Hantavirus ecology in rodent populations in three protected areas of Argentina

Orthohantavirus Infection in Two Rodent Species that Inhabit Wetlands in Argentina

Previous research conducted in central-east region of Argentina recorded potential orthohantavirus host rodents in diverse environments, but no research has focused particularly on islands, the environments that present the greatest risk to humans. For this reason, the aims of this research were to determine the orthohantavirus host in the rodent community focused on islands of Paraná River Delta, central-east region of Argentina, to identify temporal and spatial factors associated with orthohantavirus prevalence variations, to compare the functional traits of seropositive and seronegative rodents, and to explore the association between orthohantavirus prevalence and rodent community characteristics between August 2014 and May 2018. With a trapping effort of 14,600 trap-nights, a total of 348 sigmodontine rodent specimens belonging to seven species were captured 361 times. The overall antibody prevalence was 4.9%. Particularly, 14.9% of Oligoryzomys flavescens and 1.5% of Oxymycterus rufus, mainly reproductively active adult males, had antibodies against orthohantavirus. Even though O. flavescens inhabit all islands, our results suggest spatial heterogeneity in the viral distribution, with two months after periods of low temperature presenting increases in seroprevalence. This could be a response to the increased proportion of adults present in the rodent population. In addition, an association was found between the high seroprevalence and the diversity of the rodent assemblage. We also found 1.5% of O. rufus exposed to orthohantavirus, which shows us that further investigation of the ecology of the virus is needed to answer whether this species act as a spillover or a new competent host.

Modelling relative abundance of Oligoryzomys flavescens, an Orthohantavirus reservoir, in an endemic hantavirus pulmonary syndrome zone

Hantavirus pulmonary syndrome (HPS) is a zoonotic emerging infectious disease caused by New World orthohantaviruses (family Hantaviridae) hosted by rodents of the family Cricetidae. In Argentina, one of its main hosts is the sigmodontine rodent Oligoryzomys flavescens, a widely distributed mouse of the Pampas, Delta and Espinal ecoregions of central-east Argentina. Because the abundance of the reservoir and its proportion in the rodent community affects both virus prevalence and human exposure risk, its estimation throughout its known geographical distribution is of key importance for the design of public health strategies to prevent HPS. The aim of this study was therefore to model the relative abundance of O. flavescens in most of the Pampas ecoregion within Buenos Aires Province, Argentina, where hantavirus pulmonary syndrome is endemic. To do this we used owl-pellet samples collected between 2006 and 2008 from 51 sites distributed throughout most of Buenos Aires province. Mammalian prey in each pellet was identified to the lowest possible taxonomic level by examination of the skulls, dentaries and molars. We modelled the frequency of O. flavescens found in each sample as a function of climatic, environmental, and topographic data of each site. The two best models were applied to a Geo referential Information System to build maps of estimated frequency (as a proxy of relative abundance) within Buenos Aires province. Estimated relative abundance of O. flavescens in Buenos Aires province was significantly associated with annual mean temperature, annual precipitation and presence of freshwater bodies, and varied among sub-regions, with the Inland and Rolling Pampas being the regions with highest frequencies. Knowing in which areas O. flavescens abundance is expected to be higher can be used to concentrate limited sanitary efforts in those areas that are most needed in order to reduce transmission and increase detection.

Virus isolation data improve host predictions for New World rodent orthohantaviruses

Identifying reservoir host species is crucial for understanding the ecology of multi-host pathogens and predicting risks of pathogen spillover from wildlife to people. Predictive models are increasingly used for identifying ecological traits and prioritizing surveillance of likely zoonotic reservoirs, but these often employ different types of evidence for establishing host associations. Comparisons between models with different infection evidence are necessary to guide inferences about the trait profiles of likely hosts and identify which hosts and geographical regions are likely sources of spillover. Here, we use New World rodent-orthohantavirus associations to explore differences in the performance and predictions of models trained on two types of evidence for infection and onward transmission: RT-PCR and live virus isolation data, representing active infections versus host competence, respectively. Orthohantaviruses are primarily carried by muroid rodents and cause the diseases haemorrhagic fever with renal syndrome (HFRS) and hantavirus cardiopulmonary syndrome (HCPS) in humans. We show that although boosted regression tree (BRT) models trained on RT-PCR and live virus isolation data both performed well and capture generally similar trait profiles, rodent phylogeny influenced previously collected RT-PCR data, and BRTs using virus isolation data displayed a narrower list of predicted reservoirs than those using RT-PCR data. BRT models trained on RT-PCR data identified 138 undiscovered hosts and virus isolation models identified 92 undiscovered hosts, with 27 undiscovered hosts identified by both models. Distributions of predicted hosts were concentrated in several different regions for each model, with large discrepancies between evidence types. As a form of validation, virus isolation models independently predicted several orthohantavirus-rodent host associations that had been previously identified through empirical research using RT-PCR. Our model predictions provide a priority list of species and locations for future orthohantavirus sampling. More broadly, these results demonstrate the value of multiple data types for predicting zoonotic pathogen hosts. These methods can be applied across a range of systems to improve our understanding of pathogen maintenance and increase efficiency of pathogen surveillance.

