First Report of Chlamydia Seroprevalence in Slaughter Pigs in Shandong Province,Eastern China

Introduction

C hlamydia spp. are very important pathogens for humans and various species of animals' diseases for which no effective vaccine exists (Elwell et al., 2016). Until now, five Chlamydia spp. in the Chlamydiaceae family have been proved to be able to infect pigs: Chlamydia suis, Chlamydia trachomatis, Chlamydia abortus, Chlamydia pecorum, and Chlamydia psittaci, and three species have been isolated from humans: C. trachomatis, C. psittaci, and Chlamydia pneumoniae (Elwell et al., 2016, Opota et al., 2017, Witkin et al., 2017). Pigs infected by C. trachomatis, C. suis, and C. pecorum could lead to numerous reproductive problems (Pollmann et al. 2005, Schautteet and Vanrompay 2011, Englund et al. 2012). Moreover, an increasing number of studies have shown that pregnant women can acquire C. abortus when they contact with pigs and sheep (Schautteet and Vanrompay 2011, Essig and Longbottom 2015).

Chlamydia infection in pigs has induced great financial losses all over the world (Pollmann et al. 2005, Schautteet and Vanrompay 2011, Schautteet et al. 2013). In China, although seroepidemiological surveys for Chlamydia in pigs have been reported in several provinces of China (Ren et al. 1994, Yi et al. 1994, Zhou et al. 2008, Jiang et al. 2013, Yi and Zhang 2013), no data are available about Chlamydia infection in pigs in Shandong province, which is one of China's top five pig production areas. In recent years, breeding on farmed wild boars has become a new mode in China, and increasing meat production from wild boars has been favorable by Chinese people. However, limited data about Chlamydia infection in farmed wild boars are available in China (Nie et al., 2018). Hence, this study was conducted to investigate Chlamydia seroprevalence in pigs in Shandong province, eastern China, including domestic pigs and farmed wild boars, which may provide useful baseline data for the control and prevention of Chlamydia infection in pigs.

Materials and Methods

Results and Discussion

In this study, specific antibodies to Chlamydia were found in 509 of 2108 slaughter pigs by IHA with a cutoff value of 1:16. The overall seroprevalence was 24.15% (95% confidence interval: 22.32–25.97), which was lower than that in pigs in Sweden (95.83%) (Englund et al. 2012), in wild boars in Italy (63.60%) (Di et al. 2011), in pigs breeding in the major pig-producing areas of Jiangxi province, China (58.59%) (Jiang et al. 2013), and in farmed wild boars in northwestern China (39.67%) (Nie et al., 2018), but higher than that in pigs in Hunan (22.25%) (Li 2005) and Henan (17.60%) (Wang et al. 2006) provinces, and in Tibetan pigs in Tibet autonomous region of China (16.63%) (Zhang et al. 2013). Some differences of different studies such as geographical origin, environmental conditions, ages of investigated pigs, different feeding conditions, and different diagnostic methods may cause these differences in Chlamydia seroprevalence. Our study also showed that a significant difference of Chlamydia seroprevalence was detected among regions in slaughter pigs with the highest in Yantai (Table 1). For field survey, several factors may induce these differences, including worse feeding conditions, comparatively more chance to come into contact with rodents, birds, and other animals, and other animals as sources of Chlamydia infection.

This study revealed that the rearing system of pigs is one of the risk factors associated with Chlamydia seroprevalence. The free-ranging (30.26%) and backyard (29.77%) pigs have significantly higher seroprevalence than those breeding under the intensive farm (18.79%) (p < 0.001). Standardized farms usually equip disinfection systems, which may contribute to the low seroprevalence of Chlamydia in pigs when compared with free-ranging or backyard pig-breeding system. Moreover, in this study, the farmed wild boars (28.06%) have a significantly higher seroprevalence than the domestic pigs (21.19%) (p < 0.001). In recent years, breeding of farmed wild boars has become a new breeding mode in China, which usually adopted the free-range system. In this case, disinfection measures are inadequate, and farmed wild boars are more likely to be exposed to various pathogens including Chlamydia spp., which would contribute to the higher seroprevalence of Chlamydia infection in farmed wild boars than in domestic pigs.

Among the wild boar population, C. abortus, C. suis, and C. psittaci have been identified as major agents causing serious illness (Hotzel et al. 2004, Di et al. 2011). Moreover, a series of research results showed significant public health concerns, because C. psittaci and C. abortus have been considered to infect humans, resulting in many kinds of diseases, even causing abortion of pregnant women (Schautteet and Vanrompay 2011, Essig and Longbottom 2015). The risk of abortion significantly increases when pregnant women come in contact with Chlamydia-infected animals (Baud et al. 2008). Thus, further studies should be conducted to investigate the Chlamydia spp. infecting pigs in China, and their pathogenicity and zoonotic potential.

In the present study, we only obtained limited information on the slaughter pigs from butchers. However, more detailed information including sources of water and food, other things the pigs contacted, and the particular feeding environment was also required. All of these specific elements may contribute to different Chlamydia seroprevalence and should be reinvestigated in future studies to improve the data of risk factors of Chlamydia infection in slaughter pigs in China.

Conclusion

In conclusion, the results of this study indicated that Chlamydia seroprevalence is quite high in domestic pigs and farmed wild boars in Shandong province, eastern China, which poses significant public health concerns. Moreover, pig species, sampling regions, and rearing system were identified as risk factors for Chlamydia infection in Shandong province. To our knowledge, this is the first report to compare the Chlamydia seroprevalence between domestic pigs and farmed wild boars, which provided important data for the strategic control and prevention of Chlamydia infection in China.