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Forest ecosystems and zoonosis

Forests are complex ecosystems home to a wealth of different organisms. They are among the greatest natural treasures from the perspective of its overall function that impacts the natural environment and the living conditions within. Small rodents that are a known natural reservoir for numerous zoonoses (leptospirosis, tick-borne meningoencephalitis, lyme borreliosis, haemorrhagic fever with renal syndrome, etc.) form an important part of forest faunal community. The following species of mammals are most common in the continental forests of Croatia: striped field mouse (Apodemus agrarius Pall.), yellow-necked mouse (A. flavicollis Melch.), wood mouse (A. sylvaticus L.), bank vole (Clethrionomys glareolus Schreib.), common vole (Microtus arvalis Pall.), field vole (M. agrestis L.), water vole (Arvicola terrestris L.) and the European pine vole (M. subterraneus de Sel.). The spread of certain zoonoses is dependent on the abundance of rodent populations, their distribution, mobility, feeding intensity, habitat conditions and reproduction potential, as well as the abundance and distribution of wild and domesticated animals susceptible to infectious disease. Years with mild winters, dry springs and summers are favourable for increases in abundance of these species, which in turn can contribute to the spread of individual zoonoses in forests. The spread of zoonoses can occasionally unfold exceptionally quickly due to increased abundance of rodents, their great mobility and distribution, and the fact that they are commonly in contact with humans and wild and domesticated animals. The objectives of interdisciplinary studies currently ongoing in Croatia are to define the distribution of individual causative agents, and the level of infection among small rodents as the main reservoirs of causative agents of zoonoses in forest ecosystems. Etological findings about these mammals are essential in order to achieve the said objectives. The population abundance of each species changes in the course of a year or several years. In years with favourable ecological factors, it can be reasonably assumed that their numbers will substantially increase, and with that the danger of their harmful impacts. A large number of factors influences the population sizes of small rodents, and these can be classified into four basic groups: abundance and physiological state of the population, meteorological conditions, habitat and food sources, and natural enemies and disease. Establishing the natural fruit-bearing cycle for woody plants is successfully used in assessing the possible growth in population numbers. Regular controls of rodent populations and their infectiousness is significant in planning preventative epidemiological and sanitary measures in preventing outbreaks of epidemics and individual cases of illness among animal and human populations (forest workers, excursionists, mountaineers, soldiers, tourists, etc.). Sexual maturity of rodents and the behaviour associated with reproductive hormones are the result of the age of the individual and the season in which it was born.

forest ecosystems; small rodents; zoonosis; population dynamics and abundance

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