Conjunctivitis in horses: causes, symptoms, prevention

Conjunctivitis is a common condition in horses, causing pain and discomfort. It is crucial to identify it as early as possible so that it can be treated promptly to avoid complications. Find out about the causes and symptoms of conjunctivitis in horses and what you can do to prevent it from occurring.

The horse's eyes: an important asset to protect

As sensitive organs, horses' eyes are exposed to multiple risks on a daily basis that are inherent to outdoor life. Environmental factors play a major role in triggering conjunctivitis. However, infectious causes have also been observed, requiring more thorough examination by a veterinarian. Whatever the cause, preventing conjunctivitis in horses involves taking simple steps to ensure maximum safety and peace of mind for your animal.

The horse's conjunctiva: a brief anatomy refresher

The conjunctiva of the horse is a highly vascularized mucous membrane composed of:

• The palpebral conjunctiva(inner surface of the eyelids): it lines the inner surface of the eyelids, the fornix (end of the conjunctival sac), and the anterior surface of the third eyelid.
• The bulbar conjunctiva(white of the eye): it covers the anterior surface of the eyeball up to the corneal border and the posterior surface of the third eyelid.

The role of the conjunctiva is to lubricate the eye thanks to its conjunctival glands, which produce mucus that forms part of the tear film (Source: IMAIOS).
This film covers the eye and concentrates in its folds. It spreads over the eyeball with each movement of the upper and lower eyelids and the nictitating membrane (Source: Study of equine conjunctival cytology). The conjunctiva therefore helps to maintain the tear film and also protects the eye from foreign bodies or microorganisms that could cause infection.

What is conjunctivitis?

Conjunctivitis is an inflammation of the conjunctiva that can affect one or both eyes. It may or may not be infectious and is sometimes contagious. Common in horses, conjunctivitis must be identified and treated as soon as possible as it can cause serious complications, particularly in cases of bacterial or viral conjunctivitis.

What are the symptoms of conjunctivitis in horses?

It is important to regularly check your horse's eyes and behavior to ensure that they are healthy and that your horse is not suffering from any health issues.

Description

The symptoms of conjunctivitis are easily identifiable:

• Red eye,
• Swelling of the eyelids,
• Frequent blinking of the eyelids,
• Eyelids half-closed,
• Eye discharge similar to tears or thick and purulent,
• Sticky eye,
• Sensitivity to light,
• Rubbing the eye on objects in the environment or on one's leg,
• Head shaking,
• Possible agitation due to pain and stress.

Consequences of symptoms

The symptoms of conjunctivitis are painful: they cause stress inthe horse, which is reflected in its daily behavior. Your horse, which is usually so cooperative, may start to show signs of impatience during activities it normally enjoys. Your horse may develop tics such as head tremors. Some stressed horses become apathetic, while others may even become aggressive and bite.

Possible complications

Untreated viral or bacterial conjunctivitis can spread to the cornea and cause ulcerative keratitis. This involves breaks in the surface layer of the cornea, which are visible as rough areas on the surface of the eye. These corneal ulcers can be superficial or deeper and may lead to loss of the eye. The horse may also cause this ulcer by rubbing its painful eye a little too vigorously on surfaces that cause injury and trauma.

What causes conjunctivitis in horses?

There are many possible causes of conjunctivitis in horses, including environmental factors , which account for a significant proportion of the triggering factors. The origin of the disorder will determine the nature of the treatment prescribed by the veterinarian.

Pollen

Pollen is a common cause of conjunctivitis in horses, which are increasingly hypersensitive to it. This is due to the wind spreading pollen from particularly allergenic plants and trees such as grasses, ragweed, juniper, birch, and plane trees from January to May. Horses develop an allergic reaction that affects both eyes but can also cause coughing and breathing difficulties. Wearing a protective cloth cover can help prevent this problem and protect your horse from allergic conjunctivitis.

UV

Sensitivity to UV (ultraviolet)rays can also cause inflammation of the conjunctiva and significantly impact a horse's quality of life. Here again, wearing UV protection allows your horse to no longer suffer on a daily basis and protects it in all circumstances.

