A field study was undertaken to examine the efficacy of serogroup-specific vaccination for the control and elimination of virulent footrot involving 12 commercial sheep farms in south-eastern Australia. Overall, virulent footrot was eliminated from four flocks, two of which had 2 serogroups, and the others 4 or 5 serogroups. In the remaining nine flocks, in which there were more than two serogroups, footrot was eliminated from two, and controlled in all but three. Of the latter, one pulled out of the trial, and two had an initial poor response to vaccination due to the unexpected presence of serogroup M, which was not included in routine test panels at the time. Control was achieved in these flocks after vaccinating against serogroup M.
Dhungyel, O., Schiller, N., Eppleston, J., Lehmann, D., Nilon, P., Ewers, A., Whittington, R. 2013, ‘Outbreak-specific monovalent/bivalent vaccination to control and eradicate virulent ovine footrot’, Vaccine 31(13), pp. 1701-1706
Footrot is a contagious disease of small ruminants which is caused by the bacterium Dichelobacter nodosus. In its virulent form there are severe economic losses and a very significant animal welfare issue. Sheep and goats can be vaccinated for treatment and prevention of the disease. There are 10 different serogroups of D. nodosus (A-I and M) and immunity is serogroup-specific. When all 10 serogroups are presented together in a vaccine, protection persists for only a few months due to “antigenic competition”. Consequently we evaluated the use of sequential monovalent or bivalent vaccines to control/eliminate/eradicate virulent footrot in a longitudinal intervention study on 12 commercial farms in southeast Australia with flock sizes of approximately 1200-4200 sheep. Overall, virulent footrot was eradicated from 4 of the flocks, 2 of which had 2 serogroups, and the others 4 or 5 serogroups. Where there were only 1 or 2 serogroups (3 farms) the clinical response was rapid and dramatic; prevalence was reduced from 45 to 50% before vaccination to 0% (2 farms) or 0.4% (1 farm) after one round of vaccination. In the remaining 9 flocks there were more than 2 serogroups and successive bivalent vaccines were administered leading to eradication of virulent footrot on 2 farms over 4 years and control of the disease on all but 3 of the others. Of the latter farms, 1 discontinued, and 2 initially had poor response to vaccine due to misdiagnosis of serogroup ‘M’, which was previously unknown in Australia. Control was achieved after administration of a serogroup M vaccine. These results provide clear evidence for control, elimination and eradication of virulent footrot by outbreak-specific vaccination in Australia.
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