[Construction of eukaryotic expression plasmids inserting HBsAg gene and DNA immunization responses to HBsAg in mice]

OBJECTIVE

To study the HBsAg transient expression in HepG2 or COS-7 cells with eukaryotic expression plasmids inserting HBsAg gene (pCI-S and pcDNA3.1-S) and the efficacy of naked DNA immunization in mice.

METHODS

Firstly, the recombinant plasmids of pCI-S and pcDNA3.1-S were constructed by the cloning technique and the accuracy of these constructs was confirmed by restriction enzyme digestion and DNA sequencing. Secondly, plasmids of pCI-S and pcDNA3.1-S were transferred into HepG2 and COS-7 cells, respectively by means of cationic liposome. HBsAg transient expression was assayed by ELISA in cell culture supernatants and cell lysates. Thirdly, plasmids were injected into quadriceps muscles of BALB/C mice and serum samples were obtained from individual immunized or control mice 4 weeks after injection and boost injection, respectively. Anti-HBs were assayed in mice sera by ELISA. HBsAg-specific CTL responses of spleen cells from immunized mice were tested by the LDH method.

RESULTS

Plasmids of pCI-S and pcDNA3.1-S allowed HBsAg transient expression in cell culture supernatants and cell lysates of HepG2 or COS-7 cells. Intramuscular immunization of BALB/C mice with plasmids of pCI-S or pcDNA3.1-S elicited the antibody and cytotoxic T lymphocyte responses to HBsAg.

CONCLUSIONS

The vectors used in this study are effective to induce prime antibody and HBsAg-specific-cytotoxic T lymphocyte responses to HBsAg in mice after intramuscular immunization.

An attenuated herpes vaccine may protect Gyr hybrids from fatal inclusion body hepatitis. A preliminary report

Four Gyr hybrids were used for this falcon herpes vaccine experiment. Three falcons were given 1 ml of an attenuated falcon herpesvirus vaccine (DuFaHe) subcutaneously twice within 14 days, whereas the fourth falcon was used as a control. Eighteen days after the booster vaccination, all four Gyr hybrids were intranasally and ocularly challenged with a virulent low-passage falcon herpesvirus. The control falcon died 9 days after challenge with typical lesions of herpesvirus inclusion body hepatitis. The three vaccinated falcons seroconverted and did not show any symptoms. Following the challenge their antibody titres to falcon herpesvirus increased. No herpesvirus was isolated from any of the cloacal swabs taken during this experiment, indicating that there was no danger for any other birds from DuFaHe. This experiment shows that falcons can be protected from herpesvirus infection by an attenuated herpesvirus vaccine. However, it should be stressed that only four falcons were used for this experiment.

Exclusion of mouse hepatitis virus from a filtered, plastic rodent shipping container during an in transit field challenge

Although leading suppliers of laboratory mice and rats continue to use filtered shipping boxes to protect their animals from contamination during transport to the end user, no information had been available in the literature to demonstrate that any of these boxes actually accomplish this task. To test this hypothesis, 12 plastic shipping boxes with filters and tight-fitting lids and six cardboard shipping boxes without filters (controls) were each stocked with adult, adventitious disease-free mice. All 18 shipping boxes were transported to a facility housing a breeding colony of mice enzootically infected with four murine viruses, including mouse hepatitis virus (MHV), and were placed inside the colony for 15 h. The boxes were then transported to a commercial testing laboratory, at which the animals were aseptically removed and were held in microisolation cages for 28 days, after which their sera tested for antibody to all four murine viruses. All serum samples from mice held in the control boxes were positive for antibody to MHV, whereas sera from all mice held in filtered boxes were negative for antibody to any of the four viruses. This study demonstrates that at least one type of filtered shipping container protects mice from a field challenge of MHV. To the best of our knowledge, this is the first documentation of any microbial efficacy testing conducted on filtered shipping containers for laboratory animals.

