Belgian Wildlife as Potential Zoonotic Reservoir of Hepatitis E Virus

Hepatitis E is an acute human liver disease in healthy individuals but may become chronic in immunocompromised patients. It is caused by the hepatitis E virus (HEV) and can have a zoonotic origin, particularly in high-income countries. In this study, 383 sera from wild boars were selected for serology; for virological analyses, 69 sera and 61 livers from young wild boars were used. A total of 189 and 235 sera of, respectively, red deer and roe deer were collected for serological analysis. For virological analyses, 84 and 68 sera and 29 and 27 livers from, respectively, red and roe deer were sampled. An apparent seroprevalence of 34% (95% CI 29.71-39.46) was found in wild boars, of 1% (95% CI 0-2.4) in red deer and 3% (95% CI 0.8-4.2) in roe deer. To assess the ELISA screening prevalence, Western blot (WB) analyses were carried out, a receiver operating characteristic curve analysis was performed and different scenarios with varying ELISA specificities relative to WB were analysed. Seroprevalence remained high whatever the scenario in the wild boar population. In wild boar, 4 of 69 sera and 4 of 61 livers were detected as positive for HEV RNA. All sequences obtained from sera belonged to genotype HEV-3. HEV RNA, belonging to genotype HEV-3, was detected in one of 29 red deer livers. Wild boar can be considered as a host reservoir of the virus in Belgium. However, in contrast to the epidemiological role played by them in other countries, the low prevalence in deer makes these species an unlikely reservoir. This evidence needs further investigation to determine in which situation deer can serve as reservoir. These results also raise the question of the dynamics of HEV infection between wild fauna, domestic pigs and humans.

Eradicating rabies at source

Along with zoonotic influenza and antimicrobial resistance, rabies has been identified as a key One Health issue by the World Organisation for Animal Health (OIE), World Health Organization (WHO) and Food and Agriculture Organization of the United Nations (FAO). It provides an excellent example of a disease that has an impact on public, animal and environmental health, and therefore benefits from a One Health approach to management. Regrettably, this zoonotic disease is still neglected despite the fact that, annually, it kills as many as 70,000 people worldwide (chiefly children in Asia and Africa), millions of dogs suffer and die, and the disease threatens some populations of endangered wildlife. This is particularly unfortunate, given that effective means of prevention exist. As Her Royal Highness Princess Haya of Jordan pointed out in a video to mark World Rabies Day on 28 September 2013, rabies is a serious world public health problem that is all too often underestimated and even neglected. Yet we know it can be eliminated. By combatting rabies at its source in animals and vaccinating 70% of dogs, we can eradicate it.

Favourable outcome in a patient bitten by a rabid bat infected with the European bat lyssavirus-1

The classic rabies virus (genotype 1) has been eliminated in Western Europe, but related lyssaviruses still circulate in local bats. In August 2010, a Belgian photographer was bitten upon provocation of a disoriented Eptesicus serotinus bat in Spain. The bat was infected with European bat lyssavirus-1 (genotype 5). The isolate proved highly neurovirulent in mice. The patient had received preventive rabies immunisations years before the incident and received two boosters with the HDCV rabies vaccine afterwards. Available vaccines are based on the classic rabies virus, which is significantly divergent from the European bat lyssavirus-1. Fortunately, the patient's serological immune response demonstrated satisfactory neutralisation of the 2010 EBLV-1 isolate, using an intracerebral challenge model in mice. Most likely, the patient's life was saved thanks to vaccination with the classic rabies vaccine, which proved sufficiently protective against European bat lyssavirus-1. This case highlights the need for preventive rabies vaccination in people, who come in contact with bats and to seek medical council after a scratch or bite from a bat.

Alien invasive birds

A bird species is regarded as alien invasive if it has been introduced, intentionally or accidentally, to a location where it did not previously occur naturally, becomes capable of establishing a breeding population without further intervention by humans, spreads and becomes a pest affecting the environment, the local biodiversity, the economy and/or society, including human health. European Starling (Sturnus vulgaris), Common Myna (Acridotheres tristis) and Red-vented Bulbul (Pycnonotus cafer) have been included on the list of '100 of the World's Worst Invasive Alien Species', a subset of the Global Invasive Species Database. The 'Delivering Alien Invasive Species Inventories for Europe' project has selected Canada Goose (Branta canadensis), Ruddy Duck (Oxyura jamaicensis), Rose-ringed Parakeet (Psittacula krameri) and Sacred Ibis (Threskiornis aethiopicus) as among 100 of the worst invasive species in Europe. For each of these alien bird species, the geographic range (native and introduced range), the introduction pathway, the general impacts and the management methods are presented.

