Vesicular stomatitis is a viral disease that more commonly affects horses living in warmer climates. The disease typically results in blister-like lesions (referred to as vesicles) forming in and around the mouths of horses and other farm animals. This condition is usually self-limiting, meaning it resolves without medical intervention.

African horse sickness (AHS) is a viral infection transmitted by biting midges. Up to 90% of horses infected with the virus die after initial infection. ^[1] Due to international trade and climate change, there is a risk of AHS spreading into countries previously considered "AHS free". There are three major forms of African horse sickness: the pulmonary form, the cardiac form, and horsesickness fever. Horses can also develop a mixed form which has combined symptoms of pulmonary and cardiac disease. Common symptoms of AHS include fever, difficulty breathing, swelling of the head, and fluid leaking from the nostrils. Veterinarians can diagnose AHS on a blood test or by submitting tissues after performing a necropsy. There is no known treatment for AHS, and most horses die shortly after developing symptoms of disease.

Horse eyes are prominent, making them prone to injury. This is especially true of the cornea, which is the outermost layer of the eye. An injury to this layer is known as a corneal ulcer or keratitis. Corneal ulcers can cause varying degrees of ocular damage in horses. Severity can range from superficial cuts or abrasions in the corneal epithelium (outermost layer of the cornea), all the way to full thickness corneal punctures (known as perforations), accompanied by prolapse (dislocation) of the iris.

Equine recurrent uveitis (ERU) is an autoimmune disease and the leading cause of blindness in horses. The disease results in the immune system repeatedly attacking the structures of the eye causing tissue damage, inflammation, and eventually blindness. The underlying cause of equine recurrent uveitis is usually unknown, but Appaloosa horses, Warmblood horses, and Icelandic horses appear to have a genetic predisposition. Horses that develop leptospirosis or other infectious diseases also have an increased risk of ERU.

Ear mites are tiny, wingless, external parasites that live in the ears of horses and cause psoroptic mange. They are round with eight legs and are sometimes visible to the naked eye. They do not burrow into the horse but rather feed on the skin's secretions. Mites are directly contagious between infected animals and spread easily between horses living in close contact. The ear mite can survive for a long time in the environment without a host, so transmission is equally likely through contact with infected equipment or premises.

Mange is a skin and coat condition in horses caused by microscopic parasites called mites. Although mange is not common in horses, specific conditions can lead to a mite infestation that can spread rapidly between horses in direct contact. Mange can affect various parts of the horse's body including the legs, base of the tail, head, neck, shoulder, girth, and back. Regardless of specific subtype involved, all cases of horse mange exhibit similar symptoms. The primary symptom of mange is significant itching (pruritis) that prompts horses to scratch incessantly.

As with other parasites that feed on blood, mosquitoes can transmit diseases between hosts. In horses, Eastern, Western, and Venezuelan Equine Encephalitis (EEE, WEE, and VEE, respectively) and West Nile Virus are mosquito-borne illnesses. Equine encephalitis and West Nile viruses affect the brain and are variably fatal with Eastern and Venezuelan Equine Encephalitis being especially deadly. Horses are dead end or amplifying hosts of these viruses, which means they do not pass these diseases on to other horses or to humans.

Lice are an external parasite found on the hair or fur of mammalian hosts, including horses. A lice infestation is also referred to as pediculosis. There are different species of these small, wingless insects, and horses are usually infested with either the "sucking" or "biting" type. Lice are usually transmitted by direct contact with an infected animal. Since lice can live in the environment without a host for a few weeks, they can also be transmitted indirectly by sharing space or equipment with infected horses.

Cataracts are cloudy areas within the horse's lens, the structure within the eye that directs light to the retina. ^[1] The lens must be clear to allow light to pass through correctly, meaning that cataracts can cause blindness in the affected eye. Most cases of equine cataracts result from equine recurrent uveitis (ERU), a disorder where the immune system attacks structures within the eye. Other causes of cataracts include traumatic injuries or abnormal lens development during gestation. The only treatment available for cataracts is surgical removal of the lens. Surgery is typically reserved for horses with severe cataracts causing complete blindness in the eye. Removal can restore some vision and allows horses to return to their typical lifestyle.

Glaucoma refers to increased intraocular pressure, the fluid pressure within the eyeball that gives the eye its shape. ^[1] Glaucoma in horses develops when there is an imbalance in fluid drainage at the front of the eye, leading to increased pressure. Causes include inflammation, traumatic injuries, and improper development of the eye. Symptoms of glaucoma in horses can be subtle. The main symptom is haziness or cloudiness to the eye, however many horses also show additional symptoms such as squinting, tearing, and redness.

Equine degenerative myeloencephalopathy (EDM) is a degenerative neurologic disease affecting the brain and spinal cord in horses. ^[1] The precise cause of EDM is unknown, but it may be related to a combination of vitamin E deficiency in the diet and genetic predisposition. Horses with EDM usually develop symptoms within the first year of life. Symptoms include uncoordinated movement, weakness, and behavioral changes. Veterinarians examining the horse must rule out other diseases that can cause similar symptoms before diagnosing EDM.

Neurectomy refers to the surgical cutting and removal of a nerve to prevent pain sensation. In horses, neurectomy is considered a salvage procedure, meaning it is a last resort only performed if no other treatments were effective. Veterinarians may recommend neurectomy in horses with chronic (long-term) lameness issues, such as navicular disease or arthritis. The two most common neurectomy procedures are performed on plantar/palmar digital and lateral plantar nerves.