Toxoplasmosis

Contributor: John Dacus, MD;                                                                                                                                
Last Update: 9/19/2012

Toxoplasmosis in Pregnancy                    

Pathogenesis
Toxoplasmosis is an ubiquitous disease caused by the protozoan toxoplasma gondii.  Its life cycle is composed of the tachyzoite, which is the mobile form that can invade body tissues and traverse the placenta; the tissue cyst lying dormant in various tissues such as striated muscle; and the oocyst found in the intestinal tract of the cat family.  Humans may become infected by eating undercooked contaminated meat or ingestion of oocysts from cat feces or fresh vegetables.

Maternal Effects
Majority assymptomatic

• 10% have flu like symptoms including lymphadenopathy
•  Rarely chorioretinitis may occur.

Fetal Effects
Fetal effects of acute toxoplasmosis infection during pregnancy include:

• ventriculomegaly
• intracranial calcifications
• hepatic calcifications
• hepatomegaly
• splenomegaly
• ascites
• IUGR
• microcephaly

Transmission Rate
The transmission rate of toxoplasmosis depends upon the trimester of pregnancy in which acute infection occurs.  The severity of the fetal infection decreases as the gestational age of the acute infection advances.

• 1st trimester  15%
• 2nd trimester  20% – 30%
• 3rd trimester  60% – 66%

Diagnosis
Serology is necessary for the diagnosis of toxoplasmosis.  IgG and IgM toxoplasma antibodies should be obtained.

Individuals with a positive IgG and IgM require further testing through a reference laboratory such as Toxoplasmosis Reference Laboratory at Stanford University in Palo Alto, California.  (Toxoplasmosis Reference Laboratory at the Palo Alto Medical Foundation- Phone # 650-853-4828) Alternate testing including dye test, differential  agglutination, avidity and double sandwich ELISA may be used to distinguish recent from old infection.

Management 
If maternal serology indicates recent toxoplasmosis or its possibility, intrauterine infection may be confirmed by PCR evaluation of amniotic fluid in a high percentage of cases (sensitivity of 64%) with a positive predictive value of 100% and a negative predictive value of 88%.  Monthly ultrasound examinations are also recommended in women suspected of or diagnosed with acute toxoplasmosis during pregnancy.

Spiramycin decreases the transmission of toxoplasmosis transplacentally and is indicated throughout gestation, unless intrauterine infection is documented by amniotic fluid PCR.  Those patients diagnosed with intrauterine infections should be offered pyrimethamine, sulfadiazine and folinic acid.  All patients on pyrimethamine should have periodic CBC determinations because of potential hematologic toxicity.  Spiramycin may be stopped when intrauterine infection is documented.

Indications for Testing

• Ultrasound findings suggestive of fetal toxoplasmosis infection.
• Behavior that increases natural risk of infection, i.e. frequent gardening, eating undercooked meat, ownership of cats that spend time outdoors and indoors.
• Maternal anxiety.

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References

1.       Montoya JG, Rosso F.  Diagnosis and management of toxoplasmosis Clinics in perinatology 32 (2005) 705—726.
2.       Duff P. Maternal and perinatal infection – bacterial. Obstetrics: Normal and abnormal pregnancies. Churchill Livingstone  5th edition (2007) 1245-1246.