Oral fluid for the serological and molecular diagnosis of measles

OBJECTIVES

Since measles presents mostly in children, a non-invasive sample collection technique such as oral fluid sampling would be very useful in the early detection of measles RNA and antibodies. The aim of this study was to validate the detection of anti-measles IgM and measles virus RNA in oral fluid and to make a comparison with the gold standard methods of ELISA using serum (Enzygnost(®) anti-Measles IgM) and in-house nested reverse transcriptase polymerase chain reaction (RT-PCR) using nasopharyngeal secretions.

METHODS

Three samples each from 73 measles-positive and 44 measles-negative subjects (serum, oral fluid, and nasopharyngeal secretions) were analyzed.

RESULTS

The anti-measles IgM ELISA (MicroImmune) on oral fluid was validated against the IgM ELISA (Siemens) for serum and this resulted in a sensitivity of 92% and specificity of 100%. A molecular nested RT-PCR using oral fluid was validated against the standard assay on nasopharyngeal secretions and gave a sensitivity of 100% and specificity of 100%.

CONCLUSIONS

The results confirm that both serological and molecular oral fluid assays are suitable for routine use. The use of oral fluid samples for the detection of measles virus may encourage patients, general practitioners, and pediatricians to participate in the Belgian measles surveillance system and other epidemiological studies in the framework of the World Health Organization elimination program.

Influenza outbreak in a well-vaccinated nursing home population in Belgium

Elderly people in nursing home communities are vulnerable to contagious infections, including the influenza virus. Systematic anti-influenza vaccination is an important preventive measure; however, vaccination does not provide absolute protection. We report an outbreak of influenza A infection in a well-vaccinated nursing home population. Several factors can facilitate the occurrence of this type of outbreak. This report mainly addresses the discrepancy between the circulating viral strain and strains present in the recommended vaccine.

Distribution of hepatitis C virus genotypes among injecting drug users in contact with treatment centers in Belgium, 2004-2005

The aim of this study was to determine the current prevalence of HCV genotypes in injecting drug users recruited at treatment centers all over Belgium, and to analyze if the distribution of genotypes was correlated with demographic characteristics, at-risk behaviors, and co-infection with other viruses. Therefore 147 anti-HCV-positive serum samples were selected for subsequent HCV RNA detection and genotyping. HCV RNA could be detected in 98 (67%) of the 147 serum samples. Genotype 1 (38%) and 3 (49%) were the most common genotypes followed by genotype 4 (9%) and genotype 2 (2%). One mixed infection (1%) was detected. The subtype could be determined in 80 cases: genotype 3a was the most prevalent (49%), followed by genotype 1a (16%) and genotype 1b (15%). No significant difference was found between the distribution of genotypes and the location of treatment centers, at-risk behaviors and co-infection with other viruses. Nevertheless, a slight variation over time could be identified (P = 0.06): one in two genotype 3 drug users started with their injecting drug use in the last 10 years (33% in the period 1995-1999 and 21% in the period > or =2000) compared to only one in four genotype 1 drug users (20% in the period 1995-1999 and 9% in the period > or =2000).

Echinococcus multilocularis and Toxocara canis in urban red foxes (Vulpes vulpes) in Brussels, Belgium

During the last decades, European red foxes (Vulpes vulpes) have been implicated in the transmission of several viral or parasitic pathogenic agents to domestic animals and humans. In urban areas, risks of zoonoses transmission are likely to increase as a result of a higher rate of intra- and inter-species contacts. Foxes occur on 35% of the Brussels-Capital Region area and local densities reach up to 4 family groups per square kilometre. According to the directive 2003/99/ECC, a first survey for the presence in foxes of Echinococcus multilocularis and Toxocara canis was conducted in Brussels from 2001 to 2004. None of 160 foxes were found to be infected with E. multilocularis and 24 of 134 foxes were found to be infected with T. canis. Considering numbers of examined foxes, the sensitivity and the specificity of tests used for diagnosis, the 95% credibility intervals for the true prevalence of E. multilocularis and T. canis were estimated in a Bayesian framework to be 0 to 1.87% (median value of 0%) and 12.7 to 26% (median value of 18.7%), respectively. For T. canis, a significantly higher risk to be a carrier occurs in cubs and a significantly lower risk in adults.

