Practitioners may soon have a new treatment tool for feline herpes virus type 1 (FHV-1) and related conjunctivitis. A study completed recently by veterinarians at Colorado State University shows that cidofovir, a medication used effective in humans and cattle infected with herpes virus 1, may be easier to use than two common antiviral medications.

Cynthia Powell, DVM, MS, DACVO, completed a masked study on 12, six-month-old kittens earlier this year and expects to widen her research with a larger study soon. The kittens were split into two groups – one that got the drug and one that received a placebo – and received topical applications of the antiviral drug twice daily for a 10-day period. Symptoms in all the kittens cleared up but significant differences were noted in the group that received a half percent of cidofovir administered with eye drops, such as less severe clinical signs and lower amounts of the virus were present. The fact that cidofovir can be given twice instead of four to six times daily could be a huge boon for pet owners.

“That would be a big advantage,” said Keith Collins, DVM, MS, DACVO. “Cats are less tolerant of repetitive treatments than dogs. They run and hide; their behavior changes.” An international comparison of six antiviral drugs – including cidofovir – was recently published online and cidofovir fared well.

Overall, Powell estimates that 90 percent of cats – in shelters and privately-owned – are infected with FHV-1, which manifests with recrudescent or reoccurring ocular disease that can be triggered by stress. Reoccurrence of the virus is usually limited to ocular problems that – if minor – are not always treated by pet owners because the treatments have been difficult to administer, Powell said.

Young kittens infected with the virus, which is transmitted through sneezes and touch, can show respiratory and ocular symptoms as minor as sneezing and nasal discharge and as severe as corneal ulcers, Powell said. Younger cats are more likely to develop ocular symptoms, which is why researchers chose the six-month-old cats that were later adopted out of the clinic, Powell said. Although most cats receive a FHV-1 vaccine, it does not prevent the disease, but does decrease clinical signs.

Powell hopes to initiate a broad clinical trial to test the efficacy of cidofovir on cats that contract the disease naturally. If that test is successful, cidofovir could act as an alternative to the two popularly used antiviral drugs that require five to six applications per day for a two-week period.

There are two other antiviral medications used by physicians to treat conjunctivitis, one of which is sold commercially. Both medications require five to six applications daily for two weeks and can cause irritation, Powell said.

“This gives practitioners one more medication they can use,” she explained. The twice daily application offers “benefits to pets and their owners,” Powell added. Cidofovir has a longer half life in ocular tissues, and should cost about the same as Trifluridine, which is commercially available. The other drug, Idoxuridine is usually compounded, Powell said.