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We screened lung tissue from 770 sigmodontine rodents sampled in the Delta and Paraná Islands ecoregion for Borrelia spp. and obtained sequences clustered within the Borrelia burgdorferi sensu lato (s.l.) complex. Seventeen individuals were PCR-positive (prevalence 2.2%), distributed mainly in Akodon azarae ( n  = 11) and across five additional species. Using GLMMs that accounted for site and trapping session, infection probability was positively associated with individual body length and with ecological proxies of prior host and vector abundance: Ak. azarae abundance two sessions earlier (lag S −2 ) and Ixodes loricatus nymph abundance in the previous session (lag S −1 ) were the strongest predictors. These results point to transmission dynamics driven by recent host and immature-tick abundance rather than by climatic descriptors. Presence of cattle was associated with lower Borrelia prevalence in grazed grids (0.5% vs. 4.8% in Ak. azarae ), and a univariable model restricted to Ak. azarae detected a significant negative association with cattle; however, this effect was not statistically significant in multivariable models that included host size and lagged abundance metrics. Our findings indicate localized endemic circulation of B. burgdorferi s.l. linked to host/vector demography, and highlight the need for integrated vector and reservoir monitoring to resolve mechanistic pathways and potential implications for animal and public health.

Fil: Antoniazzi, Leandro Raúl. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Ciencias Veterinarias del Litoral. Universidad Nacional del Litoral. Facultad de Ciencias Veterinarias. Instituto de Ciencias Veterinarias del Litoral; Argentina

In this study, we review the taxonomic status of the parasitic nematodes Stilestrongylus oryzomysi and Guerrerostrongylus uruguayensis (Heligmonellidae), which had been described only once from sigmodontine rodents from Argentina and Uruguay, respectively. To this aim, we examined 38 complete helminth sets deposited in the Helminthological Collection of the Museo de La Plata (MLP-He), Argentina, including type material of G. uruguayensis , S. oryzomysi , and a closely related species, Stilestrongylus azarai . We also examined voucher rodent specimens deposited in the Mammal Collection of the Museo de La Plata (MLP-Mz) to assess the identity of the symbiotypes and other rodent hosts. Based on these observations, S. oryzomysi is proposed as a junior synonym of S. azarai ; the identity of the symbiotype of S. oryzomysi and Trichofreitasia lenti (Heligmonellidae) is emended from Oligoryzomys flavescens to Akodon azarae ; G. uruguayensis is proposed as a junior synonym of Guerrerostrongylus zeta ; S. azarai is redescribed based on type and voucher material; and the latter species and G. zeta are molecularly characterised using the ITS+ gene. We extend the geographic distribution of S. azarai to include Uruguay and provide a new host record for T. lenti ( A. azarae , type host species), a new host record for G. zeta in Argentina ( O. flavescens ), and the first record of helminths for Oligoryzomys nigripes in Uruguay.

Hassalstrongylus dollfusi (Díaz-Ungría, 1963) Durette-Desset, 1971 was described in a wild house mouse, Mus musculus , from Venezuela and, since then, has never been reported again in the type host or in any other host. In this work, specimens assignable to H. dollfusi were found at 10 localities in Northeast Argentina, in five species of sigmodontine rodents. The nematodes were attributed to H. dollfusi based on diagnostic characters such as: synlophe with 22–31 subequal ridges; in males, hypertrophy of right ray 4 of the male bursa, thickening of the dorsal ray and bases of rays 8, distal tip of the spicules bent and spoon shaped; and, in females, presence of subventral postvulvar alae supported by hypertrophied struts. The new host recorded are: Oligoryzomys fornesi , O. flavescens , O. nigripes , Holochilus chacarius and Akodon azarae . The parasite showed a strong preference for host species of Oligoryzomys , which appear to act as primary hosts. The parasite could be present, parasitizing different species of Oligoryzomys , in a geographic area from the type locality in Venezuela southward to north Corrientes in Argentina. It has not been reported from populations of Oligoryzomys spp. of the Argentinean and Brazilian Atlantic Forest, nor south of 28° S, which may be explained by constraints in the environmental conditions required by the free-living stages of the parasite. This study provides the first identification and redescription of H. dollfusi in southern South America, from autochthonous hosts, six decades after its description. Hassalstrongylus dollfusi (Díaz-Ungría, 1963) Durette-Desset, 1971 a été décrit chez une souris grise sauvage, Mus musculus , au Venezuela et, depuis lors, n’a plus jamais été signalé chez l’hôte-type ni chez aucun autre hôte. Dans ce travail, des spécimens attribuables à H. dollfusi ont été trouvés dans dix localités du nord-est de l’Argentine, chez cinq espèces de rongeurs Sigmodontinae. Les nématodes ont été attribués à H. dollfusi sur la base de caractères diagnostiques tels que : synlophe avec 22–31 crêtes subégales; chez le mâle, hypertrophie de la côte 4 droite de la bourse, épaississement de la côte dorsale et des bases des côtes 8, extrémité distale des spicules recourbée et en forme de cuillère; et, chez les femelles, présence d’ailes postvulvaires subventrales à fort support cuticulaire. Les nouveaux hôtes signalés sont : Oligoryzomys fornesi , O. flavescens , O. nigripes , Holochilus chacarius et Akodon azarae . Le parasite a montré une forte préférence pour les espèces hôtes du genre Oligoryzomys , qui semblent agir comme hôtes primaires. Le parasite pourrait être présent, parasitant différentes espèces d’ Oligoryzomys , dans une zone géographique allant de la localité-type au Vénézuéla vers le sud jusqu’au nord de Corrientes en Argentine. Il n’a pas été signalé dans les populations d’ Oligoryzomys spp. de la Forêt Atlantique argentine et brésilienne, ni au sud de 28° S, ce qui peut s’expliquer par des contraintes dans les conditions environnementales requises par les stades libres du parasite. Cette étude fournit la première identification et redescription d’ H. dollfusi dans le sud de l’Amérique du Sud, à partir d’hôtes autochtones, six décennies après sa description.