Management of potential human cases of influenza A/H5N1: lessons from Belgium

Since the first human cases of influenza A/H5N1 were widely reported from Turkey in early January, many European patients with suspected influenza

Population-level retrospective study of neurologically expressed disorders in ruminants before the onset of bovine spongiform encephalopathy (BSE) in Belgium, a BSE risk III country

A retrospective epidemiological study (n = 7,875) of neurologically expressed disorders (NED) in ruminants before the onset of the bovine spongiform encephalopathy epidemic (years studied, 1980 to 1997) was carried out in Belgium. The archives of all veterinary laboratories and rabies and transmissible spongiform encephalopathy (TSE) epidemiosurveillance networks were consulted. For all species, a significantly higher number of NED with virological causes (rabies) was reported south of the Sambre-Meuse Valley. During the period 1992 to 1997, for which the data were complete, (i) the predicted annual incidence of NED varied significantly as a function of species and area (higher numbers in areas where rabies was present) but was always above 100 cases per million, and (ii) the mean incidence of suspected TSE cases and, among them, those investigated by histopathological examination varied significantly as a function of species and area. The positive predictive value of a presumptive clinical diagnosis of NED ranged from 0.13 (game) to 0.63 (sheep). Knowledge of the positive predictive value permits the definition of a reference point before certain actions (e.g., awareness and training campaigns) are undertaken. It also shows the usefulness of a systematic necropsy or complementary laboratory tests to establish an etiological diagnosis. TSE analysis of a small, targeted historical sampling (n = 48) permitted the confirmation of one case and uncovered another case of scrapie. The results of the present study help to develop and maintain the quality of the worldwide clinical epidemiological networks for TSE, especially in countries that in the past imported live animals, animal products, and feedstuffs from countries with TSE cases.

Prevalence of Echinococcus multilocularis in the red fox (Vulpes vulpes) in southern Belgium

Between June 1998 and February 2002, 709 red foxes killed in Wallonia (south of Belgium) were available for parasitological examination of the gut. The identification of Echinococcus multilocularis was based on morphological data. E. multilocularis adults were observed in 20.2% of the animals. The analysis of data revealed marked differences between the geological areas of Wallonia; the highest prevalence (33%) was found in the Ardenne and the lowest (0%) on the Plateau de Herve. Host gender and the collection season had no effect on the prevalence. However, the latter was significantly higher in juveniles (<8 months of age). The geographical distribution of E. multilocularis in Belgium is much wider than originally thought.

Survey for Trichinella spp. in red foxes (Vulpes vulpes) in Belgium

Concurrently with a survey for Echinococcus multilocularis in the red fox (Vulpes vulpes) in Flanders, northern Belgium, serological and parasitological analyses for Trichinella spp. were carried out from 1996 to 1999. Muscle samples from foxes in Wallonia, southern Belgium, were obtained during a survey for rabies and alveolar echinococcosis from 1998 to 2000. In muscle samples from tongue, diaphragm, hindlegs and tail of 179 Flemish foxes no larvae were found by trichinoscopy. Serum and muscle juice of, respectively 176 and 26 animals were examined using an ELISA for the detection of antibodies against excretory-secretory (ES) antigen. There were eight (4.5%) positive sera, but no positive muscle juice samples. All muscle samples from 639 foxes in Wallonia proved to be negative for larvae in artificial digestion. Serum and muscle juice of 130 and 478 foxes, respectively were examined in ES-ELISA. There were 61 (46.9%) positive sera and 90 (18.8%) positive muscle juice samples. A comparison between 88 serum and muscle juice samples of the same foxes showed that only half of the serum-positive animals were detected using muscle juice. However, for establishing the true meaning of these results, a more profound epidemiological study on the vulpine population in Belgium is necessary.