Expanded distribution of orthohantavirus Pergamino genotype: First record in Entre Rios province, Argentina

Hantavirus Pulmonary Syndrome (HPS) is an emerging infectious disease of the Americas. Eight native rodent species have been identified as HPS virus reservoirs in Argentina. The aim of this work was to detect the orthohantavirus genotypes present in a rodent community that inhabits a zone where a fatal HPS case occurred within an endemic locality of Central Argentina. We captured 27 rodents with a trapping effort of 723 trap nights. We detected 14.3% of infected Akodon azarae with the Pergamino genotype. This result expands the known distribution of this orthohantavirus. Although the Pergamino genotype has not been associated with human cases, the information about its distribution is relevant for risk assessment against potential changes in the virus infectivity.

First Evidence of Akodon-Borne Orthohantavirus in Northeastern Argentina

Orthohantaviruses (genus Orthohantavirus, family Hantaviridae) are the etiologic agents of Hantavirus Pulmonary Syndrome in the Americas. In South America, orthohantaviruses are highly diverse and are hosted by sigmodontine rodents (subfamiliy Sigmodontinae, family Cricetidae), an also diverse group of rodents. The aims of this work were to (1) identify orthohantavirus hosts and (2) to study the spatial and temporal variations in the prevalence of infection and their associations with community, environmental and individual characteristics, in different environments of Misiones province, northeastern Argentina. Live-capture sessions were carried out during two years in different land uses, with a trapping effort of 31,653 trap nights. We captured 719 individuals from the species Akodon montensis, Rattus rattus, Mus musculus, Calomys tener, Thaptomys nigrita, Oligoryzomys nigripes, Euryoryzomys russatus, Oligoryzomys flavescens, Brucepattersonius sp., and Juliomys pictipes. Antibodies against orthohantavirus were detected in Akodon montensis in one natural protected and one periurban areas, and it was the most abundant species in almost every study sites. We observed the presence of spatial focality of orthohantavirus infection and a positive association with host abundance suggesting the existence of a threshold density. At the individual level, large, reproductively active, and male individuals were more likely to have antibodies against orthohantavirus. This is the first record of orthohantavirus infection in A. montensis in Argentina, which shows the importance of investigations about emerging diseases.

Population survey of small rodents on islands located inside a region of endemism for hantavirus pulmonary syndrome

Ecological studies of rodent species, especially as reservoirs of zoonoses, can identify spatiotemporal conditions associated with irruptions of abundances, as well as predict areas and times with higher risk of disease transmission. The aims of this research were to describe and identify (i) the rodent community composition; (ii) their population structure and breeding season; (iii) temporal and spatial variations in their population abundance; and (iv) the environmental factors associated with these variations on islands of upper Paraná River Delta, a zone of endemism for hantavirus pulmonary syndrome (HPS) in Argentina (Entre Ríos and Santa Fe provinces). We carried out seasonal surveys over 3 years (2014–2017) with live capture traps on seven islands (natural protected areas and under livestock grazing). Three hundred seventy-seven sigmodontine rodents of seven species were captured. While the maximum richness was seven, only four species coexisted at most on an island at the same time. Although changes in reproduction were detected throughout the year, seasonality, land use, and vegetation structure did not explain changes in abundance of rodents. Rodent abundances were affected mainly by flooding-related factors and meteorological conditions (rainfall and temperatures). The recovery of rodent populations after river flooding was species-specific and heterogeneous. The abundance of Oxymycterus rufus and Akodon azarae was affected by El Niño Southern Oscillation (ENSO); A. azarae did not recover after the flood at least during the study period. After the flood, populations of Oligoryzomys flavescens, the reservoir of HPS, also declined; however, this species’ populations were the first to recover its numbers, becoming dominant in the post-flood rodent community.

