Larval Digenean Parasitizing Amphibian Hosts from the Argentinian Chaco Region.

PURPOSE: The diversity of larval digenetic trematodes can provide information on one or more intermediate hosts prior to maturation into the definitive host; on host activity and distribution; and in some cases, on environmental perturbations. In this context, the goal of the present study was to analyse the trematode larvae found in adult amphibians collected from the Argentinian Chaco Region. Few studies have been reported on the systematics of larval digeneans in amphibians. METHODS: A total of 167 specimens of frogs (Leptodactylus macrosternum, Leptodactylus latinasus, Lepidobatrachus laevis, Lepidobatrachus llanensis and Lysapsus limellum) and toads (Rhinella bergi) were examined for larval digeneans. Frogs and toads were collected in two Argentinian ecoregions (Dry Chaco and Humid Chaco); between June 2002 and December 2019. Morphology of each taxon was studied in detail using light microscopy and scanning electron microscopy (SEM). RESULTS: Fourteen different taxa of the families Diplostomidae (Alariinae gen sp., Didelphodiplostomum sp., Pharingostomoides sp. and Tylodelphys sp.), Proterodiplostomidae (Heterodiplostomum lanceolatum), and Strigeidae (Strigea spp.) were found infecting the body cavity, mesentery, muscle, fluid in the spinal cord canal, and cranial cavity of amphibians. All species are described and illustrated, and their life cycles are briefly discussed. CONCLUSION: These infections provide new information on the morphology, morphometry, and composition of the diversity of mesocercariae and metacercariae in amphibians, thus contributing to the knowledge of potential intermediate hosts. In addition, our results serve as an indicator of parasite and host biodiversity in different ecoregions of the Gran Chaco.

Biodiversity of trematodes associated with amphibians from a variety of habitats in Corrientes Province, Argentina.

The main goals of this study were to compare the richness of parasitic trematodes in amphibians with diverse habits (terrestrial, fossorial, semi-aquatic and arboreal), and to evaluate whether the composition of the trematode community is determined by ecological relationships. Specimens were collected between April 2001 and December 2006 from a common area (30 ha) in Corrientes Province, Argentina. Trematodes of amphibians in this area comprised a total of 19 species, and were dominated by common species. Larval trematodes presented highest species richness, with the metacercaria of Bursotrema tetracotyloides being dominant in the majority (7/9, 78%) of the parasite communities. Adults of the trematode Catadiscus inopinatus were dominant in the majority (6/9, 67%) of amphibians. The amphibians Leptodactylus latinasus, Leptodactylus bufonius and Scinax nasicus presented a high diversity of trematodes, whereas Leptodactylus chaquensis had the lowest diversity even though it presented with the highest species richness. The patterns of similarity among amphibian species showed groups linking with their habitats. Leptodactilid amphibians, with a generalist diet and an active foraging strategy showed highest infection rates with adult trematodes. The mean richness of trematode species related to host's habitat preferences was higher in semi-aquatic amphibians. Results suggest that semi-aquatic amphibians, present in both aquatic and terrestrial environments, present a greater diversity of parasites as they have a higher rate of exposure to a wider range of prey species and, hence, to diverse infective states. The trematode composition is related to the diets and mobility of the host, and habitat.

Larval nematodes found in amphibians from northeastern Argentina.

Five species of amphibians, Leptodactylus podicipinus, Scinax acuminatus, S. nasicus, Rhinella fernandezae and Pseudis paradoxa, were collected in Corrientes province, Argentina and searched for larval nematodes. All larval nematodes were found as cysts in the serous of the stomach of hosts. Were identified one superfamily, Seuratoidea; one genus, Spiroxys (Superfamily Gnathostomatoidea) and one family, Rhabdochonidae (Superfamily Thelazioidea). We present a description and illustrations of these taxa. These nematodes have an indirect life cycle and amphibians are infected by consuming invertebrate, the intermediate hosts. The genus Spiroxys and superfamily Seuratoidea were reported for the first time for Argentinean amphibians.

Helminth community structure of Scinax nasicus (Anura: Hylidae) from a South American subtropical area.