Kinetics of humoral immune response after rabies VR-G oral vaccination of captive fox cubs (Vulpes vulpes) with or without maternally derived antibodies against the vaccine

In western Europe during the spring, the largest proportion of fox populations are cubs and the key to successful rabies oral vaccination campaigns is cub vaccination. In this paper we report on studies of the serology of 93 fox (Vulpes vulpes) cubs born to unvaccinated and orally vaccinated captive vixens, some of which were orally vaccinated at 30 or at 90 days of age with the vaccinia recombinant vaccine (VR-G) that expresses the rabies virus glycoprotein. The duration of cub passively acquired antibody, the development of immune responses to oral vaccination at either 30 or 90 days of age, possible interference between passive and active immunity to such vaccination and resistance to a potentially lethal rabies challenge dose when five months old were measured. The study showed that rabies neutralising antibody can be passed to their cubs by vixens orally vaccinated with VR-G during pregnancy. Maternally derived antibody titres in cubs declined with time and disappeared by 45-75 days after birth. Thirty days old cubs serologically responded to oral vaccination. No interference between antibody of maternal origin and active immunity conferred by VR-G oral vaccination or between antibody of maternal origin and protection was observed. Thus, very young cub immunisation against rabies with VR-G per os is possible whatever the immune status of their mothers. Provided a vaccine-bait suitable for such young cubs exists, oral vaccination at den entrances with VR-G is a feasibility.

Humoral and cell-mediated immune responses of foxes (Vulpes vulpes) after experimental primary and secondary oral vaccination using SAG2 and V-RG vaccines

Humoral and cell-mediated immune responses of 36 captive foxes to two oral vaccines against rabies currently used for foxes in Europe were studied. The Street Alabama Dufferin (SAD) mutant Gif (SAG2) vaccine has been selected by double mutation from the SAD virus. The vaccinia recombinant virus (V-RG) expresses the rabies glycoprotein. Both vaccines induce similar humoral and cell-mediated responses after primary and secondary oral administration. We observed a typical anamnestic response, although of a limited duration, after the booster vaccination. Therefore, our results suggested that two successive oral vaccination campaigns should not significantly improve the immunisation of foxes. Lymphocyte in vitro proliferative response to the SAD antigen highlighted the presence in blood of a T-cell specific memory 6 months after vaccination. The synthesis of several vulpine cytokines was detected in peripheral blood mononuclear cells (PBMC) stimulated by SAD antigen via reverse transcription polymerase chain amplification. The data showed a concomitant expression of interleukin (IL)-4 and interferon-gamma in PBMC of vaccinated foxes. No change was detected in the level of IL-2, IL-10 and IL-12 synthesis, whereas the pro-inflammatory cytokine tumour necrosis factor-alpha seemed involved in the activation of naive T lymphocytes.

Animals, public health and the example of cowpox

Public attitudes towards animals are often contradictory. In developed countries where the problem of food security has been solved to a large degree, public concern is concentrated on food safety and animal welfare, along with a debate on the social status of both domestic and wild animals. Zoonoses are often the focal point of these concerns. In developing countries (which often have the greatest biodiversity), wildlife constitutes an uncontrollable source of often unknown zoonoses. The authors attempt to analyse the link between animals and public health. Special attention is given to the example of cowpox, a disease which has been recognised as a zoonosis for more than two centuries but the epidemiology of which has recently been rediscovered.

Tick-borne rickettiosis in Guadeloupe, the French West Indies: isolation of Rickettsia africae from Amblyomma variegatum ticks and serosurvey in humans, cattle, and goats

Twenty-seven rickettsiae were isolated and/or detected from 100 Amblyomma variegatum ticks collected on Guadeloupe in the French West Indies. In this study, the polymerase chain reaction procedure appeared to be more sensitive in detecting rickettsiae in ticks than the shell-vial technique. Sequencing a portion of the outer membrane protein A-encoding gene showed that these rickettsiae appeared to be identical to Rickettsia africae, a member of the spotted fever group rickettsiae recently described as an agent of African tick-bite fever occurring in sub-Sahelian Africa. A high seroprevalence of antibodies to R. africae was demonstrated among mammals, particularly humans, cattle, and goats. These results and a recently reported case of an infection due to R. africae on Guadeloupe demonstrate that R. africae is present on this island. Although this disease has been underdiagnosed there, it may be frequent and may exist on other Caribbean islands where A. variegatum has propagated dramatically over recent years.

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.

