Hantavirus infection and biodiversity in the Americas

Biodiversity and human health: A scoping review and examples of underrepresented linkages

Mounting evidence supports the connections between exposure to environmental typologies(such as green and blue spaces)and human health. However, the mechanistic links that connect biodiversity (the variety of life) and human health, and the extent of supporting evidence remain less clear. Here, we undertook a scoping review to map the links between biodiversity and human health and summarise the levels of associated evidence using an established weight of evidence framework. Distinct from other reviews, we provide additional context regarding the environment-microbiome-health axis, evaluate the environmental buffering pathway (e.g., biodiversity impacts on air pollution), and provide examples of three under- or minimally-represented linkages. The examples are (1) biodiversity and Indigenous Peoples' health, (2) biodiversity and urban social equity, and (3) biodiversity and COVID-19. We observed a moderate level of evidence to support the environmental microbiota-human health pathway and a moderate-high level of evidence to support broader nature pathways (e.g., greenspace) to various health outcomes, from stress reduction to enhanced wellbeing and improved social cohesion. However, studies of broader nature pathways did not typically include specific biodiversity metrics, indicating clear research gaps. Further research is required to understand the connections and causative pathways between biodiversity (e.g., using metrics such as taxonomy, diversity/richness, structure, and function) and health outcomes. There are well-established frameworks to assess the effects of broad classifications of nature on human health. These can assist future research in linking biodiversity metrics to human health outcomes. Our examples of underrepresented linkages highlight the roles of biodiversity and its loss on urban lived experiences, infectious diseases, and Indigenous Peoples' sovereignty and livelihoods. More research and awareness of these socioecological interconnections are needed.

Impact of vector richness on the risk of vector-borne disease: The role of vector competence

A central goal of disease ecology is to identify the factors that drive the spread of infectious diseases. Changes in vector richness can have complex effects on disease risk, but little is known about the role of vector competence in the relationship between vector richness and disease risk. In this study, we firstly investigated the combined effects of vector competence, interspecific competition, and feeding interference on disease risk through a two-vector, one-host SIR-SI model, and obtained threshold conditions for the occurrence of dilution and amplification effects. Secondly, we extended the above model to the case of N vectors and assumed that all vectors were homogeneous to obtain analytic expressions for disease risk. It was found that in the two-vector model, disease risk declined more rapidly as interspecific competition of the high-competence vector increased. When vector richness increases, the positive effects of adding a high-competence vector species on disease transmission may outweigh the negative effects of feeding interference due to increased vector richness, making an amplification effect more likely to occur. While the addition of a highly competitive vector species may exacerbate the negative effects of feeding interference, making a dilution effect more likely to occur. In the N-vector model, the effect of increased vector richness on disease risk was fully driven by the strength of feeding interference and interspecific competition, and changes in vector competence only quantitatively but not qualitatively altered the vector richness-disease risk relationship. This work clarifies the role of vector competence in the relationship between vector richness and disease risk and provides a new perspective for studying the diversity-disease relationship. It also provides theoretical guidance for vector management and disease prevention strategies.

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.

Effect of epidemic diseases on wild animal conservation

Under the background of global species extinction, the impact of epidemic diseases on wild animal protection is increasingly prominent. Here, we review and synthesize the literature on this topic, and discuss the relationship between diseases and biodiversity. Diseases usually reduce species diversity by decreasing or extinction of species populations, but also accelerate species evolution and promote species diversity. At the same time, species diversity can regulate disease outbreaks through dilution or amplification effects. The synergistic effect of human activities and global change is emphasized, which further aggravates the complex relationship between biodiversity and diseases. Finally, we emphasize the importance of active surveillance of wild animal diseases, which can protect wild animals from potential diseases, maintain population size and genetic variation, and reduce the damage of diseases to the balance of the whole ecosystem and human health. Therefore, we suggest that a background survey of wild animal populations and their pathogens should be carried out to assess the impact of potential outbreaks on the population or species level. The mechanism of dilution and amplification effect between species diversity and diseases of wild animals should be further studied to provide a theoretical basis and technical support for human intervention measures to change biodiversity. Most importantly, we should closely combine the protection of wild animals with the establishment of an active surveillance, prevention, and control system for wild animal epidemics, in an effort to achieve a win-win situation between wild animal protection and disease control.

The impact of wildlife and environmental factors on hantavirus infection in the host and its translation into human risk

Identifying factors that drive infection dynamics in reservoir host populations is essential in understanding human risk from wildlife-originated zoonoses. We studied zoonotic Puumala orthohantavirus (PUUV) in the host, the bank vole (Myodes glareolus), populations in relation to the host population, rodent and predator community and environment-related factors and whether these processes are translated into human infection incidence. We used 5-year rodent trapping and bank vole PUUV serology data collected from 30 sites located in 24 municipalities in Finland. We found that PUUV seroprevalence in the host was negatively associated with the abundance of red foxes, but this process did not translate into human disease incidence, which showed no association with PUUV seroprevalence. The abundance of weasels, the proportion of juvenile bank voles in the host populations and rodent species diversity were negatively associated with the abundance index of PUUV positive bank voles, which, in turn, showed a positive association with human disease incidence. Our results suggest certain predators, a high proportion of young bank vole individuals, and a diverse rodent community, may reduce PUUV risk for humans through their negative impacts on the abundance of infected bank voles.

