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Clifford Astbury C, Lee KM, Mcleod R, Aguiar R, Atique A, Balolong M, Clarke J, Demeshko A, Labonté R, Ruckert A, Sibal P, Togño KC, Viens AM, Wiktorowicz M, Yambayamba MK, Yau A, Penney TL. Policies to prevent zoonotic spillover: a systematic scoping review of evaluative evidence. Global Health 2023; 19:82. [PMID: 37940941 PMCID: PMC10634115 DOI: 10.1186/s12992-023-00986-x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/05/2023] [Accepted: 11/01/2023] [Indexed: 11/10/2023] Open
Abstract
BACKGROUND Emerging infectious diseases of zoonotic origin present a critical threat to global population health. As accelerating globalisation makes epidemics and pandemics more difficult to contain, there is a need for effective preventive interventions that reduce the risk of zoonotic spillover events. Public policies can play a key role in preventing spillover events. The aim of this review is to identify and describe evaluations of public policies that target the determinants of zoonotic spillover. Our approach is informed by a One Health perspective, acknowledging the inter-connectedness of human, animal and environmental health. METHODS In this systematic scoping review, we searched Medline, SCOPUS, Web of Science and Global Health in May 2021 using search terms combining animal health and the animal-human interface, public policy, prevention and zoonoses. We screened titles and abstracts, extracted data and reported our process in line with PRISMA-ScR guidelines. We also searched relevant organisations' websites for evaluations published in the grey literature. All evaluations of public policies aiming to prevent zoonotic spillover events were eligible for inclusion. We summarised key data from each study, mapping policies along the spillover pathway. RESULTS Our review found 95 publications evaluating 111 policies. We identified 27 unique policy options including habitat protection; trade regulations; border control and quarantine procedures; farm and market biosecurity measures; public information campaigns; and vaccination programmes, as well as multi-component programmes. These were implemented by many sectors, highlighting the cross-sectoral nature of zoonotic spillover prevention. Reports emphasised the importance of surveillance data in both guiding prevention efforts and enabling policy evaluation, as well as the importance of industry and private sector actors in implementing many of these policies. Thoughtful engagement with stakeholders ranging from subsistence hunters and farmers to industrial animal agriculture operations is key for policy success in this area. CONCLUSION This review outlines the state of the evaluative evidence around policies to prevent zoonotic spillover in order to guide policy decision-making and focus research efforts. Since we found that most of the existing policy evaluations target 'downstream' determinants, additional research could focus on evaluating policies targeting 'upstream' determinants of zoonotic spillover, such as land use change, and policies impacting infection intensity and pathogen shedding in animal populations, such as those targeting animal welfare.
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Affiliation(s)
- Chloe Clifford Astbury
- School of Global Health, York University, Toronto, ON, Canada
- Dahdaleh Institute for Global Health Research, York University, Toronto, ON, Canada
- Global Strategy Lab, York University, Toronto, ON, Canada
| | - Kirsten M Lee
- School of Global Health, York University, Toronto, ON, Canada
- Dahdaleh Institute for Global Health Research, York University, Toronto, ON, Canada
| | - Ryan Mcleod
- School of Global Health, York University, Toronto, ON, Canada
| | - Raphael Aguiar
- Dahdaleh Institute for Global Health Research, York University, Toronto, ON, Canada
| | - Asma Atique
- School of Global Health, York University, Toronto, ON, Canada
| | - Marilen Balolong
- Applied Microbiology for Health and Environment Research Group, College of Arts and Sciences, University of the Philippines Manila, Manila, Philippines
| | - Janielle Clarke
- School of Global Health, York University, Toronto, ON, Canada
| | | | - Ronald Labonté
- School of Epidemiology and Public Health, University of Ottawa, Ottawa, ON, Canada
| | - Arne Ruckert
- School of Epidemiology and Public Health, University of Ottawa, Ottawa, ON, Canada
| | - Priyanka Sibal
- School of Health Policy and Management, York University, Toronto, ON, Canada
| | - Kathleen Chelsea Togño
- Applied Microbiology for Health and Environment Research Group, College of Arts and Sciences, University of the Philippines Manila, Manila, Philippines
| | - A M Viens
- School of Global Health, York University, Toronto, ON, Canada
- Global Strategy Lab, York University, Toronto, ON, Canada
| | - Mary Wiktorowicz
- School of Global Health, York University, Toronto, ON, Canada
- Dahdaleh Institute for Global Health Research, York University, Toronto, ON, Canada
| | - Marc K Yambayamba
- School of Public Health, University of Kinshasa, Kinshasa, Democratic Republic of Congo
| | - Amy Yau
- Department of Public Health, Environments and Society, London School of Hygiene & Tropical Medicine, London, UK
| | - Tarra L Penney
- School of Global Health, York University, Toronto, ON, Canada.