Liver-specific alpha 2 interferon gene expression results in protection from induced hepatitis

The current therapy for hepatitis B and C is based on systemic administration of recombinant human alpha interferon (r-hIFN-alpha). However, systemic delivery of r-hIFN-alpha is associated with severe side effects, but more importantly, it is effective in only a small percentage of patients. In an effort to maximize IFN-alpha antiviral efficacy, we have explored the therapeutic potential of murine IFN-alpha2 (mIFNalpha2) selectively expressed in the liver. To this end, we have developed a helper-dependent adenovirus vector (HD) containing the mIFN-alpha2 gene under the control of the liver-specific transthyretin promoter (HD-IFN). Comparison with a first-generation adenovirus carrying the same mIFN-alpha2 expression cassette indicates that at certain HD-IFN doses, induction of antiviral genes can be achieved in the absence of detectable circulating mIFN-alpha2. Challenge of injected mice with mouse hepatitis virus type 3 showed that HD-IFN provides high liver protection. Moreover, liver protection was also observed in acute nonviral liver inflammation hepatitis induced by concanavalin A at 1 month postinfection. These results hold promise for the development of a gene therapy treatment for chronic viral hepatitis based on liver-restricted expression of IFN-alpha2.

The hydropericardium syndrome and inclusion body hepatitis in domestic fowl

Hydropericardium syndrome, an emerging disease of poultry, has recently been detected in some countries of Asia and America, particularly in broiler birds aged 3-6 weeks. The disease is characterized by its sudden occurrence with high mortality of up to 80% in broilers and low mortality of under 10% in layers, associated with hydropericardium. Its course is of 7-15 days under natural conditions. The causative agent is probably fowl adenovirus serotype 4, belonging to group I aviadenovirus genus of the family adenoviridae, which can be cultivated in primary cell cultures of chicken kidney and embryo liver cells. The transmission of disease occurs laterally by the oral-faecal route. The livers of affected birds show necrotic foci, and basophilic intranuclear inclusion bodies fill the entire enlarged nucleus of some of the hepatocytes. The disease can be diagnosed from its gross lesions, histopathological changes in the liver and by serological tests, such as agar gel diffusion, counter immunoelectrophoresis, indirect haemagglutination and ELISA. It has been brought under control by inactivated liver organ vaccines (0.25 ml/bird) or inactivated cell culture vaccines (10(3.5) LD50/bird) given by the subcutaneous route at 10-15 days of age. The vaccine is effective in the face of an outbreak and significantly reduces the mortality.

Protective immunity against murine hepatitis virus (MHV) induced by intranasal or subcutaneous administration of hybrids of tobacco mosaic virus that carries an MHV epitope

Hybrids of tobacco mosaic virus (TMV) were constructed with the use of fusion to the coat protein peptides of 10 or 15 amino acids, containing the 5B19 epitope from the spike protein of murine hepatitis virus (MHV) and giving rise to TMV-5B19 and TMV-5B19L, respectively. The TMV hybrids were propagated in tobacco plants, and the virus particles were purified. Immunogold labeling, with the use of the monoclonal MAb5B19 antibody, showed specific decoration of hybrid TMV particles, confirming the expression and display of the MHV epitope on the surface of the TMV. Mice were immunized with purified hybrid viruses after several regimens of immunization. Mice that received TMV-5B19L intranasally developed serum IgG and IgA specific for the 5B19 epitope and for the TMV coat protein. Hybrid TMV-5B19, administered by subcutaneous injections, elicited high titers of serum IgG that was specific for the 5B19 epitope and for coat protein, but IgA that was specific against 5B19 was not observed. Mice that were immunized with hybrid virus by subcutaneous or intranasal routes of administration survived challenge with a lethal dose (10 x LD50) of MHV strain JHM, whereas mice administered wild-type TMV died 10 d post challenge. Furthermore, there was a positive correlation between the dose of administered immunogen and protection against MHV infection. These studies show that TMV can be an effective vaccine delivery vehicle for parenteral and mucosal immunization and for protection from challenge with viral infection.

