Human interaction with cats
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 kitty 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. 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 is even the official title of 'Chief Mouser to the Cabinet Office' since the 1500s (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 USA cats inflict about 400,000 bites per year. 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. The compulsive hoarding of cats, a symptom of obsessive compulsive disorder (OCD), has long  been associated with "crazy cat ladies". Allergic reactions to cats are relatively common, happening in as many as every 3 in 10 Americans. The major allergen, Fel d 1, is found in the saliva and/or dander of all cat breeds. There have been attempts to breed hypoallergenic cats, which would be less likely to provoke an allergic reaction but. Some humans who are allergic to cats—typically manifested by hay fever, asthma, or a skin rash—quickly acclimate themselves to a particular animal and live comfortably in the same house with it, while retaining an allergy to cats in general . Whether the risk of developing allergic diseases such as asthma is increased or decreased by cat ownership is uncertain. Some owners cope with this problem by taking allergy medicine, along with bathing their cats frequently, since weekly bathing will reduce the amount of dander shed by a cat. As well as posing health risks, interactions with cats may improve health and reduce physical responses to stress: for example the presence of cats may moderately decrease blood pressure. Cat ownership may also improve psychological health by providing emotional support and dispelling feelings of depression, anxiety and loneliness. Their ability to provide  companionship and friendship are common reasons given for owning a cat. From another point of view, cats are thought to be able to improve the general mood of their owners by alleviating negative attitudes. According to a Swiss study carried out in 2003, cats may change the overall psychological state of their owner as their company's effect appears to be comparable to that of a human partner. The researchers concluded that, while cats were not shown to promote positive moods, they do alleviate negative ones. The purring from cats is also believed to contain healing properties. An individual cat 's purring can range from 20 Hz up to 150 Hz. These vibration levels are believed to aid in bone growth and repair. A year-long study done by Dr. Clinton Rubin and his team found that bones of older sheep began showing signs of repair after being exposed to 30 Hz of vibrations for 20 minutes, five days a week. For humans, vibrational therapy has been found to not only aid in bone repair but also strengthen tendons and joints. Cats purrs are believed to work similarly on the human body alongside reducing risk of blood pressure, heart disease , and symptoms of dyspnea. One study found that cat ownership is associated with a reduced risk of heart attacks and strokes at the 95% confidence interval. Several studies have shown that cats develop affection towards their owners. However, the effect of these pets on human health is closely related to the time and effort the cat owner is able to invest in it, in terms of bonding and playing. Therapy cats. Some cats, called "therapy cats" are trained to help ailing humans in a medically beneficial way to take advantage of the human-animal interaction for purposes of relaxation and  healing. Certain breeds are desirable when looking into therapy cats due to their personality and temperament. Some examples of preferred breeds are Ragdolls, Maine Coons, American Shorthairs, Siamese, and Persians. The important traits to look for in a cat include a steady demeanor with tolerance to sights and sounds that are unfamiliar or sudden, petting that could be awkward or rough, and the ability to stay calm when being poked or pulled in unusual manners. Therapy cats must also be acclimated to humans of all ages and enjoy engaging with strangers daily. Some therapy cats are used as alternatives to  therapy dogs due to the cats size and nature, allowing them to work with patients/people who might otherwise be scared of dogs. Therapy cats should still be accustomed to dogs since most visits happen in conjunction with one another. The presence of cats in addition to their purring as well as petting them can deliver both psychological and physical benefits. Therapy cats are being used as companions to help the recovery and well-being of people who have had strokes, high blood pressure, anxiety, and/or depression to name a few. Therapy cats are utilized as companions at juvenile detention  centers; for children with developmental disabilities; and for children with language, speech and hearing difficulties. Therapy cats are also sometimes used in hospitals to relax children who are staying there, as well as helping those in hospice care cope with their terminal illness. Indoor scratching. A natural behavior in cats is to hook their front claws periodically into suitable surfaces and pull backwards. Cats, like humans, keep their muscles trim and their body flexible by stretching. Additionally, such periodic scratching serves to clean and sharpen their claws. Indoor cats may benefit from being provided with a scratching post so that  they are less likely to use carpet or furniture, which they can easily ruin. However, some cats may simply ignore such a device. Commercial scratching posts typically are covered in carpeting or upholstery. Using a plain wooden surface, or reversing the carpeting on the posts so that the rougher texture of the carpet backing, may be a more attractive alternative to the cat than the floor covering. Scratching posts made of sisal rope or corrugated cardboard are also common. Although scratching can serve cats to keep their claws from growing excessively long, their nails can be trimmed if necessary. Another  response to indoor scratching is onychectomy, commonly known as declawing. This is a surgical procedure to remove the claw and first bone of each digit of a cat's paws. Declawing is most commonly only performed on the front feet. A related procedure is tendonectomy, which involves cutting a tendon needed for cats to extend their claws. Declawing is a major surgical procedure and can produce pain and infections. Since this surgery is almost always performed for the benefit of owners, it is controversial and remains uncommon outside of North America. In many countries, declawing is prohibited by animal welfare  laws and it is ethically controversial within the veterinary community. While both the Humane Society of the United States and the American Society for the Prevention of Cruelty to Animals strongly discourage or condemn the procedure, the American Veterinary Medical Association supports the procedure under certain guidelines and finds "no scientific evidence that declawing leads to behavioral abnormalities when the behavior of declawed cats is compared with that of cats in control groups." They further argue that many cats would be given up and euthanized were declawing not performed. Waste. Being fastidious self-cleaners, cats detest their own waste and  instinctually bury their urine and feces. House cats are usually provided with a box containing litter, generally consisting of bentonite, but sometimes other absorbent material such as shredded paper or wood chips, or sometimes sand or similar material can be used. It should be cleaned daily and changed often, depending on the number of cats using it and the type of litter; if it is not kept clean, a cat may be fastidious enough to find other locations for urination or defecation. This may also happen for other reasons; for instance, if a cat becomes constipated and defecation is uncomfortable , it may associate the discomfort with the litter box and avoid it in favor of another location. Daily attention to the litter box also serves as a monitor of the cat's health. Bentonite or clumping litter is a variation which absorbs urine into clumps which can be sifted out along with feces, and thus stays cleaner longer with regular sifting, but has sometimes been reported to cause health problems in some cats. Some cats can be trained to use the human toilet, eliminating the litter box and its attendant expense, unpleasant odor, and the need to use landfill space  for disposal. An exhibit at the San Diego Natural History Museum states that cat feces from urban runoff carry "Toxoplasma gondii" parasites to the ocean and kill sea otters. Genetic similarities with humans. The order of eight genes on the cats' Y chromosome closely resembles that in humans. Genes on X chromosomes of cats and humans are arranged in a similar way. Domestic cats are affected by over 250 naturally occurring hereditary disorders, many of which are similar to those in humans, such as diabetes, hemophilia and Tay–Sachs disease. For example, Abyssinian cat's pedigree contains a genetic mutation  that causes retinitis pigmentosa, which also affects humans. The domestic cat is also an excellent model for human infectious diseases, including HIV/AIDS. Feline immunodeficiency virus (FIV) is a genetic relative of HIV.