Digenean infections in snails (cercariae stage) in Can Gio Mangrove Biosphere Reserve, Ho Chi Minh City, Vietnam

Foodborne zoonotic trematodiasis is a public health problem in many countries. A study on digenean larvae (cercariae stage) obtained from snails in all ten main small canals and two rice fields was carried out in Can Gio Mangrove Biosphere Reserve, Ho Chi Minh city, Vietnam to identify the snail composition and digenean prevalence in snails. The snails were sampled in the dry season (January 2022) and the wet season (June 2022). In the ten canals, 23 snail species belonging to 16 genera, 10 families from the samplings were found; however, there were no cercariae in these 23 snail species. In the two rice fields, 11 snail species in 11 genera and 7 families were collected. In which, Bithynia siamensis in Ly Nhon rice field and Thiara scabra in Binh Khanh rice field infected xiphidio cercariae. For Bithynia siamensis, the prevalence in the dry season (5.6%) was higher than in the wet season (4.6%) (P > 0.05). In Binh Khanh rice field, only one Thiara scabra infected cercariae in the wet season. Further research on digenean infection in different months and in other water bodies in Can Gio Mangrove Biosphere Reserve should be done to contribute to the control of digeneans and reserve the biodiversity.

Effects of metacercariae of Prosorhynchoides sp. (Trematoda: Bucephalidae) on the swimming ability and blood parameters of the intertidal fish Girella laevifrons (Osteichthyes: Kyphosidae)

Parasites may have various effects on their host's health. It is important to determine the type of the effects but also to decipher the physiological mechanisms underlying a parasitic infection. In this study, swimming ability (by a fixed swim speed test) and haematological analyses (by blood parameters) were compared between juvenile fish Girella laevifrons non-parasitised and parasitised with metacercariae of Prosorhynchoides sp. Fish were infested in the laboratory using natural parasitised mussels. Aerobic swimming time, total erythrocyte and leukocyte counts were compared among four groups of fish: non-parasitised (NP), non-parasitised but manipulated (NPM), parasitised 3 days (PT1), and 10 days (PT2) post-infection. Differentiated haematological components were also compared among NP, PT1 and PT2 fish groups. Parasitised fish (PT1 and PT2) swam between 32% and 55% less time than unparasitised fish. Erythrocyte counts were lower in PT1, indicating anemia, and total leukocyte counts were higher in PT1, showing immune action. Macrophages and basophils were observed only in parasitised fish, independent of the post-infection time. There was a negative correlation between swimming time and leukocyte counts. Increased leukocytes in the blood indicate activation of the innate cellular immune response, which may be metabolically costly for the host. Moreover, the anemia in parasitised fish would reduce the oxygen transport necessary to carry out aerobic exercise, reducing the swimming capacity. In fish several days post-infection (PT2), the erythrocytes count reached normal values, and some kinds of leukocytes decreased in comparison to fish PT1. This suggests that parasitised fish with metacercariae were recovering.

Three new species of Creptotrema (Trematoda, Allocreadiidae) with an amended diagnosis of the genus and reassignment of Auriculostoma (Allocreadiidae), based on morphological and molecular evidence

Diversity of Creptotrema was investigated using morphological and molecular tools, including data for Creptotrema creptotrema (type-species). Three new species, parasites of Brazilian fishes, are described: Creptotrema conconae n. sp. (type-host, Imparfinis mirini Haseman), Creptotrema schubarti n. sp. (type-host, Characidium schubarti Travassos) and Creptotrema megacetabularis n. sp. (type-host, Auchenipterus osteomystax (Miranda Ribeiro)). The diagnosis of the genus was amended to include new features. The new species differ from each other mainly in terms of body shape, relative sucker size, and testes position. DNA sequences were obtained from Creptotrema spp. from Brazil, including 28S, ITS and COI. Genetic divergences among the new species and C. creptotrema varied from 2.1 to 5.2% (21–49 bp) for 28S, and 6.6 to 16.4% (21–45 bp) for COI. Phylogenetic analysis (28S) placed the newly generated DNA sequences of Creptotrema in a clade (Creptotrema clade sensu stricto) composed of C. creptotrema, the new species described herein, and all species previously described as Auriculostoma, revealing that Auriculostoma is best interpreted as a synonym of Creptotrema based on the principle of priority of zoological nomenclature. Creptotrema funduli, the single sequence of the genus previously available, was not grouped within the Creptotrema clade sensu stricto, suggesting the need for reevaluation of the taxonomic status of this species. Our results showed that Creptotrema represents a monophyletic genus of trematodes widely distributed across the Americas, which currently comprises 19 valid species of parasites of teleosts and anurans.

Digenean parasites of Sigmodontinae rodents from Argentina: a list of species, new host, and geographical records

INTRODUCTION

Among Argentinean rodents, only one species of Muridae and seven of Cricetidae were reported as digenean hosts. Despite the available data, the taxonomic diversity of the Digenea from rodents has been little explored. An update on digeneans of Sigmodontinae rodents (Cricetidae-Muroidea) in Cuenca del Plata is provided. New host and geographical data are recorded and taxonomic and ecological data are summarized.

METHODS

Rodents were collected from 11 localities in the region Cuenca del Plata, Argentina. Moreover, other unidentified specimens from four localities, deposited in the Colección de Helmintología del Museo de La Plata, were studied. Prevalence, mean intensity, and mean abundance are provided.

RESULTS

Eight species of digeneans belonging to four families were identified. Twelve new geographical records for five provinces of Argentina are presented. In addition, six new host-parasite associations are reported. The information is presented in a taxonomic list for each digenean species: site of infection, host records, locality records, and comments.

CONCLUSIONS

It becomes interesting to explore the diets and habits of each rodent species to understand the dispersal and transmission ability of each group of digeneans. This survey constitutes an update on digeneans of Sigmodontinae rodents in Cuenca del Plata, Argentina.