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Journal of Clinical Medicine Research

Original Article

Volume 10, Number 1, January 2018, pages 27-31

Toxoplasma gondii Infection and Headache: A Matched Case-Control Study in a Public Hospital in Durango City, Mexico

Toxoplasma gondii (T. gondii) is one of the most successful parasites in the world due to its ability to infect and persist in most warm-blooded animals [1]. About 30% of the human population worldwide is chronically infected with T. gondii [2]. Transmission of T. gondii may occur horizontally by ingestion of oocysts from the environment or ingestion of tissue cysts contained in meat from many different animals, vertically during pregnancy, by blood transfusion, and organ transplantation [3]. Infections in humans are commonly asymptomatic [2, 4]. When symptoms are present, they typically resemble a mononucleosis or flulike illness [5]. Infection with T. gondii may also lead to chorioretinitis [6]. Reactivation of a latent infection in immunodeficiency conditions can cause fatal toxoplasmic encephalitis [7]. When primary infection of the mother occurs during pregnancy, there is likelihood of a transplacental infection that can lead to congenital toxoplasmosis with affection of brain and retina [8].

T. gondii can persist in the central nervous system of a variety of hosts including humans [1]. The parasites persist as intraneuronal cysts that are controlled, but not eliminated by the immune system of the host [9]. Infection with T. gondii in brain in immunocompetent individuals may cause headache [10-12], confusion [10], and difficulty concentrating [12]. Headache of the migraine type has been linked to T. gondii infection [13]. In a cohort of 261 postnatal cases of acute toxoplasmosis in Brazil, headache was present in 10.7% of patients [14]. Very little is known about the frequency of T. gondii infection in patients suffering from headache. In a study of 108 cases of new daily persistent headaches in Dominican Republic, T. gondii infection was found in 3.7% of patients [15]. It is unclear how higher the frequency of T. gondii infection is in patients with headache as compared to subjects without headache. Therefore, we sought to determine the association between T. gondii infection and headache in patients attending at the Department of Neurology in a public hospital in the northern Mexican city of Durango.

We performed a case-control seroprevalence study of 105 patients suffering from headache (cases) and 105 people without headache from the general population (controls) in Durango City, Mexico. This study was performed from April 2016 to March 2017. Inclusion criteria for enrollment of the cases were: 1) patients suffering from headache attending in the Department of Neurology at the public Hospital “Dr. Santiago Ramon y Cajal” in Durango City; 2) aged 13 years and older; and 3) who voluntarily participate in the study. Only patients with diagnosis of headache made by two neurologists (GQC and JTG) were selected for inclusion in the study. Exclusion criterium was subjects suffering from a severe disease who were unable to decide themselves about their enrollment in the study. Gender, socioeconomic status, and occupation of patients were not restrictive criteria for inclusion in the study. In total, 82 females and 23 males suffering from headache were enrolled in the study. Cases were 13 - 86 years old (mean = 42.71 ± 15.79). Diagnoses of headache in patients were based on the International Statistical Classification of Diseases and related Health Problems version 2016 (ICD-10) (http://apps.who.int/classifications/icd10/browse/2016/en). Table 1 shows the types of headache diagnosed in the studied patients. Concerning the control group, 105 subjects without headache were randomly selected from the general population in Durango City. All control subjects were matched with patients by age (± 4 years) and gender. Controls were 15 - 86 years old (mean = 42.65 ± 15.40), and included 82 females and 23 males. There was no difference in age between cases and controls (P = 0.97).

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Table 1. Diagnoses of Headache and Frequency of T. gondii Infection in the Study Population

Sera of cases and controls were analyzed for anti-T. gondii IgG antibodies with the commercially available enzyme immunoassay kit “Toxoplasma IgG” (Diagnostic Automation Inc., Woodland Hills, CA, USA). This test allows qualitative and quantitative determinations of anti-T. gondii IgG antibodies. A cut-off of ≥ 8 IU/mL of specific anti-T. gondii IgG antibody was considered for seropositivity. IgG seropositive serum samples of cases and controls were further analyzed for anti-T. gondii IgM antibodies by the commercially available enzyme immunoassay “Toxoplasma IgM” kit (Diagnostic Automation Inc.). All IgG and IgM tests were performed following the instructions of the manufacturer. Positive and negative controls included in the kits were analyzed in each run. Criterium for diagnosis of T. gondii infection was based on results of the IgG test.

Cases with anti-T. gondii IgG antibodies were further examined for detection of T. gondii DNA by nested-polymerase chain reaction (PCR). DNA extraction from whole blood was performed according to the instructions of a commercially available kit (QIAamp DNA Blood Mini kit; Qiagen, Germany). DNA amplification was performed with primers directed against the B1 gene of T. gondii and following the protocol described by Burg et al [16]. The PCR products were analyzed by using a 2% agarose gel electrophoresis stained with ethidium bromide. Visualization of the PCR products was performed with an ultraviolet transilluminator.

Statistical analyses were carried out using the Microsoft Excel 2010, SPSS version 15.0 (SPSS Inc. Chicago, IL, USA), and Epi Info version 7 (Centers for Disease Control and Prevention: http://wwwn.cdc.gov/epiinfo/) software. For calculation of the sample size, we used a 95% two-sided confidence level, a power of 80%, a 1:1 ratio of cases and controls, and a reference seroprevalence of 7.4% [17] as the expected frequency of exposure in controls. The result of the sample size calculation was 101 cases and 101 controls. The paired Student’s t-test was used to compare age values among the groups. The association between seroprevalence and characteristics of cases was assessed by bivariate analysis. We calculated the odds ratios (ORs) and 95% confidence intervals (CIs), and statistical significance was set at a P value less than 0.05.

