Author: Marie Hartley, Staff Writer, 2009.
Toxoplasmosis is a worldwide infection caused by the protozoan parasite Toxoplasma gondii. T gondii infects up to one-third of the world's population. Prevalence of the infection varies with the age of the population studied and by geographic location. The likelihood of having antibodies to T gondii present in the blood (indicating past infection) increases with increasing age. In New Zealand, around 20% of people aged 16–24 and 34% of people aged 25–44 years have had past infection with T gondii.
T gondii is an intestinal parasite of cats, but can infect virtually all warm-blooded vertebrates. Cats become infected by eating infected rodents, birds, or other small animals. The cat then sheds millions of microscopic oocysts in its faeces for 1–3 weeks. Mature cats are less likely to shed T gondii if they have been previously infected. Humans can become infected via the following routes of transmission:
In healthy individuals, infection with T gondii goes unnoticed. Some people (around 10%) experience 'flu-like symptoms with enlarged lymph nodes, and in rare instances chorioretinitis (inflammation in the eye) can occur. Very rarely, myocarditis, pneumonitis, or encephalitis (inflammation of the heart, lungs or brain respectively) may occur. After an acute infection the parasite remains in the body in an inactive (encysted) state and can become reactivated if immunity is impaired.
In patients with impaired immunity (for example, patients with AIDS) toxoplasmosis can be life-threatening. The illness is usually caused by reactivation of chronic infection. Encephalitis and pneumonitis is common in these patients.
Congenital toxoplasmosis is one of the so-called TORCH complex infections and has a range of clinical presentations, from mild to severe disease. Symptoms may be present in the newborn period or may not be apparent for many years. Infection is more severe if the transmission is in early pregnancy. Congenital T gondii infection can result in miscarriage, stillbirth or neonatal death. Most affected newborns are symptom-free at birth; however in 10% there is chorioretinitis with blindness and in 20% there is more generalised disease (such as fever, anaemia, jaundice, and enlargement of the liver and spleen) or neurological symptoms (deafness, seizures, and mental retardation). Chorioretinitis and other neurological symptoms may develop later in life.
Toxoplasmosis eye disease (chorioretinitis) can result from congenital or acquired (e.g. foodborne or zoonotic) T gondii infection. Eye infection leads to acute inflammation of the retina, which resolves leaving scarring. The eye disease can reactivate months or years later, each time causing more damage to the retina. Symptoms include eye pain, blurred vision, photophobia, and blindness.
Dermatological manifestations are rare.
Skin lesions of congenital toxoplasmosis
Skin lesions of acute acquired toxoplasmosis
The diagnosis of toxoplasmosis is usually made by serology, i.e. the detection of Toxoplasma-specific antibodies in the blood. Several tests are available to detect these antibodies within several weeks of infection:
Polymerase chain reaction (PCR) can be used to detect T gondii DNA in amniotic fluid during pregnancy.
Serologic tests may be unreliable in patients with impaired immunity.
Treatment is required for:
The most effective treatment is sulfadiazine in combination with pyrimethamine. For patients allergic to sulfonamides, clindamycin is used. Currently recommended medications primarily treat the active form of T gondii (called the tachyzoite stage), but do not eradicate the inactive, encysted form of the parasite.
Patients with impaired immunity without evidence of prior T gondii infection and pregnant women can take the following precautions:
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