Availability Of Intermediate Hosts Research Articles

Host weight, seasonality and anthropogenic factors contribute to parasite community differences between urban and rural foxes

Pathogens often occur at different prevalence along environmental gradients. This is of particular importance for gradients of anthropogenic impact such as rural-urban transitions presenting a changing interface between humans and wildlife. The assembly of parasite communities is affected by both the external environmental conditions and individual host characteristics. Hosts with low body weight (smaller individuals or animals with poor body condition) might be more susceptible to infection. Furthermore, parasites' mode of transmission might affect their occurrence: rural environments with better availability of intermediate hosts might favour trophic transmission, while urban environments, typically with dense definitive host populations, might favour direct transmission. We here study helminth communities (141 intestinal samples) within the red fox (Vulpes vulpes), a synanthropic host, using DNA metabarcoding of multiple marker genes. We analysed the effect of urbanisation, seasonality and host-intrinsic (weight, sex) variables on helminth communities. Helminth species richness increased in foxes with lower body weight and in winter and spring. Season and urbanisation, however, had strong effects on the community composition, i.e., on the identity of the detected species. Surprisingly, transmission in two-host life cycles (trophic transmission) was more pronounced in urban Berlin than in rural Brandenburg. This disagrees with the prevailing hypothesis that trophically transmitted helminths are less prevalent in urban areas than in rural areas. Generally, co-infestations with multiple helminths and high infection intensity are associated with lighter (younger, smaller or low body condition) animals. Both host-intrinsic traits and environmental drivers together shape parasite community composition and turnover along urban-rural gradients.

Temporal variation in helminth infracommunities of the Gafftopsail pompano, Trachinotus rhodopus (Pisces: Carangidae) off the Pacific coast of Mexico.

Temporal variation of the helminth infracommunity structure in the Gafftopsail pompano Trachinotus rhodopus was studied during bi-monthly revisions of samples collected offshore from Puerto Ángel, Oaxaca (Mexican Pacific) in 2018. In total, 110 specimens of T. rhodopus were subjected to a parasitic review. Helminths found were identified to the lowest possible taxonomic level (six species and three genera) by means of morphological and molecular data. Attributes of the helminth infracommunities are described through statistical analyses, showing stability in terms of their richness throughout the year. However, variations were found in helminth abundance related to the seasonality of samplings, which may be associated with the life cycles of the parasites, the host species' gregarious behavior, the availability of intermediate hosts, and/or the diet of T. rhodopus.

SEASONAL VARIATION IN THE PREVALENCE, ABUNDANCE, AND MEAN INTENSITY OF ACANTHOCEPHALA INFECTING SNAKE HEADED FISH, Channa punctatus (BLOCH 1793) IN HOOGHLY DISTRICT, WEST BENGAL, INDIA

The seasonal variation of acanthocephalan parasite Pallisentis sp. infecting Channa punctatus (Bloch 1793) was studied over a period of two years from June 2017- May 2019. The sampling of host fish was done from local fish markets of different regions of the Hooghly district. The prevalence, mean intensity, and abundance of infection were studied and statistically verified. A total of 300 fishes were examined, out of which 141 fishes were found to be infected with acanthocephalan parasites. The infection was higher during the pre-monsoon season, moderate during monsoon, and lower during the post-monsoon season. Availability of Pallisentis sp. was found to be affected by biotic factors like the feeding habit of host fish, availability of intermediate hosts i.e. arthropods, and also abiotic factors (temperature, relative humidity, rainfall, etc).

Prevalence of Fox Tapeworm in Invasive Muskrats in Flanders (North Belgium).

Simple SummaryFox tapeworms are pathogens that need two hosts to complete their life cycle. The reproductive part of the cycle takes place in foxes and the intermediate step usually occurs in rodents. Muskrats can also act as the intermediate host for fox tapeworms. This increases the total number of potential hosts which can also increase the number of pathogens in the environment. In Belgium, where muskrats are non-native, this is one of the ways in which an invasive alien species can have a negative effect on its new environment. From 2009 to 2017 all muskrats caught in Flanders and across the border with Wallonia and France were collected and dissected to estimate how often they were infected with fox tapeworms. Visual examination of the livers of 15,402 muskrats revealed 202 infected animals (1.31%). In Flanders, we found 82 infected animals out of 9421 (0.87%). The percentage of infected animals did not increase during the research period. All the infected animals in Flanders were found in municipalities along the Walloon border. We did not observe a northward spread of EM infection from Wallonia to Flanders.One way in which invasive alien species affect their environment is by acting as pathogen hosts. Pathogens limited by the availability of the native host species can profit from the presence of additional hosts. The muskrat (Ondatra zibethicus) is known to act as an intermediate host for the fox tapeworm (Echinococcus multilocularis). From 2009 to 2017, 15,402 muskrats caught in Flanders and across the border with Wallonia and France were collected and dissected with the aim of understanding the prevalence of this parasite in muskrats. Visual examination of the livers revealed 202 infected animals (1.31%). Out of the 9421 animals caught in Flanders, we found 82 individuals (0.87%) infected with E. multilocularis. No increase in prevalence was observed during this study. All of the infected animals in Flanders were found in municipalities along the Walloon border. We did not observe a northward spread of E. multilocularis infection from Wallonia to Flanders. We hypothesise that the low prevalence is the result of the reduced availability of intermediate hosts and the successful control programme which is keeping muskrat densities in the centre of the region at low levels and is preventing influx from other areas. Our results illustrate that muskrats are good sentinels for E. multilocularis and regular screening can gain valuable insight into the spread of this zoonosis.

