The role of the environment in transmission of Dichelobacter nodosus between ewes and their lambs

Abstract

Dichelobacter nodosus (D. nodosus) is the essential causative agent of footrot in sheep. The current study investigated when D. nodosus was detectable on newborn lambs and possible routes of transmission. Specific qPCR was used to detect and quantify the load of D. nodosus in foot swabs of lambs at birth and 5-13 h post-partum, and their mothers 5-13 h post-partum; and in samples of bedding, pasture, soil and faeces. D. nodosus was not detected on the feet of newborn lambs swabbed at birth, but was detected 5-13 h after birth, once they had stood on bedding containing naturally occurring D. nodosus. Multiple genotypes identified by cloning and sequencing a marker gene, pgrA, and by multi locus variable number tandem repeat analysis (MLVA) of community DNA from swabs on individual feet indicated a mixed population of D. nodosus was present on the feet of both ewes and lambs. There was high variation in pgrA tandem repeat number (between 3 and 21 repeats), and multiple MLVA types. The overall similarity index between the populations on ewes and lambs was 0.45, indicating moderate overlap. Mother offspring pairs shared some alleles but not all, suggesting lambs were infected from sources(s) other than just their mother's feet. We hypothesise that D. nodosus is transferred to the feet of lambs via bedding containing naturally occurring populations of D. nodosus, probably as a result of transfer from the feet of the group of housed ewes. The results support the hypothesis that the environment plays a key role in the transmission of D. nodosus between ewes and lambs.

Keywords: D. nodosus; Disease reservoirs; Footrot; Pathogen transmission.

Fig. 1

Presence of D. nodosus in the environmental samples. Absolute quantification of rpoD gene in bedding samples from the storage area, used bedding samples and faeces compacted within the interdigital space. Each bar is the average of triplicate analyses, error bars represent ± standard deviation.

Fig. 2

Detection of pgr variants in the community DNA. Presence of pgrA, pgrB and rpoD on the feet of 10 ewes and 10 lambs. pgrA/B was absent/below the detection limit in the samples where no data is shown. (E = Ewe; L = Lamb).