Abstract
Since 2015, outbreaks of foot-and-mouth disease (FMD) in the Middle East have been caused by a new emerging viral lineage, A/ASIA/G-VII. Invitro vaccine matching data indicated that this virus poorly matched (low r1-value) with vaccines that were being used in the region as well as most other commercially available vaccines. The aim of this study was to assess the performance of two candidate vaccines against challenge with a representative field virus from the A/ASIA/G-VII lineage. The results from an initial full dose protection study provided encouraging data for the A/MAY/97 vaccine, while the A22/IRQ/64 vaccine only protected 2/7 vaccinated animals. In view of these promising results, this vaccine was tested in a potency test (PD50) experiment in which 5 cattle were vaccinated with a full dose, 5 cattle with a 1/3 dose and 5 cattle with a 1/9 dose of vaccine. At 21 days post vaccination these vaccinated cattle and 3 control cattle were challenged intradermolingually with a field isolate from the A/ASIA/G-VII lineage. The intra-serotype heterologous potency test resulted in an intra-serotype heterologous potency of 6.5 PD50/dose. These data support previous studies showing that a high potency emergency vaccine can protect against clinical disease when challenged with a heterologous strain of the same serotype, indicating that not only the r1-value of the vaccine, but also the homologous potency of a vaccine should be taken into account when advising vaccines to control an outbreak.
Highlights
Foot-and-mouth disease (FMD), caused by foot-and-mouth disease (FMD) virus (FMDV), is a contagious disease of even-toed ungulates, of which cattle, water buffalo, pigs, sheep and goats are the most important affected domesticated livestock species
In one of the cattle vaccinated with A22 /IRQ/64, FMDV genome could be detected by RT-PCR for 1 day
Serological (virus neutralisation test (VNT) titre against challenge strain A/IRN/22/2015 at the day of challenge) and virological results in the 8-day period following challenge, in the full dose protection test in cattle vaccinated with A22 /IRQ/64 and A/MAY/97 vaccine, and unvaccinated animals challenged with
Summary
Foot-and-mouth disease (FMD), caused by FMD virus (FMDV), is a contagious disease of even-toed ungulates, of which cattle, water buffalo, pigs, sheep and goats are the most important affected domesticated livestock species. FMD free countries that experience an outbreak of FMD suffer high losses due to loss of access to export markets. FMDV serotypes are based on complete absence of cross-protection. There are 7 serotypes of FMDV and many different genetic and antigenic variants within these serotypes which exhibit complete to partial degrees of cross-protection [2]. The level of cross-protection within a serotype can sometimes be low, and it is essential to monitor whether new strains will escape vaccine-induced protection. In 2015, FMDV serotype A viruses from the A/ASIA/G-VII lineage
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