Changes in rainfall patterns caused by anthropogenic global climate change or planetary-scale events, such as the El Niño Southern Oscillation, can significantly affect the abundance and distribution of organisms. Despite the evidence of such effects on marine and terrestrial systems, ecological consequences of rainfall fluctuations in coastal marine ecosystems remain poorly understood. Here we evaluate the effects of rainfall intensity on the interaction between the cordgrass Spartina densiflora and Azara’s grass mouse Akodon azarae in a southwestern Atlantic salt marsh (Mar Chiquita coastal lagoon, Argentina). Field surveys showed that the abundance of A. azarae increased during rainy summers (i.e. El Niño 2005 and 2007) and had lowest values during dry summers (i.e. La Niña 2008). Salt content in sediment and plant tissue were negatively related with rainfall. In addition, field experiments showed that increased sediment salinity resulted in increased salt content in plant tissues. Elevated soil salinity also increased the proportion of senescent S. densiflora tissues and reduced plant growth. The consumption of S. densiflora leaves by A. azarae also decreased with increased soil salinity. The proportion of S. densiflora in feces collected during the driest summer was very small. Therefore, changes in the abundance of A. azarae could be mediated by plant–rodent trophic interaction or by plant cover changes. In conclusion, rainfall fluctuations changed the abiotic environment (i.e. salinity), decreasing primary production and indirectly modifying habitat use by the omnivore A. azarae and its trophic interaction with S. densiflora. The present study provides evidence that rainfall can modify ecological processes that affect the structure and dynamics of coastal marine ecosystems.

Calodium hepaticum (Trichinellida: Capillaridae) is a parasitic nematode of mammals distributed worldwide. Although this parasite can infect the liver of a wide diversity of mammals (including humans), it is mostly associated with Muroidea hosts. Sigmodontinae rodents were recently recognized as important hosts of this parasite in Argentina, but the impact of this parasitism on these hosts has not been established. Here we report results of histopathological analyses of 40 livers of Akodon azarae infected with C. hepaticum. Lesions were classified into 4 categories: level 0, absence of lesions; level 1, with focal granulomatous hepatitis; level 2, presence of multifocal granulomatous hepatitis, fibrosis and focal necrosis with neutrophils, and level 3, absence of intact adult parasites, diffuse distribution, necrosis, and fibrosis. Most samples presented lesions of level 2 (55%), but all categories of lesions were found. This is the first study to describe the lesions caused by C. hepaticum in the liver of Sigmodontinae rodents, and the results suggest that infection by this parasite is costly to A. azarae populations.

