Responses of small mammals to habitat fragmentation: epidemiological considerations for rodent-borne hantaviruses in the Americas

Association between anthropization and rodent reservoirs of zoonotic pathogens in Northwestern Mexico

The world is facing a major pulse of ecological and social changes that may favor the risk of zoonotic outbreaks. Such risk facilitation may occur through the modification of the host's community diversity and structure, leading to an increase in pathogen reservoirs and the contact rate between these reservoirs and humans. Here, we examined whether anthropization alters the relative abundance and richness of zoonotic reservoir and non-reservoir rodents in three Socio-Ecological Systems. We hypothesized that anthropization increases the relative abundance and richness of rodent reservoirs while decreasing non-reservoir species. We first developed an Anthropization index based on 15 quantitative socio-ecological variables classified into five groups: 1) Vegetation type, 2) Urbanization degree, 3) Water quality, 4) Potential contaminant sources, and 5) Others. We then monitored rodent communities in three regions of Northwestern Mexico (Baja California, Chihuahua, and Sonora). A total of 683 rodents of 14 genera and 27 species were captured, nine of which have been identified as reservoirs of zoonotic pathogens (359 individuals, 53%). In all regions, we found that as anthropization increased, the relative abundance of reservoir rodents increased; in contrast, the relative abundance of non-reservoir rodents decreased. In Sonora, reservoir richness increased with increasing anthropization, while in Baja California and Chihuahua non-reservoir richness decreased as anthropization increased. We also found a significant positive relationship between the anthropization degree and the abundance of house mice (Mus musculus) and deer mice (Peromyscus maniculatus), the most abundant reservoir species in the study. These findings support the hypothesis that reservoir species of zoonotic pathogens increase their abundance in disturbed environments, which may increase the risk of pathogen exposure to humans, while anthropization creates an environmental filtering that promotes the local extinction of non-reservoir species.

Immunogenetic-pathogen networks shrink in Tome's spiny rat, a generalist rodent inhabiting disturbed landscapes

Anthropogenic disturbance may increase the emergence of zoonoses. Especially generalists that cope with disturbance and live in close contact with humans and livestock may become reservoirs of zoonotic pathogens. Yet, whether anthropogenic disturbance modifies host-pathogen co-evolutionary relationships in generalists is unknown. We assessed pathogen diversity, neutral genome-wide diversity (SNPs) and adaptive MHC class II diversity in a rodent generalist inhabiting three lowland rainforest landscapes with varying anthropogenic disturbance, and determined which MHC alleles co-occurred more frequently with 13 gastrointestinal nematodes, blood trypanosomes, and four viruses. Pathogen-specific selection pressures varied between landscapes. Genome-wide diversity declined with the degree of disturbance, while MHC diversity was only reduced in the most disturbed landscape. Furthermore, pristine forest landscapes had more functional important MHC-pathogen associations when compared to disturbed forests. We show co-evolutionary links between host and pathogens impoverished in human-disturbed landscapes. This underscores that parasite-mediated selection might change even in generalist species following human disturbance which in turn may facilitate host switching and the emergence of zoonoses.

Distribution and prevalence of Sin Nombre hantavirus in rodent species in eastern New Mexico