Discrimination between epidemiological cycles of rabies in Mexico

BACKGROUND

The design of efficient rabies control programs within a geographic area requires an appropriate knowledge of the local epidemiological cycles. In Latin America, there is a geographical overlap of the two main epidemiological cycles: (a) the terrestrial cycle, where the dog is the main terrestrial vector and the principal cause of human transmission; and (b) the aerial cycle, in which the vampire bat Desmodus rotundus is representative in Mexico. This bat is the major sylvatic rabies vector transmitting rabies to cattle. The purpose of this study was to distinguish between the epidemiological cycles of rabies virus (aerial and terrestrial) circulating in Mexico, using restriction fragment length polymorphism (RFLP).

METHODS

Thirty positive rabies isolates were obtained from different species (including humans, domestic, and wildlife animals) and geographical regions. The methodology included the extraction of RNA, and synthesis of cDNA, PCR, and RFLP using four restriction endonucleases. To determine the aerial cycle, BsaW I and BsrG I were utilized, and for terrestrial cycle, BamH I and Stu I. Most of the samples belonged to the aerial and terrestrial cycles, except for two skunk isolates from Northwestern Mexico, which were not cut by any of the enzymes.

RESULTS

Three different migration patterns were detected: (a) the first was observed in six amplicons, which were cut by BsaW I and BsrG I (aerial cycle); (b) 19 amplified samples were digested with BamH I and Stu I enzymes (terrestrial cycle); and (c) two skunk isolates from Northwest Mexico, were not cut by any of the enzymes utilized in the experiments (hypervariable cycle).

CONCLUSIONS

This concludes that RFLP can be used for the classification of rabies field samples in epidemiological studies. Moreover, it has demonstrated its usefulness, not only for differentiating between the main epidemiological rabies cycles present in Mexico, but also to detect new cycles in wildlife species.

Epidemiology and elimination of rabies in western Europe

In 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. Between 1989 and 1995, several million VRG vaccine doses have been dispersed in Western Europe for the vaccination of red foxes, leading to the elimination of sylvatic rabies from large areas, which have consequently been freed from the need for vaccination. This approach may have consequences for the regulation of pet movement within the whole European Union.

Experimental rabies infection and oral vaccination in vampire bats (Desmodus rotundus)

A rabies virus variant isolated from a vampire bat (Desmodus rotundus) and characterized by genome sequencing was used for the standardization of an experimental infection in this species. The parenteral administration of 10(6) MICLD50 of this variant was capable of inducing death from rabies in 89% of animals. The mean duration of post-challenge survival was 12 days. None of the experimental rabid vampire bats showed aggressive behaviour. A vaccinia-rabies glycoprotein recombinant virus vaccine was administered orally to vampire bats on days -120, -90, -30 or -18 pre-challenge, on the same day of challenge, or on day +5 post-challenge. A significant protection was noticed only in animals vaccinated on days -18 or -30 pre-challenge. A longer period of incubation was observed in animals vaccinated 5 days post-challenge.

Field use of a vaccinia-rabies recombinant vaccine for the control of sylvatic rabies in Europe and North America

During recent years, most research on the control of sylvatic rabies has concentrated on developing methods of oral vaccination of wild rabies vectors. To improve both the safety and the stability of the vaccine used, a recombinant vaccinia virus, which expresses the immunising glycoprotein of rabies virus (VRG), has been developed and tested extensively in the laboratory as well as in the field. From 1989 to 1995, approximately 8.5 million VRG vaccine doses were dispersed in Western Europe to vaccinate red foxes (Vulpes vulpes), and in the United States of America (USA) to vaccinate raccoons (Procyon lotor) and coyotes (Canis latrans). In Europe, the use of VRG has led to the elimination of sylvatic rabies from large areas of land, which have consequently been freed from the need for vaccination. Nevertheless, despite very good examples of cross-border cooperation, reinfections have occurred in some regions, due to the difficulty of co-ordinating vaccination plans among neighbouring countries. In the USA, preliminary data from field trails indicate a significant reduction in the incidence of rabies in vaccinated areas.

