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.