Orthohantaviruses are diverse zoonotic RNA viruses. Small mammals, such as mice and rats are common chronic, asymptomatic hosts that transmit the virus through their feces and urine. In North America, hantavirus infection primarily causes hantavirus cardiopulmonary syndrome (HCPS), which has a mortality rate of nearly 36%. In the United States of America, New Mexico (NM) is leading the nation in the number of HCPS-reported cases (N = 129). However, no reported cases of HCPS have occurred within eastern NM. In this study, we assessed the prevalence of Sin Nombre virus (SNV) in rodent assemblages across eastern NM, using RT-qPCR. We screened for potential rodent hosts in the region, as well as identified areas that may pose significant infection risk to humans. We captured and collected blood and lung tissues from 738 rodents belonging to 23 species. 167 individuals from 16 different species were positive for SNV RNA by RT-qPCR, including 6 species unreported in the literature: Onychomys leucogaster (Northern grasshopper mouse), Dipodomys merriami (Merriam's kangaroo rat), Dipodomys ordii (Ord's kangaroo rat), Dipodomys spectabilis (Banner-tailed kangaroo rat), Perognathus flavus (Silky pocket mouse), and Chaetodipus hispidus (Hispid pocket mouse). The infection rates did not differ between sexes or rodent families (i.e., Cricetidae vs. Heteromyidae). Generalized linear model showed that disturbed habitat types positively influenced the prevalence of SNV at sites of survey. Overall, the results of this study indicate that many rodent species in east New Mexico have the potential to maintain SNV in the environment, but further research is needed to assess species specific infectivity mechanisms and potential risk to humans.

Differential Impact of Forest Fragmentation on Fluctuating Asymmetry in South Amazonian Small Mammals

(1) Background: Southern Amazonia encompasses some of the most human-impacted and deforested regions of South America, resulting in a hyper-fragmented landscape. In this context, by using a geometric morphometrics approach, we aimed to examine the effect of forest fragmentation on developmental instability (DI) of the mandible, assessed by variation of fluctuating asymmetry (FA), in four neotropical small mammal species inhabiting the municipality of Alta Floresta (Brazil). (2) Methods: The impact of fragment area, fragment shape, isolation, and edge length on DI were assessed by measuring variation in mandibular FA in the long-tailed spiny rat (Proechimys longicaudatus), the hairy-tailed bolo mouse (Necromys lasiurus), the woolly mouse opossum (Marmosa demerarae), and the Amazonian red-sided opossum (Monodelphis glirina). Mandibles from a total of 304 specimens originating from different-sized fragments (ranging from 5 to 900 ha) were used. Twelve homologous landmarks were digitized in photographs of the mesial view of each hemi-mandible. (3) Results: The two largest species, P. longicaudatus and M. demerarae, exhibited significantly higher levels of FA in mandibular shape in small fragments (5–26 ha) in comparison to large ones (189–900 ha). Edge length negatively impacted M. demerarae, the only arboreal species, reinforcing its strongest dependence on core forest habitats. (4) Conclusions: For small mammal communities, we propose that fragments >~200 ha should be the focus of conservation efforts, as both resilient and more sensitive species would benefit from their more preserved biotic and abiotic conditions. Conversely, fragments <~25 ha seem to lead to a significant increase in stress during developmental stages.

A Review of Mammarenaviruses and Rodent Reservoirs in the Americas

In the Americas, infectious viral diseases caused by viruses of the genus Mammarenavirus have been reported since the 1960s. Such diseases have commonly been associated with land use changes, which favor abundance of generalist rodent species. In the Americas-where the rates of land use change are among the highest worldwide-at least 1326 of all 2277 known rodent species have been reported. We conducted a literature review of studies between 1960 and 2020, to establish the current and historical knowledge about genotypes of mammarenaviruses and their rodent reservoirs in the Americas. Our overall goal was to show the importance of focusing research efforts on the American continent, since the conditions exist for future viral hemorrhagic fever (VHF) outbreaks caused by rodent-borne viruses, in turn, carried by widely distributed rodents. We found 47 species identified down to the species level, and one species identified only down to the genus level (Oryzomys sp.), reported in the Americas as reservoirs of mammarenaviruses, most these are ecological generalists. These species associate with 29 genotypes of Mammarenavirus, seven of which have been linked to VHFs in humans. We also highlight the need to monitor these species, in order to prevent viral disease outbreaks in the region.

