Seroprevalence and detection of Toxoplasma gondii and Echinococcus granulosus in humans by indirect immunoglobulin G enzyme-linked immunosorbent assays in Baghdad

1. Introduction

Toxoplasma gondii is an intracellular protozoan infecting around one-third of the world's people. Humans and almost all warm-blooded animals are intermediate hosts of T. gondii, and cats play a crucial role in the epidemiology of T. gondii as the definitive host (Montoya et al., 2004). Human infection generally occurs through congenital transmission, organ transplantation, food or drink contaminated with oocysts, and tissue cysts from undercooked meat (Weiss and Dubey, 2009). The dormant form of T. gondii mainly resides in nervous and muscle tissues in infected hosts, and until recently, latent infections in people were expected to be asymptomatic (Flegr, 2009). Symptomatic infection is generally described as congenital infections acquired through the first trimester and more severe than those acquired in the second and third trimesters. Lymphadenopathy, reticular cell hyperplasia, and finally, ocular toxoplasmosis can be observed after congenital or acquired infection as a result of acute infection or reactivation (Bhopale, 2003). The tissue cyst-forming coccidium is a polygynous protozoan with a facultative heterogeneous life cycle. Human T. gondii infection is one of the most significant public health challenges, affecting one-third of the world's population (Tenter et al., 2000), especially immunocompromised people, such as HIV-positives, cancer patients, and organ transplant recipients. Toxoplasma gondii, as an opportunistic protozoa, can lead to life-threatening consequences for patients. Moreover, after congenital infection, acute disease and ocular infection can occur (Brinkman et al., 1998; Singh et al., 1996; Goebel et al., 2007). Cystic echinococcosis has international prevalence partially due to the capability of worms to adapt to the extensive variability of house and wild middle and final hosts (Eckert et al., 2000; Al-Shammary, 2002). This infection severely affects the health of humans and animals (Snabel et al., 2009) and has frequently been observed in countries in moderate regions, including parts of Africa, Australia, South America, Central Asia, and China (Dakkak, 2010). In light of the aforementioned issues, the present study aimed to detect T. gondii and Echinococcus granulosus in humans and examine the seroprevalence of the parasite regarding gender, age group, and female gender in humans.

2. Materials and Methods

2.1. Human sample collection

This field study was conducted on 1,500 human blood samples from private clinics in different areas of Baghdad from December 2023 to April 2023. Blood samples were collected from humans (580 males and 920 females) aged between < 20 and ≥ 40 years. Echinococcus granulosus was passed out to 192 humans from different regions of Baghdad. Blood tests were collected from humans of both genders and different ages.

2.2. Serological technique

The human blood samples were disrupted in several wells (two for controls and more specimens) and plates in strip containers. Incubation was performed at room temperature (15-25°C) for 10 min; subsequently, 100 ul of enzyme conjugate was washed, enhanced, and stored at room temperature for 5 min. Following that, 100 ul of the chromogen was added to each well. It was mixed well by gently patting the lateral part of the band holder with the directory member for about 15 sec.

2.3. Statistical Analysis

The data were analyzed in SAS software (version 20.1). A two-way ANOVA and least significant differences (LSD) post hoc test were performed to assess significant differences among the means of the groups. The results were expressed as mean ± standard errors, and p-values of < 0.05 were considered statistically significant (Cary, 2012).

3. Results

A total of 1,500 human blood samples were registered as infected with T. gondii. The total rate of infection was 62% in human immunoglobulin G (IgG). Regarding the age groups, subjects younger than 20 recorded a 25.1% infection rate, while this rate was 88.5% among 20-29-year-old cases. The highest rate of infection was recorded as 90.2% in the 30-39-year-old subjects, followed by the ≥ 40-year age group (33.8%), with significant differences (P≤0.01) (Table 1). In terms of gender, females (16.2%) accounted for the highest infection rate, while the infection rate was 3.7% in males, with non-significant differences (P>0.01) (Table 2). Finally, the present study recorded a high rate of infection in pregnant women (70.4%), with a lower rate in non-pregnant ones (53.6%) (Table 3). The total number of hydatidosis patients was 7.8% in this study (Table 4). In females, there were 9 infections (10.2%), compared to 6 infections (5.7%) in males (Table 5). These cases were in the age range of 20-40 years old. The most infected cases were in the age group of ≥ 40 years (14%), while the 30-39 age group had the lowest rate of infection (6.6%) (Table 6). Regarding gender, the highest infection rate was 10.2% in females, while the infection rate was 5.7% in males.

