The conjunctival membranes of a cat's eyes, including the pink areas beneath the eyelids and the lining of the eyelids themselves, play a vital role in eye health. When these membranes become irritated, they take on a reddish hue and can cause discomfort, itching, dryness, and various other discomforts. In some cases, the inflammation can even extend to the cornea, the clear dome-like covering of the eye, leading to cloudiness or ulceration. Reduced tear production further compounds the problem, resulting in chronically dry and uncomfortable eyes.
In cats, conjunctivitis is often of viral origin, with feline herpesvirus-1 (FHV-1) being the primary culprit. Herpesviruses tend to thrive in body tissues that interface with the environment, such as the upper respiratory tissues and conjunctiva. The infection typically begins with an initial phase characterized by severe symptoms, but the virus doesn't vanish. Instead, it retreats to the trigeminal ganglion, a neurologic structure in the head, where the cat's immune system keeps it in check. During periods of stress, the virus may escape the ganglion via nerve pathways, leading to the recurrence of symptoms. Thus, while the infection is permanent, the symptoms are episodic.
Symptoms and Course of Feline Herpes Viral Conjunctivitis
The symptoms of FHV-1 infection encompass conjunctivitis, as previously described, as well as nasal and respiratory symptoms, including sniffles, runny nose, and fever—essentially mirroring the signs of an upper respiratory infection. The initial episode of infection is usually the most severe, with subsequent episodes tending to be milder. Cats typically start recovering after 10 to 14 days of symptoms, and the episode usually resolves within three weeks. The highly contagious nature of the virus means it spreads easily through close contact, making infection common among feline populations.
Special Consideration: Herpes in Baby Kittens
Herpes infection is especially prevalent in young kittens, particularly those subjected to additional stresses like fleas, malnutrition, or exposure to cold environments. Stray kittens, outdoor kittens, shelter kittens, and the like face a higher risk of herpes infection. Young kittens can produce copious ocular discharge, often sealing their eyes shut due to the accumulation of infected secretions. It's imperative to manually open their eyelids to allow drainage and apply medication. In severe cases, the swelling of the conjunctiva can be so extreme that the eye itself becomes obscured. In the worst instances, the eye may rupture, leading to permanent blindness. Timely and proper treatment, including topical therapy, is essential.
Respiratory signs are also common in kittens with herpes, potentially causing life-threatening loss of appetite and dehydration. In contrast, adult cats with mature immune systems usually experience mild respiratory signs. Kittens displaying obvious discomfort should be promptly examined by a veterinarian, often requiring oral antibiotics and, at times, hospitalization for proper supportive care.
Managing Herpes in Adult Cats
Given the prevalence of herpes in kittens, it's not uncommon to encounter adult cats with a history of herpes infection. These individuals tend to experience recurrent conjunctivitis during periods of stress. Symptoms include slight squinting in one eye, increased eye discharge (typically brownish), conjunctival redness, or a combination of these signs.
Diagnosis Dilemma: Is it Herpes?
Numerous feline infectious diseases can cause conjunctivitis, many of which are linked to upper respiratory infections. Frequently, multiple agents are involved simultaneously. Identifying which agents are present can be challenging and may not always be necessary. In practice, it's often more pragmatic to initiate treatment for bacterial agents and secondary bacterial infections initially, with antiviral medications considered if needed.
Determining an active herpes infection can be elusive. PCR testing is presently the most sensitive method available, capable of detecting even small amounts of herpes DNA. However, it's important to note that many cats in a given area may test positive for herpes, indicating they harbor the virus in their bodies. Having a herpes infection doesn't necessarily equate to an active infection. Testing can confirm the presence of the virus but not its activity. Therefore, a stressed cat with conjunctivitis involving the cornea likely has an active herpes infection.
Treatment Options for Feline Herpes Viral Conjunctivitis
Managing herpes conjunctivitis involves several treatment approaches that can be combined for the best results:
- Topical Antibiotics: These help control secondary bacterial infections that often complicate herpes conjunctivitis. While antibiotics don't target the herpesvirus itself, they can alleviate symptoms by addressing bacterial infections.
- Topical Anti-virals: Several eye drops are available that directly combat the herpesvirus. Options include idoxuridine, Viroptic® (trifluorothymidine), cidofovir (obtained through compounding pharmacies), and Vira-A® (vidarabine). These medications may require multiple daily administrations, except for cidofovir, which accumulates in eye tissues and allows for twice-daily dosing.
- Oral Anti-virals: Famciclovir, initially developed as a human herpes treatment, has proven effective against feline herpes. Dosing and protocols are still being refined, but higher oral doses of famciclovir can result in therapeutic levels in tears, effectively providing topical treatment through an oral medication. Combining oral famciclovir with topical antibiotics is a viable approach for managing feline herpes conjunctivitis.
- Probiotics (Fortiflora®): Adding this probiotic powder to the diet has been shown to reduce the severity of herpes conjunctivitis in cats.
- Hyaluronate Eye Drops: Topical hyaluronate supports mucus-producing cells in the conjunctiva, helping maintain proper eye moisture. This helps keep the eye comfortable and washes away inflammatory products generated by the infection.
Complications: Eosinophilic Keratitis and Corneal Sequestrum
Herpes infection can lead to two challenging complications in cats:
- Eosinophilic Keratitis: This condition involves the formation of thick white plaques on the eye's surface. A microscopic examination of these plaques can reveal the presence of eosinophils, white blood cells, confirming a diagnosis of eosinophilic keratitis. These plaques result from an abnormal immune response to the virus and require immune-suppressive topical medications for management. Lifelong treatment is often necessary.
- Corneal Sequestrum: Persian cats are particularly susceptible to this complication, where a portion of the cornea dies and turns black or dark brown. The fastest route to resolution involves surgical removal of the dead tissue and the application of a tissue graft. Not all veterinarians are equipped to perform this surgery, so a consultation with a veterinary ophthalmologist may be advisable. Non-surgical management with antibiotics and anti-inflammatory topicals is also an option but should be discussed with a specialist.
Can Humans Contract Feline Herpes, and Vice Versa?
Fortunately, feline herpesvirus and human herpes are not transmissible between species. Feline herpes is contagious only among cats, and human herpes is contagious exclusively among humans. Thus, there's no risk of interspecies transmission of these viruses.
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