Environmental variables determining the distribution of an avian parasite: the case of the Philornis torquans complex in South America

Philornis flies are the major cause of myiasis in nestlings of Neotropical birds, being of major concern in geographically-restricted and endangered bird species. Despite its relevance for the conservation of birds, there is little information about the environmental dimensions determining Philornis spp. geographical range. By using maximum entropy, we identified for the first time the macro-environmental variables constraining the abiotic niche of the P. torquans complex in South America, and provided a model map of its potential distribution based on environmental suitability. We identified the minimum temperature of the coldest month as the most relevant variable, associated with the largest decrease in habitat suitability in Brazil and northern South America. Furthermore, the mean temperature of the warmest quarter limited suitability mostly along with the Andean range. In addition, humidity and moisture are influential factors in most of Argentina, northern Chile, and coastal Peru. The geographical projection suggests that environments in most of central-eastern Argentina, and in a broad area in central Chile, are suitable for the presence of the P. torquans complex. Besides providing information about the ecology of Philornis spp., this study represents a tool for bird conservation and a reference for future work on the distribution of this genus.

Orthohantavirus genotype Lechiguanas in Oligoryzomys nigripes (Rodentia: Cricetidae): New evidence of host-switching

To identify and predict situations of increased risk of orthohantavirus infection in humans, it is necessary to study the relationships between the virus and its rodent hosts. The present study investigated orthohantavirus infection in an assemblage of wild Sigmodontinae rodents of the Paraná Delta, Argentina, and providing new evidence of host-switching events. Rodents belonging to the species Oxymycterus rufus (n = 187), Akodon azarae (n = 82), Oligoryzomys flavescens (n = 80), Oligoryzomys nigripes (n = 47), Scapteromys aquaticus (n = 38), Deltamys kempi (n = 7) and Holochilus brasiliensis (n = 2) were captured at 4 sampling sites during 20 trapping sessions. Blood samples were analyzed by IgG ELISA and livers by a nested reverse transcription PCR for the diagnosis of orthohantavirus infection. The amplified products of the S and M orthohantavirus genomes were sequenced and analyzed to determine similarities with species of the Orthohantavirus genus. The species of the Oligoryzomys positive to the virus were confirmed by amplifying and sequencing the complete cyt b gene. Of the 443 serum samples analyzed by IgG ELISA, A. azarae presented the highest host-specific prevalence value (10/82, 12.2%) followed by Ol. nigripes (4/47, 8.5%) and Ox. rufus (1/187, 0.5%). All the sero-positive Ol. nigripes (n = 4) were positive to the amplification of the S and M segments of the Lechiguanas genotype (98% nucleotide identity for both segments). This is surprising given that Ol. nigripes has been previously associated with Juquitiba genotype, not Lechiguanas. The latter is generally associated with Ol. flavescens, which in our study were all sero-negative. In addition, the association Ox. rufus - Pergamino genotype found here is, to our knowledge, novel and another potential evidence of host-switching considering that Pergamino has been originally associated with A. azarae. These findings contribute to the building evidence that contradicts the one-genotype-one-reservoir species premise in the association between rodent reservoirs and orthohantaviruses, and supports the hypothesis that the community structure of sympatric host species may contribute to orthohantavirus dynamics.

First report of Trypanosoma evansi in a canine in Argentina

An Argentinian Dogo which suffered from anorexia, lymphadenopathy, cachexia and paresis of the hind limbs was diagnosed with trypanosomiasis in Argentina in 2013. In this study, we describe the clinical profile and its evolution as well as the molecular method employed to identify and quantify Trypanosoma evansi.

Sexually dimorphic expression of receptor-alpha in the cerebral cortex of neonatal Caiman latirostris (Crocodylia: Alligatoridae)

In mammals, estrogens have been described as endocrine and paracrine modulators of neuronal differentiation and synapse formation. However, the functional role of circulating estrogens and the distribution of estrogen receptors (ERs) in the cerebral cortex of reptiles have not been clearly established. Caiman latirostris (C. latirostris) is a South American species that presents temperature-dependent sex determination (TSD). By using immunohistochemistry, we have studied the distribution of ERα in the cerebral cortex of neonatal caimans. We studied brain samples from ten-day-old TSD-females and TSD-males and from female caimans that were administered estradiol during embryonic development (hormone-dependent sex determination, HSD-females). ERα was detected in the medial (MC), dorsal (DC) and lateral (LC) cortices. ERα expression in the MC showed sex-associated differences, being significantly greater in TSD-females compared to TSD-males. Interestingly, the highest ERα expression in the MC was exhibited by HSD-females. In addition, the circulating levels of estradiol were significantly higher in females (both TSD and HSD) than in TSD-males. Double immunostaining showed that ERα is expressed by neural precursor cells (as detected by ERα/doublecortin or ERα/glial fibrillary acidic protein) and mature neurons (ERα/neuron-specific nuclear protein). Our results demonstrate that the expression of ERα in the neonatal caiman cortex is sexually dimorphic and is present in the early stages of neuronal differentiation.

