Linking anthropogenic resources to wildlife-pathogen dynamics: a review and meta-analysis

Disentangling the link between supplemental feeding, population density, and the prevalence of pathogens in urban stray cats

BACKGROUND

Supplemental feeding of free-roaming animals, including wildlife and feral or stray animals, is well known to have a substantial impact on various aspects of animal ecology including habitat use, activity patterns, and host-pathogen interactions. Among them, an increased population density (PD) of animals receiving supplemental food raises concerns regarding the transmission of pathogens in these host populations. The primary aim of this study was to investigate how supplemental feeding is associated with host PD and prevalence of pathogens with different transmission modes in urban stray cats. We hypothesized that supplemental feeding would be positively associated with host PD and the prevalence of pathogens with density-dependent transmission modes compared with pathogens with transmission modes that are considered relatively density-independent.

METHODS

This study was conducted in six districts in Seoul, Republic of Korea which were selected based on different degrees of supplemental feeding and cat caretaker activity (CCA). The PD of stray cats was estimated by mark-recapture surveys. Stray cat blood samples (N = 302) were collected from stray cats by local animal hospitals from each district performing the trap-neuter-release which tested for eight pathogens with different transmission modes (feline immunodeficiency virus, feline leukemia virus (FeLV), feline panleukopenia virus, feline calicivirus, feline herpesvirus-1, Bartonella henselae, hemoplasma, and Toxoplasma gondii) with molecular or serological assays. Associations between the prevalence of each pathogen and PD, CCA, and sex of cats were statistically analyzed.

RESULTS

In contrast to initial predictions, the cat PD was generally higher in low CCA districts. The prevalence of (FeLV), which is transmitted through direct contact, was significantly higher in areas with a high CCA, conforming to our hypothesis. On the other hand, the prevalence of feline parvovirus, which can be spread by environmental transmission, was higher in low CCA districts. The remaining six pathogens did not show any association with the CCA; however, they had a unique association with the PD or the sex of the stray cats.

DISCUSSION

Our findings suggest that in addition to influencing the PD, supplemental feeding may affect the prevalence of pathogens in urban animals by mechanisms such as increased aggregation and/or altered foraging strategies, with different consequences depending on the transmission mode of each pathogen.

Handling times and saturating transmission functions in a snail-worm symbiosis

All dynamic species interaction models contain an assumption that describes how contact rates scale with population density. Choosing an appropriate contact-density function is important, because different functions have different implications for population dynamics and stability. However, this choice can be challenging, because there are many possible functions, and most are phenomenological and thus difficult to relate to underlying ecological processes. Using one such phenomenological function, we described a nonlinear relationship between field transmission rates and host density in a common snail-oligochaete symbiosis. We then used a well-known contact function from predator-prey models, the Holling Type II functional response, to describe and predict host snail contact rates in the laboratory. The Holling Type II functional response accurately described both the nonlinear contact-density relationship and the average contact duration that we observed. Therefore, we suggest that contact rates saturate with host density in this system because each snail contact requires a non-instantaneous handling time, and additional possible contacts do not occur during that handling time. Handling times and nonlinear contact rates might also explain the nonlinear relationship between symbiont transmission and snail density that we observed in the field, which could be confirmed by future work that controls for other potential sources of seasonal variation in transmission rates. Because most animal contacts are not instantaneous, the Holling Type II functional response might be broadly relevant to diverse host-symbiont systems.

Opening the file drawer: Unexpected insights from a chytrid infection experiment

Infection experiments are critical for understanding wildlife disease dynamics. Although infection experiments are typically designed to reduce complexity, disease outcomes still result from complex interactions between host, pathogen, and environmental factors. Cryptic variation across factors can lead to decreased repeatability of infection experiments within and between research groups and hinder research progress. Furthermore, studies with unexpected results are often relegated to the “file drawer” and potential insights gained from these experimental outcomes are lost. Here, we report unexpected results from an infection experiment studying the response of two differentially-susceptible but related frogs (American Bullfrog Rana catesbeiana and the Mountain yellow-legged frog Rana muscosa) to the amphibian-killing chytrid fungus (Batrachochytrium dendrobatidis, Bd). Despite well-documented differences in susceptibility between species, we found no evidence for antibody-mediated immune response and no Bd-related mortality in either species. Additionally, during the study, the sham-inoculated R. catesbeiana control group became unexpectedly Bd-positive. We used a custom genotyping assay to demonstrate that the aberrantly-infected R. catesbeiana carried a Bd genotype distinct from the inoculation genotype. Thus R. catesbeiana individuals were acquired with low-intensity infections that could not be detected with qPCR. In the Bd-inoculated R. catesbeiana treatment group, the inoculated genotype appeared to out-compete the cryptic infection. Thus, our results provide insight into Bd coinfection dynamics, a phenomenon that is increasingly relevant as different pathogen strains are moved around the globe. Our experiment highlights how unexpected experimental outcomes can serve as both cautionary tales and opportunities to explore unanswered research questions. We use our results as a case study to highlight common sources of anomalous results for infection experiments. We argue that understanding these factors will aid researchers in the design, execution, and interpretation of experiments to understand wildlife disease processes.

A new pathogen spillover from domestic to wild animals: Plasmodium juxtanucleare infects free-living passerines in Brazil

Habitat modification may facilitate the emergence of novel pathogens, and the expansion of agricultural frontiers make domestic animals important sources of pathogen spillover to wild animals. We demonstrate for the first time that Plasmodium juxtanucleare, a widespread parasite from domestic chickens, naturally infects free-living passerines. We sampled 68 wild birds within and at the border of conservation units in central Brazil composed by Cerrado, a highly threatened biome. Seven out of 10 passerines captured in the limits of a protected area with a small farm were infected by P. juxtanucleare as was confirmed by sequencing a fragment of the parasite's cytochrome b. Blood smears from these positive passerines presented trophozoites, meronts and gametocytes compatible with P. juxtanucleare, meaning these birds are competent hosts for this parasite. After these intriguing results, we sampled 30 backyard chickens managed at the area where P. juxtanucleare-infected passerines were captured, revealing one chicken infected by the same parasite lineage. We sequenced the almost complete mitochondrial genome from all positive passerines, revealing that Brazilian and Asian parasites are closely related. P. juxtanucleare can be lethal to non-domestic hosts under captive and rehabilitation conditions, suggesting that this novel spillover may pose a real threat to wild birds.

