Helminth Diversity Research Articles

Annotated checklist of fish cestodes from South America.

An exhaustive literature search supplemented by a critical examination of records made it possible to present an annotated checklist of tapeworms (Cestoda) that, as adults or larvae (metacestodes), parasitize freshwater, brackish water and marine fishes, i.e. cartilaginous and bony fishes, in South America. The current knowledge of their species diversity, host associations and geographical distribution is reviewed. Taxonomic problems are discussed based on a critical evaluation of the literature and information on DNA sequences of individual taxa is provided to facilitate future taxonomic and phylogenetic studies. As expected, the current knowledge is quite uneven regarding the number of taxa and host-associations reported from the principal river basins and marine ecoregions. These differences may not only reflect the actual cestode richness but may also be due to the research effort that has been devoted to unravelling the diversity of these endoparasitic helminths in individual countries. A total of 297 valid species, 61 taxa identified to the generic level, in addition to unidentified cestodes, were recorded from 401 species of fish hosts. Among the recognized cestode orders, 13 have been recorded in South America, with the Onchoproteocephalidea displaying the highest species richness, representing c. 50% of all species diversity. The majority of records include teleost fish hosts (79%) that harbour larval and adult stages of cestodes, whereas stingrays (Myliobatiformes) exhibit the highest proportion of records (39%) among the elasmobranch hosts. Fish cestodes are ubiquitous in South America, being mostly recorded from the Warm Temperate Southeastern Pacific (WTSP; 31%) for marine hosts and the Amazon River basin (45%) for freshwater ones. The following problems were detected during the compilation of literary data: (i) unreliability of many records; (ii) poor taxonomic resolution, i.e. identification made only to the genus or even family level; (iii) doubtful host identification; and (iv) the absence of voucher specimens that would enable us to verify identification. It is thus strongly recommended to always deposit representative specimens in any type of studies, including faunal surveys and ecological studies. An analysis of the proportion of three basic types of studies, i.e. surveys, taxonomic and ecological papers, has shown a considerable increase of ecological studies over the last decade.

A survey study on the helminth parasites of two wild jirds, Meriones shawi and M. libycus (Rodentia: Gerbillinae), in Tunisian desert areas

A parasitological survey of 107 jirds, belonging to two species, Meriones shawi and M. libycus, was carried out. Rodents were trapped in three separate desert regions of Tunisia: Bouhedma (in the centre), Dghoumes (in the southwest) and Sidi Toui (in the southeast). The survey revealed infection with nine helminth species – six cestodes: Raillietina sp., Meggittina numida, Meggittina gerbilli and Inermicapsifer madagascariensis, and two Taeniidae species: Taenia endothoracicus and Taenia sp.; and three nematodes: Gongylonema neoplasticum, Physaloptera sp. and Trichuris gerbilli. The overall prevalence of helminth infection was 68.22% (73/107); the highest rate was in M. shawi (80.82%, 59 cases), whereas it was 41.17% (14 cases) in M. libycus. The most frequent helminth was Raillietina sp. (53.27%) followed by Meggittina numida (21.5%). Meriones shawi showed the highest helminth diversity with eight parasite species, with synchronous infections of two, three and four species of helminths in one rodent, compared to M. libycus in which only two cestode species were found, without synchronous infection. Moreover, significant differences in the overall infection prevalence between sexes (60.27 and 39.73% for males and females, respectively) and age were detected; only one juvenile specimen of M. shawi was found infected. Prevalence depended also on habitat: the highest infection rate was in Bouhedma (80%), followed by Dghoumes (58.33%), and the lowest was in Sidi Toui (47.82%).

Nematodes associated with Iguana iguana (Linnaeus, 1758) (Squamata, Iguanidae) in Semi-arid areas of Northeastern Brazil.

Nematodes were analyzed in Iguana iguana, a large lizard Iguanidae that is widely distributed throughout the Americas. The aims of the study were investigate the helminths associated with the lizard, I. iguana in semi-arid areas of northeastern Brazil and analyze the parasitological indices (prevalence, and mean intensity of infection). A total of 18 specimens of I. iguana were examined (8 males and 10 females). The overall prevalence of infection was 66.6% (12/18), while in males, it was 75% (6/8) and in females, 60% (6/10). Iguana iguana was identified as a new host for Physaloptera sp., Atractis sp., Piratuba sp. and Subulura sp. This registered contributes to the knowledge of helminth diversity associated with this host.

