is a protozoan parasite that infects most species of warm blooded
animals, including humans, causing the disease toxoplasmosis.
Members of the cat
family (Felidae) are the only known definitive hosts for the sexual
stages of T. gondii and thus are the main reservoirs of
infection. Cats become infected with T. gondii by carnivorism
After tissue cysts or oocysts are ingested by the cat, viable organisms
are released and invade epithelial cells of the small intestine where
they undergo an asexual followed by a sexual cycle and then form
oocysts, which are excreted. The unsporulated oocyst takes 1 to 5 days
after excretion to sporulate (become infective). Although cats shed
oocysts for only 1 to 2 weeks, large numbers may be shed. Oocysts can
survive in the environment for several months and are remarkably
resistant to disinfectants, freezing, and drying, but are killed by
heating to 70°C for 10 minutes.
Human infection may be acquired in several ways: A) ingestion of
undercooked infected meat containing Toxoplasma cysts
B) ingestion of the oocyst from fecally contaminated hands or food
C) organ transplantation or blood transfusion; D) transplacental
transmission; E) accidental inoculation of tachyzoites. The parasites
form tissue cysts, most commonly in skeletal muscle, myocardium, and
brain; these cysts may remain throughout the life of the host.
prevalence data indicate that toxoplasmosis is one of the most common of
humans infections throughout the world. Infection is more common in
warm climates and at lower altitudes than in cold climates and
mountainous regions. High prevalence of infection in France has been
related to a preference for eating raw or undercooked meat, while high
prevalence in Central America has been related to the frequency of stray
cats in a climate favoring survival of oocysts. The overall
seroprevalence in the United States as determined with specimens
collected by the third National Health and Nutritional Assessment Survey
(NHANES III) between 1988 and 1994 was found to be 22.5%, with
seroprevalence among women of childbearing age (15 to 44 years) of 15%.
with Toxoplasma in immunocompetent persons is generally an
asymptomatic infection. However, 10% to 20% of patients with acute
infection may develop cervical lymphadenopathy and/or a flu-like
illness. The clinical course is benign and self-limited; symptoms
usually resolve within a few months to a year. Immunodeficient patients
often have central nervous system (CNS) disease but may have
retinochoroiditis, or pneumonitis. In patients with AIDS, toxoplasmic
encephalitis is the most common cause of intracerebral mass lesions and
is thought to be caused by reactivation of chronic infection.
Toxoplasmosis in patients being treated with immunosuppressive drugs may
be due to either newly acquired or reactivated latent infection.
Congenital toxoplasmosis results from an acute primary infection
acquired by the mother during pregnancy. The incidence and severity of
congenital toxoplasmosis vary with the trimester during which infection
was acquired. Because treatment of the mother may reduce the incidence
of congenital infection and reduce sequelae in the infant, prompt and
accurate diagnosis is important. Most infants with subclinical
infection at birth will subsequently develop signs or symptoms of
congenital toxoplasmosis unless the infection is treated. Ocular
Toxoplasma infection, an important cause of retinochoroiditis in the
United States, is frequently a result of congenital infection. Patients
are often asymptomatic until the second or third decade of life, when
lesions develop in the eye.
The diagnosis of
toxoplasmosis may be documented by:
parasites in patient specimens, such as bronchoalveolar lavage
material from immunocompromised patients, or lymph node biopsy.
parasites from blood or other body fluids, by intraperitoneal
inoculation into mice or tissue culture. The mice should be tested
for the presence of Toxoplasma organisms in the peritoneal
fluid 6 to 10 days post inoculation; if no organisms are found,
serology can be performed on the animals 4 to 6 weeks post
parasite genetic material by PCR, especially in detecting congenital
infections in utero.
testing is the routine method of diagnosis, because the techniques
described above are technically complex and generally not rewarding.
Treatment is not
needed for a healthy person who is not pregnant. Symptoms will usually
go away within a few weeks. Treatment may be recommended for pregnant
women or persons who have weakened immune systems.