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Status
report
Microbial
Releases
Deliberate release of a recombinant vaccinia-rabies virus
vaccination of wild animals against rabies
Paul-Pierre Pastoret, Bernard Brochier, Paul Coppens
Department of Virology-Immunology, Faculty of Veterinary Medicine, University of Liege, B43, Sart Tilman, B-4000 Liege, Belgium
Abstract. Since 1978, several European countries have conducted, at different times, large-scale field trials of oral vaccination of foxes (Vulpes vulpes) against rabies, using the SAD, standard or B19-modified attenuated strains of rabies virus. The use of attenuated strains of rabies virus remains controversial as far as safety and stability are concerned, since these virus strains retain pathogenicity for rodents or other wildlife species and are heat-sensitive. To improve both safety and stability of the vaccine used in the field, a recombinant vaccinia virus expressing the immunogenic G protein of rabies vi rus has been developed and released in the field. The first safety-efficacy results are very encouraging.
Key words: Rabies - Oral vaccination - Recombinant vaccinia-rabies virus - Safety - Efficacy
Introduction
Control of infections in wild animals is difficult to achieve, mainly because such animals are free ranging, making them difficult to handle by conventional veteri nary means. Vaccination is the most appropriate way of controlling infections at a population level, but in these cases the only practical route of administration is the oral one.
Sylvatic rabies provides the best example of control of a wildlife infection. In northern countries, rabies is a zoonotic disease, the epidemiology of which is solely linked to a wildlife reservoir. In western Europe, the main vector is the red fox (Vulpes vulpes), whereas in North America, it is either the red fox, the raccoon
(Procyon lotor) or the striped skunk (Mephitis mephi tis). In this respect, "vector" refers to the animal host
that is most susceptible to rabies in a region at a given time and that is solely responsible for maintaining the infection. The control of the infection within the vector species thus permits overall control of the infection and,
Correspondence to: P.-P. Pastoret
most importantly, eliminates the risk of transmission to man (Pastoret and Brochier 1991).
In western Europe, control measures to reduce fox populations were only temporarily effective and did not prevent the disease from spreading. For this reason, oth er methods such as oral immunization of foxes needed to be assessed. Research has focused on oral vaccina tion, the only means allowing the immunization of a sufficient proportion (75%) of wild foxes, through the distribution of vaccine baits. Since 1978, several Euro pean countries have organized large-scale field trials of oral vaccination of foxes using the standard or modified (B19) attenuated strain of rabies virus, Street Alabama Dufferin (SAD) (Blancou et al. 1988). The promising re sults obtained from these vaccination campaigns attest to the feasibility and the efficacy of the method. Howev er, the use of attenuated rabies virus remains controver sial as far as safety and stability are concerned, as these virus strains are still pathogenic for laboratory and wild rodents or wildlife species such as the chacma baboon
(Papio ursinus) (Bingham et al. 1992) and target species
such as the striped skunk (Leblois and Flamand 1988); moreover, these strains may still be pathogenic to man. Pathogenicity of attenuated rabies virus strains can be abolished by mutating Arg residues at position 333 of the glycoprotein, although such strains can still revert to virulence (Tuffereau et al. 1989).
Thus, in order to improve both the safety and stabili ty of the vaccines used, a recombinant vaccinia virus which expresses the immunizing glycoprotein of rabies virus has been developed and tested in the field for oral vaccination of wildlife vectors against rabies.
Construction of the recombinant vaccinia-rabies virus
The glycoprotein of rabies virus is the sole viral protein present on the external surface of the membrane. It is the only viral antigen capable of eliciting the formation of rabies virus-neutralizing antibodies and has been shown to be capable of conferring immunity to rabies. Thus, the rabies virus glycoprotein is an ideal candidate for use in the construction of subunit vaccines.
Nucleotide sequence analysis of the glycoprotein gene reveals an open reading frame of 524 amino acids. Ex pression of exogenous protein-coding sequences in vac cinia virus involves essentially two steps. First, the exo genous coding sequence is aligned with a vaccinia pro moter and inserted in vitro at a site within a (non-essen tial) segment of vaccinia DNA cloned into a suitable bacterial plasmid replicon. Second, the flanking vaccinia sequences permit homologous recombination in vivo be tween the plasmid and the viral genome. Double reci procal recombination results in transfer of the DNA in sert from the plasmid to the viral genome, wherein it is propagated and expressed. The rabies virus glycoprotein gene has been inserted into the thymidine-kinase (TK) gene of vaccinia virus in this way, generating a selectable TK - virus (Kieny et al. 1984; Wiktor et al. 1984) known as VVT Gg RAB.
Efficacy of the virus in target species
VVT Gg RAB has been tested for efficacy and safety in the main target species in western Europe and North America: fox, raccoon and striped skunk (Blancou et al. 1986; Tolson et al. 1987; Rupprecht et al. 1988; Des mettre et al. 1990).
The results of tests for efficacy in foxes can be sum marized as follows: all but one of 26 adult foxes inocu lated by various routes developed high titres of rabies neutralizing antibodies and resisted wild rabies virus challenge on day 28 after vaccination (Blancou et al. 1986). The duration of immunity conferred by VVT Gg RAB, a minimum of 12 months in cubs and 18 months in adult animals, corresponds to the length of protection required for fox vaccination in the field, due to the high population turnover of the fox population (Brochier et al. 1988; Blancou et al. 1989). Foxes receiving less than the recommended dose showed a clear dose-dependent response. A second administration of VVT Gg RAB in duces an increase of rabies-neutralizing antibodies (booster effect). Oral administration is the only route appropriate for the vaccination of wild animals. Ac cordingly, the vaccine must be presented in a form suit able for ingestion.