The Ethical Committee of the Institute of Security and Social Services for State Workers in Durango City, Mexico approved this project. The purpose and procedures of this case-control study were explained to all participants. A written informed consent was obtained from all subjects and from the next of kin of minor participants.

Anti-T. gondii IgG antibodies were found in five (4.8%) of the 105 cases and in seven (6.7%) of the 105 controls. No difference in the seroprevalence of T. gondii infection between cases and controls was found (OR = 0.70; 95% CI: 0.21 - 2.28; P = 0.76). All five anti-T. gondii IgG positive cases had anti-T. gondii IgG antibody levels higher than 150 IU/mL. In contrast, of the seven anti-T. gondii IgG positive controls, only one (14.3%) had anti-T. gondii IgG antibody levels higher than 150 IU/mL (Table 2). The frequency of high (> 150 IU/mL) levels of anti-T. gondii IgG antibodies among anti-T. gondii IgG positive individuals was significantly (P = 0.01) higher in cases (5/5) than in controls (1/7). Anti-T. gondii IgM antibodies were found in one (20.0%) of the five IgG seropositive cases, and in three (42.9%) of the seven IgG seropositive controls (P = 0.57 by two-tailed Fisher exact test). T. gondii DNA was not detected in any of the five anti-T. gondii IgG positive cases.

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Table 2. Anti-Toxoplasma IgG Levels in Cases and Controls

Bivariate analysis of IgG seropositivity to T. gondii and ICD-10 codes did not show an association between T. gondii infection and specific types of headache (Table 1).

The epidemiological impact of T. gondii infection on headache has been poorly studied. Some people infected with T. gondii suffer from headache [10-12]; however, it is unclear how many people suffering from headache has an infection with T. gondii. We are not aware of any age- and gender-matched case-control study on the association between T. gondii infection and headaches. Therefore, we decided to carry out this age- and gender-matched case-control study to determine the association of seropositivity to T. gondii and headache in patients attending at the Neurology Department in a public hospital in Durango City, Mexico. The seroprevalence of T. gondii infection in patients suffering from headache was low (4.8%), and the seropositivity rate of anti-T. gondii IgG and IgM antibodies in patients suffering from headache and in control subjects was similar. The seroprevalence of T. gondii infection found in patients with headache is comparable to seroprevalences of T. gondii infection reported in the general population (6.1%) [18], and healthy blood donors (7.4%) [16] in the same Durango City. In contrast, the seroprevalence observed in patients suffering from headache is lower than seroprevalences of T. gondii infection reported in high risk groups in the same Durango City including waste pickers (21.1%) [19], inmates (21.1%) [20], and psychiatric patients (18.2%) [21]. The low prevalence of T. gondii infection found in patients suffering from headache which is similar to or lower than those reported in controls and other population groups of the same city suggests that T. gondii infection did not contribute substantially for a higher risk of headache in our population studied. The low frequency of infection with T. gondii in patients with headache was unexpected since infection with T. gondii is considered a cause of headache in immunocompetent [10-12], and immunocompromised patients [22]. Seroprevalence results suggest that factors other than T. gondii infection might contribute for headache in our population studied. No association between T. gondii infection and types of headache was found. However, the number of specific types of headache was small. Intriguingly, all five patients with headache and anti-T. gondii IgG antibodies had high (> 150 IU/mL) levels of anti-T. gondii IgG antibodies. This frequency was significantly higher than that found in control subjects. This finding might suggest a recent infection or a constant high antigenic stimulation. These results indicate an association between high anti-T. gondii IgG antibody concentration and headache. Very few studies have reported anti-T. gondii IgG concentrations in patients with headache. In a study in Poland, a high anti-T. gondii IgG concentration (mean: 189 ± 85 IU/mL) was found in patients with recurrent headache as the main symptom of acquired cerebral toxoplasmosis [11]. In a case report of a patient with systemic erythematosus lupus presenting with fever, headache, and mental change, high anti-T. gondii IgG titers in cerebrospinal fluid and in serum were found [23]. In the present study, no testing of anti-T. gondii IgM antibodies in subjects seronegative to anti-T. gondii IgG antibodies was performed. This was due to the low diagnostic value of an IgM positive test in subjects seronegative to IgG. A high number of false-positive IgM results have been reported using commercially available enzyme immunoassays for detection of anti-T. gondii IgM antibodies [24, 25].

The present study has some limitations. A small number of specific types of headache were studied. In addition, patients were enrolled in a single hospital, and most patients had a medium socioeconomic status. Further studies with larger number of patients with specific types of headache, enrolled in several hospitals or health care centers, and of several socioeconomic statuses to determine the association between T. gondii infection and headache should be conducted. Additional studies to determine the role of anti-T. gondii IgG concentration in headache are needed.

This is the first age- and gender-matched case-control study on the association between T. gondii infection and headache. Results suggest that high anti-T. gondii IgG antibody levels, but not T. gondii seropositivity, were associated with headache in the population studied. Because a small number of specific types of headache were studied, further studies to determine the association between T. gondii infection and types of headache are needed.

Competing Interests

The authors declare that they have no competing interests.

Financial Support

This study was financially supported by Secretary of Public Education, Mexico (Grant No. DSA/103.5/14/11311).

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