Multiparasitism in a wild cat (Leopardus colocolo) (Carnivora: Felidae) in southern Brazil.

Parasitic diseases reflect the health and balance of ecosystems, affecting not only individuals but also entire populations or communities. The aim of this study was to report on the diversity of parasitic helminths detected in the feces of a wild feline in southern Brazil. Parasites were obtained from fecal samples, and four techniques were used for parasitological examination: direct examination, centrifugal flotation with zinc sulfate (Faust technique), simple sedimentation (Hoffman technique) and Baermann-Moraes. The parasites were identified through micrometry and morphology, as follows: Ancylostoma sp., Toxocara sp., Trichuridae, Aelurostrongylus abstrusus, Alaria sp., and Spirometra sp. We recorded the genus Ancylostoma parasitizing L. colocolo for the first time.

Influence of Massive and Long Distance Migration on Parasite Epidemiology: Lessons from the Great Wildebeest Migration.

Very little is known about the influence of massive and long distance migration on parasite epidemiology. Migration can simultaneously minimize exposure to common parasites in their habitats and increase exposure to novel pathogens from new environments and habitats encountered during migration, while physiological stress during long distance movement can lead to immune suppression, which makes migrants vulnerable to parasites. In this paper, we investigated the diversity, prevalence, parasite load, co-infection patterns and predilection sites of adult gastrointestinal helminths in 130 migrating wildebeests and tested for their relation with animal age, sex and migration time (which also could indicate different migration routes), and compared them with the non-migratory wildebeest. Surprisingly, only four parasite species were found, Oesophagostomum columbianum, Haemonchus placei, Calicophoron raja and Moniezia expansa, which were lower than in non-migratory wildebeest reported in the literature. These parasites were generalists, infecting livestock, and suggests that wildebeest and livestock, because of their interaction during migration, have a cross-infection risk. There was a negative relation between parasites diversity, prevalence and intensity of infection, and host age, which suggests that wildebeests acquire protective immunity against these parasites as they get older. Prevalence and intensity of infection were higher among wildebeest crossing the Mara Bridge (early migrants) compared to those crossing the Serena (late migrants), which suggests that early migrants (or migrants originating from different areas) have varying infection intensities. The prevalence and intensity of infection were higher in males compared to females and may be due to ecological, behavioural, or physiological differences between males and females. Our findings compared to those of previous studies suggest that migration may provide a mechanism to minimize exposure of hosts to common parasites through migratory escape, but this result awaits examination of helminths epidemiology of non-migratory wildebeests from areas of migrant origins. The potential parasitic cross-infection between wildebeests and livestock is a real risk to be taken into account in the management of wildebeest migration corridors.

Diversity of helminth parasites in aquatic invertebrate hosts in Latin America: how much do we know?

Helminths in aquatic invertebrate hosts have been overlooked in comparison with vertebrate hosts. Therefore, the known diversity, ecology and distribution of these host-parasite systems are very limited in terms of their taxonomic diversity, habitat and geographic regions. In this study we examined the published literature on helminth parasites of aquatic invertebrates from Latin America and the Caribbean (LAC) to identify the state of the knowledge in the region and to identify patterns of helminth diversity. Results showed that 67% of the literature is from Argentina, Mexico and Brazil. We found records for 772 host-parasite associations. Most records relate to medically or economically important hosts. Molluscs were the most studied host group with 377 helminth records (80% trematodes). The lymnaeids and planorbids were the most studied molluscs across LAC. Arthropods were the second most studied host group with 78 helminth records (trematodes 38%, cestodes 24% and nematodes 20%), with shrimps and crabs being the most studied hosts. Host species with the largest number of helminth taxa were those with a larger sampling effort through time, usually in a small country region. No large geographical-scale studies were identified. In general, the knowledge is still too scarce to allow any zoogeographical or helminth diversity generalization, as most hosts have been studied locally and the studies on invertebrate hosts in LAC are substantially uneven among countries.

Spatiotemporal distributions of intestinal helminths in female lesser scaup Aythya affinis during spring migration from the upper Midwest, USA.

