In certain regions of the United States, ticks have become a problem akin to vermin in large cities. The expansion of humans and horses into tick habitats and vice versa means that ticks are being encountered more frequently and tick bites are relatively common. In turn, tick-borne diseases, such as Lyme disease, are on the rise. And that makes many owners hyperaware of the tick population problem.
“Equine veterinarians should work with their clients to teach them about ticks in their region, including identification and how to prevent tick bites to best protect horses from tick-borne pathogens,” advised Erika Machtinger, PhD, CWB® (certified wildlife biologist). She is an assistant professor in the Department of Entomology at Pennsylvania State University.
Only a Few Bad Apples
Of the many types of ticks living in the fields and forests on and around farms, only a small handful of ticks pose problems for horses and their owners. Instead, most ticks are specialized to a single host—and most of the time that host isn’t a human or a horse.
According to Machtinger, tick species found on horses vary depending on geographic location. Species identification matters because each tick species is associated with different risks of tick-borne diseases or conditions. Machtinger encourages veterinarians to focus client education on the ticks specific to their regions. Practitioners can also help clients understand that not all ticks are found in all areas.
One of the most important ticks in the U.S. is the blacklegged tick, capable of transmitting the pathogens that cause Lyme disease as well as Anaplasma phagocytophila.
“In addition, equine piroplasmosis can be transmitted by at least 33 species of ticks in six genera, most often Dermacentor, Rhipicephalus and Hylaomma,” Machtinger said.
Even if ticks don’t have a high chance of transmitting disease, their presence is still an annoyance, and the bites can be painful.
Tick Bite Prevention: The “Suite” Smell of Success
Social media, word of mouth and a desire to avoid chemicals on horses have some owners reaching for the all-natural herbal tick repellents. While these products usually are about as effective as throwing water on a drowning, they can potentially play a role in a balanced tick-prevention plan.
“Owners need to be made aware of the suite of strategies they can use to reduce a horse’s risk of tick-borne pathogens,” noted Machtinger.
Reducing Host and Horse Interactions
“Clean up places where rodents like to hide because rodents are hosts for many juvenile stages of important ticks,” advised Machtinger.
In addition, she recommended keeping grass short in the pastures where horses graze and creating a nine-foot “buffer” between horse pastures and surrounding forests/grasses. This cumbersome strategy involves removing logs, sticks, grass and brush between the fence and the surrounding tick habitats.
Chemical Treatment of Tick Habitats
Machtinger said that owners can spray pyrethroids on their own, but for large properties/areas it will be a process. Thus, many owners hire companies to perform this service, usually in the spring and fall in the midwest and northeast when adult ticks typically feed on horses. The timing of those sprays could be different based on your location in the United States and the life cycle of the local ticks.
“Pyrethroids are toxic to nontarget animals, so the sprays should be directed to target areas where the ticks are. These products are incompatible with aquatic wildlife, so do not spray in areas near ponds, streams or other bodies of water,” Machtinger warned.
If these warnings send owners rushing for the “natural” products (such as essential oils), they should be made aware that even “natural” products can be toxic to nontarget animals, require frequent application because they wash away easily, and have limited efficacy data supporting their use.
“If owners still choose to use natural or herbal products instead of pyrethroids, they should be prepared to spray at least every two weeks,” said Machtinger.
On-Horse Tick Prevention
“This is by far the most important component of a tick-control program that owners can use,” advised Machtinger.
The four on-horse options include the following:
- Commercial spot-on repellents help reduce, but do not eliminate, the number of ticks that attach. Encourage owners to follow the manufacturers’ directions when using.
- Tick-repelling sprays contain permethrin as the main ingredient, usually in a low concentration, about 0.9%. “In one of our recent studies, we found that 5-10% permethrin effectively repels ticks for 24 hours, but similar efficacy was not appreciated at lower concentrations,” said Machtinger. That said, actively deter your clients from purchasing the concentrated 10% permethrin! “The 10% product is commercially available but not licensed for horses despite the fact that some have a picture of a horse on them! Concentrated products can cause a lot of damage to the horse’s skin,” shared Machtinger. If owners choose to use repellent sprays, encourage them to use a microfiber mitt or brush to apply these products daily. “Repellents might be useful in the short-term, so it would be worth coating your horse with repellent before riding in tick-risky areas like the woods or tall grasses,” said Machtinger. And keep in mind that herbal sprays have not been tested against ticks.
- Fipronil is another topical (spot-on) product, but it is not a repellent like the spot-ons mentioned in the first bullet point above. It is important that owners are aware that with fipronil, ticks need to bite in order to die. Owners should consult with a veterinarian prior to using this product because it is not labeled for use on horses.