Population connectivity in voles (Microtus sp.) as a gauge for tall grass prairie restoration in midwestern North America

Ecological restoration can promote biodiversity conservation in anthropogenically fragmented habitats, but effectiveness of these management efforts need to be statistically validated to determine ’success.’ One such approach is to gauge the extent of recolonization as a measure of landscape permeability and, in turn, population connectivity. In this context, we estimated dispersal and population connectivity in prairie vole (Microtus ochrogaster; N = 231) and meadow vole (M. pennsylvanicus; N = 83) within five tall-grass prairie restoration sites embedded within the agricultural matrix of midwestern North America. We predicted that vole dispersal would be constrained by the extent of agricultural land surrounding restored habitat patches, spatially isolating vole populations and resulting in significant genetic structure. We first employed genetic assignment tests based on 15 microsatellite DNA loci to validate field-derived species-designations, then tested reclassified samples with multivariate and Bayesian clustering to assay for spatial and temporal genetic structure. Population connectivity was further evaluated by calculating pairwise F_ST, then potential demographic effects explored by computing migration rates, effective population size (N_e), and average relatedness (r). Genetic species assignments reclassified 25% of initial field identifications (N = 11 M. ochrogaster; N = 67 M. pennsylvanicus). In M. ochrogaster population connectivity was high across the study area, reflected in little to no spatial or temporal genetic structure. In M. pennsylvanicus genetic structure was detected, but relatedness estimates identified it as kin-clustering instead, underscoring social behavior among populations rather than spatial isolation as the cause. Estimates of N_e and r were stable across years, reflecting high dispersal and demographic resilience. Combined, these metrics suggest the agricultural matrix is highly permeable for voles and does not impede dispersal. High connectivity observed confirms that the restored landscape is productive and permeable for specific management targets such as voles and also demonstrates population genetic assays as a tool to statistically evaluate effectiveness of conservation initiatives.

Land-use change and rodent-borne diseases: hazards on the shared socioeconomic pathways

Land-use change has a direct impact on species survival and reproduction, altering their spatio-temporal distributions. It acts as a selective force that favours the abundance and diversity of reservoir hosts and affects host-pathogen dynamics and prevalence. This has led to land-use change being a significant driver of infectious diseases emergence. Here, we predict the presence of rodent taxa and map the zoonotic hazard (potential sources of harm) from rodent-borne diseases in the short and long term (2025 and 2050). The study considers three different land-use scenarios based on the shared socioeconomic pathways narratives (SSPs): sustainable (SSP1-Representative Concentration Pathway (RCP) 2.6), fossil-fuelled development (SSP5-RCP 8.5) and deepening inequality (SSP4-RCP 6.0). We found that cropland expansion into forest and pasture may increase zoonotic hazards in areas with high rodent-species diversity. Nevertheless, a future sustainable scenario may not always reduce hazards. All scenarios presented high heterogeneity in zoonotic hazard, with high-income countries having the lowest hazard range. The SSPs narratives suggest that opening borders and reducing cropland expansion are critical to mitigate current and future zoonotic hazards globally, particularly in middle- and low-income economies. Our study advances previous efforts to anticipate the emergence of zoonotic diseases by integrating past, present and future information to guide surveillance and mitigation of zoonotic hazards at the regional and local scale. This article is part of the theme issue 'Infectious disease macroecology: parasite diversity and dynamics across the globe'.

Impact of Predator Exclusion and Habitat on Seroprevalence of New World Orthohantavirus Harbored by Two Sympatric Rodents within the Interior Atlantic Forest

Understanding how perturbations to trophic interactions influence virus-host dynamics is essential in the face of ongoing biodiversity loss and the continued emergence of RNA viruses and their associated zoonoses. Herein, we investigated the role of predator exclusion on rodent communities and the seroprevalence of hantaviruses within the Reserva Natural del Bosque Mbaracayú (RNBM), which is a protected area of the Interior Atlantic Forest (IAF). In the IAF, two sympatric rodent reservoirs, Akodon montensis and Oligoryzomys nigripes, harbor Jaborá and Juquitiba hantavirus (JABV, JUQV), respectively. In this study, we employed two complementary methods for predator exclusion: comprehensive fencing and trapping/removal. The goal of exclusion was to preclude the influence of predation on small mammals on the sampling grids and thereby potentially reduce rodent mortality. Following baseline sampling on three grid pairs with different habitats, we closed the grids and began predator removal. By sampling three habitat types, we controlled for habitat-specific effects, which is important for hantavirus-reservoir dynamics in neotropical ecosystems. Our six-month predator exclusion experiment revealed that the exclusion of terrestrial mammalian predators had little influence on the rodent community or the population dynamics of A. montensis and O. nigripes. Instead, fluctuations in species diversity and species abundances were influenced by sampling session and forest degradation. These results suggest that seasonality and landscape composition play dominant roles in the prevalence of hantaviruses in rodent reservoirs in the IAF ecosystem.

