Could an economic downturn be linked to more cases of tick-borne encephalitis?

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Zoonotic diseases emerge through changes both in human activities and in their natural wildlife cycles. Tick-borne encephalitis (TBE), one of Europe's most significant vector-borne zoonoses, doubled in incidence in 1993. The abstract attributes that increase largely to the socioeconomic transition from communism to capitalism and associated environmental changes.

To examine the effect of the economic recession, the researchers conducted an observational country-level comparison across 14 European countries. They compared unemployment in 2009 and various socioeconomic indices with weather indices derived from principal component analyses, testing them as predictors of changes in TBE case numbers in 2009 relative to 2004–08.

The largest increases in TBE incidence occurred in Latvia, Lithuania and Poland: 91%, 79% and 45%, respectively. Weather was rejected as an explanatory variable. Indicators of high underlying poverty, such as the percentage of household expenditure spent on food, were significant predictors. The combination of the increase in unemployment in 2009 relative to 2008 and ‘in-work risk of poverty’ was the only multivariate model in which a second term was significant.

The authors concluded that background socioeconomic conditions shape susceptibility to TBE risk, and interpreted increased unemployment as a trigger for a sudden rise in risk. Possible mechanisms they proposed included stress-related reductions in resistance to infection, reduced uptake of costly vaccination, and greater exposure to infected ticks in forest habitats as people made more use of wild forest foods. They highlighted Lithuania and Poland in particular, where such products offer major marketing opportunities. These were proposed explanations, rather than mechanisms established by the reported comparison.

The authors suggested that recognizing these risk factors could support more effective protection through education and a vaccination programme targeted at the most economically vulnerable.