Comparison of the effectiveness of two protocols of antirabies bait distribution for foxes (Vulpes vulpes).

In a plateau and hill region of France (the Doubs), two protocols of rabies vaccine bait distribution targeted at foxes were compared: helicopter distribution of vaccine baits alone (control zone) and a combined aerial distribution by helicopter with an additional deposit of vaccine baits at fox den entrances by foot (test zone). In the test zone covering an area of 436 km2, baits were distributed by helicopter at a rate of 13.4 baits/km2. Additionally, an average of 11.4 vaccine baits at the entrances of 871 fox dens were terrestrially distributed by 110 persons (9,964 baits). In this test zone, 90% of the young foxes were marked with tetracycline which permitted estimation of the bait consumption; however, only 38% had significant titre of rabies antibodies and less than one fox cub per 2.4 of those having consumed at least one bait were immunized. In the control zone, these percentages were significantly lower: respectively, 35 and 17% and one fox cub per 4.2. The relative lack of benefit between bait uptake and rate of immunological response may be due to maternal immunity which could have interfered with fox cub active immunization. A booster effect following a second distribution of baits by foot may be suggested in both adult foxes and their offspring. That these baits needed to be terrestrially distributed in order to obtain a booster effect is uncertain. Terrestrial distribution at fox den entrances is difficult to do and entails additional expenses not incurred in aerial distribution. The cost of terrestrial vaccination is 3.5 times higher than classical aerial vaccination and takes 63.5 times longer. A cost effective analysis of this type of supplementary terrestrial intervention determined that bait deposit at den entrances can be recommended for restricted areas, where residual focii exist, as a complement to the aerial distribution of baits.