Seropositivity of Toxoplasma gondii and Toxocara spp. in Children with Cryptogenic Epilepsy, Benha, Egypt

Epilepsy is a group of neurological disorders characterized by epileptic seizures [1,2]. Two types of epilepsy are known: idiopathic epilepsy with unknown etiology and the secondary epilepsy which originates from cerebral lesions that may be traumatic, hypoxic, or infectious in origin [3,4]. In about 60% of cases, the cause is unknown [5]. Epilepsy is affecting about 1% of people worldwide (65 million) [6]. Another report indicates that 8.5 per 1,000 persons have epilepsy [7,8], and the prevalence of the disease is higher in poor countries and nearly 80% of cases occur in developing countries [9]. In high-income countries, traumatic head/brain injuries and stroke are the main causes of epilepsy [10,11], whereas in low- and middle-income countries, central nervous system infections due to viral, bacterial, and parasitic infections seem to contribute to the high prevalence of epilepsy [7]. Epidemiological studies suggest helminthic infections in association with epilepsy in low income countries of the world. Toxoplasma infections are implicated to have an association with epilepsy either as a cause or a potential risk factor [12].

Toxocara spp. is one of the common helminthic parasites that can affect human central nervous system (CNS). Several studies have reported an association between Toxocara canis infection and epilepsy in different geographic locations through case-control studies using serological tests [13-15]. The diagnosis of human toxocariasis depends on serological test (ELISA) by using excretory-secretory antigens from Toxocara larvae because it is very difficult to detect infective Toxocara larvae in biopsy specimens. Until present, there is no precise report on anti-Toxoplasma and anti-Toxocara antibodies in epileptic children in Benha City, Egypt. Therefore, the objective of the present investigation was to examine the antibody response to T. gondii and Toxocara infections in epileptic children using ELISA test.

The current study was carried out between June 2014 and March 2015. The study was approved by the Ethical Committee of Faculty of Medicine, Benha University, Egypt in 2014. The purpose and procedures of the study were explained and written informed consent was obtained from all parents or legal guardians of the children participating in the study on behalf of all child participants. Total 90 children aged between 9 months to 18 years were enrolled (Table 1). Children were divided into 3 groups (G1, G2, and G3). Group1 (G1) composed of 40 cryptogenic epileptic children presented with recurrent epileptic fits with unknown etiology. All selected patients had no past history of head trauma, brain surgery, previous meningitis, encephalitis, with normal brain Magnetic Resonance Imaging scan (MRI), and no family history of epilepsy. The second group (G2) composed of 30 epileptic children presented with recurrent epileptic seizures with known causes as head trauma, family history of epilepsy, brain surgery, previous encephalitis, or meningitis. The third group (G3) composed of 20 completely healthy volunteer children. The epileptic cases were selected from those attending the pediatrics outpatient clinic of Benha University Hospital, pediatrics neurology unit, and from Benha Specialized Hospital of children. Three-ml of blood was taken from all children, centrifuged at 1,000 rpm, and the sera were stored at -20˚C until use.

Table 1.

Sociodemographic data of studied groups

Anti-T. gondii IgG antibody levels were determined using commercially available quantitative ELISA kit, i.e., DRG^® Toxoplasma IgG (TORCH) Catalog No. EIA-1798 (DRG International, Inc., Mountainside, New Jersey, USA). The test was performed following the manufacture’s guidance. In brief, 100 μl of each diluted serum samples (1:40) was added to T. gondii antigen coated microtiter wells. Following incubation for 30 min, 100 μl of 1:1,000 diluted horseradish peroxidase-conjugated anti-human IgG was added. After a second incubation, tetramethylbenzidine (TMB) substrate was then added to each well to stop solution. The optical density (OD) values were read at 450 nm using an automated microplate reader.

Serum samples were also analyzed for anti-T. canis IgG antibodies by a commercially available quantitative ELISA using RIDASCREEN Toxocara-IgG ELISA (R-Biopharm AG, Darmstadt, Germany) kit which detects antibodies against the excretory-secretory antigen of Toxocara larvae. The test was performed following the manufacturer’s instructions.

