Abstract
Chlamydia, a kind of obligate intracellular Gram-negative bacteria, can infect humans and animals worldwide, including pigs. However, the information on Chlamydia infection is unavailable in pigs in Shandong province, eastern China. To assess the seroprevalence and risk factors of Chlamydia infection in pigs in Shandong province, eastern China, a total of 2108 serum samples of slaughter pigs were collected between January 2017 and December 2018, and specific antibodies against Chlamydia were detected by the indirect hemagglutination assay. The overall Chlamydia seroprevalence was 24.15% (509/2108, 95% confidence interval: 22.32–25.97). Species, sampling regions, and rearing systems of pigs were considered as risk factors for Chlamydia infection through statistical analysis by SAS analysis (p < 0.05). These results indicated that Chlamydia is highly prevalent in slaughter pigs in Shandong province, eastern China, and may pose a potential risk for human health. To our knowledge, this is the first investigation of Chlamydia seroprevalence in slaughter pigs in Shandong province, eastern China. Moreover, this is the first report to compare the Chlamydia seroprevalence between domestic pigs and farmed wild boars in a same study, which may provide important data for preventing and controlling Chlamydia infection in pigs in China.
Introduction
C
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
Collection and preparation of serum samples
This study was approved by the Animal Ethics Committee of Jilin Agricultural University (Approval No. JAUAEC2016-011). From January 2017 to December 2018, a total of 2108 blood samples of slaughter pigs were randomly collected from three administrative regions (Weihai, Yantai, and Rizhao) of Shandong province, eastern China (Table 1). Information on pigs was obtained by owners, including region, species, and rearing system. Blood samples taken to the laboratory were kept at atmospheric temperature for 2 h and then were centrifuged at 3000 × g for 10 min to obtain sera. The sera were stored at °20°C until further tested.
Seroprevalence of Chlamydia Infection in Slaughter Pigs in Shandong Province, Eastern China, by the Indirect Hemagglutination Assay
CI, confidence interval; IHA, indirect hemagglutination assay.
Serological examination
The specific antibodies to Chlamydia were detected by a commercially available Indirect Hemagglutination Assay (IHA) kit purchased from Lanzhou Veterinary Research Institute, Chinese Academy of Agricultural Sciences, Lanzhou, China, according to the manufacturer's instructions as previously described (Hu et al., 2018, Nie et al., 2018). The sensitivity and specificity of the IHA kit are 100% and 95%, respectively (Qin et al., 2014). In each test, positive, negative, and blank controls should be included. Serum reaction at dilutions of 1:16 or higher was considered positive for Chlamydia antibodies. Reaction dilutions between 1:4 and 1:16 were considered “suspect” and should be retested.
Statistical analysis
Differences in the seroprevalence of Chlamydia among pigs of different geographical origins, species, sampling time, and rearing systems were analyzed with chi-square tests using the SAS (Statistical Analysis System, version 9.1). A p value <0.05 was considered statistically significant.
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.
Footnotes
Author Disclosure Statement
The authors have declared that no competing interests exist.
