Diagnosis of footrot based on humoral immune responses to Dichelobacter nodosus

The primary and anamnestic serological responses in sheep with footrot were evaluated under controlled conditions as work continued on a new diagnostic approach based on testing blood samples.

Whittington, R. J. (1996) Further observations on the primary and anamnestic humoral responses to Dichelobacter nodosus in sheep in relation to the diagnosis of footrot. Research in Veterinary Science, 60, 126-133. 10.1016/s0034-5288(96)90006-5

Summary: An anamnestic serological test for ovine footrot was evaluated. Footrot-free lambs were infected with Dichelobacter nodosus and treated four, six or eight weeks later. There were strong linear correlations between the severity of the lesions and both the primary response and the anamnestic response evoked by the subcutaneous injection of an antigen from D nodosus 16 weeks after the treatment of the lambs; the latter correlation was stronger than the correlations reported elsewhere in mature sheep. Similar anamnestic responses were elicited six and 12 months after the treatment of mature sheep which had had severe lesions. Natural anamnestic responses were demonstrable in sheep which had had recurrent clinical episodes of virulent footrot. The non-specific humoral responses after the anamnestic challenge of footrot-free sheep increased with age and did not depend on the dose of the antigen between 10 and 200 ug. Using the pooled data from sheep of all ages and a positive-negative cut-off which was selected to obtain a sensitivity of 75 per cent, the specificity of the anamnestic test was 90 per cent, similar to that reported for the primary response when it was used to diagnose footrot. The anamnestic test can be applied to determine the presence and severity of footrot in young sheep.

If you would like a copy of the scientific paper, please send a request by email to: richard.whittington@sydney.edu.au