The data were analyzed statistically using SPSS version 16 software (SPSS Inc., Chicago, Illinois, USA. Categorical data were presented as number and percentages. Chi-square test, Fisher’s test, and Student’s t-test were used as tests of significance. The values of P<0.05 were considered to be statistically significant.

Gender differences with epilepsy were not clear. There is broad agreement between studies that females have a marginally lower incidence of epilepsy and unprovoked seizures than males. In the present study, epilepsy was slightly higher in females (52.5% of cryptogenic and 53.3% of non-cryptogenic epileptics) vs 47.5% of cryptogenic and 46.7% of non-cryptogenic epileptic males [16]. In our study, 64.3% of epileptic groups were residing in rural areas and 35.7% were residing in urban areas. This significant difference indicates that epilepsy is more common in rural areas, which doesn’t match with what was recorded by El-Tantawy et al. [12] who reported no significant relations between epilepsy and residence. Cerebral toxoplasmosis has been reported to cause seizures in about 25% of infected cases [16] by producing diffuse encephalitis or localized lesions [17].

In the present study, there was a significant association of T. gondii exposure and cryptogenic epilepsy, as 20% of epileptic cryptogenic group were seropositive compared to 10% of the controls (P=0.017) (Table 2). Thus, latent toxoplasmosis may be an underlying cause for cryptogenic epilepsy [13,18].

Table 2.

Anti-Toxoplasma and anti-Toxocara seropositivity among epileptic and non-epileptic children

This correlation can be explained by either the presence of dormant T. gondii cysts that can cause epileptic foci. Some of the tissue cysts may rupture and cause marked inflammation that can trigger microglial formation which may represent the ‘tombstones’ of Toxoplasma cysts and end to scarring [19]. The cryptogenic epilepsy patients could be also more susceptible than others to such infections for reasons unrelated to epilepsy, or due to intrinsic immunologic differences that predispose them to epilepsy [13,20]. On the other hand, no relationship was reported between cryptogenic epilepsy and T. gondii IgG seropositivity [21].

Our findings demonstrated that Toxoplasma seropositivity was more common in males (75%) than in females (25%), as males are more frequently infected than females in most endemic areas [22], especially those from rural (87.5%) areas with low social class (62.5%) [12]. Another important risk factor associated with Toxoplasma infection is animal contact (Table 3). In this work, there was significant correlation between Toxoplasma infection and positive history of contact with animals (mainly cats and dogs), as 5 out of the 8 anti-Toxoplasma seropositive cases (62.6%) gave positive history for contact with animals.

Table 3.

Sociodemographic data for anti-Toxoplasma seropositive epileptic cases

The association between toxocariasis and epilepsy is well documented. However, few data are available concerning the relationship between T. canis infection and epilepsy in Egypt. Our results did not observe any association between toxocariasis and epilepsy, as there was no statistically significant difference between epileptic cases and healthy controls (P>0.6). anti-Toxocara IgG antibodies were found in 4 epileptic children (3 in cryptogenic and only 1 in non-cryptogenic groups), and 2 seropositive cases were found in control subjects.

Similar findings were reported by El-Tantawy et al. [12] who found no association between Toxocara seropositivity and epilepsy, as 64 (48.5%) of children with cryptogenic epilepsy have positive anti-Toxocara antibodies in comparison to controls, 28 (46.7%). Arpino et al. [23] reported an association between anti-Toxocara antibody titers and seizures and suggested that toxocariasis might have a role as a cofactor in epileptic seizures. Many other case-control studies have been carried out in different locations to investigate the possible association between T. canis seropositivity and epilepsy. A positive and significant association has been reported in Bolivia, Burundi, UK, Italy, and USA [14,15,20,24,25]. The difference in visceral larva migrans types as well as the differences in diagnosis practices across tropical regions may help to explain the differences in the prevalence of epilepsy resulting from toxocariasis [26].

Based on the data of the current study, toxoplasmosis should be considered as a possible epilepsy risk factor, as there was a significant association between T. gondii seropostivity and cryptogenic epilepsy.