Livestock abundance predicts vampire bat demography, immune profiles and bacterial infection risk

Human activities create novel food resources that can alter wildlife-pathogen interactions. If resources amplify or dampen, pathogen transmission probably depends on both host ecology and pathogen biology, but studies that measure responses to provisioning across both scales are rare. We tested these relationships with a 4-year study of 369 common vampire bats across 10 sites in Peru and Belize that differ in the abundance of livestock, an important anthropogenic food source. We quantified innate and adaptive immunity from bats and assessed infection with two common bacteria. We predicted that abundant livestock could reduce starvation and foraging effort, allowing for greater investments in immunity. Bats from high-livestock sites had higher microbicidal activity and proportions of neutrophils but lower immunoglobulin G and proportions of lymphocytes, suggesting more investment in innate relative to adaptive immunity and either greater chronic stress or pathogen exposure. This relationship was most pronounced in reproductive bats, which were also more common in high-livestock sites, suggesting feedbacks between demographic correlates of provisioning and immunity. Infection with both Bartonella and haemoplasmas were correlated with similar immune profiles, and both pathogens tended to be less prevalent in high-livestock sites, although effects were weaker for haemoplasmas. These differing responses to provisioning might therefore reflect distinct transmission processes. Predicting how provisioning alters host-pathogen interactions requires considering how both within-host processes and transmission modes respond to resource shifts.This article is part of the theme issue 'Anthropogenic resource subsidies and host-parasite dynamics in wildlife'.

Consequences of resource supplementation for disease risk in a partially migratory population

Anthropogenic landscape features such as urban parks and gardens, landfills and farmlands can provide novel, seasonally reliable food sources that impact wildlife ecology and distributions. In historically migratory species, food subsidies can cause individuals to forgo migration and form partially migratory or entirely sedentary populations, eroding a crucial benefit of migration: pathogen avoidance through seasonal abandonment of transmission sites and mortality of infected individuals during migration. Since many migratory taxa are declining, and wildlife populations in urban areas can harbour zoonotic pathogens, understanding the mechanisms by which anthropogenic resource subsidies influence infection dynamics and the persistence of migration is important for wildlife conservation and public health. We developed a mathematical model for a partially migratory population and a vector-borne pathogen transmitted at a shared breeding ground, where food subsidies increase the nonbreeding survival of residents. We found that higher resident nonbreeding survival increased infection prevalence in residents and migrants, and lowered the fraction of the population that migrated. The persistence of migration may be especially threatened if residency permits emergence of more virulent pathogens, if resource subsidies reduce costs of infection for residents, and if infection reduces individual migratory propensity.This article is part of the theme issue 'Anthropogenic resource subsidies and host-parasite dynamics in wildlife'.

Potential virulence factors of bacteria associated with tail fan necrosis in the spiny lobster, Jasus edwardsii

Tail fan necrosis (TFN) is a common condition found in commercially exploited spiny lobsters that greatly diminishes their commercial value. Bacteria possessing proteolytic, chitinolytic and lipolytic capabilities were associated with TFN in spiny lobsters, Jasus edwardsii. In this study, 69 bacterial isolates exhibiting all the three enzymatic capabilities from the haemolymph and tail fans of J. edwardsii with and without TFN were further characterized and compared, including morphology, biofilm formation, antimicrobial activity, antimicrobial resistance, and production of siderophores, melanin and ammonia. The genomic patterns of the most common Vibrio crassostreae isolates were also compared between TFN-affected and unaffected lobsters. Biofilm formation was stronger in bacterial isolates from both haemolymph and tail fans of TFN-affected lobsters compared to those from the unaffected lobsters, while melanin production and siderophore production were stronger in the isolates from tail fans of lobsters with TFN. By contrast, the other characteristics of isolates were similar in lobsters with and without TFN. The Vib. crassostreae isolates from the affected lobsters had similar genomic patterns. Overall, the results indicate that in addition to proteolytic, chitinolytic and lipolytic activities, the bacteria associated with TFN commonly have enhanced activity of important virulence factors, including biofilm formation, melanin production and siderophore production.

Moving in the Anthropocene: Global reductions in terrestrial mammalian movements

Animal movement is fundamental for ecosystem functioning and species survival, yet the effects of the anthropogenic footprint on animal movements have not been estimated across species. Using a unique GPS-tracking database of 803 individuals across 57 species, we found that movements of mammals in areas with a comparatively high human footprint were on average one-half to one-third the extent of their movements in areas with a low human footprint. We attribute this reduction to behavioral changes of individual animals and to the exclusion of species with long-range movements from areas with higher human impact. Global loss of vagility alters a key ecological trait of animals that affects not only population persistence but also ecosystem processes such as predator-prey interactions, nutrient cycling, and disease transmission.

Fecal parasite risk in the endangered proboscis monkey is higher in an anthropogenically managed forest environment compared to a riparian rain forest in Sabah, Borneo

Understanding determinants shaping infection risk of endangered wildlife is a major topic in conservation medicine. The proboscis monkey, Nasalis larvatus, an endemic primate flagship species for conservation in Borneo, is endangered through habitat loss, but can still be found in riparian lowland and mangrove forests, and in some protected areas. To assess socioecological and anthropogenic influence on intestinal helminth infections in N. larvatus, 724 fecal samples of harem and bachelor groups, varying in size and the number of juveniles, were collected between June and October 2012 from two study sites in Malaysian Borneo: 634 samples were obtained from groups inhabiting the Lower Kinabatangan Wildlife Sanctuary (LKWS), 90 samples were collected from groups of the Labuk Bay Proboscis Monkey Sanctuary (LBPMS), where monkeys are fed on stationary feeding platforms. Parasite risk was quantified by intestinal helminth prevalence, host parasite species richness (PSR), and eggs per gram feces (epg). Generalized linear mixed effect models were applied to explore whether study site, group type, group size, the number of juveniles per group, and sampling month predict parasite risk. At the LBPMS, prevalence and epg of Trichuris spp., strongylids, and Strongyloides spp. but not Ascaris spp., as well as host PSR were significantly elevated. Only for Strongyloides spp., prevalence showed significant changes between months; at both sites, the beginning rainy season with increased precipitation was linked to higher prevalence, suggesting the external life cycle of Strongyloides spp. to benefit from humidity. Higher prevalence, epgs, and PSR within the LBPMS suggest that anthropogenic factors shape host infection risk more than socioecological factors, most likely via higher re-infection rates and chronic stress. Noninvasive measurement of fecal parasite stages is an important tool for assessing transmission dynamics and infection risks for endangered tropical wildlife. Findings will contribute to healthcare management in nature and in anthropogenically managed environments.

Climate Change and the Neglected Tropical Diseases

Climate change is expected to impact across every domain of society, including health. The majority of the world's population is susceptible to pathological, infectious disease whose life cycles are sensitive to environmental factors across different physical phases including air, water and soil. Nearly all so-called neglected tropical diseases (NTDs) fall into this category, meaning that future geographic patterns of transmission of dozens of infections are likely to be affected by climate change over the short (seasonal), medium (annual) and long (decadal) term. This review offers an introduction into the terms and processes deployed in modelling climate change and reviews the state of the art in terms of research into how climate change may affect future transmission of NTDs. The 34 infections included in this chapter are drawn from the WHO NTD list and the WHO blueprint list of priority diseases. For the majority of infections, some evidence is available of which environmental factors contribute to the population biology of parasites, vectors and zoonotic hosts. There is a general paucity of published research on the potential effects of decadal climate change, with some exceptions, mainly in vector-borne diseases.

