Evidence of Clostridium botulinum and its toxin (BoNT) in milk and udder tissue samples from dairy cows has led German researchers to call for "statistically relevant testing of healthy and sick cows from healthy and affected farms."
Their findings have important implications for reconsidering the "whole complex of the zoonosis 'botulism'," they write in Veterinary Record.
"Positive milk samples containing botulinum toxin or bacteria raise concern of food safety for the human consumer," say Helge Böhnel and Frank Gessler from Miprolab mikrobiologische Diagnostik GmbH in Göttingen.
Between 2002 and 2010, the pair analyzed 99 milk samples from 37 farms, and 51 udder specimens from 52 farms in Germany. All farms were known to be affected by botulism.
Milk samples were taken at the farms during milking, and udder tissue samples were taken within 24 hours of a cow's death, and all deceased cows had been milked on the previous day. After culturing samples for 4 days, toxicity of the bacteria was demonstrated by injecting them into, or feeding them to mice that were monitored for 96 hours for signs of illness or death.
A total of five (13.5%) out of 37 farms had milk samples that were positive for C. botulinum or BoNT, and 17 (33.3%) of 51 farms had positive udder samples for these bacterium. Statistical analysis revealed no chance that season had had an impact on the number of positive results per farm, note the researchers.
Three milk samples that were positive for BoNT and two that were positive for C. botulinum contained types A, B, and E, which are considered to be the most dangerous strains for humans.
While the findings do not explain the origin of C. botulinum and BoNT in the udder tissue samples, Böhnel and Gessler suggest that future investigations could consider "the possible role of mastitis parameters in toxicogenesis."
They add that improved risk analysis strategies for dairy farms could include feed management, transparent transport and storage conditions of dairy products, and testing of healthy and sick animals from farms with, and without, known botulism involvement.
"It should be emphasised that the pathogen may spread, mainly as spores, by aerosols or surface contamination within different areas of a dairy, where a variety of milk products intended for addition to novel food preparations are being stored," the researchers conclude.
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