An outbreak of type C botulism in 12 horses and a mule.

The research was conducted by a USDA Early Response Team to investigate the deaths of several horses and a mule in Arizona. The study found out that these deaths were due to an outbreak of type C botulism, possibly transferred through birds from a nearby horse burial site.

Investigation into Animal Deaths

• The researchers performed a comprehensive study at the request of local animal health officials, after 13 animals including 12 horses and one mule died between August 1998 and January 1999. These animals were housed at five different facilities within a 7.4 square mile area in Northern Arizona.
• The team observed the clinical signs displayed by the affected animals, such as rapid progression to lateral recumbency, muscular weakness, and paresis of the tongue, throat, or lips. Despite these symptoms, the animals remained alert and expressed interest in eating and drinking, even while recumbent.

Euthanization and Sample Collection

• All 13 affected animals were eventually euthanized due to their condition.
• In an attempt to determine the cause of death, the researchers collected samples of faeces or intestinal contents from three of the affected horses. From these samples, they were able to isolate Clostridium botulinum type C, a bacteria known to produce a deadly neurotoxin leading to botulism.

Source of Botulism

• Further investigation and sample collection led researchers to detect preformed botulinum toxin in soil samples and bird droppings collected from a nearby horse burial site.
• The researchers generated a hypothesis that the outbreak was a result of birds, presumably ravens, feeding at the burial site and then transferring the botulism toxin to the facilities housing the live animals. This conclusion was based on the fact that botulism toxin can persist in the environment and may be carried into feed or water sources by birds, thereby infecting susceptible animals.

Implications of the Research

• This research draws attention to the potential risks associated with improper animal burial practices and the potential for botulism outbreaks in certain environments. The findings suggest that further preventive measures may be needed to prevent such outbreaks, such as bird deterrent strategies and improved sanitation measures around animal housing facilities.
• Furthermore, this study underscores the importance of rapid response investigations in understanding the causes and transmission patterns of outbreaks, which can assist in the development of more effective disease prevention and control strategies.