A Generalist Predator Regulating Spread of a Wildlife Disease: Exploring Two Infection Transmission Scenarios

Ecoepidemiology is a well-developed branch of theoretical ecology, which explores interplay between the trophic interactions and the disease spread. In most ecoepidemiological models, however, the authors assume the predator to be a specialist, which consumes only a single prey species. In few existing papers, in which the predator was suggested to be a generalist, the alternative food supply was always considered to be constant. This is obviously a simplification of reality, since predators can often choose between a number of different prey. Consumption of these alternative prey can dramatically change their densities and strongly influence the model predictions. In this paper, we try to bridge the gap and explore a generic ecoepidemiological system with a generalist predator, where the densities of all prey are dynamical variables. The model consists of two prey species, one of which is subject to an infectious disease, and a predator, which consumes both prey species. We investigate two main scenarios of infection transmission mode: (i) the disease transmission rate is predator independent and (ii) the transmission rate is a function of predator density. For both scenarios we fulfil an extensive bifurcation analysis. We show that including a second dynamical prey in the system can drastically change the dynamics of the single prey case. In particular, the presence of a second prey impedes disease spread by decreasing the basic reproduction number and can result in a substantial drop of the disease prevalence. We demonstrate that with efficient consumption of the second prey species by the predator, the predator-dependent disease transmission can not destabilize interactions, as in the case with a specialist predator. Interestingly, even if the population of the second prey eventually vanishes and only one prey species finally remains, the system with two prey species may exhibit different properties to those of the single prey system.

Spatial Management of Wildlife Disease

The spread of wildlife diseases is a major threat to livestock, human health, resource-based recreation, and biodiversity conservation (Cleaveland, Laurenson, and Taylor). The development of economically sound wildlife disease-management strategies requires an understanding of the links between ecological functions (e.g., disease transmission and wildlife dispersal) and economic choices, and the associated tradeoffs. Spatial linkages are particularly relevant. Yet while ecologists have long-argued that space is important (Hudson et al.), prior economic work has largely ignored spatial issues. For instance, Horan and Wolf analyzed a case study of bovine tuberculosis (bTB) in Michigan deer, a problem where the disease appears to be confined to a single, spatially confined, wildlife population—an island. But wildlife disease matters generally are not spatially confined. Barlow, in analyzing bTB in possums in New Zealand, accounted for immigration of susceptible possums into a disease reservoir. However, he modeled immigration as fixed and unaffected by management. Bicknell, Wilen, and Howitt, also focusing on possums in New Zealand, developed a model that incorporates simple density-dependent net migration. This allowed the authors to account for endogenous immigration when deriving optimal culling strategies.

The Economics of Managing Wildlife Disease

The spread of infectious disease among and between wild and domesticated animals has become a major problem worldwide. Upon analyzing the dynamics of wildlife growth and infection when the diseased animals cannot be identified separately from healthy wildlife prior to the kill, we find that harvest-based strategies alone have no impact on disease transmission. Other controls that directly influence disease transmission and/or mortality are required. Next, we analyze the socially optimal management of infectious wildlife. The model is applied to the problem of bovine tuberculosis among Michigan white-tailed deer, with non-selective harvests and supplemental feeding being the control variables. Using a two-state linear control model, we find a two-dimensional singular path is optimal (as opposed to a more conventional bang-bang solution) as part of a cycle that results in the disease remaining endemic in the wildlife. This result follows from non-selective harvesting and intermittent wildlife productivity gains from supplemental feeding.

Minnesota wildlife disease investigation : a compilation of monthly reports to the Division of Game and Fish, Minnesota Department of Conservation /

"Conducted by University of Minnesota, Bureau of Biological Survey, Minnesota Department of Conservation."

Reflecting on ethical and legal issues in wildlife disease

Disease in wildlife raises a number of issues that have not been widely considered in the bioethical literature. However, wildlife disease has major implications for human welfare. The majority of emerging human infectious diseases are zoonotic: that is, they occur in humans by cross-species transmission from animal hosts. Managing these diseases often involves balancing concerns with human health against animal welfare and conservation concerns. Many infectious diseases of domestic animals are shared with wild animals, although it is often unclear whether the infection spills over from wild animals to domestic animals or vice versa. Culling is the standard means of managing such diseases, bringing economic considerations, animal welfare and conservation into conflict. Infectious diseases are also major threatening processes in conservation biology and their appropriate management by culling, vaccination or treatment raises substantial animal ethics issues. One particular issue of great significance in Australia is an ongoing research program to develop genetically modified pathogens to control vertebrate pests including rabbits, foxes and house mice. Release of any self-replicating GMO vertebrate pathogen gives rise to a whole series of ethical questions. We briefly review current Australian legal responses to these problems. Finally, we present two unresolved problems of general importance that are exemplified by wildlife disease. First, to what extent can or should 'bioethics' be broadened beyond direct concerns with human welfare to animal welfare and environmental welfare? Second, how should the irreducible uncertainty of ecological systems be accounted for in ethical decision making?