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.

Host community composition, community assembly pattern, and disease transmission mode jointly determine the direction and strength of the diversity-disease relationship

Rapid global biodiversity loss and increasing emerging infectious diseases underscore the significance of identifying the diversity-disease relationship. Although experimental evidence supports the existence of dilution effects in several natural ecosystems, we still know very little about the conditions under which a dilution effect will occur. Using a multi-host Susceptible-Infected-Recovered model, we found when disease transmission was density-dependent, the diversity-disease relationship could exhibit an increasing, decreasing, or non-monotonic trend, which mainly depended on the patterns of community assembly. However, the combined effects of the host competence-abundance relationship and species extinction order may reverse or weaken this trend. In contrast, when disease transmission was frequency-dependent, the diversity-disease relationship only showed a decreasing trend, the host competence-abundance relationship and species extinction order did not alter this decreasing trend, but it could reduce the detectability of the dilution effect and affect disease prevalence. Overall, a combination of disease transmission mode, community assembly pattern, and host community composition determines the direction or strength of the diversity-disease relationship. Our work helps explain why previous studies came to different conclusions about the diversity-disease relationship and provides a deeper understanding of the pathogen transmission dynamics in actual communities.

Host competence, interspecific competition and vector preference interact to determine the vector-borne infection ecology

Understanding how ecological interactions affect vector-borne disease dynamics is crucial in the context of rapid biodiversity loss and increased emerging vector-borne diseases. Although there have been many studies on the impact of interspecific competition and host competence on disease dynamics, few of them have addressed the case of a vector-borne disease. Using a simple compartment model with two competing host species and one vector, we investigated the combined effects of vector preference, host competence, and interspecific competition on disease risk in a vector-borne system. Our research demonstrated that disease transmission dynamics in multi-host communities are more complex than anticipated. Vector preference and differences in host competence shifted the direction of the effect of competition on community disease risk, yet interspecific competition quantitatively but not qualitatively changed the effect of vector preference on disease risk. Our work also identified the conditions of the dilution effect and amplification effect in frequency-dependent transmission mode, and we discovered that adding vector preference and interspecific competition into a simple two-host-one-vector model altered the outcomes of how increasing species richness affects disease risk. Our work explains some of the variation in outcomes in previous empirical and theoretical studies on the dilution effect.

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.

Pathways linking biodiversity to human health: A conceptual framework

Biodiversity is a cornerstone of human health and well-being. However, while evidence of the contributions of nature to human health is rapidly building, research into how biodiversity relates to human health remains limited in important respects. In particular, a better mechanistic understanding of the range of pathways through which biodiversity can influence human health is needed. These pathways relate to both psychological and social processes as well as biophysical processes. Building on evidence from across the natural, social and health sciences, we present a conceptual framework organizing the pathways linking biodiversity to human health. Four domains of pathways-both beneficial as well as harmful-link biodiversity with human health: (i) reducing harm (e.g. provision of medicines, decreasing exposure to air and noise pollution); (ii) restoring capacities (e.g. attention restoration, stress reduction); (iii) building capacities (e.g. promoting physical activity, transcendent experiences); and (iv) causing harm (e.g. dangerous wildlife, zoonotic diseases, allergens). We discuss how to test components of the biodiversity-health framework with available analytical approaches and existing datasets. In a world with accelerating declines in biodiversity, profound land-use change, and an increase in non-communicable and zoonotic diseases globally, greater understanding of these pathways can reinforce biodiversity conservation as a strategy for the promotion of health for both people and nature. We conclude by identifying research avenues and recommendations for policy and practice to foster biodiversity-focused public health actions.

Mixed Effects of Habitat Degradation and Resources on Hantaviruses in Sympatric Wild Rodent Reservoirs within a Neotropical Forest

Understanding the ecology of rodent-borne hantaviruses is critical to assessing the risk of spillover to humans. Longitudinal surveys have suggested that hantaviral prevalence in a given host population is tightly linked to rodent ecology and correlates with changes in the species composition of a rodent community over time and/or habitat composition. We tested two hypotheses to identify whether resource addition and/or habitat composition may affect hantavirus prevalence among two sympatric reservoir hosts in a neotropical forest: (i) increased food resources will alter the rodent community and thus hantaviral prevalence; and (ii) host abundance and viral seroprevalence will be associated with habitat composition. We established a baseline of rodent-virus prevalence in three grid pairs of distinct habitat compositions and subjected one grid of each pair to resource augmentation. Increased rodent species diversity was observed on grids where food was added versus untreated control grids during the first post-treatment sampling session. Resource augmentation changed species community composition, yet it did not affect the prevalence of hantavirus in the host population over time, nor was there evidence of a dilution effect. Secondly, we show that the prevalence of the virus in the respective reservoir hosts was associated with habitat composition at two spatial levels, independent of resource addition, supporting previous findings that habitat composition is a primary driver of the prevalence of hantaviruses in the neotropics.