Oral immunization of wildlife against rabies: concept and first field experiments

The possibility of immunizing carnivores against rabies with live attenuated vaccine administered by the oral route was raised by North American scientists in the 1960s. Subsequently, several American and European teams tested different vaccine strains in the laboratory for efficacy and safety and studied vaccine stabilization, vaccine delivery systems, bait acceptance by wild animals, and bait distribution schemes. The first field trial of a cloned SAD (Street Alabama Dufferin) strain in baits designed to immunize foxes orally was conducted in an Alpine valley in Switzerland in 1978. A population containing approximately 60% immune foxes at the valley entrance stopped the spread of the disease into untreated upper parts of the valley. The strategic use of oral vaccination of foxes in additional regions of Switzerland resulted in freedom from the zoonosis in four-fifths of the country.