More common are diseases that inflict cats only and that are spread through contact with other cats. Two diseases that kill large numbers of cats each year are feline leukemia and feline immunodeficiency virus. Both diseases are transmitted from cat to cat and, once contracted, result in the eventual death of the animal due to a compromised immune system. Keeping cats inside helps prevent the transmission of these killers. Outdoor cats inevitably pick up fleas and ticks and then bring these pests into the home with them.
Fleas can cause anemia, skin irritations, and allergies in cats.
These parasites also pose risks to humans since they can transmit disease through their bites. Ridding the pet and home of fleas and ticks is difficult and can expose the pet to harmful chemicals. Indoor cats aren't generally exposed to fleas, ticks, ear mites, or other parasites. Most cats love to chew on greens, but their fondness can be safely satisfied with grass grown in an indoor pot. Other cats, dogs, and wildlife are potential enemies of cats and often engage in fights that leave a cat injured.