Spring is officially here, and with the warm weather come insects that could cause harm to horses. Often overlooked compared to mosquitoes, ticks are capable vectors of several equine diseases and can cause adverse effects ranging from local irritation to acute and chronic disease. Proactive tick management is an essential component of equine preventive care, particularly as many regions continue to report increased numbers of tick bites and changes in tick species distributions.
In the United States, notable tick-borne diseases affecting horses include:
- Equine Granulocytic Anaplasmosis (Anaplasma phagocytophilum): The most common signs of infection include fever, lethargy, limb edema, and ataxia. In equines, A. phagocytophilum is most commonly transmitted by the blacklegged tick (Ixodes scapularis) in the Northeast, Midwest, and parts of the Southeast. It is also transmitted by the Western blacklegged tick (Ixodes pacificus) on the West Coast.
- Lyme Disease (Borrelia burgdorferi): Although horses are less susceptible than dogs or humans, infection can result in chronic weight loss, shifting lameness, behavioral changes, and neurologic signs. This disease can be difficult to diagnose in equines, as a positive blood test indicates exposure to the pathogen but not necessarily current disease status. Lyme disease is also transmitted by I. scapularis.
- Equine Piroplasmosis (EP): This disease is caused by Babesia caballi and Theileria equi. It is reportable in the mainland U.S. but endemic in Puerto Rico and the U.S. Virgin Islands. Transmission can occur through tick bites (most commonly from Dermacentor or Rhipicephalus spp.), but most U.S. cases are associated with iatrogenic transmission from contaminated equipment during unsanctioned racing events or through illegal importation of infected Quarter Horse racehorses across the southern border.
- Tularemia (Francisella tularensis): This rare tick-borne zoonotic disease in horses is associated with Dermacentor spp. and Amblyomma spp. ticks. This pathogen can be transmitted through bites from fleas and flies and through contaminated water sources but is most commonly associated with tick bites. While rare in horses, it is significant due to its ability to persist in the environment, multiple modes of transmission, and zoonotic disease potential.
- Tick Paralysis and Hypersensitivity: Toxins in tick saliva might cause neuromuscular dysfunction or localized inflammatory responses in sensitive animals.
Emerging Tick Species: Asian Longhorned Tick
The Asian longhorned tick (Haemaphysalis longicornis) is an invasive species that has been detected in numerous U.S. states along the East Coast and Appalachian Mountains, including Kentucky, where it has been detected on wildlife, cattle, equines, dogs, and people. Here are some key characteristics about this species:
- It reproduces asexually via parthenogenesis, enabling rapid population growth and large infestations, particularly on livestock.
- This tick has been documented on horses in the U.S., although no confirmed cases of equine disease have been associated with it.
- Internationally, H. longicornis can transmit pathogens of veterinary and medical concern, causing diseases such as anaplasmosis, babesiosis, ehrlichiosis, theileriosis, and rickettsiosis.
- Its ability to cause anemia and death in cattle raises concern for similar effects in heavily infested horses, particularly if infestations go unnoticed, though such cases have not yet been reported.
- Because horses can develop hypersensitivity reactions to tick and other arthropod bites, even mild infestations of H. longicornis could exacerbate stress, pruritus, and allergic dermatitis, affecting welfare and performance even in the absence of pathogen transmission.
Most Common Equine-Associated Tick Species in the U.S.
The most common tick species of concern to horses include:
- Amblyomma americanum (lone star tick)
- Amblyomma maculatum (Gulf Coast tick)
- Amblyomma mixtum (Cayenne tick)
- Dermacentor albipictus (winter tick)
- Dermacentor andersoni (Rocky Mountain wood tick)
- Dermacentor variabilis (American dog tick)
- Haemaphysalis longicornis (Asian longhorned tick)
- Ixodes scapularis (blacklegged tick)
Integrated Tick Prevention and Property Management
Most tick species prefer habitats with shade, moisture, and vegetation, including wooded edges, brush, and tall grasses commonly found on or adjacent to horse properties, or along trail riding locations. Reducing equine tick exposure involves implementing available environmental, behavioral, and chemical strategies to decrease the number of ticks on the property. This can include pasture and property management to minimize areas likely to harbor ticks or tick-carrying wildlife. Integrated management also includes on-animal prevention strategies, such as topical deterrents and removing ticks quickly when they do attach to animals.
Pasture and property management strategies include:
- Mow and maintain pastures frequently to reduce habitat more likely to harbor ticks.
- Create buffer zones between wooded or brushy areas and paddocks.
- Remove brush, leaf litter, and overgrown field margins.
- Exclude wildlife (e.g., deer, raccoons) via fencing or deterrents to reduce tick introduction and movement of disease-causing pathogens.
- Control rodents through exclusion and secure feed storage; rodents serve as reservoirs for immature ticks and several tick-borne pathogens.
On-horse prevention strategies include:
- Perform daily tick checks, focusing on thin-skinned, less-visible areas such as ears, eyelids, muzzle, chest, belly, mane, and tail. Full-body tick checks are recommended after equines have been in areas where ticks are common, such as after trail rides in brushy habitat.
- Apply EPA-registered pyrethroid-based sprays labeled for equine use. Reapplication might be needed based on rainfall or sweat exposure and is typically only effective for short-term applications.
- Fly sheets or insect barriers might provide partial protection from both biting flies and ticks.
- Avoid off-label or overuse of pesticide products to prevent skin irritation or systemic absorption. Horse owners should consult with their veterinarian before applying on-animal chemical products.
The Veterinarian’s Role in Surveillance and Education
Veterinarians are well-positioned to contribute to equine welfare by educating owners and caretakers about tick-borne diseases and preventive approaches for tick and other arthropod-borne diseases and associated conditions. In many states, ticks can be submitted for identification through the Department of Agriculture, Environmental Health or Public Health Department, or through state Extension services. In Kentucky, suspected Asian longhorned ticks can be submitted through the University of Kentucky Cooperative Extension Service by bringing them to your county Extension office, mailing them to the Entomology Department through the contact information below, or by contacting the Office of the State Veterinarian at statevet@ky.gov.
Related Reading
- Disease Du Jour: Equine Infectious Disease Patterns and Threats
- Unearthing the Secrets of Anaplasmosis in Horses
- A Refresher on Protecting Horses Against Arboviruses
Stay in the know! Sign up for EquiManagement’s FREE weekly newsletters to get the latest equine research, disease alerts, and vet practice updates delivered straight to your inbox.