Hantavirus pulmonary syndrome outbreaks associated with climate variability in Northwestern Argentina, 1997-2017

Background

Rodent-borne hantaviruses (genus Orthohantavirus) are the etiologic agents causing two human diseases: hemorrhagic fever with renal syndrome (HFRS) in Euroasia; and hantavirus pulmonary syndrome (HPS) in North and South America. In South America fatality rates of HPS can reach up to 35%–50%. The transmission of pathogenic hantaviruses to humans occurs mainly via inhalation of aerosolized excreta from infected rodents. Thus, the epidemiology of HPS is necessarily linked to the ecology of their rodent hosts and the contact with a human, which in turn may be influenced by climatic variability. Here we examined the relationship between climatic variables and hantavirus transmission aim to develop an early warning system of potential hantavirus outbreaks based on ecologically relevant climatic factors.

Methodology and main findings

We compiled reported HPS cases in northwestern Argentina during the 1997–2017 period and divided our data into biannual, quarterly, and bimestrial time periods to allow annual and shorter time delays to be observed. To evaluate the relationship of hantavirus transmission with mean temperature and precipitation we used dynamic regression analysis. We found a significant association between HPS incidence and lagged rainfall and temperature with a delay of 2 to 6 months. For the biannual and quarterly models, hantavirus transmission was positively associated with lagged rainfall and temperature; whereas the bimestrial models indicate a direct relationship with the rainfall but inverse for temperature in the second lagged period.

Conclusions/Significance

This work demonstrates that climate variability plays a significant role in the transmission of hantavirus in northwestern Argentina. The model developed in this study provides a basis for the forecast of potential HPS outbreaks based on climatic parameters. Our findings are valuable for the development of public health policies and prevention strategies to mitigate possible outbreaks. Nonetheless, a surveillance program on rodent population dynamics would lead to a more accurate forecast of HPS outbreaks.

Hantavirus pulmonary syndrome (HPS) is a Pan-American emerging disease with a high mortality rate caused by a rodent-borne virus. In Argentina, almost half of the HPS infections occur in the northwestern endemic region. Most of the reported cases (75%) developed severe respiratory insufficiency, of which 30% required mechanical ventilation and 15% with a fatal outcome. In this study area, nearly half of the population is below the poverty line, particularly in rural areas, where most infections occur. Since there are no vaccines currently available nor specific therapeutic treatments, prevention of hantavirus infection involves mainly environmental management practices and educational campaigns. Our results provide a framework for the planning and implementation of early public health prevention campaigns based on the significant relationship between hantavirus outbreaks and delayed climatic variables.

Ecology of Neglected Rodent-Borne American Orthohantaviruses

The number of documented American orthohantaviruses has increased significantly over recent decades, but most fundamental research has remained focused on just two of them: Andes virus (ANDV) and Sin Nombre virus (SNV). The majority of American orthohantaviruses are known to cause disease in humans, and most of these pathogenic strains were not described prior to human cases, indicating the importance of understanding all members of the virus clade. In this review, we summarize information on the ecology of under-studied rodent-borne American orthohantaviruses to form general conclusions and highlight important gaps in knowledge. Information regarding the presence and genetic diversity of many orthohantaviruses throughout the distributional range of their hosts is minimal and would significantly benefit from virus isolations to indicate a reservoir role. Additionally, few studies have investigated the mechanisms underlying transmission routes and factors affecting the environmental persistence of orthohantaviruses, limiting our understanding of factors driving prevalence fluctuations. As landscapes continue to change, host ranges and human exposure to orthohantaviruses likely will as well. Research on the ecology of neglected orthohantaviruses is necessary for understanding both current and future threats to human health.

New data about home range and movements of Oligoryzomys flavescens (Rodentia: Cricetidae) help to understand the spread and transmission of Andes virus that causes Hantavirus Pulmonary Syndrome

Hantavirus pulmonary syndrome is an emerging infectious disease caused by viruses of the genus Orthohantavirus. The rodent Oligoryzomys flavescens is distributed along four countries of South America. In Argentina, O. flavescens acts as a reservoir of three genotypes of ANDV orthohantavirus. The aims of this work were to estimate home range size and movements-with spool-and-line and radiotelemetry-of infected and non-infected O. flavescens in order to understand the spread and transmission of the virus. O. flavescens use a wide area to satisfice its requirements, reaching a home range of 1.82 ha during spring. Orthohantavirus infection did not change the behaviour of individuals. We observed a great overlapping in the home range of infected and non-infected individuals resulting in a high probability of virus dispersion on rodent population. These results show that human health risks could be high on island environments and knowledge about the movement ecology of O. flavescens provides useful information on prevention.

