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PubMed2002

Food-borne intestinal trematode infections in the Republic of Korea.

A total of 19 species of food-borne intestinal trematodes have been reported in humans in the Republic of Korea. They include 12 species of the Heterophyidae, Metagonimus yokogawai, M. takahashii, M. miyatai, Heterophyes nocens, H. heterophyes (imported), H. dispar (imported), Heterophyopsis continua, Pygidiopsis summa, Stellantchasmus falcatus, Centrocestus armatus, Stictodora fuscata, and S. lari; four species of the Echinostomatidae, Echinostoma hortense, E. cinetorchis, Echinochasmus japonicus, and Acanthoparyphium tyosenense; and one species each of the Neodiplostomidae, Neodiplostomum seoulense, Plagiorchiidae, Plagiorchis muris, and Gymnophallidae, Gymnophalloides seoi. Fresh water fish harbor the metacercarial stage of M. yokogawai, M. takahashii, M. miyatai, C. armatus, E. hortense, E. cinetorchis, E. japonicus, or P. muris. Brackish water fish serve as the second intermediate hosts for H. nocens, H. continua, P. summa, S. falcatus, S. fuscata, and S. lari. Brackish water bivalves are the source of infection with A. tyosenense. Tadpoles and frogs are the second intermediate hosts for N. seoulense, but the major source of human infection is the grass snake Rhabdophis tigrina, a paratenic host. The metacercariae of G. seoi are observed in oysters. The natural definitive hosts are, in most cases, mammals such as rats, cats and dogs. However, several species (C. armatus, S. lari, E. japonicus, A. tyosenense, and G. seoi) have birds as natural definitive hosts. Host-parasite relationships, pathogenesis and pathology, immunity, clinical aspects, differential diagnosis, treatment, prevention and control of these intestinal trematodes are briefly discussed.

Animals↗

PubMed1998

Larval trematode infections in freshwater gastropods from the Albufera Natural Park in Spain.

Malacological samplings were made from January 1994 to December 1996 in the Albufera Natural Park (Valencia, Spain) to trace the dynamics of molluscan populations and the prevalence and intensity of infection by larval trematodes. A total of 10,533 freshwater gastropods belonging to seven species (Lymnaea auricularia, L. truncatula, L. palustris, L. peregra, Bithynia tentaculata, Physa acuta and Gyraulus chinensis) was examined, and 110 (1.04%) were found to harbour some of the nine distinguishable types of cercariae, namely four echinostome cercariae (Hypoderaeum conoideum, Echinoparyphium recurvatum, Euparyphium albuferensis, and Echinostoma sp.), four furcocercous cercariae, and one xiphidiocercous cercaria. This study shows that the composition of the snail and trematode communities may be determined by the particular environmental conditions present and the human intervention in the area.

Animals↗

PubMed2001

Trematode infection and the distribution and dynamics of parthenogenetic snail populations.

According to the Red Queen hypothesis for sex, cross-fertilization should be positively associated with the probability of exposure (risk) to virulent parasites. Unfortunately, risk is difficult to measure in the wild, and prevalence of infection is often substituted for risk. Here I suggest that prevalence of infection may not generally suffice as a surrogate for risk, since the Red Queen model can make opposite predictions depending on the distribution of risk in the wild. Specifically, the results of a matching-alleles model suggest that asexual populations should be more infected than sexual populations, when (1) the variance in risk among populations is small, and (2) the mean risk of exposure to parasites is near the point where selection switches to favouring sex over asex. If, however, the variance in risk among populations is large, sexual reproduction should be positively associated with the prevalence of infection. In addition, the coefficient of variation for reproductive mode should increase sharply at the switch point. In light of these results, I re-evaluated data from two studies on the distribution of males in 95 populations of a freshwater snail (Potamopyrgus antipodarum). Populations of these snails are often mixtures of sexual and asexual individuals, and the frequency of males is correlated with the frequency of sexual females in the population. The results show a large, highly skewed variance among populations for prevalence of infection by larval trematodes. The results also show a positive, significant relationship between prevalence of infection and the frequency of males, with a sharp increase in the coefficient of variation at intermediate prevalence. In addition, experimental studies suggest that some of the necessary conditions of the Red Queen hypothesis are also met in this system. Specifically, the most common trematode infecting these snails is (1) adapted to infecting local host populations of the snail, and is (2) more infective to clones that were common in the recent past. It is too early to knoxv if the parasite theory is sufficient to explain the widespread distribution of sex. I suggest that the theory is not sufficient, but that parasites in combination with mutation accumulation in clonal lines may explain the maintenance of sex in species that occasionally produce apomictic mutants.