Landscape Seroprevalence of Three Hemorrhagic Disease-Causing Viruses in a Wild Cervid

Disease plays a major role in shaping wildlife populations worldwide, and changes in landscape conditions can significantly influence risk of pathogen exposure, a threat to vulnerable wild species. Three viruses that cause hemorrhagic disease affect cervid populations in the USA (Odocoileus hemionus adenovirus, bluetongue virus, and epizootic hemorrhagic disease virus), but little is known of their distribution and prevalence in wild populations. We explored the distribution and co-occurrence of seroprevalence of these three pathogens in southern mule deer (Odocoileus hemionus fuliginatus), a subspecies of conservation concern and a harvested species native to southern California, to evaluate the distribution of exposure to these pathogens relative to landscape attributes. We found that habitat type, level of development, and proximity to livestock may affect hemorrhagic disease seroprevalence in southern mule deer. Continued monitoring of hemorrhagic disease-causing viruses in areas where deer are in proximity to cattle and human development is needed to better understand the implications of future outbreaks in wild populations and to identify opportunities to mitigate disease impacts in southern mule deer and other cervid species.

Transdisciplinary Research Priorities for Human and Planetary Health in the Context of the 2030 Agenda for Sustainable Development

Human health and wellbeing and the health of the biosphere are inextricably linked. The state of Earth's life-support systems, including freshwater, oceans, land, biodiversity, atmosphere, and climate, affect human health. At the same time, human activities are adversely affecting natural systems. This review paper is the outcome of an interdisciplinary workshop under the auspices of the Future Earth Health Knowledge Action Network (Health KAN). It outlines a research agenda to address cross-cutting knowledge gaps to further understanding and management of the health risks of these global environmental changes through an expert consultation and review process. The research agenda has four main themes: (1) risk identification and management (including related to water, hygiene, sanitation, and waste management); food production and consumption; oceans; and extreme weather events and climate change. (2) Strengthening climate-resilient health systems; (3) Monitoring, surveillance, and evaluation; and (4) risk communication. Research approaches need to be transdisciplinary, multi-scalar, inclusive, equitable, and broadly communicated. Promoting resilient and sustainable development are critical for achieving human and planetary health.

Land-Use Change Alters Host and Vector Communities and May Elevate Disease Risk

Land-use change has transformed most of the planet. Concurrently, recent outbreaks of various emerging infectious diseases have raised great attention to the health consequences of anthropogenic environmental degradation. Here, we assessed the global impacts of habitat conversion and other land-use changes on community structures of infectious disease hosts and vectors, using a meta-analysis of 37 studies. From 331 pairwise comparisons of disease hosts/vectors in pristine (undisturbed) and disturbed areas, we found a decrease in species diversity but an increase in body size associated with land-use changes, potentially suggesting higher risk of infectious disease transmission in disturbed habitats. Neither host nor vector abundance, however, changed significantly following disturbance. When grouped by subcategories like disturbance type, taxonomic group, pathogen type and region, changes in host/vector community composition varied considerably. Fragmentation and agriculture in particular benefit host and vector communities and therefore might elevate disease risk. Our results indicate that while habitat disturbance could alter disease host/vector communities in ways that exacerbate pathogen prevalence, the relationship is highly context-dependent and influenced by multiple factors.

