INTRODUCTION

Toxoplasma gondii is able to infect and invade multiple cell types of all warm-blooded animals with a worldwide distribution (Tenter et al., 2000). Usually, T. gondii infection does not cause clinical signs in healthy humans and animals but T. gondii infection in pregnant women can result in fetal diseases with severe problems including abortion, encephalitis, mental retardation and blindness (Montoya and Liesenfeld, 2004). Infection of AIDS patients and other immunocompromised patients with T. gondii can cause death (Montoya and Liesenfeld, 2004).

Humans can be infected by consuming undercooked or raw meat (e.g., pork, lamb) containing tachyzoites or bradyzoites or through food, water or unwashed vegetables contaminated with oocysts excreted by cats (Schlundt et al., 2004). The serological prevalence of T. gondii in humans, especially in pregnant women has been reported in many countries indicating a common high exposure to T. gondii (Jeannel et al., 1988; Punda-Polic et al., 2000; Alvarado-Esquivel et al., 2006; Xu et al., 2005; Liu et al., 2009).

However, little is known of the seroprevalence T. gondii infection in people working on the pig farms though the prevalence of T. gondii in pigs were high (Hejlicek et al., 1997; Suarez-Aranda et al., 2000; Kuang, 2002; Ma et al., 2003; Saavedra and Ortega, 2004; Klun et al., 2006; Jiang et al., 2007a, b; Dubey and Jones, 2008; Huang et al., 2010). Hence, the objective of the present study was to examine the seroprevalence of T. gondii infection in people working on the pig farms in Longyan city, southeastern China. The results would provide base-line data for the prevention and control of T. gondii infection in humans working on pig farms.

MATERIALS AND METHODS
Serum samples: A total of 212 blood samples from humans of different occupations in different pig farms in Longyan city were collected. Serum samples were obtained by centrifugation at 3,000 g for 10 min and stored at -20°C until analysis by Enzyme-Linked-Immunosorbent Serologic Assay (ELISA).

Detection reagents: Antibodies (IgG) to T. gondii were determined using a commercially marketed ELISA kit purchased from Zhuhai S.E.Z. Haitai Biological Pharmaceuticais Co., Ltd, Zhuhai, China.

Detection procedure: The detection procedure followed the manufacturer’s instructions. In brief, the test serum (1:100 dilution) was added to each well in the coated plate (provided by the Kit) and incubated for 30 min at 37°C. After additional washing with Washing Solution, the 50 μL peroxidase-conjugated anti-human Immunoglobulin G (IgG) was added to the wells with incubation at 37°C for 30 min followed by three washings with Washing Solution.

The color reactions were developed with adding 50 μL substrate and 50 μL reagent at 37°C for 10 min and then the reaction was stopped with adding Stopping Solution. OD450 nm-values were measured and ratios (OD450 nm value of serum sample/OD450 nm value of negative control) were calculated after correction for the OD450 nm value of the blank. The test serum samples were considered as positive when the ratio ≥2.1.

The statistical analysis of T. gondii prevalence in people of different occupations, ages and sexes were performed by χ²-test with Excel (Microsoft^® Excel 2003). The differences were considered statistically significant when p<0.05.

RESULTS AND DISCUSSION

The survey of people from different pig farms in Longyan city by ELISA showed that the seroprevalence with T. gondii IgG was 12.26% (26/212). The farm managers had the highest prevalence (23.53%, 4/17) which was followed by the pig breeders (11.54%, 21/182) and the farmers (7.69%, 1/13) had the lowest prevalence (Table 1). There was no statistically significant difference in the prevalence of T. gondii in people of different ages and sexes (Table 2 and 3).

Table 1: Prevalence of Toxoplasma gondii IgG in people of different occupations working on pig farms in Longyan city, southeastern China by Enzyme-Linked-Immunosorbent Serologic Assay (ELISA) χ2 = 16.66, p = 0.0002<0.01

Table 2: Prevalence of Toxoplasma gondii IgG in people of different ages in Longyan city, southeastern China by Enzyme-Linked-Immunosorbent Serologic Assay (ELISA) χ2 = 2.26, p = 0.32>0.05

Table 3: Prevalence of T. gondii IgG in people of different sexes in Longyan city, southeastern China by Enzyme-Linked-Immunosorbent Serologic Assay (ELISA) χ2 = 0.0086, p = 0.93>0.05

The prevalence (12.26%) of T. gondii IgG in people working on pig farms in Longyan city, China is higher than that reported for the animal feeders (6.54%) and veterinarians (10.89%) in Wuhan (Yu et al., 2007). This seroprevalence is also higher than that in the pregnant women and pet owners in some of the previous investigations (4.5-10.46%) (Lai et al., 1993; Zhang and Li, 2005; Wu and Yang, 2005; Wu, 2004; Liu et al., 2009).

Among the people working on the pig farms, the managers had the highest IgG prevalence (23.53%), this could be due to that the farm managers need to be veterinarians in addition to being managers in their pig farms and hence have many more ospportunities to contact with animals. The pig feeders in the farms are often temporary workers and their jobs are changed quite often in China. The prevalence of the farmers is lowest because the farmers are the bosses of the pig farms in China and usually they have limited opportunities to feed the pigs or manage their farms.

CONCLUSION

The results of the present investigation indicated that prevalence of T. gondii infection in people working on the pig farms in Longyan city, southeastern China is high, in particular in farm managers. Therefore, integrated and improved control strategies and measures should be implemented to prevent and control T. gondii infection in both humans and animals in these farms.

ACKNOWLEDGEMENTS

Project support was provided in part by grants from the Science and Technology Program of Fujian Province (Grant No. 2008N2005) and the State Key Laboratory of Veterinary Etiological Biology, Lanzhou Veterinary Research Institute, CAAS. The researchers thank Mr Lin Xin-Long, the manager of Eastern Along Pharmaceutical Co., Ltd., for coordinating with the pig farms to facilitate this study.