Abundance Of Intermediate Hosts Research Articles

The impact of climate change and pollution on trematode-bivalve dynamics

Coastal ecosystems and their marine populations are increasingly threatened by global environmental changes. Bivalves have emerged as crucial bioindicators within these ecosystems, offering valuable insights into biodiversity and overall ecosystem health. In particular, bivalves serve as hosts to trematode parasites, making them a focal point of study. Trematodes, with their life cycles intricately linked to external factors, provide excellent indicators of environmental changes and exhibit a unique ability to accumulate pollutants beyond ambient levels. Thus, they act as living sentinels, reflecting the ecological condition of their habitats. This paper presents a comprehensive review of recent research on the use of bivalve species as hosts for trematodes, examining the interactions between these organisms. The study also investigates the combined impact of trematode infections and other pollutants on bivalve molluscs. Trematode infections have multifaceted consequences for bivalve species, influencing various aspects of their physiology and behavior, including population-wide mortality. Furthermore, the coexistence of trematode infections and other sources of pollution compromises host resistance, disrupts parasite transmission, and reduces the abundance of intermediate hosts for complex-living parasites. The accumulation process of these parasites is influenced not only by external factors but also by host physiology. Consequently, the implications of climate change and environmental factors, such as temperature, salinity, and ocean acidification, are critical considerations. In summary, the intricate relationship between bivalves, trematode parasites, and their surrounding environment provides valuable insights into the health and sustainability of coastal ecosystems. A comprehensive understanding of these interactions, along with the influence of climate change and environmental parameters, is essential for effective management and conservation strategies aimed at preserving these delicate ecosystems and the diverse array of species that rely on them.

Parasite prevalence in intermediate hosts increases with waterbody age and abundance of final hosts.

Prevalence of a parasite may be influenced by age of the habitat (= time available for hosts and parasites to colonize habitats), assemblage composition of host and non-host species, or biotic and abiotic habitat features. For a trophically transmitted parasite, the intermediate host may be consumed by both final hosts and 'dead-end' predators that are incompetent to host the parasite. We tested biotic and abiotic factors that might influence parasite prevalence in a freshwater host-parasite system using a dataset collected from 36 water bodies in the vicinity of Edmonton, Alberta, Canada. In this system, eggs of thorny-headed worms (Acanthocephala: Polymorphus spp.) are eaten by intermediate-host amphipods (Gammarus lacustris Sars), which are then consumed by final vertebrate hosts (certain aquatic birds and muskrats) and various non-host waterbird species. We found that acanthocephalan prevalence in amphipods was positively correlated with waterbody age and with abundance of final-host species. In contrast, abundance of the intermediate host G. lacustris was less important and was negatively correlated with parasite prevalence ('encounter-dilution effect'). Similarly, parasite prevalence showed a marginally significant and negative correlation with abundance of 'dead-end' Gammarus-eating birds. We conclude that in our study system, time available for colonization and abundance of final hosts are more important for parasite prevalence in intermediate hosts than is abundance of intermediate and dead-end hosts.

Influence of physico-chemical parameters on the intermediate host of Schistosoma haematobium and Schistosoma mansoni in Makwaye and Kubanni Reservoirs, Zaria, Nigeria

Objective: This research was conducted to determine the influence of physico-chemical characteristics on diversity of the intermediate host of schistosomes in Makwaye and Kubanni reservoirs, Zaria, Nigeria. Materials and methods: Physico-chemical characteristics and diversity of the intermediate host of schistosomes in Makwaye and Kubanni reservoirs, Zaria, Nigeria, were investigated for a 12-month period (January to December, 2014). Physico-chemical properties were analyzed according to the standard procedures for examination of water and waste waters. The molluscs were collected using an Ekman grab model number 923, measuring 19 cm by 14 cm with an area of 0.0266 m2. PAST software was used to run Principal Component Analysis, Shanon-Weiner diversity index and Cluster analysis. Results: A total of 978 Bulinus globosus and 3612 Biomphalaria pfefferi were recorded in Makwaye reservoir with high abundance in dry season while a total of 163 B. globosus and 602 B. pfefferi was recorded in Kubanni reservoir with higher abundance in wet season. Shanon-Weiner diversity index of Makwaye reservoir also ranged from 2.01-2.22 and 1.16-1.31 in Kubanni reservoir. Significant variations (P≤0.05) were observed in physicochemical parameters, schistosomes intermediate host abundance with seasons. Principal Component Analysis (PCA) revealed significant influence (P≤0.05) of physicochemical properties on schistosome intermediate host composition, with BOD, DO, pH and Calcium significantly influencing the presence of B. globosus and B. pfefferi in both reservoirs. Conclusion: It is concluded that the presence of these molluscs in the study areas may constitute a predisposing factor to schistosomiasis and therefore, various management strategies and recommend preventive measures to people coming in contact with these two reservoirs.

