Study of an attenuated strain of feline infectious enteritis (panleucopaenia) virus: I. Spread of vaccine virus from cats affected with feline respiratory disease

In the course of developing a living attenuated feline infectious enteritis (panleucopaenia) vaccine, it was found that respiratory disease-infected cats newly inoculated with this vaccine spread vaccine virus to respiratory disease-infected in-contact controls. These in-contact controls were able to infect other cats with which they were placed in contact so that after five natural transmissions in this way and two oral administrations and subsequent re-isolations, reversion to virulence became evident. It is clear that before general release of a new living feline infectious enteritis vaccine, there must be satisfactory evidence that concurrent infection will not affect the safety of the modified antigen.     

Study of an attenuated strain of feline infectious enteritis (panleucopaenia) virus: II. Removal of the spread factor by further passaging in tissue culture

The propensity of an attenuated strain of feline infectious enteritis (panleucopaenia) virus to spread from vaccinated cats affected with intercurrent feline respiratory disease to unvaccinated in-contact cats was eradicated by further passaging of the vaccine virus in tissue culture. No virus was recovered from, and no antibody was found in the sentinel cats in contact with seven vaccinated animals. Thus, a further 27 passages of the vaccine virus in tissue culture has eliminated the spread factor.     

VP5-deficient mutant virus induced protection against challenge with very virulent infectious bursal disease virus of chickens

A mutant infectious bursal disease virus (IBDV) deficient in expressing VP5, rGx-F9VP2ΔVP5, was generated using reverse genetics technology. In comparison to the characteristics of rGx-F9VP2 virus in vitro, the mutant virus demonstrated lower viral titer and cytopathogenicity. To understand the role of VP5 in the pathogenicity of IBDV in vivo, animal experiments were conducted. rGx-F9VP2ΔVP5 caused reduced bursal lesion of SPF chickens compared to rGx-F9VP2. Although rGx-F9VP2ΔVP5 induced lower serum antibody than rGx-F9VP2 did, both inoculated groups were fully protected against vvIBDV challenge 4 weeks post-inoculation. In addition, immunosuppression induced by VP5-deficient virus was studied in 2-week-old SPF chickens immunized with AIV inactivated vaccine. And there was reduced immunosuppression as shown in our experimental results. The results showed that AIV hemagglutination inhibition (HI) antibodies of the rGx-F9VP2ΔVP5 inoculated group were similar to those of the mock-inoculated group, however, they were higher than those of the rGx-F9VP2 inoculated group, indicating that deficiency of VP5 decreased the immunosuppression of rGx-F9VP2ΔVP5 in chickens. All data indicated that VP5 played an important role in viral replication and pathogenesis both in vitro and in vivo. The VP5-deficient mutant virus could be a good candidate as a marked vaccine.     

Rinderpest virus (RPV) ISCOM vaccine induces protection in cattle against virulent RPV challenge

Rinderpest virus (RPV), a member of genus Morbillivirus in the family Paramyxoviridae, causes an acute and often fatal disease in cattle and other large ruminants. A subunit rinderpest vaccine consisting of an immune-stimulating complex (ISCOM) incorporating the RPV haemaggulutinin (H) protein, was examined for its ability to induce protective immunity in cattle, the natural host of RPV. All of four cattle vaccinated with the ISCOM vaccine survived challenge with virulent virus. Three were solidly protected, showing no clinical signs of infection, while the fourth animal developed only mild and transient symptoms. Virus neutralizing antibodies were produced at a significant level in all vaccinated cattle. These results indicate that this ISCOM vaccine is effective in producing protective immunity in cattle and should be a suitable means of delivering glycoprotein antigens from other morbilliviruses.     

BacMam virus-based surface display of the infectious bronchitis virus (IBV) S1 glycoprotein confers strong protection against virulent IBV challenge in chickens

Avian infectious bronchitis virus (IBV) is associated with production inefficiencies in domestic fowl, and causes massive economic losses to the poultry industry worldwide. Progress has been made in designing novel and efficient candidate vaccines to control IBV infection. BacMam virus, a modified baculovirus mediating transgene expression under the control of a mammalian promoter, has emerged as a versatile and safe vector during vaccine development. In previous work, we generated the BacMam virus Ac-CMV-S1, which expressed the S1 glycoprotein of IBV-M41. We showed that Ac-CMV-S1 induced excellent cellular immunity, but did not confer adequate protection in chickens compared with the conventional inactivated vaccine. In the current study, we generated an improved BacMam virus, BV-Dual-S1. This virus displayed the S1 glycoprotein on the baculovirus envelope, and was capable of expressing it in mammalian cells. BV-Dual-S1 elicited stronger humoral and cell-mediated immune responses, and showed greater capacity for induction of cytotoxic T lymphocyte responses, compared with Ac-CMV-S1 in specific pathogen-free chickens. A significant difference was not observed for protection rates between chickens immunized with BV-Dual-S1 (83%) or inactivated vaccine (89%) following challenge with virulent IBV-M41. Our findings show that the protective efficacy of BV-Dual-S1 could be significantly enhanced by baculovirus display technology. BacMam virus-based surface display strategies could serve as effective tools in designing vaccines against IB and other infectious diseases.     

