The role of serogroup specific vaccines in the control of footrot in sheep

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Nabb, Elizabeth J. ORCID: https://orcid.org/0000-0001-7281-0203 (2023). The role of serogroup specific vaccines in the control of footrot in sheep. University of Birmingham. Ph.D.

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Abstract

Lameness in sheep is a welfare concern and the most commonly reported cause of lameness in sheep flocks in England is footrot, a polymicrobial disease that requires the presence of the fimbriated bacterium Dichelobacter nodosus. There are ten antigenically distinct serogroups of D. nodosus, named A-I and M. Serogroups A-I are known to be randomly distributed in English sheep flocks and are all contained in the only commercially available vaccine, Footvax®. The efficacy of multivalent footrot vaccines is limited by antigenic competition. Flock-specific bivalent serogroup vaccines have been used to reduce or eliminate footrot from flocks in Nepal, Bhutan and Australia. This strategy had not been
tested under commercial flock conditions in England.
A randomised, double blinded controlled trial was performed in three commercial flocks in South-West England to compare the effect of flock-specific bivalent footrot vaccines against Footvax® and a negative control (saline) on the incidence of lameness and footrot. Within each flock approximately one third of ewes were allocated to each treatment group. The bivalent vaccines contained two of the most prevalent D. nodosus serogroups present in the flock being vaccinated, which were identified by direct PCR of interdigital skin swabs from 20-21 ewes with footrot. Ewes from all treatment groups were mixed together and were monitored every week for lameness and foot lesions for 24 weeks. The prevalence of
injection site reactions at 4,12,16 and 20 weeks after vaccination was measured. Survival analysis was performed to calculate the relative risk of lameness and footrot between the three treatment groups.
It was possible to identify at least one of the two most prevalent serogroups in two of the three flocks by sampling 21 ewes with footrot. Across the combined flocks, the bivalent vaccine significantly reduced the incidence of lameness and footrot cases compared to
saline. The bivalent vaccine was not significantly more protective than Footvax®. The response to vaccination was heterogenous between flocks and within sub-populations of the flocks. Both vaccines were significantly protective in only one flock, in which lameness prevalence was high and the main cause of lameness was footrot. Ewes that had been vaccinated with Footvax® were at three times the odds of developing an injection site
reaction compared to ewes that had been vaccinated with the bivalent vaccine.
The aetiology and prevalence of both infectious and non-infectious causes of lameness varies between commercial flocks in England, and the inclusion of footrot vaccination as part of a lameness control strategy needs to be tailored to individual flocks.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

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