Corneal Lesions Associated With Feline Herpesvirus‐1 Modified Live Vaccine Strain F2 in Two Cats

Feline herpesvirus‐1 (FHV‐1) modified live vaccine (MLV) is designated as a core vaccine for cats. As reported here, two 2‐month‐old domestic short hair cats (Cat 1 and Cat 2; the two were littermates) initially presented with sneezing, nasal and ocular discharge, and ocular discomfort (Day 0), which had persisted since their vaccination. At 1.5 months of age, both cats were vaccinated with a vaccine containing the FHV‐1 MLV strain F2 at another clinic. A few days later, they developed sneezing and ocular discharge almost simultaneously. Ten days after vaccination, they were diagnosed with allergic conjunctivitis and administered corticosteroid eye drops for 7 days. On Day 0, both cats presented with dendritic ulcers in one eye and a superficial corneal ulcer in the other eye. Treatment with oral antiherpesvirus medication and hyaluronic acid eye drops was initiated. A genomic analysis of FHV‐1 strains isolated on Day 0 and of specimens obtained on Day 3 for real‐time PCR suggested that both cats were infected with the same strain as the F2 strain and that there was no mixed infection with the field strain. Real‐time PCR was performed to identify ocular surface pathogens other than FHV‐1, and feline calicivirus (FCV) was detected in specimens collected from the superficial corneal ulcers of both cats on Day 3. On Day 6, dendritic ulcers in both cats healed. On Day 15, superficial corneal ulcers in both cats developed corneal crystalline deposits and deep neovascularization. In the eyes with superficial corneal ulcers in both cats, symblepharon subsequently developed in Cat 1, and eosinophilic keratitis subsequently developed in Cat 2. In conclusion, findings suggested that corneal ulcers caused by the F2 strain may be associated with the development of specific corneal lesions in cats that were young, that had a coinfection with FCV, and that were administered corticosteroids.