Diagnosis and Treatment of FHV-1 Ocular Disease with Dr. Shelby Reinstein, DACVO
In this VETgirl online veterinary continuing education blog, Dr. Shelby Reinstein, DVM, DACVO reviews the diagnosis and treatment of Feline Herpes Virus-1 (FHV-1) and how to diagnose ocular disease secondary to it. In last week’s VETgirl blog, she reviewed the basics of Feline Herpes Virus-1, so make sure to check that out first!
Establishing a diagnosis of FHV-1 via clinical testing is challenging and many times uncecessary. The diagnosis is most often achieved by combining a high level of incidence with compatible history and clinical exam findings. Multiple studies have shown that available testing methods such as virus isolation (VI) and fluorescent antibody (FA) tests are insensitive in cats with chronic conjunctivitis. Measurement of antibody titers is only valuable in unvaccinated cats. Polymerase chain reaction (PCR) testing is very sensitive for the detection of viral DNA, however many clinically normal cats will harbor FHV-1 DNA in their ocular tissues, making this test difficult to interpret in the face of disease.
Conjunctival scrapings can be useful for confirming an active, neutrophilic conjunctivitis, but could also provide evidence for a concurrent, or possibly sole infection with Chlamydophila felis or Mycoplasma spp. Conjunctival cytology of FHV-1 conjunctivitis will reveal epithelial cells and neutrophils. C. felis will often demonstrate typical large, basophilic cytoplasmic inclusion bodies; however, the lack of these does not rule out the disease. Mycoplasma will appear as numerous, small, darkly staining inclusion bodies within the cytoplasm of epithelial cells.
Treatment of FHV-1 Ocular Disease
Although some cats will not require treatment and improve on their own, cats should be treated for their disease when they demonstrate:
• Ocular pain associated with moderate conjunctivitis
• Corneal ulceration
• Kittens suffering from acute respiratory disease from primary FHV-1 infection
• Chronic ocular disease
Topical antibiotics should be used to prevent secondary bacterial infections in cases of moderate or erosive conjunctivitis and in all cases of corneal ulceration. Systemic antibiotics are often indicated for kittens with significant upper respiratory tract disease. The chosen antibiotic should be broad spectrum and also aimed at other possible etiologies, such as Mycoplasma – amoxicillin or amoxicillin-clavulanic acid are appropriate choices. Topical erythromycin ointment is the authors antibiotic of choice for prophylactic therapy, which is very well tolerated in the vast majority of cats. Topical antibiotics containing neomycin or polymyxin B should be avoided in cats, due to reports of anaphylactic episodes post-administration, some of which were fatal. If there is concern for an actively infected corneal ulcer (severe edema, stromal depth, corneal melt) then aggressive, broad-spectrum antibiotic therapy is indicated. Appropriate choices include Ofloxacin and Ciprofloxacin solutions with the frequency based upon the severity of the disease, but often given up to every 2 hours for severe bacterial infection.
Antivirals are the mainstay of therapy for primary and recurrent FHV-1 disease. Numerous efficacy and safety studies have evaluated both oral and topical antiviral therapy and form the basis for the currently recommended protocols.
Cidofovir is a topical antiviral that is compounded into a 0.5% solution. Studies show that cidofovir used twice daily was shown to reduce viral shedding and clinical disease scores. The lower necessary dosing frequency is thought to be due to a long half-life of some of the metabolites of the parent drug. The author uses this medication preferentially for topical treatment of FHV-1.
Famciclovir is an oral antiviral that is quite efficacious for FHV-1 disease. Complex pharmacokinetics and the effects of various active metabolites are still undergoing investigation, however the currently recommended dose range is 40-90 mg/kg every 8-12 hours. The initial duration is most often 14-21 days, however extended courses (months) have been utilized for chronic or severe disease.
There is abundant evidence that topical corticosteroids can exacerbate herpetic disease and should be avoided. Topical non-steroidal anti-inflammatories, such as diclofenac 0.1%, are considered safe for use with concurrent viral disease and are generally well tolerated by cats. Topical tacrolimus 0.03% aqueous drops can be beneficial for treatment of surface inflammatory disease, and some cats may benefit from long-term treatment control chronic keratitis and/or secondary qualitative tear film disorders.
There are many conflicting studies available on the use of L-lysine supplementation in cats with FHV-1 in both shelter and experimental conditions. There have been no studies performed on client-owned cats in home environments. Lysine should not be used as a sole agent in the treatment of FHV-1 and is not considered an effective antiviral for active FHV disease. Rather, it can be considered to provide twice daily bolus administration of 250 mg to kittens and 500 mg to adult cats with chronic FHV disease, as long as this supplementation does not add due stress to the cat. A variety of products are available including powders, gels, foams, and treats.
Therapy for Corneal Sequestrum
In addition to the appropriate antiviral and antibiotic therapy, sequestra may require mechanical intervention. Depending upon the size, depth, and degree of ulceration associated with the lesion, some cats may slough the sequestrum if given enough time. Clients should be warned that this process can leave a significant corneal defect, can take months to years to occur, and cats may experience persistent discomfort. Surgery to remove the sequestrum results in faster resolution of the clinical signs and generally an acceptable cosmetic outcome. Depending upon the depth of the required keratectomy, a conjunctival or corneal graft may be necessary. Post-operatively, antiviral medications should be continued in addition to standard antibiotic, anti-inflammatory, and pain control.
Therapy for Eosinophilic Keratoconjunctivitis
The massive immune-mediated inflammation is dramatically responsive to topical steroids, which should be used at a frequency of 2-4 times daily depending upon the severity of the disease. Corneal ulceration is often present surrounding the inflammatory foci and necessitates topical antibiotics, however does not preclude steroid use for this specific condition only. Topical diclofenac or cyclosporine may also be used; however the response is usually more gradual as compared to steroids. Concurrent antiviral therapy is also recommended, most often oral famciclovir. All topical anti-inflammatory therapy should be slowly tapered once the condition is clinically controlled to the lowest effective frequency and eventually discontinued. Owners should be made aware of the possibility of recurrence even months to years later, and few cats require chronic therapy to control the disease.