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ŠUMARSKI LIST 9-10/2018 str. 34     <-- 34 -->        PDF

Apodemus species (A. agrarius and A. sylvaticus) were positive on F. tularensis. All three positive samples originated from the locality of Lipovljani.
WHO guidelines on tularemia from 2007 highlighted the importance of continuous monitoring of disease occurrence and spread, as well as reports of outbreaks in humans and animal population (Travnik, 2007). The last complex epidemiological and epizootic investigations of tularemia and search for endemic areas in Croatia dates from around 1960s and 1970s, all of the malong Sava Valley. In three reported outbreaks, hares (Lepus europaeus), were found to be a source of infection for humans. Hence, in the fourth one, reported in 1974, epizooty of tularemia among small rodents and insectivores was determined as potential source for human infection. This outbreak correlated with peak in field mouse and shrew populations (Borcić et al., 1975). More over, F. tularensis was isolated from rodents of Apodemus species collected in emerging areas during epizootic research in the mid-960s. This notion and the fact that Apodemus species predominated among small rodents population, marked them as main reservoir of F. tularensis in investigated period (Heneberg et al., 1967; Borcić et al., 1968).
Recently, Tadin et al. (2016) detected two field mice (A. agrarius) positive on F. tularensis, trapped in locality of Draganić in central Croatia. However, there is no current information about the real presence of Francisella among rodent population in Croatia. The current survey is a part of the program approached by Croatian Government, Ministry of Agriculture, with the aim of systematic monitoring of F. tularensis occurrence among animals, including small mammals in Republic of Croatia (2016). Tularemia occurrence was initially associated with “lowland” and “water” ecosystems (Borcić, 1973), therefore, most of the localities included in our study are situated in region of Sava Valley, known as natural marsh area. Sava Valley is known as natural focus for diverse rodent-borne zoonotic pathogens, such are Leptospira spp. (Borcić et al., 1982; Tadin et al., 2016), Hantaviruses (Borcic and Puntaric, 1996; Tadin et al., 2016; Tadin et al., 2012) and Babesia spp. (Tadin et al., 2012). This region was also mentioned as a natural focus of tularemia in Croatia (Borcic et al., 1976). A common vole, animal of high reproductive capacity, and very sensitive to tularemia infection, was determined as a main carrier of F. tularensis and the most important species for the spread of tularemia in mentioned ecosystem (Borcic et al., 1976). However, in this study, the presence of F. tularesnsis has not been demonstrated in any of the examined species of voles. The reason for this may be a dominance of the mice species within collected samples.
There are substantial differences in number of collected samples, between distinct localities included in our survey. We presume that small number of animals obtained in some areas, as Stara Gradiška and Nova Subocka, is primarily related to a time of the year when the collection was performed. Indeed, during the spring and summer seasons, the population of small rodents and insectivores usually decreases. Next, restricted food sources (forest seed yields) also affects the abundance of their population.
Last reported human tularemia outbreak was described in 1998., when small rodents were presumed as potential source of human infection (Brkić et al., 2005). Although, in recent years, human tularemia in Croatia occurs sporadically, fluctuation in rodent population, leading to the occasional rodent abundance and epizootic outbreaks of tularemia may present high risk for human infection. Three mice positive on Francisella, detected in locality of Lipovljani, present significant result, leading to the conclusion that Francisella still maintains among small mammals in Croatia. More over, locality of Lipovljani is situated in central part of Sava Valley, revealing that this region might remain natural foci of Francisella species in Croatia.
As this study involved only eight small regions in Croatia, there is a need for extended epizootic and investigation studies. Further survey should include larger and diverse geographic areas, asmountain-parts (Lika, Gorski Kotar) and coastal parts of Croatia, aswell as other animals (hares, rabbits) and vectors (ticks, mosquitos).
Financial support
Grant of University of Rijeka (Grant No., Grants of Ministry of Agriculture and Croatian Science Foundation (HRZZ-IP-2016-06-9003 and IP-11-2013-4250) supports this work.
Borcić, B., A. Rudež, S. Lasić, I. Špalj, D. Horvat, Š. Ferizović, I. Smok, 1968: Novi val tularemije u dugoselskom žarištu, Zdrav. nov., 21:8-14.
Borcić, B. 1973: Epidemiološka obilježja tularemije u njenim prirodnim žarištima u Hrvatskoj, Disertacija, Sveučilište u Zagrebu, Zagreb.
Borcić, B., F. Gugić, J. Kolić, N. Tvrtković, V. Bilić, S. Bujas, L. Nikolić, 1975: Nova (četvrta) epidemija tularemije u Srednjoj Posavini,Medicina 27: 70-72.