Exotic Pinus radiata Plantations do not Increase Andes Hantavirus Prevalence in Rodents

Andes south virus (ANDV) is the etiologic agent of hantavirus cardiopulmonary syndrome (HCPS) in Chile and southern Argentina. Farm and forestry workers have been identified as a group at high risk of acquiring HCPS caused by ANDV due to their close exposure to rodents or their secretions in rural areas. Therefore, investigation on the effect of landscape composition on ANDV in wild rodents becomes relevant for disease prevention and control. In this study, we analyzed the influence of Monterey pine (Pinus radiata) plantations, an important monoculture in the global forest industry, on small mammal assemblage and on ANDV seroprevalence and abundance of seropositive rodents from central Chile. Small mammals were sampled seasonally during 2 years in native forests, adult pine plantations and young pine plantations. A total of 1630 samples from seven rodent species were analyzed for antibody detection. ANDV seroprevalence and abundance of seropositive rodents were significantly higher in the native forest compared to pine plantations. Furthermore, Monterey pine plantations decrease the abundance and relative abundance of Oligoryzomys longicaudatus (the principal reservoir of ANDV) and do not change sex ratio and distribution of age classes of this rodent species, which are variables that are important for ANDV transmission. Our findings indicate that Monterey pine plantations would not pose a higher risk of human exposure to ANDV compared to the temperate native forest. Our results can be useful for hantavirus risks assessment in human-dominated areas where ANDV is endemic.

Spatiotemporal Dynamics of Hantavirus Cardiopulmonary Syndrome Transmission Risk in Brazil

BACKGROUND

Hantavirus disease in humans is rare but frequently lethal in the Neotropics. Several abundant and widely distributed Sigmodontinae rodents are the primary hosts of Orthohantavirus and, in combination with other factors, these rodents can shape hantavirus disease. Here, we assessed the influence of host diversity, climate, social vulnerability and land use change on the risk of hantavirus disease in Brazil over 24 years.

METHODS

Landscape variables (native forest, forestry, sugarcane, maize and pasture), climate (temperature and precipitation), and host biodiversity (derived through niche models) were used in spatiotemporal models, using the 5570 Brazilian municipalities as units of analysis.

RESULTS

Amounts of native forest and sugarcane, combined with temperature, were the most important factors influencing the increase of disease risk. Population at risk (rural workers) and rodent host diversity also had a positive effect on disease risk.

CONCLUSIONS

Land use change-especially the conversion of native areas to sugarcane fields-can have a significant impact on hantavirus disease risk, likely by promoting the interaction between the people and the infected rodents. Our results demonstrate the importance of understanding the interactions between landscape change, rodent diversity, and hantavirus disease incidence, and suggest that land use policy should consider disease risk. Meanwhile, our risk map can be used to help allocate preventive measures to avoid disease.

Current Situation and Perspectives on Hantaviruses in Mexico

Hantaviruses are transmitted by rodents producing the hantavirus pulmonary syndrome (HPS) in the Americas. Today, no human cases of HPS have been reported in Mexico in spite of similar environmental conditions with Central America and the USA where several cases have occurred. To understand the current situation of hantaviruses in Mexico and the public health risk, a systematic review of studies was conducted reporting hantaviruses in rodents to known state seroprevalence and hantavirus genotypes. Simultaneously, this study identified the potential hantaviruses based on the phylogenetic diversity (PD) of hantaviruses reported in the Americas in hosts with the distribution in Mexico. A total 3862 rodents belonging to 82 species have been tested since 1999 to 2017. Overall, 392 individuals representing 43 rodent species were seropositive, and the seroprevalence ranged from 0 to 69.22%. Seven hantaviruses genotypes have been described in Mexico and three are zoonotic. Four host species of rodents are widely distributed in Mexico harboring the highest PD of viruses. According to the hosts distribution, 16 genotypes could be circulating in Mexico and some of these represent a potential risk for public health. This study proposed multidisciplinary and interinstitutional collaborations to implement systematic surveillance in rodents.

