Susceptibility of Bithynia inflata mollusks from discrete populations for Opisthorchis felineus infestation from different foci of opisthorchiasis

Experiments were conducted on crossed infection of the specific intermediate host of Opisthorchis, molluscs of Bithynia inflata from different and remote populations, with eggs of O. felineus from different nidi of the disease. The strains of the agent were found to be heterogeneous that is expressed in different degree of compatibility with the intermediate host.     

Heterogeneity of populations of the mollusc Bithynia inflata according to the degree of trematode infestation in opisthorchiasis foci

Results of studies of differences in the infection rate of natural populations of Bithynia inflata with trematodes (including Opisthorchis felineus) in the nidi of opisthorchiasis in the Sumsk and Chernigov Districts of the Ukrainian SSR and Tomsk District of the RSFSR are given. It has been shown that in the Ukrain over 1/3 of all populations of the specific intermediate host of opisthorchis does not take part in the circulation of the agent due to fundamentally different reasons: resistence to the infection and hyperinfection with parthenites of trematodes.     

Experimental grounds of a new concept of Opisthorchis felineus infection formation in a definitive host

In the course of experiments in was found out that golden hamsters having the bilious duct operationally blocked display receptivity to the infection with the non-excysted Opisthorchis felineus metacercariae passed to the stomach. Excysted metacercariae injected to the system of the portal vein settle down in the bilious pathways of the liver and develop there up to the adult stage. In vitro, the metacercariae survive in the blood serum of the intact golden hamsters during one day. Based on the experiments, it is hypothesized that the early stage of O. felineus infection in the bilious duct of definitive hosts is performed by means of hematogenic migration of metacercariae through the portal veins system from the mucous layer of the alimentary tract of the host.     

Infection of the mollusc Littorina saxatilis with parthenites of trematodes and their impact on a shell form: analysis of populations inhabiting the littoral coast of the White Sea

12 rocky shore populations of Littorina saxatilis from three islands of Chupa Inlet (Kandalaksha Bay, White Sea) were examined for infection with trematodes. Morphometric characters (6 indexes of the shell and aperture shape) of molluscs were investigated for all these populations. Exposed and sheltered sites were considered at every island and high and low littoral samples were fulfilled at every site. Seven species of trematodes, Podocotyle atomon, Cryptocotyle lingua, Renicola sp., Himasthla sp., Microphallus piriformes, M. pygmaeus, M. pseudopygmaeus, were found. Uneven distribution of trematodes was confirmed by log-linear analysis. Sheltered populations of L. saxatilis have the greater infection prevalence than exposed ones. This is due to the heavy infection with M. piriformes and M. pygmaeus. The prevalences by these trematodes are up to 52.97% and 27.16% respectively in sheltered populations of the host. The prevalence of M. piriformes tend to be higher at the upper shore level of sheltered sites. In a contrast, the prevalence of M. pygmaeus is significantly higher at the low part of such sites. Factor analysis shows a significant association of the indices of L. saxatilis shell shape with three factors. The first one is associated with the "elongation" of a shell and reveals L. saxatilis from the exposed rocky shore to be more elongated than the molluscs from sheltered sites. The second one is connected with the "aperture shape" index. There is an association of this factor with the shore level position of samples. The third factor reflects the affect of trematodes on the shell shape. The molluscs infected with M. piriformes show "elongated" shell shape and relatively smaller aperture. Shall peculiarities of the hosts infected with M. piriformes and M. pygmaeus are somewhat different. The results of the factor analysis is justified by the series of analysis of variances on the values of shell indices (MANOVA) according to the factors "exposure", "shore level" and "infection".     

Trichobilharzia ocellata in Lymnaea stagnalis: a flow cytometric approach to study its effects on hemocytes.

Flow cytometric analysis was performed on hemocytes in suspension derived from individual Lymnaea stagnalis. The distribution of cell sizes within the hemocyte population was comparable in all 40 specimens studied. The size distribution of circulating hemocytes is unimodal and continuous, with no discrete subpopulations, and is not affected by age or by infection with Trichobilharzia ocellata. Flow cytometry proved to be a very useful technique in analysis of hemocyte populations in snails and anti-hemocyte monoclonal antibodies can be employed in these studies. The use of individual instead of pooled hemolymph samples in studying hemocyte populations of molluscs is stressed.     

