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Seasonality of host-seeking Ixodes ricinus nymph abundance according to different climates
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Edité par CCSD -
International audience. There is a growing concern about climate change and its impact on human health. Specifically, global warming could increase the probability of emerging infectious diseases, notably because of changes in the geographical and seasonal distributions of disease vectors such as mosquitos and ticks. For the tick Ixodes ricinus, which is widespread in Europe, there is evidence of settlement further north and at higher altitudes. However, little is known about the seasonal variation in tick activity in different climates. Studies on the seasonality of I. ricinus abundance are rare and often limited in time, which impedes their generalizability. Our objective was to describe seasonal variations in I. ricinus abundance under different climates. Therefore, a longitudinal study was carried out in France, in six locations corresponding to different climates. Questing nymphs of I. ricinus were collected monthly during six years, using the drag sampling method. Meteorological variables (temperature, relative humidity) were recorded hourly and summarized daily. Seasonal patterns of I. ricinus nymphal abundance were investigated for the 6 different sites using linear regression incorporating sine and cosine functions of time as covariates (harmonic regression). The model parameters were estimated separately for each location. The seasonal patterns of evolution were different depending on the climate considered. "Temperate oceanic" sites showed an early spring peak, a summer minimum and a moderate autumn and winter activity. "Continental" sites show a later peak in spring, and a minimum in winter. The pick occurred in summer for the "mountainous" site, with no winter activity. In most cases, the timing of the spring peak could be related to the sum of degree days since the beginning of the year. Winter activity was positively correlated to the corresponding temperature. While until now mostly based on expert opinions reported in the literature, the seasonality of tick abundance was estimated from field data in the present study. We were able to clearly describe different patterns in different climates thanks to long term monthly samplings at several sites
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