Changing landscapes of Southeast Asia and rodent-borne diseases: decreased diversity but increased transmission risks

The reduction in biodiversity from land use change due to urbanization and agricultural intensification appears to be linked to major epidemiological changes in many human diseases. Increasing disease risks and the emergence of novel pathogens result from increased contact among wildlife, domesticated animals, and humans. We investigated the relationship between human alteration of the environment and the occurrence of generalist and synanthropic rodent species in relation to the diversity and prevalence of rodent-borne pathogens in Southeast Asia, a hotspot of threatened and endangered species, and a foci of emerging infectious diseases. We used data from an extensive pathogen survey of rodents from seven sites in mainland Southeast Asia in conjunction with past and present land cover analyses. At low spatial resolutions, we found that rodent-borne pathogen richness is negatively associated with increasing urbanization, characterized by increased habitat fragmentation, agriculture cover and deforestation. However, at a finer spatial resolution, we found that some major pathogens are favored by environmental characteristics associated with human alteration including irrigation, habitat fragmentation, and increased agricultural land cover. In addition, synanthropic rodents, many of which are important pathogen reservoirs, were associated with fragmented and human-dominated landscapes, which may ultimately enhance the opportunities for zoonotic transmission and human infection by some pathogens.

The Impact of Global Environmental Changes on Infectious Disease Emergence with a Focus on Risks for Brazil

Environmental changes have a huge impact on the emergence and reemergence of certain infectious diseases, mostly in countries with high biodiversity and serious unresolved environmental, social, and economic issues. This article summarizes the most important findings with special attention to Brazil and diseases of present public health importance in the country such as Chikungunya, dengue fever, yellow fever, Zika, hantavirus pulmonary syndrome, leptospirosis, leishmaniasis, and Chagas disease. An extensive literature review revealed a relationship between infectious diseases outbreaks and climate change events (El Niño, La Niña, heatwaves, droughts, floods, increased temperature, higher rainfall, and others) or environmental changes (habitat fragmentation, deforestation, urbanization, bushmeat consumption, and others). To avoid or control outbreaks, integrated surveillance systems and effective outreach programs are essential. Due to strong global and local influence on emergence of infectious diseases, a more holistic approach is necessary to mitigate or control them in low-income nations.

Species Identity Supersedes the Dilution Effect Concerning Hantavirus Prevalence at Sites across Texas and México

Recent models suggest a relationship exists between community diversity and pathogen prevalence, the proportion of individuals in a population that are infected by a pathogen, with most inferences tied to assemblage structure. Two contrasting outcomes of this relationship have been proposed: the "dilution effect" and the "amplification effect." Small mammal assemblage structure in disturbed habitats often differs from assemblages in sylvan environments, and hantavirus prevalence is often negatively correlated with habitats containing high species diversity via dilution effect dynamics. As species richness increases, prevalence of infection often is decreased. However, anthropogenic changes to sylvan landscapes have been shown to decrease species richness and/or increase phylogenetic similarities within assemblages. Between January 2011 and January 2016, we captured and tested 2406 individual small mammals for hantavirus antibodies at 20 sites across Texas and México and compared differences in hantavirus seroprevalence, species composition, and assemblage structure between sylvan and disturbed habitats. We found 313 small mammals positive for antibodies against hantaviruses, evincing an overall prevalence of 9.7% across all sites. In total, 40 species of small mammals were identified comprising 2 taxonomic orders (Rodentia and Eulipotyphla). By sampling both habitat types concurrently, we were able to make real-world inferences into the efficacy of dilution effect theory in terms of hantavirus ecology. Our hypothesis predicting greater species richness higher in sylvan habitats compared to disturbed areas was not supported, suggesting the characteristics of assemblage structure do not adhere to current conceptions of species richness negatively influencing prevalence via a dilution effect.

