Microclimate and the zoonotic cycle of tick-borne encephalitis virus in SwitzerlandArchived

Burri C, Bastic V, Maeder G, Patalas E, Gern L.Institute of Biology, Laboratory of Eco-Epidemiology of Parasites, University of Neuchâtel, Emile-Argand 11, 2000 Neuchâtel, Switzerland.Journal of medical entomology 2011 May;48(3):615-27.

The focal distribution of tick-borne encephalitis virus (TBEV; Flaviviridae, Flavivirus) appears to depend mainly on cofeeding transmission between infected Ixodes ricinus L. nymphs and uninfected larvae. To better understand the role of cofeeding ticks in the transmission of TBEV, we investigated tick infestation of rodents and the influence of microclimate on the seasonality of questing I. ricinus ticks. A 3-yr study was carried out at four sites, including two confirmed TBEV foci. Free-living ticks and rodents were collected monthly, and microclimatic data were recorded. A decrease in questing nymph density was observed in 2007, associated with low relative humidity and high temperatures in spring. One site, Thun, did not show this decrease, probably because of microclimatic conditions in spring that favored the questing nymph population. During the same year, the proportion of rodents carrying cofeeding ticks was lower at sites where the questing nymph density decreased, although the proportion of infested hosts was similar among years. TBEV was detected in 0.1% of questing ticks, and in 8.6 and 50.0% of larval ticks feeding on two rodents. TBEV was detected at all but one site, where the proportion of hosts with cofeeding ticks was the lowest. The proportion of hosts with cofeeding ticks seemed to be one of the factors that distinguished a TBEV focus from a non-TBEV focus. The enzootic cycle of TBEV might be disrupted when dry and hot springs occur during consecutive years.

VBORNET comment: 30/9/2011: This is further field evidence of the important role of co-feeding ticks in sustaining foci of Tick-borne encephalitis virus. Such field-based studies are crucial in ensuring that risk modeling approaches are evidence based, and in ensuring that the impact of changing weather or climatic trends can be properly assessed to understand and predict the changing transmission zones for TBE in Europe.