Animals↗

PubMed2001

Progenesis and reduced virulence as an alternative transmission strategy in a parasitic trematode.

The complexity of the life-cycle of many parasitic helminths has driven the evolution of several well-documented adaptations serving to facilitate the completion of each difficult step in the cycle. In some trematode taxa, selection has even favoured the truncation of the life-cycle: progenetic larval stages (metacercariae) are capable of producing eggs inside their usual intermediate hosts, eliminating the need to be transmitted by predation to a definitive host. In some species, progenesis is shown by all individuals, whereas in other species both the normal and truncated life-cycles coexist in the same populations. Here, the strategies chosen by normal and progenetic metacercariae of the trematode Coitocaecum parvum are investigated and compared. Normal metacercariae, i.e. metacercariae that only develop into adults following ingestion by a suitable fish definitive host, were not capable of manipulating the behaviour of their amphipod intermediate host in ways that could facilitate their capture by fish. These metacercariae were associated with increased mortality in amphipods. Progenetic metacercariae, on the other hand, showed lower virulence levels than normal metacercariae. At the time of their death, amphipods harbouring progenetic metacercariae contained close to the maximum number of eggs that can be produced by progenetic metacercariae, suggesting that the parasite lowers its virulence to keep its host alive long enough to maximize egg output. The maintenance of the 2 strategies in the C. parvum population suggests that they may have equal fitness payoffs: progenesis and low virulence guarantee the production of at least some eggs, whereas the normal life-cycle and its associated higher virulence in the intermediate host provides a low probability of much higher fecundity.

Animals↗

PubMed1999

Influence of the trematode Aphalloïdes caelomicola Dollfus, Chabaud & Golvan, 1957 on the fecundity and survival of Pomatoschistus microps (Krøyer, 1838) (Teleostei: Gobiidae).

Monthly data collected during 1993 in the Vaccarès lagoon (Rhône Delta, France) were used to investigate the influence of the trematode Aphalloïdes coelomicola on the survival of the common goby Pomatoschistus microps, which acts both as second intermediate and definitive host. Prevalence of the parasite did not increase with fish size in either sex. Mean abundance and variance to mean abundance ratio gave evidence that the trematode could have an impact on host mortality. Gonad weight of parasitized females was reduced and the parasite seemed to provoke a gonadal regression above a certain parasitic biomass. Fecundity and egg diameters did not differ between parasitized and unparasitized females, we thus hypothesize that the energy content of eggs (composition in lipids and proteins) was probably modified as an adaptation to energy losses. Prevalence of infection in males compared to females and influence of the parasite on host survival and reproductive effort are discussed.

Analysis of Variance↗

PubMed2002

Larval trematode infections in freshwater snails from the highveld and lowveld areas of Zimbabwe.

Between November 1998 and October 2000, freshwater snails were collected monthly from the highveld and lowveld areas of Zimbabwe to determine the occurrence of larval trematodes. A total of 13,789 snails, representing ten species, were collected from 21 sites and 916 (6.6%) harboured patent trematode infections. Eight morphologically distinguishable types of cercariae were identified. Bulinus tropicus had the highest overall prevalence of infection (13.1%). The echinostome was the most common type of cercaria recovered, contributing 38.2% of all infections. Schistosoma cercariae were recovered mainly from the highveld and comprised 8.0% of all infections. Amphistome cercariae contributed 37.6% of all infections and were recorded from both the highveld and lowveld areas with a peak prevalence occurring during the post-rainy period (March-May). The main intermediate host for amphistomes was B. tropicus. Infections in B. globosus, B. forskalii and Biomphalaria pfeifferi with amphistome cercariae are new records for Zimbabwe.

Animals↗

PubMed2006

Pollutant-induced effects on immunological and physiological interactions in aquatic host-trematode systems: implications for parasite transmission.

Under conditions of pollution both host and parasite are susceptible to the pathogenic effects of toxicants, which in turn may result in detrimental changes to their immunological and physiological processes. Digenetic trematodes, which encompass species of both medical and economic importance, possess complex life cycles and are common parasites of both vertebrates and molluscs. The combined stress induced by pollution and parasitism influences the physiology of the host which can have implications not only on host survival but also on the functional biology of resident parasite populations. The present paper reviews the effects of pollutants on the immunology and physiology in both vertebrate and molluscan host-trematode systems and the implications for parasite transmission.

