1. Introduction

Epilepsy is a chronic neurological disorder that affects approximately 70 million people of all ages worldwide ^[1]. Nearly 80% of people with epilepsy are found in developing countries, where it remains a major public health problem, not only because of its health implications but also for its social, cultural, psychological and economic connotations ^[2]. According to the Commission on Classification and Terminology of the International League Against Epilepsy in 1985-1989 ^[3], cryptogenic epilepsies are defined as epilepsy syndromes for which an aetiology is unknown, but an underlying brain disease is suspected affecting approximately 20% of all patients with epilepsy ^[4].

Parasitic infections are considered as serious public health problems in many developing countries ^[5] affecting various tissues including the brain leading to neurological dysfunction and constitute important risk factors for epilepsies ^[6]. Simultaneously, these infections represent a controllable risk as they can be prevented through immunization or treatment. Among these parasitic infections, toxoplasmosis and toxocariasis have been suggested as an important risk factor for epilepsy needing confirmation ^{[Epilepsia, 42 (3):436-438, 2001.">7, Neurology, 23;58(8):1256-61, 2002.">8]}.

Toxoplasmosis is caused by Toxoplasma gondii, a protozoan and is estimated to infect one-third of the world’s human population ^{[Toxoplasma gondii: from animals to humans", Int J Parasitol, 30:1217-1258, 2000.">9, Toxoplasma gondii infection in humans and animals in the United States", Int J Parasitol, 38:1257-1278, 2008.">10]}. Toxoplasma is an obligate intracellular parasite founded in two forms in humans. The actively proliferating trophozoites are usually seen in the early phases of the infection while the resting forms or tissue cysts are primarily found in muscle and brain ^[11]. Cerebral toxoplasmosis has been reported to cause seizures in about 25% of infected cases ^[12] by producing diffuse encephalitis or localized lesions ^[13].

Toxocariasis is a zoonosis caused by Toxocara canis and T. catis, the nematode parasites of dogs and cats, respectively ^[14]. The principal source of infection is eggs which are released from the feces of dogs and result in contamination of the soil ^{[Toxocara egg contamination in sandpits of public parks", Am J Trop Med Hyg, 52:21-24, 1995.">15, Toxocara canis", J Helminthol, 82(4):293-6, 2008.">16]}. Children are more susceptible to this infection because they handle (playing habits) contaminated soil ^[17]. When infective eggs containing larvae are ingested by human, the larvae become free in the intestine and pass through the intestinal wall to migrate through tissues provoking inflammatory tissue reactions with multisystem involvement leading to the clinical syndrome referred to as visceral larva migrans ^[18]. The larvae can locate in the central nervous system leading to a variety of neurological disorders ^[19]. Seizures have been reported as the initial CNS manifestation of toxocariasis in quite a number of patients ^[20]. A possible association between Toxocara infection and epilepsy has been hypothesized and toxocariasis has been suggested as a cofactor for epilepsy ^[21].

Both Toxoplasma and Toxocara infections are implicated to have an association with epilepsy either as a cause or a potential risk factor for its occurrence. There has been long-standing interest in investigating this possible association. But, yet the evidence for such a relationship is far from conclusive. So, our study was aimed to investigate the relationship between Toxoplasma and Toxocara seropostivity in children with cryptogenic epilepsy.

2. Subjects and Methods

The present case-control seroprevalence study was carried out with a total of 132 consecutive pediatric age patients with cryptogenic epilepsy who were evaluated and followed up in the Neurology Unit at Mansoura University Children’s Hospital, Mansoura, Egypt. This prospective study was conducted in the period from April 2012 to June 2013. Diagnosis of cryptogenic epilepsy was based on: a negative family history of epilepsy, no history of head trauma, previous meningitis/encephalitis or brain surgery and normal magnetic resonance imaging (MRI) study and electroencephalogram (EEG). All patients were subjected to full history taking and complete physical examination. The demographic and life style information was obtained through a survey questionnaire. The epileptic patients were classified into three age groups; group I (≤ 5 years), group II (> 5 years to ≤ 10 years), and group III (> 10 years to ≤ 14 years).

The control group consisted of 60 age matched volunteers with informed consent from parient/guardian from children attending out-patient clinic for other causes without any personal or family history of seizures. The study was approved by Ethics Committee of Pediatric department at Mansoura University Children’s Hospital-Mansoura University.

Three ml of venous blood was drawn aseptically from each subject included in the study. Serum was separated by centrifugation and each sample is divided into two tubes and stored at −20°C until tested.

Serum samples were tested for both anti-Toxocara IgG antibodies detection using RIDASCREEN Toxocara-IgG ELISA (R-Biopharm AG, Germany) kit which detects antibodies against the excretory/secretory antigen of the Toxocara larvae. For anti-Toxoplasma IgG antibodies detection, (Adaltis, Italy) kit was used. According to the manufacturer’s recommendations, serum samples were diluted and used for testing; each serum sample was tested in triplicates. Positive and negative controls were included in the kit.

Collected epidemiological, clinical and laboratory data were computerized and statistically analyzed using SPSS 16.0 (SPSS Inc., Chicago, IL.). Results were presented as frequencies [n (%)]. Chi-squared test was used in comparing the results. A p value of < 0.05 was considered significant.