Exposure of rabbits to ultraviolet light-inactivated rabbit haemorrhagic disease virus (RHDV) and subsequent challenge with virulent virus

This study investigated whether exposure to inactivated rabbit haemorrhagic disease virus (RHDV) can produce an antigenic response in rabbits and protect them from a subsequent challenge with virulent virus. The aim was to determine if the spreading of baits containing RHDV, which is a common management practice in New Zealand to reduce rabbit numbers, could result in protective immunity in wild rabbits. RHDV was inactivated by ultraviolet (UV) light using an electronic UV crosslinker with a UV dose of 168.48 W-s/cm2 and a UV intensity of 0.0078 W/cm2. Two groups of four rabbits were then inoculated with inactivated virus via oral and intramuscular routes. Rabbits were monitored for 30 days post-inoculation and then challenged orally with virulent virus. No rabbit exposed to inactivated RHDV developed clinical signs of RHD or had antibodies at day 30 post-infection and all animals died within 82 h after challenge with virulent virus. No antibodies were detected at the time of death. These findings suggest that exposure to virus completely inactivated by UV light in the field or on baits will not protect rabbits against challenge with virulent virus.     

Development of a tailored vaccine against challenge with very virulent infectious bursal disease virus of chickens using reverse genetics

Due to the problems associated with traditional methods for infectious bursal disease virus (IBDV) vaccine development and the pressure of evolution and variation of very virulent strains, it is urgent to develop IBDV vaccine rapidly with novel approaches. Using reverse genetics, the aim of this study was to generate a tailored vaccine strain (rGtHLJVP2) with its VP2 gene similar to very virulent IBDV (vvIBDV) to prevent the prevalence of IBDV. Characteristics of rGtHLJVP2 were evaluated in both cell culture and SPF chickens. rGtHLJVP2 replicated well as its parental strain Gt in vitro and in vivo. Immunization of SPF chickens with rGtHLJVP2 resulted in comparable antibody titers against IBDV as that of the medium virulent live vaccine B87, which was significant higher than that of attenuated vaccine Gt. Challenge studies with 10⁴ ELD₅₀ of prevalent homogeneous or heterogenous vvIBDV revealed complete (100%) protection in the groups immunized with rGtHLJVP2. No significant clinical and pathological lesions were observed in chickens immunized with rGtHLJVP2. Our data demonstrated that rGtHLJVP2 could be used as a novel vaccine candidate for prevention against vvIBDV.     

Protection against oronasal challenge with virulent feline leukaemia virus lasts for at least 12 months following a primary course of immunisation with Leukocell 2 vaccine

The duration of immunity provided by a feline leukemia virus (FeLV) vaccine, Leukocell 2, was determined. Kittens were vaccinated when 9 and 12 weeks of age and were challenged 12 months later with FeLV-A/Glasgow-1. An oronasal challenge protocol without corticosteroid enhancement was developed in order to induce a persistent viraemia in a high proportion of adult cats. Fourteen of 18 (80%) of the vaccinated cats challenged in this way remained non-viraemic while 9/15 (60%) of age-matched controls became persistently infected, a preventable fraction of 63%. This difference was statistically significant (P=0.038). For comparison, 10 of 12 (83%) 15-17-week-old kittens challenged in the same way became persistently infected, confirming the relative resistance of adult animals to FeLV. Tests for virus neutralising and anti-feline oncornavirus-associated cell membrane antigen (FOCMA) antibodies suggested that the former were more important than the latter in protection. Thus, Leukocell 2 protected a significant proportion of cats from FeLV challenge 1 year after primary vaccination as kittens.     

Preparation of lyophilized rabies street virus material from infective submaxillary glands for challenge purposes

A method is described for the preparation of lyophilized rabies street virus material from infected submaxillary glands for challenge purposes. The lyophilized material gives consistent and reproducible results on intracerebral or intramuscular titration over long periods.     

