AAEP 2002: Botulism in Foals: A Survivable Disease

Historically, botulism has usually been seen as a fatal problem for the young foal. However, Pamela Wilkins, DVM, PhD, of the Graham French Neonatal Intensive Care Unit at the University of Pennsylvania’s New Bolton Center, said that she has had a positive experience in treating affected foals. In her AAEP Convention presentation “Botulism in Foals: A Survivable Disease,” she said that botulism in foals less than six months of age is readily treated, with a survival rate of more than 95% in appropriately treated foals. Treatment can include nursing care, intravenous fluid support, nasogastric or nasoesophageal tube feeding, broad-spectrum antimicrobials (excluding aminoglycoside and tetracycline classes), oxygen therapy, and the administration of botulism antitoxin. Approximately 33% of affected foals might require positive pressure mechanical ventilation, she said.

Wilkins and her colleagues did a retrospective study in which they examined data from 28 botulism-affected foals under the age of six months treated at the Graham French Neonatal Intensive Care Unit from 1989 to 2001. Of the 28 foals, 25 survived with no reported long-term or career-limiting problems.  All surviving foals were treated with botulism antitoxin shortly after arrival at the clinic. One foal died from respiratory failure and cardiac arrest, while two foals were euthanized for economic reasons.

There are three primary ways that the botulism toxin can enter the horse--intestinal toxicoinfection, ingestion of preformed toxin, and absorption of toxin from wounds infected with <I>Clostridium botulinum.<I> The toxin then affects the neuromuscular (nerve-muscle) junction, resulting in weakness that progresses to flaccid paralysis (paralysis with a loss of muscle tone). In addition, foals can suffer from difficulty swallowing (dysphagia), muscle trembling, and recumbency (unable to rise). Some cases experience respiratory failure as a result of weakness of the respiratory muscles. Acute respiratory failure is common in human infants and adults with botulism, and thirteen of the 28 foals in this study experienced respiratory failure. Ventilatory management--such as monitoring arterial blood gas parameters, administering oxygen by intra-nasal insufflation, and mechanical ventilation--might then be indicated, according to Wilkins.

“Recognition of the severity of respiratory compromise is essential for appropriate management of these cases and requires the ability to obtain reliable arterial blood gas data,” she continued. “The availability of ‘bedside’ blood-gas monitors should allow the practitioner to manage many of these cases in field situations, given the ability to administer botulism antitoxin, to provide supplemental oxygen by intra-nasal insufflation, and to recognize when respiratory failure is severe enough to warrant referral and more extensive respiratory therapy.”

Younger foals born to unvaccinated mares and those with failure of passive transfer are at an increased risk, as are older foals when maternal antibodies are decreasing. The good news is that vaccination in adults is usually protective, said Wilkins. Cost of treatment might be a determining factor for survival, and this depends on the length of hospitalization and treatments needed, which varies by clinic.

“Foals requiring parenteral nutrition or mechanical ventilation will be significantly more expensive to treat,” said Wilkins. She said that the cost of the polyvalent antitoxin alone was around $1,000, although a monovalent product that has recently become available is less costly. Diagnosis is through clinical signs and can be confirmed through isolation of the toxin in blood or feces samples; however, sometimes tests can still be negative. Prognosis is guarded to poor for adult horses that become recumbent.

About the Author

Sarah Evers Conrad

Sarah Evers Conrad has a bachelor’s of arts in journalism and equine science from Western Kentucky University. As a lifelong horse lover and equestrian, Conrad started her career at The Horse: Your Guide to Equine Health Care magazine. She has also worked for the United States Equestrian Federation as the managing editor of Equestrian magazine and director of e-communications and served as content manager/travel writer for a Caribbean travel agency. When she isn’t freelancing, Conrad spends her free time enjoying her family, reading, practicing photography, traveling, crocheting, and being around animals in her Lexington, Kentucky, home.

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