Toxoplasmosis

Toxoplasmosis is a parasitic disease caused by the protozoan Toxoplasma gondii. The parasite infects most genera of warm-bloodedanimals, including humans, but the primary host is the felid (cat) family. Animals are infected by eating infected meat, by ingestion of fecesof a cat that has itself recently been infected, or by transmission from mother to fetus. Although cats are often blamed for spreading toxoplasmosis, contact with raw meat is a more significant source of human infections in many countries, and fecal contamination of hands is a greater risk factor.

Up to one third of the world's human population is estimated to carry a Toxoplasma infection. The Centers for Disease Control and Prevention notes that overall seroprevalence in the United States as determined with specimens collected by the National Health and Nutritional Examination Survey (NHANES) between 1999 and 2004 was found to be 10.8%, with seroprevalence among women of childbearing age (15 to 44 years) 11%.

During the first few weeks post-exposure, the infection typically causes a mild flu-like illness or no illness. Thereafter, the parasite rarely causes any symptoms in otherwise healthy adults. However, those with a weakened immune system, such as AIDS patients or pregnantwomen, may become seriously ill, and it can occasionally be fatal. The parasite can cause encephalitis (inflammation of the brain) andneurologic diseases, and can affect the heart, liver, inner ears, and eyes (chorioretinitis).

Signs and symptoms

Infection has two stages:

Acute toxoplasmosis

During acute toxoplasmosis, symptoms are often influenza-like: swollen lymph nodes, or muscle aches and pains that last for a month or more. Rarely, a patient with a fully functioningimmune system may develop eye damage from toxoplasmosis. Young children and immunocompromised patients, such as those with HIV/AIDS, those taking certain types ofchemotherapy, or those who have recently received an organ transplant, may develop severe toxoplasmosis. This can cause damage to the brain (encephalitis) or the eyes (necrotizing retinochoroiditis). Infants infected via placental transmission may be born with either of these problems, or with nasal malformations, although these complications are rare in newborns.

Swollen lymph nodes are more commonly found in the neck followed by axillae and then groin. Swelling may occur at different times after the initial infection, persist, and/or recur for various times independently of antiparasitic treatment. It is usually found at single sites in adults, but in children multiple sites may be more common. Enlarged lymph nodes will resolve within one to two months in 60% of patients. However, a quarter of patients take 2–4 months to return to normal and 8% take 4–6 months. A substantial number of patients (6%) do not return to normal until much later.

Latent toxoplasmosis

It is easy for a host to become infected with Toxoplasma gondii and develop toxoplasmosis without knowing it. In most immunocompetent patients, the infection enters a latent phase, during which only bradyzoites are present, forming cysts in nervous and muscle tissue. Most infants who are infected while in the womb have no symptoms at birth but may develop symptoms later in life.

Cutaneous toxoplasmosis

While rare, skin lesions may occur in the acquired form of the disease, including roseola and erythema multiforme-like eruptions, prurigo-like nodules, urticaria, and maculopapular lesions. Newborns may have punctate macules, ecchymoses, or “blueberry muffin” lesions. Diagnosis of cutaneous toxoplasmosis is based on the tachyzoite form of T. gondii being found in the epidermis. It is found in all levels of the epidermis, is about 6 μm by 2 μm , bow-shaped, the nucleus being one-third of its size. It can be identified by electron microscopy or by Giemsa staining tissue where the cytoplasm shows blue, the nucleus red.

Possible link to psychiatric disorders

Studies have been conducted that show the toxoplasmosis parasite may affect behavior and may present as or be a causative or contributory factor in various psychiatric disorders such as depression, anxiety and schizophrenia. In 11 of 19 scientific studies, T. gondii antibody levels were found to be significantly higher in individuals affected by first-incidence schizophrenia than in unaffected persons. Individuals with schizophrenia are also more likely to report a clinical history of toxoplasmosis than those in the general population. Recent work at the University of Leeds has found that the parasite produces an enzyme with tyrosine hydroxylase and phenylalanine hydroxylase activity. This enzyme may contribute to the behavioral changes observed in toxoplasmosis by altering the production of dopamine, a neurotransmitter involved in mood, sociability, attention, motivation and sleep patterns. Schizophrenia has long been linked to dopamine dysregulation.

Diagnosis

Detection of Toxoplasma gondii in human blood samples may be achieved by using the polymerase chain reaction (PCR). Inactive cysts may exist in a host which would evade detection.