The effects of food and parasitism on reproductive performance of a wild rodent

Food and parasitism can have complex effects on small mammal reproduction. In this study, we tested the effects of sex, food, and parasitism on reproductive performance of the Taiwan field mouse (Apodemus semotus). In a field experiment, we increased food availability for a portion of the mice in the population by providing sorghum seeds to a set of food stations. We reduced parasite intensity of randomly chosen mice through ivermectin treatment. We determined the number and quality of offspring for the mice using paternity analysis. We quantified seed consumption with stable carbon isotope values of mouse plasma and parasite intensity with fecal egg counts of intestinal nematodes and cestodes (FEC). In a laboratory experiment, we reduced parasite intensity of randomly chosen mice through ivermectin treatment. We quantified their immune functions by total white blood cell count, percent granulocyte count, and percent lymphocyte count through hematological analyses. We measured the FEC and energy intake of the mice. From the field experiment, the number of offspring in A. semotus increased with increasing seed consumption. Due to the trade‐off between number and quality of offspring, the offspring quality decreased with increasing seed consumption for the females. The ivermectin treatment did not affect offspring number or quality. However, the FEC was positively correlated with number of offspring. In the laboratory experiment, the percent lymphocyte/granulocyte count changed with parasite intensity at low energy intake, which was relaxed at high energy intake. This study demonstrated positive effects of food availability and neutral effects of parasitism on A. semotus reproduction. However, the benefits of food availability for the females need to take into account the offspring number–quality trade‐off, and at high infection intensity, parasitism might negatively affect offspring quality for the males. We suggest that food availability could mediate the relationships between parasite intensity and immune responses.

Using host species traits to understand the consequences of resource provisioning for host-parasite interactions

Supplemental food provided to wildlife by human activities can be more abundant and predictable than natural resources, and subsequent changes in wildlife ecology can have profound impacts on host-parasite interactions. Identifying traits of species associated with increases or decreases in infection outcomes with resource provisioning could improve assessments of wildlife most prone to disease risks in changing environments. We conducted a phylogenetic meta-analysis of 342 host-parasite interactions across 56 wildlife species and three broad taxonomic groups of parasites to identify host-level traits that influence whether provisioning is associated with increases or decreases in infection. We predicted dietary generalists that capitalize on novel food would show greater infection in provisioned habitats owing to population growth and food-borne exposure to contaminants and parasite infectious stages. Similarly, species with fast life histories could experience stronger demographic and immunological benefits from provisioning that affect parasite transmission. We also predicted that wide-ranging and migratory behaviours could increase infection risks with provisioning if concentrated and non-seasonal foods promote dense aggregations that increase exposure to parasites. We found that provisioning increased infection with bacteria, viruses, fungi and protozoa (i.e. microparasites) most for wide-ranging, dietary generalist host species. Effect sizes for ectoparasites were also highest for host species with large home ranges but were instead lowest for dietary generalists. In contrast, the type of provisioning was a stronger correlate of infection outcomes for helminths than host species traits. Our analysis highlights host traits related to movement and feeding behaviour as important determinants of whether species experience greater infection with supplemental feeding. These results could help prioritize monitoring wildlife with particular trait profiles in anthropogenic habitats to reduce infectious disease risks in provisioned populations.

Anthropogenic food provisioning and immune phenotype: Association among supplemental food, body condition, and immunological parameters in urban environments

Direct or indirect supplemental feeding of free-ranging animals occurs worldwide, resulting in significant impacts on population density or altered demographic processes. Another potential impact of increased energy intake from supplemental feeding is altered immunocompetence. As immune system maintenance is energetically costly, there may be trade-offs between immune responses and other energy-demanding physiological processes in individual animals. Although increased availability of food sources through supplemental feeding is expected to increase the overall immunocompetence of animals, empirical data verifying the association between supplemental feeding and different immune parameters are lacking. Understanding the potential influence of supplemental feeding on immune phenotypes is critical, as it may also impact host-pathogen dynamics in free-ranging animals. Using urban stray cats as a study model, we tested for associations between the intensity of supplemental feeding due to cat caretaker activity (CCA); body condition; and immune phenotype (bacterial killing assay (BKA), immunoglobulin G (IgG) concentration, and leukocyte counts). Significantly higher bacterial killing ability was observed in cats from high CCA districts, whereas higher IgG concentration and eosinophil counts were observed in cats from low CCA districts. Other leukocyte counts and body condition indices showed no significant association with CCA. We observed varying patterns of different immune components in relation to supplemental feeding. Out data suggest that supplemental feeding influences immune phenotype, not only by means of energy provisioning, but also by potentially reducing exposure rates to parasite infections through stray cat behavioral changes.

Stress hormones predict a host superspreader phenotype in the West Nile virus system

Glucocorticoid stress hormones, such as corticosterone (CORT), have profound effects on the behaviour and physiology of organisms, and thus have the potential to alter host competence and the contributions of individuals to population- and community-level pathogen dynamics. For example, CORT could alter the rate of contacts among hosts, pathogens and vectors through its widespread effects on host metabolism and activity levels. CORT could also affect the intensity and duration of pathogen shedding and risk of host mortality during infection. We experimentally manipulated songbird CORT, asking how CORT affected behavioural and physiological responses to a standardized West Nile virus (WNV) challenge. Although all birds became infected after exposure to the virus, only birds with elevated CORT had viral loads at or above the infectious threshold. Moreover, though the rate of mortality was faster in birds with elevated CORT compared with controls, most hosts with elevated CORT survived past the day of peak infectiousness. CORT concentrations just prior to inoculation with WNV and anti-inflammatory cytokine concentrations following viral exposure were predictive of individual duration of infectiousness and the ability to maintain physical performance during infection (i.e. tolerance), revealing putative biomarkers of competence. Collectively, our results suggest that glucocorticoid stress hormones could directly and indirectly mediate the spread of pathogens.

