Cross-border surveillance differences: tick-borne encephalitis and lyme borreliosis in the Czech Republic and Poland, 1999-2008.

We compared neighbouring regions of the Czech Republic (CZ) and Poland (PL) situated within 100 km of the country border, in order to compare surveillance systems performance in measuring the burden of tick-borne diseases in both countries. We used routine surveillance notifications from 1999-2008 on tick-borne encephalitis (TBE) and Lyme borreliosis (LB). We assessed the crude risk ratio (RR) across the country border, and its estimates adjusted for both population density and the expected epidemiological gradient across the region, using negative binomial regression. The crude RR between CZ and PL was 7.43 (95% Cl 6.20-8.90) for TBE, and 1.80 (1.76-1.83) for LB. The adjusted RR for TBE increased from 4.47 in 1999-2001 to 10.01 in 2005-2008, but for LB decreased from 9.30 to 2.51 during the respective periods. Those results reflect possible differences in surveillance systems performance between the two countries, as the administrative boundaries cannot constitute a barrier for zoonotic diseases and no biological processes alone can explain such large differences in disease occurrence.

A tick-borne encephalitis ceiling in Central Europe has moved upwards during the last 30 years: possible impact of global warming?

The geographic/temporal pattern of cases of tick-borne encephalitis (TBE) registered in the Czech Republic since 1970 was analysed to verify the surmise of a global warming effect. Using a geographic information system, over 8,700 notified places of infection were pin-pointed on a map and overlaid with a digital elevation model to estimate the vertical distribution of the cases. Series of yearly disease ceilings (assessed alternatively as the respective maximum altitude or mean altitudes of the upper 5 or 10 cases) were tested against the null hypothesis of random elevation course and analysed for correlation with concomitant factors (yearly TBE incidence rate, mean yearly temperature, population density of small rodents and roe deer). Statistical tests proved that the TBE ceiling has gradually moved upwards in the course of the last three decades. The average rate of ascension within this period was approx. 5.4 +/- 1.7 m yearly, which corresponds well with concurrent mean temperature rising of approx. 0.036 +/- 0.007 degrees C yearly, and the vertical temperature gradient of 0.0065 +/- 0.0004 degrees C m(-1). The TBE-ceiling estimates significantly correlated with TBE-incidence data and the mean yearly temperature recorded 1-2 years earlier. Although TBE incidence correlated with rodent population density that was observed 1-2 years earlier, the TBE ceiling does not seem to be influenced by rodent population dynamics nor did the population dynamics correlate with mean yearly temperatures. TBE incidence as well as mean altitudes of the upper 10 cases also correlated with official data on harvested roe deer. Overall, the fluctuations of TBE incidence and TBE ceiling proved to be synchronous processes that correspond with temperature changes. Although the dependence of TBE on temperature is not a direct one and various factors could be involved, an impact of climate warming on the vertical disease distribution in Central Europe is evident.