The development and use of a vaccinia-rabies recombinant oral vaccine for the control of wildlife rabies; a link between Jenner and Pasteur

To improve both safety and stability of the oral vaccines used in the field to vaccinate foxes against rabies, a recombinant vaccinia virus, which expresses the immunizing G protein of rabies virus has been developed by inserting the cDNA which codes for the immunogenic glycoprotein of rabies virus into the thymidine kinase (TK) gene of the Copenhagen strain of vaccinia virus. The efficacy of this vaccine was tested by the oral route, primarily in foxes. The immunity conferred, a minimum of 12 months in cubs and 18 months in adult animals, corresponds to the duration of the protection required for vaccination of foxes in the field. Innocuity was tested in foxes, domestic animals, and in numerous European wild animal species that could compete with the red fox for the vaccine bait. No clinical signs or lesions were observed in any of the vaccinated animals during a minimum of 28 days post vaccination. Moreover, no transmission of immunizing doses of the recombinant occurred between foxes or other species tested. To study the stability of the vaccine strain, baits containing the vaccine were placed in the field. Despite considerable variations of environmental temperatures, the vaccine remained stable for at least one month. Because bait is taken within one month, it can be assumed that most animals taking the baits are effectively vaccinated. To test the field efficacy of the recombinant vaccine, large-scale campaigns of fox vaccination were set up in a 2200 km2 region of southern Belgium, were rabies was prevalent. A dramatic decrease in the incidence of rabies was noted after the campaigns. The recombinant is presently used to control wildlife rabies in the field both in several European countries and in the United States.

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.

Stability of recombinant vaccinia-rabies vaccine in veterinary use

Wildlife vaccination depends on vaccines which can be orally administered by a baiting system. Therefore only two possibilities exist: either the use of attenuated strains of viruses, or recombinant vector viruses. As far as rabies is concerned, the choice of the recombinant vaccinia-rabies virus was made because it was safer and more stable. An in vitro stability study of the recombinant product compared to wild rabies virus at different temperatures (4 degrees C, 20 degrees C, 37 degrees C, 45 degrees C) showed that the recombinant virus was more stable. The stability of the recombinant virus was also tested under field conditions; besides natural freezing and thawing cycles, the virus titre remained unchanged in the bait for a month. Taking into account the fact that all baits are eaten by wild animals within this period, one can assume that the vaccine is efficacious for all baiting animals in field conditions. The stability of the recombinant vaccinia-rabies vaccine is of considerable interest in such uncontrolled conditions.

Environmental safety assessment of vaccines derived from biotechnology

Products derived from biotechnology are generally safer than previous products obtained by conventional, more empirical methods. Given the great variety of biotechnology-derived products and use situations, risk assessment procedures must be based on a case-by-case analysis. It is therefore difficult to propose a generic, well-defined risk assessment procedure. In the case of vectored vaccines, two main risks must clearly be assessed: the possible risk of tissue or species tropism modification, with special regard to non-target species, the risk of recombination with wild counterparts of the vector. This paper begins with a classification and description of the main biotechnology-derived products to be used in veterinary medicine, including deoxyribonucleic acid (DNA) vaccines, and then attempts to define general rules for the risk assessment of each category of products.

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.

Field trials of a recombinant rabies vaccine

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 for the whole infected area in Belgium (10,000 km2). Five campaigns of fox vaccination, were carried out from autumn 1989 until 1991. Each time, 150,000 vaccine-baits were dropped 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 initially 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 confined campaigns were carried out along political borders only. These campaigns induced a new decrease of incidence; no rabid fox could be detected in 1993 in spite of an improved epidemiological surveillance. In 1994, rabies was again confirmed in 13 foxes collected in an area close to the French border. These cases demonstrated the persistence of a border rabies focus and justify further restricted vaccination campaigns.

Comparison of the susceptibility of the red fox (Vulpes vulpes) to a vaccinia-rabies recombinant virus and to cowpox virus

Sylvatic rabies can be efficiently controlled by vaccination of foxes with a vaccinia-rabies recombinant virus. However, the risk of recombination between the engineered vaccine virus and other orthopoxviruses endemic in wildlife, such as cowpox virus, still needs to be investigated. In this study, foxes inoculated orally and intradermally with cowpox virus were found to be not very susceptible to cowpox virus, which was isolated from only the oropharynx and tonsils, at low titre and for only five days after inoculation. Thus the risk of recombination between these viruses in foxes is very low.

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.

Rabies eradication in Belgium by fox vaccination using vaccinia-rabies recombinant virus

Oral immunization of foxes against rabies, by distributing vaccine-baits in the field, has been in progress since 1993 in the whole of the infected area of Belgium (10,000 km2). A vaccinia-rabies recombinant virus (VR-G) was used as vaccine because of its efficacy, safety and heat-stability. The successive campaigns of fox vaccination have induced a drastic decrease in rabies incidence and in 1993 there were no cases of rabies detected in the fox population. A marked decrease of human post-exposure treatments and the elimination of the disease in domestic animals have been the consequence of fox rabies control.

