Protection in sheep against heterologous challenge with serotype Asia-1 foot-and-mouth disease virus using high potency vaccine

Abstract

Foot-and-mouth disease virus (FMDV) serotype Asia-1 is prevalent in countries considered high risk for incursion into Australia, and has recently been responsible for a number of outbreaks in India, Bangladesh, Pakistan and Turkey. In vitro vaccine matching has shown a number of contemporary FMDV Asia-1 strains vary antigenically to the Asia-1 Shamir vaccine strain, which could result in poor protection with use of this vaccine. Therefore it was important to test the ability of the Asia-1 Shamir vaccine to protect sheep from challenge with a recent, heterologous strain at different days post-vaccination (dpv), including in an emergency vaccination scenario (challenge 4 or 7 dpv). Sheep (5 per group) were challenged with the Asia-1/PAK/19/2014 isolate by intra-nasopharyngeal instillation 21 (V21), 7 (V7) or 4 (V4) dpv with high-potency (>6 PD₅₀) Asia-1 Shamir vaccine. An additional five sheep were mock-vaccinated with adjuvant only (antigen-free preparation) 4 days prior to challenge (A4), and five unvaccinated (UV) control sheep were also challenged. All V21, V7 and V4 sheep were protected from clinical FMD. Eighty percent of V21 sheep and 40% of V7 sheep had sterile immunity, however all V4 sheep became systemically infected. Vaccination reduced excretion of virus in nasal and oral secretions but had no effect on the development of persistent infection. All A4 sheep and UV control sheep developed clinical FMD. The high-potency Asia-1 Shamir vaccine will protect against disease should an outbreak of contemporary Asia-1 viruses occur. Intranasopharyngeal instillation is an effective challenge method for use in vaccine efficacy studies in sheep.

Keywords: Foot-and-mouth disease virus; Heterologous challenge; Sheep; Vaccine efficacy.