Tularaemia seroprevalence of captured and wild animals in Germany: the fox (Vulpes vulpes) as a biological indicator

Abstract

A total of 2475 animals from Germany, both captive and wild, were tested for antibodies against Francisella tularensis to obtain more knowledge about the presence of this pathogen in Germany. An indirect and a competitive ELISA served as screening methods, positive and inconclusive samples were confirmed by Western blot. Of the zoo animals sampled between 1992 and 2007 (n = 1122), three (0·3%) were seropositive. The seroconversion of a hippopotamus in Berlin Zoo was documented. From 1353 serum samples of wild foxes (Vulpes vulpes), raccoon dogs (Nyctereutes procyonoides) and wild boars (Sus scrofa), collected between 2005 and 2009 in the federal state of Brandenburg (surrounding Berlin), a total of 101 (7·5%) tested positive for antibodies to F. tularensis lipopolysaccharide. Our results indicate a higher seroprevalence of F. tularensis in wildlife in eastern Germany than commonly assumed. Furthermore, we found foxes and raccoon dogs to be biological indicators for tularaemia.

Fig. 1.

(a) Sampling sites of captive animals in Germany (sample collection 1, red numbers indicate the sampling sites) and wild animals (serum collection 2, green area). (b) Regional map of Brandenburg depicting sampling locations of wild animals. Coloured boxes indicate individuals that tested positive, grey boxes those that tested negative. Each box represents one individual; green, raccoon dogs; red, foxes; blue, wild boars.

Fig. 2.

Western blot for confirmation of ELISA samples tested positive. (a) Examples of positive samples of raccoon dogs and foxes from serum collection 2 showing the typical lipopolysaccharide (LPS) ladder. (b) Western blot with F. tularensis LPS extract showing sera of the hippopotamus that tested positive from serum collection 1 (zoo animals), depicting the seroconversion of the animal. Note the typical LPS ladder only in positive samples from 2004 and 2006. (+), Positive control; (–) negative control; raccoon dogs and foxes = serum collection 2; sera from hippopotamus (serum collection 1); 1, from 2001; 2, from 2003; 3, from 2004; 4, from 2006.