Hasle et al. Acta Veterinaria Scandinavica 2010, 52:55 http://www.actavetscand.com/content/52/1/55 these two non-bovine Babesia species were found. It is therefore unlikely that these Babesia species would influence the number of seropositive cows in this study significantly. There are no published studies on these Babesia species in Norway, but a Swedish study sug- gested that babesiosis caused by B. capreoli is very rare in Sweden [46]. An alternative to antibody testing is to test directly for the presence of the pathogen in cattle blood samples. Calder et al. [47] found an approximately 80% sensitivity for detecting Babesia bovis by PCR in steers, up to 300 days after experimental infection. The method these investigators used required a concentration step invol- ving ultracentrifugation of haemolysed blood. We con- sidered this to be too laborious a method to be useful as a field assay. We did attempt direct PCR to detect B. divergens without performing the concentration step in 30 samples from areas where we found the highest inci- dence of B. divergens by IFAT, but none of these sam- ples were found to be B. divergens-positive by this method. Cultivation of Babesia in cell culture, which enables detection of Babesia at a level of 10 parasites per 1 ml of blood [48], is another possibility for map- ping the distribution of this parasite, but it is not feasi- ble to use this method when sampling is being carried out in scattered locations. For our purposes, therefore, we found that antibody screening was a much more convenient method for assessment of the occurrence of B. divergens in a locality than any of the other methods that are available for detecting this pathogen. Gerbil- derived antigen is found to be equally specific to B. divergens obtained from cattle [49], and could be a cheaper alternative in future studies. In the communities on the coast of southern Norway where cows are pastured, the animals are confined to the farms on which they are kept. Consequently, testing cows for the presence of B. divergens infection should provide results that are specific to a given locality, as opposed to performing serological testing on other hosts of tick-borne pathogens, such as wildlife, dogs or humans. Because B. divergence is unlikely to survive for more than a decade in regions where cattle are not pas- turing and cattle is the only host for B. divergens at the Southern coast of Norway, testing cow sera appears to be an effective method for mapping B. divergens over the area of distribution of I. ricinus. The same is not the case if using cattle as sentinel animals for serological testing for other tick-borne pathogens, such as Ana- plasma, Borrelia or the TBE virus, that infect a wider range of hosts. Malandrin et al. [48] found a drop in IFAT antibody titre from 320, 320 and 1280 to 80, 80 and 320 respec- tively in samples from three cows taken 6 and 9 months after acute babesiosis, indicating an antibody duration of Page 7 of 9 more than a year, but much shorter than the cows’ life- span. Sahibi et al. [50] found no significant cumulative effect of cow age on the presence of Babesia-antibodies. This is consistent with a short duration of antibodies in the bloodstream after infection, meaning that detection of antibodies indicates a recent infection, as is illustrated by the seasonal variation of B. divergens-antibodies that was found by l’Hostis et al. [38], indicating repeated infections during the season. This implies that the life- time risk of acquiring bovine babesiosis is higher than the current rate of infection that was determined in the study we present here. Our IFAT data indicate that there are two areas along the southern Norwegian coast in which bovine babesio- sis is highly endemic, consisting of one western area (Lista-Mandal) and one eastern area (Kroger-Risør) (Fig- ure 1, Table 1). This uneven distribution was not reported by Thambs-Lyche in a study carried out along the same part of coastal Norway [29]. For other Babesia species, it has been shown that reduction of the inci- dence of tick bites can bring the reproduction rate of the parasite below 1, indicating that it could be possible to eradicate the parasite [41,51]. Our results indicate that, in the area from Sandaled to Arundel, which is within the distribution area of I. ricinus and is an area where cattle are pastured in a natural setting, B. diver- gens occurs at very low frequencies or not at all. In fact, the disease associated with this pathogen has virtually disappeared since the 1930 s, when Thambs-Lyche reported babesiosis in this area. This seems promising with regard to the possibility of eradicating this disease. An attempt to eradicate the disease would require the implementation of control measures over its entire dis- tribution because wild hosts can spread infected ticks. Cervid animals are the most important hosts for adult ticks [52]. Red deer, roe deer and moose have yearly migratory ranges of 200, 100 and 50-60 kilometres respectively [53], and Cervid animals, therefore, have the potential for transporting large numbers of ticks over long distances. Furthermore, birds can transport ticks across geographical barriers. In a recent study, 7.3% of northward migratory passerine birds were found to carry one or more ticks [54], so, in a situation where cows are pastured in an area that is free of B. divergens, or where there is an unstable population of the patho- gen, B. divergens could conceivably be introduced by birds. Conclusions At present, bovine babesiosis is a limited animal health problem in Norway. The most obvious possible cause of the decline in incidence since the 1930 s is changes in the use of pastures. Changes in legislation leading to increased use of wood pasturing may reverse the decline