Hantavirus infection and biodiversity in the Americas

Species diversity has been proposed to decrease prevalence of disease in a wide variety of host-pathogen systems, in a phenomenon labeled the dilution effect. This phenomenon was first proposed and tested for vector-borne diseases but was later extended to directly transmitted parasite systems such as hantavirus. Though there seems to be clear evidence for the dilution effect in some hantavirus/rodent systems, the generality of this hypothesis remains debated. In the present meta-analysis, we examined the evidence supporting the dilution effect for hantavirus/rodent systems in the Americas. General linear models employed on data from 56 field studies identified the abundance of the reservoir rodent species and its relative proportion in the community as the only relevant variables explaining the prevalence of antibodies against hantavirus in the reservoir. Thus, we found no clear support for the dilution effect hypothesis for hantavirus/rodent systems in the Americas.

A 19 Year Analysis of Small Mammals Associated with Human Hantavirus Cases in Chile

Small mammals present in areas where hantavirus cardiopulmonary syndrome (HCPS) cases had occurred in central and southern Chile were captured and analyzed to evaluate the abundance of rodents and seroprevalence rates of antibodies to Andes orthohantavirus (ANDV). Sampling areas ranged from the Coquimbo to Aysén regions (30–45° S approx.) regions. Ninety-two sites in peridomestic and countryside areas were evaluated in 19 years of sampling. An antibody against ANDV was detected by strip immunoassay in 58 of 1847 specimens captured using Sherman traps. Of the eleven species of rodents sampled, Abrothrix olivacea, Oligoryzomys longicaudatus and Abrothrix hirta were the most frequently trapped. O. longicaudatus had the highest seropositivity rate, and by logistic regression analysis, O. longicaudatus of at least 60 g had 80% or higher probability to be seropositive. Sex, age and wounds were significantly related to seropositivity only for O. longicaudatus. Across administrative regions, the highest seropositivity was found in the El Maule region (34.8–36.2° S), and the highest number of HCPS cases was registered in the Aysén region. Our results highlight the importance of long term and geographically extended studies, particularly for highly fluctuating pathogens and their reservoirs, to understand the implications of the dynamics and transmission of zoonotic diseases in human populations.

Hantavirus Pulmonary Syndrome Risk in Entre Ríos, Argentina

Hantavirus pulmonary syndrome (HPS) is a severe emerging endemic disease of the Americas. Because hantavirus reservoirs are sylvatic rodents, HPS risk has been associated with occupational and recreational activities in natural and rural environments. The aim of this study was to analyze the risk of HPS in an endemic province of Argentina. For this, we explored the relationship between HPS cases occurring in Entre Ríos province between 2004 and 2015 and climate, vegetation, landscape, reservoir population, and rodent community characteristics by means of generalized linear models. We modeled HPS occurrence at each site, and both the incidence and number of cases grouped by department. The resulting best model of each analysis was applied in a GIS to build HPS risk maps. Risk of occurrence of HPS increased with tree cover and decreased with distance to rivers. We identified the south of Entre Ríos as the area with higher HPS risk, and therefore, where HPS prevention measures should be more urgently applied. Risk maps based on data available in the public domain are a useful tool that should be used by decision makers to concentrate surveillance and control efforts in those areas with highest HPS risk.

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.

Long-Term Study of a Hantavirus Reservoir Population in an Urban Protected Area, Argentina

