Effects of corticosteroids mediated immunosuppression on the distribution of rabies vaccine virus in red foxes orally immunized against rabies

Subversion of the Immune Response by Rabies Virus

Rabies has affected mankind for several centuries and is one of the oldest known zoonoses. It is peculiar how little is known regarding the means by which rabies virus (RABV) evades the immune response and kills its host. This review investigates the complex interplay between RABV and the immune system, including the various means by which RABV evades, or advantageously utilizes, the host immune response in order to ensure successful replication and spread to another host. Different factors that influence immune responses—including age, sex, cerebral lateralization and temperature—are discussed, with specific reference to RABV and the effects on host morbidity and mortality. We also investigate the role of apoptosis and discuss whether it is a detrimental or beneficial mechanism of the host’s response to infection. The various RABV proteins and their roles in immune evasion are examined in depth with reference to important domains and the downstream effects of these interactions. Lastly, an overview of the means by which RABV evades important immune responses is provided. The research discussed in this review will be important in determining the roles of the immune response during RABV infections as well as to highlight important therapeutic target regions and potential strategies for rabies treatment.

The safety and efficacy of the oral rabies vaccine SAG2 in Indian stray dogs

India is one of the countries with the highest prevalence of human rabies throughout the world. Dogs are primarily responsible for rabies transmission. Among them, stray dogs play a major role in that country. Parenteral vaccination programmes are insufficient to eliminate rabies partly due to difficulties in establishing satisfactory immunisation coverage in the dog population in view of the high proportion of stray dogs. Oral vaccination may be a useful adjunct to parenteral vaccination by increasing dog vaccination coverage. Safety, immunogenicity and efficacy of Rabidog SAG2 bait were evaluated in Indian stray dogs in captivity. Safety of SAG2 was demonstrated by the absence of adverse clinical sign, salivary excretion and absence of replication of the vaccine strain in brain and salivary glands of 21 vaccinated dogs, even when immunodepressed. Efficacy was shown 109 days post-vaccination after challenge with a highly virulent street rabies virus which killed all five controls whereas all nine vaccinated dogs survived, despite the fact that only five out of nine had seroconverted before challenge.

Towards a unique and transmissible vaccine against myxomatosis and rabbit haemorrhagic disease for rabbit populations

Currently available vaccines against myxomatosis and rabbit hemorrhagic disease virus (RHDV) are not suited to immunise wild rabbit populations, as vaccines need to be delivered individually by conventional veterinary practices. As an alternative approach, research in Spain has focused on the development of a transmissible vaccine. A recombinant virus has been constructed based on a naturally attenuated myxoma virus (MV) field strain, expressing the RHDV capsid protein (VP60). Following inoculation of rabbits, the recombinant virus (MV-VP60) induced specific antibody responses against MV and RHDV, conferring protection against lethal challenges with both viruses. Furthermore, the recombinant MV-VP60 virus showed a limited horizontal transmission capacity, either by direct contact or in a flea-mediated process, promoting immunisation of contact uninoculated animals. Efficacy and safety of the vaccine have been extensively evaluated under laboratory conditions and in a limited field trial. The development of the transmissible vaccine strategy and the steps being taken to obtain the marketing authorisation for the vaccine in the European Union are presented in this review.

Safety evaluation of a recombinant myxoma-RHDV virus inducing horizontal transmissible protection against myxomatosis and rabbit haemorrhagic disease

We have recently developed a transmissible vaccine to immunize rabbits against myxomatosis and rabbit haemorrhagic disease based on a recombinant myxoma virus (MV) expressing the rabbit haemorrhagic disease virus (RHDV) capsid protein [Bárcena et al. Horizontal transmissible protection against myxomatosis and rabbit haemorragic disease using a recombinant myxoma virus. J. Virol. 2000;74:1114-23]. Administration of the recombinant virus protects rabbits against lethal RHDV and MV challenges. Furthermore, the recombinant virus is capable of horizontal spreading promoting protection of contact animals, thus providing the opportunity to immunize wild rabbit populations. However, potential risks must be extensively evaluated before considering its field use. In this study several safety issues concerning the proposed vaccine have been evaluated under laboratory conditions. Results indicated that vaccine administration is safe even at a 100-fold overdose. No undesirable effects were detected upon administration to immunosuppressed or pregnant rabbits. The recombinant virus maintained its attenuated phenotype after 10 passages in vivo.