3. Results

Of the 132 cryptogenic epilepsy patients included in the study, 62 (47%) were females and 70 (53%) were males; their age range was between 1-14 years (8.7 ± 3.9). The control group consisted of 60 subjects, 34 (56.7%) were males and 26 (43.3%) were females; their age range was between 1-14 years of age (9.9 ± 3.7). The epileptic patients and controls groups were quite similar regarding age groups and sex (p > 0.05). The overall seroprevalence of both Toxoplasma and Toxocara antibodies in both groups were 55.02 % and 47.91% respectively.

As regard T. gondii seroprevalence results, 80 epilepsy patients (60.6%) had statistically significant T. gondii seropositive rates, as compared to 26 (43.3%) seropositive controls (P = 0.026) (Table 1). Among T. gondii seropositive patients, there was male predominance (57.8%). Children residing in rural areas have higher T. gondii seropostivity than children residing urban areas (45 vs. 38).

Table 1. Seropositivity rates for both T. gondii and Toxocara spp

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As regard Toxocara results, 64 (48.5%) of children with cryptogenic epilepsy have positive anti-Toxocara antibodies in comparison to control ones 28 (46.7%). There is no significant association between epilepsy and Toxocara seropostivity (p= 0.815) (Table 1).

Table 2. Demographic characteristics of cases and control subjects

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4. Discussion

Cryptogenic epilepsies are a group of epilepsy syndromes for which the etiology is hidden or occult ^[22] and it comprises about 20% of all epilepsy syndromes ^[23]. Epidemiological links suggest an association between Helminth infection and epilepsy, particularly in the poorer areas of the world ^[24].

Toxoplasma gondii can form asymptomatic dormant cysts in the brain and could have the potential to cause epilepsy ^[7]. Also, the migrating Toxocara larvae can be found in the human brain causing an epileptic focus ^[25]. There is no precise report from both anti-Toxocara and anti-Toxoplasma antibodies in cryptogenic epileptic patients in our region. Our study screened the cryptogenic epileptic patients and the controls for T. gondii and Toxocara to investigate the possible correlation between these infections and cryptogenic epilepsy.

We found a statistically significant association between T. gondii infection and cryptogenic epilepsy was detected but no significant association between Toxocariasis and cryptogenic epilepsy. This significant correlation can be explained by either (i) dormant T. gondii cysts containing bradyzoites may cause epileptic foci and cryptogenic epilepsy in animal models it is proposed that some tissue cysts rupture and in doing so causes marked inflammation of that area and hence triggers microglial formation which may represent the ‘tombstones’ of Toxoplamsa cysts and lead to scar tissue formation ^[26]; or (ii) The cryptogenic epilepsy patients could be more susceptible to this infections ^[27].

Regarding the association between Toxoplasma infection and cryptogenic epilepsy, our results are consistent with that of Yazar et al. ^[28] who have reported that the level of T. gondii IgG showed a statistically significantly high value in a study of cryptogenic epilepsy. And also with Stommel et al. ^[7] who suggested that chronic T. gondii infection with brain cysts may be a cause of cryptogenic epilepsy. On the other hand, Akyol et al. ^[29] reported no relationship between cryptogenic epilepsy and positive T. gondii serology in his study which was carried on 100 cryptogenic epileptic patients and 50 healthy volunteers that had no history of epilepsy in their first degree relatives.

However, we found no significant association between Toxocara infection and cryptogenic epilepsy. To our knowledge, there is no previous data about this relation except a study from Turkey which also did not find any association between cryptogenic epilepsy and seropositivity to Toxocara ^[29]. Also, there is less data about the association between Toxocara species and epilepsy. Most of them describe a significant association in the United States ^[29], Italy ^{[Toxocara infection and epilepsy in children: a case-control study", Epilepsia 31:33-36,1990.">21, Epilepsia, 49(4):594-9, 2008.">30]} and Iran ^[31]. In these studies, increased Toxocara seropostivity may be due to increased susceptibility to helminth infection.

Our findings demonstrated that the seropositivity to Toxocara and Toxoplasma cases were in the age group 5-10 years, the age where rate of infection is high and seropostivity were more in males than females as males are more frequently infected than females in most endemic areas ^[32]. As contact with cats and dogs is important risk factor of Toxocara infection ^{[Transactions of the Royal Society of Tropical Medicine and Hygiene, 88:531-533, 1994.">33, Toxocara infection in children from an urban large setting in Northeast Brazil", Acta Trop, Jul 8, 2013.">34]}. We also asked about contact with animals in our cases but we found no significant relationship between animal contact and Toxocara-Toxoplasma seropostivity rates. We found that there was a significant relationship in antibody positivity against Toxoplasma and Toxocara and rural areas. This in accordance with that of ^{[Toxocara infection and epilepsy in children: a case-control study", Epilepsia 31:33-36,1990.">21, Toxocara infection and epilepsy in children", J Pediatr, 94:75-8, 1979">35, Toxocara canis larvae in the brain of a British child", Trans R Soc Trop Med Hyg, 79:351-4, 1985.">36]} who have found that the risk for developing Toxocara and Toxoplasma infection is higher in rural areas than in urban areas.

5. Conclusion

The study results have indicated that there was a statistically significant association between Toxoplasma gondii seropostivity and cryptogenic epilepsy and no significant association between Toxocara spp seropostivity and cryptogenic epilepsy. This correlation should be further evaluated. The results of the current study reemphasize the importance/significance of public health measures to prevent and control exposure of pediatric age/susceptible population to such parasitic infections.

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