Hundreds of millions of cats are kept as pets around the world. Cats have either a mutualistic or commensal relationship with humans.
Pets
Cats are common pets in all continents of the world permanently inhabited by humans, and their global population is difficult to ascertain, with estimates ranging from anywhere between 200 million to 600 million. In 1998 there were around 76 million cats in Europe, 7 million in Japan and 3 million in Australia. A 2007 report stated that about 37 million US households owned cats, with an average of 2.2 cats per household giving a total population of around 82 million; in contrast, there are about 72 million pet dogs in that country. Cats exceeded dogs in number as pets in the United States in 1985 for the first time, in part because the development of cat litter in the mid-20th century eliminated the unpleasantly powerful smell of cat urine.
Although cat ownership has commonly been associated with women, a 2007 Gallup poll reported that men and women in the United States of America were equally likely to own a cat. The ratio of pedigree/purebred cats to random-bred cats varies from country to country. However, generally speaking, purebreds are less than 10% of the total population.
in the United States, human owners of cats typically keep cats indoors at all times. In typically rural settings, cats oftentimes live outside and are used as a deterrent to rodents, snakes, and other pests. In the United Kingdom most cats go outdoors from time to time, with 26% being indoors at all times.
The compulsive hoarding of cats, a symptom of obsessive compulsive disorder (OCD), has long been associated with "cat ladies" although there is no evidence that older women are more likely than other people to hoard cats.
Fur
According to the Humane Society of the United States, as well as being kept as pets, cats are also used in the international fur trade. Cat fur is used in coats, gloves, hats, shoes, blankets and stuffed toys. About 24 cats are needed to make a cat fur coat. This use has now been outlawed in several countries, including the United States, Australia and the European Union countries. However, despite being outlawed, some cat furs are still made into blankets in Switzerland as folk remedies that are believed to help rheumatism.
Pest control
Cats, as with the traditional farm cat and ship's cat, are also used for pest control, particularly in the case of rat or mouse infestation. As such, they are sometimes referred to as a "mouser", and in the United Kingdom there has been one at Number 10 since the 1500s (officially titled 'Chief Mouser to the Cabinet Office' since 2011; additional duties include "greeting guests to the house, inspecting security defences, and testing antique furniture for napping quality").
Domesticated varieties
The current list of cat breeds is quite large: with the US Cat Fanciers' Association recognizing 41 breeds, of which 16 are "natural breeds" that probably emerged before humans began breeding pedigree cats, while the others were developed over the latter half of the 20th century. Because of common crossbreeding, many cats are simply identified as belonging to the homogeneous breeds of domestic longhair and domestic shorthair, depending on their type of fur.
Effects on human health
Because of their small size, domesticated house cats pose little physical danger to adult humans. However, in the US cats inflict about 400,000 bites per year that result in emergency room visits, almost 90% of which may be bites from provoked animals. This number represents about one in ten of all animal bites. Cat bites may become infected, sometimes with serious consequences such as cat-scratch disease, or, very rarely, rabies. Cats may also pose a danger to pregnant women and immunosuppressed individuals, since their feces, in rare cases, can transmit toxoplasmosis. A large percentage of cats are infected with this parasite, with infection rates ranging from around 40 to 60% in both domestic and stray cats worldwide. Research indicates a correlation between the parasite Toxoplasma gondii, which sexually reproduces exclusively in cats, and numerous human psychiatric conditions, including OCD.