Toxoplasmosis can't be detected with immunostaining. Lymph nodes affected by toxoplasma have characteristic changes, including poorly demarcated reactive germinal centers, clusters of monocytoid B cells and scattered epithelioid histiocytes.

Transmission

Transmission may occur through:

• Ingestion of raw or partly cooked meat, especially pork, lamb, or venison containing Toxoplasma cysts. Infection prevalence in countries where undercooked meat is traditionally eaten has been related to this transmission method. Oocysts may also be ingested during hand-to-mouth contact after handling undercooked meat, or from using knives, utensils, or cutting boards contaminated by raw meat.
• Ingestion of contaminated cat feces. This can occur through hand-to-mouth contact following gardening, cleaning a cat's litter box, contact with children's sandpits, or touching leach, and can survive in the environment for over a year. It is, however, susceptible to high temperatures—above 66 degrees Celsius (150 degrees Fahrenheit), and is thus killed by thorough cooking, and would be killed by 24 hours in a typical domestic freezer.

Cats excrete the pathogen in their faeces for a number of weeks after contracting the disease, generally by eating an infected rodent. Even then, cat faeces are not generally contagious for the first day or two after excretion, after which the cyst 'ripens' and becomes potentially pathogenic. Studies have shown that only about 2% of cats are shedding oocysts at any one time, and that oocyst shedding does not recur even after repeated exposure to the parasite. Although the pathogen has been detected on the fur of cats, it has not been found in an infectious form, and direct infection from handling cats is generally believed to be very rare

Pregnancy precautions

Congenital toxoplasmosis is a special form in which an unborn child is infected via the placenta. A positive antibody titer indicates previous exposure and immunity and largely ensures the unborn baby's safety. A simple blood draw at the first pre-natal doctor visit can determine whether or not the woman has had previous exposure and therefore whether or not she is at risk. If a woman receives her first exposure to toxoplasmosis while pregnant, the baby is at particular risk. A woman with no previous exposure should avoid handling raw meat, exposure to cat feces, and gardening (cat feces are common in garden soil). Most cats are not actively shedding oocysts and so are not a danger, but the risk may be reduced further by having the litterbox emptied daily (oocysts require longer than a single day to become infective), and by having someone else empty the litterbox. However, while risks can be minimized, they cannot be eliminated. For pregnant women with negative antibody titer, indicating no previous exposure to T. gondii, as frequent as monthly serology testing is advisable as treatment during pregnancy for those women exposed to T. gondii for the first time decreases dramatically the risk of passing the parasite to the fetus.

Despite these risks, pregnant women are not routinely screened for toxoplasmosis in most countries (Portugal, France, Austria,Uruguay, and Italy being the exceptions) for reasons of cost-effectiveness and the high number of false positives generated. As invasiveprenatal testing incurs some risk to the fetus (18.5 pregnancy losses per toxoplasmosis case prevented), postnatal or neonatal screening is preferred. The exceptions are cases where fetal abnormalities are noted, and thus screening can be targeted.

Some regional screening programmes operate in Germany, Switzerland and Belgium.

Treatment is very important for recently infected pregnant women, to prevent infection of the fetus. Since a baby's immune system does not develop fully for the first year of life, and the resilient cysts that form throughout the body are very difficult to eradicate with anti-protozoans, an infection can be very serious in the young.

Treatment

Treatment is often only recommended for people with serious health problems, because the disease is most serious when one's immune system is weak.

Orphaned kittens

Kittens require a high-calorie diet that contains more protein than the diet of adult cats. Young orphaned kittens require milk every two to four hours, and they need physical stimulation to defecate and urinate. Cat milk replacement is manufactured to feed to young kittens, because cow's milk does not provide all of their necessary nutrients.

Hand-reared kittens tend to be affectionate to humans as adults and more dependent on them than those reared by their mothers, but they can also show volatile mood swings and aggression.

Cat play and toys

Domestic cats, especially young kittens, are known for their love of play. This behavior mimics hunting and is important in helping kittens learn to stalk, capture, and kill prey. Cats will also engage in play fighting, with each other and with humans. This behavior may be a way for cats to practice the skills needed for real combat, and might also reduce any fear they associate with launching attacks on other animals.

