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.     

Invasion character and distribution of the Diplostomum huronense (La Rue, 1927) Hugnes, 1929 metacercariae in roach of Lake Ladoga

Estimation of the invasion character and distribution of the Diplostomum huronense metacercariae depending on the fish host age has been carried out in roach of Lake Ladoga. Distribution of D. huronense in the young roach (up to age 5+) is negative binomial. Aggregation of the parasite is caused not only by individual differences in the fish host resistance to the metacercariae invasion, but by a high mortality of hyperinfected fishes as well. In older individual hosts the host-parasite system is destroyed, and the parasite distribution approximates to normal. The parasite system of the diplostomids in roach is characterized by the spatial asymmetry, when most part of parasites inhabit few individual hosts, and probability of the case when a parasite get into previously infected host is higher than that of the invasion of parasite-free host. Thus, the Diplostomum huronense metacercaria is an important factor regulating the fish fry number both in direct (death of infected fry) and indirect (elimination of hyperinfected fishes by ichthyophagous birds) way.     

Streblonema (Ectocarpales,Phaeophyceae) infection in the kelp Laminaria saccharina (Laminariales,Phaeophyceae) in the western Baltic

The brown alga Laminaria saccharina is the dominant subtidal macroalga in Kiel Bay, western Baltic. It is infected by the microscopic brown alga, Streblonema aecidioides. Infected thalli may show symptoms of Streblonema disease, i.e. alterations of blade and stipe, ranging from dark spots to heavy deformations and completely crippled thalli. Samples taken from a single locality all year round show that (i) the host population is infected at a high rate of 87±13% (SD), but that (ii) a considerable proportion of thalli containing Streblonema does not show disease symptoms, and that (iii) juvenile hosts, which mainly appear in autumn, are infected at almost the same rate. Thus the infection seems to occur early in the host's life. Juveniles in nature show fewer symptoms of the disease than adults. Two months after infection, oxygen production and growth in laboratory-raised experimentally infected juvenile hosts was not different from uninfected controls. Experimental thalli showed more severe morphological alterations than uninfected controls only four months after infection. Both field and laboratory observations indicate that a lag phase exists between infection and outbreak of the disease.     

Taxonomic status, redescription, and surface ultrastructure of Ascocotyle (Phagicola) pindoramensis n. comb. (Digenea: Heterophyidae)

Pygidiopsis pindoramensis Travassos, 1928, is redescribed from the holotype and specimens obtained from experimental infections of hamsters with metacercariae of the naturally infected poeciliids Poecilia vivipara and Phalloptychus januarius from Rio de Janeiro, Brazil. Ascocotyle (Phagicola) pindoramensis (Travassos, 1928) n. comb. is proposed, based on the presence of a solid, tapering muscular posterior prolongation of the oral sucker and Ascocotyle (Phagicola) mollienisicola (Sogandares-Bernal and Bridgman, 1960) is synonymized with A. (P.) pindoramensis because of the identical morphology and measurements of adults and metacercariae, similar spectrum of fish intermediate hosts (poeciliids), and the same site of infection of the metacercariae. Trematodes designated as Pygidiopsis pindoramensis, previously reported from Argentina and Mexico, represent another species of Pygidiopsis Looss, 1907, because they possess circumoral spines and their oral sucker is devoid of the posterior muscular prolongation. Data on the surface morphology of metacercariae and adults of A. (P.) pindoramensis are inferred from scanning electron microscopy observations.     