Seasonal and Spatial Environmental Influence on Opisthorchis viverrini Intermediate Hosts, Abundance, and Distribution: Insights on Transmission Dynamics and Sustainable Control.

BackgroundOpisthorchis viverrini (Ov) is a complex-life-cycle trematode affecting 10 million people in SEA (Southeast Asia). Human infection occurs when infected cyprinid fish are consumed raw or undercooked. Ov requires three hosts and presents two free-living parasitic stages. As a consequence Ov transmission and infection in intermediate and human hosts are strongly mediated by environmental factors and understanding how environmental variability influences intermediate host abundance is critical. The objectives of this study were 1) to document water parameters, intermediate hosts abundance and infection spatio-temporal variation, 2) to assess their causal relationships and identify windows of transmission risk.Methodology/Principal FindingsFish and snails were collected monthly for one year at 12 sites in Lawa Lake, an Ov-endemic region of Khon Kaen Province in Northeast Thailand. Physicochemical water parameters [pH, temperature (Tp), dissolved oxygen (DO), Salinity, electrical conductivity (EC), total dissolved solid (TDS), nitrite nitrogen (NO2-N), lead (Pb), total coliform bacteria (TCB) and fecal coliform bacteria (FCB)] were measured. Multivariate analyses, linear models and kriging were used to characterize water parameter variation and its influence on host abundance and infection prevalence. We found that sampling sites could be grouped in three clusters and discriminated along a nitrogen-salinity gradient where higher levels in the lake’s southern region predicted higher Bithynia relative abundance (P<0.05) and lower snail and fish species diversity (P<0.05). Highest Bithynia abundance occurred during rainy season (P<0.001), independently of site influence. Cyprinids were the most abundant fish family and higher cyprinid relative abundance was found in areas with higher Bithynia relative abundance (P<0.05). Ov infection in snails was anecdotal while Ov infection in fish was higher in the southern region (P<0.001) at sites showing high FCB.Conclusions/SignificanceOur results indicate that water contamination and waterways configuration can influence freshwater communities’ assemblages possibly creating ideal conditions for sustained transmission. Sustainable control may require a better appreciation of the system’s ecology with wise governance and development planning particularly in the current context of SEA agricultural intensification and landscape modification.

Patterns of parasite community dissimilarity: the significant role of land use and lack of distance‐decay in a bat–helminth system

Increasing community dissimilarity across geographic distance has been described for a wide variety of organisms and understanding its underlying causes is key to understanding mechanisms driving patterns of biodiversity. Both niche‐based and neutral processes may produce a distance decay relationship; however, disentangling their relative influence requires simultaneous examination of multiple potential drivers. Parasites represent a unique opportunity in which to study distance decay because community dissimilarity may depend on environmental requirements and dispersal capability of parasites as well also those of their hosts. We used big brown bats Eptesicus fuscus and their intestinal helminths to investigate: 1) independent contributions of geographic and environmental distances on dissimilarity of intestinal helminth component communities between populations of big brown bats; 2) which environmental variables best explained variation in community dissimilarity; and 3) whether similar patterns of decay with geographic or environmental distance were observed for within‐host population and within‐individual host parasite communities. We used compositional measures of community dissimilarity to examine how parasite communities may change with geographic distance and varying environmental conditions. Non‐spatial variables strongly influenced compositional parasite community dissimilarity over multiple community scales, and we observed little evidence for spatial processes such as distance decay. Environment surrounding roost sites better predicted helminth community dissimilarity than any other class of variables and landcover classes representing anthropogenic modification consistently explained variation in community structure. Our results indicate that human disturbance drives significant patterns of parasite community dissimilarity, most likely by changing the presence or abundance of intermediate hosts in an area.

Density- and trait-mediated effects of a parasite and a predator in a tri-trophic food web.

