Orthohantavirus infection in two rodent species that inhabit wetlands in the central-east region of Argentina

Hantavirus pulmonary syndrome (HPS) is an emerging infectious disease caused by orthohantaviruses associated to rodents of the Cricetidae family, Sigmodontinae subfamily, in the American continent. Previous research carried out in central-east region of Argentina, recorded potential orthohantavirus host rodents in diverse environments, but infected rodents were particularly present on Paraná wetlands islands. The aims of this research were (1) to determine the orthohantavirus host in the rodent community focused on islands of Paraná River Delta, an endemic zone of HPS, (2) to identify temporal and spatial factors associated with orthohantavirus prevalence variations, (3) to compare the individual characteristics of seropositive and seronegative rodents and, (4) to explore the association between orthohantavirus seroprevalence and rodent community characteristics in the Paraná River Delta, central-east region of Argentina. Capture of small rodents was done between August 2014 and May 2018 on seven islands located in central-east region of Argentina. In this HPS endemic zone, 14.9% of Oligoryzomys flavescens and 1.5% of Oxymycterus rufus of the sampled rodents had antibodies against orthohantavirus. The individuals that were more likely to become seropositive were the reproductively active adult males. Even though O. flavescens inhabit all islands, the seropositive individuals were only present in two of these, suggesting spatial heterogeneity in the viral distribution. We found that two months later of periods with low temperature, seroprevalence increased probably due to a higher proportion of adults in the population. Additionally, higher seroprevalence was associated with greater diversity of the rodent assemblage. This association could support the idea that a rescue effect or amplification of the prevalence of orthohantavirus would be taking place by means of secondary host as O. rufus, a novelty for this species and for the region. This finding may be significant if one takes into account that O. rufus was the second most abundant species in the area of islands studied and is one of the most abundant species on the islands and riparian sectors of the study zone. In conclusion, the relative risk of HPS could be high on wetlands of Paraná River Delta in the central-east region of Argentina where several favourable factors for the transmission of orthohantavirus are combined, such as the presence of several host species, two of them numerically dominant, high percentages of infection and a high degree of occupational exposure of the human population due to rural activities, the most frequently associated nationwide with HPS.

The phytoplankton community as a descriptor of environmental variability: a case study in five reservoirs of the Paraná River basin

Aim We aimed to characterize the structure of the phytoplankton community and identify the main environmental factors driving the community in five reservoirs constructed in the region of the high Paraná River. Methods The phytoplankton and environmental variables were collected at the lacustrine region of the reservoir, between November 2013 and November 2014, with interval between collections ranged from 3 to 6 months. The richness and biomass of the phytoplankton community were measured as a response to the spatial and temporal environmental variability. Data from environmental variables was analyzed by Principal Component Analysis (PCA). Non-Metric Multidimensional Scaling Analyzes (NMDS) were performed on the richness and biomass data of the phytoplankton community. Results We identified 80 taxa distributed in 11 taxonomic classes, from which Cyanobacteria and Chlorophyceae were best represented. We did not observe significant temporal variation for either environmental variables or attributes of the phytoplankton community, which may be related to the prolonged drought in this period in the Brazilian Southwest. Higher phytoplankton richness and biomass were found in the Três Irmãos (Tiete River), reservoir located in the most anthropized basin in the country. Cyanobacteria and dinoflagellates dominated the biomass in all reservoirs during the studied period. The Ilha Solteira, Jupiá and Porto Primavera reservoirs showed a tendency to decrease in the values of phytoplankton richness and biomass, and the reservoirs built in series in the Paraná River probably have strong interdependence, according to the CRCC concept. Conclusions Spatial variation in phytoplankton attributes was influenced mainly by the position occupied by the reservoir in the hydrographic basin, water retention time (RT) and nutrient concentrations in each reservoir.

Reproduction and fecundity of invader of internal insemination Trachelyopterus galeatus in a Neotropical floodplain

After the formation of Itaipu Reservoir, the invader Trachelyopterus galeatus colonized the upper Paraná River. Light microscopy was used to describe gametogenesis and the reproductive phases of females and males. The following data were verified: diameter of the oocytes, spawning type, batch fecundity by ovary weight, standard length, and total weight of the fish, along with the regions where this species reproduced in the upper Paraná River floodplain. A total of 470 specimens were collected quarterly in 2016, 2018 and 2019, and bimonthly in 2017. The gonads were fixed in a Karnovsky solution, dehydrated, infiltrated, and embedded in historesin. The histological slides were stained using PAS + iron hematoxylin + metanil yellow, analyzed and photographed under an image-capturing microscope. As regards diameter of the oocytes and fecundity estimates, ovaries whose oocytes were measured under a stereomicroscope were sampled. In the oogenesis, undifferentiated and differentiated oogonia, early primary growth oocytes, secondary growth oocytes, full-grown oocytes and maturing oocytes were recorded. In the spermatogenesis, primary and secondary spermatogonia, primary and secondary spermatocytes, spermatids and spermatozoa were recorded. The reproductive phases found for females and males were: immature, early development, late development, spawning/sperm-releasing capable, regression, and regeneration. Trachelyopterus galeatus prefers to occupy and reproduce in the Ventura, Patos, Guaraná, Fechada, Garças, and Pau Véio lagoons. The diameter of the oocytes varied from 0.4 to 2.9 mm. Females spawn, on average, 113 oocytes per batch. Batch fecundity variation shows that the larger the ovary, standard length, and total weight, the larger the number of oocytes to be spawned. This invader possesses reproductive success in the upper Paraná River floodplain, especially in lagoons.

LIVE BAIT TRADE AS A PATHWAY FOR THE INTRODUCTION OF NON-NATIVE SPECIES: THE FIRST RECORD OF Dilocarcinus pagei IN THE PARANAPANEMA RIVER BASIN

Brazil has one of the most significant diversity of freshwater fish in the world, and this drives trade and fishing tourism. Several species of sport fish have characteristics and behaviors that favor fishing tourism and its related activities. Live baits are widely used in fisheries across the country, and at the end of fisheries, is common that anglers may release the remaining bait in rivers, lakes or reservoirs. Here we report for the first time the crab Dilocarcinus pagei in the Paranapanema River basin, and list the freshwater species that were introduced similarly. During field samplings between 2012/2016, and 2018/2019, we captured 10 individuals of D. pagei. One female in the Rosana Reservoir; and two juveniles, one female and six males in the Taquaruçu Reservoir. The literature review revealed 16 species used as live bait, the crab D. pagei and 15 fish species. Gymnotiformes were the largest number of species used as live bait. The basins that had introduction cases were in the Upper Paraná, Iguaçu, and Paraíba do Sul Rivers. The Paraguay-Lower Paraná River was the system that contributed with nine species to the most invaded ecoregion in Brazil, the Upper Paraná River basin. Anglers and live bait farmers should be aware of the risks and consequences of these constant introduction actions (propagule pressure), not releasing baits. In addition, the live bait trade must be monitored and controlled to occur only with species in their original river basin.