Effect of temperature on emergence, survival and infectivity of cercariae of the marine trematode Renicola roscovita (Digenea: Renicolidae)

Marine bivalves harbour a diversity of trematode parasites affecting population and community dynamics of their hosts. Although ecologically and economically important, factors influencing transmission between first (snail) and second (bivalve) intermediate hosts have rarely been studied in marine systems. In laboratory experiments, the effect of temperature (10, 15, 20, 25 degrees C) was investigated on (1) emergence from snails, (2) survival outside hosts and (3) infectivity in second intermediate hosts of cercariae of the trematode Renicola roscovita (Digenea: Renicolidae), a major parasite in North Sea bivalves. Emergence of cercariae peaked at 20 degrees C (2609 +/- 478 cercariae snail(-1) 120 h(-1)) and was considerably lower at 10 degrees C (80 +/- 79), 15 degrees C (747 +/- 384) and 25 degrees C (1141 +/- 334). Survival time decreased with increasing temperature, resulting in 50% mortality of the cercariae after 32.8 +/- 0.6 h (10 degrees C), 26.8 +/- 0.8 h (15 degrees C), 20.2 +/- 0.5 h (20 degrees C) and 16.6 +/- 0.3 h (25 degrees C ). Infectivity of R. roscovita cercariae in cockles Cerastoderma edule increased with increasing temperature and was highest at 25 degrees C (42.6 +/- 3.9%). However, mesocosm experiments with infected snails and cockle hosts in small aquaria, integrating cercarial emergence, survival and infectivity, showed highest infection of cockles at 20 degrees C (415 +/- 115 metacercariae host(-1)), indicating 20 degrees C to be the optimum temperature for transmission of this species. A field experiment showed metacercariae of R. roscovita to appear in C. edule with rising water temperature in April; highest infection rates were in August, when the water temperature reached 20 degrees C. Since another trematode species (Himasthla elongata; Digenea: Echinostomatidae) occurring at the experimental site showed a similar temporal pattern, trematode transmission to second intermediate bivalve hosts may peak during especially warm (> or = 20 degrees C) summers in the variable climate regime of the North Sea.     

The incidence of the Pea crab, Pinnotheres pisum in the two types of Mytilus (Mollusca: Bivalvia) from Padstow, south-west England

Significant differences in the infection of M. edulis and the "Padstow type" mussel with P. pisum are recorded, and some possible explanations for these differences are discussed.
Both types of Mytilus from the mid and lower regions of the mussel bed showed heavier infections than mussels higher on the shore. Even so, the differences between the two types were still maintained.
A relationship exists between crab and mussel size, larger crabs being found only in larger hosts. The smallest mussel found to be infected with Pinnotheres measured 3·35 cm in length.
Infection in M. edulis was found to increase with increased size of host, the largest occurring mussels having from 80 to 100% infection. Larger mussels occurred in greater numbers in the low shore. It is assumed that infection in the "Padstow type" would show a similar relationship if sufficient recordings had been available.
The presence of the crab causes gill damage, and infected mussels show considerably lower tissue weights and slightly greater shell weights than uninfected mussels of similar size.
The presence of the crab does not appear to influence the reproductive capacity of the mussel.     

Behavioral responses of Poecilia vivipara (Osteichthyies: Cyprinodontiformes) to experimental infections of Acanthocollaritrema umbilicatum (Digenea: Cryptogonimidae)

The swimming behavior of Poecilia vivipara was evaluated using an image analysis system comparing laboratory-reared uninfected fish before and after experimental infection with different intensities of cercariae of the trematode Acanthocollaritrema umbilicatum. Two experiments were performed, each with 30 fish which were individually exposed to 30 and 50 cercariae, respectively, shed from experimentally infected molluscs, Heleobia australis. Before and after (17–27 days) infection, the behavior of each fish was monitored in terms of Distance travelled, Ambulatory time, Stereotypic time, Resting time and Average speed. At the end of the experiments, the fish were dissected to count the number of metacercariae recovered. In the experiment with 30 cercariae, fish with 2–10 metacercariae did not exhibit any significant differences in their swimming activity, but those with 11–22 metacercariae had a significantly enhanced Stereotypic time and a reduced Time Resting. In the experiment with 50 cercariae, fish with 5–22 metacercariae had an enhanced Distance travelled and a reduced Average speed; highly significant differences occurred with regard to all behavioral parameters when considering the subgroup 23–36 metacercariae: Distance travelled, Stereotypic time, Resting time, Ambulatory time and Average speed. The swimming behavior of P. vivipara changed influenced by an intensity-dependence on metacercariae of A. umbilicatum, supporting the prediction that parasites are able to alter the behavior of their hosts.     