1. Despite growing interest in ecological consequences of parasitism in food webs, relatively little is known about effects of parasites on long-term population dynamics of non-host species or about whether such effects are density or trait mediated.2. We studied a tri-trophic food chain comprised of (i) a bacterial basal resource (Serratia fonticola), (ii) an intermediate consumer (Paramecium caudatum), (iii) a top predator (Didinium nasutum) and (iv) a parasite of the intermediate consumer (Holospora undulata). A fully factorial experimental manipulation of predator and parasite presence/absence was combined with analyses of population dynamics, modelling and analyses of host (Paramecium) morphology and behaviour.3. Predation and parasitism each reduced the abundance of the intermediate consumer (Paramecium), and parasitism indirectly reduced the abundance of the basal resource (Serratia). However, in combination, predation and parasitism had non-additive effects on the abundance of the intermediate consumer, as well as on that of the basal resource. In both cases, the negative effect of parasitism seemed to be effaced by predation.4. Infection of the intermediate consumer reduced predator abundance. Modelling and additional experimentation revealed that this was most likely due to parasite reduction of intermediate host abundance (a density-mediated effect), as opposed to changes in predator functional or numerical response.5. Parasitism altered morphological and behavioural traits, by reducing host cell length and increasing the swimming speed of cells with moderate parasite loads. Additional tests showed no significant difference in Didinium feeding rate on infected and uninfected hosts, suggesting that the combination of these modifications does not affect host vulnerability to predation. However, estimated rates of encounter with Serratia based on these modifications were higher for infected Paramecium than for uninfected Paramecium.6. A mixture of density-mediated and trait-mediated indirect effects of parasitism on non-host species creates rich and complex possibilities for effects of parasites in food webs that should be included in assessments of possible impacts of parasite eradication or introduction.

Distribution and Abundance ofSebekia mississippiensis(Sebekidae) in the American Alligator,Alligator mississippiensis

Pentastomids are the most common endoparasite that infects the respiratory tracts of saurapsid reptiles, such as crocodilians. In this study we examined lung pentastomid parasitism in the American alligators, Alligator mississippiensis from northern Florida and southern Louisiana, U.S.A. (partitioned into the Louisiana West Zone and Louisiana East Zone) to determine the potential effects of alligator gender, size, and location on pentastomid distribution and abundance. In total, 1,405 lung pentastomids identified as Sebekia mississippiensis were found in 69 alligators (81.2% prevalence). Male alligators were found to have a higher pentastomid prevalence and intensity in comparison to females, which may be the effect of disparate life-history traits between the sexes and the larger size of males. Host size classes were found to be a significant trait influencing parasitism, as pentastomid prevalence and intensity increased in conjunction with alligator maturation. Our results also indicated that S. mississippiensis has a higher prevalence among Louisiana West Zone alligators, whereas the intensity was found to be higher among Florida alligators. Variation of intermediate host abundance is likely the primary cause for the differing pentastomid distribution among study locations. As such, these data further our understanding of the patterns of alligator pentastomiasis.

Spatial heterogeneity and temporal variations in Echinococcus multilocularis infections in wild hosts in a North American urban setting

Echinococcus multilocularis, the causative agent of human alveolar echinococcosis, has the potential to circulate in urban areas where wild host populations and humans coexist. The spatial and temporal distribution of infection in wild hosts locally affects the risk of transmission to humans. We investigated the spatial and temporal patterns of E. multilocularis infection in coyotes and rodent intermediate hosts within the city of Calgary, Canada, and the association between spatial variations in coyote infection and the relative composition of small mammal assemblages. Infection by E. multilocularis was examined in small mammals and coyote faeces collected monthly in five city parks from June 2012 to June 2013. Coyote faeces were analysed using a ZnCl2 centrifugation and sedimentation protocol. Infection in intermediate hosts was assessed through lethal trapping and post-mortem analysis. Parasite eggs and metacestodes were morphologically identified and molecularly confirmed through species-specific PCR assays. Of 982 small mammals captured, infection was detected in 2/305 (0.66%) deer mice (Peromyscus maniculatus), 2/267 (0.75%) meadow voles (Microtus pennsylvanicus), and 1/71 (1.41%) southern red backed voles (Myodes gapperi). Overall faecal prevalence in coyotes was 21.42% (n=385) and varied across sites, ranging from 5.34% to 61.48%. Differences in coyote faecal prevalence across sites were consistent with local variations in the relative abundance of intermediate hosts within the small mammal assemblages. Infections peaked in intermediate hosts during autumn (0.68%) and winter (3.33%), and in coyotes during spring (43.47%). Peaks of infections in coyote faeces up to 83.8% in autumn were detected in a hyper-endemic area. To the best of our knowledge, our findings represent the first evidence of a sylvatic life-cycle of E. multilocularis in a North American urban setting, and provide new insights into the complexity of the parasite transmission ecology.

