Bacterial, Fungal, Viral and Parasitic Conjunctivitis

Conjunctivitis, also known as "red eye," is probably the most common eye disorder that dog owners see. It is an inflammation of the conjunctiva, the eye's protective mucous membrane that lines the inside of the eyelids and the surface of the eyeball as far as the cornea. The condition often occurs when the conjunctiva is irritated by a hair or a foreign body. Watery discharge from a single eye is usually caused by a foreign body. If both eyes are inflamed, however, it may be an indication of more serious problems elsewhere, either within the eyeball itself or in other parts of the body. A clear, colorless discharge usually indicates that the eye is suffering form a physical or allergic irritation. Dust, wind blowing in the face, and cold air may all trigger a watery discharge from both eyes. Allergens such as pollen can do the same, but allergy is often accompanied by itchiness that makes the dog rub its face. A jelly-like discharge of mucus may result from irritation by a foreign body or from an infection. Both of these problems will trigger increased mucus production from the conjunctiva. A yellowish-green discharge is pus, which means that infection is present and must be treated without delay.

Bacterial And Fungal Conjunctivitis

Like the skin, the conjunctiva acts as host to many normal bacteria and fungi. Injuries, foreign bodies in the eye, viral infections, or, most important of all, a reduction in tear production, will allow some of these bacteria and fungi to grow rapidly. As a result, they cause an infection. Signs of one of these infections include redness, a yellowish-green discharge, and crusting of the eyelids. Dogs may blink, squint slightly, or paw at and rub their eyes. In neonatal conjunctivitis, a newborn puppy may suffer an infection before or after the eyelids have separated, usually between 10 and 14 days. Pups with fused eyelids (ankyloblepharon) are prone to neonatal conjunctivitis. The eyelids bulge or appear swollen, and there may be a discharge. If your puppy is affected, you must let your vet know at once in order to prevent more serious disease.

Canine corneal ulcer
Melting corneal ulceration

It is very important to determine the cause of bacterial or fungal conjunctivitis. The infection itself is diagnosed by culture or sensitivity tests and is treated with the appropriate topical antibiotics. Sterile saline eyewash can be used to flush the eye several times a day. If there is a crust, it can be removed with washcloth soaked in warm water.

Viral Conjunctivitis

The viruses that cause canine distemper and hepatitis also predispose the eyes to developing bacterial conjunctivitis. Distemper, in particular, is associated with reduced tear production and the subsequent development of dry eye. Many ocular signs of canine distemper have been reported, including acute and chronic conjunctivitis, keratoconjunctivitis sicca, anterior uveitis, retinochoroiditis, optic neuritis and cortical blindness.

Acute conjunctivitis is found in the early stages of distemper in conjunction with systemic signs. An early diagnosis of distemper is sometimes made by examining a conjunctival scraping for viral particles. Initially the ocular discharge is clear. Over 7-10 days the discharge becomes pus-filled as secondary bacterial conjunctivitis develops. Acute and chronic keratoconjunctivitis sicca have been reported with canine distemper. In most dogs, spontaneous recovery and normal tear production have been reported to occur over 4-8 weeks, but chronic keratoconjunctivitis may result, presumably depending on the degree of lacrimal gland damage during infection. Symptomatic treatment includes topical tear replacements and topical broad-spectrum antibacterials. If tear production does not return in 2 or 3 months, parotid duct transposition may be necessary.

Conjunctivitis Caused By Canine Adenovirus Infection

A conjunctivitis may accompany anterior uveitis in canine adenovirus infections. A wide range of bacterial species has been implicated in conjunctivitis, but Gram-positive organisms predominate, most notably Staphylococcus and Streptococcus species. Fusidic acid, chloramphenicol and neomycin are active against these species and are usually first-line treatment for canine bacterial conjunctivitis. Pseudomonas aeruginosa may cause conjunctivitis, infect the cornea if there is overlying epithelial damage, and induce corneal ulcers. Gentamicin or tobramycin are active against Pseudomonas species. If melting corneal ulceration is present, specialist advice should be sought urgently.

Parasitic Conjunctivitis

In the western United States there is a parasitic worm, Thelazia californiensis that can inhabit the conjunctival sac (the space between the eyelids and the eye) and cause thelaziasis, a type of parasitic conjunctivitis. Locating the worm by eye examination confirms the infection. The worms are removed using local anesthetic and forceps. Alternatively, the eye is flushed with an ophthalmic antiparasitic solution.



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