- Dahdaleh Institute for Global Health Research, York University, Toronto, ON, Canada.
- Global Strategy Lab, York University, Toronto, ON, Canada.
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Schreiner CL, Basinski AJ, Remien CH, Nuismer SL. Optimizing the delivery of self-disseminating vaccines in fluctuating wildlife populations. PLoS Negl Trop Dis 2023; 17:e0011018. [PMID: 37594985 PMCID: PMC10468088 DOI: 10.1371/journal.pntd.0011018] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2022] [Revised: 08/30/2023] [Accepted: 07/30/2023] [Indexed: 08/20/2023] Open
Abstract
Zoonotic pathogens spread by wildlife continue to spill into human populations and threaten human lives. A potential way to reduce this threat is by vaccinating wildlife species that harbor pathogens that are infectious to humans. Unfortunately, even in cases where vaccines can be distributed en masse as edible baits, achieving levels of vaccine coverage sufficient for pathogen elimination is rare. Developing vaccines that self-disseminate may help solve this problem by magnifying the impact of limited direct vaccination. Although models exist that quantify how well these self-disseminating vaccines will work when introduced into temporally stable wildlife populations, how well they will perform when introduced into populations with pronounced seasonal population dynamics remains unknown. Here we develop and analyze mathematical models of fluctuating wildlife populations that allow us to study how reservoir ecology, vaccine design, and vaccine delivery interact to influence vaccine coverage and opportunities for pathogen elimination. Our results demonstrate that the timing of vaccine delivery can make or break the success of vaccination programs. As a general rule, the effectiveness of self-disseminating vaccines is optimized by introducing after the peak of seasonal reproduction when the number of susceptible animals is near its maximum.
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Affiliation(s)
- Courtney L. Schreiner
- Department of Ecology and Evolutionary Biology, University of Tennessee, Knoxville, Tennessee, United States of America
| | - Andrew J. Basinski
- Institute for Interdisciplinary Data Sciences, University of Idaho, Moscow, Idaho, United States of America
| | - Christopher H. Remien
- Department of Mathematics and Statistical Sciences, University of Idaho, Moscow, Idaho, United States of America
| | - Scott L. Nuismer
- Department of Biological Sciences, University of Idaho, Moscow, Idaho, United States of America
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Quantifying the effectiveness of betaherpesvirus-vectored transmissible vaccines. Proc Natl Acad Sci U S A 2022; 119:2108610119. [PMID: 35046024 PMCID: PMC8794881 DOI: 10.1073/pnas.2108610119] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 12/14/2021] [Indexed: 11/26/2022] Open
Abstract
Spillover of infectious diseases from wildlife populations into humans is an increasing threat to human health and welfare. Current approaches to manage these emerging infectious diseases are largely reactive, leading to deadly and costly time lags between emergence and control. Here, we use mathematical models and data from previously published experimental and field studies to evaluate the scope for a more proactive approach based on transmissible vaccines that eliminates pathogens from wild animal populations before spillover can occur. Our models are focused on transmissible vaccines designed using herpes virus vectors and demonstrate that these vaccines—currently under development for several important human pathogens—may have the potential to rapidly control zoonotic pathogens within the reservoir hosts. Transmissible vaccines have the potential to revolutionize how zoonotic pathogens are controlled within wildlife reservoirs. A key challenge that must be overcome is identifying viral vectors that can rapidly spread immunity through a reservoir population. Because they are broadly distributed taxonomically, species specific, and stable to genetic manipulation, betaherpesviruses are leading candidates for use as transmissible vaccine vectors. Here we evaluate the likely effectiveness of betaherpesvirus-vectored transmissible vaccines by developing and parameterizing a mathematical model using data from captive and free-living mouse populations infected with murine cytomegalovirus (MCMV). Simulations of our parameterized model demonstrate rapid and effective control for a range of pathogens, with pathogen elimination frequently occurring within a year of vaccine introduction. Our results also suggest, however, that the effectiveness of transmissible vaccines may vary across reservoir populations and with respect to the specific vector strain used to construct the vaccine.
