Ticks Are Rearing Their Ugly Heads Again

Fall and Winter bring hungry ticks- but their bite can carry potentially fatal diseases for your horse.

Ticks can number in the hundreds on an infested horse.

Despite the cold of winter, ticks are busy at work hitching a ride on our horses and helping themselves to a warm blood meal in order to continue their life cycles and propagate for Spring. 

Ticks are slow moving arthropods that insidiously creep in numbers onto our horses when they lay down, walk through grass, or put their heads down to graze. Ticks burrow their heads deep into the skin and inject saliva into the bite site. The saliva causes an inflammatory reaction in the horse which in turn increases blood circulation to the area. Unfortunately, ticks can carry a number of diseases in their saliva. These diseases can be life-threatening if not diagnosed and treated early.


Anaplasmosis (previously called Erlichiosis) is an intracellular bacterial infection that causes high fever, anemia, limb swelling and diarrhea. It can rapidly progress to death in some instances. In others, horses can overcome the infection and gain immunity naturally. The vast majority of cases involve veterinary intervention using antibiotics, anti-inflammatories, and IV fluid therapy support. 

This disease is transmitted by deer ticks and usually appears about a month after the horse is bitten. Veterinarians can diagnose anaplasmosis with blood testing but generally must make an on-the-spot executive decision to treat it based on physical signs, since horses are usually so sick that they cannot wait for days while test results come back. Luckily, the infection subsides with 7 to 10 days of daily antibiotic therapy- sometimes given intravenously or sometimes given orally. 

Horses can fully recover from an anaplasmosis infection within a couple of weeks. Anemia caused by the disease can be corrected thanks to the large reserve or red blood cells that the horse stores in its spleen. Unfortunately, being clinically infected with anaplasmosis does not guarantee that the horse will have long standing immunity to the disease. Some horses are reported to contract the disease twice in the same year!

Lyme disease

Lyme disease occurs in varying degrees depending on geographic location. It is virtually unheard of on the West Coast, but far more common on the East Coast. Most horses that are bitten by the Ixodes tick that carries the bacteria that cause Lyme disease never become sick – they simply develop immunity to the bacteria without incident. 

For the small subset of horses that do become sick, fever, stiffness, muscle pain and swollen joints are most commonly reported. It is possible that longstanding infection with Lyme disease can cause permanent arthritic changes in multiple joints. While some testing methods for this disease have been developed, results can be difficult to interpret. Many veterinarians empirically treat for the disease if they see clinical signs that are consistent with it. Treatment is similar to that for anaplasmosis and most often, horses recover without incident.


With the increased importation of horses from countries in which this tick-borne disease is endemic, we are hearing more and more reports about horses that carry it. Piroplasmosis is caused by parasites called Babesia or Theileria. The parasites gain entry into the horse by inoculation from the mouthpiece of a biting Dermacentor or Boophilus tick. Horses can take 1 to 3 weeks to show signs of infection post-bite.

Mild forms of the disease present as weakness and inappetence, while more acute cases show fever, anemia, jaundiced (yellow) gums and eyelids, a swollen abdomen, and labored breathing. Other signs of EP include central nervous system disturbances, roughened-hair coats, constipation, colic, red urine. In some cases, death may occur. 

Horses that survive the acute phase of infection continue to carry the parasites for long periods of time. These horses are potential sources of infection to other horses through tick-borne transmission or mechanical transfer by biting ticks, needles, or surgical instruments. Horses infected with Piroplasmosis can be treated with varying degrees of success. Treatments can take many months and have to be repeated several times. They are also costly. 

The United States Department of Agriculture has a disease surveillance branch that works to identify and contain any sources of Piroplasmosis in the country. They do not permit import of any horses that test positive for the disease. Despite the federal effort to stop the disease from occurring here, there are still horses in almost every state that are considered carriers. Most of these horses tested negative for the disease during import but then reverted back to a positive carrier state later on. The mechanism by which this reversion occurs is unknown.

For all of the diseases listed above, no vaccination is available. Therefore, prevention and/or early detection and intervention to treat infection are key. Here are some tips for each:


Clear brush and plant debris out of your horse’s living area since ticks tend to be concentrated in high numbers there.

Groom and carefully inspect your horse daily to look for invaders. You can pick ticks off with your fingers- but make sure to put them into a container with rubbing alcohol or some other caustic agent to kill them. Simply throwing them on the ground will result in them being back. Ticks seem to love the throat latch area, under the elbows and between the front legs, along the crest of the mane, and around the tail. With tht said, they can latch on just about anywhere so no bump should go unexamined.

Fly sprays and spot on insecticides have varying degrees of efficacy when it comes to repelling ticks. Use of products like EquiSpot has been reported to be beneficial, especially when it is applied every two to three weeks.

Early Detection and Intervention

If you happen to find a tick on your horse, identifying it may help to narrow the list of potential horse-specific diseases it can be carrying. Check out this useful mobile App to help you identify ticks on-the-spot!Because most of the diseases that ticks transmit have an incubation period of weeks, it can be difficult to remember to watch for signs of the diseases over time.

One practice that can be easily added to the daily management regimen is to take your horse’s rectal temperature with a digital thermometer. Fever is one of the first signs of all of the tick-transmitted diseases, and it can take just seconds to detect a fever if you use a thermometer daily. If you are able to catch a disease in the early stages, treatment can be shorter, less invasive and less expensive than if you have to address the problem at its worst.

Closing Thoughts

Stay tick-vigilant this holiday season! They can hide in our horses’ long hair and evade detection for long periods of time. Take your horse’s temperature daily as a matter of routine- temperatures greater than 101 F should be considered to be suspicious- especially if your horse shows any other signs consistent with a tick-borne disease. Early veterinary intervention and mean the difference between life and death in the some cases of tick-borne illness, so don’t delay in calling if you suspect one of these diseases.

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