Alaria alata mesocercariae in raccoons (Procyon lotor) in Germany

Alaria alata is a trematode of carnivores from Europe. The mesocercarial stage was recently identified in wild boar meat from Europe. Previous histopathologic studies showed the presence of unidentified parasitic cysts within the tongues of raccoons from northern Germany. For identification of the parasite species, tissue samples of 105 raccoons originating from a National Park in northern Germany and from Berlin metropolitan area were collected. Histological examination of cryotome sections of frozen as well as paraffin-embedded tongues were used to identify parasite cysts. These were located in the connective and adipose tissue and in close proximity to small arterioles, suggesting a hematogenous spread of the parasite. Often, cysts were surrounded with mild infiltration by inflammatory cells. Additionally, mesocercariae were isolated from defrosted tongue samples of 11 raccoons. Molecular-biology assays confirmed the parasite species as A. alata. Except for one positive raccoon from Berlin City, all other positive raccoons originated from the sylvan Müritz National park, indicating an abundance of intermediate hosts in this area. Our results show that raccoons can act as paratenic hosts for A. alata and extend the broad host range of this parasite to a species introduced into Germany.

Disease Prevention Strategies for QX Disease (Marteilia sydneyi) of Sydney Rock Oysters (Saccostrea glomerata)

The Sydney rock oyster (Saccostrea glomerata) forms the basis of an important aquaculture industry on the east coast of Australia. During the 1970s, production of S. glomerata began to decline, in part as a result of mortalities arising from Queensland unknown (QX) disease. Histological studies implicated the paramyxean parasite Marteilia sydneyi in the disease outbreaks. Disease zoning was implemented to prevent the spread of M. sydneyi-infected oysters. This control measure hindered rock oyster farming, which historically has relied on transferring wild-caught spat between estuaries for on-growing to market size and has not prevented the subsequent occurrence of QX disease in the Georges and Hawkesbury rivers in central New South Wales. Management of QX disease has been hampered by the complicated life cycle of M. sydneyi, with outbreaks of QX disease likely to be regulated by a combination of the abundance of intermediate host of M. sydneyi, environmental stressors, and the immunocompetence of S. glomerata. The future of the Sydney rock oyster industry relies on understanding these factors and progressing the industry from relying on farming wild-caught seed to the successful commercialization of hatchery-produced QX-resistant S. glomerata.

Intestinal parasites of the Arctic fox in relation to the abundance and distribution of intermediate hosts

The intestinal parasite community of Arctic foxes (Vulpes lagopus) on the Svalbard archipelago in the High Arctic was investigated in relation to the abundance and distribution of intermediate hosts. Five species of cestodes (Echinococcus multilocularis, Taenia crassiceps, Taenia polyacantha, Taenia krabbei and Diphyllobothrium sp.), ascaridoid nematodes and one unidentified acanthocephalan species were found. The cestodes E. multilocularis, T. crassiceps and T. polyacantha all showed a decreasing prevalence in the fox population with increasing distance from their spatially restricted intermediate host population of sibling voles (Microtus levis). In addition, the prevalence of E. multilocularis in a sample from the vole population was directly related to the local vole abundance. The cestode T. krabbei uses reindeer as intermediate host, and its prevalence in female foxes was positively related to the density of reindeer (Rangifer tarandus platyrhyncus). Finally, the prevalence of the ascaridoid nematodes also decreased with increasing distance from the vole population, a finding that is consistent with the idea that voles are involved in transmission, most likely as paratenic hosts. The prevalence of the remaining species (Diphyllobothrium sp. and an unidentified acanthocephalan) was very low. We conclude that the distribution and abundance of intermediate host structure the gastrointestinal parasite community of the Arctic fox on the Svalbard archipelago.

