feline leukaemia virus (felv)

This virus is mainly spread through saliva exchanged between cats during mutual grooming, from bites, or from an infected mother to her kittens. After being infected cats may show no signs for months or even years. Signs that develop include anaemia and other blood disorders, diseases of the immune system and secondary infections. Most cats will die within three years. A vaccine is available against FeLV but may not always offer complete protection.

SOURCE: cats.org.uk