4. Discussion

It is crucial to understand the status of Toxoplasma infection in the general population, especially humans. This study estimated the seroprevalence of T. gondii infection rate in the Iraq population using the serological diagnosis. In this study, 62% of IgG seropositive cases were recorded. The results of this research were inconsistent with those carried out in neighboring countries, such as Pakistan and Qatar. The overall seroprevalence rates of infection were recorded at 29.45% and 29.8%, respectively (Tasawar et al., 2012; Abu-Madi et al., 2008).

A related study in Iran demonstrated that the seroprevalence of Toxoplasma infection was 39%. At the same time, Latin America, Central and Eastern Europe, and Southeast Asia have a high seroprevalence of T. gondii infection (75%-85%) (Bobi et al., 1998; Song et al., 2005; Ruiz-Fons et al., 2006). In a study by Galvan-Ramirez et al. (2012) in Mexico, the seroprevalence of T. gondii infection was reported as 20.26%. Moreover, in China and India, seroprevalence estimations were 12.5% and 30.9%, respectively. Although some of these risk factors may have the lowest effect on the epidemiological condition, they can alter the epidemiologic pattern of infection in various regions, with geographical and climatic conditions being significant variables (Daryani et al., 2014). The results of this research are in agreement with those obtained in a study by Fan et al. (2007), in which the adult age group (≥45 years) had significantly higher serological rates (80%) than the younger one (20%). Our findings revealed that seroprevalence-positive cases were predominantly detected in the older age group of ≥ 40 years (55%) than in the younger age groups of 0-19 years (29%) and 20-39 years (44%). Other studies reported similar results (Shin et al., 2009; Alvarado-Esquivel et al., 2011).

The reason for the increasing rate of serology in older age groups is unclear. It can be ascribed to their longer exposure to the risk factors, with increased contact with pets and consumption of contaminated food and water being two of the modes of transmission. The study revealed that the prevalence rate was lower in males (57%) than in females (65.1%). However, the two genders exhibited no significant difference in Toxoplasma serological tests. The results related to Echinococcus infection were in line with those of previous results by Al-Qadhi, and Werner and Feliza, demonstrating that the age range of 11-40 years had the highest rate of disease incidence (Al-Qadhi 2005, Werner and Feliza 1990). In disagreement with Al-Jeboori, who illustrated that the highest rate of infection pertained to the 20-30 age group, Taher et al. (2017) recorded that the highest rate of hydatidosis was related to patients aged 21-30, while the seroprevalence of Echinococcus granulosus infection was obtained at 1.24% in an Uruguayan rural human (Bonifacino,1991). Andrabi et al. (2020) recorded the seroprevalence of Echinococcus granulosus infection at 4.36% in South Kashmir, India, using an enzyme-linked immunosorbent assay. In Iran, around 7.4% of cases were

reported to be in line with the findings of Galeh et al. (2018), while the seroprevalence study on antibodies against hydatid cysts from Sarkari et al. (2010) showed a rate of 7.2%. This result can be attributed to the disruption experienced by this group of rural and other social workers, leading to increased exposure to sources of contamination. Clinically, cats are important reservoirs of zoonotic parasites. Toxoplasma gondii and Echinococcus infections represent a considerable parasitic disease. The dearth of data in this regard highlights the necessity of research on molecular epidemiology and clinical pathology aspects of Toxoplasma and Echinococcus granulosus infection in Iraq. Controlling pets that serve as hosts for zoonotic parasites is essential to reduce the prevalence of the parasite. This involves limiting the number of pets and ensuring they receive veterinary treatment. Toxoplasma and Echinococcus granulosus are some of the most common parasites in developed countries and may cause chronic diseases.