Occurrence of coxsackievirus hepatitis in baby rabbits and protection by a formalin-inactivated polyvalent vaccine

It was observed that 23-day-old New Zealand white rabbits came down with acute hepatitis demonstrable 3 days after intraperitoneal injection with 12 coxsackievirus group B strains. The model was used to evaluate a polyvalent, formalin-inactivated virus vaccine prepared with prototype strains of coxsackievirus groups B1-6. Seven-day-old animals received one intraperitoneal and two subcutaneous injections containing the vaccine or placebo. The regimen was repeated at 15 days of age. At 23 days of age, groups of rabbits were challenged with 1 x 10(5) plaque-forming units of a clinical strain of group B coxsackievirus and sacrificed 3 days later. The mean neutralizing antibody titer for the 12 strains tested (log2) was 4.5 +/- 1.0 eight days after the second dose of vaccine. In vaccinated animals, elevated liver function tests in the serum, and titer of virus and histopathologic abnormalities in the liver were significantly reduced for each strain tested compared with infected, unvaccinated controls. Cultures of the heart, skeletal muscle, pancreas, blood, and spleen were all negative. Thus, clinical strains of coxsackie group B viruses produced isolated hepatitis in baby rabbits. Prophylaxis with a polyvalent, inactivated-virus vaccine significantly reduced the severity of liver involvement for all 12 clinical strains tested.

Protective effects of a novel quinone derivative, E3330, on mouse hepatitis virus (MHV)-induced chronic hepatitis in athymic nude mice

In this experiment, we examined the protective effects of a novel quinone derivative, E3330, on MHV-2cc-induced chronic hepatitis in athymic nude mice for up to 3 weeks after virus infection. The daily dose of 25 mg/kg b.w. suppressed the viral replication in the liver and the progression of hepatic lesions. The expansion of small focal lesions at 1 week after viral inoculation (WAI) was suppressed at 2 WAI, and the lesions were still small at 3 WAI in E3330-administered group, whereas small focal lesions at 1 WAI were expanded at 2 WAI to fuse with each other at 3 WAI in the control group. E3330 therefore showed protective effects on MHV-2cc-induced chronic hepatitis in athymic nude mice, but further studies are needed to analyze the mechanism.

Protective effect of recombinant interferon (IFN)-alpha/beta on MHV-2cc-induced chronic hepatitis in athymic nude mice

The protective effects of recombinant IFN-alpha/beta on MHV-2cc-induced chronic and persistent hepatitis in athymic nude mice were examined. The mice intraperitoneally (ip) inoculated with MHV-2cc at day 0 of experiment were divided into 4 groups. Three of them were administered ip with recombinant IFN-alpha/beta at a daily dose of 1 x 10(3) IU from -1 (-1D-group), 0 (0D-group), and +1 day of experiment (+1D-group), respectively, for 3 consecutive weeks. The remaining one (control group) was given 0.1 ml/mouse of PBS from +1 day of the experiment in the same way. Three mice in each group were killed at 1, 2 and 3 weeks post inoculation (WPI) with MHV, respectively. The liver virus titer in the control group increased gradually and maintained high levels throughout the experimental period. In the IFN-groups, particularly in the -1D- and 0D-groups, the virus titers were significantly lower than that in control group. Histopathologically, focal hepatic lesions were observed at 1WPI and large irregular inflammatory lesions developed at 3WPI in the control group. Similar but somewhat less severe lesions were observed in the +1D-group. In the -1D- and 0D-groups, lesions were not observed at 1WPI and only small organized lesions with mononuclear cell infiltration were seen at 3WPI. In conclusion, it was clarified in the present study that the progression of MHV-2cc-induced chronic hepatitis in athymic nude mice was effectively prevented by extrinsic IFN-alpha/beta when administered from -1 day and 0 day of the virus infection.

Resistance of naive mice to murine hepatitis virus strain 3 requires development of a Th1, but not a Th2, response, whereas pre-existing antibody partially protects against primary infection

Murine hepatitis virus strain 3 (MHV-3) produces a strain-dependent spectrum of disease. The development of liver necrosis has been shown to be related to production of a unique macrophage procoagulant activity (PCA), encoded by the gene fgl-2, in susceptible mice. These studies were designed to examine the influence of Th1/Th2 cells on resistance/susceptibility and production of macrophage PCA in resistant (A/J) and susceptible (BALB/cJ) strains of mice following infection with MHV-3. Immunization of A/J mice with MHV-3 induced a Th1 cellular immune response, and one Th1 cell line (3E9.1) protected susceptible mice and inhibited PCA production by macrophages both in vitro and in vivo. In contrast, immunization of BALB/cJ mice with an attenuated variant of MHV-3 derived from passaging MHV-3 in YAC-1 cells resulted in a Th2 response. Transfer of spleen cells and T cell lines from immunized BALB/cJ mice failed to protect naive susceptible syngeneic mice from infection with MHV-3 and augmented macrophage PCA production to MHV-3 in vitro. However, serum from immunized BALB/cJ mice contained high titrated neutralizing Ab that protected naive BALB/cJ animals from lethal primary MHV-3 infection. These results demonstrate that susceptible BALB/cJ mice generate a Th2 response following MHV-3 infection and that these Th2 cells neither inhibit MHV-3-induced macrophage PCA production nor protect naive mice from MHV-3 infection. The results suggest that Ab protects against primary infection but cannot eradicate ongoing infection. Thus, these data define the differential role of Th1/Th2 lymphocytes in primary and secondary MHV-3 infection and emphasize the importance of PCA in the pathogenesis of MHV-3 infection.

