Sophie Rossi

Incidence and persistence of classical swine fever in free-ranging wild boar (Sus scrofa)

Although veterinary authorities aim to limit persistence of classical swine fever (CSF) in wild boar (Sus scrofa), to avoid potential transmission to pigs, factors influencing CSF transmission and persistence are not clearly understood. Here we analyse incidence and persistence in a CSF epidemic that occurred in the French Vosges Forest. Higher incidence was found in large forests compared to smaller isolated ones, being highest near the starting point of the epidemic, but poorly related to the local density. We hypothesize that the spatial and social structure of wild boar populations may be responsible for this variability of incidence over space. Persistence was highest near the starting point of the epidemic and where initial density was highest. We hypothesize that persistence was favoured by the abundance of young wild boar, itself encouraged by CSF. Our results allow us to propose management measures aimed at limiting CSF persistence.

Preventive vaccination contributes to control classical swine fever in wild boar (Sus scrofa sp.)

Over the last 20 years, oral vaccination implementing a live attenuated vaccine has been experimented in Europe in order to control classical swine fever (CSF) in Wild Boar (Sus scrofa sp.). This has generally led to an enhanced seroprevalence and a decreased viroprevalence at the scale of the whole vaccinated populations, but no quantitative analysis has demonstrated the protective effect of preventive vaccination or intensive baiting. In the present paper we conducted a retrospective analysis at the scale of the municipality, taking into account the local dynamics and possible covariates of infection to test the effect of preventive vaccination and of the baiting effort. To be efficient, vaccination was expected to increase seroprevalence above the level considered as suitable for preventing disease invasion (40-60%) independently of infection, to protect free areas from disease invasion or contribute to control subsequent disease intensity and duration. We also hypothesized that a better baiting effort would be correlated with an improvement of immunisation and disease control. In uninfected municipalities, seroprevalence increased up to 40% after 1 year, i.e., three vaccination campaigns. We observed a significant protective effect of preventive vaccination, especially within municipalities that had been vaccinated at least 1 year before disease emergence and where virus detection did not last more than one quarter. On the other hand, we did not detect a significant effect of the baiting effort on local seroprevalence or disease dynamics, suggesting that the baiting system could be improved. We discuss these results regarding the improvement of management measures and further research perspective.

Environmental Factors Associated with the Seroprevalence of Toxoplasma gondii in Wild Boars (Sus scrofa), France

Toxoplasma gondii is a protozoan parasite infecting humans and animals. Wild boars Sus scrofa are a potential source of human infection and an appropriate biological model for analyzing T. gondii dynamics in the environment. Here, we aimed to identify environmental factors explaining the seroprevalence of toxoplasmosis in French wild boar populations. Considering 938 individuals sampled from 377 ‘communes’, overall seroprevalence was 23% (95% confidence interval: [22–24]). Using a Poisson regression, we found that the number of seropositive wild boars detected per ‘commune’ was positively associated with the presence of European wildcats (Felis silvestris) and moderate winter temperatures.

Controlling of CSFV in European wild boar using oral vaccination: a review.

Classical swine fever (CSF) is among the most detrimental diseases for the swine industry worldwide. Infected wild boar populations can play a crucial role in CSF epidemiology and controlling wild reservoirs is of utmost importance for preventing domestic outbreaks. Oral mass vaccination (OMV) has been implemented to control CSF in wild boars and limit the spill over to domestic pigs. This retrospective overview of vaccination experiences illustrates the potential for that option. The C-strain live vaccine was confirmed to be highly efficacious and palatable baits were developed for oral delivery in free ranging wild boars. The first field trials were performed in Germany in the 1990’s and allowed deploying oral baits at a large scale. The delivery process was further improved during the 2000’s among different European countries. Optimal deployment has to be early regarding disease emergence and correctly designed regarding the landscape structure and the natural food sources that can compete with oral baits. OMV deployment is also highly dependent on a local veterinary support working closely with hunters, wildlife and forestry agencies. Vaccination has been the most efficient strategy for CSF control in free ranging wild boar when vaccination is wide spread and lasting for a sufficient period of time. Alternative disease control strategies such as intensified hunting or creating physical boundaries such as fences have been, in contrast, seldom satisfactory and reliable. However, monitoring outbreaks has been challenging during and after vaccination deployment since OMV results in a low probability to detect virus-positive animals and the live-vaccine currently available does not allow serological differentiation of infected from vaccinated animals. The development of a new marker vaccine and companion test is thus a promising option for better monitoring outbreaks during OMV deployment as well as help to better determine when to stop vaccination efforts. After rabies in red fox, the use of OMV against CSF in European wild boar can be considered as a second example of successful disease control in wildlife. The 30 years of disease control experience included in this review may provide options for improving future disease management within wild populations.

Options for the Control of Disease 1: Targeting the Infectious or Parasitic Agent

There are three basic approaches to managing diseases: directly reduce the reproductive rate of the pathogen, reduce host (or infected host) density, or manipulate the environment to reduce contact between diseased and susceptible animals. In this chapter we will look at the first of these approaches. Since disease transmission results from direct or indirect contact between infectious and susceptible individuals, there are two ways to target an infectious agent: either limit the number of susceptible individuals by vaccinating them, or treat infected individuals in order to reduce the duration or intensity of the infectious period and the number of infectious individuals present at any given time. The overall aim of this chapter is to consider the conditions under which vaccination and treatment may make a valuable contribution to the control of infectious diseases in wild mammal populations. Both field research and mathematical modelling approaches have been used to address this question. For vaccination, early mathematical models of infectious disease dynamics suggested a simple answer: vaccination is useful as soon as the rate of control ensures that a sufficient proportion of the population is immune for a sufficient period of time (Bailey 1957). At the individual level, this herd immunity means that any given infectious individual has a low probability of encountering a susceptible animal. If the disease is introduced into a vaccinated population, the mean number of secondary infections caused by each infected case will be lower than unity, thus preventing further outbreaks from occurring (R <: see Chapter 3). However, this generalised scenario may be considered overly simplistic, as the practicalities of vaccination campaigns often complicate matters. For example, modelling studies often include assumptions about perfect vaccine efficacy, and the efficiency of delivering the vaccine to a population that may or may not reflect the situation in the field.

