Bernard Brochier

Examination of red foxes (Vulpes vulpes) from Belgium for antibody to Neospora caninum and Toxoplasma gondii

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Epidemiology and control of fox rabies in Europe.

During recent years, most of the research on the control of sylvatic rabies has concentrated on developing methods of oral vaccination of wild rabies vectors. In order to improve both the safety and the stability of the vaccine used, a recombinant vaccinia virus which expresses the immunizing glycoprotein of rabies virus (VRG) has been developed and extensively tested in the laboratory as well as in the field. From 1989 until 1995, several million VRG vaccine doses have been dispersed in western Europe for vaccination of red foxes. In Europe, the use of VRG has lead to the elimination of sylvatic rabies from large areas, which have consequently been freed from vaccination. This may have consequences on the regulation of pets movements within the whole European Union.

Use of a vaccinia-rabies recombinant virus for the oral vaccination of foxes against rabies

The vaccination of wild animals against rabies has been developed most extensively in Europe. Experiments have demonstrated the efficacy of a vaccinia-rabies recombinant virus administered by the oral route in foxes. The innocuity of this vaccine was tested in the target species as well as in several non-target wild and domestic species. Because of its safety and heat-stability, this recombinant virus should offer an excellent alternative to the attenuated strains of rabies virus currently used in the field. A large scale field trial was conducted in Belgium in October 1988 to assess the efficacy of this new vaccine-bait systems.

Potential pathogenicity for rodents of vaccines intended for oral vaccination against rabies: a comparison.

Different oral vaccines intended to control fox rabies were administered to 271 wild rodents. Vaccines were administered orally or by the mucosal route to four different European species belonging to the genera Apodemus, Arvicola, Clethrionomys and Microtus. These rodents are likely to consume baits and to have contact with the vaccine. Two genetically engineered vaccines were tested: SAG1 (an avirulent mutant of the rabies virus) and V-RG (vaccinia recombinant virus expressing the rabies glycoprotein gene). Both were found to be completely innocuous when administered orally or by the mucosal route. The residual pathogenicity of conventional modified live vaccines derived from the SAD strain was confirmed.

Use of recombinant vaccinia-rabies virus for oral vaccination of fox cubs (Vulpes vulpes, L) against rabies

Thirteen fox cubs were orally administered 10(7.2) plaque-forming units of live vaccinia-rabies glycoprotein recombinant virus. On Day 28 post-vaccination, all but 1 cub had produced rabies virus antibodies. Twelve animals were intramuscularly inoculated with 10(3.2) mouse intracerebral LD50 of rabies virus suspension on Days 33 (5 foxes), 180 (4 foxes) or 360 (3 foxes) after vaccination. Eleven of them resisted rabies challenge. Unvaccinated foxes, either put in contact with 1 vaccinated animal or used as controls, died after challenge applied on Day 33. The absence of horizontal transmission of this vaccine strain and its innocuity to cubs were also demonstrated.

Elimination of fox rabies from Belgium using a recombinant vaccinia-rabies vaccine: an update

To improve both safety and stability of the vaccines used in the field to vaccinate foxes against rabies by the oral route, a recombinant vaccinia virus, expressing the glycoprotein of rabies virus (VVTGgRAB) has been developed. VVTGgRAB innocuity was verified in target species and in domestic animals as well as in numerous wild animal species that could compete with the red fox in consuming vaccine baits in Europe. Oral immunization of foxes, by distributing VVTGgRAB vaccine-baits, was undertaken in the whole of the infected area of Belgium (10,000 km2). Five campaigns of fox vaccination covering the whole infected area were carried out from the autumn of 1989 until 1991. Each time, 150,000 vaccine-baits were dispersed by air at a mean density of 15 per km2. These campaigns induced a drastic decrease in the incidence of rabies and the elimination of the disease from 80% of the initial infected area. Regarding the geographical evolution of rabies in Belgium and in adjacent regions in neighbouring countries, new spatial strategies for bait dispersal were planned for 1992, 1993 and 1994: successive restricted campaigns were carried out along political borders only. These campaigns induced a new decrease of incidence; no rabid foxes could be detected in 1993 in spite of an improved epidemiological surveillance. In 1994, rabies was confirmed again in 13 foxes collected in a region situated close to the French border. These cases demonstrate the persistence of a focus of rabies on the border and justify further restricted campaigns of vaccination.

The Role of Latency in the Epizootiology of Infectious Bovine Rhinotracheitis

Latency is one of the major problems associated with the infection of cattle by the virus of Infectious Bovine Rhinotracheitis/Infectious Pustular Vulvovaginitis, or Bovineherpesvirus 1 (BHV 1). Both wild virulent strains and the attenuated vaccine strains can remain latent in cattle and may be reactivated by several stimuli including the use of glucocorticoids, such as dexamethasone.

Serological survey for orthopoxvirus infection of wild mammals in areas where a recombinant rabies virus is used to vaccinate foxes.

Several fox vaccination campaigns against rabies have been undertaken in Belgium by using a vaccinia-rabies recombinant virus distributed in baits in the field. However, foxes and other wild animals that may ingest the baits could be infected at the same time by another orthopoxvirus, such as cowpox virus, which circulates in wildlife. Recombination between the two viruses could therefore occur. A serological survey for antibodies to orthopoxvirus, and particularly to cowpox virus, was undertaken in foxes and in several other wild species. Antibodies were detected only in two rodent species, in 16 of 25 bank voles (64 per cent) and in two of 29 woodmice (7 per cent). The risk of virus recombination in wildlife can therefore be considered to be extremely low.

Excretion and reexcretion of thermosensitive and wild-type strains of infectious bovine rhinotracheitis virus after co-infection or two successive infections.

Twelve cattle were divided into 2 groups. The first was intranasally co-infected with 2 strains of infectious bovine rhinotracheitis virus (Bovine herpesvirus 1; BHV 1): the thermosensitive vaccine strain IBR/ts RLB106 and a Belgian field isolate IBR/Cu5. Reactivation of BHV 1 was induced by dexamethasone treatment 2 months later and again 5 months later for 3 animals that only reexcreted small quantities of virus during the first dexamethasone treatment. The second group was intranasally infected with IBR/Cu5. Two months later, an attempt to reinfect this group with IBR/ts RLB106 failed. Four months after the primary infection, these cattle were treated with dexamethasone. Except after reinfection and at the beginning or the end of the (re)excretion periods, excreted and reexcreted viruses replicated at 35, 37 and 40 degrees C, indicating the presence of the wild-type virus. Only one isolate, out of 116 cloned from the nasal exudates collected during the excretion and reexcretion periods, expressed the thermosensitive phenotype. This isolate was characterized by its mean plaque size as the IBR/ts RLB106 strain. The epizootiological significance of these findings is discussed, with emphasis on the weak spreading capacity of the ts vaccine strain and the possibility of emergence of recombinant viruses.

Towards rabies elimination in Belgium by fox vaccination using a vaccinia-rabies glycoprotein recombinant virus

Oral immunization of foxes by distributing vaccine baits was experimentally assessed and subsequently employed in the whole of the infected area of Belgium (10,000 km2). A vaccinia-rabies glycoprotein recombinant virus (VR-G) was used as vaccine because of its efficacy, safety and heat stability. Five full campaigns of fox vaccination, carried out from 1989 until 1991, induced a drastic decrease in the incidence of rabies. The disease has disappeared from the major part of the initial infected area. In 1992 and 1993, three defence campaigns, carried out along international borders, completely eliminated rabies virus infection from the fox population in 1993.