Abstract
BackgroundThe emergence of zoonoses is due both to changes in human activities and to changes in their natural wildlife cycles. One of the most significant vector-borne zoonoses in Europe, tick-borne encephalitis (TBE), doubled in incidence in 1993, largely as a consequence of the socio-economic transition from communism to capitalism and associated environmental changes.MethodsTo test the effect of the current economic recession, unemployment in 2009 and various socio-economic indices were compared to weather indices (derived from principal component analyses) as predictors for the change in TBE case numbers in 2009 relative to 2004-08, for 14 European countries.ResultsGreatest increases in TBE incidence occurred in Latvia, Lithuania and Poland (91, 79 and 45%, respectively). The weather was rejected as an explanatory variable. Indicators of high background levels of poverty, e.g. percent of household expenditure on food, were significant predictors. The increase in unemployment in 2009 relative to 2008 together with 'in-work risk of poverty' is the only case in which a multivariate model has a second significant term.ConclusionBackground socio-economic conditions determine susceptibility to risk of TBE, while increased unemployment triggered a sudden increase in risk. Mechanisms behind this result may include reduced resistance to infection through stress; reduced uptake of costly vaccination; and more exposure of people to infected ticks in their forest habitat as they make greater use of wild forest foods, especially in those countries, Lithuania and Poland, with major marketing opportunities in such products. Recognition of these risk factors could allow more effective protection through education and a vaccination programme targeted at the economically most vulnerable.
Highlights
The emergence of zoonoses is due both to changes in human activities and to changes in their natural wildlife cycles
We report considerable increases in national mean tick-borne encephalitis (TBE) incidence in 2009 relative to average levels over the previous five years in three countries
In ‘western’ Europe, reactions to the relatively modest increases in unemployment are less likely to include more frequent visits to tick-infested forests. This is the second of two natural experiments in recent years, both of which reveal the immediacy of the impact of disparate factors on TBE incidence acting through changes in human activities, rather than via the slower responses of the natural enzootic cycles of the virus between ticks and wildlife hosts
Summary
The emergence of zoonoses is due both to changes in human activities and to changes in their natural wildlife cycles. In western Europe, increases in incidence have been more gradual [4,5]; in Italy, for example, emergence has occurred in areas where forest types favour roe deer (Capreolus capreolus), the principal host for ticks [6,7] Against this background, spikes in annual incidence occur sporadically in some countries for reasons that are not always apparent (e.g. in 2003 in the Baltic States - Estonia, Latvia and Lithuania - and Poland), but exceptional ones in 2006 in Switzerland, Germany, Slovenia, and the Czech Republic have been related to the unusual weather conditions during the second half of that year, apparently favouring both mushroom growth and outdoor recreation [8,9]. The response to such weather again varied with the national cultural and socio-economic contexts
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