The efficacy of VVT Gg RAB (108 TCID
50) con tained in a machine-made baiting system has been tested (Brochier et al. 1990). Twenty-two young foxes were divided into three experimental groups of six and a con trol group of four animals. Foxes in the first three groups were fed one, two and three vaccine baits, re spectively, on successive days. The four unvaccinated foxes were housed separately. As shown by the incorpo ration of a tetracycline biomarker into their bones, all the baited foxes ingested at least one bait. Thirty days after baiting, seroconversion to rabies was observed in 15 of 18 foxes and seroconversion to vaccinia in 14 of 18. Of the 18 baited foxes, 16 resisted a wild rabies virus challenge 90 days after baiting. One cub was protected against rabies despite the absence of detectable anti-ra bies antibodies. These results demonstrate that the bait ing-sachet system used permits an efficient release of the virus suspension into the mouth.
Safety of the virus
A vaccine virus most not only be efficacious but also in nocuous for the target species. VVT Gg RAB was ob served to be non-pathogenic in the fox whatever the dose of inoculation (102-1010 TCIDso), or route of ad ministration ( oral, intramuscular, intraduodenal, subcu taneous, intradermic, conjunctiva! or intranasal).
It is preferable that a vaccine virus used for oral vac cination of wildlife not be horizontally transmitted to unvaccinated animals. In order to test for horizontal transmission, unvaccinated control animals have been held in close contact with vaccinated ones. Using this as sessment method, no transmission of immunizing amounts of VVT Gg RAB was found to occur in adult or young foxes, with the exception of one adult fox bit ten by a freshly inoculated animal.
It is also of major importance to preclude epizootio logical risks, such as the emergence of asymptomatic carriers of wild rabies virus (Brochier et al. 1989a). This situation could occur in the field by the vaccination of naturally infected animals during the incubation period. The influence of vaccination with VVT Gg RAB on the onset of the disease and on the delay before death in foxes previously infected with wild rabies virus, has been investigated. All foxes, vaccinated or not, died from rabies. Animals vaccinated early after challenge died after a shorter period of incubation than unvacci nated controls. On the other hand, animals vaccinated belatedly after challenge died after the controls. The re sults show that "early" and "late" death phenomena oc cur as a consequence of interactions between oral vacci nation with VVT Gg RAB and rabies infection, but pre clude the risk of the emergence of asymptomatic carriers of wild-rabies virus after vaccination.
Similar results have been obtained with the raccoon and the skunk. The safety of VVT Gg RAB for adminis tration to pregnant female raccoons has been evaluated, revealing an absence of epigenetic transmission to offspring, as well as the absence of the recombinant in the cerebrospinal fluid (Hanlon et al. 1989). There was no evidence of active in utero or lactogenic transmission of the recombinant. These results are in contrast with those obtained with attenuated strains of rabies virus in the skunk (Rupprecht et al. 1990).
Field trials with attenuated strains of rabies virus have shown that several non-target wildlife species com pete with foxes for bait consumption. It must also be taken into account that, within the orthopoxvirus group, vaccinia virus has a wide range of host species. In fact, bait uptake surveillance and tetracycline (bio marker) detection controls, performed after vaccination campaigns, proved that mustelids, wild boars (Sus scro fa) and domestic carnivores can ingest the vaccine baits.
Moreover, a significant proportion of the baits are part ly eaten by small mammals. It is important, therefore, to verify the safety of VVT Gg RAB for non-target spe cies (both domestic and wild).
Several non-target wild species have been chosen for testing in Europe because of their opportunistic feeding behaviour and their presence in the areas where the
vac-cine must be distributed (Brochier et al. 1989b). Safety of the vaccine has been tested in Daubenton's bat (Myo tis daubentom), wild boar, Eurasian badger (Me/es me/es) wood mouse (Apodemus sylvaticus), yellow necked mouse (Apodemus flavicollis), bank vole (Cle thrionomys glareolus), common vole (Microtus arvalis),
field vole (Microtus agrestis), water vole (Arvicola ter restris), common buzzard (Buteo buteo), kestrel (Falco tinnunculus), carrion crow (Corvus corone), magpie
(Pica pica) and jay (Garrulus glandarius). Clinical signs of rabies and/or pox-inflicted lesions were never ob served in the vaccinated animals during the observation period (28 days minimum after vaccination).
Similar experiments have been carried out with wild species from North America (Artois et al. 1990), includ
ing meadow vole (Microtus pennsylvanicus), woodchuck
(Marmota monax), grey squirrel (Sciurus carolinensis),
ring-billed gull (Larus delawarensis), red-tailed hawk
(Buteo jamaicensis), great horned owl (Bubo virginia nus) and coyote (Canis latrans). Comparable results were observed in these studies. Recent experiments have also shown that the recombinant virus, administered either by scarification or by the oral route, is also safe for squirrel monkeys (Saimiri sciureus) and for chim panzees (Pan troglodytes) (Rupprecht et al. 1992).
Multiplication site of the virus in foxes
When assessing a recombinant virus for use in vaccina tion, it is also of great importance to detect any varia tion in tissue specificity compared with the parental vec tor strain. Experiments have been designed to determine the multiplication site in foxes of the recombinant virus, compared with the parental strain of vaccinia virus, by virus isolation, titration and indirect immunofluores cence. The polymerase chain reaction was also used to detect specific virus DNA in several fox organs (Thomas et al. 1990). Foxes were fed with 108 TCID50 of either VVT Gg RAB or vaccinia virus, and were killed 12, 24, 48 or 96 h after inoculation by the oral route.
Using these different techniques, VVT Gg RAB or vaccinia virus could be detected during the first 48 h fol lowing vaccination by the oral route, but only in the tonsils, buccal mucosa and soft palate. Similar results have been obtained in raccoons using virus isolation (Rupprecht et al. 1988). Results of other experiments de monstrate that tonsillectomy of foxes does not com pletely impede seroconversion (I. Thomas et al., unpub lished data).
