Gebbiena M. Bron

Discussions around managing hunting and the consumption of wild animal meat increasingly emphasizes public health concerns and the risk of zoonotic spillover. In this article, we explore factors that may lead to under- or overestimating health risks from wild meat and break down key terminology for a multidisciplinary audience. We outline key principles of disease ecology and epidemiology that are often overlooked when quantifying spillover risk, and reflect on the importance of contextualizing health risks relative to food-health systems more broadly. We discuss how misrepresenting risks, intentionally or unintentionally, to justify conservation practices can have unintended negative conservation and public health consequences—despite the importance of conservation in protecting human health more broadly. We stress the importance of considering individual and local health outcomes (food security, neglected tropical diseases, etc.), not only those impacting global health (i.e. pandemic prevention). Finally, we advocate for evidence-informed, context-appropriate strategies for wild meat management.

Outbreaks of Japanese encephalitis (JE) can have severe health and economic impacts in both humans and susceptible animal species and are estimated to cause ~68,000 human disease cases in Asia annually. The disease is caused by infection with the mosquito‐borne JE virus (JEV), which continues to expand its geographical range from its endemic region in Asia. Since appropriate vertebrate host and mosquito vector species are present in Europe and average European summer temperatures continue to increase, JEV introduction could lead to the establishment of the pathogen in native mosquito species and wild birds and disease outbreaks among humans, pigs, and horses. Incursions could occur through movements of infected pigs and mosquitoes but also via migratory birds that act as reservoirs. Introduction and establishment of JEV in these populations may not be apparent at first, providing time for virus spread before spillover to the human population. Further complicating serological detection of JEV is the extensive cross‐reactivity with other orthoflaviviruses circulating in Europe (i.e., tick‐borne encephalitis virus [TBEV], West Nile virus [WNV], and Usutu virus [USUV]). In addition, viremia in clinical cases may be short, hindering virus detection. To facilitate European preparedness for detection, surveillance, and monitoring of JEV introduction and spread, five veterinary national reference laboratories in Europe collaborated with the aim to align JEV diagnostic pipelines to prepare for future emergence of JEV in Europe. All institutes assessed established and newly developed serological and molecular assays to build capability with sensitive and specific diagnostic tools for JEV detection. Additionally, methods for whole‐genome sequencing (WGS) were established and compared. In summary, this project provides a framework for communication and international collaboration between arboviral researchers at national veterinary institutes. The sharing of knowledge and expertise, and alignment of diagnostic techniques, has facilitated improvement of diagnostic pipelines for JEV detection and contributed to preparedness for JEV introduction into Europe.

Rift Valley fever virus (RVFV) is a (re)emerging mosquito-borne pathogen impacting human and animal health. How RVFV spreads through a population depends on population-level and individual-level interactions between vector, host and pathogen. Here, we estimated the probability for RVFV to transmit to naive animals by experimentally exposing lambs to a bite of an infectious mosquito, and assessed if and how RVFV infection subsequently developed in the exposed animal. Aedes aegypti mosquitoes, previously infected via feeding on a viremic lamb, were used to expose naive lambs to the virus. Aedes aegypti colony mosquitoes were used as they are easy to maintain and readily feed in captivity. Other mosquito spp. could be examined with similar methodology. Lambs were exposed to either 1-3 (low exposure) or 7-9 (high exposure) infectious mosquitoes. All lambs in the high exposure group became viremic and showed characteristic signs of Rift Valley fever within 2-4 days post exposure. In contrast, 3 out of 12 lambs in the low exposure group developed viremia and disease, with similar peak-levels of viremia as the high exposure group but with some heterogeneity in the onset of viremia. These results suggest that the likelihood for successful infection of a ruminant host is affected by the number of infectious mosquitoes biting, but also highlights that a single bite of an infectious mosquito can result in disease. The per bite mosquito-to-host transmission efficiency was estimated at 28% (95% confidence interval: 15 - 47%). We subsequently combined this transmission efficiency with estimates for life traits of Aedes aegypti or related mosquitoes into a Ross-McDonald mathematical model to illustrate scenarios under which major RVFV outbreaks could occur in naïve populations (i.e., R₀ >1). The model revealed that relatively high vector-to-host ratios as well as mosquitoes feeding preferably on competent hosts are required for R₀ to exceed 1. Altogether, this study highlights the importance of experiments that mimic natural exposure to RVFV. The experiments facilitate a better understanding of the natural progression of disease and a direct way to obtain epidemiological parameters for mathematical models.

