(5/2018) It was 6 pm and my vet tech called me. A client had just gotten home from work. When she went out to feed her horses, she noticed that her horse's head was swollen from being bitten by a snake. I listened carefully to her history. As it was 38 degrees outside, and snakes are usually not active in the cold, I was already skeptical about the snake bite. I thought about other possible causes of the horse's swollen head.

I'd been to the farm several months ago when one of Mrs. Green's other horses had coliced. Mrs. Green owns a small farm with a horse barn and riding ring. She rides a few times a week but other than a quick walk down the road and back, she never takes her horses off the property. The horses are loved and well cared for. They are well fed and receive frequent vet and farrier care. However based on how worried she was when I treated a mild colic for her, I also knew that she tended to be overly concerned with minor health issues.

When I arrived at the farm, Mrs. Green told me that she thought she had seen a little swelling on her horse yesterday but it had gotten dramatically worse while she was at work. She was not overreacting. Her horse had thick yellow snot pouring out of her nostrils, the entire head was swollen and pus was oozing from the horse's throat. I immediately told her Mrs. Green that this was not a snake bite but that I was instead highly suspicious this was strangles. Strangles is a very contagious respiratory infection caused by the bacteria streptococcus equi. Signs of infection include fever, snotty nose, swollen, and abscessed lymph nodes.

Mrs. Green assured me that she didn't take her horse anywhere recently and no other horses came on to the property. However another one of her horses was also starting to act a little sick. After a quick physical exam of her other horse who also had snotty nose and a single swollen lymph node, I told her I was almost positive that this was strangles and that perhaps a visiting friend had brought the disease onto the property. A nasal swab lab test could confirm the diagnosis in a few days.

It was then that Mrs. Green told me that an unlicensed equine lay dentist had come and floated the horses teeth about 10 days ago. The incubation period for strep equi is 3-21 days. I told Mrs. Green that the lay dentist was the likely source of infection. The dentist had probably forgotten to clean his tools between barns and had floated the teeth of a horse who was shedding strep. Horses can shed strep bacteria and not show obvious signs of illness. Some horses will carry the bacteria in their guttural pouches of the throat, and periodically shed the organism and infect other horses. Multiple antibiotic flushes of the guttural pouches can clear the bacteria and prevent these horses from causing outbreaks, if the owner is aware that their horse is carrying the bacteria and receives treatment.

Unlike human dentists who have long training and required licensure, in some states, equine lay dentists do not have to go to training to call themselves dentists. While some are very knowledgeable and skilled, others do not know proper floating techniques and have minimal knowledge of basic hygiene and transmission of bacteria and viruses. Any time dental tools are not cleaned correctly between uses, infections can be spread.

While I always recommend that show horses and horses that travel off the farm receive an intranasal strangles vaccine (or a blood test titer to show that the horse is immune), Mrs. Green is the type of client that I would consider low risk. Her stay at home horses would be horses who might skip the vaccine. Usually, horses who are not showing or exposed to other horses don't get infected with strangles. Unfortunately, her horses were infected due to human error Luckily her horses have responded well to antibiotic treatment and are on the mend.

One of the things I have learned from this is that in addition to asking people if they plan to take their horse places where they are exposed to other horse, I will also be asking if they have other possible sources of exposure. This includes asking if they use a good dentist that understands disease transmission and cleans his tools.