[Experiences with oral immunization of foxes against rabies in Hesse]

Since spring 1983 a field trial to immunize foxes by the oral route against rabies has been carried out in a heavily infected area of Hessen measuring about 1,500 km2. The vaccine strain SAD B 19, produced by the Federal Research Institute for Animal Virus Diseases at Tübingen and filled into 2 ml aliquots, was inserted into chicken heads and distributed by forest rangers in the trial area, 15 baits per km2. Up to the present day five baiting campaigns, two per year in spring and autumn, have been completed and in all 110,000 vaccine baits additionally marked with 150 mg tetracycline were layed out. Four baitings have been previously evaluated. With the exception of some rabies cases on the border to the unvaccinated region in the northwest, rabies was reduced impressively. A secondary outbreak in the region of Hausen/Kiedrich, caused by an extremely high density of the fox population, was eradicated by increasing the baits to 25 per km2. The number of rabies cases, which amounted to 238 within 15 months prior to the vaccination trial, went down from 38 in the first 6 months to 6 cases after the fourth baiting. As innocuity control 2,273 wild and domestic animals from the vaccination area were examined for the presence of the vaccine virus. The results were always negative indicating that rabies strain SAD B 19 had not established an infective cycle in wildlife. As could be shown by the marker studies, an average of 78 per cent of the foxes (variation of the baitings from 62 per cent to 82 per cent) had taken up one or more baits. Seroconversion had been achieved in 65 per cent of the foxes (variation from 43 per cent to 70 per cent) as demonstrated by the presence of neutralizing antibodies. From experiences in Switzerland it can be expected, that rabies will be extinguished, if 50 per cent of the population are successfully immunized. This value has been surpassed in the field trial in Hessen. These very promising results have led to the project of an enlargement of the vaccination area to 12,000 km2. The neighbouring states of Rheinland-Pfalz and Nordrhein-Westfalen have joined in this effort, which has started in autumn 1985 with a new artificial vaccine bait developed at the Tübingen research institute.