Mathematical modelling of the impact of climatic conditions in France on Rhipicephalus sanguineus tick activity and density since 1960Archived

Beugnet F, Kolasinski M, Michelangeli PA, Vienne J, Loukos H. 1 Merial, 29 Av. Tony Garnier, F-69007 Lyon, France2 CLIMPACT, 79 rue du Faubourg Poissonnière, F-75009 Paris, FranceGeospatial Health. 2011 May;5(2):255-63.

Rhipicephalus sanguineus, the brown dog tick, has a worldwide distribution in areas with a relatively warm climate, including mild winters. This tick plays an important role as vector for various animal and human pathogens, including bacteria and protozoa. Based on precise daily meteorological data from the past 40 years, combined with mathematical modeling designed to predict tick activity, two modeling approaches were developed. The first examined the evolution of the number of weeks with favorable biological conditions for ticks in four French cities located at various latitudes of the country: Nimes in the south, Paris in the north, Lyon in the east and Nantes in the west. The second analyzed the extension of the geographical surface area in km(2) where the biological conditions favor tick activity for at least 12 weeks per year. Both analyses revealed clear evidence of increased temperatures coupled with an augmented tick activity index in three of the four cities. However, the change was not significant in Nimes, where the climate is Mediterranean and the tick is already endemic. For Paris, Lyon and Nantes, the activity index values have increased significantly, i.e. by 4.4%, 4.0% and 3.4%, respectively. The distribution of the activity index values is evolving strongly with significantly fewer values below 50% since the 1960s and a clear decrease of values between 20% and 50% during the latest decade. Between 1960 and 2000, the theoretical extension of the surface area where the climatic index is suitable for R. sanguineus has increased by 66%. Even though several other important factors, such as changes in biotopes or human activity, are not included in this study, the resulting patterns and trends are noticeable. Our models constitute the first demonstration of the impact of climate change on the activity and distribution of ticks and confirm the observed northward migration trend for this Mediterranean domestic tick.

VBORNET comment, 30/9/2011: Rhipicephalus sanguineus is the kennel tick and a vector of a number of human and veterinary diseases. The role of dogs in dispersing this tick throughout Europe and into previously non-endemic locations has been a topic of discussion in recent years, particularly in relation to European Union pet travel legislation. This paper presents a mathematical model that shows that more suitable environmental conditions have developed since the 1960s to facilitate a theoretical expansion of the surface area for the climatic index for suitability of Rhipicephalus sanguineus in Europe, with a reported expansion by 66 % between 1960 and 2000 gaining 130,000 km2.