The Prevalence of Cestodes in Raccoons (Procyon lotor) from North-Central Texas

Over 9 mo, 2,280 cestodes were collected and identified from 35 raccoons (Procyon lotor) in Archer and Wichita counties of north-central Texas. Overall prevalence of total cestode species was 71.4%. Three taxa of tapeworms were identified, including Atriotaenia procyonis, Mesocestoides sp., and immature Taenia pisiformis. This is the first record of the genus Taenia from P. lotor in North America. Atriotaenia procyonis was the most prevalent cestode, comprising 86.9% of all cestodes found in P. lotor. The number and species of cestodes found were compared by host sex, weight, age, and season of capture. Season of capture played an important role in the total number and species of cestodes isolated from the hosts, with the winter season having significantly lower counts than summer. Mesocestoides sp. was most abundant in spring and winter, whereas A. procyonis was most abundant in summer, although mixed infections were apparent. Host weight and sex played no significant role in the number or species of cestodes found. Host age class played no significant role in total cestode or in A. procyonis counts but was marginally significant regarding Mesocestoides sp. counts. The seasonal differences in number of A. procyonis and Mesocestoides sp. is likely due to seasonal fluctuation in intermediate host abundance and may reflect the seasonal shifting of foraging habits of raccoons in north-central Texas.

Parasites of the endangered Cantabrian capercaillie (Tetrao urogallus cantabricus): correlates with host abundance and lek site characteristics

In April 2000, we collected and analyzed for parasites 174 feces belonging to 48 different and identified Cantabrian capercaillies (Tetrao urogallus cantabricus) from 39 lek sites in the Cantabrian Mountains (North Spain) and determined the factors related with prevalence and abundance of propagule excretion: (1) interrelations with other parasite species, (2) characteristics of the capercaillie population (number of capercaillies in the lek site, number of occupied lek sites in a 2-km area, and abundance trend), and (3) characteristics of the lek site (orientation and altitude). The higher prevalence was observed for Eimeria sp. oocysts (29% of feces). Capillaria-like eggs were the most frequently detected among nematodes (9%). Excretion of Heterakis sp., Ascaridia sp., and Trichostrongylus sp. eggs was low. The presence of Capillaria propagules in feces was negatively related with those of Eimeria and Heterakis. This could be explained by differences in parasite transmission and capercaillie exposure because Eimeria and Heterakis have direct life cycle, whereas subfamily Capillariinae includes many heteroxenous species. Capillaria eggs were more prevalent in lek sites at lower altitude, which could be explained by altitude-related factors such as humidity, temperature, or soil characteristics that may affect intermediate host abundance. Although no relation was found with host abundance, the low parasite species diversity, prevalence, and abundance may indirectly reflect the decline of the Cantabrian capercaillie populations.

Plasticity of predation behaviour as a putative driving force for parasite life‐cycle dynamics: the case of urban foxes andEchinococcus multilocularistapeworm

SummaryParasite transmission frequently depends on an intermediate host species being subject to predation by a definitive host. We hypothesized that the population dynamics of this type of parasite would be affected by plasticity of the predation behaviour of the final host.The zoonotic tapewormEchinococcus multilocularisLeuckart is transmitted to foxes (Vulpes vulpesL.) by predation on infected rodents. One possible mechanism underlying the significant decrease in the prevalence ofE. multilocularisin red foxes observed towards the centre of Zurich (Switzerland) is that the relative abundance of intermediate hosts varies between different urbanized habitats.The water vole,Arvicola terrestris schermanL., which is the major intermediate host, was less abundant in urban compared with peri‐urban areas, due to both a reduced availability of suitable habitats and lower numbers within those habitats. Stomach content analyses indicated that foxes in urban areas consumed more anthropogenic food but preyed less frequently on rodents – and those rodents taken belonged to species less susceptible toE. multilocularisinfection.We conclude that the functional response of final hosts to changes in supply of intermediate hosts and alternative food sources can significantly affect the transmission dynamic of dixenous parasites, such as this zoonotic tapeworm.

Occurrence of intermediate hosts and structure of digenean communities of the black-headed gull, Larus ridibundus (L.).

The factors contributing to the similarity between digenean parasite assemblages parasitizing the black-headed gull were investigated. Thirteen different digenean species from the digestive tract and the bursa of Fabricus were found. We predicted that the structure of parasite communities is not random at either component community or infracommunity levels. We searched for nested patterns in the digenean community, and explored the possible factors contributing to nestedness. We found that digenean species which occupy a narrow range of intermediate hosts are placed out of order in the nested matrix. The influence of several variables related to the water reservoir, geographical distances, and the abundance of intermediate hosts on the species diversity and similarity of parasite communities were tested as well. Because of the complexity in bird digenean life-cycles we supposed that intermediate hosts and ecological characters of their environment could play a major role. We showed that the presence of intermediate hosts is the factor limiting the qualitative and quantitative similarity of parasite communities among different host populations as well as influencing the digenean species diversity in the definitive host. The similarity in abundance of intermediate hosts between different localities was facilitated by the presence of vegetation in water reservoir and more diversified type of water bottom. Digenean species diversity was higher when the water reservoir was exposed to temporal drying. We hypothesized that this factor could facilitate the inclusion of molluscs infected by digeneans in the diet of birds. Both species diversity and dominance were influenced by the bottom type of water reservoir and temporal drying up. Geographical distances between localities influenced the quantitative similarity of digenean communities as well as species richness.