As no virus could be detected in the salivary glands of foxes (parotid or maxillary), the risk of transmission from one animal to another through saliva can be as sumed to be negligible. Furthermore, the fact that VVT Gg RAB only multiplies in restricted sites minimizes the potential risk of recombination with other wild ortho poxviruses. In these experiments, no difference was ob served between the multiplication sites of VVT Gg RAB and vaccinia virus, demonstrating that the recombina tion event did not modify the tropism of the virus. Ad ditionally, virus was never detected in the brain. These
193 results are in agreement with those from studies on rac coons vaccinated orally with VVT Gg RAB (Hanlon et al. 1989) that report the absence of detectable cytologi cal abnormalities in the cerebrospinal fluid.
Deliberate release of the virus
Taking into account all the available experimental data concerning the safety of the VVT Gg RAB for target and non-target species and its efficacy in foxes, initial limited field trials of fox vaccination were authorized first by the Belgian (Pastoret et al. 1988) and then by the French public health authorities. In the Belgian trial (17-18 October 1987) a total of 250 vaccine baits (chick en heads) were delivered manually on a 6 km2 area situ ated in the central part of a military zone.
With the safety of the VVT Gg RAB being confirmed by this small trial, the Belgian authorities agreed for an enlarged open field trial (Brochier et al. 1990). This was conducted in a 435 km2 area in the southern part of the country, chosen because it has the lowest average hu man population density in the country (42 inhabitants km -2) as well as high rabies incidence in foxes. Further more, the region is characterized by various habitats housing most of the animal species liable to consume bait. Each bait contained a suspension of 108 TCID
50 of VVT Gg RAB (2.2 ml by volume) within a plastic sachet and 150 mg tetracycline as a long-term biomarker of bait uptake. After the vaccination campaign, 222 dead wild animals belonging to 19 species were collected in the vaccination area. After necropsy, the following tis sues were removed: brain for rabies diagnosis, jaws for tetracycline detection and blood for the titration of vac cinia and rabies antibodies.
Tetracycline was detected in foxes (61 OJo), stone mart ens (Martes Joina; 40%), domestic feral cats (Pelis ca tus; 27%), wood mice (Apodemus sp.; 10%), wild boars (47%) and carrion crows (10%), showing that wild boars, mustelids and feral cats are strong competitors of the foxes for bait uptake (Brochier et al. 1990b). Twelve months of monitoring failed to detect any ecological hazard or public health risk. The vaccine was very stable even following natural freezing and thawing cycles. The VVT Gg RAB vaccine has been shown to retain its ca pacity to immunize for at least 1 month in field condi tions, a period which corresponds to the delay of uptake that many baits may undergo in the field (Brochier et al. 1990b).
Following this enlarged trial, three fox-vaccination campaigns using VVT Gg RAB were then carried out in Belgium in November 1989, April 1990 and October 1990 in order to check for efficacy in an area of 2200 km2 with a mean baiting density of 15 baits km -2 (Brochier et al. 1991a). The 25 000 baits were dropped by helicopter. After each vaccination campaign, foxes found dead (or shot by hunters) were collected for rabies diagnosis and bone tetracycline analysis. The three col lection periods permitted the collection of 10 rabid and 178 healthy foxes. The bait uptake rate determined from tetracycline status in 23 adult foxes (9 rabid, 14 healthy)
Nucleotide sequence analysis of the glycoprotein gene reveals an open reading frame of 524 amino acids. Ex pression of exogenous protein-coding sequences in vac cinia virus involves essentially two steps. First, the exo genous coding sequence is aligned with a vaccinia pro moter and inserted in vitro at a site within a (non-essen tial) segment of vaccinia DNA cloned into a suitable bacterial plasmid replicon. Second, the flanking vaccinia sequences permit homologous recombination in vivo be tween the plasmid and the viral genome. Double reci procal recombination results in transfer of the DNA in sert from the plasmid to the viral genome, wherein it is propagated and expressed. The rabies virus glycoprotein gene has been inserted into the thymidine-kinase (TK) gene of vaccinia virus in this way, generating a selectable TK - virus (Kieny et al. 1984; Wiktor et al. 1984) known as VVT Gg RAB.
Efficacy of the virus in target species
VVT Gg RAB has been tested for efficacy and safety in the main target species in western Europe and North America: fox, raccoon and striped skunk (Blancou et al. 1986; Tolson et al. 1987; Rupprecht et al. 1988; Des mettre et al. 1990).
The results of tests for efficacy in foxes can be sum marized as follows: all but one of 26 adult foxes inocu lated by various routes developed high titres of rabies neutralizing antibodies and resisted wild rabies virus challenge on day 28 after vaccination (Blancou et al. 1986). The duration of immunity conferred by VVT Gg RAB, a minimum of 12 months in cubs and 18 months in adult animals, corresponds to the length of protection required for fox vaccination in the field, due to the high population turnover of the fox population (Brochier et al. 1988; Blancou et al. 1989). Foxes receiving less than the recommended dose showed a clear dose-dependent response. A second administration of VVT Gg RAB in duces an increase of rabies-neutralizing antibodies (booster effect). Oral administration is the only route appropriate for the vaccination of wild animals. Ac cordingly, the vaccine must be presented in a form suit able for ingestion.
The efficacy of VVT Gg RAB (108 TCID5o) con tained in a machine-made baiting system has been tested (Brochier et al. 1990). Twenty-two young foxes were divided into three experimental groups of six and a con trol group of four animals. Foxes in the first three groups were fed one, two and three vaccine baits, re spectively, on successive days. The four unvaccinated foxes were housed separately. As shown by the incorpo ration of a tetracycline biomarker into their bones, all the baited foxes ingested at least one bait. Thirty days after baiting, seroconversion to rabies was observed in 15 of 18 foxes and seroconversion to vaccinia in 14 of 18. Of the 18 baited foxes, 16 resisted a wild rabies virus challenge 90 days after baiting. One cub was protected against rabies despite the absence of detectable anti-ra bies antibodies. These results demonstrate that the bait ing-sachet system used permits an efficient release of the virus suspension into the mouth.
