Toxoplasmosis

Toxoplasmosis is an infectious disease caused by a parasite (an organism that depends on or is sustained by a host organism). Toxoplasmosis is found in humans, most birds and many different types of mammals. It's considered one of the most prevalent infectious diseases in the United States. In fact, in some populations more than 50 percent of people have been infected.


Causes/associated factors
Toxoplasmosis is caused by the parasite Toxoplasma gondii. Members of the cat family are the only hosts that excrete eggs formed by the parasite. When a cat is infected (by eating uncooked meat or infected mice, for example), the parasite lives in the cat's intestines and produces egg cells. For up to two weeks, these egg cells enter the environment through the cat's feces. After one to five days outside the cat's body, the egg cells are capable of infecting other animals or humans. Highly resistant to disinfectants, freezing and drying, the egg cells can survive in a favorable environment such as warm, moist soil for more than a year.
If ingested, the egg cells develop and infect tissues throughout the body, sometimes forming protective cysts. In healthy people and animals, the immune system stops the infection but the cysts remain in body tissues such as the brain, heart and muscles. In turn, this tissue can be a source of infection if it's later ingested or transplanted.

You develop immunity to the toxoplasmosis parasite after an initial infection. Unless you have a weak immune system, a second bout with the infection is rare.


Transmission
You can be infected with toxoplasmosis in a variety of ways, such as:
touching the feces of an infected cat (which may contain the organism), handling litter boxes improperly, playing in sandboxes or yards where cats have left stools, or drinking water contaminated with cat feces
through contact with insects (such as flies or cockroaches) that might have been exposed to cat feces or ingested foods contaminated by cat feces
eating raw or undercooked meat from infected animals (especially pork, lamb and wild game), drinking unpasteurized milk (especially goat's milk) or eating raw or undercooked eggs. (Infected meat cannot cause an infection if it's cooked adequately, smoked or cured.)
through a lab accident
rarely, through a blood transfusion or organ transplant
If you're pregnant, you can pass the infection to your unborn baby through your blood, which circulates through the placenta. Other modes of transmission may also exist, but are currently unknown.

The incubation period (time from exposure until symptoms appear) ranges from five to 23 days.


Signs/symptoms
For humans, there are four clinical types of toxoplasmosis. Symptoms of each are described below.
Acute toxoplasmosis in a healthy person
Eighty to 90 percent of healthy people who have toxoplasmosis have no symptoms. If symptoms do develop, they may include:


swollen lymph nodes, especially in the neck
fatigue
muscle or joint pain
sore throat
rash
fever
enlarged liver and spleen
rarely, visual changes due to retinitis (inflammation of the retina)
rarely, encephalitis (inflammation of the membrane covering the brain)
Toxoplasmosis in someone with a weak immune system
For people who have weak immune systems, disseminated (widespread) toxoplasmosis is usually caused by reactivation of the disease. People who have HIV (the virus that causes AIDS) or AIDS are at particularly high risk for disseminated toxoplasmosis. The condition can develop into a brain infection, which may cause fever, headache, confusion, lethargy, seizures, and loss of motor or sensory function in a body part. Other complications may include visual loss, pneumonia, heart failure and fever.

Congenital toxoplasmosis
Congenital toxoplasmosis may develop in a baby whose mother contracted toxoplasmosis for the first time during pregnancy. Rarely, congenital toxoplasmosis can develop if the mother contracted toxoplasmosis before conception. The risk of transmission is highest during the third trimester, but this is associated with the least severe form of toxoplasmosis. On the other hand, the risk for transmission is lowest in the first trimester, but this leads to more severe disease. The mother's symptoms are often mild or nonexistent. Most babies born with toxoplasmosis show no symptoms at birth but develop potentially serious problems later.

Ocular toxoplasmosis
Ocular toxoplasmosis causes necrotizing retinitis (inflammation and death of the retina, the light-sensitive tissue found at the back of the eye that sends nerve impulses to the brain). If ocular toxoplasmosis develops, it's usually in people who were born with congenital toxoplasmosis. Symptoms may not appear until the 20s to 40s. Rarely, ocular toxoplasmosis may develop in someone who's had a recent toxoplasmosis infection.

