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Editor,—During pregnancy primary toxoplasmic infection of the mother is a well known cause of congenital chorioretinitis due to fetal contamination by Toxoplasma gondii. It is generally thought that women infected before conception have no risk of transmitting the disease to the fetus unless they are severely immunocompromised.1 We report two children with severe ocular lesions due to congenital toxoplasmosis transmitted by preconceptionally immune mothers.
A 1 year old girl presented with a convergent squint as a consequence of bilateral large macular scars. She was the first child of a healthy immunocompetent mother. Three months before conception, the systematic French prenuptial serological screening of the mother showed a recent toxoplasmic infection diagnosed by a high titre of specific immunoglobulin M (IgM) (IgM 5200, Biotrol Merck (normal <200), IgG= 40 IU/ml) (Table 1). She was treated with spiramycin 3 MIU per day for a month. At the time of referral, the mother’s titre of IgM had significantly decreased (IgM 200) and showed a slightly higher rate of IgG (140 IU/ml). Her daughter’s serological status showed a high titre of specific IgG (624 IU/ml), the presence of specific IgA (6 /12 index ISAGA; immunosorbent agglutination assay, Biomérieux, index 0–12) and specific IgM (11/12 index ELISA) confirming a fetal infection. Intracerebral calcifications, suggestive of congenital toxoplasmosis, were found on the computed tomogram (Fig 1). The child was otherwise healthy and was not treated.
A 1 month old boy was referred because of a congenital cataract in the right eye and a macular atrophic lesion surrounded by an active whitish ring. He was the third child of an immunocompetent woman, a native of Saint-Domingue (Haïti).1 She had long standing toxoplasmic immunity, confirmed by the absence of specific IgM and stable IgG rates at the fourth and the 10th weeks of her pregnancy (ELISA, IgG 49 and 54 IU/ml respectively) providing proof of an anterior toxoplasmic infection (Table 1). The serology of the neonate showed evidence of active T gondii infection with a high IgG titre (ELISA >1200 IU/ml), a positive specific IgM (10/12 index ISAGA) as well as a positive specific IgA (6/12 specific ISAGA). The serological study of the mother, after the birth, showed a dramatically increased level of IgG (ELISA IgG > 1200 IU/ml) with specific IgA (12/12 index ISAGA); however, no specific IgM was detected. The child was operated on for his cataract and was treated orally with pyrimethamine and sulphadiazine.
Congenital chorioretinitis may be a challenging clinical situation for which fetal infections must be considered, in particular, congenital toxoplasmosis.
Because of the concept that the offspring of an immune woman is protected, the diagnosis of infection by T gondii may be overlooked in rare cases especially when there are only ocular manifestations.
In our two cases, the mothers were considered to be immune to T gondii; nevertheless, they transmitted the disease to their children who presented with sight threatening manifestations and no systemic symptoms. The mothers were not immunocompromised, thus excluding toxoplasmosis reactivation due to immunodeficiency.2 Different pathophysiological mechanisms may be suggested and may be illustrated by our two cases.
Regarding our first patient, it has been reported recently that, exceptionally, congenital toxoplasmosis may be a consequence of primary maternal toxoplasmosis infection preceding conception.3 4Despite medical treatment, the parasitaemia may remain active even months after the onset of the disease and could be responsible for fetal contamination. An emerging immune response as well as the mother’s treatment, reducing the parasitaemia of the child, may explain the attenuated clinical manifestation5 leading to ocular manifestations without other clinical systemic involvement and without miscarriage.
The development of toxoplasmosis in the second case may be explained by reinfection of the mother.5 The mother’s positive specific IgA suggested that there was reinfection of the mother by the parasite, as these immunoglobulins are produced during the digestive phase of the acute infection.1 5 Strains of different virulence have been described, and reinfection by a particularly virulent strain could explain the inability of the mother’s immune system to protect the fetus.6 The absence of IgM in the mother after the birth of the child is striking and the origin remains unclear although a similar serological status has already been described in a case of spontaneous abortion due to presumed reinfection of a preconceptionally immune mother.5
The possibility of the rupture of endometrial toxoplasmic cysts, contaminating the fetus during pregnancy or at birth, can be raised according to Langer7 but this theory has been considered with reservation by other authors.8 Nevertheless, because of the IgA level in the mother of our second patient, we assume that there is reinfection and not reactivation.
Consecutive toxoplasmic infection in siblings may occur. Indeed, siblings with ocular toxoplasmosis have been reported9-11and pose the question of congenital or acquired origin of these iterative intrafamilial toxoplasmic infections. In none of these papers has the congenital origin of the infection been proved calling into question congenital reinfection of these siblings.
Positive toxoplasmic screening before or at the beginning of the pregnancy may be wrongfully reassuring and may lead to an underestimate the toxoplasmic origin of some congenital chorioretinitis. The presentation of these two children with severe ocular manifestations of congenital toxoplasmosis shows indeed that this diagnosis cannot be totally excluded even if the mother has been infected by the parasite before conception.
We thank Mr Carlos Pavesio (London), consultant ophthalmic surgeon, for interesting comments concerning our two cases and Mr Phillip Harris (Edinburgh) for his help.