Safety of the virus
A vaccine virus most not only be efficacious but also in
nocuous for the target species. VVT Gg RAB was ob served to be non-pathogenic in the fox whatever the dose of inoculation (102-1010 TCIDso), or route of ad ministration (oral, intramuscular, intraduodenal, subcu taneous, intradermic, conjunctiva! or intranasal).
It is preferable that a vaccine virus used for oral vac cination of wildlife not be horizontally transmitted to
unvaccinated animals. In order to test for horizontal transmission, unvaccinated control animals have been held in close contact with vaccinated ones. Using this as sessment method, no transmission of immunizing amounts of VVT Gg RAB was found to occur in adult or young foxes, with the exception of one adult fox bit ten by a freshly inoculated animal.
It is also of major importance to preclude epizootio logical risks, such as the emergence of asymptomatic carriers of wild rabies virus (Brochier et al. 1989a). This situation could occur in the field by the vaccination of naturally infected animals during the incubation period. The influence of vaccination with VVT Gg RAB on the onset of the disease and on the delay before death in foxes previously infected with wild rabies virus, has been investigated. All foxes, vaccinated or not, died from rabies. Animals vaccinated early after challenge died after a shorter period of incubation than unvacci nated controls. On the other hand, animals vaccinated belatedly after challenge died after the controls. The re sults show that "early" and "late" death phenomena oc cur as a consequence of interactions between oral vacci nation with VVT Gg RAB and rabies infection, but pre clude the risk of the emergence of asymptomatic carriers of wild-rabies virus after vaccination.
Similar results have been obtained with the raccoon and the skunk. The safety of VVT Gg RAB for adminis tration to pregnant female raccoons has been evaluated, revealing an absence of epigenetic transmission to offspring, as well as the absence of the recombinant in the cerebrospinal fluid (Hanlon et al. 1989). There was no evidence of active in utero or lactogenic transmission of the recombinant. These results are in contrast with those obtained with attenuated strains of rabies virus in the skunk (Rupprecht et al. 1990).
Field trials with attenuated strains of rabies virus have shown that several non-target wildlife species com pete with foxes for bait consumption. It must also be taken into account that, within the orthopoxvirus group, vaccinia virus has a wide range of host species. In fact, bait uptake surveillance and tetracycline (bio marker) detection controls, performed after vaccination campaigns, proved that mustelids, wild boars (Sus scro f a) and domestic carnivores can ingest the vaccine baits.
Moreover, a significant proportion of the baits are part ly eaten by small mammals. It is important, therefore, to verify the safety of VVT Gg RAB for non-target spe cies (both domestic and wild).
Several non-target wild species have been chosen for testing in Europe because of their opportunistic feeding behaviour and their presence in the areas where the
vac-cine must be distributed (Brochier et al. 1989b). Safety of the vaccine has been tested in Daubenton's bat (Myo tis daubentom), wild boar, Eurasian badger (Me/es metes) wood mouse (Apodemus sylvaticus), yellow necked mouse (Apodemus flavicollis), bank vole (Cle thrionomys glareolus), common vole (Microtus arvalis),
field vole (Microtus agrestis), water vole (Arvicola ter restris), common buzzard (Buteo buteo), kestrel (Falco tinnunculus), carrion crow (Corvus corone), magpie
(Pica pica) and jay (Garrulus glandarius). Clinical signs of rabies and/or pox-inflicted lesions were never ob served in the vaccinated animals during the observation period (28 days minimum after vaccination).
Similar experiments have been carried out with wild species from North America (Artois et al. 1990), includ
ing meadow vole (Microtus pennsylvanicus), woodchuck
(Marmota monax), grey squirrel (Sciurus carolinensis),
ring-billed gull (Larus delawarensis), red-tailed hawk
(Buteo jamaicensis), great horned owl (Bubo virginia nus) and coyote (Canis latrans). Comparable results were observed in these studies. Recent experiments have also shown that the recombinant virus, administered either by scarification or by the oral route, is also safe for squirrel monkeys (Saimiri sciureus) and for chim panzees (Pan troglodytes) (Rupprecht et al. 1992).
Multiplication site of the virus in foxes
When assessing a recombinant virus for use in vaccina tion, it is also of great importance to detect any varia tion in tissue specificity compared with the parental vec tor strain. Experiments have been designed to determine the multiplication site in foxes of the recombinant virus, compared with the parental strain of vaccinia virus, by virus isolation, titration and indirect immunofluores cence. The polymerase chain reaction was also used to detect specific virus DNA in several fox organs (Thomas et al. 1990). Foxes were fed with 108 TCID50 of either VVT Gg RAB or vaccinia virus, and were killed 12, 24, 48 or 96 h after inoculation by the oral route.
Using these different techniques, VVT Gg RAB or vaccinia virus could be detected during the first 48 h fol lowing vaccination by the oral route, but only in the tonsils, buccal mucosa and soft palate. Similar results have been obtained in raccoons using virus isolation (Rupprecht et al. 1988). Results of other experiments de monstrate that tonsillectomy of foxes does not com pletely impede seroconversion (I. Thomas et al., unpub lished data).
As no virus could be detected in the salivary glands of foxes (parotid or maxillary), the risk of transmission from one animal to another through saliva can be as sumed to be negligible. Furthermore, the fact that VVT Gg RAB only multiplies in restricted sites minimizes the potential risk of recombination with other wild ortho poxviruses. In these experiments, no difference was ob served between the multiplication sites of VVT Gg RAB �nd vaccinia virus, demonstrating that the recombina tion event did not modify the tropism of the virus. Ad ditionally, virus was never detected in the brain. These
193 results are in agreement with those from studies on rac coons vaccinated orally with VVT Gg RAB (Hanlon et al. 1989) that report the absence of detectable cytologi cal abnormalities in the cerebrospinal fluid.