Opisthorchis felineus (Rivolta, 1884) and Metorchis bilis (Braun, 1890) infections in population of some regions of the Ob River Basin

The incidence of Opisthorchis felineus (Rivolta, 1884) and Metorchis bilis (Braun, 1890) infections among people living in several regions of the Ob River basin in the West Siberia has been assesed in this work. Our results suggest that Metorchis bilis infection was common in many of the serologically tested people. Moreover, this helminth was obtained from the biliary ducts of humans in autopsy.     

Snail control strategies for reduction of schistosomiasis transmission

As intermediate hosts, molluscs play a major role in the transmission of schistosomes; they are the sites of an intense multiplication of parasites. Thus, snail control strategies are considered a priority for the reduction of schistosomiasis transmission. Here, Vinca Lardans and Colette Dissous review the efficacy of environmental management and the use of molluscicides and biological agents to control snail populations. They then describe the development of diagnostic tests, based on the detection of parasite antigens or specific parasite DNA sequences in snail tissues, to detect the early infection of snails. Finally, they discuss progress in studying the molecular basis of susceptibility and resistance phenotypes, and the possible application of the genetic manipulation of molluscs.     

Diversity of trematode larvae in gastropod molluscs in water bodies of Belarus

The analysis of literary data and own investigations of gastropod molluscs on existence of cercariae of trematodes in Belarus was carried out. 13 856 specimens of 11 species and 2 species complexes of freshwater gastropod molluscs were examined on infection with cercariae of trematodes in 2010 by the authors of this article. Total infestation was 13.1% and infection of some molluscs species varied from 0.4% (Dnieper River, Gomel region) to 66.7% (Lukomskoe reservoir, Vitebsk region). The cercariae of 90 trematode species were found. The majority (51 species) at the adult stage parasitize birds. The cercariae of 14 trematode species have medical significance.     

Molecular data suggest that microsporidian parasites in freshwater snails are diverse

Microsporidian parasites infect almost all invertebrate and vertebrate hosts and have significant effects on individual and population fitness. Phylogenetic analysis demonstrates that the phylum is highly divergent and that some lineages show strong associations with host taxa. We here examine the diversity and distribution of parasites in gastropod molluscs to test for host-parasite co-association. 16 populations representing 10 species of freshwater snails were screened using microsporidian specific small subunit rDNA primers. Four novel microsporidian parasite sequences were detected within populations of three host species from the genera Bulinus, Biomphalaria and Planorbis. Prevalence ranged from 5 to 84%. Phylogenetic analysis of these novel sequences reveals that they group together as a paraphyletic assemblage in the microsporidian tree basal to the two lineages containing the genera Encephalitozoon and Nosema. Preliminary observation of one microsporidian infection, show parasites distributed in all tissue systems of Bulinus globosus. However, infection is most prevalent in the digestive gland while also in the egg sacs, suggesting that the microsporidium is using a mixed strategy of horizontal and vertical transmission in this population.     

The occurrence and life history of Asymphylodora kubanicum (Platyhelminthes: Digenea: Monorchidae) in the Worcester-Birmingham canal, with special reference to the feeding habits of the definitive host, Rutilus rutilus

Two hundred roach and over 400 molluscs were examined over a one year period to investigate the occurrence and life history of Asymphylodora kubanicum in the Worcester-Birmingham canal. Larval stages, infective to the fish definitive host, were present in molluscs throughout the year but did not show a seasonal fluctuation in numbers. Parasites in the intestine of the roach showed a marked annual cycle of occurrence and maturation: low winter infection levels preceded a dramatic increase in infection during the spring and summer. Maturation of the parasite population was rapid during the spring and summer and in late summer and early autumn the parasites laid their eggs and subsequently died. The death of parasites after egg-laying resulted in the low winter infection level during which time little recruitment occurred.
Roach became infected mainly in their third year when molluscs become a dominant component of their diet. Thereafter the older fishes (<2+) are all equally susceptible to infection, but the larger (older) fishes become more heavily infected because of the greater consumption of molluscs per fish. The sex of the fish made no difference to infection with the parasite.     