We examined the associations between intestinal helminth infracommunity structure and infection parameters and the age, size, and year and region of collection of 130 female lesser scaup (Aythya affinis) during their 2014-2015 spring migrations through the upper Midwest, USA. We identified a total of 647,174 individual helminths from 40 taxa, including 20 trematodes, 14 cestodes, 4 nematodes and 2 acanthocephalans parasitizing lesser scaup within the study area. Lesser scaup were each infected with 2-23 helminth taxa. One digenean, Plenosoma minimum, is reported for the first time in lesser scaup and in the Midwest. Mean trematode abundance and total helminth abundance was significantly less in 2015 than 2014, and we suspect that colder weather late in 2015 impacted the intermediate host fauna and caused the observed differences. Brillouin's species diversity of helminths was greatest in the northernmost region of the study area, which coincides with the range of a non-indigenous snail that indirectly causes annual mortality events of lesser scaup. While host age and size were not determined to be influential factors of helminth infracommunity structure, non-parametric ordination and permutational analysis of co-variance revealed that year and region of collection explained differences in helminth infracommunities. Our results suggest that spatiotemporal variations play an important role in the structure of intestinal helminth infracommunities found in migrating lesser scaup hosts, and may therefore impact host ability to build endogenous reserves at certain stopover locations in the Midwest.

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.

Ecological analysis of helminths in vendace and smelt from lake Onego

The parasite fauna of LakeOnegocommercial fish species – vendace, Coregonus albula L., and smelt, Osmerus eperlanus L., was studied. The prevalence, abundance distribution and age structure of the cestode Proteocephalus longicollis (Zeder, 1800) in vendace were determined. Seasonal variations of Eubothrium crassum (Bloch, 1779) infection in vendace were traced, and the role of vendace in the life cycle of this cestode was identified. A comparative analysis of long-term changes in the parasite fauna of vendace and smelt was carried out. The species diversity of helminths and its structure proved to be relatively stable. Changes were mainly observed in the intensity of infection. These results suggest that the two major plankton-feeders, vendace and smelt, quite successfully coinhabitLakeOnego.

Molecular Phylogenetic Analysis of Infidum similis, Including Morphological Data and Estimation of its Genome Size.

: Infidum similis Travassos, 1916 (Dicrocoeliidae: Leipertrematinae) was found in the gall bladder of Leptophis diplotropis Günther, 1872 from El Podrido, Acapulco, Guerrero, Mexico. A phylogenetic analysis based on partial sequences of the 28S ribosomal RNA using maximum likelihood (ML) and Bayesian inference (BI) analyses was carried out to assess its phylogenetic position within suborder Xiphidiata, alongside members of the superfamilies Gorgoderoidea and Plagiorchoidea. The phylogenetic trees showed that the genus is most-closely related to the Plagiorchoidea rather than to the Gorgoderoidea, in keeping with previous taxonomic designations. Phylogenies obtained from ML and BI analysis of the 28S rDNA gene revealed a well supported clade in which Choledocystus hepaticus (Lutz, 1928) Sullivan, 1977 is sister to I. similis. On the other hand, a tree obtained using a partial sequence of the cytochrome c oxidase subunit 1 (cox1) mtDNA gene (ML and BI analysis), with species supposed to be closely related to I. similis according to 28S, does not support this relatedness. Based on the independence of Infidum from the subfamily Leipertrematinae Yamaguti, 1958 , our results clearly demonstrated that the genus corresponds to a different family and with species closely related to C. hepaticus within Plagiorchoidea. New data are presented about the tegumental surface of I. similis by scanning electron microscopy as well as the estimation of its haploid genome size using Feulgen Image Analysis Densitometry of sperm nuclei as part of the characterization of this species. This is the first genome size estimated for a member of Plagiorchiida, and these data will provide a new source of knowledge on helminth diversity and evolutionary studies. This constitutes the first host record, and new geographical distribution, for this species in Mexico.

