Characteristics of the localization of Ancyrocephalus paradoxus (Monogenea) on the pike perch Stizostedion lucioperca

In one summer old fishes of the pike perch, caught in the K urish Gulf of the Baltic Sea in August-September of 1984, at 100% infection with A. paradoxus 94% of monogeneans were localized under the lower anterior angle of the operculum on the lateral surface of the intergill space (isthmus). In fishes 1+ on the isthmus there were found 52%, in pike perches 2+ 42%, and in fishes 3+ 67% of worms. In older fishes (4-10+) the number of worms on the isthmus accounts for 5% of their total number while others are localized on gill filaments. Variability of sizes, chitinoid structures and microlocalization of worms depending on the age of fish were established.     

Mating rendezvous in monogenean gill parasites of the humbug Dascyllus aruanus (Pisces: Pomacentridae)

The gills of the humbug, Dascyllus aruanus (Pomacentridae), were infected by a monogenean genus Haliotrema at a high prevalence (83%) but with a low mean intensity (5.6 worms/fish). All the gill arches of 365 fish, caught on the fringing reef of Moorea Island (French Polynesia), were examined for parasites. Each hemibranch was divided into 12 subequal sections. Monogeneans showing microhabitat overlap were defined as couples. Hosts with low intensity of infection (fewer than 5 monogeneans per gill) were selected and couples were recorded. Among the 37 hosts harboring 2 worms on their gills, 18 fish were infected with these 2 monogeneans on the same gill side of the body; 50% (n = 9) of these harbored monogeneans within the same gill arch and 55% (n = 5) of these last fish showed individual parasites within the same section of the gill. In the case of hosts with few monogeneans (3 and 4 individuals; n = 37) on the same arch, more than 40% (n = 16) harbored worms in couples. There may be some chemical communication that allowed these monogeneans to migrate toward each other and thus enhance mating success. Mating rendezvous appears to be a more important factor than site location for these gill monogeneans.     

The subcutaneous attachment of the monogenean Heterobothrium elongatum (Diclidophoridae) in the gills of Torquigener pleurogramma (Pisces: Tetraodontidae)

Heterobothrium elongatum predominantly occurred on the most anterior pair of gill arches of infected pufferfish, Torquigener pleurogramma. Juvenile and immature stages attached to gill lamellae and were concentrated on the ventral regions of the anterior pair of gill arches. Following penetration of subcutaneous tissues, young adult worms formed a subcutaneous channel either directly above or below the transverse septum, a tissue layer connecting the bases of adjacent gill rays. Large, sexually mature worms extended for most or all of the length of the gill arch where they filled the area normally occupied by the longitudinal lymphatic vessel (branchial vein) or lay adjacent to the efferent branchial and colateral arteries. Subcutaneous attachment by the parasite induced a marked inflammatory reaction in the host. During growth, the mid-region of the parasite became markedly elongate and formed a stalk connecting the haptor lying in the dorsal region of the gill and the body which emerged from the lower margin of the gill where penetration began.     

The Mode of Transmission of the Acephaline Gregarine Parasites of Earthworms

SYNOPSIS. Speculations regarding the mode of transmission of monocystid parasites of earthworms over a period of more than 100 years have never been tested experimentally under controlled conditions. In order to do so a stock of infectionfree Eisenia foetida (Sav.) was raised from cocoons and experimental infections were induced in this host using sporocysts of the gregarine parasites Apolocystis elongata Phillips & Mackinnon 1946, and Nematocystis elmassiani (Hesse, 1909). Experimental infections were obtained by feeding to uninfected worms sporocysts obtained directly from infected host worms. This proved that the intervention of a vector is not a necessary condition of infection. Infections could not be induced by injecting sporocysts through the body wall into the body cavity. Infections are thus probably acquired in nature by the ingestion of sporocysts. Sporocysts do not leave the body of the host by being passed from coelom to lumen of the gut, nor do they pass directly to the exterior through apertures of the body wall. There was no evidence of parasitic autotomy. It is therefore concluded that death and decay of the host is the normal method of dissemination of sporocysts. Sporocysts were not infective after drying in air for three weeks. Other sporocysts lost potency after storage in moist conditions for several months. Infections involving the organisms specified were sporadic and unpredictable; modifying factors, such as variations in host susceptibility and latency in infection, appeared to be operating.     