A recombinant Newcastle disease virus (NDV) expressing infectious laryngotracheitis virus (ILTV) surface glycoprotein D protects against highly virulent ILTV and NDV challenges in chickens

Infectious laryngotracheitis (ILT) is a highly contagious acute respiratory disease of chickens caused by infectious laryngotracheitis virus (ILTV). Currently, modified live ILTV vaccines are used to control ILT infections. However, the live ILTV vaccines can revert to virulence after bird-to-bird passage and are capable of establishing latent infections, suggesting the need to develop safer vaccines against ILT. We have evaluated the role of three major ILTV surface glycoproteins, namely, gB, gC, and gD in protection and immunity against ILTV infection in chickens. Using reverse genetics approach, three recombinant Newcastle disease viruses (rNDVs) designated rNDV gB, rNDV gC, and rNDV gD were generated, each expressing gB, gC, and gD, respectively, of ILTV. Chickens received two immunizations with rNDVs alone (gB, gC, and gD) or in combination (gB + gC, gB + gD, gC + gD, and gB + gC + gD). Immunization with rNDV gD induced detectable levels of neutralizing antibodies with the magnitude of response greater than the rest of the experimental groups including those vaccinated with commercially available vaccines. The birds immunized with rNDV gD showed complete protection against virulent ILTV challenge. The birds immunized with rNDV gC alone or multivalent vaccines consisting of combination of rNDVs displayed partial protection with minimal disease and reduced replication of challenge virus in trachea. Immunization with rNDV gB neither reduced the severity of the disease nor the replication of challenge virus in trachea. The superior protective efficacy of rNDV gD vaccine compared to rNDV gB or rNDV gC vaccine was attributed to the higher levels of envelope incorporation and infected cell surface expression of gD than gB or gC. Our results suggest that rNDV expressing gD is a safe and effective bivalent vaccine against NDV and ILTV.     

Meeting the challenge of epidemic infectious disease outbreaks: an agenda for research

Challenges arising from epidemic infectious disease outbreaks can be more effectively met if traditional public health is enhanced by sociology. The focus is normally on biomedical aspects, the surveillance and sentinel systems for infectious diseases, and what needs to be done to bring outbreaks under control quickly. Social factors associated with infectious disease outbreaks are often neglected and the aftermath is ignored. These factors can affect outbreak severity, its rate and extent of spread, influencing the welfare of victims, their families, and their communities. We propose an agenda for research to meet the challenges of infectious disease outbreaks. What social factors led to the outbreak? What social factors affected its severity and rate and extent of spread? How did individuals, social groups, and the state react to it? What are the short- and long-term effects on individuals, social groups, and the larger society? What programs can be put in place to help victims, their families, and affected communities to cope with the consequences--impaired mental and physical health, economic losses, and disrupted communities? Although current research on infectious disease outbreaks pays attention to social factors related to causation, severity, rate and extent of spread, those dealing with the "social chaos" arising from outbreaks are usually neglected. Inclusion, by combining traditional public health with sociological analysis, will enrich public health theory and understanding of infectious disease outbreaks. Our approach will help develop better programs to combat outbreaks and equally important, to help survivors, their families, and their communities cope better with the aftermath.     

An attenuated Ehrlichia ruminantium (Welgevonden stock) vaccine protects small ruminants against virulent heartwater challenge

Heartwater is a tick-borne disease of ruminants caused by the intracellular rickettsia Ehrlichia ruminantium. The only commercially available immunization procedure involves infecting animals with cryopreserved sheep blood containing virulent E. ruminantium organisms, followed by treatment with tetracyclines when fever develops. The virulent Welgevonden stock of E. ruminantium was attenuated by continuous propagation of the organisms in a canine macrophage-monocyte cell line (DH82), followed by re-adaptation to grow in a bovine endothelial cell line (BA 886). The material used for the present experiments consisted of the attenuated stock between passages 43 and 64 after re-adaptation. When inoculated into sheep or goats the attenuated organisms did not produce disease, and the only symptom observed was a rise in body temperature in most, but not all, animals. All sheep injected with 2 ml of culture suspension were subsequently found to be fully protected against a lethal needle challenge with the virulent homologous stock or with one of four different heterologous stocks (Ball 3, Gardel, Mara 87/7, Blaauwkrans). Titrations of elementary body suspensions showed that 2ml of a 1:10,000 dilution of culture suspension injected into sheep or goats was still sufficient to trigger an immune response which resisted a lethal needle challenge with the virulent Welgevonden stock. Adult Amblyomma hebraeum ticks, fed as nymphs on sheep immunized with DH82-derived organisms of passage 111, were able to transmit the attenuated stock to a naive sheep, which was found to be protected against a subsequent lethal homologous needle challenge.