Supplementary feeding as a source of multiresistant Salmonella in endangered Egyptian vultures

Wild birds have repeatedly been highlighted as vectors in the dissemination of livestock and human pathogens. Here, the occurrence, serotypes and antimicrobial resistance of Salmonella were assessed in adult Egyptian vultures (Neophron percnopterus), to test the hypothesis that infection is associated with the consumption of swine carcasses provided at supplementary feeding stations (SFSs). Faeces of year-round resident griffon vultures (Gyps fulvus) were also tested to assess whether infection was acquired in the breeding grounds of both species or in the African wintering quarters of Egyptian vultures. Depending on the shedding rate criteria considered, the occurrence of infection in Egyptian vultures varied between the three consecutive sampling days in a range with a minimum of 23%-41% and a maximum of 64%-92% of individuals (n = 11-14 individuals, 27-39 faeces). The occurrence in the single sampling of griffon vultures was 61% of faeces (n = 18). Vultures mostly fed on pig carcasses, which together with their predominant infection with multiresistant serotypes (mostly the monophasic 4,12:i:- variant resistant to aminopenicillins, aminoglycosides and tetracyclines) typically found in pigs from Spain, strongly supports a carcass-to-vulture transmission and cross-infection routes at SFSs. Efforts are encouraged to avoid discarding carcasses of pigs with Salmonella at SFSs established for the conservation of threatened scavengers. This could contribute to reducing the long-distance transmission of resistant pathogens with an impact on livestock and human health while avoiding infection risk and its effects on wildlife.

Enhanced access to anthropogenic food waste is related to hyperglycemia in raccoons (Procyon lotor)

Urban landscapes have well-known effects on wildlife populations. Many species of urban wildlife feed on anthropogenic food wastes, and little is known regarding the sub-lethal physiological consequences of this novel diet. We use samples from three populations of raccoons to test the hypothesis that access to anthropogenic food waste will lead to elevated body mass, blood glucose and serum leptin. Each population varied in their presumed access to food waste. We found that raccoons from the site with the highest presumed access to food waste were significantly heavier and had significantly higher levels of glycated serum protein (GSP, a marker of elevated blood glucose). In addition, GSP concentration was positively related to body mass. No significant differences in serum leptin were detected, nor was serum leptin related to body mass. Urban diets may have significant physiological consequences for urban wildlife related to glucose metabolism. Further research will be needed to determine the evolutionary consequences of the novel urban diet, and whether adaptation is occurring.

Quantifying direct and indirect contacts for the potential transmission of infection between species using a multilayer contact network

Detecting opportunities for between-species transmission of pathogens can be challenging, particularly if rare behaviours or environmental transmission are involved. We present a multilayer network framework to quantify transmission potential in multi-host systems, incorporating environmental transmission, by using empirical data on direct and indirect contacts between European badgers Meles meles and domestic cattle. We identify that indirect contacts via the environment at badger latrines on pasture are likely to be important for transmission within badger populations and between badgers and cattle. We also find a positive correlation between the role of individual badgers within the badger social network, and their role in the overall badger-cattle-environment network, suggesting that the same behavioural traits contribute to the role of individual badgers in within- and between-species transmission. These findings have implications for disease management interventions in this system, and our novel network approach can provide general insights into transmission in other multi-host disease systems.

Host stress hormones alter vector feeding preferences, success, and productivity

Stress hormones might represent a key link between individual-level infection outcome, population-level parasite transmission, and zoonotic disease risk. Although the effects of stress on immunity are well known, stress hormones could also affect host-vector interactions via modification of host behaviours or vector-feeding patterns and subsequent reproductive success. Here, we experimentally manipulated songbird stress hormones and examined subsequent feeding preferences, feeding success, and productivity of mosquito vectors in addition to defensive behaviours of hosts. Despite being more defensive, birds with elevated stress hormone concentrations were approximately twice as likely to be fed on by mosquitoes compared to control birds. Moreover, stress hormones altered the relationship between the timing of laying and clutch size in blood-fed mosquitoes. Our results suggest that host stress could affect the transmission dynamics of vector-borne parasites via multiple pathways.

Vegetation Management and Host Density Influence Bee-Parasite Interactions in Urban Gardens

Apocephalus borealis phorid flies, a parasitoid of bumble bees and yellow jacket wasps in North America, was recently reported as a novel parasitoid of the honey bee Apis mellifera Linnaeus (Hymenoptera: Apidae). Little is known about the ecology of this interaction, including phorid fecundity on bee hosts, whether phorid-bee parasitism is density dependent, and which local habitat and landscape features may correlate with changes in parasitism rates for either bumble or honey bees. We examined the impact of local and landscape drivers and host abundance on phorid parasitism of A. mellifera and the bumble bee Bombus vosnesenskii Radoszkowski (Hymenoptera: Apidae). We worked in 19 urban gardens along the North-Central Coast of California, where phorid parasitism of honey bees was first reported in 2012. We collected and incubated bees for phorid emergence, and surveyed local vegetation, ground cover, and floral characteristics as well as land cover types surrounding gardens. We found that phorid parasitism was higher on bumble bees than on honey bees, and phorids produced nearly twice as many pupae on individual bumble bee hosts than on honey bee hosts. Parasitism of both bumble and honey bees increased with abundance of honey bees in a site. Differences in landscape surroundings did not correlate with parasitism, but local factors related to bee resource provisioning (e.g., tree and shrub abundance) positively correlated with increased parasitism. This research thus helps to document and describe conditions that may have facilitated phorid fly host shift to honey bees and further elucidate how resource provisioning in urban gardens influences bee-parasite interactions.

Urban landscapes can change virus gene flow and evolution in a fragmentation-sensitive carnivore

Urban expansion has widespread impacts on wildlife species globally, including the transmission and emergence of infectious diseases. However, there is almost no information about how urban landscapes shape transmission dynamics in wildlife. Using an innovative phylodynamic approach combining host and pathogen molecular data with landscape characteristics and host traits, we untangle the complex factors that drive transmission networks of feline immunodeficiency virus (FIV) in bobcats (Lynx rufus). We found that the urban landscape played a significant role in shaping FIV transmission. Even though bobcats were often trapped within the urban matrix, FIV transmission events were more likely to occur in areas with more natural habitat elements. Urban fragmentation also resulted in lower rates of pathogen evolution, possibly owing to a narrower range of host genotypes in the fragmented area. Combined, our findings show that urban landscapes can have impacts on a pathogen and its evolution in a carnivore living in one of the most fragmented and urban systems in North America. The analytical approach used here can be broadly applied to other host-pathogen systems, including humans.

Novel hemotropic mycoplasmas are widespread and genetically diverse in vampire bats

Bats (Order: Chiroptera) have been widely studied as reservoir hosts for viruses of concern for human and animal health. However, whether bats are equally competent hosts of non-viral pathogens such as bacteria remains an important open question. Here, we surveyed blood and saliva samples of vampire bats from Peru and Belize for hemotropic Mycoplasma spp. (hemoplasmas), bacteria that can cause inapparent infection or anemia in hosts. 16S rRNA gene amplification of blood showed 67% (150/223) of common vampire bats (Desmodus rotundus) were infected by hemoplasmas. Sequencing of the 16S rRNA gene amplicons revealed three novel genotypes that were phylogenetically related but not identical to hemoplasmas described from other (non-vampire) bat species, rodents, humans, and non-human primates. Hemoplasma prevalence in vampire bats was highest in non-reproductive and young individuals, did not differ by country, and was relatively stable over time (i.e., endemic). Metagenomics from pooled D. rotundus saliva from Peru detected non-hemotropic Mycoplasma species and hemoplasma genotypes phylogenetically similar to those identified in blood, providing indirect evidence for potential direct transmission of hemoplasmas through biting or social contacts. This study demonstrates vampire bats host several novel hemoplasmas and sheds light on risk factors for infection and basic transmission routes. Given the high frequency of direct contacts that arise when vampire bats feed on humans, domestic animals, and wildlife, the potential of these bacteria to be transmitted between species should be investigated in future work.