Variation in the sex ratio of Rhabdochona fortunatowi (Spirurida: Rhabdochonidae) in Capoeta capoeta gracilis (Cypriniformes: Cyprinidae), relative to levels of infection, host size and temperature

In the present study, 81 specimens of Capoeta capoeta gracilis (Keyserling, 1861) were collected from the Shiroud River, the Caspian drainage basin, Iran in June and October 2007. The fish were examined for infection with the nematode Rhabdochona fortunatowi (Dinnik, 1933). Nematodes were counted and sexed, then the sex ratio and intestinal site preference of the R. fortunatowi individuals and the intersexual interactions of the parasites were investigated. Significant differences were observed in the prevalence and intensity of infection in relation to host size and sampling season, but not host sex. Parasite burden (mean intensity) was higher in October than in June and the results revealed a decrease in female-to-male sex ratio (FMR) in the fish in October compared to the ones in June. In other words, as the mean intensity of infection of R. fortunatowi increases, the proportion of male worms increases, too. The female-biased sex ratio in June was replaced by a male-biased one in October. Nematode distribution rose to a significant peak in the mid-region of the fish intestine relative to the anterior and posterior parts. Some changes in the distribution of male and female worms in different parts of the host intestine were also observed during June and October. Density-dependent selection and intersexual competition seem to be the main factors driving such a shift in the sex ratio and its variation in different parts of the host intestine.     

Parasitism in species of Bathymodiolus (Bivalvia: Mytilidae) mussels from deep-sea seep and hydrothermal vents

Bivalve species, especially mussels, are biomass dominants in many deep-sea chemosynthetic ecosystems. As in shallow-water environments, parasites are likely to be important factors in the population dynamics of bivalve communities in chemosynthetic ecosystems, but there has been little study of parasitism in deep-sea seep or vent molluscs. In this study, parasite types, diversity, prevalence, infection density and non-infectious indicators of stress or disease as related to host age, reproductive condition, and endosymbiont density were assessed in mussels (Bathymodiolus heckerae) from 2 seep sites and mussels (B. puteoserpentis) from 2 vent sites. We identified 10 microbial or parasitic agents in histological sections. Parasite types included 3 viral-like gut inclusions, 2 rickettsia-like gill inclusions, a rickettsia-like mantle inclusion, a bacterial gill-rosette, a chlamydia-like gut inclusion, gill-dwelling ciliates, and an unidentified inclusion in gut tissues. Parasite species richness was greater in seep mussels than in vent mussels, with the seep mussels possessing 9 types of parasites compared to 2 in the vent mussels. One of the viral-like inclusions infecting the seep mussel B. heckerae was pathogenic, causing lysis of the digestive tubules. The prevalence and intensity of infection by this pathogen were greater in hosts with shell lengths less than 100 mm. Mussels from all 4 sites also exhibited intense infiltration of tissues and blood spaces by enlarged hemocytes. Hemocytic infiltration (hemocytosis) showed variable degrees of severity that were not associated with other host factors examined.     

Infection rates and pathogenicity of trypanosomatid gut parasites in the water strider Gerris odontogaster (Zett.) (Heteroptera: Gerridae)

Summary Trypanosomatid flagellates are common protozoan gut parasites of a wide range of insect species. Water striders (Gerridae) harbour the trypanosomatid Blastocrithidia gerridis. Three different populations of the water strider Gerris odontogaster in northern Sweden were sampled to assess the infection rate dynamics of trypanosomatids. The initially very low infection rates (0%–15%) early in the season were followed by a rapid increase during the reproductive period of the water striders, reaching very high levels (80%–90%). The pathogenic effects of trypanosomatids on G. odontogaster adults were studied in laboratory experiments. The parasites caused a general reduction of host vigour. Male skating endurance was negatively correlated with the intensity of the trypanosomatid infection. However, infection of trypanosomatids increased the mortality among adults only when the water striders were subjected to food stress. The trypanosomatids did not reduce the fecundity of females provided with food. We suggest that trypanosomatid gut parasites may be an important mortality factor in water strider populations. Since the pathogenicity of the parasites is enhanced by stress, parasitism by trypanosomatids may contribute to the regulation of host populations.     

