The first vaccine for feline immunodeficiency virus (FIV) has been approved for commercial production and veterinary use by the US Department of Agriculture (USDA).

The vaccine should be available to veterinarians in the USA by the summer. 'This vaccine offers the first effective protection for cats against this often fatal disease,' said Niels Pedersen, director of the Center for Companion Animal Health and an international authority on retroviruses and immunologic disorders of small animals. The success of the FIV vaccine also offers hope that eventually a vaccine will be developed that will effectively protect against AIDS in humans.'

Pedersen and immunologist Janet Yamamoto, now a professor in the University of Florida 's College of Veterinary Medicine , first isolated the FIV in cats at UC Davis in 1986. Yamamoto began work on a vaccine for the virus at UC Davis and continued her research at the University of Florida , Gainesville . She has worked with researchers at Fort Dodge Animal Health for more than a decade to develop the vaccine.

Feline immunodeficiency virus is transmitted from cat to cat mainly through bite wounds, because the virus is present at high levels in the saliva. Like human AIDS, the virus attacks the body's immune system, making the animal susceptible to diseases and infections that usually would have little effect on an FIV-free animal.

Cats infected with FIV may remain healthy for 5 to 10 years before symptoms such as diarrhoea, weight loss, fever, swollen lymph nodes, and chronic infections appear. Although infected cats may recover from their initial illness, they become lifelong carriers of the virus. It is estimated that between 2 per cent and 25 per cent of the global domestic cat population is infected with the virus, according to the USDA. Infection rates are highest in Japan and Australia and lowest in the United States and Europe . Outdoor roaming cats, older cats, and cats with chronic ill-health are more likely to be infected.

Aggressive free-roaming males, which are most likely to get into fights with other cats, are at greatest risk for contracting FIV. FIV does not infect or cause disease in humans.

The newly approved vaccine is known as a 'killed vaccine', made from an inactivated form of the FIV virus itself. The vaccine stimulates the protective immune response in the animal's body without the danger of inadvertently causing the viral disease. The new vaccine is composed of virus strains from two different types of FIV, one from North America and one from Asia.

In a study demonstrating the efficacy of the vaccine, cats received three doses of the FIV vaccine and a year later were exposed to a different strain of the virus. It was found that 67 per cent of the vaccinated cats were protected against the virus, while 74 per cent of the non-vaccinated cats became infected with FIV. Studies indicate that the vaccine provides protection against FIV for at least 12 months.

The American Association of Feline Practitioners is concerned that vaccinal antibodies will give false positive results when cats are tested with the commonly used Elisa test for FIV infection and have written to the USDA expressing concerns about this. If FIV-vaccinated cats were to develop antibodies indistinguishable from those induced by natural infection, veterinary surgeons would lose the use of their most reliable diagnostic tool for the disease. Their concern is that it will not be possible to distinguish infected cats from vaccinated cats.