Abstract

Fox rabies established itself in France in 1968. Since 1989, the incidence of the disease has dramatically declined. This decline is a direct result of fox vaccination campaigns using vaccine baits distributed by helicopter over the infected zones.

However, following these campaigns we observed a significant increase in fox populations and there is a common opinion of game keepers and country inhabitants that fox density is higher than before the rabies outbreak. As a result, we observed a decrease in the number of foxes marked with tetracycline (a biologic marker incorporated in baits) and in the percentage of immunized foxes. Furthermore, we had to tackle several residual foci, mainly near the borders with Belgium and Germany.

Program Implementations

This new epidemiologic problem required us to improve the efficacy of vaccination campaigns while studying their cost-effectiveness.

The first steps were to improve the quality system of the whole process:

1.  We carefully planned each helicopter flight by mapping the areas indicating precise densities of baits that had to be evenly distributed. After every flight, the flight parameters were checked and recorded.

2.  We titrated vaccine baits before and after dropping. Previous studies had demonstrated the paramount importance of vaccine titre and its stability in the fields.

3.  Field trials were organized over large areas for testing the effect of several parameters. We examined the increased density of baits in relation with fox density index. We examined the effectiveness of distribution campaigns at various seasons. Two distributions (one during spring, one during autumn); three distributions (spring, summer and autumn); two distributions (spring and autumn) with a double distribution during the same season as a short-delayed booster. We examined distribution system by helicopter only or combined with a hand distribution at the entrances of fox dens.

The results obtained on the percentage of foxes marked with tetracycline, and of immunized adult and cub foxes, were compared between large adjacent areas either treated according to the new, or the classic vaccination campaign protocols.

Cost effective protocols are proposed in the context of emergency or difficult situations, these being a new rabies outbreak occurring in an area densely populated with foxes, or remnant foci in endemic areas.