Owing to the close similarity between play and hunting, cats prefer to play with objects that resemble prey, such as small furry toys that move rapidly, but rapidly lose interest (they become habituated) in a toy they have played with before. Cats also tend to play with toys more when they are hungry. String is often used as a toy, but if it is eaten it can become caught at the base of the cat’s tongue and then move into the intestines, a medical emergency which can cause serious illness and death. Owing to the risks posed by cats eating string, it is sometimes replaced with a laser pointer's dot, which cats may chase. While concerns have been raised about the safety of these lasers, Professor John Marshall, an ophthalmologist at St Thomas' Hospital, has stated that it would be "virtually impossible" to blind a cat with a laser pointer.

Nomenclature and etymology

The word cat derives from Old English catt, which belongs to a group of related words in European languages, including Welsh cath, Spanish gato, French chat (French pronunciation: [ʃɑ]), Basque katu, Byzantine Greek Κάτια kátia, Old Irish cat, Frisian and Dutch kat, German Katze, Armenian katu, and Old Church Slavonic kotka. The ultimate source of all these terms isLate Latin catus, cattus, catta "domestic cat", as opposed to feles "European wildcat". It is unclear whether the Greek or the Latin came first, but they were undoubtedly borrowed from an Afro-Asiatic language akin to Nubian kadís and Berber kaddîska, both meaning "wildcat". The term puss (as in pussycat) may come from Dutch poes or from Low GermanPuuskatte, dialectal Swedish kattepus, or Norwegian pus, pusekatt, all of which primarily denote a woman and, by extension, a female cat.

Classification based on human interaction

Population	Food source	Shelter	Socialized
Pedigree	Fed by owner	Human homes	Yes
Pet	Fed by owner	Human homes	Yes
Semi-feral	General feeding	Buildings	Yes
Feral	General feeding/foraging	Buildings	No
Pseudo-wildcat	Foraging/hunting	None	No

While wildcats are the ancestral species from which domestic cats are descended, there are several intermediate stages between domestic pet and pedigree cats and these entirely wild cats. The semi-feral cat is a cat that is not owned by any one individual, but is generally friendly to people and may be fed by several households. Feral catsare associated with human habitations and may be fed by people or forage in rubbish, but are wary of human interaction. Pseudo-wildcats are descended from domestic cats, but now tend to live entirely independently from people.

A group of cats is referred to as a "clowder", a male cat is called a "tom" (or a "gib", if neutered), and a female is called a "molly" or "queen". The male progenitor of a cat, especially a pedigreed cat, is its "sire", and its female progenitor is its "dam". An immature cat is called a "kitten" (which is also an alternative name for young rats, rabbits, hedgehogs, beavers, squirrels and skunks).

In medieval Britain, the word kitten was interchangeable with the word catling. A cat whose ancestry is formally registered is called a pedigreed cat, purebred cat, or a show cat. In strict terms, a pure-bred cat is one whose ancestry contains only individuals of the same breed. A pedigreed cat is one whose ancestry is recorded, but may have ancestors of different breeds. Cats of unrecorded mixed ancestry are referred to as domestic longhairs and domestic shorthairs or commonly as random-bred, moggies, mongrels, or mutt-cats.

Indoor scratching

A natural behavior in cats is to periodically hook their front claws into suitable surfaces and pull backwards. This marks their territory and exercises their legs, in addition to cleaning and sharpening their claws. Indoor cats benefit from being provided with a scratching post so that they are less likely to use carpet or furniture which they can easily ruin. Commercial scratching posts typically are covered in carpeting or upholstery, but some authorities advise against this practice, as not making it clear to the cat which surfaces are permissible and which are not; they suggest using a plain wooden surface, or reversing the carpeting on the posts so that the rougher texture of the carpet backing is a more attractive alternative to the cat than the floor covering. Scratching posts made of sisal rope or corrugated cardboard are also common.

Close-up of a cat's claw, with the quick clearly visible.

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, infections and permanent lameness.

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 Animalsstrongly 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.

Cat breed

The concept of a cat breed appeared in Britain during the late 19th century. The current list of cat breeds is quite large: with the 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. The owners and breeders of show cats compete to see whose animal bears the closest resemblance to the "ideal" definition and standard of the breed (see selective breeding). Because of common crossbreeding in populated areas, many cats are simply identified as belonging to the homogeneous breeds of domestic longhair and domestic shorthair, depending on their type of fur. In the United Kingdom and Australasia, non-purebred cats are referred in slang as moggies (derived from "Maggie", short for Margaret, reputed to have been a common name for cows and calves in 18th century England and latter applied to housecats during the Victorian era). In the United States, a non-purebred cat is sometimes referred to in slang as a barn or alley cat, even if it is not a stray.