Interactions between multiple helminths and the gut microbiota in wild rodents

The gut microbiota is vital to host health and, as such, it is important to elucidate the mechanisms altering its composition and diversity. Intestinal helminths are host immunomodulators and have evolved both temporally and spatially in close association with the gut microbiota, resulting in potential mechanistic interplay. Host–helminth and host–microbiota interactions are comparatively well-examined, unlike microbiota–helminth relationships, which typically focus on experimental infection with a single helminth species in laboratory animals. Here, in addition to a review of the literature on helminth–microbiota interactions, we examined empirically the association between microbiota diversity and composition and natural infection of multiple helminth species in wild mice (Apodemus flavicollis), using 16S rRNA gene catalogues (metataxonomics). In general, helminth presence is linked with high microbiota diversity, which may confer health benefits to the host. Within our wild rodent system variation in the composition and abundance of gut microbial taxa associated with helminths was specific to each helminth species and occurred both up- and downstream of a given helminth's niche (gut position). The most pronounced helminth–microbiota association was between the presence of tapeworms in the small intestine and increased S24–7 (Bacteroidetes) family in the stomach. Helminths clearly have the potential to alter gut homeostasis. Free-living rodents with a diverse helminth community offer a useful model system that enables both correlative (this study) and manipulative inference to elucidate helminth–microbiota interactions.

Helminths of saiga antelope (Saiga tatarica L.) in the “Askania Nova” Biosphere Reserve, Ukraine

Abstract Analysis of the species composition and community structure of helminths in saiga antelope (Saiga tatarica) was performed using multi-year (1979-2013) data collected from the “Askania Nova” Biosphere Reserve, Ukraine. During this period, 31 saiga antelopes of different ages (7 calves, 24 adults) were examined; totally, more then 63,900 helminth specimens were collected and identified by morphological criteria. Levels of saiga infection by nematodes were from 39 to 671 EPG (207±132 SD); seasonal fluctuations in saiga infections were insignificant (Mann-Whitney test; p>0.05). Nineteen helminth species were found in saigas in the “Askania Nova”: 3 species of Cestoda (Avitellina centripunctata, Moniezia expansa and Taenia hydatigena) and 16 species of Nematoda (Chabertia ovina, Haemonchus contortus, Marshallagia marshalli, Cooperia oncophora, Camelostrongylus mentulatus, Aonchotheca bovis, Skrjabinema ovis, Oesophagostomum venulosum, Trichostrongylus axei, T. colubriformis, T. probolorus, Ostertagia ostertagi, O. circumcincta, O. trifurcata, Nematodirus spp., Trichurus ovis). From 2 to 13 species per one host were observed. Nematodes dominated within the parasite community and composed more then 99 % of the total helminths found. Significant differences were found in helminth diversity between young and adult saigas (p<0.05). Prevalence- frequency distribution revealed multimodal structure of helminth community with dominant, subdominant, background and rare species. The highest number of helminthes (14 species and 50 % of the total amount) inhabited the small intestine; 11 species (45 %) were found in the abomasum and 9 species (5 %) in the large intestine. The Bray-Curtis cluster analysis revealed significant differences within the helminth communities in saigas from the “Askania Nova” Biosphere Reserve and saigas from Kazakhstan, Dagestan and Kalmykia.

Host specificity and seasonality of helminth component communities in central European grebes (Podicipediformes) and loons (Gaviiformes)

Structure and pattern of helminth component communities parasitizing grebes and loons are poorly understood. Here we analyze the prevalence, intensity and diversity of helminths in 505 Czech grebes (Podiceps cristatus, Podiceps nigricollis, Tachybaptus ruficollis) and loons (Gavia arctica, Gavia stellata) collected between 1962 and 2014. The species richness of helminth component communities ranged from 31±8 (P. cristatus) to 50±4 (G. stellata) species, with helminth load similar in all five host species, but with strong differences in prevalence and intensity of infection at a helminth species-specific level. The dominance was low, ranging from 0.11 (P. cristatus and G. stellata) to 0.21 (P. nigricollis). Dominant species (>25% prevalence) in P. cristatus were Confluaria sp., Tylodelphys clavata, Echinochasmus coaxatus, Petasiger neocomense and Ligula colymbi; in P. nigricollis and T. ruficollis: Confluaria sp. and Tatria sp.; in G. arctica and G. stellata: Tetrabothrius microcephalus, Stephanoprora denticulata, Cryptocotyle concava, Diplostomum gavium and Ichthyocotylurus erraticus; in G. stellata only: Echinochasmus (Monilifer) spinulosus. Four (12%) of the grebe digenean species were not locally acquired (with non-sympatric intermediate hosts) despite the fact that they represented 25% of digenean individuals found. In loons, five (28%) of digenean species and striking 38% of individuals found used the non-sympatric intermediate host species. Component communities of grebes were similar to each other (Sørensen similarity index 0.47–0.65) but differed strongly from those hosted by loons (0.00–0.20). We present the first systematically collected evidence of intra-annual changes of helminth component communities in grebes, and provide 20 new host records.