Does the impact of biodiversity differ between emerging and endemic pathogens? The need to separate the concepts of hazard and risk

Biodiversity is of critical value to human societies, but recent evidence that biodiversity may mitigate infectious-disease risk has sparked controversy among researchers. The majority of work on this topic has focused on direct assessments of the relationship between biodiversity and endemic-pathogen prevalence, without disentangling intervening mechanisms; thus study outcomes often differ, fuelling more debate. Here, we suggest two critical changes to the approach researchers take to understanding relationships between infectious disease, both endemic and emerging, and biodiversity that may help clarify sources of controversy. First, the distinct concepts of hazards versus risks need to be separated to determine how biodiversity and its drivers may act differently on each. This distinction is particularly important since it illustrates that disease emergence drivers in humans could be quite different to the general relationship between biodiversity and transmission of endemic pathogens. Second, the interactive relationship among biodiversity, anthropogenic change and zoonotic disease risk, including both direct and indirect effects, needs to be recognized and accounted for. By carefully disentangling these interactions between humans' activities and pathogen circulation in wildlife, we suggest that conservation efforts could mitigate disease risks and hazards in novel ways that complement more typical disease control efforts.This article is part of the themed issue 'Conservation, biodiversity and infectious disease: scientific evidence and policy implications'.

Trypanosoma cruzi reservoir-triatomine vector co-occurrence networks reveal meta-community effects by synanthropic mammals on geographic dispersal

Contemporary patterns of land use and global climate change are modifying regional pools of parasite host species. The impact of host community changes on human disease risk, however, is difficult to assess due to a lack of information about zoonotic parasite host assemblages. We have used a recently developed method to infer parasite-host interactions for Chagas Disease (CD) from vector-host co-occurrence networks. Vector-host networks were constructed to analyze topological characteristics of the network and ecological traits of species’ nodes, which could provide information regarding parasite regional dispersal in Mexico. Twenty-eight triatomine species (vectors) and 396 mammal species (potential hosts) were included using a data-mining approach to develop models to infer most-likely interactions. The final network contained 1,576 links which were analyzed to calculate centrality, connectivity, and modularity. The model predicted links of independently registered Trypanosoma cruzi hosts, which correlated with the degree of parasite-vector co-occurrence. Wiring patterns differed according to node location, while edge density was greater in Neotropical as compared to Nearctic regions. Vectors with greatest public health importance (i.e., Triatoma dimidiata, T. barberi, T. pallidipennis, T. longipennis, etc), did not have stronger links with particular host species, although they had a greater frequency of significant links. In contrast, hosts classified as important based on network properties were synanthropic mammals. The latter were the most common parasite hosts and are likely bridge species between these communities, thereby integrating meta-community scenarios beneficial for long-range parasite dispersal. This was particularly true for rodents, >50% of species are synanthropic and more than 20% have been identified as T. cruzi hosts. In addition to predicting potential host species using the co-occurrence networks, they reveal regions with greater expected parasite mobility. The Neotropical region, which includes the Mexican south and southeast, and the Transvolcanic belt, had greatest potential active T. cruzi dispersal, as well as greatest edge density. This information could be directly applied for stratification of transmission risk and to design and analyze human-infected vector contact intervention efficacy.

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.

Community perceptions of health and rodent-borne diseases along the Inter-Oceanic Highway in Madre de Dios, Peru

Background

Madre de Dios is located in the southeastern Amazonian region of Peru. Rodents have been estimated to be the reservoirs for up to 50 % of emerging zoonotic pathogens, including a host of viruses, bacteria, and parasites. As part of a larger study involving both human and animal research, this study serves to obtain a broader understanding of the key challenges and concerns related to health and rodent-borne illnesses from the perspective of the people living in these communities.

Methods

We used a mixed methods approach, which comprised of 12 focus group discussions, 34 key informant interviews and the application of a survey (n = 522) in four communities along the Inter-Oceanic Highway (IOH) in Madre de Dios, Peru over a two-year period.

