The source of the infection is Toxoplasma gondii, a relative of Plasmodium, the parasite that causes malaria. Wild and domestic cats are the natural hosts of Toxoplasma. It can infect birds and all known warm blooded mammals. It is usually found in the brain but can infect almost any cell in the body.
Prevalence
One third to one half of the world's population may have toxoplasmosis. In the United States, the Centers for Disease Control estimates about sixty million people are likely to have the infection. Toxoplasmosis is a major cause of death in sea otters and is found in other sea mammals as well.
Those with weak immune systems and unborn children are at greatest risk of serious injury from the infection. A pregnant woman can pass the infection to the fetus which can lead to blindness, brain damage, or seizures in the baby.
How the Infection is Spread
Toxoplasmosis is spread most often by food, usually by eating meat that contains parasite cysts. Other ways it spreads:
- from mother to unborn child – about 1 in 5000 babies in the United States is born with the infection (congenital toxoplasmosis)
- soil – ingesting contaminated soil such as from sandboxes, gardening or eating unwashed plants
- less frequently blood transfusions or organ transplants are a source of the infection
- contact with contaminated knives or surfaces used to prepare meat.
Life Cycle of Toxoplasmosis
Toxoplasma is a crescent shaped microbe that reproduces sexually and asexually. It only reproduces sexually within the intestines of a cat. During the active stage the parasite goes through three phases of reproduction, oocysts, tachyzoites, and bradyzoites.
When it sexually reproduces in a cat's intestines, toxoplasma forms oocysts, an egg form of the parasite. During the acute phase of infection, a cat will shed millions of oocysts through its feces.
Outside the body, oocysts can survive up to eighteen months in warm moist soil and six months in water. Oocysts remain in the same form until they infect a bird or some other animal, called an intermediate host.
After entering a new host, oocysts transform into tachyzoites. These are carried by the lymph system and blood throughout the body. Tachyzoites enter cells forming tissue cysts, often in the brain, eyes, muscles, or lymph nodes.
Tachyzoites can also invade the heart, lungs, or spinal cord. In this form the parasite does the most harm. Tachyzoites reproduce until they fill a cell causing it to swell and burst. This destroys the tissue, triggering inflammation and an immune response.
As the acute phase of infection passes, the parasites form tissue cysts, protective cysts containing parasite cells called bradyzoites. These replicate more slowly and embed themselves in the brain, eyes, muscles, organs, or other body tissues. They can survive in the inactive state for the lifetime of their host.
When the immune system is weakened, as with HIV or autoimmune disorders, the infection can reactivate. The tissue cysts will burst releasing bradyzoites which infect cells. This enables them to feed and produce tachyzoites setting off a new cycle of inflammation and disease.
Symptoms
Toxoplasmosis symptoms are most often mild, even in the acute phase of infection. The following symptoms are seen with toxoplasmosis.
Mild Symptoms
- Swollen lymph glands
- Mild flu-like symptoms
- Muscle aches
- Fatigue
Severe Symptoms
- Seizures
- Blurred vision
- Parkinsonian tremors
- Confusion
- Inflammation of the retina
- Symptoms of schizophrenia, or bipolar disorder
- Inflammation of the heart
- Encephalitis
Prevention
- All meat should be cooked until it is fully done. There should be no pink in the center and the juices should be clear. It is not safe to taste the meat before it is completely cooked.
- Use gloves when gardening and when cleaning a cat litter box wash hands with soap and water when finished.
- Cover outside sandboxes.
- Peel and wash vegetables and fruits before eating..
- After any food preparation wash hands, utensils, cutting boards and other areas that came in contact with the food.
- Do not feed cats raw or undercooked meat.
- Do not drink water from streams or other sources that may be contaminated.
Diagnosis and Treatment
Testing for toxoplasmosis may include blood tests, CT or MRI scans, or biopsy.
The drugs available to treat toxoplasmosis can reduce the population of tachyzoites during the infection’s active phase. They do not eradicate the tissue cysts which can reactivate the infection when the immune system is weakened.
Subtle Symptoms May be Misleading
The mildness or absence of symptoms can be misleading. Even in the acute phase of the disease, a pregnant woman may have no symptoms of illness whatsoever and appear perfectly healthy. If she does carry the infection, it can be passed to her unborn child.
With psychiatric or neurological symptoms such as seizures, or Parkinson’s tremors, there may be no signs or history of even mild illness that would clearly point to toxoplasmosis. Routine evaluation could identify those whose symptoms may be linked to infection.
According to the Toxoplasmosis Research Institute in Chicago, nine out of ten pregnant women in the United States are vulnerable to acquiring toxoplasmosis while they are pregnant. Even during the severe phase of the infection there may be no symptoms. Women who are pregnant, or planning to be, need to be tested to prevent passing the infection to the fetus.
Toxoplasmosis is a lifelong infection. Early diagnosis, treatment and a strong immune response to tachyzoites can force the parasite into a dormant phase where slow growing tissue cysts produce few or no obvious symptoms. Prevention and maintaining a strong immune system can help slow the spread of the infection and prevent some of the devastating injury that may be triggered by toxoplasmosis.
Resources
Toxoplasmosis Research Institute and Center
(Information and resources for physicians and the public)
Sources
Centers for Disease Control and Prevention
Carruthers VB, Suzuki Y; Effects of Toxoplasma gondii Infection on the Brain; Schizophr Bull (2007) 33 (3): 745-75
Zimmer Carl; Parasite Rex; Touchstone Press; United States, 2001
Disclaimer: "This article is only for informational purposes and not meant to diagnose or treat any disease or condition. If you have any concerns, consult you doctor or health care professional."
Zoe Langley - Zoe Langley is a writer living in Kentucky. She is a past winner of the Seattle Writers in Performance Award. She has a passionate ...
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