Neonatal exposure to bisphenol A modifies the abundance of estrogen receptor alpha transcripts with alternative 5'-untranslated regions in the female rat preoptic area

The xenoestrogen bisphenol A (BPA) is commonly ingested by humans. We examined the effects of neonatal exposure to low versus high doses of BPA over the control of estrogen receptor alpha (ERalpha) expression in the preoptic area (POA) of prepubertal female rats. Pups received s.c. injections every 48 h of BPA (high dose, 20 mg/kg and low dose, 0.05 mg/kg) or diethylstilbestrol (DES, 0.02 mg/kg) from postnatal day (PND) 1 to PND7 and were killed at PND8 or PND21. Relative expression of ERalpha transcripts containing alternative 5'-untranslated regions OS, ON, O, OT, and E1 in POA were evaluated by RT-PCR. Methylation status of ERalpha promoters was determined by bisulfited DNA restriction analysis and ERalpha protein by immunohistochemistry. In PND8, the high dose of BPA and DES diminished total ERalpha mRNA levels, mediated by the decreased expression of ERalpha-O and ERalpha-OT variants. In contrast, the low dose of BPA augmented total ERalpha mRNA by increasing the expression of the ERalpha-E1 variant. In PND21, both BPA doses increased total ERalpha mRNA by means of the augmented expression of ERalpha-O and ERalpha-OT variants. In PND21, the methylation status of the ERalpha promoters and the circulating levels of estradiol were similar in all experimental groups. At PND8 and PND21, DES and the high dose of BPA decreased, while the low dose of BPA increased ERalpha protein in the POA. These findings show that neonatal BPA exposure alters the abundance of hypothalamic ERalpha transcript variants and protein in a dose-dependent manner.

Diethylstilbestrol alters the population dynamic of neural precursor cells in the neonatal male rat dentate gyrus

Little is known about how estrogens influence neurogenesis in the newborn male rodent. Herein, we examined the effects of neonatal diethylstilbestrol (DES) exposure on the proliferation and survival of type-1 and type-2 neural precursor cells (NPC) in the dentate gyrus of male rats. This was achieved by exposing newborn male pups to DES on postnatal day (PND) 1, PND3, PND5, and PND7, sacrificed at PND8 or PND21, followed by double immunohistochemistry and morphometric analysis of hippocampal dentate gyrus. Furthermore, vascular endothelial growth factor (VEGF) and brain-derived neurotrophic factor (BDNF) mRNA expression was evaluated in hippocampal tissue blocks by real time RT-PCR. At PND8, the density of total proliferating NPC decreased in DES-treated animals. This reduction was due to a significant decrease in the mitotic rate of type-2 cells only, since type-1 NPCs did not show changes in the proliferation index. Type-2 NPCs expressed the cell-cycle inhibitor p27(kip1) and its expression was clearly augmented in the DES-treated group. Furthermore, the number of apoptotic cells in the dentate gyrus of DES-treated rats decreased. Surprisingly, DES treatment enhanced cell survival and increased NPCs proliferation when animals were examined 14 days after treatment. VEGF mRNA expression showed a positive correlation with NPCs proliferation and BDNF mRNA levels were higher in DES-treated animals at both time points examined. Collectively, these results indicate that hippocampal NPCs proliferation and survival is a critical target of DES exposure during the early postnatal period. VEGF and BDNF are proposed as key mediators of DES-induced NPC mitotic response.

The estrogen receptor alpha sigma3 mRNA splicing variant is differentially regulated by estrogen and progesterone in the rat uterus

The gene for estrogen receptor alpha (ER alpha) has been shown to be under complex hormonal control and its activity can be regulated by mRNA alternative splicing. Here we examined the regulation of ER alpha transcription and translation in the rat uterus by ovarian steroid hormones. We examined whether expression of ER alpha mRNA splice isoforms is hormonally regulated in ovariectomized (OVX) and cycling rats. Adult OVX female rats were treated daily with 17-beta estradiol (E2) (0.05 microg/rat or 5 microg/rat), progesterone (P4) (1 mg/rat) or a combination of both hormones for 4 days. Animals were killed 24 h after the last injection and uterine horns were removed. In order to determine whether ER alpha mRNA isoforms are differentially expressed under various physiological conditions, animals were evaluated at proestrus, estrus and diestrus. The ER alpha protein and mRNA were detected by immunohistochemistry and comparative RT-PCR analysis respectively. The presence of ER alpha mRNA isoforms was evaluated using a nested RT-PCR assay. In OVX control rats, ER alpha mRNA and protein levels were high, demonstrating a constitutive expression of the ER alpha gene in the uterus. When animals received P4 or the high dose of E2, a significant decrease in both ER alpha mRNA and protein was observed in the uterus. However, when rats were protein was treated with the low dose of E2, only the ER alpha down-regulated; no changes were observed in ER alpha mRNA expression. In addition to the full-length ER alpha mRNA, OVX control rat uteri expressed three shorter transcripts: sigma3, sigma4 and sigma3,4 (lacking exon 3, exon 4, or both 3 and 4 respectively). Surprisingly, when OVX animals were treated with P4, the low dose of E2 or a combination of both steroids, expression of the sigma3 isoform was completely abolished. During the estrous cycle, all ER alpha mRNA splicing variants were detected at proestrus and estrus. However, in diestrus, significant low levels of the sigma3 isoform were observed. In summary, our results suggest a dose-dependent relationship between E2 concentrations and the level of control in the ER alpha transcription-translation cascade. Moreover, the alternative splicing of the ER alpha primary transcript is influenced by the hormonal milieu, suggesting that these events could affect the estrogen responsiveness of the rat uterus during the estrous cycle.