Eel parasite diversity and intermediate host abundance in the River Rhine, Germany.

European eels (Anguilla anguilla) from 2 sampling sites on the Rhine river (near Karlsruhe and near Worms) were investigated with respect to their parasite communities. Nine different metazoan species were found to live in and on the eels. The highest number of species was recorded from the intestine, which contained up to 6 different helminths. Among these, acanthocephalans were the most prevalent worms with the eel-specific parasite Paratenuisentis ambiguus as the dominant species of the intestinal component communities at both sites. Comparing the intestinal parasites from eels caught near Karlsruhe with those from Worms, the acanthocephalans showed a significantly lower abundance at Worms. A significantly lower mean number of intestinal helminth species as well as a significantly lower Brillouin's Index was found at Worms compared with Karlsruhe. This difference could be related to the abundance of the respective intermediate crustacean hosts. At the sampling site Worms the amphipod Corophium curvispinum was the dominant crustacean. Additionally, only the isopod Jaera istri and the amphipod Dikerogammarus villosus were found. All these crustacean species have only recently colonized the Rhine river system via the Main-Danube canal, built in the early 1990s. They are not known to act as intermediate hosts for any of the acanthocephalans found in the eels. The site near Karlsruhe exhibited a higher crustacean diversity, including Asellus aquaticus and different species of the genus Gammarus, which are all known intermediate hosts for the acanthocephalans found. Therefore, changes of eel parasite diversity can be correlated with the appearance of invading crustacean species (neozoans).

How environmental stress affects the impacts of parasites

Parasites occur in nearly every population. They often interact in complex ways with other stressors. In some cases, the interaction may lead to a disproportionately negative effect on the host population. In other cases, the stressor may ameliorate the effects of parasitism. Here we illustrate intersections of four types of environmental stressors with infectious diseases. First, pollutants may increase parasitism by increasing host susceptibility or by increasing the abundance of intermediate hosts and vectors. Pollutants can also decrease parasitism if infected hosts suffer differentially high mortality, parasites are more susceptible to pollution than their hosts, or if pollutants negatively affect intermediate hosts or vectors. These effects vary depending on the particular parasite and pollutant that interact. Second, habitat alterations such as impounding water or development can affect both intermediate host and vector populations such that the abundance of their attendant parasites is either increased or reduced. Third, fisheries can impact populations already stressed by disease. However, they may act to lower the density of a host population below the threshold for sustained transmission to such an extent that the parasite population can no longer persist. Fourth, introduced species may introduce new diseases to susceptible native populations or they may gain an advantage if they invade without the parasites from their native range. The complexity and ubiquity of these interactions are good arguments for considering parasitism when evaluating stressors of aquatic systems.

A population study of cod, Gadus morhua L., in northern Norway using otolith structure and parasite tags

A total of 502 cod, Gadus morhua L., was taken during spring and autumn sampling from three different localities in northern Norway: the Barents Sea, a silled fjord (Balsfjord) and an open fjord (Malangen). Each cod was allocated, according to its otolith structure, to one of two types, coastal or Arcto-Norwegian, and was then examined for infections of four species of parasite: the myxosporeans Myxidium oviforme and Zschokkella hildae, the digenean Hemiurus levinseni, and the copepod Lernaeocera branchialis. Both types of cod were present at each locality, with coastal cod dominating in the fjords in both seasons and in the Barents Sea in spring, but with Arcto-Norwegian cod dominating in the Barents Sea in autumn. Differences in the proportions of the two types of cod and in parasite prevalences between seasons and localities were interpreted as indicating a migration of coastal cod from the Barents Sea sampling area into the fjords between March and October. We found no evidence that Arcto-Norwegian cod from the Barents Sea migrate into the fjords, but our results suggest that the fjords contain local resident populations of Arcto-Norwegian cod. It is concluded that local parasite faunas are not greatly influenced by genetic differences between the two types of cod, but that their compositions are determined largely by variations in the abundance of intermediate hosts.