The hardy arachnids pose threats to both horses and handlersTicks are external parasites of warm-blooded animals. They are gross little disgusting creatures which must have blood for survival. Heavy infestation can lead to anemia, but this is not the major problem ticks can cause.
Ticks are vectors for several diseases of both animals and man, and this is the main reason they must be controlled. And control is the only choice; while certain tick-borne diseases may be treated, there is no method for prevention of tick infestation.
There are many species of tick and most are not host-specific. Mother Nature has made ticks a hardy life-form and has provided us with a wide variety, suited to a wide range of climatic conditions. There are winter ticks, which range as far north as Canada; tropical ticks, which live in Mexico and the Caribbean and as far north as Florida and Texas; and various other types which inhabit all areas in between, so wherever your horses are, ticks are there for them.
The ear of the horse is a favorite site of attachment indeed, one species is called the ear tick. Infestation here may be the main cause of suffering for horses. The ticks travel deep into the ear canal and create an irritation manifested by ear rubbing and/or head shaking. Secondary bacterial otitis frequently ensues. Diagnosis is made by finding the ticks in the ear, and this must usually be done by otoscopic examination under tranquilization or sedation. Treatment requires the introduction of a suitable pesticide into the ear canal, a procedure not particularly pleasurable to the horse. Be careful when doing this; a horses swinging head weighs considerably more than your stationary one. If bacterial otitis exists, antibiotic or antibiotic/steroid ointments must be used also.
The two most common diseases horses can contract via ticks are Lyme disease and piroplasmosis. Lyme disease is caused by a bacterium carried by ticks of the genus Ixodes, while the causative agent of piroplasmosis is a protozoan carried by the tropical horse tick.
Lyme disease takes on added importance because it is also an increasingly serious problem in man, especially in the northeast and far west. Signs of the disease in both man and horse are basically nonspecific, but include fever, muscle soreness, and stiffness of the joints. In man, it can easily be mistaken for a cold or flu in its early stages. In horses, diagnosis is made by clinical signs, history, and response to therapy. The ticks responsible for Lyme disease are most commonly found in the tail and under the mane and, again, a topical pesticide is the treatment of choice to remove them.
Piroplasmosis in the United States has occurred in Florida, but is most serious and widespread in the Caribbean. Horses exported from the U. S. to Caribbean nations must have a negative blood test for piro; this must be for the purpose of protecting the native infectious organisms from competition, because the first thing that happens to a horse when it steps off the plane on a Caribbean island is to be bitten by a tropical tick, thus contracting the disease.
Clinical signs vary in severity and include fever, depression, edema, weakness, and abortion in seriously affected pregnant mares. The causative organism destroys red blood cells, so anemia is evident in a blood count. There are drugs available now which can aid in the prevention of piro, and treatment is also effective, but a persistent carrier state exists so a cured horse may still be positive on a blood test.
Tick paralysis, spread by a tick most commonly found in the western half of the U.S., is also a problem in both horses and man. The bite of a single infected tick can lead to paralysis, so this is a particularly threatening condition.

Control/prevention
Tick control is the key to minimization of tick-borne diseases. The tick population can be kept to a minimum by maintaining fields and paddocks in a closely mowed state, and horses should be kept out of wooded or overgrown areas.
Routine examinations should be performed on the horses. The primary sites of tick infestation are the ears, mane, tail, and under the tail, around the anus and vulva. In a tropical country, I have seen in excess of 100 ticks in these latter areas on a single mare.
Manually removing the ticks is tedious and may well not be fully appreciated by the horse, especially in the anal-vulvar area, so the proper use of parasiticides or pesticides is the treatment of choice. Remember: a tick is not an insectit is an arachnidtherefore, most insecticides are of no help. Pyrethrins and permethrins are effective, but it is essential to strictly follow the instructions on the label.
The life cycle of some ticks is two or three years, so if you do choose to
remove them manually (which you may well do in the case of only a few ticks), dont just flick them onto the ground or the stall floor. Do something to kill them. The brick-and-hammer method is especially effective, but much easier and more convenient is the maintenance of a small bucket (or coffee can) of water, into which you can drop the removed ticks. They are notoriously poor swimmers.