1. Background
Toxoplasma gondii is a coccidian parasite, which causes infection in a variety of hosts, including humans, but can only sexually reproduce in cats. Human can be infected with the parasite by ingestion of undercooked meat containing Toxoplasma tissue cysts or food contaminated by its’ oocysts (1, 2). Infection is mostly self-limiting with no or subtle symptoms, yet can cause severe disease and disorders in infants, when infected during pregnancy, and also in immunocompromised individuals (3, 4). The parasite stays dormant for a long time in form of tissue cysts and causes no symptoms (5), yet some authors believe that it causes some personality changes at this stage (6, 7).
The disease is present all around the world. The prevalence of the infection is fairly high around the world, yet is higher in temperate regions. In Iran, like other countries, many studies have been carried out in different regions and the highest rates of the infection were reported from North of Iran (5, 8).
The prevalence of the infection varies in different reports from the same places; for example, in Khuzestan province the prevalence of the infection was reported as 12% in 1997, 31.9% in 1997, and 60.95% in 1993 (5, 9). These data showed that the estimation of the frequency of infection could be different when different methods and equipment in different populations are used. Thus, updated information about the prevalence of the infection in each region and time period with accurate methods seems to be necessary.
2. Objectives
The aim of the present study was to determine the prevalence of the infection with T. gondii in humans referred to Dr. Sharifi clinical laboratory of Isfahan, Iran, during January 2014 to January 2015.
3. Methods
In a retrospective study, 1287 individuals that had anti-Toxoplasma IgM and/or IgG test from January 2013 to January 2015 were selected and included in the study. All the study population were residents of Isfahan city, central Iran. All the available variables such as anti-Toxoplasma IgG and IgM concentrations, gender and age were recorded and analyzed. Quantitative determination of anti-Toxoplasma IgM and IgG was performed using antibody capture chemiluminescence immunoassay (CLIA) kits (LIAISON® Toxo IgM and IgG, DiaSorin S.P.A, Italy) applied using the LIAISON (DiaSorin, Germany) device.
All steps of the tests were done by the device according to the manufacturer’s instructions. Samples with IgM concentrations below 6 IU/mL were regarded as negative, between 6 and 8 IU/mL graded as equivocal and equal and higher than 8 IU/mL were considered as positive results. Although, samples with IgG concentrations below 7.2 IU/mL were regarded as negative, between 7.2 and 8.8 IU/mL graded as equivocal and equal, and higher than 8.8 IU/mL were considered as positive results.
Data was gathered and analyzed with the SPSS v.16 software (SPSS Inc., Chicago, ILL, USA) using t- and chi-square tests.
4. Results
Overall, 1287 individuals including 1215 (94.4%) females and 72 (5.6%) males with mean age of 28.64 years (minimum: one day, maximum: 78 years old) were studied. The results showed that 36 (2.8%) out of 888 and 325 (25.3%) out of 1243 individuals were anti-Toxoplasma IgM and IgG seropositive, respectively. There was no significant relationship among genders and IgG (P = 0.205) and IgM (P = 0.094) seropositivity (Table 1). Additionally, the mean serum concentration of anti-Toxoplasma IgM and IgG were not significantly different among the genders (Table 2). Also mean age was significantly higher in IgG positive individuals (P < 0.001), yet not in IgM positive cases (P = 0.065) (Table 3).
Table 1. Odds Ratio Estimated for Anti-Toxoplasma IgG And IgM Among Different Genders
| Negative | Positive | Total | OR | 95%CI | P Value | |
|---|---|---|---|---|---|---|
| IgG | ||||||
| Gender | 0.766, 2.165 | 0.205 | ||||
| Female | 869 | 303 | 1172 | 1.288 | ||
| Male | 49 | 22 | 71 | 1 | ||
| Total | 918 | 325 | 1243 | |||
| IgM | ||||||
| Gender | 0.858, 6.125 | 0.094 | ||||
| Female | 796 | 31 | 827 | 2.293 | ||
| Male | 56 | 5 | 61 | 1 | ||
| Total | 852 | 36 | 888 | |||
Table 2. Mean Anti-Toxoplasma IgG and IgM Serum Concentrations Amongst Different Genders
| N | Mean | St. Deviation | St. Error Mean | t | Mean Deference | 95%CI | P Value | |
|---|---|---|---|---|---|---|---|---|
| IgM | ||||||||
| Gender | -0.885 | 0.749 | -2.411, 0.912 | 0.376 | ||||
| Female | 827 | 1.686 | 6.411 | 0.222 | ||||
| Male | 61 | 2.436 | 5.957 | 0.762 | ||||
| IgG | ||||||||
| Gender | -1.428 | 10.227 | -24.492, 4.037 | 0.157 | ||||
| Female | 1172 | 16.820 | 44.836 | 1.309 | ||||
| Male | 71 | 27.047 | 59.319 | 7.039 | ||||
Table 3. Mean Age Amongst Anti-Toxoplasma IgG and IgM Seropositive Individuals
| Age Mean | N | Mean | St. Deviation | St. Error Mean | t | Mean Deference | 95%CI | P Value |
|---|---|---|---|---|---|---|---|---|
| IgG | ||||||||
| Negative | 864 | 27.924 | 7.525 | 0.256 | -4.944 | 2.573 | -3.594, -1.552 | 0.001 > |
| Positive | 303 | 30.498 | 8.517 | 0.489 | ||||
| IgM | ||||||||
| Negative | 799 | 28.748 | 8.325 | 0.294 | 1.846 | 2.662 | -0.167, 5.492 | 0.065 |
| Positive | 35 | 26.085 | 8.889 | 1.502 | ||||
5. Discussion
In the present study, 1287 patients that had anti-Toxoplasma IgM or IgG test from January 2013 to January 2015 were selected and included in the study. Overall, 1287 individuals including 1215 (94.4%) females and 72 (5.6%) males with mean age of 28.64 years (minimum: one day, maximum: 78 years) were studied. The results showed that 36 (2.8%) out of 888 and 325 (25.3%) out of 1243 were anti-Toxoplasma IgM and IgG seropositive, respectively.