Cats come in a variety of colors and patterns. These are physical properties and should not be confused with a breed of cat. Furthermore, cats may show the color and/or pattern particular to a certain breed without actually being of that breed. For example, cats may have seal point coloration, but not be Siamese.

Some original cat breeds that have a distinct phenotype that is the main type occurring naturally as the dominant domesticated cat type in their region of origin are sometimes considered as subspecies and also have received names as such in nomenclature, although this is not supported by feline biologists. Some of these cat breeds are:

• F. catus anura – the Manx – The Manx is a stocky, solid cat with a dense double coat (long or short), a compact body, very short back, hind legs that are visibly longer than the front legs, big bones, a wide chest, and greater depth of flank (sides of the cat nearest the rear) than other cats. A female Manx would not weigh more than 10 pounds and a male does not weigh over 12 pounds. Specific to this breed is the way their ears appear as a "cradle" when looked at from behind. A Manx cat is mainly recognized by its appearance as it does not have a tail. Although some of them may have a small tail, most Manx cats are tailless. Because of the genetic deformation of these cats they are susceptible of developing what is called Manx Syndrome, a condition that could be fatal for a kitten. Although the gene normally affects only the tail, there is the risk of causing damage to the spine such as fused vertebrae.

F. catus siamensis – the Siamese – Siamese cats are amongst the firstly recognized Oriental cats, a type of cat with a long body but an elegant posture. The length is the main characteristic based on which these cats are distinguished. Their body, legs and tail are all long and still Siamese cats are known for their grace. Also, they are famous because of their blue almond eyes and they are also called "people cats" because of the affection they show to their owners.

• F. catus cartusenensis – the Chartreux – The Chartreux is a natural French breed, which is easily recognized by its size, grayish color and double coat. These cats are also famous because of the paradox coming from the combination between a massively build body and smiling expression and sweet voice.
• F. catus angorensis – the Turkish Angora

Sociability

Although wildcats are solitary, the social behavior of domestic cats is much more variable and ranges from widely dispersed individuals to feral cat colonies that form around a food source, based on groups of co-operating females. Within such groups one cat is usually dominant over the others.Each cat in a colony holds a distinct territory, with sexually active males having the largest territories, which are about ten times larger than those of female cats and may overlap with several females' territories. These territories are marked by urine spraying, by rubbing objects at head height with secretions from facial glands and by defecation. Between these territories are neutral areas where cats watch and greet one another without territorial conflicts. Outside these neutral areas, territory holders usually chase away stranger cats, at first by staring, hissing, and growling, and if that does not work, by short but noisy and violent attacks. Despite some cats cohabiting in colonies, cats do not have a social survival strategy, or a pack mentality and always hunt alone.

Domestic cats use many vocalizations for communication, including purring, trilling, hissing, growling, snarling and several different forms ofmeowing. In contrast, feral cats are generally silent. Their types of body language, including position of ears and tail, relaxation of whole body, and kneading of paws, are all indicators of mood. The tail and ears are particularly important social signal in cats, with a raised tail acting as a friendly greeting. Tail raising also indicates the cat's position in the group's social hierarchy, with dominant individuals raising their tails less often than subordinate animals. Nose-touching is also a common greeting and may be followed by social grooming, which is solicited by one of the cats raising and tilting its head.However, some pet cats are poorly socialized. In particular older cats may show aggressiveness towards newly arrived kittens, which may include biting and scratching; this type of behavior is known as Feline Asocial Aggression.

For cats, life in proximity with humans (and other animals kept by humans) amounts to a "symbiotic social adaptation". They may express great affection towards their human companions, especially if they imprint on them at a very young age and are treated with consistent affection. It has been suggested that, ethologically, the human keeper of a cat functions as a sort of surrogate for the cat's mother, and that adult domestic cats live their lives in a kind of extended kittenhood, a form of behavioral neoteny. Conversely, the high-pitched purrs cats make to solicit food may mimic the cries of a hungry human infant, making them particularly hard for humans to ignore.