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Layman NC, Tuschhoff BM, Nuismer SL. Designing transmissible viral vaccines for evolutionary robustness and maximum efficiency. Virus Evol 2021; 7:veab002. [PMID: 33680502 PMCID: PMC7920745 DOI: 10.1093/ve/veab002] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022] Open
Abstract
The danger posed by emerging infectious diseases necessitates the development of new tools that can mitigate the risk of animal pathogens spilling over into the human population. One promising approach is the development of recombinant viral vaccines that are transmissible, and thus capable of self-dissemination through hard to reach populations of wild animals. Indeed, mathematical models demonstrate that transmissible vaccines can greatly reduce the effort required to control the spread of zoonotic pathogens in their animal reservoirs, thereby limiting the chances of human infection. A key challenge facing these new vaccines, however, is the inevitability of evolutionary change resulting from their ability to self-replicate and generate extended chains of transmission. Further, carrying immunogenic transgenes is often costly, in terms of metabolic burden, increased competition with the pathogen, or due to unintended interactions with the viral host regulatory network. As a result, natural selection is expected to favor vaccine strains that down-regulate or delete these transgenes resulting in increased rates of transmission and reduced efficacy against the target pathogen. In addition, efficacy and evolutionary stability will often be at odds; as when longer, more efficacious antigens experience faster rates of evolutionary decay. Here, we ask how such trade-offs influence the overall performance of transmissible vaccines. We find that evolutionary instability can substantially reduce performance, even for vaccine candidates with the ideal combination of efficacy and transmission. However, we find that, at least in some cases, vaccine stability and overall performance can be improved by the inclusion of a second, redundant antigen. Overall, our results suggest that the successful application of recombinant transmissible vaccines will require consideration of evolutionary dynamics and epistatic effects, as well as basic measurements of epidemiological features.
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Affiliation(s)
| | - Beth M Tuschhoff
- Department of Mathematics, University of Idaho, 875 Perimeter Drive, Moscow, ID 83844, USA
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Barnett KM, Civitello DJ. Ecological and Evolutionary Challenges for Wildlife Vaccination. Trends Parasitol 2020; 36:970-978. [PMID: 32952060 PMCID: PMC7498468 DOI: 10.1016/j.pt.2020.08.006] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/26/2020] [Revised: 08/23/2020] [Accepted: 08/24/2020] [Indexed: 12/13/2022]
Abstract
Wildlife vaccination is of urgent interest to reduce disease-induced extinction and zoonotic spillover events. However, several challenges complicate its application to wildlife. For example, vaccines rarely provide perfect immunity. While some protection may seem better than none, imperfect vaccination can present epidemiological, ecological, and evolutionary challenges. While anti-infection and antitransmission vaccines reduce parasite transmission, antidisease vaccines may undermine herd immunity, select for increased virulence, or promote spillover. These imperfections interact with ecological and logistical constraints that are magnified in wildlife, such as poor control and substantial trait variation within and among species. Ultimately, we recommend approaches such as trait-based vaccination, modeling tools, and methods to assess community- and ecosystem-level vaccine safety to address these concerns and bolster wildlife vaccination campaigns.
