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Scientific Opinion on foot-and-mouth disease in Thrace
Introduction of FMDV into Thrace by wildlife is less likely than introduction due to movement of domestic animals or animal products. Based on a systematic literature review, currently available data of surveillance in wildlife and the epidemiological model, FMD will not be sustainable in the wildlife population in Thrace although limited spread of FMDV in time and space may occur. There are several potential risk factors associated with both introduction and spread of the FMDV infection in the region. The most important of these are biosecurity, movement of live animals and animal products, swill feeding and access to landfill waste. The absence of significant clinical signs in sheep in particular, and the increased levels of livestock movements associated with particular festivals in this region, give rise to specific concerns. Active surveillance for early detection of FMDV infection in wildlife could be a useful addition to an effective passive surveillance system in domestic animals. The EFSAwbFMD model indicated that when the sampling strategy in wildlife was based on hunting alone, the time needed to detect at least one seropositive animal for an FMDV incursion in January and July would be 39 and 13 weeks after incursion of the virus into the population respectively, whilst, when regular sampling was implemented over the whole year, about one month is needed. The precise pathway for the introduction of FMDV into Bulgaria for the 2010/2011 outbreak and its subsequent spread is not known. One possible explanation based on the genetic relationships between viruses in Bulgaria is a single introduction of virus into the country from Anatolian Turkey but it is also possible that the common ancestor was introduced into Turkish Thrace and quickly moved to Bulgaria either through a single introduction or through several introductions from the same source within a relatively short time span.
© European Food Safety Authority, 2012
Following a request from the European Commission and the Bulgarian Food Safety Risk Assessment Agency–Risk Assessment Centre, the Panel on Animal health and Welfare was asked to deliver a scientific opinion on foot-and-mouth disease (FMD) in Thrace. The scientific opinion addresses the following three terms of reference (TOR):
TOR 1. The relative significance of -and the role played by- wild and feral bi-ungulates, notably wild boar and deer species in the epidemiology of foot-and-mouth disease (FMD) in Thrace (Bulgaria, Turkey and Greece), taking into account the different FMD virus (FMDV)strains circulating in the region.
Introduction of FMDV into Thrace by wildlife is less likely than introduction due to movement of domestic animals or animal products.
Based on a systematic literature review focusing on experimental FMDV infections in wild boar and deer, it was concluded that transmission from wild boar or deer to domestic animals et vice versa can occur so wildlife can play a role in the spread of FMD. The evidence however did not prove that such cross-transmission of the virus will occur in a natural setting when proximity of infected animals may be much lower than under experimental conditions.
Historical observations of FMD in wildlife populations and a systematic literature review of observational studies in wildlife revealed no evidence for maintenance of infection within wildlife in Europe. The important issues were considered to be whether these wildlife animals are active players in the spread of the disease and can transmit the virus to domestic animals or whether they only become infected through contact (direct or indirect) with FMDV infected domestic animals but do not pose a threat to domestic animals.
In the recent outbreak in Bulgaria, 2011, no virus was isolated from wildlife except for the index case. Results of the sero-surveillance of wildlife in Bulgaria and Turkey (February 2011 to January 2012) suggested that circulation of FMDV in wildlife was spatially related to the outbreaks in livestock. There was no evidence of disease occurrence in wildlife anywhere else in Turkish Thrace or further north in Bulgaria. The relatively low sero-prevalence and clustered spatial distribution of positive wild boar and deer indicated that the wildlife FMD event in the Bulgarian-Turkish cross-border area apparently failed to develop into a large scale epidemic wave. It remains questionable, if and for how long after the last series of outbreaks, the virus could have been present in the population of wild boar, and to which extent the FMD affected domestic livestock contributed to the disease spread in wildlife in April 2011.
