Researchers from Olomouc and Brno have demonstrated that a higher risk of tick infections is related to a vole overpopulation

The discovery of a team of scientists from the Faculty of Science of the Palacký University and the Faculty of Veterinary Hygiene and Ecology of UVPS Brno could significantly contribute in the future to the early warning of the population of sites with an increased risk of Lyme disease and tick-borne encephalitis. The team has established a link between the intensity of these dangerous infectious diseases and vole overpopulation.

Rodents are the main hosts of tick larvae and nymphs, which then attack larger mammals, including humans. An article describing the results of the research published in the prestigious international infectiology journal Emerging Infectious Diseases.

The prevalence of small rodents in Europe can predict the risk of becoming infected by tick-borne diseases one year in advance. “In this work, we show that years of increased risk of Lyme disease and tick-borne encephalitis can easily be predicted by the prevalence of the common vole the preceding year. Using data on the prevalence of the common vole in the Czech Republic, we have been able to successfully predict the occurrence of diseases not only in the Czech Republic but also in Germany, Austria and Slovenia,” says Emil Tkadlec, Head of the Department of Ecology and Environment of the Faculty of Science, Palacký University Olomouc, describing the results of the three-year research.

The researchers observed the prevalence of our most abundant rodent, the common vole (Microtus arvalis), which is known to regularly overpopulate in two- to four-year intervals. For example, this year there has been an overpopulation of voles in Moravia. “By applying the method of time series analysis we have shown that the fluctuations in the occurrence of both tick diseases are strongly dependent on cyclic fluctuations in the prevalence of the common vole. The forecast was further improved by the addition of climatic effects,” says Tomáš Václavík from the Department of Ecology and the Environment.

The researchers believe that the prevalence of the common vole and other rodents results in better larval survival, and a higher number of infectious tick nymphs the following year. “A higher number of nymphs will then infect more people than usual in outbreak hotspots,” warns Emil Tkadlec.

Models based on the link between vole and tick populations, which can predict the risk of Lyme disease and tick-borne encephalitis, are very simple. The required data can be easily retrieved from public databases. “This model can therefore be applied immediately, which opens up the possibility of a general prediction of the risk of infection with other tick-borne diseases that have serious impacts not only on human health but also on animals,” notes Pavel Široký from UVPS Brno.

Predicting the risk of tick-borne diseases has become an important research subject worldwide. Lyme disease and tick-borne encephalitis are among the most important tick diseases. While Lyme disease affects people in North America, Europe and Asia, tick-borne encephalitis is a disease that is widespread in Central Europe and Asia. Unfortunately, the Czech Republic excels in the occurrence of both of these dangerous diseases. “Tick-borne encephalitis was first isolated in the former Czechoslovakia in 1948,” says Tkadlec.

The occurrence of both diseases considerably fluctuates from year to year, and researchers around the world have been searching for the cause of the year-on-year variability for decades. Therefore, researchers have focused on the ecology of the major vector of the diseases, the common tick, which carries these pathogens.

An American group led by Professor Richard Ostfeld has made the furthest ground in Lyme disease research. They have shown that the causal chain begins with a year rich in seed yield, which in the next year leads to an increase in the population of small rodents who are the main hosts of the larval stages of ticks. The following year, there is an increase in the number of infected nymphs that attack medium-sized mammals, including humans, due to better survival. “Small rodents are key hosts for tick larvae and are also reservoir animals, which store spirochetes in natural hotspots causing both Lyme-disease and tick-borne encephalitis,” concludes Pavel Široký.