Green spaces in urban areas can play a key role in protecting wildlife. However, the presence of wildlife in urban areas can lead to human health risks. Although the presence of the rodent species Oligoryzomys flavescens (hantavirus reservoir) has been recorded in cities of Argentina, its population dynamics in this type of habitat is still unknown. Here, we evaluated: (1) long-term spatial and temporal patterns of O. flavescens abundance and how these patterns were influenced by weather factors and (2) the seroprevalence of hantavirus and the identity of the viral lineage circulating in the population that inhabits the Costanera Sur Ecological Reserve, a protected area in the city of Buenos Aires. Genetic results confirmed that the pathogenic ANDES Central Lechiguanas virus is present in O. flavescens populations inhabiting this urban reserve. Abundance of O. flavescens showed interannual and seasonal fluctuations, with maximum values in winter and spring and minimum ones in summer and autumn. Summers with the highest abundances of O. flavescens were preceded by warmer winters, while winters with lower abundances were preceded by warmer summers. On the other hand, accumulated precipitations in the previous 6 months positively affected winter abundance. These results could help the authorities in charge of the green spaces of Buenos Aires to identify priority areas and times of the year for the implementation of preventive measures that minimize the contact of rodents with visitors. Such measures could be intensified when winters are warmer than normal, and summers are cooler and wetter than normal.

Rodent Abundance and Hantavirus Infection in Protected Area, East-Central Argentina

We captured 3 hantavirus rodent hosts in Otamendi Natural Reserve, Argentina, during 2007-2012. Hantavirus antibodies were found only in Akodon azarae grass mice, mainly in males and old animals. Higher abundance of this species was associated with warm and rainy weather and high water levels, which peaked after a strong El Niño event.

Global Diversity and Distribution of Hantaviruses and Their Hosts

Rodents represent 42% of the world's mammalian biodiversity encompassing 2,277 species populating every continent (except Antarctica) and are reservoir hosts for a wide diversity of disease agents. Thus, knowing the identity, diversity, host-pathogen relationships, and geographic distribution of rodent-borne zoonotic pathogens, is essential for predicting and mitigating zoonotic disease outbreaks. Hantaviruses are hosted by numerous rodent reservoirs. However, the diversity of rodents harboring hantaviruses is likely unknown because research is biased toward specific reservoir hosts and viruses. An up-to-date, systematic review covering all known rodent hosts is lacking. Herein, we document gaps in our knowledge of the diversity and distribution of rodent species that host hantaviruses. Of the currently recognized 681 cricetid, 730 murid, 61 nesomyid, and 278 sciurid species, we determined that 11.3, 2.1, 1.6, and 1.1%, respectively, have known associations with hantaviruses. The diversity of hantaviruses hosted by rodents and their distribution among host species supports a reassessment of the paradigm that each virus is associated with a single-host species. We examine these host-virus associations on a global taxonomic and geographical scale with emphasis on the rodent host diversity and distribution. Previous reviews have been centered on the viruses and not the mammalian hosts. Thus, we provide a perspective not previously addressed.

Evaluation of habitat requirements of small rodents and effectiveness of an ecologically-based management in a hantavirus-endemic natural protected area in Argentina

Hantavirus pulmonary syndrome is a severe cardio pulmonary disease transmitted to humans by sylvan rodents found in natural and rural environments. Disease transmission is closely linked to the ecology of animal reservoirs and abiotic factors such as habitat characteristics, season or climatic conditions. The main goals of this research were: to determine the biotic and abiotic factors affecting richness and abundance of rodent species at different spatial scales, to evaluate different methodologies for studying population of small rodents, and to describe and analyze an ecologically-based rodent management experience in a highly touristic area. A 4-year study of small rodent ecology was conducted between April 2007 and August 2011 in the most relevant habitats of El Palmar National Park, Argentina. Management involved a wide range of control and prevention measures, including poisoning, culling and habitat modification. A total of 172 individuals of 5 species were captured with a trapping effort of 13 860 traps-nights (1.24 individuals/100 traps-nights). Five rodent species were captured, including 2 hantavirus-host species, Oligoryzomys nigripes and Akodon azarae. Oligoryzomys nigripes, host of a hantavirus that is pathogenic in humans, was the most abundant species and the only one found in all the studied habitats. Our results are inconsistent with the dilution effect hypothesis. The present study demonstrates that sylvan rodent species, including the hantavirus-host species, have distinct local habitat selection and temporal variation patterns in abundance, which may influence the risk of human exposure to hantavirus and may have practical implications for disease transmission as well as for reservoir management.