Deliberate release of a recombinant vaccinia-rabies virus for vaccination of wild animals against rabies

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 virus has been developed and released in the field. The first safety-efficacy results are very encouraging.

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.

Large-scale eradication of rabies using recombinant vaccinia-rabies vaccine

Rabies infection of domestic and wild animals is a serious problem throughout the world. The major disease vector in Europe is the red fox (Vulpes vulpes) and rabies control has focused on vaccinating and/or culling foxes. Culling has not been effective, and the distribution of five vaccine baits is the only appropriate method for the vaccination of wild foxes. Although some European countries have conducted field vaccination campaigns using attenuated rabies virus strains, their use has not been extensively approved because they retain pathogenicity for rodents and can revert to virulence. These strains cannot be used in North America because they are pathogenic for the striped skunk (Mephitis mephitis) and are ineffective in the raccoon (Procyon lotor). We have constructed a recombinant vaccinia virus, VVTGgRAB, expressing the surface glycoprotein (G) of rabies virus (ERA strain). The recombinant was a highly effective vaccine in experimental animals, in captive foxes and in raccoons. We report here the results of a large-scale campaign of fox vaccination in a 2,200 km2 region of southern Belgium, an area in which rabies is prevalent. After distribution, 81% of foxes inspected were positive for tetracycline, a biomarker included in the vaccine bait and, other than one rabid fox detected close to the periphery of the treated area, no case of rabies, either in foxes or in domestic livestock, has been reported in the area.

Biological control of wild animal infections

Until recently, there were few examples of biological control of wild animal infections. The most significant development in this field is the use of a vaccinia--rabies recombinant virus or other recombinants for the control of rabies by oral vaccination of vectors, both in Europe and in North America.

[Epidemiological study of toxoplasmosis at Kinshasa and in lower Zaire]

An epidemiological survey of human toxoplasmosis was carried out in urban Kinshasa and in rural Kwilu-Ngongo (Bas-Zaïre). First contact with Toxoplasma gondii occurred earlier in children from Kinshasa, but adults aged over 30 were more often carriers of IgG antibodies in Kwilu-Ngongo (65.5%) compared to those in Kinshasa (50.2%). In Zaire, nutritional diet and telluric contact seem to be very important.

Use of vaccinia rabies recombinant for oral vaccination of wildlife

A vaccinia rabies recombinant virus was constructed and shown to induce the synthesis of rabies virus glycoprotein in infected cells and to induce rabies virus neutralizing antibodies and protection in susceptible animals. Active when orally administered, this recombinant is a good candidate for the development of vaccines for wild animal rabies vectors. This recombinant was found stable, safe for target and non-target animal species, and protective for most of the rabies vectors. After extensive experimental studies conducted under controlled conditions, it as used in limited field trials and in an extensive open field trial. The preliminary results confirmed its basic properties and potential for rabies eradication.

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.

Primary multiplication site of the vaccinia-rabies glycoprotein recombinant virus administered to foxes by the oral route

The primary multiplication site of VVTGgRAB, a recombinant vaccinia virus (VV) expressing the rabies virus G glycoprotein, was studied in comparison with that of the parental VV Copenhagen strain, after oral administration to foxes. Foxes were fed with 10(8) TCID50 of either VVTGgRAB or VV and were sacrificed 12, 24, 48 or 96 h after inoculation. Both viruses were detected by viral isolation in the tonsils during the first 48 h after inoculation at titres between 10(2) and 10(4.3) TCID50/ml. Indirect immunofluorescence confirmed the presence of the virus in tonsils of some of the foxes. The polymerase chain reaction allowed the detection of VVTGgRAB in the tonsils of both of two foxes tested after 24 h, three of three foxes after 48 h, in the buccal mucosa of one of two foxes tested after 24 h and two of three foxes after 48 h and in the soft palate of one of two foxes tested after 24 h and one of three foxes after 48 h. VV was detected in the tonsils of one fox tested after 48 h, in the buccal mucosa of another fox tested after 24 h, and in the first fox after 48 h by the same reaction. Foxes were inoculated with virus isolated from fox tonsils 24 h after oral administration (with or without cell culture amplification) to perform back passages. No virus could be isolated in either case after this passage. The innocuity of VVTGgRAB was also demonstrated when foxes were inoculated with passaged virus.