Parasitism and the burrowing depth of the beach hopper Talorchestia quoyana (Amphipoda: Talitridae)

Talitrid amphipods spend their days burrowed in sand to avoid predators as well as desiccation and heat stress, although other factors may influence burrowing depth. We investigated the potential role of mermithid nematode parasites in determining burrowing depth in the amphipod Talorchestia quoyana. Mermithids grow as parasites inside amphipods until they reach adulthood, when they must emerge from their host into moist sand to complete their life cycle and reproduce. When allowed to burrow to a depth of their choice in experimental situations, large amphipods burrowed deeper than small ones. In addition, deep-burrowing amphipods were more likely to be infected by mermithid nematodes, and harboured longer worms, on average, than amphipods that burrowed close to the sand surface. This last result is not an artefact of the larger size of deep-burrowing amphipods: the increase in worm length with increasing depth was found after statistical correction for host size. In other words, amphipods that burrowed deeper harboured longer worms than expected based on their body size, whereas those that stayed near the surface of the sand column harboured worms shorter than one would expect based on host size. This implies that the greater burrowing depth of infected amphipods is a consequence, and not a cause, of infection. These results emphasize the importance of parasitism as a determinant of the small-scale spatial distribution of their hosts.     

Comparison of in vitro-cultured and wild-type Perkinsus marinus. II. Dosing methods and host response

Endoparasites must breach host barriers to establish infection and then must survive host internal defenses to cause disease. Such barriers may frustrate attempts to experimentally transmit parasites by 'natural' methods. In addition, the host's condition may affect a study's outcome. The experiments reported here examined the effect of dosing method and host metabolic condition on measures of virulence for the oyster parasite Perkinsus marinus. Oysters, Crassostrea virginica, were challenged with wild-type and cultured forms of P. marinus via feeding, shell-cavity injection, gut intubation and adductor-muscle injection. For both parasite types, adductor-muscle injections produced the heaviest infections followed by shell-cavity injection, gut intubation, and feeding. There was no difference in parasite burdens between oysters fed cultured cells by acute vs chronic dosing, and parasite loads stabilized over time, suggesting a dynamic equilibrium between invasion and elimination. P. marinus distribution among tissues of challenged oysters indicated that parasites invaded the mantle and gill, as well as the gut, which has been considered the primary portal of entry. Frequency distributions of P. marinus in oysters challenged with 3 different culture phases indicated an aggregated distribution among hosts and suggested that stationary-phase parasites were easiest for the oyster to control or eliminate and log-phase parasites were the most difficult. Host metabolic condition also affected experimental outcomes, as indicated by increased infection levels in oysters undergoing spawning and/or exposed to low oxygen stress.     

Impacts of the swimbladder nematode Anguillicola crassus on Anguilla anguilla: variations in liver and spleen masses

Variations in the liver and spleen masses of the eel Anguilla anguilla were analysed in relation to the parasite load of Anguillicola crassus at autopsy (current infection by swimbladder lumen worms) and in relation to the severity of damage observed in the swimbladder (a way of assessing the intensity of past infections). None of these measures of parasite pressure were shown to account for variation in the relative liver mass, either when controlling for somatic mass or eel age. In marked contrast, a significant increase in spleen size was revealed in eels harbouring many lumen worms and also in eels with severe damage in the swimbladder. Splenic enlargement was nearly two‐fold higher among severely affected eels (harbouring more than seven lumen parasites and showing severe damage in the swimbladder) than among infection‐free eels (no lumen parasites and no pathological signs in the swimbladder). Several possible hypotheses are reviewed before arguing for an adaptive host response involving the haematological and immunological functions of the spleen. Indeed, among eels with no pathological signs in the swimbladder, the relative spleen mass was positively associated with the mass of lumen parasites, which suggests a hyper‐synthesis of blood cells by the spleen in response to the bloodsucking activity of lumen worms. Nevertheless, among eels with no lumen parasites at autopsy, there was still an increase in spleen size in relation to the severity of the swimbladder damage, which also suggests a hyper‐synthesis of splenic immune cells (lymphocytes and macrophages) in reaction to damaged tissues and particularly to larvae in the swimbladder wall.     