Dynamics of Anguillicola crassus larval infections in a paratenic host,the ruffe (Gymnocephalus cernuus) from the Oder River on the border of Germany and Poland

The course of infection of 2-year-old ruffe (Gymnocephalus cernuus L.) from the Oder River (Germany/Poland) with third-stage larvae (L3) of Anguillicola crassus (Nematoda: Anguillicolidae) was investigated at monthly intervals between March 1994 and March 1995. Of 230 fish examined, 152 (66%) harboured viable L3. Monthly prevalences fluctuated between 12 and 96%; mean intensities ranged from 1.0 to 5.6 L3 per infected fish. Temperature-dependent differences in infection were noted with the prevalence and mean intensity of infection being significantly higher (Chi-Square test and Mann-Whitney-U-test, respectively; ) at water temperatures less than 10 degrees C (cold period) than at those above (warm period). These differences remained significant even after the division of fish samples into two size classes (8.5-10.5 cm, 11-13 cm). Although the paratenic hosts may acquire infections year round, the results suggest that ruffe become infected mainly during the cold season and that the host's feeding ecology determines the final course of infection.     

Evolutionary avenues for, and constraints on, the transmission of frog lung flukes (Haematoloechus spp.) in dragonfly second intermediate hosts

Metacercariae survival patterns and their distribution in second intermediate odonate hosts were examined for 4 species of frog lung flukes. Surveys of aquatic larvae and recently emerged teneral dragonflies and damselflies indicated that prevalence and mean abundance of Haematoloechus spp. metacercariae were significantly lower in teneral dragonflies than larval dragonflies, while there was no significant difference in prevalence or mean abundance of Haematoloechus spp. metacercariae among larval and teneral damselflies. Experimental infections of dragonflies indicated that metacercariae of Haematoloechus coloradensis and Haematoloechus complexus were located in the head, thorax, and branchial basket of dragonflies, whereas metacercariae of Haematoloechus longiplexus and Haematoloechus parviplexus were restricted to the branchial basket of these hosts. Metacercariae of H. coloradensis, H. complexus, and H. longiplexus infected the head, thorax, and abdomen of damselflies, but these insects were resistant to infection with H. parviplexus. Subsequent metamorphosis experiments on experimentally infected dragonflies indicated that most metacercariae of H. longiplexus were lost from the branchial basket during metamorphosis, but most metacercariae of H. coloradensis, H. complexus, and H. parviplexus survived dragonfly metamorphosis. These observations suggest that the observed ecological host specificity of H. longiplexus in semiterrestrial leopard frogs may be due to few metacercariae of H. longiplexus reaching these frogs in a terrestrial environment. Because of the uncertain validity of Haematoloechus varioplexus as a distinct species from its synonym H. parviplexus, their morphological characters were reevaluated. The morphological data on H. varioplexus and H. parviplexus indicate that they differ in their acetabulum length and width, ovary shape, testes length, and egg length and width. Experimental infections of plains leopard frogs, northern leopard frogs, and bullfrogs with worms from bullfrogs indicate that the synonymy of H. parviplexus with H. varioplexus is not warranted, and that these flukes are distinct species, i.e., H. parviplexus in bullfrogs and H. varioplexus in plains leopard frogs and northern leopard frogs.     

