Animal botulism is a neuro-paralytic disease caused by neurotoxins (BoNT) produced by a gram-positive, sporeforming anaerobic bacterium named Clostridium botulinum. BoNTs are classified into 7 serotypes from A to G on the basis of their antigenic properties. An additional serotype (known as BoNT/H) has been proposed, but its confirmation as a novel toxin serotype requires further experimental validation1. Although serology showed to be a useful tool to discriminate vaccinated from unvaccinated cows, some studies demonstrated that non-fatal natural exposure results inadequate to cause seroconversion to type D toxin2,3.
In 2012, slight signs referable to botulism were observed in a dairy cattle herd of ten lactating Simmental cows, four pregnant heifers and seven calves of the same breed. The disease spread over a period of 11 weeks with a low mortality rate (one cow). The majority of the affected animals recovered after five to eight weeks since the beginning of the symptoms. The diagnosis of botulism type C was assessed by PCR type-specific protocols, bacteriological examination and BoNT detection. An in-house ELISA was developed, validated on a vaccinated herd and applied in the studied clinical case. The ROC analysis provided a specificity of 95% and a sensitivity of 90% for the developed ELISA. All ELISA positive animals (8/14) tested positive also by PCR and neurotoxin gene characterization showed that the strain was a non-chimeric type C.
Contrary to what demonstrated for type D, our findings suggest that non-chimeric type C BoNTs can provide a seroconversion in cattle. This could be due to the fact that type C neurotoxin is less lethal to bovine than type D/C or C/D. This possibility has already been demonstrated in chicken where type C/D showed to be more toxic than type C4. This difference in toxicity could explain the slight clinical signs and the seroconversion.