Survey for Foot-and-mouth Disease in the Endangered Marsh Deer (Blastocerus dichotomus) from Marshlands of the Parana River Basin, Brazil

Habitat fragmentation and diseases have resulted in a decline of the marsh deer (Blastocerus (dichotomus) throughout its South American range. Our objectives were to determine whether marsh deer intended for translocation from a region of the Rio Parana Basin had been infected previously by foot-and-mouth disease virus (FMDV) and whether they were carrying virus We captured marsh deer from June to October 1998 and collected blood from 108 animals and esophageal-pharyngeal fluid from 53 Serum was tested for antibodies against three FMDV serotypes (O, A, and C) by liquid-phase-blocking sandwich enzyme-linked immunosorbent assay (ELISA) Esophageal-pharyngeal fluid was tested for FMDV RNA by reverse transcription polymerase chain reaction (RT-PCR) and inoculation into three successive baby hamster kidney (BHK-21) cell subcultures, followed by RT-PCR of cultures We detected low log(10) titers (range 1 0-1 5) to FM DV subtype A(24) Cruzeiro in 19 of 108 sampled marsh deer, but failed to isolate FMDV or detect FMDV RNA in any samples we conclude that marsh deer from our study site were unlikely to carry FMDV, however, as a preventive measure, the 19 animals with titers for FMDV were not sent to FMDV-free Brazilian states

Seeking a Second Opinion: Uncertainty in Disease Ecology

Analytical methods accounting for imperfect detection are often used to facilitate reliable inference in population and community ecology. We contend that similar approaches are needed in disease ecology because these complicated systems are inherently difficult to observe without error. For example, wildlife disease studies often designate individuals, populations, or spatial units to states (e.g., susceptible, infected, post-infected), but the uncertainty associated with these state assignments remains largely ignored or unaccounted for. We demonstrate how recent developments incorporating observation error through repeated sampling extend quite naturally to hierarchical spatial models of disease effects, prevalence, and dynamics in natural systems. A highly pathogenic strain of avian influenza virus in migratory waterfowl and a pathogenic fungus recently implicated in the global loss of amphibian biodiversity are used as motivating examples. Both show that relatively simple modifications to study designs can greatly improve our understanding of complex spatio-temporal disease dynamics by rigorously accounting for uncertainty at each level of the hierarchy.

Options for the Control of Disease 3: Targeting the Environment

Management of wildlife disease can be targeted at pathogens, hosts or vector populations, but may also focus on the environment. As constituent elements of any given environment, resident wildlife populations, and their pathogens, may be profoundly influenced by environmental change, in terms of their abundance, distribution and behavior. Hence, it is reasonable to expect that incorporation of environmental manipulation into a program to control wildlife diseases may potentially result in outcomes as effective as direct intervention aimed at hosts, pathogens and vectors.

Free-Ranging Wild Boar: A Disease Threat to Domestic Pigs in Switzerland?

The risk of transmission of pathogens from free-ranging wild boars (Sus scrofa scrofa) to outdoor domestic pigs (S. scrofa domesticus) is of increasing concern in many European countries. We assess this risk, using Switzerland as an example. We estimated 1) the prevalence of important pathogens in wild boars and 2) the risk of interactions between wild boars and outdoor pigs. First, we tested 252 wild boars from selected areas between 2008 and 2010 for infection with Brucella spp. Bacterial prevalence was estimated to 28.8% (confidence interval [CI] 23.0-34.0) when using bacterial culture (B. suis Biovar 2) and real-time polymerase chain reaction. Antibody prevalence was 35.8% (CI 30.0-42.0), which was significantly higher than in previous studies in Switzerland. We also tested 233 wild boars for porcine reproductive and respiratory syndrome virus (PRRSV). Antibody prevalence was 0.43% (CI 0.01-2.4) for EU-PRRSV and real-time reverse transcription polymerase chain reaction results were negative. These findings suggest that B. suis is increasingly widespread in wild boars and PRRSV is currently not of concern. Second, we documented the spatial overlap between free-ranging wild boars and outdoor piggeries by mapping data on their respective occurrence. Wild boars are most widespread in the mountain range along the western and northern Swiss borders, while most piggeries are located in central lowlands. A risk of interaction is mainly expected at the junction between these two bioregions. This risk may increase if wild boars expand eastward and southward beyond anthropogenic barriers believed to limit their range. Therefore, we evaluated the potential of expansion of the wild boar population. Population trends suggest a continuous increase of wild boars for the past 15 yr. Surveillance of selected wildlife passages using cameras on highways and main roads indicates that these barriers are permeable (average of up to 13 wild boar crossings per 100 days). Thus an increase of wild boar range should be considered. There may be a risk of B. suis spillover from wild boars in Switzerland, which could increase in the future. Data on the occurrence of interactions between pigs and wild boars are needed to assess this risk.