Methorchiasis in the residents of Novosibirsk area, Russia

Infection with Methorchis bilis was recognized for the first time in the residents of Novosibirsk area (Russia). During a serological survey (37 patients in toto), it was possible to demonstrate that 48.5% of the serum samples tested possessed antibodies to Opisthorchis felineus antigens, 37.8% to both Opisthorchis felineus and Methorchis bilis antigens, and 13.5% to Methorchis bilis antigens only.     

Parasitic fauna of the muskrat from the Upper Ob' pine forest

The gamasid mites Laelaps multispinosus and Hirstionyssus isabellinus, flea Ceratophyllus (Megabotris) rectangulatus, trematodes Plagiorchis proximus, P. eutamiatis, P. obensis, P. multiglandularis, Quinqueserialis quinqueserialis and Opisthorchis felineus, cestodes Aprostotandria macrocephala and Alveococcus multilocularis, larvae, were found in 78 specimens of Ondatra zibethica from water bodies of the Upper Ob pine forest. The mite L. multispinosus is reported as the most abundant ectoparasite of this population of the muskrat. As to helminths most abundant and frequently encountered are Q. Quinqueserialis and A. macrocephala which at high infection intensity can cause decrease in the muskrat abundance.     

The effect of mollusc grazing on seedling recruitment in artificially created grassland gaps

Two experiments conducted in spring and autumn 1992 examined the effect of mollusc grazing on seedling regeneration from natural grassland seedbanks by creating artificial gaps in plots in a grassland sward. Molluscs were excluded from half the gaps by application of molluscicide. Mollusc grazing in both the spring and autumn experiment significantly reduced seedling recruitment, though the intensity of grazing was greatest in autumn. Recruitment of five species was markedly influenced by molluscicide application. In spring, plots from which molluscs were excluded contained significantly more seedlings of Chenopodium polyspermum and Ranunculus acris. In the autumn, exclusion of molluscs resulted in increased populations of R. acris, Stellaria graminea and Rumex acetosa. Cerastium holosteoides populations were greatest in autumn grazed plots. Other species, notably the grasses Holcus lanatus and Agrostis capillaris and the legume Trifolium repens were unaffected by molluscicide application. Species diversity was significantly decreased by molluscicide application in the autumn. Gap size significantly affected the recruitment of two species. Ranunculus acris populations were significantly higher in small gaps in both spring and summer, while Chenopodium recruitment in the spring was greater in small gaps. Gap size also significantly influenced the risk of mollusc attack on Ranunculus as molluscs appeared to show an aggregative feeding response in the high seedling density small gaps. Selective grazing of vulnerable seedlings by molluscs may influence the eventual relative proportions of the species present and so provide a potent mechanism in shaping community composition in grasslands.     

Punctuated equilibria, morphological stasis and the palaeontological documentation of speciation: a biological appraisal of a case history in an African lake

The present-day faunas of the great African lakes present some of the world's best examples of 'explosive speciation'. Lakes Victoria and Malawi each probably have several hundred endemic species of cichlid fishes. Much can be inferred about the evolution of these fishes from morphology, behaviour and intra-lacustrine distribution and from the fact that they include taxa ranging from local races, through sibling species, to forms that display extensive differentiation. The time taken to acquire specific distinctness can sometimes be accurately defined, but fossil lineages are unknown. A recent study of a fossil sequence of molluscs in the Turkana basin throws new light on the history of African lake faunas. It also claims to have resolved events during speciation. While critical analysis based on our knowledge of living molluscs in this area fails to substantiate this claim, the fossil molluscs complement information provided by the biology of extant fishes and invertebrates and emphasize the importance of these lakes in the study of evolution in living and extinct populations.     

