cette maladie, la formation des techniciens dans les centres anti-tuberculeux serait l\u2019attitude la plus r\ue9aliste pour d\ue9tecter simultan\ue9ment les mycobact\ue9ries ou les \u153ufs de Paragonimus, lors de l\u2019examen du m\ueame crachat

Fasciola hepatica: Variations in redial development and cercarial production in relation to the geographic origin of the parasite

Two hundred Galba truncatula, originating from a French population, were subjected to single-miracidium infections with an allopatric isolate (origin, Argentina) of Fasciola hepatica. The control group was constituted by 100 snails coming from the same population and exposed to sympatric miracidia of F. hepatica according to the same protocol. Snail samples were collected bimonthly from both groups between day 14 and day 112 p.e. (at 20 C) and snail dissections were performed to count free rediae, intraredial morulae and free cercariae. Third and fourth generation rediae were significantly more numerous in the allopatric group, while the number of first generation rediae was significantly lower. In the sympatric group, the decrease in the number of intraredial morulae in the first, second and third redial generations was significantly faster. Free cercariae within the snail body were significantly more numerous in the sympatric than in the allopatric groups, whatever the date of snail dissection. The changes in redial development and cercarial production noted in the Argentinean group might be due to the evolution of South American flukes in a divergent way after the introduction of foreign infected ruminants in this continent from the 15th century.Facultad de Ciencias Veterinaria

La prédation de

Proposition d’un moyen de lutte biologique contre Galba truncatula, hôte intermédiaire de Fasciola hepatica. Durant l’estivation, Zonitoides nitidus est carnivore et attaque les autres espèces de Mollusques. Ce prédateur dévore indifféremment les Galba saines ou infestées ; il n’y a pas de transmission des parasites des proies aux prédateurs. Les expériences montrent qu’une fauche précoce des prairies au début de l’estivation concentre les prédateurs et permet d’éliminer ainsi Galba truncatula

Fasciola hepatica: comparative metacercarial productions in experimentally-infected Galba truncatula and Pseudosuccinea columella

As large numbers of metacercariae of Fasciola hepatica are necessary for research, experimental infections of Galba truncatula and Pseudosuccinea columella with this digenean were carried out to determine the better intermediate host for metacercarial production and, consequently, the most profitable snail for decreasing the cost price of these larvae. Pre-adult snails (4 mm in shell height) originating from two populations per lymnaeid species were individually exposed to two or five miracidia, raised at 23 °C and followed for cercarial shedding up to their death. Compared to values noted in G. truncatula, the survival of P. columella on day 30 post-exposure was significantly greater, while the prevalence of F. hepatica infection was significantly lower. In the four P. columella groups, metacercarial production was significantly greater than that noted in the four groups of G. truncatula (347–453 per cercariae-shedding snail versus 163–275, respectively). Apart from one population of G. truncatula, the use of five miracidia per snail at exposure significantly increased the prevalence of F. hepatica in P. columella and the other population of G. truncatula, whereas it did not have any clear effect on the mean number of metacercariae. The use of P. columella for experimental infections with F. hepatica resulted in significantly higher metacercarial production than that noted with G. truncatula, in spite of a lower prevalence for the former lymnaeid. This finding allows for a significant decrease in the cost price of these larvae for commercial production

(O.F. Müller, 1774) (

Samples of 5, 10 or 20 adult Galba truncatula each were introduced into 25 slope rush beds and 24 road ditches on acid soil to study the colonization of these new sites by the snail. Surveys were conducted over the following eight years to determine the area where these G. truncatula colonized in these new stations and to count the number of overwintering snails in April or May. Snail populations were present in about 50% of the sites where samples of 5 snails each were introduced and in all sites when each sample included 10 or 20 snails. The average area of these habitats showed a peak before decreasing in the following years and this peak was all the more late as the sample introduced into the station increased in size. In contrast, snail abundance in all cases peaked in the second or third year after introduction and gradually decreased thereafter. In all cases, a concentration of snails was noted in the most upstream zone, whereas the number of individuals decreased gradually towards the downstream zone. These results demonstrate that a small number of snails (10 or 20 adults per sample) allow the development of a new population of G. truncatula in new acid soil stations.The introduction of Galba truncatula samples, each comprising 5, 10 or 20 snails, in 25 slope rushes and 24 ditches on acidic soil allowed the development of new populations in 10 sites (out of 21) where samples of 5 snails each were used and in the other 28 sites when each sample included 10 or 20 snails

Paramphistomum daubneyi: the number of sporocysts developing in experimentally and naturally infected Galba truncatula.

International audienceExperimental infections of Galba truncatula with Paramphistomum daubneyi were carried out to determine at day 50 (at 24 degrees C) the numbers of sporocysts, which grew in infected snails via the count of first- and second-generation rediae. In snails individually exposed to one, two, three, four, or five miracidia, the numbers of first-generation rediae increased from the one-miracidium group to the five-miracidium snails (from a mean of 6.7 to 26.1), while second-generation rediae decreased in number (from 6.2 to 0.9, respectively). This scale of redial numbers was used to determine the number of sporocysts, which grew in naturally infected snails collected from sedimentary or acid soils between 1993 and 2006. In cercariae-containing snails, natural infections resulting from the development of one to five sporocysts were found in both samples of G. truncatula examined. The numbers of 3-, 4-, and 5-sporocyst infections were increasing over time since 1997, 2000, and 2003, respectively. The utility of such multiple-sporocyst infections is open to question, as the differentiation of second-generation rediae and that of procercariae were delayed and always limited. They might be interpreted as a consequence of a zoonosis, which has been spreading since 1990 in ruminants of central France