Results

Although 90 % of survey respondents answered that rodents can transmit diseases and had seen rodents in their homes and immediate surroundings, most could not name specific rodent-borne diseases and, when probed, described rodents as pests or nuisance animals, but were not concerned about acquiring illnesses from them. Key informant interview data suggests that there has been a perceived increase in the amount of rodents in the communities since the construction of the IOH, however this potential increase was not coupled with increased knowledge about diseases or perceived risks among these key informants. Health providers also mentioned a lack of diagnostic tools specific for rodent-borne illnesses. This may be related to the fact that although a common rodent-borne disease like leptospirosis is frequently detected in the region, it is not routinely and readily diagnosed, therefore the real burden of the disease and exposure risk can be underestimated. If rodent-borne diseases are not on the radar of health professionals, they may not consider presumptive treatment, which could result in unnecessary morbidity and mortality.

Conclusion

Awareness of rodent-borne diseases is still lacking in the area, even among health care professionals within the communities, despite the known burden of diseases like leptospirosis. We expect to report further findings as we obtain more information from all the study components.

Hantavirus seropositivity in rodents in relation to habitat heterogeneity in human-shaped landscapes of Southeast Asia

To establish how the conversion of natural habitats for agricultural purposes may impact the distribution of hantaviruses in Southeast Asia, we tested how habitat structure affects hantavirus infection prevalence of common murine rodents that inhabit human-dominated landscapes in this region. For this, we used geo-referenced data of rodents analysed for hantavirus infection and land cover maps produced for the seven study sites in Thailand, Cambodia and Lao PDR where they were collected. Rodents were tested by serological methods that detect several hantaviruses, including pathogenic ones. Rodents with a seropositive status were more likely to be found near to agriculture on steep land, and also in environments with a high proportion of agriculture on steep land. These results suggest that in Southeast Asia, hantaviruses, which are often associated with generalist rodent species with a preference for agricultural land, may benefit from land conversion to agriculture.

The diversity-disease relationship: evidence for and criticisms of the dilution effect

The dilution effect, that high host species diversity can reduce disease risk, has attracted much attention in the context of global biodiversity decline and increasing disease emergence. Recent studies have criticized the generality of the dilution effect and argued that it only occurs under certain circumstances. Nevertheless, evidence for the existence of a dilution effect was reported in about 80% of the studies that addressed the diversity-disease relationship, and a recent meta-analysis found that the dilution effect is widespread. We here review supporting and critical studies, point out the causes underlying the current disputes. The dilution is expected to be strong when the competent host species tend to remain when species diversity declines, characterized as a negative relationship between species' reservoir competence and local extinction risk. We here conclude that most studies support a negative competence-extinction relationship. We then synthesize the current knowledge on how the diversity-disease relationship can be modified by particular species in community, by the scales of analyses, and by the disease risk measures. We also highlight the complex role of habitat fragmentation in the diversity-disease relationship from epidemiological, evolutionary and ecological perspectives, and construct a synthetic framework integrating these three perspectives. We suggest that future studies should test the diversity-disease relationship across different scales and consider the multiple effects of landscape fragmentation.

Metacommunity and phylogenetic structure determine wildlife and zoonotic infectious disease patterns in time and space

The potential for disease transmission at the interface of wildlife, domestic animals and humans has become a major concern for public health and conservation biology. Research in this subject is commonly conducted at local scales while the regional context is neglected. We argue that prevalence of infection at local and regional levels is influenced by three mechanisms occurring at the landscape level in a metacommunity context. First, (1) dispersal, colonization, and extinction of pathogens, reservoir or vector hosts, and nonreservoir hosts, may be due to stochastic and niche-based processes, thus determining distribution of all species, and then their potential interactions, across local communities (metacommunity structure). Second, (2) anthropogenic processes may drive environmental filtering of hosts, nonhosts, and pathogens. Finally, (3) phylogenetic diversity relative to reservoir or vector host(s), within and between local communities may facilitate pathogen persistence and circulation. Using a metacommunity approach, public heath scientists may better evaluate the factors that predispose certain times and places for the origin and emergence of infectious diseases. The multidisciplinary approach we describe fits within a comprehensive One Health and Ecohealth framework addressing zoonotic infectious disease outbreaks and their relationship to their hosts, other animals, humans, and the environment.