[Congenital toxoplasmosis].

INTRODUCTION

Toxoplasma gondii is a ubiquitous parasite of all species of mammals and birds (1). Most often the infection in the immunocompetent persons is asymptomatic. Symptoms (if present) are usually mild and self-limited. Infection in the fetus and immunodeficient patients may lead up to clinically severe and often fatal toxoplasmosis (2).

ETIOLOGY

Toxoplasma exists in three forms: oocysts, tissue cysts and tachyzoites. The definitive hosts of Toxoplasma are members of the cat family. They shed unsporulated oocysts in the feces. After sporulation oocysts become infectious. Tachyzoites are crescent-shaped forms responsible for manifestations of acute Toxoplasma infection in the intermediate hosts (6,7). Cysts are formed, particularly in brain, heart muscle and skeletal muscles. The cyst forms of the parasite are seen in the latent stage of the infection. Postnatally acquired toxoplasmosis is a consequence of infection from cysts (by ingestion of undercooked meat of infected animals), oocysts (by ingestion of soil, fruits, vegetables contaminated by cat feces) and tachyzoites (by blood transfusion). Congenital Toxoplasma infection causes congenital toxoplasmosis.

PATHOGENESIS

Some authors represented the concept that latent (chronic) infection with Toxoplasma during pregnancy can result in congenital infection in the offspring (8-11). Now it is generally agreed that congenital transmission of Toxoplasma occurs only when the infection is acquired during gestation (6,7, 12-16). More than half of the fetuses escape infection, one-third are definitely infected, and the infection is more often subclinical than clinically obvious (15). The fetus is infected hematogenously from inflammatory foci in the placenta formed during parasitemia in the mother.

CLINICAL MANIFESTATIONS

Approximately 75% of congenitally infected newborns are asymptomatic. Wilson's study indicates that nearly all such children will develop adverse sequelae (neurologic, intellectual, audiologic and ophthalmologic) 21). Severe forms of congenital toxoplasmosis occur only in 10% of infected offsprings. Clinical manifestations of congenital toxoplasmosis are different. Clinical findings in patients with congenital toxoplasmosis may include: chorioretinitis and other ocular findings, central nervous system abnormalities (such as microcephaly, hydrocephalus, encephalomyelitis, seizures and mental retardation), icterus, hepatosplenomegaly, rash, anemia, erythroblastosis, thrombopenia.

INCIDENCE

Incidence of human congenital toxoplasmosis is different in different countries. The incidence in Britain is 0.6 subclinical infection and 0.09 severe illnesses per 1000 births (22). The incidence in USA is between 1/1000 and 1/8000 live births (23). In France the incidence is 1/2000. In Slovenia the incidence is 2.3 cases per 1000 births (25).

DIAGNOSIS

Diagnostic methods are: 1. Isolation of the parasite from the placenta, blood, body fluids (by inoculation of specimens into mice or tissue cultures). 2. Histologically by demonstration of tachyzoites in tissue sections or smears of body fluids. 3. Serologic diagnosis. The most important diagnostic methods are serologic tests. For diagnosis of congenital toxoplasmosis determination of IgM antibody (in the serum of newborn infant) has the greatest importance. The fetus is able to produce IgM specific antibody. The presence of IgM antibodies in serum obtained from the neonate is an evidence of fetus infection in utero. Maternal IgM antibodies do not pass the placenta. IgM antibodies may be demonstrable by indirect fluorescent antibody test (IgM-IFA), enzyme linked immunosorbent assay (IgM-ELISA), double sendwich IgM enzyme-linked immunosorbent assay (DS-IgM-ELISA), IgM immunosorbent agglutination assay (IgM-ISAGA) and reversed enzyme immunoassay (REI). For diagnosis of congenital toxoplasmosis the next tests are also applied: Sabin-Feldman Dye test, indirect fluorescent antibody test for IgG antibodies (IgG-IFA) and enzyme