Resource-driven encounters among consumers and implications for the spread of infectious disease

Animals share a variety of common resources, which can be a major driver of conspecific encounter rates. In this work, we implement a spatially explicit mathematical model for resource visitation behaviour in order to examine how changes in resource availability can influence the rate of encounters among consumers. Using simulations and asymptotic analysis, we demonstrate that, under a reasonable set of assumptions, the relationship between resource availability and consumer conspecific encounters is not monotonic. We characterize how the maximum encounter rate and associated critical resource density depend on system parameters like consumer density and the maximum distance from which consumers can detect and respond to resources. The assumptions underlying our theoretical model and analysis are motivated by observations of large aggregations of black-backed jackals at carcasses generated by seasonal outbreaks of anthrax among herbivores in Etosha National Park, Namibia. As non-obligate scavengers, black-backed jackals use carcasses as a supplemental food resource when they are available. While jackals do not appear to acquire disease from ingesting anthrax carcasses, changes in their movement patterns in response to changes in carcass abundance do alter jackals' conspecific encounter rate in ways that may affect the transmission dynamics of other diseases, such as rabies. Our theoretical results provide a method to quantify and analyse the hypothesis that the outbreak of a fatal disease among herbivores can potentially facilitate outbreaks of an entirely different disease among jackals. By analysing carcass visitation data, we find support for our model's prediction that the number of conspecific encounters at resource sites decreases with additional increases in resource availability. Whether or not this site-dependent effect translates to an overall decrease in encounters depends, unexpectedly, on the relationship between the maximum distance of detection and the resource density.

The history of rabies in the Western Hemisphere

Before the introduction of control programs in the 20th century, rabies in domestic dogs occurred throughout the Western Hemisphere. However, historical records and phylogenetic analysis of multiple virus isolates indicate that, before the arrival of the first European colonizers, rabies virus was likely present only in bats and skunks. Canine rabies was either rare or absent among domestic dogs of Native Americans, and first arrived when many new dog breeds were imported during the period of European colonization. The introduction of the cosmopolitan dog rabies lyssavirus variant and the marked expansion of the dog population provided ideal conditions for the flourishing of enzootic canine rabies. The shift of dog-maintained viruses into gray foxes, coyotes, skunks and other wild mesocarnivores throughout the Americas and to mongooses in the Caribbean has augmented the risk of human rabies exposures and has complicated control efforts. At the same time, the continued presence of bat rabies poses novel challenges in the absolute elimination of canine and human rabies. This article compiles existing historical and phylogenetic evidence of the origins and subsequent dynamics of rabies in the Western Hemisphere, from the era preceding the arrival of the first European colonizers through the present day. A companion article reviews the current status of canine rabies control throughout the Western Hemisphere and steps that will be required to achieve and maintain its complete elimination (Velasco-Villa et al., 2017).

Scavenging on a pulsed resource: quality matters for corvids but density for mammals

Background

Human food subsidies can provide predictable food sources in large quantities for wildlife species worldwide. In the boreal forest of Fennoscandia, gut piles from moose (Alces alces) harvest provide a potentially important food source for a range of opportunistically scavenging predators. Increased populations of predators can negatively affect threatened or important game species. As a response to this, restrictions on field dressing of moose are under consideration in parts of Norway. However, there is a lack of research to how this resource is utilized. In this study, we used camera-trap data from 50 gut piles during 1043 monitoring days. We estimated depletion of gut piles separately for parts with high and low energy content, and used these results to scale up gut pile density in the study area. We identified scavenger species and analyzed the influences of gut pile quality and density on scavenging behavior of mammals and corvids (family Corvidae).

Results

Main scavengers were corvids and red fox (Vulpes vulpes). Parts with high energy content were rapidly consumed, mainly by corvids that were present at all gut piles shortly after the remains were left at the kill site. Corvid presence declined with days since harvest, reflecting reduction in gut pile quality over time independent of gut pile density. Mammals arrived 7–8 days later at the gut piles than corvids, and their presence depended only on gut pile density with a peak at intermediate densities. The decline at high gut pile densities suggest a saturation effect, which could explain accumulation of gut pile parts with low energy content.

Conclusions

This study shows that remains from moose harvest can potentially be an important food resource for scavengers, as it was utilized to a high degree by many species. This study gives novel insight into how energy content and density of resources affect scavenging patterns among functional groups of scavengers.

Prevalence, Genotype Richness, and Coinfection Patterns of Hemotropic Mycoplasmas in Raccoons (Procyon lotor) on Environmentally Protected and Urbanized Barrier Islands

Raccoons (Procyon lotor) are successful urban adapters and hosts to a number of zoonotic and nonzoonotic pathogens, yet little is known about their hemoplasma infections and how prevalence varies across habitat types. This study identifies hemotropic Mycoplasma species infection in raccoons from urban and undisturbed habitats and compares hemoplasma infection in sympatric urban cats (Felis catus) from the same geographic region. We collected blood from raccoons (n = 95) on an urban coastal island (n = 37) and an undisturbed coastal island (n = 58) and from sympatric urban cats (n = 39) in Georgia, USA. Based on 16S rRNA gene amplification, 62.1% (59/95) of raccoons and 17.9% (7/39) of feral cats were positive for hemoplasma. There was a greater percentage of hemoplasma-infected raccoons on the undisturbed island (79.3% [46/58]) than on the urban island (35.1% [13/37]; χ2 = 16.9, df = 1, P = 0.00004). Sequencing of the full-length 16S rRNA gene amplicons revealed six hemoplasma genotypes in raccoons, including five novel genotypes that were distinct from three known hemoplasma species identified in the sympatric cats. In addition, the hemoplasma genotypes detected in raccoons were not identified in sympatric cats or vice versa. Although all six hemoplasma genotypes were found in raccoons from urban and undisturbed islands, coinfection patterns differed between sites and among individuals, with the proportion of coinfected raccoons being greater in the undisturbed site. This study shows that raccoons are hosts for several novel hemoplasmas and that habitat type influences infection patterns.IMPORTANCE This study provides information about novel hemoplasmas identified in raccoons (Procyon lotor), which can be used for assessments of the prevalence of these hemoplasmas in raccoon populations and for future studies on the potential pathogenic impacts of these hemoplasmas on raccoon health. Raccoons from the undisturbed habitat had a higher prevalence of hemoplasma infection than urban raccoons. There does not appear to be cross-species transmission of hemotropic mycoplasmas between urban raccoons and feral cats. Raccoons appear to be hosts for several novel hemoplasmas, and habitat type influences infection patterns.