Some aspects of the biology of the cercaria and metacercaria of Stephanostomum baccatum (Nicoll, 1907) Manter, 1934 (Digenea: Acanthocolpidae)

Experimental proof is presented that Cercaria neptunae Lebour is the cercaria of Stephanostomum baccatum and that the gastropods Buccinum undatum (L.) and Neptunea antiqua (L.) both act as its first intermediate hosts in the north-east Atlantic. Heavy experimental infections were associated with mortalities of 0+plaice Pleuronectes platessa (L.). The probable effects on plaice of infections at intensities below the lethal level are discussed. Under natural conditions almost all S. baccatum infection of plaice occurs in the first year of life, but newly emerged cercariae were shown experimentally to be capable of encysting in the musculature of plaice up to three years old. The thicker epidermis of older plaice may account for their resistance to infection. Common dabs were more easily infected than plaice. The ability of S. baccatum cercariae to infect plaice and common dabs is inversely related to the length of time between emergence and contact with the host. The differences in skin structure between opposite sides of the plaice body may account for the asymmetrical distribution of metacercariae in the musculature. The potential use of S. baccatum as a biological tag is discussed.     

Phyllodistomum folium (Trematoda: Gorgoderidae) infecting zebra mussels (Dreissena polymorpha) in the Ebro River, Spain

Zebra mussels (Dreissena polymorpha) were first found in the Ebro River (Spain) in Ribaroja reservoir, in the summer of 2001. This paper reports a study to detect parasites in this bivalve species. From September 2003 to August 2004, a total of 1380 zebra mussels were collected and dissected or sectioned in paraffin and haematoxylin and eosin staining. We observed the presence of Phyllodistomum folium (Olfers, 1816) in two hosts (prevalence 0.14%). Sporocysts containing metacercariae were located within the gill lamellae. One of the mussels was collected in January and the other one in July. In both cases the shell length was >2 cm. P. folium had not been previously reported in Spain and D. polymorpha is its only known intermediate host. It represents a new invasive species in this river basin, presumably introduced together with the zebra mussels.     

The epidemiology of the metacercariae of Diplostomum baeri and D. spathaceum in perch (Perca fluviatilis) from the warm water effluent of a nuclear power station

Thermal effects on the dynamics of infection with metacercariae of Diplostomum baeri and D. spathaceum were monitored between May and September, in a year-class of perch Perca fluviatilis, in an artificial lake receiving warm water discharges from a nuclear power station and in an unheated reference site, for a two year period. In the heated area the prevalence of infection of the retinal form, D. baeri, was always 100%, whereas in the unheated site there was an increase from 93% in May to 100% in June 1986. The relative density of D. baeri was found to increase gradually during the first summer in both areas, although the accumulation rate of metacercariae was significantly increased in the heated area. In August of the first year the relative density of D. baeri peaked in the heated area, whereas it continued to increase in the unheated control. However, in September of the following year, the relative densities were at the same level in both thermal regimes. A concomitant decline in the degree of overdispersion of metacercariae within the host population was observed in the heated area as the population density of metacercariae decreased, whereas the index of dispersion remained at the same level throughout the study in the unheated area. However, it was not possible to sample perch in the unheated area between October 1986 and May 1987 and changes in the parasite population could have occurred during this period. The prevalence and relative density of D. spathaceum, the lens form, was on the contrary low, especially in the unheated site where it was recorded only occasionally. The infection of D. baeri exhibited a convex pattern in both thermal regimens, although the peak infection was noticed earlier in the heated area. Regulation of the parasite infrapopulation may have been achieved by the combined effects of a decreased transmission rate of cercariae with increasing age of the host, the mortality of metacercariae as a natural termination of the life span and to selective predation of heavily infected hosts. However, regardless of an increased accumulation rate of metacercariae in the heated area, the relative densities of D. baeri became equal in both thermal regimes at the end of the study. The mortality rate of metacercariae in the heated area was therefore presumably increased as compared with the unheated reference site.     