Landscape, Environmental and Social Predictors of Hantavirus Risk in São Paulo, Brazil

Hantavirus Pulmonary Syndrome (HPS) is a disease caused by Hantavirus, which are negative-sense RNA viruses in the family Bunyaviridae that are highly virulent to humans. Numerous factors modify risk of Hantavirus transmission and consequent HPS risk. Human-driven landscape change can foster transmission risk by increasing numbers of habitat generalist rodent species that serve as the principal reservoir host. Climate can also affect rodent population dynamics and Hantavirus survival, and a number of social factors can influence probability of HPS transmission to humans. Evaluating contributions of these factors to HPS risk may enable predictions of future outbreaks, and is critical to development of effective public health strategies. Here we rely on a Bayesian model to quantify associations between annual HPS incidence across the state of São Paulo, Brazil (1993–2012) and climate variables (annual precipitation, annual mean temperature), landscape structure metrics (proportion of native habitat cover, number of forest fragments, proportion of area planted with sugarcane), and social factors (number of men older than 14 years and Human Development Index). We built separate models for the main two biomes of the state (cerrado and Atlantic forest). In both biomes Hantavirus risk increased with proportion of land cultivated for sugarcane and HDI, but proportion of forest cover, annual mean temperature, and population at risk also showed positive relationships in the Atlantic forest. Our analysis provides the first evidence that social, landscape, and climate factors are associated with HPS incidence in the Neotropics. Our risk map can be used to support the adoption of preventive measures and optimize the allocation of resources to avoid disease propagation, especially in municipalities that show medium to high HPS risk (> 5% of risk), and aimed at sugarcane workers, minimizing the risk of future HPS outbreaks.

How much effort is required to accurately describe the complex ecology of a rodent-borne viral disease?

We use data collected on 18,1-ha live trapping grids monitored from 1994 through 2005 and on five of those grids through 2013 in the mesic northwestern US to illustrate the complexity of the deer mouse (Peromyscus maniculatus)/Sin Nombre virus (SNV) host-pathogen system. Important factors necessary to understand zoonotic disease ecology include those associated with distribution and population dynamics of reservoir species as well as infection dynamics. Results are based on more than 851,000 trap nights, 16,608 individual deer mice and 10,572 collected blood samples. Deer mice were distributed throughout every habitat we sampled and were present during every sampling period in all habitats except high altitude habitats over1900 m. Abundance varied greatly among locations with peak numbers occurring mostly during fall. However, peak rodent abundance occurred during fall, winter and spring during various years on three grids trapped 12 mo/yr. Prevalence of antibodies to SNV averaged 3.9% to 22.1% but no grids had mice with antibodies during every month. The maximum period without antibody-positive mice ranged from one month to 52 months, or even more at high altitude grids where deer mice were not always present. Months without antibody-positive mice were more prevalent during fall than spring. Population fluctuations were not synchronous over broad geographic areas and antibody prevalences were not well spatially consistent, differing greatly over short distances. We observed an apparently negative, but non-statistically significant relationship between average antibody prevalence and average deer mouse population abundance and a statistically significant positive relationship between the average number of antibody positive mice and average population abundance. We present data from which potential researchers can estimate the effort required to adequately describe the ecology of a rodent-borne viral system. We address different factors affecting population dynamics and hantavirus antibody prevalence and discuss the path to understanding a complex rodent-borne disease system as well as the obstacles in that path.

Environmental Variables Associated with Hantavirus Reservoirs and Other Small Rodent Species in Two National Parks in the Paraná Delta, Argentina: Implications for Disease Prevention

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.

Daily Movements and Microhabitat Selection of Hantavirus Reservoirs and Other Sigmodontinae Rodent Species that Inhabit a Protected Natural Area of Argentina

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.

Population ecology of hantavirus rodent hosts in southern Brazil

In this study we analyze population dynamics of hantavirus rodent hosts and prevalence of infection over a 2-year period in Southern Brazil, a region with a high incidence of hantavirus pulmonary syndrome. The 14 small mammal species captured were composed of 10 rodents and four marsupials, the six most abundant species being Akodon serrensis, Oxymycterus judex, Akodon montensis, Akodon paranaensis, Oligoryzomys nigripes, and Thaptomys nigrita. These species displayed a similar pattern with increasing population sizes in fall/winter caused by recruitment and both, increase in reproductive activity and higher hantavirus prevalence in spring/summer. Specific associations between A. montensis/Jaborá Virus (JABV) and O. nigripes/Juquitiba-like Virus (JUQV-like) and spillover infections between A. paranaensis/JABV, A. serrensis/JABV, and A. paranaensis/JUQV-like were observed. Spillover infection in secondary hosts seems to play an important role in maintaining JABV and JUQV-like in the hantavirus sylvatic cycle mainly during periods of low prevalence in primary hosts.