West Nile virus (WNV) invaded the continental United States over 20 years ago and continues to cause yearly seasonal outbreaks of human and veterinary disease. In the suburbs of Chicago, Illinois, ultra-low volume (ULV) truck-mounted adulticide spraying frequently is performed to reduce populations of Culex restuans Theobald and Cx. pipiens L. mosquitoes (Diptera: Culicidae) in an effort to lower the risk of WNV transmission. The effectiveness of this control method has not been rigorously evaluated, and evidence for Culex population reduction after ULV adulticide spraying has been inconclusive. Therefore, we evaluated the results of 5 sequential weekly truck-mounted adulticide applications of Zenivex® E20 (etofenprox) in 2 paired sites located in Cook County, IL, during the summer of 2018. Mosquito population abundance, age structure, and WNV infection prevalence were monitored and compared between paired treatment and nearby control sites. Adulticide treatment did not result in consistent short-term or long-term reductions in target WNV vector Culex abundance. However, there was a significant increase in the proportion of nulliparous females in the treated sites compared to control sites and a decrease in Cx. pipiens WNV infection rates at one of the treated sites. This evidence that ULV adulticide spraying altered the age structure and WNV infection prevalence in a vector population has important implications for WNV transmission risk management. Our findings also underscore the importance of measuring these important indicators in addition to abundance metrics when evaluating the efficacy of control methods.

Rift Valley fever virus (RVFV) is a (re)emerging mosquito-borne pathogen impacting human and animal health. How RVFV spreads through a population depends on population-level interactions between hosts and vectors (e.g., vector-to-host ratio and biting preference) and also on potential differences in individual following virus exposure (e.g., transmission efficiencies from host to vector and vice versa). Here, we estimated the probability for RVFV to transmit to naive animals by experimentally exposing lambs to a bite of an infectious mosquito (the transmission efficiency) and assessed if and how RVFV infection subsequently developed in the exposed animal. Aedes aegypti mosquitoes, previously infected via feeding on a viremic lamb, were used to expose naive lambs to the virus. Lambs were either exposed to 1-3 (low exposure) or 7-9 (high exposure) infectious mosquitoes. All lambs in the high exposure group became viremic and showed characteristic signs of Rift Valley fever within 2-4 days post exposure. In contrast, 3 out of 12 lambs in the low exposure group developed viremia and disease, with similar peaks in viremia as the high exposure group but with some heterogeneity in the onset of viremia. These results suggest that the likelihood for successful infection of a ruminant host is affected by the number of infectious mosquitoes biting, but also highlights that a lamb can be infected by a single mosquito. The per bite mosquito-to-host transmission efficiency was estimated at 28% (95% confidence interval: 15 - 47%). We subsequently combined this transmission efficiency with estimates for mosquito life traits into a Ross-McDonald mathematical model to illustrate scenarios under which major RVFV outbreaks could occur in naïve populations (i.e., R ₀ >1). The model revealed that for efficient RVFV transmission relatively high vector-to-host ratios as well as strong feeding preference for competent hosts are required. Altogether, this study highlights the importance of experiments that mimic natural exposure to RVFV. The experiments facilitate a better understanding of the natural progression of disease and a direct way to obtain epidemiological parameters for mathematical models.

The health of people, the health of animals, including aquatic species and insects, the health of plants and the environment, including soils, are connected, and this is captured by the One Health approach. The Covid-19 pandemic has laid bare this interconnectedness. Zoonotic infectious disease spillover occurs most commonly where the agri-food system interfaces with natural ecosystems, as this is where humans, domesticated animals and wildlife interact. On the other hand, deficient human health adds to the favorable conditions for pathogen transmission. There are direct and indirect effects of pandemics on food systems and health; disease outbreaks disrupt overall mobility, the workforce and the supply chain. Such disruptions affect food security and, in many cases, workers’ income or the economic viability of businesses in the food system. In this chapter, we discuss the link between global food security and One Health, and how to prepare for, and minimize the chance of, future pandemics. Reducing the likelihood of spillover and onwards transmission risk of pathogens can be served through (i) reducing the need for natural habitat disruption, (ii) smart management of both sides of the interface between natural ecosystems and the agri-food system, and vigilance at the human-animal interface within the agri-food system, and (iii) improving overall human, animal and environmental health.

