Genetic characteristics of field and attenuated rabies viruses ... - Evira

of a vaccinia-rabies recombinant virus administered by the oral route in foxes. Because of
its safety and heat-stability, this recombinant virus could be an excellent alternative to the
attenuated strains of rabies virus currently used in the field (Brochier et al., 1990, 1991,
1996; Desmettre et al., 1990; Lambot et al., 2001). The high thermo stability of the
commercially produced Raboral VRG bait allows its use during the summer for
emergency vaccination campaigns (Masson et al., 1999), and is being used for the
vaccination of wild raccoons in the USA (Olson et al., 2000). The VRG vaccine has also
been tested as an oral vaccine in vampire bats and significant protection was observed in
animals vaccinated 18-30 days before challenge (Setien et al., 1998).
Oral vaccination of wild animals has been successfully conducted in many
countries: such as Austria, Croatia, Switzerland, Italy, Germany, Slovenia, Czech
Republic, Slovakia, Israel, USA, Canada, Belgium, France, etc. (Steck et al., 1982;
Westerling, 1989; Gram, 1996; Separovic, 1996; Schluter, 1996; Svrcek et al., 1996;
Matouch, 1996; Mutinelli, 1996; Linhart et al., 1997; Olson et al., 1999, 2000; Hostnik,
2000b; MacInnes et al., 2001). The sylvatic rabies epidemic of 1988-1989 was
successfully eradicated in Finland by the oral immunization of wild carnivores (Nyberg et
al., 1992), and was also used in some areas of Russia. One of these vaccination areas is
located at the Finnish-Russian border within the Leningrad region and the Republic of
Karelia. The oral vaccination was organized in 2003 within the framework of the
international Finnish-Russian collaboration program for controlling rabies in wildlife, and
financially supported by the EU and the Finnish government (Metlin et al., in press).
The most common strategy for conducting oral vaccination campaigns is to use
vaccine baits at a density of approximately 25 baits per square km, twice a year, during
the spring and autumn, to avoid the negative influence of temperature on vaccine baits
and to reach adult foxes (in spring) and juvenile foxes before they disperse (in autumn)
(Aubert et al., 1994; Vos, 2003). However, further studies on the population dynamics of
the red fox, the onset and progress of the reproductive season, and maternal immunity
and the immune response of fox cubs to oral vaccination have shown that it was
necessary to optimize the old strategy and conduct two spring vaccinations: first in
March, and then before the end of May to cover young foxes (Muller et al., 1999, 2001;
Vos et al., 2001).
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