Helminth infestation of the moor frog (Rana arvalis Nilsson, 1842) and the Siberian tree frog (Rana amurensis Boulenger, 1886) in Western Siberia

The composition of helminths and infestation indices of two frog species of living in Western Siberia (Rana arvalis (n = 1082) and Rana amurensis (n = 33)) have been studied. Nine helminth species, including four nematodes and five trematodes, have been found. The following species were dominant and infected both frog species: nematodes Rhabdias bufonis, Oswaldocruzia filiformis, and Cosmocerca ornata and trematodes Haplometra cylindracea. The moor frog also hosted Dolichosaccus rastellus, Opisthioglyphe ranae, Pharingostomum cordatum (larvae), Parastrigea robusta (larvae), and Neyraplectana schneideri. The moor frog was characterized by higher species richness and diversity of helminths than the Siberian tree frog. The overall rates of helminth infestation have been the same in the moor frog and the Siberian tree frog. The invasion extensity was 85–100%; the index of abundance was 5.2–27.5. Differences in infestation rates of certain species by helminths were due to the biological peculiarities of the frog species.

Helminth species richness of introduced and native grey mullets (Teleostei: Mugilidae)

Quantitative complex analyses of parasite communities of invaders across different native and introduced populations are largely lacking. The present study provides a comparative analysis of species richness of helminth parasites in native and invasive populations of grey mullets. The local species richness differed between regions and host species, but did not differ when compared with invasive and native hosts. The size of parasite assemblages of endohelminths was higher in the Mediterranean and Azov–Black Seas, while monogeneans were the most diverse in the Sea of Japan. The helminth diversity was apparently higher in the introduced population of Liza haematocheilus than that in their native habitat, but this trend could not be confirmed when the size of geographic range and sampling efforts were controlled for. The parasite species richness at the infracommunity level of the invasive host population is significantly lower compared with that of the native host populations that lends support to the enemy release hypothesis. A distribution pattern of the infracommunity richness of acquired parasites by the invasive host can be characterized as aggregated and it is random in native host populations. Heterogeneity in the host susceptibility and vulnerability to acquired helminth species was assumed to be a reason of the aggregation of species numbers in the population of the invasive host.

Discovery of new risk loci for IgA nephropathy implicates genes involved in immunity against intestinal pathogens.

We performed a genome-wide association study (GWAS) of IgA nephropathy (IgAN), the most common form of glomerulonephritis, with discovery and follow-up in 20,612 individuals of European and East Asian ancestry. We identified six novel genome-wide significant associations, four in ITGAM-ITGAX, VAV3 and CARD9 and two new independent signals at HLA-DQB1 and DEFA. We replicated the nine previously reported signals, including known SNPs in the HLA-DQB1 and DEFA loci. The cumulative burden of risk alleles is strongly associated with age at disease onset. Most loci are either directly associated with risk of inflammatory bowel disease (IBD) or maintenance of the intestinal epithelial barrier and response to mucosal pathogens. The geo-spatial distribution of risk alleles is highly suggestive of multi-locus adaptation and the genetic risk correlates strongly with variation in local pathogens, particularly helminth diversity, suggesting a possible role for host-intestinal pathogen interactions in shaping the genetic landscape of IgAN.