Deliberate release of the virus
Taking into account all the available experimental data concerning the safety of the VVT Gg RAB for target and non-target species and its efficacy in foxes, initial limited field trials of fox vaccination were authorized first by the Belgian (Pastoret et al. 1988) and then by the French public health authorities. In the Belgian trial (17-18 October 1987) a total of 250 vaccine baits (chick en heads) were delivered manually on a 6 km2 area situ
ated in the central part of a military zone.
With the safety of the VVT Gg RAB being confirmed by this small trial, the Belgian authorities agreed for an enlarged open field trial (Brochier et al. 1990). This was conducted in a 435 km2 area in the southern part of the
country, chosen because it has the lowest average hu man population density in the country ( 42 inhabitants km -2
) as well as high rabies incidence in foxes. Further
more, the region is characterized by various habitats housing most of the animal species liable to consume bait. Each bait contained a suspension of 108 TCID
50 of VVT Gg RAB (2.2 ml by volume) within a plastic sachet and 150 mg tetracycline as a long-term biomarker of bait uptake. After the vaccination campaign, 222 dead wild animals belonging to 19 species were collected in the vaccination area. After necropsy, the following tis sues were removed: brain for rabies diagnosis, jaws for tetracycline detection and blood for the titration of vac cinia and rabies antibodies.
Tetracycline was detected in foxes (61 OJo), stone mart ens (Martes joina; 40%), domestic feral cats (Pelis ca tus; 27%), wood mice (Apodemus sp.; 10%), wild boars (47%) and carrion crows (10%), showing that wild boars, mustelids and feral cats are strong competitors of the foxes for bait uptake (Brochier et al. 1990b). Twelve months of monitoring failed to detect any ecological hazard or public health risk. The vaccine was very stable even following natural freezing and thawing cycles. The VVT Gg RAB vaccine has been shown to retain its ca pacity to immunize for at least 1 month in field condi tions, a period which corresponds to the delay of uptake that many baits may undergo in the field (Brochier et al. 1990b).
Following this enlarged trial, three fox-vaccination campaigns using VVT Gg RAB were then carried out in Belgium in November 1989, April 1990 and October 1990 in order to check for efficacy in an area of 2200 km2 with a mean baiting density of 15 baits km -2
(Brochier et al. 1991a). The 25000 baits were dropped by helicopter. After each vaccination campaign, foxes found dead (or shot by hunters) were collected for rabies diagnosis and bone tetracycline analysis. The three col lection periods permitted the collection of 10 rabid and 178 healthy foxes. The bait uptake rate determined from tetracycline status in 23 adult foxes (9 rabid, 14 healthy)
Rabies cases (n) 600 500 400 300 200 100 0 • Wild
D
Domestic 81 82 83 84 85 86 87 88 89 90 91 92+HH
VaccinationFig. 1. Evolution of animal rabies in Belgium, 1981-1992. Ar
rows, full campaigns of fox vaccination in the infected area
(10000 km2)
during the first period was 740Jo; 6 of the 9 rabid and 11 of the 14 healthy foxes were positive for tetracycline. During the second collection period bait-uptake rates were 800Jo (25/31) in adult foxes but only 490Jo (27/55) in juveniles. During spring dispersal of baits, most cubs (born principally in March) would be expected to be confined to the immediate surroundings of the breeding den, and thus less likely to ingest baits. No rabid fox was recorded during this period (0/86). After the third phase of vaccination (October 1990), 81 OJo (64/79) of in spected animals were tetracycline positive. The one ra bid animal recorded, at the periphery of the baited area, was tetracycline-negative. Serological data are currently misunderstood because of strong discordances in the re sults obtained with the rapid fluorescent foci inhibition test (RFFIT) and the ELISA technique. The poor quali ty of blood samples collected from dead animals gener ally induces non-specific reactions. Serological results would be reliable when using fresh sera only (Brochier et al. 1990b).
Despite the dramatic decrease in the number of rabid foxes recorded after vaccine-bait distribution, the effica cy of the vaccination campaign was difficult to evaluate because systematic collection of foxes is not logistically feasible. Because transmission of rabies to domestic ani mals occurs through the bite of a rabid wild animal, however, and because notification of cases of rabies in cattle and sheep is mandatory in Belgium, the incidence of rabies in domestic livestock provides a reliable indica tor of the prevalep.ce of rabies in the wild. No case of livestock rabies has been recorded in the study zone since the second phase of vaccination. Our results there fore indicate that the dispersion of live recombinant vac cinia virus VVT Gg RAB can be an effective means of controlling rabies.
In autumn 1989, a first campaign of fox vaccination was carried out in the whole infected area of Belgium (10000 km2). Similar full campaigns were then repeated four times: in spring and autumn 1990 and spring and
autumn 1991. Starting in 1990 the VVT Gg RAB was used because of its efficacy, stability and safety. During each campaign, 150000 vaccine baits were dropped by aircraft (mean 15 baits/km -2).
As shown in Fig. 1, these campaigns have brought about a drastic decrease in the incidence of rabies, both in foxes and in domestic animals. From April 1991 to the time of writing, that is to say for more than a year, all rabies cases were recorded in a 2000-km2 region
along the border with France. Rabies has disappeared from the majority of the initial infected area. In light of this epidemiological situation a new spatial strategy for bait dispersal was initiated in 1992, namely formation of an immune belt along international borders. Two "de fence" campaigns were carried out in April and October 1992 (Brochier et al. 1991b; Coppens et al. 1992).
