An attempt to control a natural focus of leptospirosis grippotyphosa by rodenticide--a long-term study (1977-2004).

The purpose of the study was to suppress a known natural focus of field fever exerting an influence on animal hosts of leptospires--small terrestrial mammals (s.t.m.) by rodenticide. After repeated application of the zinc phosphide rodenticide, the s.t.m. were regularly live-trapped and checked for leptospirosis by dark-field microscopy and culture of their renal tissue and serological examination. Isolated leptospira strains were typed by help of rabbit factor sera. The deratization influenced the s.t.m. structure considerably: the proportion of the dominant Microtus arvalis subjects--the main reservoirs of Leptospira kirschneri serovar Grippotyphosa--were gradually and substantially reduced and, contrarily, the percentage of the potential hosts subjects--Clethrionomys glareolus and Apodemus flavicollis--rose decisively over time. Changes in culture and serological positivity for leptospirosis of s.t.m. have also been unregistered. The highest original infestation of M. arvalis have slowly but strongly decreased while that of C. glareolus and A. flavicollis has increased decisively and reached its maximum within the last years of investigation. It is probable that these two animal species have undertaken the leading role in the maintenance of the natural focus of the field fever. In other animal species analogous trends were not registered. Based on these long-term findings, there exists the possibility to suppress only partially and temporarily the epizootic process of leptospirosis in a natural focus that can be desirable in some circumstances (building or free time activities, etc.).