Trophic ecology shapes gastrointestinal helminth communities of two sympatric mesopredatory sharks in the Adriatic Sea

AbstractWe investigated and compared the structure of parasite communities in two sympatric, commercially exploited sharks. We analysed 188 gastrointestinal tracts from a crustacean feeder Mustelus punctulatus and 157 gastrointestinal tracts from a piscivorous Squalus acanthias. The overall prevalence of helminth parasites was very high (84.0%) for M. punctulatus with nematode Cucullanus micropapillatus as the most abundant species (mean abundance 13.96) and Anisakis spp. larvae as the most prevalent taxa (47.9%). In contrast, only 21.7% of S. acanthias specimens were infected, showing Anisakis spp. larvae as the most prevalent (17.8%) and abundant taxa (mean abundance 0.39). The subsample of Anisakis spp. larvae, isolated from both hosts, was molecularly identified at ITS locus as A. pegreffii. Significant variations among size classes were recorded for M. punctulatus, mainly as a consequence of higher C. micropapillatus loads in larger sharks. Seasonal patterns in prevalence and abundance of C. micropapillatus were recorded for M. punctulatus, with peaks in autumn, whereas Anisakis spp. larvae prevailed during spring, for both sharks. Sex contributed little to the observed parasite abundances, although female spiny dogfish were more prone to infections than males, and higher helminth diversity was recorded in females in both shark species. The differences in infection parameters between the two shark species likely reflect the variations in foraging strategies and availability of intermediate hosts. Our findings suggest that crustacean feeder M. punctulatus is more susceptible to helminth infections in the Adriatic Sea, which may affect the health status of local shark populations.

Trophic ecology, behaviour and host population dynamics in Echinococcus multilocularis transmission

The life cycle of the cestode Echinococcus multilocularis primarily involves canids and small mammals (rodents, lagomorphs) as definitive and intermediate hosts, respectively. Several surveys have identified marked temporal and geographical variations at different scales in the parasite’s prevalence in both types of hosts, suggesting variations in the biological and ecological factors that control transmission processes. The parasite transmission from intermediate to definitive hosts is determined by the predator–prey relationship, which theoretically depends on prey population dynamics and the complex dietary response of predators to varying densities of prey species and other food items. Parasite eggs are transmitted to intermediate hosts via carnivore faeces, whose distribution in the environment is driven by the defecating behaviour of final hosts. We reviewed field-based studies that address issues related to the trophic ecology and behaviour of definitive hosts, interactions between definitive and intermediate hosts, and E. multilocularis transmission both in wild and domestic animals in rural and urban environments. Two density-dependent mechanisms control the transmission dynamics in definitive hosts: one is based on the variations in the availability of intermediate hosts, and the other is based on the variations in the density of the definitive host and its faeces. Non-linearity and the direct and delayed responses of definitive host contamination in relation to intermediate host population variations were recorded. The dietary response of the red fox was shown to be complex when abundant alternative resources were available (anthropogenic food, multiple intermediate host prey species). Micro-local hotspots of parasite transmission to intermediate hosts in a landscape, as well as areas of higher risk for human contamination in village and urban settings, may be explained by the definitive hosts’ activity patterns and defecation behaviour.

Seasonal Influences on Parasite Community Structure ofTurdus rufiventris(Aves)

Seasonality has strong effects on natural systems by influencing resource availability, thereby interfering in plant-herbivore, prey-predator, and host-parasite interactions. We compared the seasonal structure of the helminth community of rufous-bellied thrushes (Turdus rufiventris), assessed its correlation with environmental variables, and interpreted temporal patterns of parasite abundance in relation to their life cycles and likely changes in the availability of intermediate hosts and vectors. Fifteen helminth species were found in a sample of 151 thrushes collected on a seasonal basis over 3 yr. Infracommunity structure was affected by season and year. The ordination of component communities grouped fall and winter samples within a gradient of similarity that was correlated with average relative air humidity (RH) and average ambient temperature. RH (alone or in combination with temperature, rainfall, or both) was also found to be a good predictor of the abundance of 5 helminth species.