Supplementary feeding and endoparasites in threatened avian scavengers: Coprologic evidence from red kites in their wintering stronghold

Many obligate and facultative avian scavengers are increasingly dependent on food provided in supplementary feeding stations (SFS), which are managed for the conservation of these species. Deliberate feeding can influence disease-related host demography and population dynamics through physiological changes and density-dependent parasite acquisition and transmission, but information on this threat to avian scavengers is scarce. Due to their effects on host aggregation and density, we hypothesised that the predictability and concentration of food in SFS can exacerbate parasite infection. This hypothesis was tested by comparing the prevalence, richness, abundance and mixed infection of endoparasites (coccidia and helminths) in red kites Milvus milvus foraging on livestock carcasses (mostly of pigs and poultry) in overcrowded and confined conditions at SFS, relative to those foraging alone or in small groups on wild prey unevenly randomly distributed within large areas during winter, mostly wild rabbits (Oryctolagus cuniculus). No clear differences were found between areas with and without SFS in the prevalence and abundance of oocyst of Eimeria. This coccidian genus appears to include parasites of the prey rather than the raptors, thus representing parasite transport or pseudo-parasitism rather than actual parasitism in the kites. A higher prevalence and richness of helminths, as well as mixed infections with several phyla, was found in kites exploiting SFS than in those feeding on wild prey in the area without SFS. The unsanitary conditions derived from the stack of livestock carcasses and the contamination of carrion with the faeces of multiple scavenger hosts can increase the accumulation and persistence of helminths eggs and intermediate hosts. The regular use and frequent confinement of large numbers of red kites at SFS can promote the spread of parasites to a large proportion of the European breeding population distributed across Spain during the winter. We encourage that carcasses of free roaming livestock can be left in the countryside, as well as the conservation management of wildlife exploited as food by red kites (especially wild rabbits), to attempt avoiding overcrowded and confined conditions at SFS. Further research is required to assess the impact of deliberate feeding on the spread of parasites and other disease agents in the threatened species SFS are intended to favour.

Predictors and immunological correlates of sublethal mercury exposure in vampire bats

Mercury (Hg) is a pervasive heavy metal that often enters the environment from anthropogenic sources such as gold mining and agriculture. Chronic exposure to Hg can impair immune function, reducing the ability of animals to resist or recover from infections. How Hg influences immunity and susceptibility remains unknown for bats, which appear immunologically distinct from other mammals and are reservoir hosts of many pathogens of importance to human and animal health. We here quantify total Hg (THg) in hair collected from common vampire bats (Desmodus rotundus), which feed on blood and are the main reservoir hosts of rabies virus in Latin America. We examine how diet, sampling site and year, and bat demography influence THg and test the consequences of this variation for eight immune measures. In two populations from Belize, THg concentrations in bats were best explained by an interaction between long-term diet inferred from stable isotopes and year. Bats that foraged more consistently on domestic animals exhibited higher THg. However, relationships between diet and THg were evident only in 2015 but not in 2014, which could reflect recent environmental perturbations associated with agriculture. THg concentrations were low relative to values previously observed in other bat species but still correlated with bat immunity. Bats with higher THg had more neutrophils, weaker bacterial killing ability and impaired innate immunity. These patterns suggest that temporal variation in Hg exposure may impair bat innate immunity and increase susceptibility to pathogens such as bacteria. Unexpected associations between low-level Hg exposure and immune function underscore the need to better understand the environmental sources of Hg exposure in bats and the consequences for bat immunity and susceptibility.

The history of rabies in the Western Hemisphere

Before the introduction of control programs in the 20th century, rabies in domestic dogs occurred throughout the Western Hemisphere. However, historical records and phylogenetic analysis of multiple virus isolates indicate that, before the arrival of the first European colonizers, rabies virus was likely present only in bats and skunks. Canine rabies was either rare or absent among domestic dogs of Native Americans, and first arrived when many new dog breeds were imported during the period of European colonization. The introduction of the cosmopolitan dog rabies lyssavirus variant and the marked expansion of the dog population provided ideal conditions for the flourishing of enzootic canine rabies. The shift of dog-maintained viruses into gray foxes, coyotes, skunks and other wild mesocarnivores throughout the Americas and to mongooses in the Caribbean has augmented the risk of human rabies exposures and has complicated control efforts. At the same time, the continued presence of bat rabies poses novel challenges in the absolute elimination of canine and human rabies. This article compiles existing historical and phylogenetic evidence of the origins and subsequent dynamics of rabies in the Western Hemisphere, from the era preceding the arrival of the first European colonizers through the present day. A companion article reviews the current status of canine rabies control throughout the Western Hemisphere and steps that will be required to achieve and maintain its complete elimination (Velasco-Villa et al., 2017).

Experimental evidence that parasites drive eco-evolutionary feedbacks

Host resistance to parasites is a rapidly evolving trait that can influence how hosts modify ecosystems. Eco-evolutionary feedbacks may develop if the ecosystem effects of host resistance influence selection on subsequent host generations. In a mesocosm experiment, using a recently diverged (<100 generations) pair of lake and stream three-spined sticklebacks, we tested how experimental exposure to a common fish parasite (Gyrodactylus spp.) affects interactions between hosts and their ecosystems in two environmental conditions (low and high nutrients). In both environments, we found that stream sticklebacks were more resistant to Gyrodactylus and had different gene expression profiles than lake sticklebacks. This differential infection led to contrasting effects of sticklebacks on a broad range of ecosystem properties, including zooplankton community structure and nutrient cycling. These ecosystem modifications affected the survival, body condition, and gene expression profiles of a subsequent fish generation. In particular, lake juvenile fish suffered increased mortality in ecosystems previously modified by lake adults, whereas stream fish showed decreased body condition in stream fish-modified ecosystems. Parasites reinforced selection against lake juveniles in lake fish-modified ecosystems, but only under oligotrophic conditions. Overall, our results highlight the overlapping timescales and the interplay of host-parasite and host-ecosystem interactions. We provide experimental evidence that parasites influence host-mediated effects on ecosystems and, thereby, change the likelihood and strength of eco-evolutionary feedbacks.