Hantavirus pulmonary syndrome (HPS) is a severe zoonotic disease caused by hantaviruses hosted in various rodents species. In Argentina, its transmission to humans has been associated to exposure during activities such as farming, recreation, and tourism which are carried out in wild and rural areas. The aim of this study was to analyze the macro- and micro-habitat use and spatio–temporal variation of small sylvan rodents in Pre Delta and Islas de Santa Fe national parks, located in an HPS-endemic area of Argentina. Rodent communities were studied at six sites: two islands, a riparian forest, an inland forest, a marsh, and the margins of a pond. A total of 453 individuals of five species were captured with a trapping effort of 9471 trap-nights. Maximum species richness was found at the marsh and the pond margin sites. Abundance of rodents was influenced by flooding events. Two hantavirus reservoirs, Oligoryzomys flavescens and Akodon azarae , were identified in the area. O. flavescens was captured in every habitat, but it was dominant in Islas de Santa Fe National Park where its abundance was strongly influenced by flooding. A. azarae was captured in every habitat except on the islands. A. azarae behaved as a generalist species at a micro-habitat scale in every habitat of Pre Delta National Park except for the marsh where it selected patches with low vegetation height. Based on these results, several disease prevention measures, including the use of rodent-proof containers for food, and keeping the grass short in the camp site, are proposed in order to reduce the risk to visitors and residents of contracting HPS.

In the Pampa region of Argentina, farming activities have been performed since the beginning of the 20th century, but in the 1990s, land-use patterns rapidly changed towards intensive agriculture and poultry breeding. This study compares the helminth community of Akodon azarae (Rodentia) among three habitats with different land use in pampean agroecosystems: poultry farms, mono-cultivated fields and abandoned fields (not used for 35 years), under the prediction that there will be greater helminth richness and diversity in mice from abandoned fields compared to those from the other habitats. Nevertheless, the highest abundance of A. azarae occurred on poultry farms, the habitat most disturbed by human activity, while cultivated fields showed the lowest. Helminth richness and diversity were significantly higher on poultry farms than in the other habitats, due to the presence of Trichuris laevitestis, Protospirura numidica criceticola and cysts of Taenia taeniaeformis. We suggest that the helminth fauna of A. azarae can survive on poultry farms despite disturbance from farming activities, because rodents can move and get shelter within farm perimeter fences, where dense and high vegetation grows. This farm area could offer good conditions for geohelminth development, while chicken sheds could attract insects that are intermediate hosts of helminths with indirect life cycles. On the contrary, agrochemicals applied in cultivated fields would negatively influence helminth diversity and composition, by decreasing host populations (arthropods and rodents) and affecting free larval stages of geohelminths.

The goal of this study was to analyze the variations in abundance of rodent communities over the last 24 years in a rural area, and their relation to possible changes in climatic variables and land use. The principal change in the area observed along the study period was an increase in the area covered by soybean. The habitats studied were crop fields and borders. The total abundance of rodents did not show a significant trend of variation over time in crop fields while in borders the abundance in autumn–winter (A–W) showed a significant trend to decrease over time. The different rodent species showed a differential response over time. While Calomys laucha and C. musculinus showed a decrease between the period before and after the soybean expansion, Akodon azarae did not change its abundance over time. The mean minimum temperature increased over time while the number of days with frost decreased. Total rodent abundance in A–W was positively associated with the cumulated precipitation of the previous spring–summer period and negatively with the cumulated precipitation of the same period. We conclude that rodent abundance variations in crop fields and borders of the study area are influenced by precipitation, but the observed trends of variation over time are better explained by changes in agricultural practices than by meteorological variables.

Abundance, distribution, movement patterns, and habitat selection of a reservoir species influence the dispersal of zoonotic pathogens, and hence, the risk for humans. Movements and microhabitat use of rodent species, and their potential role in the transmission of hantavirus were studied in Otamendi Natural Reserve, Buenos Aires, Argentina. Movement estimators and qualitative characteristics of rodent paths were determined by means of a spool and line device method. Sampling was conducted during November and December 2011, and March, April, June, October, and December 2012. Forty-six Oxymycterus rufus, 41 Akodon azarae, 10 Scapteromys aquaticus and 5 Oligoryzomys flavescens were captured. Movement patterns and distances varied according to sex, habitat type, reproductive season, and body size among species. O. flavescens, reservoir of the etiologic agent of hantavirus pulmonary syndrome in the region, moved short distances, had the most linear paths and did not share paths with other species. A. azarae had an intermediate linearity index, its movements were longer in the highland grassland than in the lowland marsh and the salty grassland, and larger individuals traveled longer distances. O. rufus had the most tortuous paths and the males moved more during the non-breeding season. S. aquaticus movements were associated with habitat type with longer distances traveled in the lowland marsh than in the salty grassland. Hantavirus antibodies were detected in 20% of A. azarae and were not detected in any other species. Seropositive individuals were captured during the breeding season and 85% of them were males. A. azarae moved randomly and shared paths with all the other species, which could promote hantavirus spillover events.