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Affiliation(s)
- K M Barnett
- Department of Biology, Emory University, Atlanta, GA 30322, USA.
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Nuismer SL, Bull JJ. Self-disseminating vaccines to suppress zoonoses. Nat Ecol Evol 2020; 4:1168-1173. [PMID: 32719452 DOI: 10.1038/s41559-020-1254-y] [Citation(s) in RCA: 17] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/10/2020] [Accepted: 06/22/2020] [Indexed: 01/08/2023]
Abstract
The SARS-CoV-2 epidemic is merely the most recent demonstration that our current approach to emerging zoonotic infectious disease is ineffective. SARS, MERS, Ebola, Nipah and an array of arenavirus infections sporadically spillover into human populations and are often contained only as a result of their poor transmission in human hosts, coupled with intense public health control efforts in the early stages of an emerging epidemic. It is now more apparent than ever that we need a better and more proactive approach. One possibility is to eliminate the threat of spillover before it occurs using vaccines capable of autonomously spreading through wild animal reservoirs. We are now poised to begin developing self-disseminating vaccines targeting a wide range of human pathogens, but important decisions remain about how they can be most effectively designed and used to target pathogens with a high risk of spillover and/or emergence. In this Perspective, we first review the basic epidemiological theory establishing the feasibility and utility of self-disseminating vaccines. We then outline a road map for overcoming remaining technical challenges: identifying high-risk pathogens before they emerge, optimizing vaccine design with an eye to evolution, behaviour and epidemiology, and minimizing the risk of unintended consequences.
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Affiliation(s)
- Scott L Nuismer
- Department of Biological Sciences, University of Idaho, Moscow, ID, USA. .,Department of Mathematics, University of Idaho, Moscow, ID, USA.
| | - James J Bull
- Department of Biological Sciences, University of Idaho, Moscow, ID, USA
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Nuismer SL, Basinski A, Bull JJ. Evolution and containment of transmissible recombinant vector vaccines. Evol Appl 2019; 12:1595-1609. [PMID: 31462917 PMCID: PMC6708430 DOI: 10.1111/eva.12806] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/08/2019] [Revised: 04/07/2019] [Accepted: 04/19/2019] [Indexed: 12/16/2022] Open
Abstract
Transmissible vaccines offer a revolutionary approach for controlling infectious disease and may provide one of the few feasible methods for eliminating pathogens from inaccessible wildlife populations. Current efforts to develop transmissible vaccines use recombinant vector technology whereby pathogen antigens are engineered to be expressed from innocuous infectious viral vectors. The resulting vaccines can transmit from host to host, amplifying the number of vaccine-protected individuals beyond those initially vaccinated directly through parenteral inoculation. One main engineering challenge is the potential for natural selection to favor vaccine mutants that eliminate or reduce expression of antigenic inserts, resulting in immunogenic decay of the vaccine over time. Here, we study a mathematical model of vector mutation whereby continuous elimination of the antigenic insert results in reversion of the vaccine back into the insert-free vector. We use this model to quantify the maximum allowable rate of reversion that can be tolerated for a transmissible vaccine to maintain a critical threshold level of immunogenicity against a target pathogen. Our results demonstrate that even for transmissible vaccines where reversion is frequent, performance will often substantially exceed that of conventional, directly administered vaccines. Further, our results demonstrate the feasibility of designing transmissible vaccines that yield desired levels of immunogenicity, yet degrade at a rate sufficient for persistence of the recombinant vaccine within the environment to be minimized.
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Affiliation(s)
| | | | - James J. Bull
- Department of Integrative BiologyThe University of Texas at AustinAustinTexas
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