Drivers of Bartonella infection in micromammals and their fleas in a Mediterranean peri-urban area

People living at the human/wildlife interface are at risk of becoming infected with Bartonella for which micromammals act as reservoir. We aimed to determine the factors related to the prevalence of Bartonella and its haplotype diversity in micromammals and in their fleas in a Mediterranean peri-urban environment. We analyzed 511 micromammals, chiefly 407 wood mice (Apodemus sylvaticus), captured into Barcelona metropolitan area (Spain) in spring and autumn from 2011 to 2013 in two natural and two adjacent residential areas, their fleas (grouped in 218 monospecific pools) and 29 fetuses from six Bartonella-positive female wood mice. Amplification of a fragment of ITS was carried out by real time PCR. Prevalence was 49% (57% in the dominant species, the wood mouse), and 12 haplotypes were detected. In general, prevalence was higher in those hosts more heavily infested by fleas, coincident with higher rates of capture, in autumn than in spring, and in adults than in juveniles. Prevalence did not differ between natural and residential areas except for one prevalent haplotype, which was more frequent in natural areas. Prevalence in flea pools (58%) was only explained by Bartonella occurrence in the pool host. In 56.4% of the flea pools with identified Bartonella haplotypes, we found the same haplotype in the host and in its flea pool. Prevalence in wood mouse fetuses was 69%, with at least one infected fetus in all litters, and two litters with all the fetuses infected. indicating that vertical transmission might be important in Bartonella epidemiology in the wood mouse. There is a hazard of Bartonella infection for people living in residential areas and those visiting peri-urban natural areas in Barcelona.

Urbanization and the dynamics of RNA viruses in Mallards (Anas platyrhynchos)

Urbanization is intensifying worldwide, and affects the epidemiology of infectious diseases. However, the effect of urbanization on natural host-pathogen systems remains poorly understood. Urban ducks occupy an interesting niche in that they directly interact with both humans and wild migratory birds, and either directly or indirectly with food production birds. Here we have collected samples from Mallards (Anas platyrhynchos) residing in a pond in central Uppsala, Sweden, from January 2013 to January 2014. This artificial pond is kept ice-free during the winter months, and is a popular location where the ducks are fed, resulting in a resident population of ducks year-round. Nine hundred and seventy seven (977) fecal samples were screened for RNA viruses including: influenza A virus (IAV), avian paramyxovirus 1, avian coronavirus (CoV), and avian astrovirus (AstroV). This intra-annual dataset illustrates that these RNA viruses exhibit similar annual patterns to IAV, suggesting similar ecological factors are at play. Furthermore, in comparison to wild ducks, autumnal prevalence of IAV and CoV are lower in this urban population. We also demonstrate that AstroV might be a larger burden to urban ducks than IAV, and should be better assessed to demonstrate the degree to which wild birds contribute to the epidemiology of these viruses. The presence of economically relevant viruses in urban Mallards highlights the importance of elucidating the ecology of wildlife pathogens in urban environments, which will become increasingly important for managing disease risks to wildlife, food production animals, and humans.

•

Influenza virus, coronavirus, paramyxovirus, astrovirus detected in urban Mallards

•

Viruses share intra-annual dynamics, with autumnal prevalence peak

•

Avian astrovirus had the highest prevalence in urban Mallards.

•

Prevalence of influenza and coronavirus lower in urban versus to migrating Mallard

Management and modeling approaches for controlling raccoon rabies: The road to elimination

Rabies is an ancient viral disease that significantly impacts human and animal health throughout the world. In the developing parts of the world, dog bites represent the highest risk of rabies infection to people, livestock, and other animals. However, in North America, where several rabies virus variants currently circulate in wildlife, human contact with the raccoon rabies variant leads to the highest per capita population administration of post-exposure prophylaxis (PEP) annually. Previous rabies variant elimination in raccoons (Canada), foxes (Europe), and dogs and coyotes (United States) demonstrates that elimination of the raccoon variant from the eastern US is feasible, given an understanding of rabies control costs and benefits and the availability of proper tools. Also critical is a cooperatively produced strategic plan that emphasizes collaborative rabies management among agencies and organizations at the landscape scale. Common management strategies, alone or as part of an integrated approach, include the following: oral rabies vaccination (ORV), trap-vaccinate-release (TVR), and local population reduction. As a complement, mathematical and statistical modeling approaches can guide intervention planning, such as through contact networks, circuit theory, individual-based modeling, and others, which can be used to better understand and predict rabies dynamics through simulated interactions among the host, virus, environment, and control strategy. Strategies derived from this ecological lens can then be optimized to produce a management plan that balances the ecological needs and program financial resources. This paper discusses the management and modeling strategies that are currently used, or have been used in the past, and provides a platform of options for consideration while developing raccoon rabies virus elimination strategies in the US.

Urban health and ecology: the promise of an avian biomonitoring tool

Urban-dwelling birds have the potential to serve as powerful biomonitors that reveal the impact of environmental change due to urbanization. Specifically, urban bird populations can be used to survey cities for factors that may pose both public and wildlife health concerns. Here, we review evidence supporting the use of avian biomonitors to identify threats associated with urbanization, including bioaccumulation of toxicants and the dysregulation of behavior and physiology by related stressors. In addition, we consider the use of birds to examine how factors in the urban environment can impact immunity against communicable pathogens. By studying the behavior, physiology, and ecology of urban bird populations, we can elucidate not only how avian populations are responding to environmental change, but also how unintended consequences of urbanization affect the well-being of human and non-human inhabitants.

Plumage micro-organisms and preen gland size in an urbanizing context

Urbanization of Earth's habitats has led to considerable loss of biodiversity, but the driving ecological mechanism(s) are not always clear. Vertebrates like birds typically experience urban alterations to diet, habitat availability, and levels of predation or competition, but may also be exposed to greater or more pathogenic communities of microbes. Birds have been popular subjects of urban ecological research but, to our knowledge, no study has assessed how urban conditions influence the microbial communities on bird plumage. Birds carry a large variety of microorganisms on their plumage and some of them have the capacity to degrade feather keratin and alter plumage integrity. To limit the negative effects of these feather-degrading bacteria, birds coat their feathers with preen gland secretions containing antibacterial substances. Here we examined urban-rural variation in feather microbial abundance and preen gland size in house finches (Haemorhous mexicanus). We found that, although urban and rural finches carry similar total-cultivable microbial loads on their plumage, the abundance of feather-degrading bacteria was on average three times higher on the plumage of urban birds. We also found an increase in preen gland size along the gradient of urbanization, suggesting that urban birds may coat their feathers with more preen oil to limit the growth or activity of feather-degrading microbes. Given that greater investment in preening is traded-off against other immunological defenses and that feather-degrading bacteria can alter key processes like thermoregulation, aerodynamics, and coloration, our findings highlight the importance of plumage microbes and microbial defenses on the ecology of urban birds.