Bayesian inference supports the host selection hypothesis in explaining adaptive host specificity by European bitterling

Generalist parasites have the capacity to infect multiple hosts. The temporal pattern of host specificity by generalist parasites is rarely studied, but is critical to understanding what variables underpin infection and thereby the impact of parasites on host species and the way they impose selection on hosts. Here, the temporal dynamics of infection of four species of freshwater mussel by European bitterling fish (Rhodeus amarus) was investigated over three spawning seasons. Bitterling lay their eggs in the gills of freshwater mussels, which suffer reduced growth, oxygen stress, gill damage and elevated mortality as a result of parasitism. The temporal pattern of infection of mussels by European bitterling in multiple populations was examined. Using a Bernoulli Generalized Additive Mixed Model with Bayesian inference it was demonstrated that one mussel species, Unio pictorum, was exploited over the entire bitterling spawning season. As the season progressed, bitterling showed a preference for other mussel species, which were inferior hosts. Temporal changes in host use reflected elevated density-dependent mortality in preferred hosts that were already infected. Plasticity in host specificity by bitterling conformed with the predictions of the host selection hypothesis. The relationship between bitterling and their host mussels differs qualitatively from that of avian brood parasites.     

Parasite fauna of introduced pumpkinseed fish Lepomis gibbosus: first British record of Onchocleidus dispar (Monogenea)

A survey of pumpkinseed Lepomis gibbosus from a stillwater fishery in southern England revealed infections by the ancyrocephalid monogenean Onchocleidus dispar at 100% prevalence. Host specificity of O. dispar to North American centrarchid fish suggests that it is a non-native parasite, introduced to Britain with L. gibbosus. Mean intensity of O. dispar was significantly higher in male (25.5 parasites) compared to female (15) and immature (7) hosts, but was not influenced by host standard length or sampling time. This sex-biased parasitism is likely to be related to both ecological and physiological factors, such as differential exposure to infective stages during nest building, or higher susceptibility to infection due to enhanced host stress levels. O. dispar significantly dominated the external surfaces and the outer gill arches. Analysis of the spatial distribution of the parasite between the 9 regions of gill surface determined that as density increased, higher numbers of parasites were found on the anterior and central gill regions compared to posterior (distal) regions. Apparent microhabitat selection is discussed in terms O. dispar life cycle, maximising oxygen availability, avoiding unstable areas and increasing intraspecific contact. The absence of O. dispar in the gills of roach, rudd and gudgeon sampled from the same fishery supports the assumption that this parasite is currently of little threat to native fish populations.     

Mast cell responses to Ergasilus (Copepoda), a gill ectoparasite of sea bream

Immunocytochemical, light microscopy and ultrastructural studies were conducted on gill of sea bream, Sparus aurata L., naturally parasitized with the important parasitic copepod Ergasilus sp. to assess pathology and cellular responses. Thirty-seven S. aurata were examined from a fish farm; 26 (70%) were parasitized, with infection intensity ranging from 3 to 55 parasites per fish. Hosts were divided into two groups, lightly infected fish (<15 parasites per fish) and heavily infected fish (>15 parasites per fish). In histological sections, the copepod encircled gill lamellae with its second antennae, compressed the epithelium, provoked hyperplasia and hemorrhage, occluded arteries and often caused lamellar disruption. Fusion of the secondary lamellae due to epithelial hyperplasia was common in all infected fish; heavily infected fish showed more intense branchial inflammation. In both healthy and infected fish, mast cells (MCs) were free within the connective tissue inside and outside the blood vessels of the primary lamellae and made close contact with vascular endothelial cells, mucous cells and rodlet cells (RCs). MCs were irregular in shape with a cytoplasm filled by numerous electron-dense, membrane-bound granules. Immunostaining of primary and secondary gill filaments with an antibody against the antimicrobial peptide (AMP) piscidin 3 (anti-piscidin 3 antibody, anti-HAGR) revealed a subpopulation of MCs that were positive. These MCs were more abundant in gills of heavily infected fish than in either lightly infected or uninfected fish (ANOVA, P<0.05). Our report documents the response of gill to ectoparasite infection and provides further evidence that mast cells and their AMPs may play a role in responding to branchial ectoparasite infections.     