Transmission dynamics of Toxoplasma gondii along an urban–rural gradient

Recently, several authors have proposed that the availability of intermediate hosts (IHs) for definitive hosts (DHs) may contribute to determining the dynamics and evolutionary ecology of parasites with facultative complex life cycles. The protozoa Toxoplasma gondii may be transmitted to DHs either via predation of infected IHs through a complex life cycle (CLC) or directly from a contaminated environment through a simple life cycle (SLC). This parasite is also present in contrasting host density environments. We tested the hypothesis that the relative contributions of the CLC and SLC along an urban–rural gradient depend on the IH supply. We built and analysed a deterministic model of the T. gondii transmission cycle. The SLC relative contribution is important only in urban-type environments, i.e., with low predation rate on IHs. In contrast, the parasite is predominantly transmitted through a CLC in suburban and rural environments. The association of the two cycles enables the parasite to spread in situations of low IH availability and low DH population size for which each cycle alone is insufficient.

Chemotherapy with praziquantel has the potential to reduce the prevalence of Echinococcus multilocularis in wild foxes (Vulpes vulpes).

In order to evaluate the applicability of anthelminthic treatment of wild foxes (Vulpes vulpes) to limit their infection with Echinococcus multilocularis, bait pellets, each containing 50 mg praziquantel, were repeatedly distributed in an area of 566 km2 where many foxes are infected, in southern Germany. After six baiting campaigns (15-20 baits/km2) over a period of 14 months, the prevalence of the cestode in foxes, initially 32%, had fallen to 4%. The effect was most pronounced in the central part of the treated area, where no positive fox was found in the 2 months before the end of the trial. The study was controlled for other factors that could influence the parasite's prevalence, such as the availability of intermediate hosts. While the potential of this baiting method to remove E. multilocularis from wild hosts has been demonstrated, the question of its long-term efficacy and other unresolved problems have to be addressed by consecutive studies before routine application can be recommended.

Distribution of some parasites of freshwater eels in New Zealand

Abstract Eight hundred and thirty nine short‐finned eels, Anguilla australis Richardson, 1848, and 459 long‐finned eels, A. dieffenbachii Gray, 1842, from the wild from 34 localities around New Zealand were examined for parasites. Thirty parasitic species were encountered, of which 26 were considered common and 4 accidental parasites of eels. Widespread and common were Myxidium zealandicum Hine, 1975, Myxobolus sp., Chloromyxum sp., Stegodex‐ amene anguillae Macfarlane, 1951, Telogaster opisthorchis Macfarlane, 1945, Phyllodistomum sp., Paracardicoloides yamagutii Martin, 1974, Cucullanus sp., Procamaflanus sp., and glochidia of Hyridella sp. Widespread but intermittent in distribution were Myxidium serum Hine, 1975, Myxidium acinum Hine, 1975, Paraquimperia sp., Hedruris spinigera Baylis, 1931, Eustrongy‐ lides sp., and Accmthocephalus galaxii Hine, 1977. Rarely encountred or limited in distribution were Thelohanellus sp., Henneguya sp., Coitocaecum anaspidis Hickman, 1934, Coito‐caecum zealandicum Hine, 1977. Anguillicola australiensis Johnston & Mawston, 1940, Ascaro‐phis sp., Paranisakis sp., Philometra sp., and Abergasilus amplexus Hewitt, 1978. No conclusions could be drawn on the occurrence or distribution of Trichodina sp. Deretrema minutum Manter, 1954, a hemiurid, a proteocephalid, and Neoechinorhynchus aldrichettae Edmonds, 1971 were rarely encountered and did not mature. Eels were considered to be unsuitable hosts for these parasites. Most parasite species were widespread in a variety of habitats, but Thelohanellus sp. was confined to streams on or near the coast in the southern North Island, Henneguya sp. to Lake Ellesmere, Hedruris spinigera, Acanthocephalus galaxii and Coitocaecum anaspidis to coastal areas, C. zealandicum to Wairarapa streams, and Abergasilus amplexus to Lake Ellesmere and one area of coastal rivers. Where possible distribution records were related to the need for and availability of intermediate hosts.

A comparison of the parasite fauna of young whiting, Odontogadus merlangus (L.) (Gadidae) from an inshore and an offshore location off the Isle of Man

The occurrence of 12 helminth and 4 crustacean parasites on young whiting 0–2 years old from an inshore (Port Erin Bay) and an offshore (off Bradda Head) area of the Isle of Man were compared. No parasites were found on whiting 4.5–15 mm long and the intestinal digenean Lecithaster gibbosus Rudolphi together with the larvae of the copepod Caligus rapax M. Edwards were the first parasites to appear in whiting 15–42 mm long. This appears to be the only time during the life history of the whiting that C. rapax is of importance as a parasite. In whiting 6 months‐2 years old from off Bradda Head such helminths as the acanthocephalan Echinorhynchus gadi Muller and the digeneans Podocotyle atomon Muller and Cryptocotyle lingua Creplin (metacercariae) were found in significantly fewer fish than in an equivalent group from Port Erin Bay. The differences are correlated with the availability of intermediate hosts and the different food spectra of the two groups of fish and are used to support the theory that inshore and offshore whiting of these age groups form separate populations and that the offshore fish may be more important than the inshore fish in replenishing stocks of older whiting.