New Insights on the Management of Wildlife Diseases Using Multi-State Recapture Models: The Case of Classical Swine Fever in Wild Boar

Background The understanding of host-parasite systems in wildlife is of increasing interest in relation to the risk of emerging diseases in livestock and humans. In this respect, many efforts have been dedicated to controlling classical swine fever (CSF) in the European Wild Boar. But CSF eradication has not always been achieved even though vaccination has been implemented at a large-scale. Piglets have been assumed to be the main cause of CSF persistence in the wild since they appeared to be more often infected and less often immune than older animals. However, this assumption emerged from laboratory trials or cross-sectional surveys based on the hunting bags. Methodology/Principal Findings In the present paper we conducted a capture-mark-recapture study in free-ranging wild boar piglets that experienced both CSF infection and vaccination under natural conditions. We used multi-state capture recapture models to estimate the immunization and infection rates, and their variations according to the periods with or without vaccination. According to the model prediction, 80% of the infected piglets did not survive more than two weeks, while the other 20% quickly recovered. The probability of becoming immune did not increase significantly during the summer vaccination sessions, and the proportion of immune piglets was not higher after the autumn vaccination. Conclusions/Significance Given the high lethality of CSF in piglets highlighted in our study, we consider unlikely that piglets could maintain the chain of CSF virus transmission. Our study also revealed the low efficacy of vaccination in piglets in summer and autumn, possibly due to the low palatability of baits to that age class, but also to the competition between baits and alternative food sources. Based on this new information, we discuss the prospects for the improvement of CSF control and the interest of the capture-recapture approach for improving the understanding of wildlife diseases.

Options for the Control of Disease 2: Targeting Hosts

Targeting the host has been the most common approach to managing disease in wildlife. This has essentially involved some form of host population reduction, achieved through dispersing, culling, or controlling reproduction. Dispersion of animals from the site of a disease outbreak has mainly been employed for birds (Wobeser 2007) but has also been attempted for some herding mammals such as bison (Bison bison) (Meagher 1989). This works best for noninfectious diseases; otherwise it requires that only susceptible individuals disperse, since the movement of infected animals will increase the geographic spread of disease. Unsurprisingly this method has had little success in practice, and is seldom likely to be of value in controlling infectious disease in wild mammals. Culling is a long established method of population reduction, for both disease and pest control. This approach assumes that reducing the population size of the targeted species results in a concomitant decrease in the prevalence (and more importantly the absolute number) of infectious individuals. If the aim is to eradicate the pathogen then the number of infectious individuals must fall below a level at which infection can be maintained. However, it may often be sufficient that infection is reduced to a level below which spillover to other host species (e.g. humans, domestic animals, or endangered species) either ceases or is tolerable. Wild mammal populations have most commonly been subjected to culling because they have been perceived as agricultural pests, and less often because they may transmit diseases.

Schmallenberg Virus Infection among Red Deer, France, 2010–2012

Schmallenberg virus infection is emerging in European domestic and wild ruminants. We investigated the serologic status of 9 red deer populations to describe virus spread from September 2010 through March 2012 among wildlife in France. Deer in 7 populations exhibited seropositivity, with an average seroprevalence of 20%.

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 behaviour. Hence, it is reasonable to expect that incorporation of environmental manipulation into a programme to control wildlife diseases may potentially result in outcomes as effective as direct intervention aimed at hosts, pathogens and vectors. Environments are not static, but are naturally dynamic, complex systems that exert strong influences on patterns of disease via their impact on hosts, pathogens, vectors and the interactions between them. Consequently, it can be difficult to identify which environmental variables are most important in influencing disease dynamics and hence which elements to target as part of a disease management programme. Nevertheless, environmental management has been used extensively to control

RÉSULTATS DE LA SURVEILLANCE DE MALADIES ANIMALES RÉPUTÉES CONTAGIEUSES (MARC) DANS LA FAUNE SAUVAGE EN FRANCE

The FrenchMinistry of Agriculture, the National Hunting andWildlife Agency (ONCFS) and the hunters’ associations are increasingly concerned with the impact of wildlife diseases on livestock and human health. The demographic growth of some wild species is further increasing this risk. In France, wildlife diseases aremonitored passively through the SAGIR network, whose objective is to diagnose the causes of wildlife mortality, and actively by targeting certain species and diseases with a major economic or public health impact. This surveillance programhas shown for instance that wild boars act as a reservoir for Brucella suis biovar 2 and the Aujeszky’s disease virus, and that they are responsible for the contamination of open-air pig farms, as well as for the persistence for over fifteen years of the virus of classical swine fever in the North-East of France and in other parts of Europe. Oral vaccination of wild boars had been thus implemented since 2004 in order to control the enzooty. Since 2001, cases of bovine tuberculosis due to Mycobacterium bovis have been identified in red deer and wild boar in several areas of France, which threaten disease-free livestock. Likewise, the question of a possible role of wild ruminants in the epidemiology of Bluetongue disease is being raised. Finally, wild birds constitute uncontrollable reservoirs for influenza andWest Nile viruses, among others, and may threaten domestic poultry, humans or horses. The sanitary status of wild species is thus increasingly taken into account in the management and control of livestock diseases.