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Congenital Toxoplasmosis

Historical Perspective

• In 1908, Nicolle and Manceaux described the parasite in the blood, spleen and liver of a North African rodent–gundi (Ctenodactylus gundi), due to its similar appearance as leishmania they named it Leishmania gondii.
• In 1909, Nicolle and Manceaux renamed the parasite as T. gondii.
• In 1937, Sabin & Olitsky described that Toxoplasma was an obligate intracellular parasite and could be passed onto laboratory animals by intracranial, subcutaneous, intraperitoneal inoculation of brain homogenates (The slurry of tissues and cells which results when cell structure has been mechanically disrupted). They have also suggested that ingestion of Toxoplasma contaminated tissue can result in Toxoplasmosis.
• In 1937 to 1940, Wolf and Cowen have described necrotic and granulomatous lesions on autopsy of a 3 day old infant's brain infected with Toxoplasma. They have also reported that the mothers were asymptomatic but carried antibodies against Toxoplasma and the possibility of congenital transmission was expressed.
• In 1940, Pinkerton and Weinman reported the first fatal case of Toxoplasmosis in an adult.
• In 1948, Sabin and Feldman developed a serological test to identify infected individuals by using antibodies specific to Toxoplasma, called the Sabin Feldman Dye test. The serological test when used in large population studies showed a high proportion of humans and domestic animals carried antibodies against Toxoplasma.
• In 1965, Desmonts described that ingestion of under-cooked and uncooked meat plays a role in the pathogenesis of Toxoplasmosis.
• In 1970, Dubley described the life cycle of the parasite and established that the cats are the definitive hosts and any warm blooded animal can be an intermediate host.

Risk Factors

The main risk factors for acquiring the infection is consuming raw meat and ingestion of food contaminated with Toxoplasma oocysts excreted in cat feces.
The list of risk factors include:

• Consumption of raw oyesters and clams
• Eating undercooked meat which includes pork and lamb
• Drinking unpasteurized goat’s milk
• Exposure to kitten litter

Epidemiology, Demographics

• The estimated incidence of congenital Toxoplasmosis in United States is estimated be in between 500 to 5000 every year.
• In United States ocular Toxoplasmosis affects around 1.26million people.
• In United States 89% of women in the childbearing age are susceptible to have an acute infection and at risk for transmitting the parasite to the baby if the primary infection occurs during the getational period.

Diagnosis

Laboratory Findings

Principles and methods used for the diagnosis of congenital toxoplasmosis:

Principle	Detection	Method	Findings supporting the diagnosis of Toxoplasmosis
Toxoplasma specific humoral responses	IgG, IgM, IgA	Dye test, ELISA, ELISA-like assays,ISAGA, immunofluorescence, agglutination	Positive IgM after 5 days of life and in the absence of blood transfusions Positive IgA after 10 days of life Persistence of Toxoplasma IgG beyond 1 year of age
	IgG, IgM, and IgA to specific Toxoplasma antigen	Western blot	Presence of specific bands only seen in the newborn or bands with higher intensity than maternal ones for IgG and/or IgM and/or IgA in a reference laboratory
Toxoplasma nucleic acid amplification	DNA	PCR	Positive result in any body fluid (e.g: amniotic fluid, cerebrospinal fluid, peripheral blood, urine)
Immunohistochemistry of Toxoplasma specific antigens in tissue	Antigens	Immunoperoxidase	Positive result in any tissue(e.g., brain or other fetal tissue)
Visualization by microscopy	Visual identification of tachyzoites and/or cysts	Stains such as hematoxylin/eosin, Giemsa	Positive identification in a reference laboratory
Isolation of Toxoplasma	Whole live parasite	Inoculation in peritoneal cavity of mice	Detection of live cysts from any body fluid or tissue that has been inoculated in mice in a reference laboratory
Brain imaging	Brain calcifications Hydrocephaly Microcephaly	Ultrasound, CT, brain MRI	Findings can be suggestive but are not diagnostic of congenital Toxoplasmosis since other etiologies may result in similar findings
Retinal exam	Inflammation in choroidal and retinal layers	Ophthalmological exam	Retinochoroidal lesions can be highly suggestive or, at times, diagnostic of congenital Toxoplasmosis

Table adopted from Laboratory Diagnosis of Congenital Toxoplasmosis