The epidemiological model to simulate spread and maintenance of FMD in the wild boar and deer populations also indicated that FMD will not be sustainable within a wild boar and deer host system alone but limited spread of FMDV in time and space may occur. Naturally, if there is a continued cross-over of FMDV between domestic and wildlife population then circulation may be prolonged. Moreover, the epidemiological model supported that decisive spatial differences in host density and hot summer temperatures may have shaped the limited size of the observed outbreak region in Thracian wildlife.
Epidemiological observations, published literature and modelling support the conclusion that the wildlife population is not able to maintain FMD in the absence of FMDV infection in the domestic host population. All of the FMD viruses sampled in Bulgarian Thrace were of serotype O PanAsiaII-Ant10 lineage. There is no evidence that any of the circulating strains of FMDV (serotypes O, A and Asia 1) in the wider region would cause a different outcome.
TOR 2. The risk factors and other relevant epidemiological features, in particular for the different FMD virus strains circulating in Thrace (Bulgaria, Turkey and Greece) which must be taken into account for the design of surveillance systems (including estimation of advantages and disadvantages), that could be implemented for the early detection of any FMD virus incursion in the territory of Thrace (Bulgaria, Turkey and Greece).
There are several potential risk factors associated with both introduction and spread of the FMDV infection in the region. The majority of these factors are related to biosecurity, movement of live animals and animal products (either legally or not), swill feeding or access to landfill waste, animal density, and the implementation and efficacy of vaccination programmes. The interaction between all risk factors also needs to be considered.
In addition to the above, more general risk factors for introduction of FMDV, the absence of significant clinical signs in sheep in particular, and the increased levels of livestock movements associated with particular festivals in this region, give rise to specific concerns.
An active but spatially restricted/targeted surveillance system for early detection of FMDV infection in wildlife could be a useful addition to an effective early passive detection system in domestic animals. The EFSAwbFMD model indicated that when the sampling strategy is based on hunting alone, the time needed to detect at least one seropositive animal for an FMDV incursion in January and July into a wild boar population, would be 39 and 13 weeks after incursion of the virus into the population respectively. The implementation of a surveillance system throughout the year required about a month to detect the first seropositive animal after incursion of the virus into the population. Disadvantages related to a surveillance system that could be implemented for early detection in wildlife based on hunting alone could be associated with one or more of the following adverse factors: collection of samples us limited to the hunting season (e.g. 4 months during winter); low public awareness of FMD and its association with hunted animals and poor sample quality for laboratory testing.
TOR 3.The relevance and significance of epidemiological data and genetic characteristics for the different FMD strains recently isolated in Bulgaria and Turkey, with regards to the hypothesis of single versus multiple introductions into Bulgaria.
Each of the Bulgarian outbreak viruses appear to share a single recent ancestor which is most closely related to viruses detected previously circulating in Anatolian Turkey.The precise pathway for the introduction of FMDV into Bulgaria and its subsequent spread is not known. One possible explanation based on the genetic relationships between viruses in Bulgaria is a single introduction of virus into the country from Anatolian Turkey, but it is also possible that the common ancestor was introduced into Turkish Thrace and quickly moved to Bulgaria either through a single introduction or through several introductions from the same source within a relatively short time span. Significant gaps in the genetic relationships between the sampled viruses from Bulgaria point to the potential presence of unreported (and hence unsampled) infection in domestic animals (consistent with the identification of seropositive domestic animals) and/or to spread in wildlife reservoirs (consistent with the detection of seropositive wildlife). Epidemiological data and genetic characteristics of the different FMDVs detected in Bulgarian Thrace indicate that FMD did spread through wildlife population but it also involved human transportation.
Foot-and-mouth disease, wildlife, epidemiology, Thrace, surveillance, early detection, genetic characteristics
- Spatial spread and maintenance of foot-and-mouth disease virus infections in wildlife populations of Thrace region applying epidemiological modelling
- Assessment of different monitoring strategies for early detection of FMD incursion in a free wild boar population area: a simulation modelling approach