Toxoplasma gondii is a form of microscopic protozoa that causes a disease known as, "toxoplasmosis." The disease is present in every single nation around the world today. Some estimates suggest that great than 30% of the human population is already infected. For example, in France and Germany, the majority of people already carry this parasite, while in the nation of South Korea it is rare. In excess of 60 million people in America alone are believed to be infected.
Toxoplasmosis usually does not cause people to experience any symptoms because the human immune system prevents parasites from causing illness. The disease is more troublesome for women who are pregnant and people who have weakened immune systems. Cats are the main hosts of the disease and people and other warm-blooded animals are merely intermediate hosts. Due to this fact, toxoplasma gondii is not purely a human parasite.
The disease is known to change the behavior of its host. Studies have demonstrated the capability of the parasite to make rats fearless near cats, an indicator of the evolutionary need for toxoplasma gondii to get inside of felines. When a rat is eaten by a cat, the parasite then gets inside the primary host - the cat. Studies have been performed in relation to human beings as well. The results have indicated a strong correlation between schizophrenia and toxoplasmosis. The studies also suggest that people with toxoplasmosis present with altered behaviors such as aggressiveness or promiscuity. People who are infected with toxoplasmosis also experience a decrease in reaction times. People can become infected with toxoplasma gondii by:
The life-cycle of toxoplasma gondii begins when, 'oocysts,' a resting form of the parasite, exit the primary host meaning a cat, into the cat's feces. Millions of oocysts are shed for as long as a period of three weeks after an infection. The oocysts then sporulate and become infective within a period of a few days in the environment. Oocysts are found only in the feces of wild and domesticated cats.
Birds, human beings, and other intermediate hosts become infected after ingesting food or water that is contaminated with cat feces; healthy cats can become infected in this way as well. In the stomach, oocysts transform into, 'tachyzoites,' which travel to other parts of the body through the bloodstream and continue to develop into tissue cyst, 'bradyzoites,' in neural and muscle tissues. The cysts are usually found in skeletal muscles, myocardium, the brain, and the eyes - where they might remain for decades. If a cat or a person eats an intermediate host, the tissue cysts are ingested and the parasite itself activates in the small intestine.
The Toxoplasma gondii Life Cycle
Healthy people who become infected with toxoplasmosis many times do not experience any symptoms because their immune system prevents the parasite from causing illness. Between 10 and 20% of people who become infected develop sore lymph nodes, muscle pains, and additional minor symptoms that can last for several weeks and then simply disappear - referred to as, 'acute toxoplasmosis.' The parasites remain in a person's body as tissue cysts or, 'bradyzoites,' and reactivate if the person becomes immuno-suppressed by other disease or immunosuppressive medications.
If a woman who is infected with toxoplasma gondii becomes pregnant, her unborn baby is safe because the mother has developed immunity. If a woman is pregnant and then becomes infected with toxoplasmosis during or just prior to pregnancy, she may transmit the disease to her unborn child. The earlier the transmission happens, the greater the effects of the disease. The longer the pregnancy, the greater the risk of an infection occurring. The reason for this has something to do with the penetrability of the placenta. The symptoms can include the following:
Babies usually present no symptoms initially, although they may develop vision loss, mental disability, and seizures later in life. Eye disease may be caused by congenital toxoplasmosis or an infection after birth, or rarely from acute toxoplasmosis as an adult. Eye lesions due to congenital infection are many times not present at the time of birth, although they do happen in 20-80% of people who are infected when they reach adulthood. In America, less than 2% of people who were infected after birth develop eye lesions. Eye infection leads to an acute inflammatory lesion of a person's retina, which leaves retinochoroidal scarring unfortunately. The symptoms of acute ocular toxoplasmosis can include the following:
The eye disease has the potential to reactivate later in a person's life, causing more damage to their retina. If the central structures of the person's retina become damaged, progressive vision loss can follow. People who experience weakened immune systems might develop central nervous system disease, pneumonitis, brain lesions, retinochoroiditis or other issues. For example, people with AIDS and renewed toxoplasmosis may present with symptoms including:
If latent, or chronic, toxoplasmosis reactivates in pregnant women who are immunocompromised and who were infected while pregnant, it has the potential to cause congenital infection to their child.
A diagnosis of toxoplasmosis is commonly made through serologic testing by detecting immunoglobulin antibodies within a number of weeks of infection. A person's health care provider will examine their blood sample to find, 'Toxoplasma-specific IgA, IgG, or IgM,' antibodies. Living parasites may also be found in samples of a person's cerebrospinal or other bodily fluids, although the process is more difficult and therefore not commonly used.
Direct observation of the parasite is possible in cerebrospinal fluid, stained tissue sections, or other biopsy samples, although the techniques are used less often because of the difficulties involved. A test that measures IgG determines if a person has been infected. At times it is necessary to determine the time the infection occurred, particularly if the person is a pregnant woman. In such an instance, an IgM is detected along with IgG avidity testing. Molecular techniques are used for detecting toxoplasma gondii DNA in a person's amniotic fluid in instances of congenital transmission. Ocular toxoplasmosis diagnosis is commonly based upon the symptoms a person is experiencing, the appearance of eye lesions, serologic testing, and the course of the infection itself. Serologic tests may be unreliable in people with immuno-suppression.
Toxoplasmosis may be treated with combination of pyrimethamine with either sulfadiazine or trisulfapyrimidines, with folinic acid in the form of leucovorin calcium to protect a person's bone marrow from the toxic effects of pyrimethamine. If the treatment causes a person to experience a hypersensitivity reaction, pyrimethamine and clindamycin may be used instead. If the medications are not available, a combination of sulfatheoxazole and trimethoprim might be used.
Women who are pregnant, as well as babies, may be treated but toxoplasma gondii cannot be entirely eliminated. The parasites may remain within a person's tissue cells in a less active stage in locations that are hard for the medications to get to. A medication called, 'spiramycin,' is recommended for the first four months, while sulfadiazine and pyrimethamine and folinic acid for women that have been pregnant for more than four months is recommended. If an infant is infected, the treatment is administered with medications such as sulfadiazine, pyrimethamine, and folic acid.
Treatment for people who experience ocular disease depends upon the size of their eye lesion, the characteristics - either acute or chronic, as well as the location of the lesion. People who have a compromised immune system, such as people with AIDS, need to receive treatment for toxoplasmosis until their health significantly improves.
Parasites - Toxoplasmosis (Toxoplasma infection)
Toxoplasmosis is considered to be a leading cause of death attributed to foodborne illness in the United States.
Toxoplasma gondii: from animals to humans
Horizontal transmission of T. gondii may involve three life-cycle stages, i.e. ingesting infectious oocysts from the environment or ingesting tissue cysts or tachyzoites which are contained in meat or primary offal (viscera) of many different animals.
The name Toxoplasma is derived from the shape of the organism, which is crescent-like (toxon is Greek for "arc"). T. gondii holds notoriety as the pathogen that causes the disease toxoplasmosis in humans.
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