Seroprevalence of Toxoplasma gondii Infection in Pigs in Jiangxi Province,Southeastern China

Introduction

T oxoplasma gondii is a worldwide zoonotic protozoan parasite that can infect humans and all warm-blooded animals. Domestic cats and other felids, the definitive hosts of this parasite, are able to excrete oocysts into the environment. T. gondii is considered an important foodborne pathogen (Zhou et al., 2008; Davies, 2011). Humans get infected mainly through ingestion of undercooked or raw meat containing tissue cysts or through ingestion of food or water contaminated by oocysts (Dubey, 2004). Approximately 30% of the world population shows seropositivity for T. gondii (Dubey, 2010; Zhou et al., 2011), while in China the prevalence is 7.9% (Xu et al., 2005). Although T. gondii infection is benign in most people, causing few clinical manifestations, blindness and mental retardation may occur in children who were congenitally infected. It can be serious or fatal in immunocompromised individuals such as AIDS patients (Montoya and Liesenfeld, 2004).

Public concerns associated with T. gondii clearly show the need for an epidemiological survey in pigs since they are an important source of meat for human consumption. Pigs infected with T. gondii are of veterinary and medical significance because they are potential reservoirs of human toxoplasmosis (Dias et al., 2005; Dubey, 2009). Acute toxoplasmosis including blindness may outbreak if people consume raw pork as previously reported (Choi et al., 1997).

Some serologic surveys on the prevalence of T. gondii in pigs have been carried out in other countries recently (García-Bocanegra et al., 2010; Bártová and Sedlák, 2011; Klun et al., 2011). Several studies have shown that T. gondii infection in pigs was common in some regions of China (Zhou et al., 2010; Huang et al., 2010; Tao et al., 2011; Yu et al., 2011). However, there are no data for Jiangxi Province, southeastern China, where the pork production is among the largest in China. Given this background and the zoonotic significance of T. gondii, the objective of the present study was to investigate the seroprevalence of T. gondii infection in pigs in Jiangxi Province, southeastern China. The results are expected to provide basic data for prevention and control programs of T. gondii infection in humans and other animals in this area.

Materials and Methods

Results

In the present study, specific antibodies to T. gondii were detected in 282 of 1232 (22.9%) serum samples by IHA at a dilution of ≥1:64. Positive pigs were found in each administrative district of Jiangxi Province, with the prevalence ranging from 5% to 46.2% (Table 1). Seropositive pigs were detected in all age groups. The seroprevalence of T. gondii infection in adult pigs was higher than that in all the younger ones (Table 1); it was the highest in lactating sows (35.5%), followed by nonpregnant sows (32.6%), pregnant sows (29.8%), breeding boars (28.3%), fattening pigs (16.4%), and growing pigs (7.3%). Weanling pigs, however, had the lowest seroprevalence of 3.7%. Lactating sows (OR=15.4, 95% CI=6.8–35.2, p<0.01), pregnant sows (OR=11.5, 95% CI=5.3–24.8, p<0.01), nonpregnant sows (OR=13.7, 95% CI=6.4–29.3, p<0.01), breeding boars (OR=9, 95% CI=3.8–21.4, p<0.01), and fattening pigs (OR=4.9, 95% CI=2.1–11.7, p<0.01) all had a greater risk of acquiring the infection compared to the weanling pigs, while there was no significant difference in T. gondii seroprevalence between growing pigs (7.3%) and weanling pigs (3.7%) (p>0.05). In terms of sampling seasons, pigs faced a greater risk in the spring (OR=1.7, 95% CI=1.1–2.6, p=0.01) and the summer (OR=2.1, 95% CI=1.3–3.2, p<0.01) than in the winter. No significant difference was found in T. gondii seroprevalence between pigs in autumn (16.8%) and winter (16.7%) (p>0.05).

Discussion

Consumption of undercooked or raw meat or meat products is an important route of human infection with T. gondii (Bobić et al., 2007). In China, pork is the most common meat, accounting for 65% of the meat consumption. However, before it is sold and consumed, pork is not required to be inspected for T. gondii contamination by law. The present study, therefore, was aimed to estimate T. gondii seroprevalence in pigs in Jiangxi Province, where pork is mostly consumed.

A previous study reported an overall T. gondii seroprevalence of 36% among 551 clinically healthy adult slaughtered pigs in Czech Republic (Bártová and Sedlák, 2011). García-Bocanegra et al. detected a 16.6% prevalence in domestic pigs from 100 farms in the 10 main swine production regions in Spain by the modified agglutination test (García-Bocanegra et al., 2010), and Klun et al. (2011) reported a low prevalence of T. gondii infection in slaughter pigs (9.2%) in Serbia. In this study, the overall seroprevalence of T. gondii infection in pigs in Jiangxi Province was 22.9%, which was lower than that in the Czech Republic but higher than that detected in Spain and Serbia. Compared with neighboring provinces in China, the overall T. gondii seroprevalence in pigs in Jiangxi Province was higher than that in Fujian Province (14.4%) (Hang et al., 2010), but lower than that in Hubei Province (24.5%) (Tao et al., 2011), Zhejiang Province (53.4%) (Yu et al., 2011), and Guangdong Province (27%) (Zhou et al., 2010). The reasons why T. gondii prevalence varies among different provinces could be manifold. Different regions located in different geographical areas have a different climate and environment, which may influence the presence of T. gondii. The management of pig farms, as well as pig welfare, varies from place to place. Studies vary in the serological tests used may in part account for the prevalence differences among different studies.

In the current study, we also found the prevalence variation in pigs of different ages. The prevalence of T. gondii infection in adult pigs was higher than that in all the younger ones, which may be due merely to longer exposure of adult pigs. The T. gondii seroprevalence in pigs varied also according to sampling seasons, with the seroprevalence in the summer being significantly higher than in the winter. Jiangxi has a hot, humid summer, which may be more favorable for the survival of T. gondii oocysts, but a cool, damp winter, which may be less suitable for the presence of T. gondii (Dubey, 2010).

According to a serological survey carried out in the city of Nanchang, the capital of Jiangxi Province, T. gondii antibodies were detected in 8% of the examined 1960 people (Chen et al., 2005). Jiangxi's pork industry produces about 4.5% of all pork produced in China, a large proportion of which is consumed locally. Once the meat of T. gondii–seropositive pigs is put on the market, it may put local people at risk of T. gondii infection if consumed raw or undercooked.

This study tested 1232 pig serum samples collected in Jiangxi Province within a single year for T. gondii antibodies, which is a short period of time. Thus our results may not reflect the actual status of T. gondii infection for longer periods of time. However, our findings provide useful information for further studies. Our next efforts would be directed at determining the seroprevalence of T. gondii infection in pigs over several years, as well as in other animal species and humans in this region.

In conclusion, the present study is the first report of T. gondii seroprevalence in pigs in Jiangxi Province, southeastern China. The results indicate that pigs in Jiangxi Province are frequently exposed to T. gondii. The seroprevalence of T. gondii infection in pigs in Jiangxi Province poses a risk for human infection and accordingly, is of public health significance. Hence, it is necessary to improve sanitation and management of pig farms to reduce transmission of T. gondii, and to implement routine inspection of T. gondii infection during slaughtering and postslaughter processing of pigs.