Sites of persistence of Fusobacterium necrophorum and Dichelobacter nodosus: a paradigm shift in understanding the epidemiology of footrot in sheep

Abstract

AbstractSites of persistence of bacterial pathogens contribute to disease dynamics of bacterial diseases. Footrot is a globally important bacterial disease that reduces health and productivity of sheep. It is caused byDichelobacter nodosus, a pathogen apparently highly specialised for feet, whileFusobacterium necrophorum, a secondary pathogen in footrot is reportedly ubiquitous on pasture. Two prospective longitudinal studies were conducted to investigate the persistence ofD. nodosusandF. necrophorumin sheep feet, mouths and faeces, and in soil. Molecular tools were used to detect species, strains and communities. In contrast to the existing paradigm,F. necrophorumpersisted on footrot diseased feet, and in mouths and faeces; different strains were detected in feet and mouths.D. nodosuspersisted in soil and on diseased, but not healthy, feet; similar strains were detected on both healthy and diseased feet of diseased sheep. We conclude thatD. nodosusandF. necrophorumdepend on sheep for persistence but use different strategies to persist and spread between sheep within and between flocks. Elimination ofF. necrophorumwould be challenging due to faecal shedding. In contrastD. nodosuscould be eliminated if all footrot-affected sheep were removed and fade out ofD. nodosusoccurred in the environment before re-infection of a foot.