Protection from lethal coronavirus infection by immunoglobulin fragments

Molecular mechanisms of in vitro and in vivo virus neutralization by specific Ab remain largely undefined. Murine coronaviruses provide an excellent animal model for such studies. To determine the role of Ab bivalency and the contribution of its Fc portion in the neutralization of viral infectivity and passive protection of mice by an in vitro neutralizing and in vivo protective mAb (7-10A), F(ab')2 and Fab fragments were generated and their biologic properties were examined. The two fragments reacted in ELISA like the whole Ab against viral Ag or specific anti-idiotypic Abs. The affinity constants of the different Ab preparations were determined by surface plasmon resonance using immobilized anti-idiotypic Abs. The apparent affinity constant of the whole Ab molecule was 7.0 x 10(9) M-1 and was reduced 2-fold for F(ab')2 fragments and 14-fold for Fab molecules. Like whole Ab, both F(ab')2 and Fab fragments could neutralize virus in vitro and passively protect mice in vivo. However, the efficiency of in vivo neutralization by Fab fragments was reduced compared with the bivalent molecules, despite almost identical half-lives of both types of Ab fragments. These results demonstrate that in vitro and in vivo virus neutralization mechanisms by this Ab are independent of Fc-mediated functions and bivalency, but are probably influenced by Ab avidity. Also, this is the first report of in vivo protection against a viral infection by Fab fragments of antiviral Ab.

Suramin prevents duck hepatitis B virus infection in vivo

The effect of suramin on duck hepatitis B virus (DHBV) infection was investigated in vivo. Suramin pretreatment of Pekin ducklings completely prevented DHBV infection. In contrast, suramin given at the time of or after inoculation with DHBV did not inhibit viral infection, replication, or gene expression. These data indicate that suramin effectively blocks the early stages of DHBV infection in vivo.

Evaluation of Phyllanthus amarus and Phyllanthus maderaspatensis as agents for postexposure prophylaxis in neonatal duck hepatitis B virus infection

The therapeutic potential of plant extracts of Phyllanthus amarus and Phyllanthus maderas patensis for postexposure prophylaxis against infection by Hepadnaviruses was studied in ducklings infected by the duck hepatitis B virus (DHBV). Forty-four Pekin ducklings were inoculated intraperitoneally with DHBV at 24 hr post-hatch. They were treated by intraperitoneal injection of Phyllanthus amarus (aqueous extract) (100 mg/kg body weight) or Phyllanthus mad eraspatensis (alcoholic extract) (100 mg/kg body weight) for a period of 4 weeks. Infected ducklings treated with saline served as controls. Weekly serum samples obtained before, during, and after treatment were analysed for the presence of DHBV DNA in serum by dot blot hybridisation using alpha 32P-labelled probes. Liver tissue was collected after killing the ducks at various time intervals and was studied for replicative status of the viral DNA and liver histopathology; 17 of 21 ducks were viraemic on completion of treatment with Phyllanthus amarus. At 16 week posttreatment follow-up four of seven animals remained viraemic. Similar results were obtained with Phyllanthus maderaspatensis. There was no alteration in DHBV replication in the liver. No toxicity was observed with this treatment. These observations suggest that Phyllanthus amarus and Phyllanthus maderaspatensis are not useful as therapeutic agents for postexposure prophylaxis against DHBV infection.

