Prevalence of leptospiral antibodies in the red fox (Vulpes vulpes) population of Croatia

Over a period of five years (2005-2010) a total of 358 red fox (Vulpes vulpes) serum samples were collected during regular hunting procedures, mostly in the continental part of Croatia. All samples were tested using the microscopic agglutination test (MAT) for the presence of specific antibodies (Ab) to 12 Leptospira spp. pathogenic serovars. Specific antibodies for 11 different Leptospira spp. serovars (Australis, Sejroe, Icterohaemorrhagiae, Saxkoebing, Grippotyphosa, Tarassovi, Ballum, Pomona, Poi, Batavie, and Canicola) were detected in 121 red fox serum samples (33.8%). Among the positive samples antibodies for serovar Australis were found most frequently (32.1%), followed by Abs for serovar Sejroe (18.2%) and Icterohaemorrhagiae (13.2%). The highest Ab titre (1 : 3200) was recorded for serovar Australis and together with serovars Sejroe and Icterohaemorrhagiae this serovar showed a statistically significant frequency in cross-reactions (recorded in 23.1% cases). High Ab titres for serovars Grippotyphosa and Tarassovi (1 : 800) were detected for the first time in red foxes from the continental part of Croatia. The significant percentage (≍ 35%) of seropositive reactions to Leptospira spp. serovars implies the presence of pathogenic agents in the natural habitats of red foxes in Croatian low-land territories. The high Ab prevalence for specific serovars (Australis and Sejroe) detected in the fox population suggests predator-prey chain transmission of leptospirosis between red foxes and small terrestrial mammals, whilst the high Ab prevalence for serovar Icterohaemorrhagiae indicates an occasional contact of red foxes with rats. Red foxes can be thought of as susceptible hosts for serovars Australis and Sejroe and a possible link in leptospirosis transmission to other wild carnivores such as martens, weasels and ferrets. In contrast, this serologic survey revealed no evidence of serovar Canicola interchange between domestic carnivores (dogs) and red foxes. It can be concluded that red foxes are reliable sentinels for the epidemiological monitoring of leptospirosis, especially in lowland habitats.