Animals↗

PubMed1969

Larval trematodes: double infections in common mud-flat snail.

Larvae of the trematode Zoogonus lasius are involved in most double infections of Nassarius obsoleta. The two most common trematode parasites of this snail do not occur together in double infections. Double infections were found in 14 of 340 infected snails in a total sample of 5025 snails.

Animals↗

PubMed2006

Paragonimus westermani and some rare intestinal trematodes recovered from raccoon dogs (Nyctereutes procyonoides viverrinus) introduced recently on Yakushima Island, Japan.

Helminth parasites were collected from 9 raccoon dogs (Nyctereutes procyonoides viverrinus) and 2 Japanese weasels (Mustela itatsi sho) on Yakushima Island, Japan. The former carnivore was introduced to this World Natural Heritage Area presumably within the last two decades, expanding its population thence, although detailed process(es) of the introduction is unknown. The collected trematodes from raccoon dogs included the triploid form of Paragonimus westermani, Brachylaima tokudai, Maritrema eroliae, and Pseudocryptotropa sp. Simultaneously, Paragonimus ohirai was found in one weasel killed by a traffic accident. Although the triploid form of P. westermani and P. ohirai are known to be distributed in some river-mouth areas of Yakushima Island based on previous surveys on crab hosts, natural infection was detected for the first time in wild final hosts. Particularly, the raccoon dog infected with P. westermani was caught in a mountainous area, distant from human residence or river-mouth areas. Although it is possible that the infected raccoon dog moved from a river-mouth area endemic with P. westermani after infection, the alternative scenario remains to be pursued; the endemic area of this zoonosis is expanding along with the recent expansion of raccoon dogs or feral cats (Felis catus), that became prevalent recently on this island including the mountainous areas. Maritrema eroliae taking a variety of shorebirds as its natural final hosts, and a minute trematode, Pseudocryptotropa sp., taking unknown natural final host(s) were recorded for the first time in raccoon dogs.

Animals↗

PubMed2002

Life history and life cycles: production and behavior of trematode cercariae in relation to host exploitation and next-host characteristics.

Life history trade-offs affect trematode parasites reproducing inside their 1st intermediate hosts. Within the constraint of the effect on host survival, parasite production of cercariae is subject to a size-numbers trade-off. Within each cercaria, resources must be partitioned between host-seeking and subsequent developmental functions. Three species of microphallid trematodes with the same 1st intermediate host (the gastropod Littorina saxatilis) were investigated. Maritrema arenaria periodically released many small cercariae. Microphallus similis released fewer, 15% larger, cercariae without periodicity. Microphallus similis cercariae were strong swimmers, moving toward the dark and downward in turbulent water, whereas Ma. arenaria cercariae remained suspended. Maritrema arenaria cercariae, although smaller in body and tail size, were produced at an average daily volume nearly twice that of M. similis. These differences are interpreted as transmission adaptations related to mobility and predictability of the 2nd intermediate host. Microphallus similis, with a mobile and less predictable crab host, adopted a 'bethedging' prolonged production of fewer cercariae by less intensive host exploitation, each cercaria having a high allocation to host-seeking behavior. Maritrema arenaria, with predictable sessile barnacle hosts, produced less mobile but potentially longer-lived cercariae in larger numbers. Microphallus piriformes metacercariae remain in the gastropod host. The number of M. piriformes metacercariae increased in larger hosts. The 3 species differed in the number of sporocysts and (meta)cercariae per sporocyst within the gastropod but not in the within-host volume of parasites. Variation in host exploitation and life history appeared adaptive for transmission to the next host.

Animals↗

PubMed2005

Glucocorticosteroid hormone treatment of larval treefrogs increases infection by Alaria sp. trematode cercariae.