The results of the present study indicate high prevalence of toxoplasmosis among residents of Isfahan city, central Iran, yet it is still lower than most of the other studied regions in the country (10-15). Anti-Toxoplasma IgM seropositivity was observed in 2.8% of the studied subjects, which seems very low, but based on the fact that IgM mostly rises against the parasite in the acute phase of the infection (5), even 2.8% is considerable.
Daryani et al. (2014) reported the prevalence of toxoplasmosis as 39.3% in the general population of Iran in a meta-analysis. In Isfahan, the prevalence of the infection is lower than the mean prevalence in the country. Similar to our findings, they found no significant difference between the infection rate amongst males and females and also increased rate of infection by age was observed in both studies. The highest rate of infection was reported from North of Iran (86.3%), where the climate is humid and temperate (5).
In Pakistan and Qatar, the neighboring countries, the overall seroprevalence rate of T. gondii infection was reported to be 29.45% and 29.8%, respectively (16, 17). The prevalence of the infection in India and China was reported as 30.9% and 12.5%, respectively (18, 19). In the general Mexican population, T. gondii infection rate was reported as 20.26% (20). Except China and Mexico, in the other mentioned countries, the infection rate with T. gondii is higher than that found in Isfahan.
A study in Isfahan on the prevalence of the infection in 2011 reported Toxoplasma IgG and IgM seropositivity in HIV positive patients as 49.75% and 1%, respectively. Furthermore, another study conducted on the general population of the province, reported 41.4% for anti-Toxoplasma IgG seropositivity in 2005 (21, 22). The fact that they reported a considerably higher IgG seropositivity than our study is remarkable. They used a different method, enzyme linked immunosorbent assay (ELISA), for determining the infection rate, while in the present study automated antibody capture chemiluminescence immunoassay (CLIA) was used and it has been suggested that this method is more accurate. The reported prevalence of T. gondii infection is illustrated in Table 4.
Table 4. Prevalence of Toxoplasma Infection Reported From Iran Compared to the Present Study
| Region | Toxoplasma IgG, % | Toxoplasma IgM, % | Year | Method | Reference | |
|---|---|---|---|---|---|---|
| Present study | Isfahan | 25.3 | 2.8 | 2016 | CLIA | |
| Rasouli et al. | West Azerbaijan Province | 47 | 3.5 | 2014 | ECLIA | (14) |
| Mahmoudvand et al. | Kerman province | 28.8 | 3.2 | 2015 | ELISA | (10) |
| Sharbatkhori et al. | Gorgan | 39.8 | 3.4 | 2014 | ELISA | (11) |
| Mostafavi et al. | Isfahan | 47.5 | - | 2012 | ELISA | (23) |
| Mohammadi et al. | Arak | 24.3 | 4.8 | 2015 | ELISA | (24) |
| Fallah et al. | Hamadan | 33.5 | - | 2008 | IFA | (15) |
Abbreviations: CLIA, chemiluminescence; ECLIA, electrochemiluminescence; ELISA, enzyme linked immunosorbent assay; IFA, indirect fluorescent antibody.
The prevalence of the infection varies in different reports from the same locations; for example, in Khuzestan province the prevalence of the infection was reported 12% in 1997, 31.9% in 1997, and 60.95% in 1993 (5, 9). These data show that the estimate of the frequency of infection would be different when different methods and equipment on various populations are used. In the present study, antibody capture chemiluminescence immunoassay was used for determination of anti-Toxoplasma antibodies. The method was automated and believed to be very accurate (25). Higher rates of infection, 50.8%, 29.16%, 41.4% and 51.25%, were reported in the same area, Isfahan province, which were higher than that found in the present study (5). These differences may have resulted from different methods used by previous studies and different populations that were studied.
5.1. Conclusions
According to the results of the present study, prevalence of infection with Toxoplasma is high in Isfahan area, yet it is still lower than most of the other studied regions in the country. Also, the risk of the infection rises with older age.
