Cross-Sectional Study on Swine Tuberculosis Prevalence in Gansu Province, China from February to June 2021
Liang Sun1, Yao Xi1, Jiaxin Huang1, Jifei Yang2, Zengjun Lu2, Pu Sun1, 2*, Qiaoying Zeng111* Co-corresponding authors: Pu sun, Email: sunpu@caas.cn; Qiaoying Zeng, Email: zengqy@gsau.edu.cn.
1 Laboratory of Veterinary Microbiology, College of Veterinary Medicine, Gansu Agricultural University, Lanzhou, 730070, China.
2 State Key Laboratory of Veterinary Etiological Biology, National Foot and Mouth Disease Reference Laboratory, Lanzhou Veterinary Research Institute, Chinese Academy of Agricultural Sciences, Lanzhou, 730070, China.
Running title: Cross-Sectional Survey on Seroprevalence of Swine Tuberculosis in Gansu Province, China
Corresponding authors: Qiaoying Zeng, Laboratory of Veterinary Microbiology, College of Veterinary Medicine, Gansu Agricultural University, Lanzhou, 730070, China, Tel: +8613893316398, Email: zengqy@gsau.edu.cn (Q.Z); Pu Sun, State Key Laboratory of Veterinary Etiological Biology, National Foot and Mouth Disease Reference Laboratory, Lanzhou Veterinary Research Institute, Chinese Academy of Agricultural Sciences, Lanzhou, 730070, China, Tel: +8609318378501; Email: sunpu@caas.cn (P.S.).
Summary: Tuberculosis (TB), caused by the Mycobacterium tuberculosis complex (MTBC), poses a major global threat to the health of humans and animals. The Suidae family is highly susceptible to TB and is used as screening sentinels for testing the presence of MTBC in the environment, but swine TB (STB) tends to be neglected worldwide. China has the largest pig population in the world, but epidemiological information on STB is scarce. In this study, 1379 serum samples were randomly collected from 45 herds of Gansu province, China from February to June 2021 and tested with PPD-B-ELISA. The STB prevalence at individual level was 0.22% (95% CI: 0.04%, 0.63%) and varied from 0.00% to 2.20% in different cities. The prevalence at herd level was 4.44% (95% CI: 0.54%, 15.15%) and varied from 0.00% to 33.33% in different cities. The STB prevalence in intensively raised three-crossbred pigs (0.23%, 95% CI: 0.05%, 0.68%) was higher than that in free-range raised Tibetan pigs (0.00%, 95% CI: 0.00%, 3.85%) (p = 0.81). Besides, 180 serum samples were collected from Guangxi province, China, and STB prevalence in Guangxi province (1.67%, 95% CI: 0.35%, 4.79%) was significantly higher than that in Gansu province (p< 0.05). These latest STB prevalence data are strongly suggested to conduct a randomized nationwide cross-sectional study on a regular basis for the development of an effective national program for STB surveillance and control.
Keywords : Swine tuberculosis, Gansu province, China, Cross-sectional survey, Seroprevalence, Serology
Introduction
Tuberculosis (TB) is known as an important zoonotic infectious disease since humans and animals can be cross-infected by theMycobacterium tuberculosis complex (MTBC). According to the Global Tuberculosis Report in 2021 by the World Health Organization, there were about 5.8 million new Human TB (hTB) cases and 1.5 million new deaths in 2020 (Global Tuberculosis Report in 2021). Although hTB is mainly caused by Mycobacterium tuberculosis (M. tb ), 17.0%, 26.1%, 5.3%, and 6.5% of hTB cases have been reported to be caused by Mycobacterium bovis (M. bovis ) in Ethiopia, Tanzania, Turkey, and the west bank of Palestine, respectively (Bayraktar et al., 2011; Ereqat et al., 2012; Fetene et al., 2011; Kazwala et al., 2001; Mfinanga et al., 2004; Shitaye et al., 2007).M. bovis has an extraordinary host range, including humans, cattle, pigs, and a variety of domesticated and wild animals (Cousins et al., 2005). In May 2014, the World Health Assembly passed a resolution of the post-2015 End TB Strategy with its ambitious targets to be fully realized in 2035 (Sun et al., 2021). However, MTBC infection in the multi-host system is a great barrier to achieving this goal worldwide.
The Suidae family has been reported to be highly susceptible to TB, and the detection of severe typical tubercles in pigs and wild boars suggests that those species may act as maintenance hosts rather than dead-end hosts (Di Marco et al., 2012; Naranjo et al., 2008). Due to the high susceptibility to MTBC, domestic pigs and feral swine are used as screening sentinels for testing the presence of MTBC in the environment (Bailey et al., 2013; L. A. Corner et al., 2015). Swine TB (STB) is a worldwide disease that is often neglected (Tbran et al., 2019). Therefore, as a reservoir for MTBC especially for M. bovis , swine might transmit MTBC to humans, especially in TB-endemic areas (Bollo et al., 2000; Nugent et al., 2015). STB has also been reported in other Suidae families such as bush pigs (Potamochoerus porcus ) in South Africa (Hlokwe et al., 2014), warthogs (Phacochoerus africanus ) in Africa (Miller et al., 2016), and collared peccaries (Tayassu tajacu ) in South America (Mayer et al., 2012).
Proper identification of STB, followed by implementation of suitable management strategies, is important for control of STB (Csivincsik et al., 2016). However, there are limited STB diagnosis tests available. Mycobacterial culture remains the gold standard method for infection confirmation, but it is quite difficult due to several factors including the chronic process of TB, a high proportion of persistent infection, the slow growth of MTBC, low efficiency of isolation of MTBC, and the biosafety requirement for MTBC culture, etc (Boadella et al., 2011; L. A. L. Corner et al., 2012). Standard in vivo diagnosis methods including tuberculin skin tests and interferon-gamma release assays are mainly developed and calibrated in bovine TB, but these methods also have some limitations including multiple handling events required or time constraints since blood samples must be handled in the laboratory within 24 hours after collection (Buddle et al., 2009; Schiller et al., 2010). Alternatively, antibody-based diagnosis has been widely used for STB diagnosis owing to its convenience and good performance (Boadella et al., 2011; Gil et al., 2010; Pedersen et al., 2017; Perez de Val et al., 2017). Unlike many other animals, swine appear to produce detectable humoral responses soon after M. bovis infection, and the responses are maintained during the development of the disease (Garrido et al., 2011; Roos et al., 2016). This allows rapid detection of STB by serological assays (Boadella et al., 2011).
China has the largest pig population in the world, and the pig production industry is an important driver of the China economy. Sufficient data on STB prevalence are needed for the development of an effective STB surveillance and control program, but epidemiological information on STB in China is very scarce. Therefore, a cross-sectional study was conducted for assessing the STB prevalence in Gansu province in China with PPD-B-ELISA (de Val Perez et al., 2011; Garcia-Bocanegra et al., 2012; Gil et al., 2010).
Materials and Methods
Study area
Gansu province (located in Northwestern China) lies between 32°11′-42°57′ north latitude and 92°13′-108°46′ east longitude with a total area of 425,800 square kilometers (Figure 1). Gansu has 12 prefecture cities and 2 autonomous prefectures.