Leptospira borgpetersenii and Leptospira interrogans are nonsporulating bacteria responsible for leptospirosis, which is presumed to be the most widespread zoonosis in the world. This water-borne pathogen is usually transmitted to humans through the contact with contaminated soil or water, via infected animal tissue or rat bites. Consequently, farmers, miners, fishermen, sewer workers, participants of ‘adventure tourism’ and military personnel are at greater risk for infection. The usual portal of entry is through abrasions or cuts in the skin or by inhalation of contaminated water aerosol, however infection may also take place via intact skin after prolonged immersion in water. The incidence is considerably higher in tropical and developing countries what is associated with a longer survival of bacteria with increased possibility for exposure, however the cases of leptospirosis are also reported in developed countries of various geographical latitudes, e.g., USA, Canada and the Netherlands. The great majority of infections caused by these Spirochetes are either subclinical or very mild in severity (anticteric leptospirosis), although the fatal cases of much more severe icteric leptospirosis with renal