In many amphibian species, an apparent increase has occurred in the prevalence of limb deformities caused by parasitic trematodes. We are interested in the role of environmental stressors in increasing these infections in amphibians. One mechanism by which environmental stressors could act to increase disease prevalence is to increase circulating levels of glucocorticosteroid hormones, which are released in response to stressors and can be immunosuppressive. In the present study, we treated gray treefroZg tadpoles (Hyla versicolor) with exogenous corticosterone, which is the main glucocorticosteroid "stress" hormone in amphibians. We then exposed treated tadpoles to Alaria sp. cercariae and scored the number of mesocercariae that successfully infected the tadpoles. In addition, we assayed one function of the immune response by counting the number of circulating eosinophilic granulocytes, which are thought to be important in immune responses to macroparasites. Tadpoles treated with exogenous corticosterone developed higher parasite loads than control tadpoles did, and they had lower numbers of circulating eosinophilic granulocytes. These results provide evidence of glucocorticosteroid-mediated immunosuppression in tadpoles that may help to explain apparent increases in the numbers of trematode-induced deformities in amphibian populations during recent decades.

Animals↗

PubMed1991

[Trematode infections in the small intestine of Egretta alba modesta in Kangwon-do].

We surveyed 12 migrating large egrets, Egretta alba modesta, for their infection status with intestinal trematodes, from June to September, 1990. All of them were infected with one or more flukes. Total 5 species were identified. Their infection rates and total numbers of worms were Metagonimus sp. 67% and 1,412, Centrocestus armatus 67% and 2,306, Echinochasmus japonicus 50% and 99, Strigea falconis 83% and 635, and a diplostomid fluke 33% and 36. The number of worms in a bird was in the range from 6 to 896. This is the first record that the egret is a reservoir host of Metagonimus sp., C. armatus, E. japonicus, and S. falconis. S. falconis is a new parasite fauna in Korea. Migrating birds must play an important role in the transmission and spreading of these intestinal trematodes in Korea.

Animals↗

PubMed2003

Trematode metacercariae of fishes as sentinels for a changing limnological environment.

Trematode metacercaria populations infecting cichlids in Lake Kinneret (Sea of Galilee) were used as sentinels for the changing limnological environment. Parasitological data from 0+ cichlid fingerlings (Tilapia zillii, Oreochromis aureus, Sarotherodon galilaeus) were collected from the northwest shore of the lake during 1999 to 2001 and compared with data obtained from 1982 to 1984. The results show that the composition of the metacercarial populations changed significantly between the 2 samplings periods. The total number of metacercarial species found in the Kinneret cichlids was lower in 1999 to 2001 than in 1982 to 1984. Metacercariae transmitted by the snail Bulinus truncatus (Clinostomum tilapiae, Euclinostomum heterostomum, Bolbophorus levantinus and Neascus-type metacercariae--black spot and others) that were commonly found in 1982 to 1984 were absent from the fishes sampled during 1999 to 2001. The other trematode metacercariae (Centrocestus sp. and Haplorchis sp. transmitted by Melanoides tuberculata, Pygidiopsis genata transmitted by Melanopsis costata, as well as Phagicola longa, Strigeidae sp.1, an unidentified metacercaria typically found in the liver, and glochidia) increased in abundance in fishes sampled during 1999 to 2001. The calculated 'true' species richness of the habitat, extrapolated as a function of sampling effort, was significantly lower in the 1999 to 2001 versus 1982 to 1984 samples, while significantly fewer fishes needed to be sampled ('sampling effort') during 1999 to 2001 in order to reach the 'true' species richness. The higher calculated values of species richness and diversity for the 1999 to 2001 samples despite the overall decline in species number is explained by the overall increase in metacercariae prevalence.

Animals↗

PubMed1997

A trematode metacercaria causing gill cartilage proliferation in steelhead trout from Oregon.

Gills of steelhead trout (Oncorhynchus mykiss) held in liveboxes to detect the presence of pathogens in the Willamette River (Oregon, USA) became heavily infected with trematode metacercariae. The metacercariae encysted adjacent to the cartilaginous rods of gill filaments and elicited a host response of cartilage proliferation from the perichondrium. Although some hyperplasia of gill epithelium and fusion of lamellae was apparent, the extent of damage to the respiratory surface was apparently insufficient to cause trout mortality. Morphological characteristics of the metacercariae did not allow precise identification, but they suggested affinities to either the Heterophyidae or Cryptogonimidae. Some heterophyids are known to cause proliferation of cartilage in fish gills, while cryptogonimids are not. This is the first report of trematode induced gill cartilage proliferation in steelhead trout.

Animals↗

PubMedDate not supplied

[The influence of infections with trematodes Bunocotyle progenetica (Hemiuridae) and Cryptocotyle cancavum (Heterophiidae) onto mortality of littoral molluscs Hydrobia ulvae (Gastropoda: Prosobranchia) in condition of extremely high temperature].