The main goal of this study was to evaluate the relative influence of season, year of study, host body size, and host sex on abundance of helminth species parasitic in the frog Scinax nasicus. A total of 273 frogs was collected between December 2004 and November 2006 over all seasons in Corrientes City, Province of Corrientes, Argentina. Helminth community included 21 taxa, and was dominated particularly by larval trematodes. Infected frogs harboured a maximum of 7 species. Host sex and season played no significant effect in determining infracommunity parasite species abundance. Similarly, species richness was similar for both host sexes, and across time (year and season). However, occurrence of the parasites Opisthogonimus sp. 2 and Travtrema aff. stenocotyle greatly varied over time. Host body size was the main factor for determining infrapopulation structure of Centrorhynchus sp. Species richness was significantly and positively correlated with host body size. Strong associations were observed mainly between metacercariae of some species. The transmission strategies of parasites suggest that this hylid acquires infections by ingestion of infective larvae and through direct contact with larval parasites from aquatic and terrestrial habitats.

Niche specificity of two Glypthelmins (Trematoda) congeners infecting Leptodactylus chaquensis (Anura: Leptodactylidae) from Argentina.

Sixty-five specimens of the frog Leptodactylus chaquensis were infected by 2 Glypthelmins species (Glypthelmins repandum: 41%, and Glypthelmins palmipedis: 38%) in the small intestine. This study was designed to determine the site specificity of both species along the length of the small intestine by analyzing the distribution, niche overlap, morphological characteristics, and population dynamics. The location of G. palmipedis is very restricted, with the core infection site in the anterior small intestine. In contrast, G. repandum can be characterized as having an expanded niche within the small intestine. In single infections and with different intensities, individuals of both parasitic species showed preference for the anterior small intestine. In concurrent infections and with different intensities, the distribution of G. palmipedis did not change when G. repandum was present; however, displacement of G. repandum toward the middle of the small intestine was observed. Glypthelmins species used the same microhabitat and presumably the same food resource and were generally found to overlap more than expected by chance. This finding suggests the possibility of different feeding mechanisms given by differences in their pharynx size by 37%. Also, the coexistence of these could be associated with the differentiation of realized niches.

Larval digenetic trematodes in tadpoles of six amphibian species from northeastern Argentina.

This article presents a survey of metacercariae found in tadpoles of 6 amphibian species collected near the city of Corrientes, Corrientes Province, Argentina. Larval digenetic trematodes of the following species were found: (1) Travtrema aff. stenocotyle Cohn, 1902 (Plagiorchiidae) from Physalaemus santafecinus, Physalaemus albonotatus, Odontophrynus americanus, Elachistocleis bicolor, Scinax nasicus, and Leptodactylus latinasus; (2) Styphlodora sp. (Plagiorchiidae) from O. americanus and E. bicolor; (3) Opisthogonimus sp. (Opisthogonimidae) from O. americanus and P. santafecinus; (4) Lophosicyadiplostomum aff. nephrocystis (Lutz, 1928) (Diplostomidae) from S. nasicus; (5) Bursotrema tetracotyloides Szidat, 1960 (Diplostomidae) from P. santafecinus and S. nasicus; and (6) an unknown echinostomatid species from O. americanus and S. nasicus. Metacercariae of these species are reported for the first time in tadpoles of the 6 amphibian species examined. All species are described and illustrated, and their life cycles are briefly discussed. These larvae were found infecting different body parts of tadpoles, but no relationship was observed between the metacercariae and amphibian malformations.

Seasonal maturation of Glypthelmins vitellinophilum (Trematoda: Digenea) in Lysapsus limellus (Anura: Pseudidae) from an Argentinian subtropical permanent pond.

