For most of us, treatment of feline (and canine) viral diseases can be a frustrating endeavor because there is no direct therapy for most infections. Therapy consists largely of supportive care with medications to control symptoms and therapy to maintain hydration and nutrition. For more severe viral disease such as Feline infectious peritonitis (FIP) and Parvovirus, fatality rates remain unacceptably high and for less severe infections such as calicivirus and herpes virus, long term immune mediated sequela such as stomatitis and erosive rhinitis lead to significant increases in morbidity and decreases in quality of life. Antiviral therapies are expensive, have a high rate of side effects and are not effective against all viral infections.

Interferons are a group of proteins known as cytokines, molecules used for communication between cells to trigger the protective defenses of the immune system that help eradicate pathogens. They are named for their ability to “interfere” with viral replication by protecting cells from virus infections. They also may activate immune cells and increase host defenses.

Human interferons (Alpha interferons) are readily available and have been used for many years to try and treat viral diseases in dogs and cats. Efficacy is questionable at best and is considered controversial for treatment of certain viral diseases such as FIP in cats. Feline Recombinant omega interferon (Virbagen Omega) has been under evaluation since 1998. It was first studied for use in parvovirus in dogs. In 2006, the European Committee for Medicinal Products for Veterinary Use (CVMP) agreed that the benefits of Virbagen Omega are greater than any risks to reduce mortality and clinical signs of parvovirosis in dogs from one month of age and to treat cats infected with feline leukemia virus (Felv) and/or feline immunodeficiency virus (FIV) in non-terminal cats from the age of 9 weeks. They recommended that Virbagen Omega should be given a marketing authorization making it available throughout Europe for a variety of viral diseases.

In the United States, due to lack of FDA approval, Virbagen Omega remained expensive and difficult to obtain requiring a compassionate use letter from the FDA. Recently however, a compassionate use letter is no longer necessary. The FDA states that import of this medication is allowed as defined by the Regulatory Procedures Manual, section 9-2. This rule allows an individual to import small quantities (less than 3 months use) of medication for personal use.

Since its release, limited studies have become available showing benefit with the use of Virbagen Omega for a variety of feline and canine viral diseases. It has been shown to be as efficacious as steroids for the use of feline stomatitis and has been demonstrated to show improvement in viral induced anemias in cats. Anecdotally, MedVet’s internal medicine department has seen significant improvement in some cats diagnosed with FIP, even when used as a monotherapy. As the side effect profile is low, consisting mostly of gastrointestinal related signs, the potential for benefit makes feline recombinant omega interferon an attractive option in a field where few therapies have proven beneficial.


• Ishiwata K, et al, Clinical effects of the recombinant feline interferon-omega on experimental parvovirus infection in beagle dogs, J Vet Med Sci. 1998 Aug;60(8):911-7.

• de Mari K, et al, Therapeutic effects of recombinant feline interferon-omega on feline leukemia virus (FeLV)-infected and FeLV/feline immunodeficiency virus (FIV)-coinfected symptomatic cats. J Vet Intern Med. 2004 Jul-Aug;18(4):477-82

• Ritz S, et al, Effect of feline interferon-omega on the survival time and quality of life of cats with feline infectious peritonitis, J Vet Intern Med. 2007 Nov-Dec;21(6):1193-7.

• Hennet PR, et al, Comparative efficacy of a recombinant feline interferon omega in refractory cases of calicivirus-positive cats with caudal stomatitis: a randomized, multi-centre, controlled, double-blind study in 39 cats, J Feline Med Surg. 2011 Aug;13(8):577-87.