6666’s veterinarian addresses misconceptions about strangles

Nov 4, 2011

Practical information about management of strangles in horses was provided by Dr. Glenn Blodgett at the Equine Infectious Disease and Ranch Management Symposium recently sponsored by Cargill Animal Nutrition and the Texas A&M College of Veterinary Medicine and Biomedical Sciences.

Blodgett is resident veterinarian and horse division manager at 6666’s Ranch in Guthrie, TX, that raises cattle and produces ranch, racing and western performance Quarter horses.

Blodgett has worked with ranch, rodeo, show and breeding horses during his 30 years at the 6666’s breed ing

and veterinary facility and preceding eight years in private practice.

He presented information about the transmission, clinical signs, diagnosis, treatment and prevention of strangles in ranch situations or when dealing with individual horses. Blodgett additionally addressed many misconceptions about the disease.

Strangles, a highly contagious disease of horses, is caused by the bacteria Streptococcus equi. Strangles gets its name because it can cause lymph node enlargement at the horse’s throatlatch severe enough to obstruct airways.

“I see strangles commonly in weanlings and horses that have no immunity or prior exposure to the disease,” said Blodgett. “There are probably several factors going on with foals right around weaning such as stress from separation from their mothers, a decline or absence of maternal antibodies, and other issues adjusting to their new environment.”

“I think strangles in foals can be likened to shipping fever in calves, with the same post weaning stresses except foals, in my experience, for the most part aren’t predisposed to strangles by respiratory viruses, unlike cattle. In my experience, older horses that have never been exposed to strangles and get sick with the disease, on average, handle it better than younger animals.”

Veterinary literature suggests that approximately 75 percent of horses are immune for four to five years after having strangles. However, Blodgett considers most horses he sees to have lifelong immunity after having strangles. He speculates that those recovered horses get exposed to strangles every so often as it cycles through horse populations providing opportunities to maintain their immunity. However, if many years go by without exposure, these horses may be more likely to develop disease.

The organism enters through the mouth or nose and attaches to the tonsils. The first clinical signs of strangles occur three to 14 days later in the form of elevated rectal temperature of 103 or higher. Horses go off feed and other symptoms include depression, coughing and thick, profuse nasal discharge. Lymph nodes around throatlatch or under jaws become firm, often abscessing and rupturing seven to 10 days after onset of clinical signs.

Illness can be 10 days to three weeks. However, when sick horses improve and quit coughing, they are oftentimes misconstrued to be non-contagious and reintroduced to other horses, thereby spreading the disease.

Recent additions to remudas, horse farms and stables are most often the cause of a strangles outbreak because a recovering horse may shed the organism for several weeks.

“Nasal shedding of strangles organisms begins two to three days after onset of fever and persists for two to three weeks,” Blodgett explained. “Thick nasal discharges via horse to horse contact during social behavior directly spread the bacteria. Indirect spread occurs through contact with nasal or abscess secretions in or on contaminated trailers, housing, water sources, feed, tack and clothing of handlers. There is a lack of field-based proof for prolonged environmental persistence of the strangles organism.”

Blodgett emphasized that the organism doesn’t live in soil, pastures or water for long periods of time. Outside of the horse, strangles may live a week or two maybe if it’s around water or feed troughs and out of direct sunlight. He explained that the strangles bacteria is perpetuated in guttural pouches of carrier horses who aren’t sick and have no nasal discharge. Guttural pouches are air-filled connections between a horse’s nasal passage and its inner ear capable of draining into the throat. It is similar to the Eustachian tube in humans.

“This intermittent shedding of bacteria by carriers, about 10 percent of affected animals across the board, may go on for years. We identify carriers by submitting pharyngeal lavages, fluid taken from flushing the horse’s throat, for culture and detection of presence of the organism with PCR/DNA testing,” described Blodgett . “To eliminate the carrier stage, it’s imperative to address issue of pouch infections. We use a series of guttural pouch flushes, medication infusions and subsequent testing to rid horses of this intermittent shedding problem.”

“If not treated, small masses called chondroids may form in these pouches serving as a chronic source of the infection. We see them with our endoscope when examining carrier horses. Sometimes they can be flushed out or we have an instrument to break up the larger chondroids to facilitate their removal.”

When certain susceptible horses lack sufficient immunity, the organism can spread to other sites via the blood or lymph vessels, occasionally forming intraabdominal abscess termed ‘bastard strangles.’ This syndrome’s manifested by weight loss, fever, lethargy and colic. Infrequently, secondary immune-mediated problems such as vasculitis or purpura hemorrhagica occur.

Blodgett explained that strangles can be clinically diagnosed visually; however, he thinks culturing the easily-obtained sample is good to do in some cases. But as part of his vigilance to prevent or eliminate strangles at the ranch, particularly with the seasonal movement of outside animals, Blodgett said they culture every abscess seen in horses on the premises as Strep equi can sometimes attack other tissues.

Blood testing is available for certain situations; for example, to support diagnoses of strangles-related syndromes. Blodgett also uses this testing in adult horses whose strangles vaccination history is unknown to determine their immunity and decide if vaccination is indicated. Additionally, he’ll use serology testing in situations when somebody buys or hauls a horse and wants to know what previous exposure it’s had before making decisions about vaccination.

“When treating strangles, I like to keep patients comfortable with non-steroidal anti-inflammatory drugs like Banamine or Bute. I drain abscesses when necessary,” related Blodgett. “But I try to avoid antibiotics unless the patient is so overwhelmed that they need help eliminating the infection. We know that antibiotics can prolong the course of the disease and increase likelihood of secondary complications associated with this bacteria. I think antibiotics give false sense of security, causing regression of signs or decrease of lymph node swelling only to have some cases recur a couple weeks later.”

Two commercial vaccines against strangles are available, an intranasal modified live product and a killed intramuscular vaccine. Blodgett uses the killed product for pre-foal mare vaccinations to boost immunity in colostrum and uses the intra-nasal vaccine in other horses they vaccinate.

“To date, there has not been the ideal strangles vaccine in regards to efficacy and safety . In my whole veterinary career, it has been frustrating to be unable to see the development of a good vaccine or conquer a disease that can potentially produce lifelong immunity despite years committed to dedicated research,” Blodgett lamented.

His advice for initial management of horses with strangles is to recognize those feverish, depressed horses early and isolate them before the nasal discharge is apparent. He recommends taking temperatures in those horses so they can be moved early when they are less contagious than they will be a few days later.

“Clean and disinfect items coming in contact with the bacteria with products, for example bleach, that work in the presence of organic matter,” Blodgett explained. “Drain or pump out and clean troughs then replace that water if feasible. When cleaning’s impractical, removing the contaminated water then refilling a trough will at least dilute the organism, keeping the sheer numbers of down.”

“I warn folks going to rodeos or horse shows to bring their own water buckets and not let their horses drink from a source where other horses can water. I think a lot of horses get nose to nose exposure at shows when folks are sitting around visiting.”

“Strangles is annoying.

It’s kind of like childhood diseases; they need exposure or proper vaccination at some point early to provide some immunity to carry with them. The only good thing about strangles is that if horses do see it and deal with it, then they can be kind of bomb-proof after that,” said Blodgett.

A disease Blodgett remembers hearing the old cowboys talk about as ‘distemper’ when he was a kid has given him grief for almost 40 years treating his equine patients. It’s a constant challenge. But Blodgett uses his experience coupled with current testing, carrier identification, treatment, management and isolation protocols to maintain a ‘chokehold’ on strangles. — Ginger Elliott, WLJ Correspondent