Epidemiological and environmental risk factors, including land management, acting throughout the causative chain of tick-borne diseases in Belgium
Description
Goals of the research
Tick-borne diseases (TBD) are a public health issue worldwide. Several studies indicate that the incidence of TBE has increased in Europe and America over the past two decades [1-4]. Therefore questions arise: what are the causes of this significant evolution over the last 20 years?
Understanding the spatial variation in TBD risk is essential for disease management and prevention [2]. The presence of TBD can be influenced by many complex factors acting synergistically. For TBD to circulate in a geographic area, five components of the system must overlap spatially and interact: the pathogen, a natural reservoir, a natural or accidental host, a vector and a suitable biotope for vector development [5]. Their spatial distribution is determined by diverse elements [6]: human hosts may be more influenced by socio-cultural factors rather than ecological ones like local temperature and humidity, which influence tick activity and survival. However, existing studies fail to incorporate the full complexity of spatial determinants of TBD. Various factors and their interactions will impact differently the host-vector-pathogen equilibrium and, more precisely, the two components of the risk: hazard (related to vector and host ecology) and the exposure of humans to infected vectors [13]. Although disease ecology studies have extensively studied hazard [7], factors determining human exposure, studied more by epidemiologists, are often overlooked [8]. Exposure is an essential component of risk and so TBD risk has to be studied through both the hazard and the exposure angles [9-11]. This can be done most efficiently by examining in explicit detail the full chain leading from an infectious tick bite to a recorded disease case (Figure 1). Indeed, TBD are infectious diseases transmitted by the bite of an infected tick, which constitutes the first step of the causal chain of TBD. The infectious bite may then result in an infection in the human host, who may subsequently develop clinical symptoms [12].
The goal of this thesis is to identify the epidemiological and environmental risk factors, at individual and landscape level, including land management, acting throughout the causative chain of TBD (focusing on Lyme borreliosis(LB), Anaplasmosis and Tularemia) in Belgium.
The research will focus on a single tick species, Ixodes ricinus, in a unique, understudied, spatial framework, Belgium, and target three major pathogens, Borrelia burgdorferi, Anaplasma phagocytophilum and Francisella tularensis. The infection in high-risk groups, in the general population and in borreliosis patients will be study with an integrated and interdisciplinary approach.
Objective
The workflow of the research project is framed in the causal chain of TBD (Figure 1).
First, contacts between humans and ticks are needed for a bite to happen. Those contacts and associated risk factors has already studied in part 1 of this project. A model assessing scout-ticks contacts has been developed and the results are published in Ticks and Tick-borne Diseases [13]. Data on human exposure to tick bites were collected in a collaboration between the Medical Geography unit, the Epidemiology and Biostatistics unit (UCL/IREC/EPID) and the Belgian federation The Scouts.
After the bite and depending of a complex set of factors (such as the length of tick attachment), an infection may or may not develop in the patient. Part 2 is in progress and studies the seroprevalence of the three pathogens studied and its associated environmental and activity risk factors at the landscape level in three populations in which exposure varies: a group professionally at risk, veterinarians and farmers, a blood donor population mainly living in rural areas (blood donation center in Mont-Godinne) and a blood donor population mainly living in urban area (blood donation center in Brussels).
If a person is infected, s/he can develop a symptomatic case of tick-borne disease, or not [12]. Part 3 will focus on the disease itself by studying hospitalized cases of LB from two hospitals in Belgium. In this part, I also want to assess the individual level epidemiological and environmental risk factors for Lyme disease in Belgium.
Part 4 attempts to distinguish more specifically the effect of hazard and exposure on the risk of TBD. The relevance of considering hazard and exposure to assess the risk has been documented [7, 9, 11]. But separating the risk factors pertaining to the hazard and the exposure is challenging and few studies have allowed going beyond the speculative.
Figure 1
Contact
Mathilde De Keukeleire
Annie Robert
References
1. Randolph, S.E., Evidence that climate change has caused 'emergence' of tick-borne diseases in Europe? International Journal of Medical Microbiology, Supplement, 2004. 293(37): p. 5-15.
2. Vandenesch, A., et al., Incidence and Hospitalisation rates of lyme borreliosis, France, 2004 to 2012. Eurosurveillance, 2014. 19(34).
3. Bacon, R.M., K.J. Kugeler, and P.S. Mead, Surveillance for Lyme disease--United States, 1992-2006. MMWR. Surveillance summaries : Morbidity and mortality weekly report. Surveillance summaries / CDC, 2008. 57(10): p. 1-9.
4. Lindgren, E. and T.G.T. Jaenson, Lyme borreliosis in Europe: influences of climate and climate change, epidemiology, ecology and adaptation measures. World Health Organization Regional Office for Europe, 2006. EUR/04/5046250.
5. Vu Hai, V., et al., Monitoring human tick-borne disease risk and tick bite exposure in Europe: Available tools and promising future methods. Ticks and Tick-borne Diseases, 2014. 5(6): p. 607-619.
6. Killilea, M.E., et al., Spatial dynamics of lyme disease: A review. EcoHealth, 2008. 5(2): p. 167-195.
7. Li, S., et al., A multi-level analysis of the relationship between environmental factors and questing Ixodes ricinus dynamics in Belgium. Parasites and Vectors, 2012. 5(1).
8. Méha, C., Influence of forest landscape structures on human populations' exposure to ticks. The case of Lyme Borreliosis in senart forest. Bulletin d'Association de Geographes Francais, 2012. 89(2): p. 255-266.
9. Randolph, S.E., et al., Variable spikes in tick-borne encephalitis incidence in 2006 independent of variable tick abundance but related to weather. Parasites and Vectors, 2008. 1(1).
10. Linard, C., et al., Determinants of the geographic distribution of Puumala virus and Lyme borreliosis infections in Belgium. International Journal of Health Geographics, 2007. 6.
11. Zeimes, C.B., et al., Shaping zoonosis risk: Landscape ecology vs. landscape attractiveness for people, the case of tick-borne encephalitis in Sweden. Parasites and Vectors, 2014. 7(1).
12. Braks, M., et al., Towards an integrated approach in surveillance of vector-borne diseases in Europe. Parasites and Vectors, 2011. 4(1).
13. De Keukeleire, M., et al., Scouts, forests, and ticks: Impact of landscapes on human-tick contacts. Ticks and Tick-borne Diseases, (In press).