Perspectives of the control of Opisthorchis invasion by the method of treating the molluskan population]

Sanitation of the mollusk population with highly effective cercaricide preparations can be used for the control of opisthorchosous infection. Low concentrations of molluskocides which are sublethal for non-infected mollusks have turned to be lethal for hyperinfected individuals. All tested molluskocides display a cercaricide effect in concentrations which are considerably lower than molluskocide ones. Low concentrations of cercaricides are toxic both for cercariae and parthenites from the liver of mollusks and for freely swimming cercariae. Disastrously affecting the freely swimming cercariae microdoses of cercaricides prevent the infection of the second intermediate hosts. Microdoses of cercaricides which are lethal for cercariae are not toxic for the majority of hydrobionts including fishes of all age groups. As far as the dynamics of the infection level of Bithynia with O. felineus is characterized by a one-peak curve with a distinct peak in the middle-end of July the treatment of water bodies with microdoses of cercaricides should be carried out just in this period.     

Infection patterns in white sea blue mussels Mytilus edulis of different age and size with metacercariae of Himasthla elongata (Echinostomatidae) and Cercaria parvicaudata (Renicolidae)

Infection of mussels Mytilus edulis L. by 2 trematode species was studied in a natural intertidal population in the Chupa inlet of the White Sea. The prevalence of metacercariae of Himasthla elongata (Mehlis, 1831) and Cercaria parvicaudata (Stunkard & Shaw, 1931) in mussels reached 100% in 3 to 4 yr old molluscs and remained at this level in older individuals. Infection intensity increased evenly with the age of the molluscan host, showing a tendency to decrease only in the oldest (9 yr old) mussels. These patterns of age dynamics of prevalence and infection intensity were associated with accumulation of trematode larvae in the course of the molluscs' lives. Ability of metacercariae to exist in mussels for long periods (at least 2.5 yr) was verified in the course of an experiment, during which infected molluscs were kept in a subtidal net cage. Decrease of infection intensity in the oldest individuals may reflect selective mortality of the most severely infected molluscs. Among mussels of the same age, higher infection intensity values occurred in larger individuals. This may be due to an enhanced pumping rate in large molluscs, which increases the probability of cercariae, free-living trematode larvae, infecting them via water currents.     

Comparison of resistance to environmental factors of the molluscs Hydrobia ulvae infected with trematoda parthenitae and free from infection

The influence of trematode infection, mainly with Microphallus claviformis, onto the resistance of mudsnails Hydrobia ulvae to fresh water, desiccation and extremely high temperature has been investigated. It was found out in all variants of experiments that the intensity of mortality in infected individuals is reliably higher than in individuals free of infection. It is suggested, that the negative influence of parasites on the resistance of hosts is related to the disturbance of molluscs' capability to isolate themselves from extremal condition by shutting up the shell with operculum. It is proved by the high rate of salt loss in the infected molluscs in a comparison to non-infected individuals. Our hypothesis based on results obtained and reference data suggests that the rate of trematode parthenites' influence onto the resistance of molluscs depends upon the character of interrelationships in hostparasite systems. Normally, the trematode species having the active cercaria stage in the life cycle show more negative impact onto the resistance of infected molluscs, than those species, larval stages of which develop to metacercaria inside the parthenites.     

Infection of estuarine fish populations by Cryptocotyle lingua (Creplin)

Fish populations in the Medway Estuary become infected with Cryptocotyle lingua (Creplin) shortly after their inshore migrations. The present study examines infection levels between 1973 and 1975 in four fish species; whiting, Merlangius merlangus (L.), pouting, Trisopterus luscus (L.), plaice, Pleuronectes platessa L. and flounder, Platichthys flesus (L.). Frequency of infection was highest in flounder, followed by pouting, plaice and whiting. Unusually, parasite density was lowest in plaice even though gastropod molluscs (the parasite's first intermediate host) were most common in their diet. Seasonal levels of infection are discussed and prove useful indicators to the migratory movements of individual fish populations. In whiting and pouting, incidence of infection increased with length of host while no relationship between infection and age of host was observed in either flatfish. Metacercariae were not distributed randomly over the body surface; in gadoids they were concentrated above the lateral line while in pleuronectids they were most intense in the fins and gills.