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Considering, on the one hand, the magnitude of the yearly economic damage caused by BVDV world-wide and, on the other hand, the vastly improved diagnostic and preventive means at our disposal these days, several countries decided (some of them many years ago) to run eradication programs on a national level. In other countries the buck has stopped at declarations of intent. Of course it is possible to follow a BVD eradication strategy at a regional or even at farm level, this, however, has considerable disadvantages as the risk of importing BVD into a BVD-free herd is considerable and the losses incurred might under certain circumstances be greater than with continuous endemic infection.
BVD eradication, in principle, pursues diverse strategies. However, the PI animal always has pride of place due to its overwhelming significance in the spread of the disease. The choice of strategy depends, inter alia, on the population density and seroprevalence in the country concerned [71]. Eliminate pi animals & keep farms BVD-freeThis method is at present used in all four Scandinavian countries, and also in England/Wales, Shetland and Austria and has turned out to be quite successful. PI animals are sought out (blood and milk samples) and eliminated, animal traffic at a national and international level is strictly controlled and the farmers concerned are sensitized to issues of hygiene and prevention. This strategy has various advantages: first, the epidemiological processes can be screened by means of efficient methods (e.g. antibody ELISA for bulk milk). This would be considerably more expensive if prior vaccination were used (differentiation between antibodies against certain vaccines or antibodies against wild-type virus); second, the eradication makes more economic sense insofar as this is a once-only intensive process whereas prevention by means of vaccination has to be repeated on a regular basis. Additionally, uncertainties relating to vaccines obtainable at present can be avoided. However, this procedure also has one significant disadvantage: no control or surveillance system is 100 % perfect – if a BVD-free (seronegative) herd were to be exposed to the virus this might have disastrous consequences (see also “Economic loss”). VaccinationEspecially in the US, vaccination is a very important means of BVD prevention. In Europe, it’s applied more reluctantly. For more information concerning advantages and disadvantages of BVD-vaccination, see Vaccination & Vaccines and Vaccination: the problem with BVD. Deliberate exposure to viraemic animalsAlthough quite effective, deliberate exposure to field strain virus is a very risky way of achieving immunity. Chances are the virus will spread beyond the intended range and cause damage among seronegative pregnant and non-pregnant animals. |
Epidemiology 