Evaluation of isolator caging systems for protection of mice against challenge with mouse hepatitis virus

Two isolator caging systems were evaluated against challenge with MHV-Y, an enterotropic strain of mouse hepatitis virus. The systems were similar in that they both used an identical shoebox cage equipped with a polycarbonate filter top incorporating a Reemay filter. They differed in that one system supplied HEPA-filtered air through a grommet in the filter lid so that the cage was pressurized slightly. A rack holding 60 cages (30 front and back) was utilized. Thirty cages without filter tops housed one mouse each that had been infected orally with 19,000 ID50 of MHV-Y and an uninfected cagemate. The remaining 30 cages, each housing 2 uninfected mice were divided into 3 groups of 10 cages. Group I cages (controls) had no filter top; Group II cages were equipped with filter tops; and Group III were equipped with filter tops and intracage HEPA-filtered air. The cages housing uninfected mice were interspersed between, above, below and behind cages housing infected mice. The uninfected mice were maintained in contact with the MHV-Y infected mice for 8 weeks. Transmission of MHV-Y was determined serologically by indirect ELISA. All mice housed within the Group I cages (control) seroconverted to MHV, while only 4 mice (2 cages) seroconverted in Group II, and no mice seroconverted in Group III.

Immunization with recombinant woodchuck hepatitis virus nucleocapsid antigen or hepatitis B virus nucleocapsid antigen protects woodchucks from woodchuck hepatitis virus infection

Woodchucks were immunized with recombinant woodchuck hepatitis virus (WHV) nucleocapsid antigen (WHcAg) or hepatitis B virus (HBV) nucleocapsid antigen (HBcAg) and challenged with 10(6) WHV ID50. Six out of six woodchucks immunized with WHcAg and four out of six immunized with HBcAg were protected from WHV infection. Woodchucks immunized with WHcAg or HBcAg developed high serum antibody titres against WHcAg or HBcAg. Antibodies against WHc and HBc displayed little cross-reactivity (< 1%). This confirms and extends previous reports of protection against homologous challenge after immunization with HBcAg/WHcAg which are both internal viral antigens. As the dominant B-cell epitope(s) on particulate WHcAg and HBcAg appear not to be conserved it also demonstrates that antibodies against HBcAg/WHcAg are not important for this protection. Woodchucks immunized with WHcAg/HBcAg reacted with a fast serum antibody response against viral envelope proteins upon challenge with WHV, indicative of functional intrastructural/intermolecular T-cell help as one potential mechanism of protection after immunization with an internal viral antigen.

The effects of using recombinant vaccinia viruses expressing either large or small HDAg to protect woodchuck hepadnavirus carriers from HDV superinfection

Live rVVs expressing either p24 delta or p27 delta were produced and used to immunize woodchuck hepadnavirus carriers. Upon challenge with infectious HDV, circulating HDV RNA levels appeared to be similar in both controls and vaccinees. Although extended follow-up studies of these animals is necessary before making firm conclusions, including an analysis of circulating HDAg levels, these preliminary results provide no evidence for a protective immunity conferred by the rVVs. In contrast, we have shown in other studies that repeated immunization of woodchucks with purified, recombinant p24 delta subunit does confer significant protection against HDV challenge in some of the vaccinees (A. Ponzetto, et al., this volume). The underlying immunological mechanisms responsible for the different outcome of these varied vaccination regimens remain to be elucidated.

Monoclonal antiprothrombinase (3D4.3) prevents mortality from murine hepatitis virus (MHV-3) infection

The induction of monocyte/macrophage procoagulant activity (PCA) has been implicated in the pathogenesis of murine hepatitis virus strain 3 (MHV-3) infection and disease. Previously, we have shown that induction of PCA by MHV-3 correlated with resistance/susceptibility to infection in different mouse strains. In this study, all BALB/cJ mice that were infected with 10(3) plaque-forming units of MHV-3 developed severe liver disease and died within 96-120 h. Examination of the livers of these animals showed marked hepatic necrosis, deposition of fibrin, and cellular expression of PCA by direct immunofluorescence staining in areas of necrosis as well as in hepatic sinusoids. Splenic mononuclear cells recovered from these mice expressed high concentrations of PCA with time after infection. Infusion into mice of a high-titered monoclonal antibody that neutralized PCA (3D4.3) attenuated the development of hepatic necrosis and enhanced survival in a dose-dependent manner. All of the animals receiving 100 micrograms, and 44% and 22% of the animals that received 50 and 25 micrograms per day, respectively, survived for 10 d and made a full recovery. Administration of the antibody resulted in a dose-dependent reduction in fibrin deposition, PCA expression as detected by direct immunofluorescence staining and by a functional assay. In animals treated with high concentrations of antibody, titers of antibody to PCA fell from 87 +/- 15 micrograms/ml to 100 +/- 7 ng/ml during the active phase of the disease, consistent with sequestration due to binding of the immunoglobulin to cells expressing PCA. Surviving animals, when rechallenged with MHV-3, had a 40% mortality, consistent with the known rates of metabolism of immunoglobulin. This further suggested that protection was by a passive mechanism. The results reported here demonstrate that a neutralizing antibody to PCA protects animals from fulminant hepatitis and death associated with MHV-3 infection, and supports the notion that PCA is a potent inflammatory mediator that plays a pivotal role in the pathogenesis of liver injury resulting from MHV-3 infection.

