Serological evidence for a non-protective RHDV-like virus

Area of Science:

• Veterinary Virology
• Immunology
• Wildlife Disease Ecology

Background:

• Rabbit haemorrhagic disease (RHD) is a highly contagious viral disease affecting rabbits.
• Monitoring of a wild rabbit population in France since 2000 provided data during a 2001 RHD outbreak.
• Previous observations suggested the presence of non-protective antibodies, hinting at an unknown viral agent.

Purpose of the Study:

• To investigate the nature of antibodies detected during a RHD outbreak in wild rabbits.
• To determine if these antibodies conferred protection against Rabbit Haemorrhagic Disease Virus (RHDV).
• To identify the causative agent responsible for the observed serological findings.

Main Methods:

• Analysis of blood and liver samples from deceased wild rabbits during an RHD outbreak.
• Enzyme-linked immunosorbent assay (ELISA) using VP60-RHDV antigen to detect antibodies.
• Monoclonal antibody (Mab)-based differential ELISA to determine disease form (acute/chronic).
• Sequencing of the VP60 gene from isolated viruses.

Main Results:

• RHDV was confirmed in all tested liver samples.
• 20 out of 21 rabbits tested positive for RHD antibodies with high titres (>= 1/400) using VP60-RHDV ELISA.
• Mab-specific ELISA indicated antibodies were not against RHDV, despite rabbits dying from acute RHD.
• Sequencing showed isolated RHDV strains were common, not a novel variant.
• Detected antibodies appeared prior to the fatal RHDV infection, suggesting a pre-existing, non-protective immune response.

Conclusions:

• The study identified detectable but non-protective antibodies in wild rabbits during an RHD outbreak.
• These antibodies were likely induced by a RHDV-like virus, distinct from the RHDV strains causing the fatal disease.
• This finding highlights the complexity of viral evolution and host immune responses in wildlife populations.