- Treated “clothing” such as fly masks, sheet and boots can be purchased that have pyrethroids impregnated into the fabric. This is the same class of chemical described above that is sprayed on the ground in tick-infested habitats. “These products have been tested on humans and are highly recommended for everyone going outside, but they have not yet been tested on horses to determine their effectiveness,” shared Machtinger.
Veterinarians might wish to spend a few moments demonstrating how to conduct a daily tick check on client horses. Key factors to relay are that the tick checks will be more fruitful if conducted on a clean horse. Advise owners to wear gloves to protect themselves during the process. Use a systematic approach each time, being sure to check the ears, eyes, between the legs, and under the mane, tail and belly.
“In reality, ticks can be anywhere on the horse, and the unfed adult ticks are small,” said Machtinger. “It should take about five minutes for each side of the horse.”
Ticks can be removed using a commercial tick picker or a pair of tweezers. Grasp the tick as close to the horse’s skin as possible to avoid possible pathogen transfer when squeezing.
Although there are no vaccines for Lyme disease (Borrelia burgdorferi), equine veterinarians can use the canine vaccine in horses.
“We use the Recombitek vaccine most frequently, with the initial series consisting of vaccination at 0, 30 and 90 days and then every six months,” said Laura H. Javsicas, VMD, DACVIM, of Rhinebeck Equine in New York. “We see very few, if any, side effects to the vaccine.”
When a Tick Infiltrates the Perimeter
Despite using the suite of tick-prevention strategies described above, some owners might have found ticks on their horses or have convinced themselves they see signs of Lyme disease and would like testing performed.
Testing can be done easily, and although several options are available, Javsicas recommends using the Lyme Multiplex developed by Cornell University’s Animal Health Diagnostic Center.
“The multiplex is the only test that provides quantitative measurement of antibodies present at different stages of infection,” stated Javsicas.
She added, “But there are other tests available, such as the SNAP test and Western Blot (WB). The SNAP test is qualitative, not quantitative, making it more difficult to interpret and to detect a response to treatment. The SNAP measures the C6 protein, which does correlate well with OspF levels on the Multiplex. The WB is also a subjective test, plus it is labor intensive. It does, however, identify a broad range of antibodies and is able to differentiate vaccinated from infected horses.”
Test Result Interpretation
Regardless of what test is selected, Javsicas reminded practitioners that the test results always have to be interpreted in light of the clinical signs.
“We know that many horses in the northeast are exposed to Lyme. Because of this, I like to see a high or increasing OspC and/or OspF titer on the Multiplex and to have ruled out other causes of the clinical signs,” explained Javsicas. “Some of the most common signs that owners cite as ‘proof’ their horses have Lyme include a shifting leg lameness, attitude change and increased skin sensitivity.
“Performing a full physical exam and lameness and/or neurologic exam is always recommended, and scoping for gastric ulcers is often indicated,” advised Javsicas.
When deciding whether to treat a horse for Lyme disease or not, Javsicas reminded practitioners that “treatment with antibiotics is never benign in horses as antibiotic-induced colitis is always a risk and can be fatal. Additionally, if we only have nebulous signs and questionable lab results to start with, it is hard to determine if the horse has responded to treatment.”
Bird is Not the Word
Another “natural” approach some horse owners embrace is having free-roaming chickens or guinea fowl on the farm. These are birds known for feasting on ticks. Machtinger said that these birds will consume adult ticks (not immature ones), but only if they encounter them.
“Plus, there is no evidence chickens can consume enough ticks for this to be a reasonable prevention strategy,” said Machtinger. “Adult female ticks can lay up to 3,000 eggs … it would be a challenge for a chicken to seek out and eat that many. In addition, chicken feed can attract rodent hosts and may themselves serve as tick hosts. I really wouldn’t advise going out and buying chickens and guinea fowl for tick-control purposes.”
Here are some more “tick tidbits” that you can share with clients:
- Ticks go through three active life stages: larvae, nymphs and adults. Larvae are not seen on horses and do not transmit disease.
- Ticks live for about two years.
- Adult ticks are eight-legged animals with two body regions—a small head and a larger body.
- Tick identification is typically performed on adult ticks.
- Adult ticks are seen on horses in early spring and in the fall, not typically in the middle of the summer.
For more information on tick sprays, visit https://www.spraysafeplaysafe.org/.
For additional details on ticks, refer to the book Pests and Parasites of Horses written by veterinary entomologists and an equine practitioner.
Tick control requires a concerted effort on both the horse and the environment. No single product or strategy will effectively eliminate a horse’s risk of tick bites or risk of tick-borne illness. Owners should be specifically consulting veterinarians regarding fipronil and Lyme vaccines.