Antiidiotypic vaccination against murine coronavirus infection

Rabbit polyclonal antiidiotypic antibodies were generated against a neutralizing mAb specific for a conformational epitope on the S glycoprotein of murine hepatitis virus, strain A59 (MHV-A59). These anti-Id were directed predominantly against an Id that was undetectable in rabbit and rat anti-MHV-A59 sera and weakly represented in syngeneic and allogeneic antiviral sera. However, some partial idiotypic sharing was observed between the Id-bearing antibody and a mAb with a similar antigenic site specificity. The anti-Id inhibited the virus-binding and neutralizing activities of the immunizing antibody, demonstrating that they recognize paratope-associated idiotopes. Mice immunized with affinity-purified anti-Id developed MHV-A59-specific antibodies that neutralized viral infectivity to high titers. Moreover, these animals survived an otherwise lethal challenge with viral murine hepatitis virus, unlike control mice immunized with normal rabbit Ig. These results indicate that at least a subpopulation of the polyclonal anti-Id could induce a protective immune response directed toward a biologically important MHV-A59 epitope, and demonstrate the feasibility of antiidiotypic vaccination against a coronavirus infection.

Sulfated polyanions do not inhibit duck hepatitis B virus infection

On the basis of the antiviral action of sulfated polyanions in human immunodeficiency virus and other viral infections, we studied the effect of dextran sulfate and heparin on duck hepatitis B virus infection. These agents do not affect viral uptake and replication in liver cells in vitro or in vivo. Sulfated polyanions, therefore, appear to have no potential for the treatment of hepadnavirus infections.

Inhibition of duck hepatitis B virus infection by lysosomotropic agents

The early phases of hepadnaviral infection were studied in primary duck hepatocyte cultures. Incubation of duck hepatocytes in vitro with duck hepatitis B virus (DHBV) resulted in infection with high levels of viral replication. The lysosomotropic agents ammonium chloride and chloroquine effectively inhibited viral infection, indicating that DHBV infection, similar to infection with other enveloped viruses, depends on receptor-mediated endocytosis and involves membrane fusion triggered by low pH.

Viral haemorrhagic disease of rabbits: vaccination and immune response

Results are presented for the large-scale use of a tissue vaccine, inactivated with beta-propiolactone and containing aluminium hydroxide adjuvant, against viral haemorrhagic disease of rabbits. The kinetics of haemagglutination-inhibiting antibodies over eighteen months, the response of vaccinated animals to challenge infection with field virus between six and fifteen months after vaccination, the serological response to revaccination, and the immunological mechanisms involved in primary vaccination and revaccination were investigated.

Application of control measures against viral haemorrhagic disease of rabbits in the Czech and Slovak Federal Republic

The first outbreaks of viral haemorrhagic disease (VHD) of rabbits were reported from eastern Slovakia in 1987. In 1988, the infection spread throughout the Czech and Slovak Federal Republic. Electron microscopy was used by the Veterinary Research Institute in Brno to diagnose the disease during the early stage of infection. At present, the regional laboratories of the veterinary investigation services use the haemagglutination and the direct immunofluorescence tests as the principal methods to demonstrate the causal agent. Indirect immunofluorescence and immunoperoxidase techniques have been developed to demonstrate VHD virus, while the enzyme-linked immunosorbent assay (ELISA) has been used to detect antibodies. Diagnostic kits, allowing a wide use of these methods, are now available commercially. Two types of inactivate vaccines were developed and produced in 1988 and 1989. VHD is controlled by vaccination of exposed rabbit colonies. This is accompanied by other preventive and protective measures, directed by district veterinary officers following instructions from federal authorities.

