Ian R Poxton*, Leonie Hunter. Hannah Lough and Keith Miller (1)
Department of Medical Microbiology, University of Edinburgh Medical School. Edinburgh, Scotland, UK; and (1) Biotrix Ltd.

Equine grass sickness is an often fatal dysautonomia of unkown aetiology. It is found in Northern Europe. and especially in the eastern half of the United Kingdom. It is characterised by dysfunction of the GI tract, as a result of degeneration of the enteric autonomic nerves, particularly in the ileum, and presents in acute. subacute and chronic forms. Its South American equivalent - mal seco - reported in horses from the Patagonia region of Argentina and Chile, appears clinically and pathologicallv extremely similar.
We have hypothesised that the symptoms could be caused by a toxicoinfection with type III Clostridium botulinum; possibly type C. Clinical cases and controls have been investigated for the presence of C. botulinum type Cl neurotoxin (BoNT/C) in post-mortem specimens of contents of distal ileum, and in rectal samples of living horses.
Results to date show that in clinical cases of grass sickness BoNT/C has been found in 59% of ileum specimens (43% of chronic cases and 70% acute/subacute) compared to 7% of controls (1/14 horses), and in 47% of rectal samples (61% of chronic cases and 25% acute/subacute) compared to 3% of controls (1/36).
In parallel serological studies, we have seen rising titres of specific anti-BoNT/C IgC during the course of the illness in some chronic cases. but overall, serological data is proving difficult to interpret.
Currently we are working on the hypothesis that the development of grass sickness involves a nutritional trigger but the susceptibility to disease may be determined by the immune status within the ileal mucosa. We are aware however, that although we have demonstrated an association between clinical symptoms of grass sickness and BoNT/C in the ileum, we have not yet proved that there is a causal relationship.