A description of the parthenogenetic metacercaria and cercaria of <Emphasis Type="Italic">Cercaria falsicingulae I</Emphasis> larva nov. (Digenea: Gymnophallidae) from the snails <Emphasis Type="Italic">Falsicingula</Emphasis> spp. (Gastropoda), with speculation on an unusual life-cycle

Previously unknown gymnophallid parthenogenetic metacercariae (PM), referred to as Cercaria falsicingulae I larva nov., were found in the extrapallial cavities of the snails Falsicingula mundana (Yokoyama) and F. athera (Bartsch) on coasts of Sakhalin and the Kuril Islands. Unlike all other known PM, rather than producing metacercariae infective to the definitive host, their furcocercariae emerge into the environment. The developing cercariae and metacercariae of C. falsicingulae I are described and compared with other gymnophallid larvae from littoral molluscs in the region. Experimental evidence and analysis of metacercarial group composition in naturally infected molluscs indicate that some cercariae leave their molluscan hosts and penetrate other specimens of Falsicingula in which they develop into new cercariae-producing PM. Metacercariae with developing hermaphroditic reproductive organs were never observed in naturally infected molluscs. A probable life-cycle for C. falsicingulae I is presented in which cercarial/metacercarial production is switched seasonally in order to enable the infection of the definitive hosts by PM. Importantly, the 'cercaria - PM - cercaria' component of the life-cycle appears to be somewhat autonomous.     

Mating rates and the prevalence of male‐killing Spiroplasma in Harmonia axyridis (Coleoptera: Coccinellidae)

Maternally inherited bacteria that kill male but not female hosts during embryogenesis have been widely reported in invertebrates. Harmonia axyridis is one of the species infected by male‐killing Spiroplasma. The presence of male‐killers in host populations can lead to the occurrence of extremely female‐biased sex ratios. Furthermore, infected females may have fewer chances to mate if males can discriminate between infected and uninfected females and prefer the latter. Although there have been many investigations of male‐killer infection rates in H. axyridis, little is known about the influence of host mating on male‐killer infection dynamics. We investigated copulation rates and changes in infection frequency in a wild population of H. axyridis in western Japan. Almost all infected females collected each year laid fertilized eggs and had therefore mated. Mean infection rates of females collected each year were 13% in 2003, 15% in 2012 and 23% in 2013. Statistical analysis showed that neither the copulation rate nor the infection rate differed significantly among years. These results suggest that the infection rate of H. axyridis with male‐killing Spiroplasma is kept approximately constant and that there is no difference in the chance of mating with infected and uninfected females.     

Acanthoparyphium tyosenense (Digenea: Echinostomatidae): experimental confirmation of the cercaria and its complete life history in Korea

Cercaria yamagutii Ito, 1957, was found in the marine mesogastropods Lunatia fortuni and Glossaulax didyma from the tidelands of Simpo located at the estuary of the Mankyoung River, which runs to the western coast of Korea. Metacercariae were found in a marine bivalve Mactra veneriformis after being infected with C. yamagutii experimentally. When a sea gull, Larus crassiostris, was fed with the metacercariae collected from the infected M. veneriformis, adult worms were recovered 10 days later. It was confirmed that the parasites collected from L. crassiostris were Acanthoparyphium tyosenense Yamaguti, 1939. From the results of this life cycle study, it was determined that the first intermediate hosts of A. tyosenense are L. fortuni and G. didyma. The second intermediate and final hosts are M. veneriformis and L. crassiostris, respectively. Mactra veneriformis was experimentally infected with C. yamagutii isolated from L. fortuni and G. didyma by maintaining them in a water tank for 30 min at about 20 C. The cercariae entered M. veneriformis through their incurrent siphons. Five hours after infection, the cercariae tails began to separate from the bodies, and the cercariae formed cysts. Mature cysts were formed 340 hr (14 days) after infection and identified as the metacercariae of A. tyosenense. The prevalence of A. tyosenense metacercariae was 99.5% in naturally infected M. veneriformis. This is the first report of C. yamagutii as the cercaria of A. tyosenense, and the complete life cycle of A. tyosenense was established in Korea.     