References
Artois M, Charlton KM, Tolson ND, Casey GA, Knowles MK, Campbell JB (1990) Vaccinia recombinant virus expressing the rabies virus glycoprotein: safety and efficacy trials in Canadian wildlife. Can J Vet Res 54 :504-507
Bingham J, Foggin CH, Gerber H, Hill FWG, Kappeler A, King AA, Perry BD, Wandeler AI (1992) The pathogenicity of SAD rabies vaccine in chacma baboons (Papio ursinus) given by the oral route. Vet Rec 131 :55-56
Blancou J, Kieny MP, Lathe R, Lecocq JP, Pastoret PP, Soule bot JP, Desmettre P (1986) Oral vaccination of the fox against rabies using a Jive recombinant vaccinia virus. Nature 322:373-375
Blancou J, Artois M, Brochier B, Thomas I, Pastoret PP, Des mettre P, Languet B, Kieny MP (1989) Innocuite et efficacite du virus recombinant vaccine-rage administre par voie orale chez le renard, le chien et le chat. Ann Rech Vet 20 : 195-204 Blancou J, Pastoret PP, Brochier B, Thomas I, Bogel K (1988)
Vaccinating wild animals against rabies. Rev Sci Tech Off Int Epiz 7 : 1005-1013
Brochier B, Languet B, Blancou J, Kieny MP, Lecocq JP, Costy F, Desmettre P, Pastoret PP (1988) Use of recombinant vac cinia-rabies virus for oral vaccination of fox cubs (Vulpes
vulpes L.) against rabies. Vet Microbiol 18: 103-108
Brochier B, Blancou J, Aubert MFA, Kieny MP, Desmettre P, Pastoret PP (1989a) Interaction between rabies infection and oral administration of vaccinia-rabies recombinant virus to foxes (Vulpes vulpes). J Gen Virol 70: 1601-1604
Brochier B, Blancou J, Thomas I, Languet B, Artois M, Kieny MP, Lecocq JP, Costy F, Desmettre P, Chappuis G, Pastoret PP (1989b) Use of recombinant vaccinia-rabies glycoprotein virus for oral vaccination of wildlife against rabies: innocuity to several non-target bait consuming species. J Wild Dis 25 :540-547
Brochier B, Languet B, Artois M, Zanker S, Guittre C, Blancou J, Chappuis G, Desmettre P, Pastoret PP (1990a) Efficacy of a baiting system for fox vaccination against rabies with vaccinia rabies recombinant virus. Vet Rec 127 : 165-167
Brochier B, Thomas I, Bauduin B, Leveau T, Pastoret PP, Lan guet B, Chappuis G, Desmettre P, Blancou J, Artois M (1990b) Use of vaccinia-rabies recombinant virus for the oral vaccination of foxes against rabies. Vaccine 8: 101-104 Brochier B, Kieny MP, Costy F, Coppens P, Bauduin B, Lecocq
JP, Languet B, Chappuis G, Desmettre P, Afiademanyo K, Libois R, Pastoret PP (1991a) Large-scale eradication of rabies using recombinant vaccinia-rabies vaccine. Nature 354: 520-522
Brochier B, Costy F, Hallet L, Duhaut R, Peharpre D, Afiadema nyo K, Bauduin B, Pastoret PP (1991 b) Controle de la rage en
Belgique. Resultats obtenus apres trois campagnes de vaccina tion du renard roux. Ann Med Vet 135: 191-201
Coppens P, Brochier B, Costy F, Peharpre D, Marchal A, Hallet L, Duhaut R, Bauduin B, Afiademanyo K, Libois R, Pastoret PP (1992) Lutte centre la rage en Belgique: bilan epidemiolo gique 1991 et strategie future. Ann Med Vet 136: 129-135 Desmettre P, Languet B, Chappuis G, Brochier B, Thomas I, Le
cocq JP, Kieny MP, Blancou J, Aubert M, Artois M, Pastoret PP (1990) Use of vaccinia-rabies recombinant for oral vaccina tion of wildlife. Vet Micro biol 23: 227-236
Hanlon CA, Ziemer EL, Hamir AN, Rupprecht CE (1989) Cere brospinal fluid analysis of rabid and vaccinia-rabies glycopro tein recombinant, orally vaccinated raccoons (Procyon lotor). Am J Vet Res 50 :364
Kieny MP, Lathe R, Drillien R, Spehner S, Skory D, Schmitt T, Wiktor T, Koprowski H, Lecocq JP (1984) Expression of ra bies virus glycoprotein from a recombinant vaccinia virus. Na ture 312: 163-166
Leblois H, Flamand A (1988) Studies in pathogenicity in mice of rabies virus strains used for oral vaccination of foxes in Eu rope. In: Pastoret PP, Brochier B, Thomas I, Blancou J (eds) Vaccination to control rabies in foxes. Office for Official Pub lications of the European Communities, Brussels, Luxem bourg, pp 101-104
Pastoret PP, Brochier B (1991) Biological control of wild animal infections. Curr Opin Biotechnol 2: 465-469
Pastoret PP, Brochier B, Languet B, Thomas I, Paquet A, Bau duin B, Kieny MP, Lecocq JP, Debruyn J, Costy F, Antoine H, Desmettre P (1988) First field trial of fox vaccination against rabies using a vaccinia-rabies recombinant virus. Vet Rec 123: 481-483
Pastoret PP, Brochier B, Blancou J, Artois M, Aubert MFA, Kie ny MP, Lecocq JP, Languet B, Chappuis G, Desmettre P
(1992) Development and deliberate release of a vaccinia-rabies recombinant virus for the oral vaccination of foxes against ra bies. In: Binns MM, Smith GL (eds) Recombinant poxviruses. CRC Press, Boca Raton, Fla, pp 163-206
