An attempt to control 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 fi eld fever exerting an infl uence 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-fi eld microscopy and culture of their renal tissue and serological examination. Isolated leptospira strains were typed by help of rabbit factor sera. The deratization infl uenced 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 substantionally reduced and, contrarily, the percentage of the potetial hosts subjects – Clethrionomys glareolus and Apodemus fl avicollis – rose decisively over time. Changes in culture and serological positivity for leptospirosis of s.t.m. have also been enregistered. The highest original infestation of M. arvalis have slowly but strongly decreased while that of C. glareolus and A. fl avicollis 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 fi eld fever. In other animal species analogous trends were not registered. Based on these long-term fi ndings, 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.).