The population biology of Hymenolepis tenerrima (Linstow 1882) Fuhrmann 1906 (Cestoda, Hymenolepididae) in its intermediate host Herpetocypris reptans (Ostracoda)

The occurrence of Hymenolepis tenerrima cysticercoids in a population of the intermediate host, Herpetocypris reptans is described for a one year period between October 1980 and September 1981. Parasite occurrence varied seasonally. The prevalence of infection decreased during the winter due to the death of infected hosts and low levels of transmission. Parasite transmission increased during the summer months and the maximum number of cysticercoid stages in the environment occurred in June. Juvenile ostracods were not infected and in adult ostracods a maximum of 3 cysticercoids/host was observed. The presence of H. tenerrima larval stages within the haemocoele had a marked influence upon the survival and fecundity of infected ostracod intermediate hosts.     

The crowding effect and morphometric variability in Echinostoma caproni (Digenea: Echinostomatidae) from ICR mice

Population density, or crowding, was examined to determine its effect on the morphometric variability of Echinostoma caproni (Digenea) in ICR mice. Six mice were infected with 25 and 100 metacercariae, and a single mouse was infected with 300 metacercariae. All mice were infected at necropsy 22 days postinfection with recoveries of 77%, 69%, and 7.3%, respectively. Whole mounts were prepared, and 31 characters were evaluated (25 direct measurements and 6 ratios). Univariate and multivariate statistical analysis revealed significant differences between adult worms from all 3 groups. Twenty-seven of 31 characters showed significant within-group differences, with the primary differences between worms from 25/100 versus 300 metacercariae infections. Discriminant function analysis yielded a 100% correct classification based on infection size, which is consistent with studies on distinct species of Echinostoma. The low recovery from the mouse infected with 300 metacercariae suggests inflammatory expulsion of juvenile worms and the possibility of immunity as a factor in the crowding effect. These results suggest that external factors may affect morphometric variability of digenetic trematodes to a larger degree than previously recognized.     

Infection status of Paragonimus westermani metacercariae in crayfish (Cambaroides similis) collected from Bogildo (Islet), Wando-gun, Chollanam-do, Korea

During the period from October 1996 to November 1998, the infection status of Paragonimus westermani metacercariae in freshwater crayfish (Cambaroides similis) collected from Bogildo (islet). Wando-gun, Chollanam-do, which is known for an endemic area of P. westermani in Korea, were examined. The average infection rate of Paragonimus metacercariae in crayfish was 88.6%, and mean number of metacercariae per infected crayfish was 30.2. This metacercarial density was the highest in the group of weight in 7.1-9.0 g. These results suggest that the natural life cycle of P. westermani is still well-preserved in Bogildo.     

Histopathological and ultrastructural observations of metacercarial infections of Diplostomum phoxini (Digenea) in the brain of minnows Phoxinus phoxinus

The spatial distribution and histopathological changes induced by metacercariae of the digenean trematode Diplostomum phoxini (Faust, 1918) in the brains of European minnows Phoxinus phoxinus (L.) from the River Endrick, Scotland, were studied by light and electron microscopy. Post-mortem examination of a sample of 34 minnows revealed that 50% (n = 17) of the population was infected with 13.7 +/- 2.6 (mean +/- SE; range 1 to 38) metacercariae per infected host. Serial histological sections of the infected minnow brains revealed that the metacercariae were unevenly distributed throughout the brain, with aggregations occurring in the cerebellum, the medulla oblongata and the optic lobes. In fish with highest intensities of infection, over 40% of the cerebellar area and about 30% of the medulla oblongata area were occupied by larvae. Metacercariae disrupt the integrity of brain tissue, with individuals being found in small pockets surrounded by cellular debris. Metacercariae were rarely encountered on the surface of the brain. Electron microscopic examination of infection sites revealed that the granular layer surrounding metacercariae was necrotic, exhibited nuclear degradation and was marked by vacuolation of the cytoplasm. Rodlet cells, the only inflammatory cell types recorded in this study, were found only in parasitized brains and in close proximity to the teguments of metacercariae. It is hypothesised that secretions released from the teguments of metacercariae are a counter response to protect the metacercariae from the fish brain's cellular defence mechanisms.