The peasant vole contributes to the increase of tularemia in the agricultural environment

    Researchers from the Institute for Research in Hunting Resources (IREC, CSIC-UCLM-JCCM), the University Institute for Research in Sustainable Forest Management (University of Valladolid), the Carlos III Health Institute (Madrid), and the Faculty of Medicine of the University of Castilla-la-Mancha, demonstrate an amplifying role of the peasant vole (Microtus arvalis) for the bacterium Francisella tularensis, which causes tularemia.

    Tularemia is a disease that can affect both people and animals, with rabbits, hares and rodents being especially sensitive to this bacterium. People can become infected by different routes, such as the inhalation of aerosols and plant material or infected soil, contact with carcasses of dead animals, the ingestion of meat from sick animals and/or contaminated water and the bite of ticks, mosquitoes and flies. In general, the disease begins suddenly with symptoms that vary depending on the route of transmission and, although it can cause death, most infections can be successfully treated with the use of antibiotics.

    In Castilla y León there have been two large outbreaks of tularemia, one in 1997-1998 and a later one, in 2007-2008, accumulating a total of c. 1000 confirmed cases in humans. Initially, the first outbreak was attributed to the handling of hunting hares, while the second, to an increase in the abundance of the common vole. Subsequently, in 2014, the cases of tularemia in humans increased again (95 confirmed cases), coinciding again with a significant increase in the population of peasant vole, although an epidemic of the disease was not declared in the region. The existence of a spatio-temporal association between the demographic explosions of the peasant vole and the cases of tularemia in humans in Castilla y León over these 18 years has recently been published in the journal Vector-Borne and Zoonotic Diseases by the same researchers.

    In a new article published in the journal Emerging Infectious Diseases, the researchers analyzed samples of voles from the province of Palencia (where cases of tularemia in humans have been recurrent) over two years, between 2013 and 2015, coinciding with a demographic explosion of the peasant vole in the region. Using samples of the liver and spleen of the voles and genetic analysis, the presence of the bacterium was analyzed. Francisella tularensis and its relationship with the population density of the vole.

    The mean prevalence of the bacterium Francisella tularensis in the peasant vole it was 20.16%, reaching 33% of the individuals during the population peak that took place in July 2014. Likewise, a strong correlation was observed between the prevalence of the bacterium and the abundance of the vole, that is, The increase in the population of voles contributes to a greater infection of tularemia among the individuals of the population and, consequently, to a greater spread of the bacterium in the environment.

    This study shows that the peasant vole plays a key role in the transmission and amplification of the bacterium in the agricultural environments of Castilla y León, where this species of rodent is widely distributed and can become very abundant during plagues. (with densities of up to 1000 voles per ha, of which a third can be carriers of Francisella tularensis). Therefore, it is important to carry out monitoring and surveillance of common vole populations to prevent outbreaks of tularemia, reducing the exposure of people to this disease.

    tularemia

    Rodríguez-Pastor R, Escudero R, Vidal D, Mougeot F, Arroyo B, Lambin X, Vila-Coro AM, Rodríguez-Moreno I, Anda P, Luque-Larena JJ (2017) Density-Dependent Prevalence of Francisella tularensis in Fluctuating Vole Populations, Northwestern Spain. Emerging Infectious Diseases 23: 1377-1379. doi:10.3201/eid2308.161194