Mice and "mice fever"

Borislav Aleraj, dr. med., specialist epidemiologist
Epidemiology service at Croatian institution for public health  http://www.hzjz.hr
Rockefellerova 7, 10000 Zagreb
Tel: 01/4683 004 or 01/4683 005.

What kind of disease is it?
Infectious agent and host animals
On Medvednica







What kind of disease is it?

A disease often called “mine fever” is in fact hemorrhagic fever with renal syndrome (HFRS). It is a disease with high fever, dysfunction of kidneys, and other disorders, sometimes very severe, with the need of hospital treatment. The disease is in this area always present with different incidence from year to year.

As its name indicates, it is connected with direct or indirect contact with small forest rodents and their excretions, urine, feces. People more frequently become ill in the years of large abundance of these small rodents. Various environmental factors can affect the number of rodents, such as nutrition, climate, and other, partially even unknown factors, so it often cannot be explained nor predicted. The number of affected people is in the large part a reflection of occurrences among animals.



Infectious agent and host animals

Infectious agent of this disease is a virus from a group of Hanta-viruses, distributed in several of its varieties (serotypes, species) in different parts of the world, in Europe from Scandinavia all the way to the south of the continent. In nature virus circles and survives among small forest rodents. In Croatia those are mostly bank vole ( Clethrionomys glareolus ) and yellow-necked mouse ( Apodemus flavicollis ), and besides them more seldom long-tailed field mouse ( Apodemus sylvaticus ), striped field mouse ( Apodemus agrarius ), and field vole ( Microtus agrestis ). This infection for them isn't lethal, but it makes them execrators of viruses in the environment, mostly through urine and feces.

From the described circumstances, which can lead to infection, it can be concluded that the diseased people will mostly be the ones which in the forest have repeated and long-term, direct or indirect contact with small rodents, most usually work connected (for example, forest workers, hunters, farmers, etc.).



On Medvednica

Out of the mentioned forest inhabitants living on Medvednica are bank vole, yellow-necked mouse, and long-tailed field mouse . During certain years, when the population is larger, bank vole can be seen running around even during daytime. It is characterized by beautiful reddish fur, and the easiest way to distinct it from mouse is a relatively short tail and small earlobes.

Until now, cases of this disease that could for certain be connected to excursions on Medvednica haven't been recorded, although each year thousands and thousands of people visit it. This tells us that the disease is rare in these parts; rare cases of disease have been recorded among inhabitants of some settlements in the foothills on northern and southern side of Medvednica.

Objectively small potential risk can even more be decreased and removed. We can find those measures in the following few advices:

•  During excursion keep your food and drinks away from rodents, don't leave them directly on the ground.
•  Maintain hygiene of hands, wash them, wipe off with moist tissue, etc. before meals.
•  Avoid drinking water from untended springs and puddles, because forest rodents use them as well.
•  Avoid resting (lying) directly on forest ground, especially in places where you have seen more rodents or their holes.
•  Do not catch or touch (dead) forest rodents or other animals.

Finally, most of the stated precaution measures and protection of health at the same time protect us from other diseases as well, which can be transmitted from animals to men (for example, leptospyrosis, intestinal parasites, etc.) and can therefore always be recommended to all visitors of forests.