Seasonal transmission ofRaphidascaris acus (Nematoda), a parasite of freshwater fishes,in definitive and intermediate hosts

Synopsis The seasonal transmission ofRaphidascaris acus was studied in two small lakes on Manitoulin Island, Ontario. Dragonfly nymphs and caddisfly larvae, acting as paratenic hosts, contained second-stage larvae. Several fishes, including percids and cyprinids, were intermediate hosts with second, third, and fourth-stage larvae in the liver. Yellow perch,Perca flavescens, was the most important of these. Intensities were up to 928 and increased with length and age of the perch; prevalence was 100%. Abundance ofR. acus tended to be higher in females but was not related to condition of the perch. Second-stage larvae were acquired from invertebrates in summer and developed to the fourth stage by November. They became surrounded by fibrous capsules during the next summer but remained alive for at least another year. The longevity of larvae in the intermediate host may ensure survival of the parasite through periods of low host abundance after winterkill. Northern pike,Esox lucius, was the definitive host. Abundance ofR. acus tended to be greater in larger pike but was not related to sex or condition of the fish. The parasite was acquired in late fall. Prevalence was 100% and mean intensities were over 200 in winter and spring, declining to 64–100% and less than 15, respectively, in summer. Mature worms were present from early spring through summer. Seasonality of infection in the definitive host is not attributable to seasonal availability of larvae in perch. Instead it may be controlled by timing of predation on perch and rate of development and longevity of the parasite. Transmission to pike apparently continues in summer. Low intensity may result from low recruitment rate and rapid turnover of the parasite population.     

Host resistance and tolerance of parasitic gut worms depend on resource availability

Resource availability can significantly alter host–parasite dynamics. Abundant food can provide more resources for hosts to resist infections, but also increase host tolerance of infections by reducing competition between hosts and parasites for food. Whether abundant food favors host resistance or tolerance (or both) might depend on the type of resource that the parasite exploits (e.g., host tissue vs. food), which can vary based on the stage of infection. In our study, we evaluated how low and high resource diets affect Cuban tree frog (Osteopilus septentrionalis) resistance and tolerance of a skin-penetrating, gut nematode Aplectana sp. at each stage of the infection. Compared to a low resource diet, a high resource diet enhanced frog resistance to worm penetration and tolerance while worms traveled to the gut. In contrast, a low resource diet increased resistance to establishment of the infection. After the infection established and worms could access food resources in the gut, a high resource diet enhanced host tolerance of parasites. On a high resource diet, parasitized frogs consumed significantly more food than non-parasitized frogs; when food was then restricted, mass of non-parasitized frogs did not change, whereas mass of parasitized frogs decreased significantly. Thus, a high resource diet increased frog tolerance of established worms because frogs could fully compensate for energy lost to the parasites. Our study shows that host–parasite dynamics are influenced by the effect of resource availability on host resistance and tolerance, which depends on when parasites have access to food and the stage of infection.     

Measurement of regurgitation in feeding studies of predatory fishes

Regurgitation of stomach contents in the predatory perch and pike captured in gill nets could be readily identified and occurrence measured. Stomachs following regurgitation, as opposed to true 'empty' stomachs, were large, distended, with a thin wall and little internal ridging. The mean percentage of genuinely empty stomachs over a 22-month period in perch was 20–21 % and in pike 7–10%. Regurgitation in perch was rare (<9% stomachs), normally only partial and restricted to water temperatures > 21°C: gill netting is therefore a legitimate means of sampling perch in food studies. In pike the sum of partial and complete regurgitation was important, with mean annual values in two lakes of 48 and 50%, and up to 84% in summer samples; it was related to water temperature ( x ) and described by the significant relationship y = 20.63+ x 2.84, but was unrelated to fish length and gill net mesh size. Food studies of predatory fishes using gill nets as a capture method should take account of regurgitation. Further information is required on the extent of regurgitation when other sampling methods are used.     

Heligmosomoides polygyrus (Nematoda): the dynamics of primary and repeated infection in outbred mice

