Outbreak of equine botulism type C associated with consumption of baleage in Brazil.

Overview

• Researchers investigated an outbreak of type C botulism in horses linked to the consumption of baleage in Brazil, leading to illness and deaths on a Quarter Horse stud farm.

Background and Context

• Botulism is a serious neuroparalytic illness caused by botulinum toxins produced by the bacterium Clostridium botulinum.
• There are several serotypes of botulinum toxin (A, B, C, D, E, F, G), with type C commonly associated with animal botulism, especially in birds and some mammals.
• Horses are highly sensitive to botulism and often contract it through ingestion of contaminated feed or wounds infected with the bacteria.
• Baleage is a type of preserved forage typically wrapped to ferment and retain moisture, providing a potentially favorable environment for bacterial growth if not prepared or stored correctly.

Outbreak Description

• The outbreak occurred in March 2024 on a Quarter Horse stud farm located in the Central-West region of Brazil.
• A total of 26 horses housed in stables were fed baleage, of which 22 (85%) developed symptoms of botulism.
• Clinical signs observed in affected horses included:
  • Dysphagia (difficulty swallowing)
  • Muscular weakness
  • Fasciculations (muscle twitching)
  • Progressive recumbency (inability to rise)
• Within a few days, 13 of the 22 affected horses (59%) died, underscoring the fatal nature of botulism in equines without treatment or at advanced stages.

Diagnostic Procedures

• The diagnosis was based on:
  • Clinical presentation and symptom progression consistent with type C botulism.
  • Epidemiological correlation — the feed source (baleage) was common among affected horses.
• Laboratory confirmation involved:
  • Mouse bioassays — the gold standard test for detecting botulinum toxins — which identified type C toxin in liver samples and intestinal contents of affected horses.
  • PCR (Polymerase Chain Reaction) testing — a molecular technique used to detect the presence of toxigenic Clostridium botulinum genes in the baleage, confirming it as the contamination source.

Significance and Implications

• This outbreak highlights baleage as a potential source of botulism in horses, which may be under-recognized compared to other feed types like hay or silage.
• Proper production, storage, and handling of baleage are critical to prevent Clostridium botulinum contamination.
• Veterinarians and horse owners in Brazil and other regions should consider type C botulism in cases of sudden neuromuscular disease following baleage consumption.
• Early diagnosis and intervention are essential because of the rapid progression and high fatality rate.
• Continued surveillance and research into the microbiological safety of horse feeds such as baleage can help mitigate future outbreaks.