The effect of invasion of two trematode species, Bunocotyle progenetica (Hemiuridae: Bunocotylinae) and Cryptocotyle cancavum (Heterophiidae) on the host vitality is estimated. The mortality of infected and uninfected individuals of Hydrobia ulvae after different exposure time (3, 6, 9 and 12 hours) under extremely high temperature (+42 degrees C) was compared. The total death of the host was observed after 12 hours of experiment. The death rate of molluscs infected with B. progenetica ranged from 60 to 100% and was significantly higher (p < 0.01) than mortality of individuals infected with C. cancavum and uninfected snails in each case of exposure (3, 6 and 9 hours). At the same time the mortality of individuals infected with C. cancavum was significantly higher (p < 0.05) than the mortality of uninfected snails only after 9 hours of exposure (13.3 and 3.1%, respectively). Difference in pathogen effects B. progenetica and C. cancavum is expressed in different temperature resistance of the host that may be explained by different localisation of redia, their motile activity and manner of feeding. Besides, the invasion by C. cancavum causes the sterilization and accelerated growth of hosts. Low decreasing of the resistance to overheating in snails infected with this trematode could be explained by a compensation effect of this infection. This compensation realizes due to the redistribution of some part of the reproductive energy after the sterilization. An absence of parasitic castration in the case of infection with B. progenetica is a key reason of such considerable declining of their vitality. High lethality of the host appears to be adaptive for the parasite with the monoxenous life cycle.

Animals↗

PubMedDate not supplied

Natural infection by Paramphistomoidea Stiles and Goldberger, 1910 trematodes in wild Marsh Deer (Blastocerus dichotomus Illiger, 1815) from Sérgio Mottas's hydroelectric power station flooding area.

Studies on helminthfauna of marsh deer Blastocerus dichotomus Illiger, 1815 are rare, although helminthic diseases are an important cause of mortality in these animals. Fifteen male and female adult marsh deer from Sergio Motta's hydroelectric power station flooding area at Paraná River which died during the capture and quarantine procedures, between 1998 and 1999, were necropsied. Three trematodes species, Paramphistomum cervi, Balanorchis anastrofus and Zygocotyle lunatum, all belonging to superfamily Paramphistomoidea, were identified. The obtained trematodes were identified, counted and their respectives descriptors of infection were determined. All necropsied animals were infected by helminths. Paramphistomum cervi was the most prevalent species, while Zygocotyle lunatum was found in only one animal.

Animals↗

PubMed1991

Guild structure of larval trematodes in the snail Helisoma anceps: patterns and processes at the individual host level.

Factors that influenced the infracommunity structure of trematodes parasitizing the pulmonate snail Helisoma anceps were studied over a 15-mo period; the guild included 8 species of parasites. Infracommunities were depauperate, with double patent infections observed in only 7 of 1,485 infected snails; a total of 4,899 was examined. Halipegus occidualis-Haematoloechus longiplexus was the most common dual infection. Both species share the same definitive host and, in both cases, eggs are the infective stage for the snail. Switches and losses of infections in individual snails were observed, suggesting the occurrence of dynamic interactions within the guild. A dominance hierarchy was constructed based on field observations and experimental infections. Echinostomatids were dominant; species without rediae in their life cycles were subordinates. Halipegus occidualis (which has rediae) was intermediate in dominance. Spatial and temporal heterogeneity in the distribution and abundance of trematode infective stages indicate that not all the snails have the same probability of becoming infected. Habitat structure, behavior of the definitive host, the nature of the infective stages, and snail population dynamics (mortality, recruitment, and size structure) generated spatial and temporal heterogeneity in this system. As a consequence, predictions of the probabilities of interspecific interactions based on an analysis of observed and expected frequencies of multiple infections could be inappropriate unless the potential sources of heterogeneity are considered.

Animals↗

PubMedDate not supplied

[The biology of the trematode Echinochasmus milvi under the southern conditions of the Far East].

The biology of the trematode Echinochasmus milvi Yamaguti, 1939 under the conditions of the southern Far East of the USSR is studied. The development of the trematode proceeds with the participation of intermediate hosts, molluscs of the genus Juga, additional hosts, freshwater fishes, and definitive hosts, fish-eating birds and mammals, and is completed at a temperature of 17 to 23 degrees within 21 weeks.

Animals↗