Research initiatives that engage the public (i.e., community science) increasingly provide insights into tick exposures in the United States. However, these data have limitations, particularly with respect to reported travel history and tick identification. Here, we assessed whether The Tick App provides reliable and novel insights into tick exposures across three domains—travel history and habitat exposure, broad spatial and temporal patterns of species-specific encounters, and tick identification. During 2019–2021, we received 11,424 tick encounter submissions from across the United States, with nearly all generated in the Midwest and Northeast regions. Encounters were predominantly with human hosts (71%); although one-fourth of ticks were found on animals. Half (51%) of the reported encounters resulted from peri-domestic exposures, while 37% were recreational exposures. Using phone-based location services, we detected differences in travel history outside of the users’ county of residence along an urbanicity gradient. Approximately 75% of users from large metropolitan and rural counties had travel out-of-county in the four days preceding tick detection, whereas an estimated 50–60% of users from suburban or smaller metropolitan areas did. Furthermore, we generated tick encounter maps for Dermacentor variabilis and Ixodes scapularis that accounted for travel history to the extent possible—overall mirroring previously published species distributions, while revealing 45 counties with new reports of D. variabilis exposures. Finally, using photo submissions, prompts of tick coloration and size engaged and guided users towards species and life stage classification moderately well, with 60% of users correctly identifying D. variabilis adults and 46% correctly identifying I. scapularis adults. Together, these results indicate the importance of bolstering the use of mobile applications to engage community scientists and complement other methods of active and passive tick surveillance.

Ticks and tick-borne diseases cause substantial economic losses to the livestock industry in sub-Saharan Africa. Mazao Tickoff is a novel bioacaricide developed for tick control and is based on the entomopathogenic fungusMetarhizium anisopliaesensu lato (s.l.) isolate ICIPE 7. To date, no randomized controlled study has been undertaken to demonstrate the efficacy of this bioacaricide in reducing natural tick infestation on cattle. To this end, this field trial is designed to evaluate the anti-tick efficacy of Mazao Tickoff on cattle in coastal Kenya compared to a standard chemical tick control protocol. In this prospective, multi-center randomized controlled trial, eligible herds will be randomized by the herd size to the intervention arm in a 1:1:1 ratio to either Triatix^®(active ingredient: amitraz); Mazao Tickoff (active ingredient:M.anisopliaeICIPE 7); or placebo (excipients of the Mazao Tickoff), with a total enrollment target of 1,077 cattle. Treatments will be dispensed on Day 0 (defined individually as the day each animal receives the first treatment) and thereafter every two weeks until Day 182. Ticks will be counted on every animal in each herd (herds to be included have at least one animal bearing at least one tick on Day 0), and thereafter on bi-weekly intervals until Day 182. The primary efficacy assessments of Mazao Tickoff will be based on the mean percentage reduction in tick counts at each post-treatment follow-up visit compared to the placebo group and the Triatix^®arm. Further, the effect of Mazao Tickoff on the prevalence of common cattle pathogens,Anaplasma marginaleandTheileria parva, will be determined by assessing incidence and seroprevalence at four different time points. This protocol describes the first rigorous evaluation of the efficacy of Mazao Tickoff and its potential as a viable alternative non-chemical acaricide tool for tick control in Kenya and elsewhere.

Larval source management (LSM) programs for control of malaria vectors are often vertically organized, while there is much potential for involving local communities in program implementation. To address this, we evaluated the entomological impact of community-based application of Bacillus thuringiensis var. israelensis (Bti) in a rice irrigation scheme in Ruhuha, Rwanda. A non-randomized trial with control compared a Bti implementation program that was supervised by the project team (ES) with a program that was led and carried out by local rice farming communities (CB). One other area served as a control to assess mosquito populations without Bti application. Entomological surveys were carried out every two weeks and assessed the presence and abundance of the larval, pupal, and adult stages of Anopheles mosquitoes. In ES, the per round reduction in Anopheles larval habitats was estimated at 49%. This reduction was less in CB (28%) and control (22%) although the per round reduction in CB was still significantly higher than in control. Pupal production was almost completely prevented from round 5 (out of 10) onwards in both CB (average habitat occupancy 0.43%) and ES intervention arms (average habitat occupancy 0.27%), whereas pupal occupancy rates were on average 12.8% from round 5 onwards in the control. Emergence of adult mosquitoes from rice fields was thus prevented although this was not directly noticeable in adult An. gambiae populations in houses nearby the rice fields. Together with our earlier work on the willingness to financially contribute to the LSM program and the high perceived safety and acceptance of the Bti product, the current study demonstrates that, in an environment with limited resources, communities could become more engaged in LSM program implementation and contribute directly to malaria vector control in their environment.