Border disease: virus persistence, antibody response and transmission studies

Area of Science:

• Veterinary Virology
• Animal Infectious Diseases

Background:

• Border disease (BD) is a significant viral disease affecting sheep.
• Understanding viral transmission and host immune response is crucial for disease management.

Purpose of the Study:

• To investigate the transmission of Border disease virus (BDV) to sheep offspring.
• To characterize the duration of viral shedding and identify potential transmission routes.
• To evaluate the immune response in lambs infected with BDV.

Main Methods:

• Oestrus-synchronised sheep were inoculated with BDV at a specific gestational stage.
• Virus isolation, antigen detection, and antibody response were used to confirm transmission.
• Viral shedding was monitored in saliva, urine, and faeces.
• Tissue virus titres were quantified.

Main Results:

• Transmission to offspring occurred in 12 of 19 inoculated sheep, with probable transmission in four others experiencing pregnancy loss.
• Both clinically affected and apparently normal sheep excreted virus for up to 2.5 years.
• Contact transmission to sheep and pigs was observed.
• High virus titres (10^3.5-10^5.5 TCID50/g) were found in most infected sheep tissues.
• Lamb immune responses were highly variable, with some remaining serologically negative for 2.5 years.

Conclusions:

• Border disease virus can be efficiently transmitted to sheep offspring with significant implications for flock health.
• Persistent viral shedding and prolonged infectivity pose a risk for disease spread within and between species.
• The variable immune response highlights challenges in diagnosing and controlling BDV infections.