As one of the most common infectious diseases in cats, feline leukemia virus (FeLV) spreads between cats via infected saliva and urine, affecting 2% to 3% of cats in the United States. Cats can develop anemia with a low red blood cell level, cancers, and/or suppression of the immune system after being affected. Over time, the disease will worsen and is usually fatal.
There are several vaccines available for FeLV, including recombinant subunit vaccines (Leucogen, Nobivac LeuFel).
Leucogen contains the recombinant envelope p45 protein of the outer layer of the virus, which is produced by Escherichia coli (E. coli). An aluminium hydroxide gel and a purified extract of Quillaja Saponaria are used to adjuvant antigenic suspension. Leucogen is sold by Virbac S.A.
Merck Animal Health also discovered a recombinant vaccine named Nobivac LeuFel to prevent FeLV infection. Nobivac LeuFel not only contains E. coli - produced recombinant p45 FeLV-envelope antigen, but also contains aluminium hydroxide gel and extract of Quillaja saponaria as adjuvants.