From December 1995 to November 2000, the seasonal maturation of Glypthelmins vitellinophilum Dobbin, 1958, in its definitive host, the frog Lysapsus limellus Cope, 1862, was studied in a subtropical permanent pond in northeastern Argentina. The objectives of this study were: 1) to determine the infrapopulation dynamics of the parasite, analyzing the seasonal maturation cycle throughout the years; and 2) to examine the relationship between the intensity of trematode infection in different developmental stages (recruitment, growth and maturation) and the host's body length. Of a total of 1,400 frogs examined over 60 months (5 years), 38% were found to be infected with G. vitellinophilum, and the intensity of infection was 1-15 trematodes per frog. Specimens of G. vitellinophilum were present in L. limellus throughout the years, but did not show a pronounced seasonal maturation cycle. Possible reasons for these findings are discussed with reference to climatic fluctuations and biotic factors. The infective period of the parasite (stage I) occurred in summer, autumn and spring, coinciding with the time each frog cohort appeared. These infections were found principally in small body sizes (classes 1 and 2) of L. limellus. Juvenile and nongravid specimens of worms (stage II and III) were found in frogs of different body sizes throughout the period of investigation. Gravid specimens of the parasite (stage IV) were generally recorded in autumn, winter and spring, mainly in the bodies of larger frogs. The body length of Trematodes in stages I and IV was significantly and positively correlated with that of the frogs.

Seasonal maturation of Glypthelmins vitellinophilum (Trematoda: Digenea) in Lysapsus limellus (Anura: Pseudidae) from an Argentinian subtropical permanent pond

De dezembro de 1995 a novembro de 2000, a maturação sazonal de Glypthelmins vitellinophilum Dobbin, 1958, em seu hospedeiro definitivo, a rã Lysapsus limellus Cope, 1862, foi estudada em uma lagoa permanente subtropical no nordeste da Argentina. Os objetivos deste estudo foram: 1) determinar a dinâmica de infrapopulação do parasita, analisando o ciclo de maturação sazonal ao longo dos anos; e 2) examinar a relação entre intensidade de infecção do trematódeo em diferentes estádios do desenvolvimento (recrutamento, crescimento e maturação) e o comprimento de corpo da rã. De 1.400 espécimens de rãs em 60 meses (5 anos), foram achados 38% infetados com G. vitellinophilum, e a intensidade de infecção era 1-15 trematódeos por rã. Espécimes de G. vitellinophilum estavam presentes em L. limellus ao longo dos anos, mas não mostraram um ciclo sazonal pronunciado de maturação. São discutidas possíveis razões para estes resultados com referência a flutuações climáticas e fatores bióticos. O período infectante do parasita (estádio I) aconteceu no verão, outono e primavera, coincidentemente com o tempo de aparecimento de cada corte das rãs. Estas infecções eram principalmente registradas em tamanhos de corpo pequenos (classes 1 e 2) de L. limellus. Espécimes de parasitas juvenis e não grávidas (estádios II e III) eram encontradas em diferentes tamanhos de rãs ao longo do período de investigação. Espécimes de parasitas grávidas (estádio IV) eram geralmente registradas no outono, inverno e primavera, principalmente nos tamanhos de corpo maiores de rãs. O comprimento de corpo do trematódeo dos estádios I e IV eram significativa e positivamente correlatos com o comprimento de corpo da rã.

Species affinity and infracommunity ordination of helminths of Leptodactylus chaquensis (Anura: Leptodactylidae) in two contrasting environments from northeastern Argentina.

One hundred seventy-two frogs (Leptodactylus chaquensis) were collected from November 2002 to November 2003, in agricultural (n = 132) and nonagricultural (n = 40) areas. Both sites are near the city of Corrientes, Argentina. The main goals of this study were as follows: (1) to determine the helminth parasite community in agricultural and nonagricultural habitats; (2) to analyze the relationships between helminth parasites and site of infection, frog body size, and gender; (3) to identify and examine covariation and association of helminth communities; and (4) to determine the mean richness and diversity of parasite communities. The helminth compound community of this amphibian species consisted of 24 species: 19 in agricultural habitats and 18 in nonagricultural habitats. The mean richness, mean diversity, and evenness of helminths were significantly different between the habitats (P < 0.05). The body size of the host was the important factor in determining parasite richness. Both habitats exhibited differences in community ordination. The helminth species in the 2 habitats exhibited the same interspecific relationships, although differences were observed in the intensity of infection.

[Ecological aspects between Contracaecum sp. (Nematoda, Anisakidae) and the host Serrasalmus spilopleura Kner, 1860 (Pisces, Characidae) in natural populations of northeastern Argentina]. / Aspectos ecológicos de la relación parasitaria entre larvas de Contracaecum sp. (Nematoda, Anisakidae) y Serrasalmus spilopleura Kner, 1860 (Pisces, Characidae) en poblaciones naturales del nordeste argentino.