Rupprecht CE, Hamir AN, Johnston DH, Koprowski H (1988) Efficacy of a vaccine-rabies glycoprotein recombinant virus vaccine in raccoons (Procyon lotor). Rev Infect Dis 10: 803-809
Rupprecht CE, Charlton KM, Artois M, Casey GA, Webster WA, Campbell JB, Lawson KF, Schneider LG (1990) Ineffective ness and comparative pathogenicity of attenuated rabies virus vaccines for the striped skunk (Mephitis mephitis). J Wild Dis 26 :99-102
Rupprecht CE, Hanlon CA, Cummins LB, Koprowski H (1992) Primate responses to a vaccinia-rabies glycoprotein recombi nant virus vaccine. Vaccine 10 : 368-374
Thomas I, Brochier B, Languet B, Peharpre D, Desmettre P, Kie ny MP, Pastoret PP (1990) Multiplication site of the vaccinia rabies glycoprotein recombinant virus administered by the oral route in foxes. J Gen Virol 71 :37-42
Tolson ND, Charlton KM, Stewart RB, Campbell JB, Wiktor TJ (1987) Immune response in skunks to a vaccinia virus recombi nant expressing the rabies virus glycoprotein. Can J Vet Res 51 :363-366
Tuffereau C, Leblois H, Benejean J, Coulon P, Lafaye E, Fla mand A (1989) Arginine or lysine in position 333 of ERA and CVS glycoprotein is necessary for rabies virulence in adult mice. Virology 172 :206-212
Wiktor TJ, MacFarlan RI, Reagan K, Dietzschold B, Curtis P, Wunner WH, Kieny MP, Lathe R, Lecocq JP, Mackett M, Moss B, Koprowski H (1984) Protection from rabies by a vac cinia virus recombinant containing the rabies virus glycopro tein gene. Proc Natl Acad Sci USA 81 :7194-7198
Rabies cases (n) 600 500 400 300 200 100 0 • Wild
D
Domestic 81 82 83 84 85 86 87 88 89 90 91 92tHH
VaccinationFig. 1. Evolution of animal rabies in Belgium, 1981-1992. Ar
rows, full campaigns of fox vaccination in the infected area
(10000 km2)
during the first period was 74%; 6 of the 9 rabid and 11 of the 14 healthy foxes were positive for tetracycline. During the second collection period bait-uptake rates were 80% (25/31) in adult foxes but only 49% (27/55) in juveniles. During spring dispersal of baits, most cubs (born principally in March) would be expected to be confined to the immediate surroundings of the breeding den, and thus less likely to ingest baits. No rabid fox was recorded during this period (0/86). After the third phase of vaccination (October 1990), 81 OJo (64/79) of in spected animals were tetracycline positive. The one ra bid animal recorded, at the periphery of the baited area, was tetracycline-negative. Serological data are currently misunderstood because of strong discordances in the re sults obtained with the rapid fluorescent foci inhibition test (RFFIT) and the ELISA technique. The poor quali ty of blood samples collected from dead animals gener ally induces non-specific reactions. Serological results would be reliable when using fresh sera only (Brochier et al. 1990b).
Despite the dramatic decrease in the number of rabid foxes recorded after vaccine-bait distribution, the effica cy of the vaccination campaign was difficult to evaluate because systematic collection of foxes is not logistically feasible. Because transmission of rabies to domestic ani mals occurs through the bite of a rabid wild animal, however, and because notification of cases of rabies in cattle and sheep is mandatory in Belgium, the incidence of rabies in domestic livestock provides a reliable indica tor of the prevalep.ce of rabies in the wild. No case of livestock rabies has been recorded in the study zone since the second phase of vaccination. Our results there fore indicate that the dispersion of live recombinant vac cinia virus VVT Gg RAB can be an effective means of controlling rabies.
In autumn 1989, a first campaign of fox vaccination was carried out in the whole infected area of Belgium
(10000 km2
). Similar full campaigns were then repeated four times: in spring and autumn 1990 and spring and
autumn 1991. Starting in 1990 the VVT Gg RAB was used because of its efficacy, stability and safety. During each campaign, 150 000 vaccine baits were dropped by aircraft (mean 15 baits/km -2
).
As shown in Fig. 1, these campaigns have brought about a drastic decrease in the incidence of rabies, both in foxes and in domestic animals. From April 1991 to the time of writing, that is to say for more than a year, all rabies cases were recorded in a 2000-km 2 region along the border with France. Rabies has disappeared from the majority of the initial infected area. In light of this epidemiological situation a new spatial strategy for bait dispersal was initiated in 1992, namely formation of an immune belt along international borders. Two "de fence" campaigns were carried out in April and October 1992 (Brochier et al. 1991b; Coppens et al. 1992).
