Editor's note: This article is part of TheHorse.com's ongoing coverage of topics presented at the 2012 American College of Veterinary Internal Medicine Forum, held May 30 - June 2 in New Orleans, La.
Tetanus and botulism are two diagnoses horse owners never want to receive, both of these equine illnesses are known for moderate to high fatality rates. But fortunately, owners can protect their horses from these diseases by staying up-to-date with annual vaccinations.
During a presentation at the 2012 American College of Veterinary Internal Medicine Forum, held May 30-June 2 in New Orleans, La., Allison Stewart, BVSc (Hons), MS, Dipl. ACVIM, ACVECC, associate professor of equine internal medicine at Auburn University, lectured on diagnosing and managing both tetanus and botulism.
Tetanus
An often fatal disease, tetanus (also called lockjaw) is caused by toxins released by Clostridium tetani, a bacterium that Stewart explained lives in soil, especially in areas with feces present. Horses generally contract tetanus via wound contamination with affected soil.
Stewart said that clinical signs typically take two to four weeks to develop after infection and include:
- A stiff gait;
- A "sawhorse" stance, in which the front legs are extended out in front of the horse and the back legs are positioned further out from the back of the horse;
- Prolapsed third eyelid;
- Flared nostrils;
- Retracted lips;
- Perked ears;
- Exaggerated response to stimuli; and
- Respiratory paralysis.
Veterinarians generally diagnose the disease based on clinical signs and rarely require a culture confirmation, she said.
When caring for an affected horse, Stewart recommended the following treatment protocol:
- Place the horse in a quiet, nonstimulating environment (such as a dark stall), and consider plugging his ears to reduce external stimuli;
- Provide deep bedding or, if necessary and tolerated, a sling;
- Administer sedatives and muscle relaxers to keep the patient as quiet and comfortable as possible;
- Identify any wounds or hoof abscesses and ensure they are well-drained and have good oxygen exposure;
- Treat wound infections with the antibiotic metronidazole;
- Administer antitoxin as soon as tetanus is suspected; and
- Make use of parenteral (intravenous) nutrition and intravenous electrolytes or feeding and watering via a nasogastric tube.
"The prognosis is good if 1) the horse can still drink; 2) the horse remains standing (there's an 80% mortality rate if recumbent); and 3) the horse survives more than one week after the onset of signs," Stewart said.
Although fatality rates for tetanus can reach as high as 50% to 75%, there is some good news: Tetanus is largely preventable, and an antitoxin can be effective if administered early in the disease process.
"Although horses are traditionally vaccinated with tetanus toxoid each year, protection is probably longer lasting," Stewart said. "The vaccine is cheap and effective and the best insurance you can ever buy for your horse. There is no excuse not to vaccinate horses, but in an emergency an antitoxin can be given to horses to provide very rapid, but short-lasting immunity to the toxin produced by C. tetani."
For horses without a vaccination history or not previously vaccinated against tetanus, Stewart recommends prophylaxis (disease prevention) if wounds are sustained. She recommended administering 1,500 IU of tetanus antitoxin and simultaneous vaccination with tetanus toxoid.
Botulism
Switching gears, Stewart turned her attention to diagnosing and managing botulism, an often fatal disease that affects horses of all ages.
"Botulism is caused by a toxin produced by C. botulinum," she explained. "Eight types of toxin--A, B, Ca, Cb, D, E, F, and G--have been recognized," with type B being associated with the majority of equine botulism cases each year.
Stewart said there are three ways horses can contract botulism:
- Toxin ingestion (via contaminated forage);
- Wound contamination; and
- Toxicoinfections (also known as shaker foal syndrome, this form occurs in foals when spores are consumed, germinate, and are absorbed by the gastrointestinal tract).
Clinical signs of botulism typically arise three to seven days after infection and include:
- Dysphagia (the inability to swallow);
- Progressive muscle paralysis;
- Restlessness;
- Incoordination (ataxia);
- Inability to stand or shaking as they stand up;
- Lateral recumbency;
- Decreased tongue and tail tone.
- Veterinarians generally diagnose the disease via clinical signs and identifying the toxin in feces, serum, or other tissue, she said.
- Treatment includes:
- Multivalent (multi-strain) antiserum administration;
- Movement restriction;
- Ventilation or oxygen therapy, if needed;
- Antibiotics for secondary complications;
- Cathartic (a purging medication) administration;
- Parasympathomimentic drug (which stimulates or mimics the parasympathetic nervous system) administration; and
- Supportive care.
As with tetanus, botulism caused by C. botulinum type B is largely preventable via vaccination administration, Stewart said. There are not yet vaccines available to protect against the other types, she noted.
"To prevent shaker foals, vaccinate the mare three times at monthly intervals (with the last dose coming) two to three weeks before foaling," she recommended. During subsequent pregnancies she suggested a single injection during the last month.
"For the protection of adults, (administer) yearly vaccinations after the initial series of three doses," she said.
Take-Home Message
Both tetanus and botulism can be fatal if contracted, but annual vaccination reduces horses' risk of contracting. Discuss individual vaccine recommendations if questions arise about a particular animal.
Disclaimer: Seek the advice of a qualified veterinarian before proceeding with any diagnosis, treatment, or therapy.