Seroprevalence and Risk Factors of Toxoplasma gondii in Slaughter Pigs in Shaanxi Province,Northwestern China

Introduction

T oxoplasma gondii , as an important food-borne zoonotic protozoan parasite, is prevalent in human beings and endothermic animals worldwide (Montoya and Liesenfeld 2004, Zheng et al. 2016b). Humans become infected by ingesting oocysts from the environment or tissue cysts from raw or undercooked meat (Choi et al. 1997, Dubey 2004, Gebremedhin et al. 2014) postnatally. As the definitive host, felids, especially cats, are considered as the initial source of the infection for T. gondii (Villari et al. 2009, Zheng et al. 2016a). However, infected pork is one of the principal meat sources of T. gondii infection.

China is one of the largest producers of pigs in the world, and Shaanxi Province is an important pork producer in China with an annual pork production about 1 million tons. The seroprevalence of T. gondii in pigs has been surveyed in many provinces in China (Zou et al. 2009, Yu et al. 2011, Wu et al. 2012a, 2012b, Li et al. 2015, Xu et al. 2015, You et al. 2015, Sun 2016). Nevertheless, the data about the seroprevalence of T. gondii from slaughter pigs in Shaanxi Province are still lacking. Besides, reports about T. gondii infection in people around Shaanxi Province indicated that the locals and people in adjacent areas are under a severe threat by this pathogen (Yu et al. 2007, Liu et al. 2008, Yang et al. 2012, Zhang and Cheng 2012, Wang et al. 2015). And these data also highlighted the effect of T. gondii on animals and the impact of infected pork on human. Pet keepers, butchers, and other people who might contact animals frequently have a much higher chance of exposure to T. gondii infection (Yu et al. 2007). Therefore, epidemical investigation is necessary to develop prevention and control guidelines. So, as a supplementary, seroprevalence of T. goodii infection in slaughter pigs in Shaanxi Province, Northwestern China, was reported in this study.

Materials and Methods

Results and Discussion

Antibodies to T. gondii were found in 156 of 784 slaughter pigs by IHA at a cutoff value of 1:64. The overall seroprevalence was 19.9%, which was higher than that reported in Jilin Province (Xu et al. 2015) but lower than that in Chongqing, Tibet, or Sichuan Province (Shu et al. 2011, Wu et al. 2012a, 2012b). Such difference might be caused by different climates, rearing systems, sanitary conditions, and animal welfares. Of course, the contribution of cats and rodents to Toxoplasma infection also could not be ignored (Weigel et al. 1995, Kijlstra et al. 2008). In addition, our study also showed that slaughter pigs from Zhouzhi County had the highest prevalence (Table 1), probably because of worse environment conditions, welfares, and comparatively more chance to come into contact with cats, rodents, and other sources of infection, which might contribute significantly to the transmission of T. gondii.

In addition, differences of T. gondii seroprevalence were discovered among rearing systems (nonintensive pig farms: 31.0%; intensive pig farms: 6.7%), genders (male: 19.8%; female: 20.0%), and regions (ranging from 6.7% in Shenmu to 38.2% in Zhouzhi) (Table 1) in this study. Besides, the seroprevalence in nonintensive pig farms (31.0%) was much higher than in intensive pig farms (6.7%) (odds ratio [OR] = 7.02, 95% confidence interval [CI] = 3.94–9.92, p = 0.000). And the seroprevalence in Zhouzhi County (38.2%) (OR = 8.65, 95% CI = 5.18–14.44, p = 0.000) and Chenggu County (15.9%) (OR = 2.66, 95% CI = 1.40–5.05, p = 0.003) was much higher than that in Shenmu County, respectively. The differences of them were both extremely significant. However, the difference of the seroprevalence between Xi'an and Shenmu was nonsignificant (OR = 1.04, 95% CI = 0.34–3.154, p = 0.949) (Table 1).

These results indicated that all factors investigated in this study except sex affected the prevalence of infection. This conclusion was in accordance with previous studies (Villari et al. 2009, Gebremedhin 2014, Zheng et al. 2016a, 2016b) in pigs, sheep, farmed minks, and farmed raccoon dogs. This result might indicate that gender was not a risk factor for T. gondii infection in slaughter pigs. However, region was revealed as an important risk factor for T. gondii infection in slaughter pigs (p < 0.01). Obviously, there are different climates, temperature, humidity, and other geographical conditions in different geographical locations. And these elements may contribute to T. gondii transmission. Remarkably, rearing system (p < 0.01) was considered as a significant risk factor in this study. A different rearing system means a different chance to be exposed to T. gondii, because all things slaughter pigs contacted including food and water may contain T. gondii tissue cysts or oocysts.

Unfortunately, we did not subdivide the risk factors, because we could not get more information about the slaughter pigs from which we collected samples. Thus, the significance of more specific elements including water, food, and other things the pigs contacted should be investigated in further studies to improve the data of risk factors of T. gondii infection in slaughter pigs.

Conclusion

A 19.9% seroprevalence of T. gondii infection in slaughter pigs in Northwestern China was discovered in this study. Rearing system and region were revealed as the significant risk factors for slaughter pig infection with T. gondii. These results indicated that T. gondii is highly prevalent in slaughter pigs in Northwestern China, and the infected pork is extremely likely to be an important risk factor for public health. This study provided fundamental data for the prevention and control of T. gondii infection in slaughter pigs in China.