Wind

Wind can be harsh on your horse's eyes and cause inflammation. As with UV rays, these external factors cannot be controlled, so it is essential to provide your horse with a protective mask against the wind.

Dust

Life in a stall means that horses live in a dusty environment that is difficult to control. Straw and hay contain highly volatile particles that quickly find their way into your horse's moist eyes. This causes irritation, which can quickly develop into conjunctivitis. In addition, some horses are more sensitive to dust than others, causing a series of inflammatory reactions. If the horse's living environment is damp and poorly ventilated, fungi can also proliferate and cause infectious conjunctivitis.

Foreign body

Branches, plant debris, stones, and insects are all elements that can get into a horse's eyes and cause inflammation of the conjunctiva. In severe cases, a sharp foreign object can perforate the cornea and cause ulceration.

Chemical irritation

Multiple chemical pollutants travel through the air and can affect your horse's eyes. Be careful when choosing disinfectants to use for cleaning your horse's environment. Some are highly toxic and can cause skin, respiratory, or eye reactions.

Trauma

Horses can sometimes be a little too lively and rub their eyes vigorously or bang their heads, causing injury. While this trauma can cause conjunctivitis, it can also lead to a corneal ulcer that requires prompt treatment.

Parasitic disease

Parasite infestation can cause eye symptoms, including conjunctival inflammation. Among the most common eye parasites in horses are:

• Habronemiasis: also known as "summer sore," this parasitic disease transmitted by flies appears during the summer months. It can affect the eyes, skin, and digestive system. In the conjunctival form, flies lay their larvae on the conjunctiva, causing granular lesions at the inner corner of the eyelids and acute conjunctivitis.
• Onchocerciasis: this disease is also transmitted by mosquito bites during the summer months and comes in two forms: cutaneous and ocular. In the latter, the symptoms are similar to those of uveitis. Lesions appear on the eyelids, the conjunctiva (causing conjunctivitis), the cornea, and the retina.
• Thelaziosis: this is an eye condition caused by a pathogenic nematode and transmissible to humans (zoonosis). It is the fly that deposits the parasite in the horse's eye, frequently causing conjunctivitis (Source: Ocular parasitic diseases in horses).

Bacteria

Bacterial eye infections in horses are often the result of injury or irritation to the eye. These provide valuable entry points for bacteria, which will proliferate and trigger eye symptoms, including conjunctivitis.

Virus

Certain viruses are responsible for eye damage in horses, such asequine herpesvirus, which causes viral rhinopneumonia, a highly contagious disease. It can take three different forms: respiratory, neurological, and abortive (causing spontaneous abortion). In the respiratory form, flu-like symptoms appear, with nasal discharge and watery eyes. It should be noted that your horse can be vaccinated against this viral infection.

Genetics

Some horses have a genetic predisposition to eye problems. They are therefore more likely than other horses to develop localized conditions such as conjunctivitis.

Tear deficiency

Although rare, insufficient tear production can cause conjunctivitis in horses, as in the case of keratoconjunctivitis sicca, also known as "dry eye," which causes dehydration and inflammation of the conjunctiva and cornea, eye pain, and possibly visual impairment (Source: Le Point Vétérinaire).

How to treat conjunctivitis in horses?

The treatment of conjunctivitis depends on its cause. It is therefore recommended that you consult your veterinarian as soon as possible so that they can make an accurate diagnosis and establish the most appropriate treatment protocol. This may involve symptomatic treatment only, the administration of antibiotics, eye baths, and the application of specific eye drops.

How can equine conjunctivitis be prevented?

Since most causes of conjunctivitis are environmental, it is essential to implement all necessary preventive measures. This includes protecting the horse's eyes with specific equipment such as masks and goggles. These offer the advantage of protecting the horse's eyes from all harmful factors (UV rays, insects, wind, dust, pollen, etc.) as well as injuries when working outdoors and in show jumping.

Flexible and comfortable, they can be worn by your horse in the pasture or during training sessions, without affecting its movement in any way. It is also essential to clean your horse's eyes regularly and to ensure veterinary follow-up to detect any ophthalmic damage as early as possible, the most common of which is conjunctivitis.