Gastrointestinal Helminths from Eight Species ofAspidoscelis(Squamata: Teiidae) from Mexico

Seventy-four representatives of 8 species of whiptail lizards (Aspidoscelis ssp.), from Mexico were examined for helminths: Aspidoscelis calidipes (n = 8), A. communis (n = 10), A. cozumelae (n = 9), A. gularis (n = 10), A. lineattissima (n = 9), A. motaguae (n = 11), A. parvisocia (n = 9), and A. sackii (n = 8). We found one species of Cestoda, Oochoristica scelopori, and 7 species of Nematoda, including Abbreviata terrapenis, Parapharyngodon alvarengai, Pharyngodon warneri, Spauligodon garciaprietoi, Spinicauda spinicauda, Thubunaea cnemidophorus, and Physaloptera sp. Mean helminth diversity per lizard species was 3.1 (SD 1.8). Spauligodon garciaprietoi was present in 6 of 8 (75%) of the lizard species. The specimens we examined were infected by an aggregate of helminths that were either characteristic of Aspidoscelis spp. from the United States (North America: O. scelopori, T. cnemidophorus, A. terrapenis, P. warneri) or characteristic of Aspidoscelis spp. from Mexico (Mesoamerica: S. garciaprietoi, P. alvarengai, S. spinicauda). Twentytwo new host records are reported.

The helminth community of the wood mouse Apodemus sylvaticus from the Erro River valley, Navarre, Spain.

The helminth fauna of the wood mouse, Apodemus sylvaticus, in the Erro River valley (Navarre, Spain) was investigated from a total of 150 mice between February 2001 and July 2002. An overall prevalence of 90.7% was recorded and up to 14 helminth species identified. The most prevalent species was the nematode Heligmosomoides polygyrus (78.0%), whereas Syphacia stroma was the species with the highest median abundance (19.8). The detection of Calodium hepaticum, Rodentolepis straminea and the larvae of Hydatigera taeniaeformis are significant, since these helminth species could be considered potential human parasites. The helminth infracommunity comprised no more than five species. A significant predominance of monoxenous species was detected. Statistically significant differences were also found between prevalences, helminth abundance, species richness and helminth diversity of sub-populations of the wood mouse determined by host age and season of capture, which agree with most of the studies carried out on this host. This study will shed light on the helminth community of the wood mouse from a region of Spain which has not previously been documented.

Why are the prevalence and diversity of helminths in the endemic Pyrenean brook newt Calotriton asper (Amphibia, Salamandridae) so low?

A cornerstone in parasitology is why some species or populations are more parasitized than others. Here we examine the influence of host characteristics and habitat on parasite prevalence. We studied the helminths parasitizing the Pyrenean brook newt Calotriton asper (n=167), paying special attention to the relationship between parasites and ecological factors such as habitat, sex, ontogeny, body size and age of the host. We detected two species of parasites, Megalobatrachonema terdentatum (Nematoda: Kathlaniidae) and Brachycoelium salamandrae (Trematoda: Brachycoeliidae), with a prevalence of 5.99% and 1.2%, respectively. Marginally significant differences were found in the prevalence between sexes, with females being more parasitized than males. The present results show significant differences in the body length of paedomorphic and metamorphic individuals, the former being smaller. Nevertheless, no significant correlations between parasite prevalence and either newt body length, ontogenetic stage or age were found. In comparison with other Salamandridae living in ponds, prevalence and diversity values were low. This may be due to a long hibernation period, the species' lotic habitat and its reophilous lifestyle, which probably do not allow for a high parasite load.

Helminth communities in the burrowing toad, Rhinella fernandezae, from Northeastern Argentina

The main goals of this study were to determine the richness and diversity of helminth parasites of Rhinella fernandezae at the component and infracommunity levels and determine the ecological implications of different biotic and abiotic factors. Specimens were collected near the city of Corrientes, Corrientes Province, Argentina. Prevalence of infection was 94% in the specimens examined (n = 65). The helminth component community in R. fernandezae in this area was comprised a total of 22 species. Of all helminth species, only three (Catadiscus inopinatus, Cosmocerca podicipinus and C. parva) were dominant (importance value: I > 1.0) in the community. The most abundant species were B. tetracotyloides (d = 0.43) among the larvae and C. podicipinus (d = 0.09) among adult worms. At the infracommunity level, the mean individual species richness (2.28 ± 1.48) (mean ± SD) was no more than 3 helminth species per infected host; the diversity and equitability of helminths were 0.23 ± 0.21 and 0.48 ± 0.38, respectively. The host body size was the main factor in determining the parasite abundance. Species richness was significantly and positively correlated with host body size. The parasite helminth species predominantly showed an overdispersed pattern of distribution. Helminth species showed two negative and significant pairs of covariation and one significant pair of association (P < 0.05). R. fernandezae has a wide variety of parasites relating to the host microhabitat, mobility and feeding habits.