From February 1987 to February 1989, the populational biology of Contraceacum sp. (larvae) in its paratenic host, the fish Serrasalmus spilopleura Kner, 1860, was studied in two ponds in a subtropical permanent habitat northeastern of Argentina. Fishes from Ramada Paso pond presented 80% of prevalence and 1 to 132 larvae per fish while fishes from Aeroclub pond presented 63% of prevalence and 1 to 184 larvae per fish. Fishes collected from Aeroclub pond have shown a high prevalence of infection during the first period of study (1987), diminishing the following year. In fishes from Ramada Paso pond the prevalence varied not significatively during the two years. Prevalence and mean intensity of infection increase with body length and weight of the hosts. Sex of hosts is not an influential factor in parasitic level. The lenitic "closed" environmental (Ramada Paso pond) evidenced the greatest larvae mean intensity and prevalence. Although, the lenitic "open" environmental (Aeroclub pond) showed the greatest parasitic number of individuals in an infrapopulation. The spatial dispersion in both ponds were aggregated and fit well a negative binomial model. Nevertheless, the Aeroclub pond presented the greatest overdispersion.

Spatial and seasonal trends of a natural population of Biomphalaria occidentalis in northeastern Argentina.

This study aims to analyze the age structure of a population of Biomphalaria occidentalis on a pond of Riachuelo river basin, which is one of the three most important Middle Paraná river affluents in Corrientes province. Samples were drawn from three stations, where spatial and temporal numerical variations of the snail, as well as its relation with different environmental parameters, mainly temperature, rainfall, pH and conductivity, were analyzed. Snail abundance is given in number of individuals/hour. The differences between the three sampling stations, estimated by nonparametric tests, was nonsignificant. A relative scale to the greatest shell diameter was employed to build the age pyramids. Temporal fluctuations of snail abundance correlated negatively with the highest monthly accumulated temperatures (P < 0.05). Although different floristic compositions were observed at the three stations, no significant numerical variations were detected in B. occidentalis spatial distribution. Reproductive activity took place between March-April and November with overlapping cohort system. During summer (December-February) mortality increased along with temperature and reproductive activity was not evident.

Catadiscus pomaceae sp. n. (Trematoda, Paramphistomatidae) from Pomacea canaliculata (Lamarck, 1801) (Prosobranchia, Ampullariidae).

Catadiscus pomaceae sp. n. from the intestine of the prosobranch mollusc Pomacea canaliculata (Lamarck, 1801), is described. The host snail was collected from a lenitic biotope belonging to the Riachuelo basin (Corrientes province, Argentina) during 1985-1986. So far the species of the genus Catadiscus Cohn, 1904 have been recorded in amphibians and reptiles. This is the first instance of a species of that genus parasitizing a mollusc.

Potential schistosome-vector snails and associated trematodes in ricefields of Corrients province, Argentina. Preliminary results.

Considering the possibility of introduction of schistosomiasis mansoni into Argentina as a consequence of dam construction on the Rio De La Plata basin, preliminary studies have been carried out on agrosystems such as ricefields in Corrientes province with the following purposes: 1) to survey and estimate the relative abundance of planorbids and identify potential vector species; 2) to identify environmental factors capable of influencing Biomphalaria population dynamics; and 3) to find out snail-parasite associations and estimate snail infection rates in order to detect possible competitive interactions between larval stages of native trematodes that could be used in biological control of Schistosoma mansoni. Three potential schistosome vectors were detected in ricefields, namely Biomphalaria straminea, B. tenagophila and B. peregrina, although B. orbignyi, a species refractory to infection with S. mansoni, proved the most frequent and abundant. Positive correlations (P less than 0.05) were found between Biomphalaria abundance and some environmental parameters: conductivity, hardness, calcium, nitrites plus nitrates, ammonium and bicarbonates. Water temperature correlation was negative (P less than 0.05). No correlation (P less than 0.05) was found in total iron, phosphates (SRP), pH and soil granulometry.