Genetic evidence for tula virus in Microtus arvalis and Microtus agrestis populations in Croatia

To determine the threat of hantavirus infection to U.S. Forces, small mammals were sampled from training areas within Croatia. Of the 152 samples, 20 were positive for Tula virus (TUL), 12 common voles (Microtus arvalis) and eight field voles (Microtus agrestis). Sequences from M. agrestis were found in five and sequences from M. arvalis were found in six of seven sequence groups. The high percentage of the same TUL sequences in M. agrestis and M. arvalis suggests the co-occurrence of this virus in both Microtus species is not an accident. If M. agrestis field voles were accidentally infected with TUL, the percentage of polymerase chain reaction-positive animals should be lower than that of M. arvalis. Because the infection rate in M. arvalis (11.8%) was less than half of that found in M. agrestis (27.6%), it is unlikely that the predominance of positive M. agrestis could be due to accidental exposure. It is much more likely that the Croatian virus is circulating between both rodent species.