Toxoplasma gondii is a protozoan (type Sporazoa) that causes a disease known as Toxoplasmosis. The organism is crescent-shaped, with no appendages or prominent internal structures other than a nucleus. It lives only in the intestines of felines, which generally become infected after eating other such infected animals as mice, birds, raw meat, or through the feces of other cats. Over 300 mammallian species and 20 species of birds have been identified as intermediate hosts for this particular protozoa. However, it can only complete its sexual cycle in the intestinal tract of felines, which include ocelots, bobcats, cougars, leopards, etc., as well as the domesticated house cat. It is estimated that over 80% of household cats carry the organism, with no signs or symptoms of the parasite infestation.
Transmission is usually from the handling of cats and their feces, children playing in sandboxes that have been used by cats, uncooked meats, as well as from cockroaches and flies that have been contaminated and then come in contact with foods. Drinking water can also become contaminated by cat feces. Transmission has also occurred via organ transplants. It is recommended that high risk individuals (pregnant women or the immunocompromised) use rubber gloves when gardening or emptying the cat litter box. Humans are not the only ones susceptible to toxoplasmosis. Dogs can also become blind or neurologically impaired after an infection (often caused by eating cat feces).
The disease is presented in one of three forms:
- a self-limiting disease with fever and swollen lymph gland,
- a highly lethal infection in those with a compromised immune system,
- and the congenital infection of infants.
The disease is often so mild that it is passed off as just another illness. Some never show symptoms. Others may take years to form, surfacing only when the immune system becomes weakened. After reaching the intestines, the organism will take two or three days to become infectious. As the immune system begins to produce antibodies, T. gondii remains inside the infected cells to form aggregates of several thousand parasitic cells that become enclosed in a fine membrane forming an oocyst, or a living egg. Within each oocyst are eight sporozoites (each a potential source of infection). The oocyst produces no further clinical symptoms in the host, nor does it cause any tissue damage, but the enclosed parasite can remain protected from the host’s defence mechanisms for a lifetime. However, these cysts can still serve as a source of infection to others that may ingest infected tissues, as in cases of animals eating other animals or humans eating raw or undercooked meats. The oocysts can live up to four months in soil and eighteen months in water, and takes either the heat of thoroughly cooked food or the very low temperatures of hard freezing to kill them.
Congenital toxoplasmosis is more serious after the first trimester when there is a 50% chance of such defects developing as blindness, cleft palate, hearing loss, mental retardation, seizures, and cerebral palsy. Generally, the organism focuses on the tissues of the brain and eyes, causing many fetuses to die before birth or soon after. About 60% of the newborns shows no signs of illness, but carry a latent infection to appear later in life. Others may suffer such disorders as hydrocephalus, a condition where there is an abnormal accumulation of fluid around the brain that causes the skull to enlarge, compressing the brain tissue. It can also cause calcification. Approximately 9% will die.
Symptoms of the disease resemble those of mononucleosis, with chills, fever, headaches, swollen lymph glands, respiratory illness, low blood sugar, rash, anemia, enlarged spleen, and extreme fatigue. These symptoms will worsen as the disease progresses. In those with a compromised immune system, the parasite goes on to affect the CNS (central nervous system), brain, lungs, eyes, and heart. An active infection can cause the inflammation of the brain, paralysis, delusional behavior and headaches that painkillers cannot touch. Chronic phases will resemble hepatitis or Hodgkin’s disease.
Toxoplasmosis can occur in any part of the world. Research has shown that at least half the world’s population has been, or is now, infected with this parasite. Another similar parasite that is treated the same way as toxoplasmosis is caused by protozoan Sarcocystis bovicanis, and is contracted through the eating of undercooked meat or ingesting spores. It releases a toxin, called sarcocystin, that affects the CNS, heart, lungs, adrenal, glands, liver, and intestines resulting pain, swelling, and degeneration.