Pathology of sarcoptic mange in red foxes (Vulpes vulpes): macroscopic and histologic characterization of three disease stages

Sarcoptic mange is a highly contagious skin disease that can have a devastating impact on affected wild mammal populations. There are notable variations in the clinical and pathologic picture of sarcoptic mange among species and among conspecifics. However, the origin of these variations is unclear. We propose a classification scheme for skin lesions associated with Sarcoptes scabiei infestation to provide a basis for a subsequent risk factor analysis. We conducted a case-control study focused on macroscopic and histologic examination of the skin, using 279 red foxes (Vulpes vulpes) found dead or shot in Switzerland between November 2004 and February 2006. All animals were submitted to gross necropsy following a detailed protocol. Selection criteria for cases (n=147) vs. controls (n=111) were the presence or absence of mange-like lesions, mite detection by isolation or histologic examination, and serologic testing for S. scabiei antibodies. Characteristic features of mange lesions were scored macroscopically in all foxes and histologically in 67 cases and 15 controls. We classified skin lesions and associated necropsy findings into three types of mange: A) early stage (n=45): focal-extensive skin lesions, thin crusts, mild to moderate alopecia, few mites, numerous eosinophils, and mild lymph node enlargement; B) hyperkeratotic, fatal form (n=86): generalized skin lesions, thick crusts with or without alopecia, foul odor, abundance of mites, numerous bacteria and yeasts, numerous lymphocytes and mast cells, severe lymph node enlargement, and emaciation; C) alopecic, healing form (n=16): focal lesions, no crusts, severe alopecia, hyperpigmentation and lichenification, absence of mites, mixed cell infiltration, and rare mild lymph node enlargement. We hypothesize that after stage A, the animal either enters stage B and dies, or stage C and survives, depending on largely unknown extrinsic or intrinsic factors affecting the host ability to control mite infestation.

Effective coordination and management of emerging infectious diseases in wildlife populations

A transdisciplinary, One Health approach is proposed for the coordination of wildlife health diagnostics, research, and policy development. In some countries, considerable effort has been made to establish specific activities including surveillance and integration of wildlife health within diagnostic and research laboratories. We suggest that some of these activities can be improved and many countries still require national structures to deal with wildlife disease investigation and management. We also suggest that scientists in this field should actively engage with national and international organizations and conferences to influence the development of policy, diagnostics, research, and management of emerging wildlife diseases.

Reservoir-host amplification of disease impact in an endangered amphibian

Emerging wildlife pathogens are an increasing threat to biodiversity. One of the most serious wildlife diseases is chytridiomycosis, caused by the fungal pathogen, Batrachochytrium dendrobatidis (Bd), which has been documented in over 500 amphibian species. Amphibians vary greatly in their susceptibility to Bd, with some species tolerating infection, while others experience rapid mortality. Reservoir hosts - species that carry infection while maintaining high abundance, but are rarely killed by disease - can increase extinction risk in highly susceptible, sympatric species. However, whether reservoir hosts amplify Bd in declining amphibian species has not been examined. We combine a laboratory study with field surveys, disease sampling, and statistical modeling to investigate the role of reservoir hosts in chytridiomycosis dynamics and species decline in an amphibian community in south-eastern Australia. We show that the non-declining common eastern froglet (Crinia signifera) is a reservoir host for Bd, with laboratory animals carrying intense infection burdens over 12 weeks and the majority of wild sampled individuals carrying intense infections. We find that the presence of C. signifera is strongly associated with Bd prevalence in the sympatric, IUCN red-listed northern corroboree frog (Pseudophryne pengilleyi). Consistent with disease amplification by a reservoir host, we find that P. pengilleyi has declined from areas with high C. signifera abundance. Our results suggest that when reservoir hosts are present, population declines can continue long after the initial emergence of Bd, highlighting an urgent need to assess extinction risk in remnant populations of other declined amphibian species. Reintroductions and in situ management strategies must focus on identifying reservoir hosts and minimizing exposure of threatened species.

Conjunctivitis associated with Chlamydia pecorum in three koalas (Phascolarctos cinereus) in the Mount Lofty Ranges, South Australia

Chlamydiosis is a significant factor contributing to the decline of koala (Phascolarctos cinereus) populations in Australia but has not previously been reported in South Australia. We describe conjunctivitis in three wild koalas from South Australia, with Chlamydia pecorum identified by quantitative PCR.