Strangles Management and Prevention
by: Nancy S. Loving, DVM
November 01 2007, Article # 10688
New strategies for management and prevention.
It is not uncommon for strangles infections to recur on a farm, and until recent years there have been misconceptions about how this disease is maintained in a population of horses. These days scientists understand the phenomenon and can better explain it. We now know a farm that has experienced an outbreak of strangles, caused by Streptococcus equi sppbacteria, might have an ongoing problem, not because the bacteria remain in the environment, but because they persist within the horse, specifically within the guttural pouches or sinuses. Even though a horse might appear to have recovered, he remains an avenue to transmit disease to others by harboring the bacteria within his guttural pouches.
In the interest of eradicating strangles infection from endemic farms (those on which the disease is recurrent) and from the horse population at large, researchers have suggested new strategies to manage horses and facilities to reduce risk of an outbreak. They've also described ways to eliminate the bacteria from carrier horses.
Disease Opportunity
Josie Traub-Dargatz, DVM, Dipl. ACVIM, professor of equine medicine and epidemiology at Colorado State University's veterinary school, has been instrumental in developing prevention and recognition programs to protect the equine industry from contagious diseases. Aligning with this focus, she is part of the study group that has been making industry recommendations on equine strangles control.
Traub-Dargatz explains that a horse might be exposed to the causative S. equi bacteria either by the nasal or oral route. Nose-to-nose contact and shared water supplies are efficient means of transmission. She suggests paying close attention to the use of shared water sources, since S. equi is easily transmitted through contaminated water.
Rob Holland, DVM, PhD, a private practitioner and an equine field veterinarian for Pfizer Animal Health, is working with the American Association of Equine Practitioners' (AAEP) Infectious Disease Task Force to formulate the most-up-to-date strategies for equine immunization, and he has extensive experience with the dynamics of strangles transmission. Holland concurs, "This disease is often spread through oral contact, such as in water, on bits, or lip chains and twitches. Studies have shown that S. equi obtained through the oral route goes right to the tonsillar region quickly."
Traub-Dargatz adds, "Even a water hose that has been contaminated with the bacteria--because the hose was touched by people with the bacteria on their hands or the end of the hose was dropped into the bucket of an infected horse--can serve as a source of infection. When the hose is dunked into a bucket as it fills, it then inoculates the water with infectious bacteria."
She stresses that while these bacteria survive most efficiently in the horse, in the environment S. equi bacteria persist more effectively in water as compared to soil--the bacteria can survive for three to four weeks in water tanks contaminated by discharges. Although solar radiation and normal soil bacteria play a role in killing off S. equi, how effective they are in killing the bacteria is variable, depending on the surface and the weather conditions, as well as the dose of bacteria present.
CAUTION: BACTERIA SPREADING! 1. A hose can carry bacteria from one bucket to another when you dunk the end in each bucket to fill.
2. S. equi can survive for three to four weeks in water in tanks contaminated by discharges.
3. Bacteria shielded in pus can live longer than if just contained in a drop of clear watery fluid from the horse's nose.
4. In wintertime, pus and contaminated discharges that freeze can persist to infect others when the ground thaws.
5. S. equi lives three days in the soil, seven days on a fence post, and 30-40 days in a water trough.
6. At events, if possible, it is best to leave your horse by your trailer rather than using shared stalls that might be contaminated.
7. Water buckets should not be shared at horse shows.
8. Some horses that continue to shed S. equi past 30 days might clear infections on their own, but it is possible for a horse to shed for weeks, months, or years.
9. Ask owners of visiting or new resident horses about the strangles status of these horses and consider screening for shedding, especially if there is a history of strangles.
10. Contaminated pastures should be empty for at least a month.
11. Water tanks should be cleaned/disinfected daily during an outbreak.
12. When possible, assign specific personnel to handle only the sick animals. Clean hands thoroughly after handling each horse. 13. Work with sick animals last if you are handling healthy and sick horses. 13. Supply disposable coveralls and foot covers or rubber boots that are to be worn only when in contact with sick horses, and arrange for specific changing areas for putting on protective clothing.--Nancy S. Loving, DVM
"It can persist for days in the environment, but not likely for months," she says. "If bacteria are shielded in pus, then there is potential for longer persistence than if it is just contained in a drop of clear watery fluid from the horse's nose."