Epidemiology and current situation of viral haemorrhagic disease of rabbits and the European brown hare syndrome in Italy

Rabbit production is of considerable economic importance in Italy. In the last thirty years, meat production has risen and the number of intensive husbandry establishments has grown. The major region of production (about 60%) lies in the northern part of the country. In addition, approximately one million live animals and more than 14,000 tons of meat are imported yearly. More than 150,000 hares are also imported for restocking and hunting purposes. During the second half of the 1980s a "new" disease (X disease), characterised by haemorrhagic and degenerative lesions and high mortality, was observed on traditional farms in some regions. This form spread throughout the country between 1986 and 1988. In 1988, diagnostic research led to identification of a viral agent. Because of its morphology, the virus was at first considered a picornavirus. More recent research has included the virus in the Caliciviridae family. This agent reproduces the disease experimentally. Between 1988 and 1989, many intensive establishments in several regions were affected by the disease, known as viral haemorrhagic disease (VHD); the losses were always very high. In 1989, after mortality among free-living hares had been observed in the northern part of Italy for some years, the agent of the European brown hare syndrome (EBHS) was identified as being morphologically similar to the VHD virus. The antigenic relationship between VHD and EBHS and the possibility of cross-infection between rabbits and hares are currently being studied. Hygienic measures and vaccination are the most reliable methods of control. International cooperation has greatly helped in the study of the disease and in the adoption of control measures.

Vaccination against and immune response to viral haemorrhagic disease of rabbits: a review of research in the People's Republic of China

Viral haemorrhagic disease (VHD) of rabbits is an acute entity with high mortality which affects adult rabbits. Several vaccines have been developed in China and extensive use of these vaccines in the field has controlled the spread of the disease. Formalin inactivated tissue vaccine induces solid immunity on the third to fourth day post vaccination and immunity lasts for at least six months. The oil-emulsion tissue vaccine which has been developed has longer lasting potency. Successful adaptation of VHD virus (VHDV) to cultured cells and preliminary immunisation will provide the possibility of large-scale production of cell-cultured virus vaccine. Passive, emergency immunisation with hyperimmune antiserum provides short-term protection of threatened rabbits as well as treatment of infected rabbits in the field. Histopathological and pathophysiological studies reveal that immune cells and organs are the most affected targets in infected rabbits; owing to the damage to the endothelial system of blood vessels, extensive disseminated intravascular coagulation (DIC) occurs in the parenchymal tissues. Destruction of the immune system and the occurrence of DIC lead to acute illness and sudden death post infection. Experimental immunological studies demonstrate that the induction of rapid immunity is coordinated by macrophages and T and B lymphocytes in the initial, post-immunisation stage, whereas humoral immunity plays the main role in long-term protection against VHDV infection. The positive association of post-vaccination protection with haemagglutination inhibition antibody can also be observed. Interferon probably takes effect as an anti-VHDV agent soon after vaccination.

Incidence, epizootiology and control of viral haemorrhagic disease of rabbits and the European brown hare syndrome in Germany

Viral haemorrhagic disease (VHD) among domestic and wild rabbits and European brown hares have been observed in most of the Federal states of Germany. Acute outbreaks of viral haemorrhagic disease are most prevalent in small, fancy domestic rabbitries, with mortality varying between 5 and 90%, while mostly sporadic losses due to VHD are seen among wild rabbits. In hares, accumulated losses from the European brown hare syndrome (EBHS) can occasionally be observed in areas where fresh green feed, such as young O.O-rape plants, is available. VHD of rabbits and EBHS are caused by calicivirus strains. The natural virus reservoirs are wild rabbit and hare populations. Mutual infection of rabbits and hares seems to be possible. Transmission and spread of infectious virus occurs by direct contact of animals, or indirectly by contaminated excrement, green feed or living vectors. Calicivirus infections are widespread in several states, with accumulation of losses among domestic and wild rabbits by VHD, or in hares by EBHS, within certain areas. Disease hygiene, together with vaccination, are the officially preferred control measures in domestic rabbitries.