References
Artois M, Charlton KM, Tolson ND, Casey GA, Knowles MK, Campbell JB (1990) Vaccinia recombinant virus expressing the rabies virus glycoprotein: safety and efficacy trials in Canadian wildlife. Can J Vet Res 54: 504-507
Bingham J, Foggin CH, Gerber H, Hill FWG, Kappeler A, King AA, Perry BD, Wandeler AI (1992) The pathogenicity of SAD rabies vaccine in chacma baboons (Papio ursinus) given by the oral route. Vet Rec 131: 55-56
Blancou J, Kieny MP, Lathe R, Lecocq JP, Pastoret PP, Soule bot JP, Desmettre P (1986) Oral vaccination of the fox against rabies using a live recombinant vaccinia virus. Nature 322:373-375
Blancou J, Artois M, Brochier B, Thomas I, Pastoret PP, Des mettre P, Languet B, Kieny MP (1989) Innocuite et efficacite du virus recombinant vaccine-rage administre par voie orale chez le renard, le chi en et le chat. Ann Rech Vet 20: 195-204 Blancou J, Pastoret PP, Brochier B, Thomas I, Bogel K (1988)
Vaccinating wild animals against rabies. Rev Sci Tech Off Int Epiz 7: 1005-1013
Brochier B, Languet B, Blancou J, Kieny MP, Lecocq JP, Costy F, Desmettre P, Pastoret PP (1988) Use of recombinant vac cinia-rabies virus for oral vaccination of fox cubs (Vulpes
vulpes L.) against rabies. Vet Microbial 18: 103-108
Brochier B, Blancou J, Aubert MF A, Kieny MP, Desmettre P, Pastoret PP (1989a) Interaction between rabies infection and oral administration of vaccinia-rabies recombinant virus to foxes (Vulpes vulpes). J Gen Virol 70: 1601-1604
Brochier B, Blancou J, Thomas I, Languet B, Artois M, Kieny MP, Lecocq JP, Costy F, Desmettre P, Chappuis G, Pastoret PP (1989b) Use of recombinant vaccinia-rabies glycoprotein virus for oral vaccination of wildlife against rabies: innocuity to several non-target bait consuming species. J Wild Dis 25:540-547
Brochier B, Languet B, Artois M, Zanker S, Guittre C, Blancou J, Chappuis G, Desmettre P, Pastoret PP (1990a) Efficacy of a baiting system for fox vaccination against rabies with vaccinia rabies recombinant virus. Vet Rec 127: 165-167
Brochier B, Thomas I, Bauduin B, Leveau T, Pastoret PP, Lan guet B, Chappuis G, Desmettre P, Blancou J, Artois M (1990b) Use of vaccinia-rabies recombinant virus for the oral vaccination of foxes against rabies. Vaccine 8: 101-104 Brochier B, Kieny MP, Costy F, Coppens P, Bauduin B, Lecocq
JP, Languet B, Chappuis G, Desmettre P, Afiademanyo K, Libois R, Pastoret PP (1991a) Large-scale eradication of rabies using recombinant vaccinia-rabies vaccine. Nature 354: 520-522
Brochier B, Costy F, Hallet L, Duhaut R, Peharpre D, Afiadema nyo K, Bauduin B, Pastoret PP (1991 b) Controle de la rage en
Belgique. Resultats obtenus apres trois campagnes de vaccina tion du renard roux. Ann Med Vet 135: 191-201
Coppens P, Brochier B, Costy F, Peharpre D, Marchal A, Hallet L, Duhaut R, Bauduin B, Afiademanyo K, Libois R, Pastoret PP (1992) Lutte contre la rage en Belgique: bilan epidemiolo gique 1991 et strategie future. Ann Med Vet 136: 129-135 Desmettre P, Languet B, Chappuis G, Brochier B, Thomas I, Le
cocq JP, Kieny MP, Blancou J, Aubert M, Artois M, Pastoret PP (1990) Use of vaccinia-rabies recombinant for oral vaccina tion of wildlife. Vet Micro biol 23: 227-236
Hanlon CA, Ziemer EL, Hamir AN, Rupprecht CE (1989) Cere brospinal fluid analysis of rabid and vaccinia-rabies glycopro tein recombinant, orally vaccinated raccoons (Procyon lotor). Am J Vet Res 50:364
Kieny MP, Lathe R, Drillien R, Spehner S, Skory D, Schmitt T, Wiktor T, Koprowski H, Lecocq JP (1984) Expression of ra bies virus glycoprotein from a recombinant vaccinia virus. Na ture 312: 163-166
Leblois H, Flamand A (1988) Studies in pathogenicity in mice of rabies virus strains used for oral vaccination of foxes in Eu rope. In: Pastoret PP, Brochier B, Thomas I, Blancou J (eds) Vaccination to control rabies in foxes. Office for Official Pub lications of the European Communities, Brussels, Luxem bourg, pp 101-104
Pastoret PP, Brochier B (1991) Biological control of wild animal infections. Curr Opin Biotechnol 2: 465-469
Pastoret PP, Brochier B, Languet B, Thomas I, Paquot A, Bau duin B, Kieny MP, Lecocq JP, Debruyn J, Costy F, Antoine H, Desmettre P (1988) First field trial of fox vaccination against rabies using a vaccinia-rabies recombinant virus. Vet Rec 123:481-483
Pastoret PP, Brochier B, Blancou J, Artois M, Aubert MFA, Kie ny MP, Lecocq JP, Languet B, Chappuis G, Desmettre P
(1992) Development and deliberate release of a vaccinia-rabies recombinant virus for the oral vaccination of foxes against ra bies. In: Binns MM, Smith GL (eds) Recombinant poxviruses. CRC Press, Boca Raton, Fla, pp 163-206
Rupprecht CE, Hamir AN, Johnston DH, Koprowski H (1988) Efficacy of a vaccine-rabies glycoprotein recombinant virus vaccine in raccoons (Procyon lotor). Rev Infect Dis 10: 803-809
Rupprecht CE, Charlton KM, Artois M, Casey GA, Webster WA, Campbell JB, Lawson KF, Schneider LG (1990) Ineffective ness and comparative pathogenicity of attenuated rabies virus vaccines for the striped skunk (Mephitis mephitis). J Wild Dis 26:99-102
Rupprecht CE, Hanlon CA, Cummins LB, Koprowski H (1992) Primate responses to a vaccinia-rabies glycoprotein recombi nant virus vaccine. Vaccine 10: 368-374
Thomas I, Brochier B, Languet B, Peharpre D, Desmettre P, Kie ny MP, Pastoret PP (1990) Multiplication site of the vaccinia rabies glycoprotein recombinant virus administered by the oral route in foxes. J Gen Virol 71 : 37-42
Tolson ND, Charlton KM, Stewart RB, Campbell JB, Wiktor TJ (1987) Immune response in skunks to a vaccinia virus recombi nant expressing the rabies virus glycoprotein. Can J Vet Res 51:363-366
Tuffereau C, Leblois H, Benejean J, Coulon P, Lafaye E, Fla mand A (1989) Arginine or lysine in position 333 of ERA and CVS glycoprotein is necessary for rabies virulence in adult mice. Virology 172: 206-212
Wiktor TJ, MacFarlan RI, Reagan K, Dietzschold B, Curtis P, Wunner WH, Kieny MP, Lathe R, Lecocq JP, Mackett M, Moss B, Koprowski H (1984) Protection from rabies by a vac cinia virus recombinant containing the rabies virus glycopro tein gene. Proc Natl Acad Sci USA 81: 7194-7198