Symptoms may include:

blurred vision
scotoma (spots in the visual fields)
eye pain
photophobia (an abnormal intolerance to light)
impairment or loss of central vision

Diagnosis
Your blood may be tested for antibodies (compounds that help neutralize or destroy foreign substances in the blood) for the toxoplasmosis organism. Unfortunately, the blood tests for Toxoplasma sometimes only indicate whether there was a previous infection -- not whether Toxoplasma is responsible for the current symptoms. During the initial infection, the parasite may also be detected in your blood. Sometimes, a tissue biopsy is necessary. If the biopsy carries a significant risk (as it would for a person with HIV or AIDS who has an abnormal brain lesion, for example) and the doctor strongly suspects toxoplasmosis, treatment with an anti-Toxoplasma medication may be recommended to see if the symptoms improve. If so, sometimes this is enough circumstantial evidence to diagnose toxoplasmosis.
Unfortunately, there are no reliable tests to determine if a cat is passing the egg cells in its feces.


Treatment
Your doctor will tailor your treatment depending on several factors, including:
your health status, including whether you have a healthy immune system
whether you're pregnant
whether your central nervous system is affected
If you have a normal immune system and an acute mild infection and you're not pregnant, no treatment is necessary. If your symptoms are severe and persistent or you have a weak immune system, the doctor may prescribe drug therapy with a sulfonamide drug and pyrimethamine for at least three to six weeks. These drugs attack the offending organism. Folinic acid (the active kind of folic acid, which is a component of the vitamin B complex) may be given to help alleviate side effects caused by pyrimethamine. If you're allergic to sulfa drugs, pyrimethamine and clindamycin are an equally effective treatment option.

For ocular toxoplasmosis, pyrimethamine is typically given along with sulfadiazine for at least three to six weeks. Again, folinic acid may be given to help alleviate side effects. Prednisone may also be used if certain parts of the eye are involved.

If you're unable to tolerate the medications used to treat toxoplasmosis, other drugs may be used. Your doctor will also decide whether inpatient or outpatient treatment is best for you.

Preventive drug therapy may be given if you are infected with HIV and your antibody test for toxoplasmosis is positive, especially if your CD4+ cell count (the cells that help fight infection) is below 100.


Complications
For a pregnant woman, toxoplasmosis can cause miscarriage, premature birth or stillbirth.
Infants born with congenital toxoplasmosis may develop serious complications, including:

visual impairment or blindness due to retinitis (which may not be apparent until the 20s to 40s)
hearing disorders
seizures
hydrocephaly (fluid accumulation in the brain)
microcephaly (an abnormally small head)
developmental delays
mental retardation
If your immune system is weak, toxoplasmosis may lead to:

encephalitis
hepatitis (inflammation of the liver)
pneumonitis (inflammation of the lungs)
myocarditis (inflammation of the heart muscle)

Pregnancy-specific information
Again, if you're pregnant and contract toxoplasmosis, your unborn child may develop serious medical problems. If you suspect you've been exposed to toxoplasmosis or developed the infection, contact your doctor immediately.

Senior-specific information
For older adults, prevention is especially important if you have a weak immune system. You may be more susceptible to reactivation of the infection and less able to control its spread.

Prevention
Prevention is most important for pregnant women and those who have weak immune systems and no evidence of a prior infection based on blood antibody tests. To prevent toxoplasmosis, keep the following suggestions in mind.
Avoid contact with cat feces. If you have a cat, change the litter box daily and routinely disinfect it with hot (almost boiling) water. Wear gloves, and wash your hands thoroughly after you've finished. If you're pregnant or have a weak immune system, ask someone else in your household to handle these tasks.

If you have a cat, don't feed it raw meat and keep it indoors to discourage hunting.

If you're pregnant, don't bring a new kitten or cat into your home. It's not necessary to get rid of a cat you already have, however. Studies have shown that most women who've had a cat for a while are already immune to toxoplasmosis.

If you want to adopt or buy a cat and you have a weak immune system, be sure the cat is at least one year old and healthy.

Avoid handling stray cats and kittens.

Protect play areas and sandboxes from cat feces.

Wear gloves when gardening, and wash your hands after having contact with soil or sand in case it's been contaminated with cat feces.

Peel or thoroughly wash fruits and vegetables before eating in case they came in contact with soil contaminated with cat feces.

Wash your hands before preparing food or eating.

Do not drink unpasteurized milk or eat raw or undercooked or eggs or meat (especially pork, lamb and venison).

Be careful when handling raw meat, poultry, seafood and unwashed fruits and vegetables. Avoid touching your face. When finished, always wash your hands, kitchen surfaces and utensils thoroughly with hot soapy water.

To kill Toxoplasma cysts, cook meat thoroughly to an internal temperature of at least 160°F. It should no longer be pink in the center.

Keep flies and other insects that may have been exposed to cat feces away from your food.