Host resistance and tolerance of parasitic gut worms depend on resource availability

Resource availability can significantly alter host-parasite dynamics. Abundant food can provide more resources for hosts to resist infections, but also increase host tolerance of infections by reducing competition between hosts and parasites for food. Whether abundant food favors host resistance or tolerance (or both) might depend on the type of resource that the parasite exploits (e.g., host tissue vs. food), which can vary based on the stage of infection. In our study, we evaluated how low and high resource diets affect Cuban tree frog (Osteopilus septentrionalis) resistance and tolerance of a skin-penetrating, gut nematode Aplectana sp. at each stage of the infection. Compared to a low resource diet, a high resource diet enhanced frog resistance to worm penetration and tolerance while worms traveled to the gut. In contrast, a low resource diet increased resistance to establishment of the infection. After the infection established and worms could access food resources in the gut, a high resource diet enhanced host tolerance of parasites. On a high resource diet, parasitized frogs consumed significantly more food than non-parasitized frogs; when food was then restricted, mass of non-parasitized frogs did not change, whereas mass of parasitized frogs decreased significantly. Thus, a high resource diet increased frog tolerance of established worms because frogs could fully compensate for energy lost to the parasites. Our study shows that host-parasite dynamics are influenced by the effect of resource availability on host resistance and tolerance, which depends on when parasites have access to food and the stage of infection.

Urbanization and Disease Emergence: Dynamics at the Wildlife-Livestock-Human Interface

Urbanization is characterized by rapid intensification of agriculture, socioeconomic change, and ecological fragmentation, which can have profound impacts on the epidemiology of infectious disease. Here, we review current scientific evidence for the drivers and epidemiology of emerging wildlife-borne zoonoses in urban landscapes, where anthropogenic pressures can create diverse wildlife-livestock-human interfaces. We argue that these interfaces represent a critical point for cross-species transmission and emergence of pathogens into new host populations, and thus understanding their form and function is necessary to identify suitable interventions to mitigate the risk of disease emergence. To achieve this, interfaces must be studied as complex, multihost communities whose structure and form are dictated by both ecological and anthropological factors.

Surviving winter: Food, but not habitat structure, prevents crashes in cyclic vole populations

Vole population cycles are a major force driving boreal ecosystem dynamics in northwestern Eurasia. However, our understanding of the impact of winter on these cycles is increasingly uncertain, especially because climate change is affecting snow predictability, quality, and abundance. We examined the role of winter weather and snow conditions, the lack of suitable habitat structure during freeze‐thaw periods, and the lack of sufficient food as potential causes for winter population crashes. We live‐trapped bank voles Myodes glareolus on 26 plots (0.36 ha each) at two different elevations (representing different winter conditions) in southeast Norway in the winters 2013/2014 and 2014/2015. We carried out two manipulations: supplementing six plots with food to eliminate food limitation and six plots with straw to improve habitat structure and limit the effect of icing in the subnivean space. In the first winter, all bank voles survived well on all plots, whereas in the second winter voles on almost all plots went extinct except for those receiving supplemental food. Survival was highest on the feeding treatment in both winters, whereas improving habitat structure had no effect. We conclude that food limitation was a key factor in causing winter population crashes.

Epidemic host community contribution to mosquito-borne disease transmission: Ross River virus

Most vector-borne diseases infect multiple host species, but disentangling the relative importance of different host species to transmission can be complex. Here we study how host species' abundance and competence (duration and titre of parasitaemia) influence host importance during epidemic scenarios. We evaluate this theory using Ross River virus (RRV, family Togaviridae, genus Alphavirus), a multi-host mosquito-borne disease with significant human health impacts across Australia and Papua New Guinea. We used host contribution models to find the importance of key hosts (possums, wallabies, kangaroos, horses, humans) in typical mammal communities around five Australian epidemic centres. We found humans and possums contributed most to epidemic RRV transmission, owing to their high abundances, generally followed by macropods. This supports humans as spillover hosts, and that human-mosquito and possum-mosquito transmission is predominant during epidemics. Sensitivity analyses indicate these findings to be robust across epidemic centres. We emphasize the importance of considering abundance and competence in identifying key hosts (during epidemics in this case), and that competence alone is inadequate. Knowledge of host importance in disease transmission may help to equip health agencies to bring about greater effectiveness of disease mitigation strategies.

Spatial pattern of genetic diversity and selection in the MHC class II DRB of three Neotropical bat species

Background

Although bats are natural reservoirs of many pathogens, few studies have been conducted on the genetic variation and detection of selection in major histocompatibility complex (MHC) genes. These genes are critical for resistance and susceptibility to diseases, and host–pathogen interactions are major determinants of their extensive polymorphism. Here we examined spatial patterns of diversity of the expressed MHC class II DRB gene of three sympatric Neotropical bats, Carollia perspicillata and Desmodus rotundus (Phyllostomidae), and Molossus molossus (Molossidae), all of which use the same environments (e.g., forests, edge habitats, urban areas). Comparison with neutral marker (mtDNA D-loop) diversity was performed at the same time.

Results

Twenty-three DRB alleles were identified in 19 C. perspicillata, 30 alleles in 35 D. rotundus and 20 alleles in 28 M. molossus. The occurrence of multiple DRB loci was found for the two Phyllostomidae species. The DRB polymorphism was high in all sampling sites and different signatures of positive selection were detected depending on the environment. The patterns of DRB diversity were similar to those of neutral markers for C. perspicillata and M. molossus. In contrast, these patterns were different for D. rotundus for which a geographical structure was highlighted. A heterozygote advantage was also identified for this species. No recombination or gene conversion event was found and phylogenetic relationships showed a trans-species mode of evolution in the Phyllostomids.

Conclusions

This study of MHC diversity demonstrated the strength of the environment and contrasting pathogen pressures in shaping DRB diversity. Differences between positively selected sites identified in bat species highlighted the potential role of gut microbiota in shaping immune responses. Furthermore, multiple geographic origins and/or population admixtures observed in C. perspicillata and M. molossus populations acted as an additional force in shaping DRB diversity. In contrast, DRB diversity of D. rotundus was shaped by environment rather than demographic history.

Electronic supplementary material

The online version of this article (doi:10.1186/s12862-016-0802-1) contains supplementary material, which is available to authorized users.

On the benefits of systematic reviews for wildlife parasitology

Systematic reviews and meta-analyses are widely accepted as the best means to synthesise quantitative or qualitative scientific evidence. Many scientific fields have embraced these more rigorous review techniques as a means to bring together large and complex bodies of literature and their data. Unfortunately, due to perceived difficulties and unfamiliarity with processes, other fields are not using these options to review their literature. One way to provide guidance for a specific field is to examine critically recent reviews and meta-analyses and to explain the advantages and disadvantages of the various review techniques. In this paper, we examine review papers in the emerging field of wildlife parasitology and compare five different literature review types-configurative narrative review, aggregative scoping review, aggregative literature review, aggregative meta-analysis, and aggregative systematic review. We found that most literature reviews did not adequately explain the methodology used to find the literature under review. We also found that most literature reviews were not comprehensive nor did they critically appraise the literature under review. Such a lack severely reduces the reliability of the reviews. We encourage all authors to consider using systematic reviews in the future, and for authors and peer-reviewers to be aware of the limitations of non-systematic reviews.