The population dynamics of Heligmosomoides polygyrus were studied in outbred male MF1 mice subject either to primary or repeated experimental infection. Little variability in susceptibility was observed between mice, but heterogeneity increased with both duration and intensity of primary infection; this result indicates that there are differences in parasite survival between hosts. The rate of parasite-induced host mortality was 4 X 10(-4) per parasite per host per parasite lifespan. The mortality rates of male and female larvae during their development in the intestinal wall were estimated as 0.033 and 0.021 per parasite per day respectively, and estimates of the expected lifespans of the adult male and female parasites in primary infection of 11.22 and 9.92 weeks were obtained. Approximately 40% of female worms were observed in copula at any one time, although this proportion was significantly depressed in hosts harbouring fewer than 50 parasites and during the first four weeks of infection. Parasite fecundity was markedly age-dependent; each female worm produced approximately 31,000 eggs during its lifespan. No density dependence in either worm survival or fecundity in primary infection was apparent. The only detectable effect of worm density was in association with spatial distribution in the intestine; high levels of infection were associated with a posterior shift in the location of a proportion of the parasite population. Characterization of the dynamics of primary infection allowed predictions to be made about the expected dynamics of repeated infection. The comparison of predicted results and observed data revealed unequivocal epidemiological evidence for the density-dependent regulation of parasite population growth during repeated infection, affecting both parasite survival and parasite fecundity. The results also demonstrated the existence of two types of host individual in which the dynamics of repeated infection were markedly different. It is concluded that immunological differences between mice (possibly under genetic control) may be responsible for the observed effects; approximately 25% of MF1 mice seem unable to generate any protective immunity against H. polygyrus, whereas 75% become almost completely refractory to reinfection. This experimental system could be used for quantitative investigation of the impact of acquired immunity and genetic heterogeneity on helminth population dynamics. Both are of obvious relevance with respect to the control of infections of medical and veterinary significance.     

Species-specific prevalence of mermithid parasites in populations of six congeneric host caddisflies of Ecnomus McLachlan, 1864 (Trichoptera: Ecnomidae)

Mermithid nematodes are entomophagous parasites and, despite being present in diverse aquatic insects, studies of caddisflies acting as definitive hosts are few and the ecological impacts on host populations are largely unknown. During a four-year study in a stream in southeastern Australia, parasitic mermithid worms were commonly found inside adult caddisflies, but only species of the genus Ecnomus McLachlan, 1864 (Ecnomidae). Ecnomus were the definitive host and parasite prevalence ranged from <1% to nearly 50% across six species. Species-specific prevalence varied little between years and was typically higher in males than in females. Parasite intensity ranged from 1 to 6 (median = 1), but did not vary between species or sexes. Infected hosts could fly, but were castrated and died when worms emerged. High prevalence and virulence (reproductive failure and death of the host) suggests that these parasites could potentially play a role in the population dynamics of some Ecnomus spp.     

Prevalence and intensity ofCapillaria catostomi (Nematoda: Trichuroidea) in white sucker (Catostomus commersoni) in southern Lake Huron,Canada

Synopsis A total of 314 white suckers (Catostomus commersoni) taken monthly during May to December 1975 and in April and May 1976 from southern Lake Huron, Ontario, Canada, were examined forCapillaria catostomi.Prevalence determined from fresh white suckers (66%) was significantly lower than from frozen white suckers (81%). However, there was no significant difference in prevalence ofC. catostomi in samples taken at monthly intervals; in male and female white suckers; or in the age categories.Mean intensity of infection was not significantly different in fresh (9.6 [± 13.41]) or frozen (10.4 [± 13.11]) white suckers. There was no significant difference in intensities between monthly samples in male and female white suckers or in the age categories. Suckers were infected with 1–172 worms. The percentage of male, female and immature worms did not change with sex or age of host or by month. The frequency distribution showed the parasites were overdispersed.A possible life cycle forC. catostomi involving an oligochaete intermediate host is discussed and an attempt made to explain the almost constant levels of prevalence and intensity.     

Systemic infection with Alaria americana (Trematoda).

Alaria americana is a trematode, the adult of which is found in mammalian carnivores. The first case of disseminated human infection by the mesocercarial stage of this worm occurred in a 24-year-old man. The infection possibly was acquired by the eating of inadequately cooked frogs, which are intermediate hosts of the worm. The diagnosis was made during life by lung biopsy and confirmed at autopsy. The mesocercariae were present in the stomach wall, lymph nodes, liver, myocardium, pancreas and surrounding adipose tissue, spleen, kidney, lungs, brain and spinal cord. There was no host reaction to the parasites. Granulomas were present in the stomach wall, lymph nodes and liver, but the worms were not identified in them. Hypersensitivity vasculitis and a bleeding diathesis due to disseminated intravascular coagulation and a circulating anticoagulant caused his death 8 days after the onset of his illness.