First Report of Chlamydiaceae Seroprevalence in Tibetan Pigs in Tibet,China

Introduction

C hlamydiaceae, obligate intracellular bacteria, are the etiological agents of chlamydiosis and are responsible for a broad spectrum of diseases in animals and humans (Raso et al. 2010, Rohde et al. 2010, Schautteet and Vanrompay 2011). Four Chlamydiaceae species have been isolated from pigs: Chlamydia suis, Chlamydophila psittaci, Chlamydophila abortus, and Chlamydophila pecorum (Pantchev et al. 2010, Rohde et al. 2010, Schautteet and Vanrompay 2011), and infections with these agents are usually associated with pneumonia (Reinhold et al. 2008), severe dyspnea (Sachse et al. 2004), conjunctivitis (Becker et al. 2007), arthritis, and necrotizing enteritis in pigs. In addition, numerous reproductive problems such as vaginitis, endometritis, returning to estrus, abortion, mummification, delivery of weak piglets, and increased neonatal mortality in sows (Schautteet and Vanrompay 2011), as well as orchitis, epididymitis, and vesiculitis in boars (Camenisch et al. 2004, Schautteet and Vanrompay 2011), can be caused by infection with members of the Chlamydiaceae.

Chlamydiaceae infections in pigs have been reported worldwide (Eggemann et al. 2000, Vanrompay et al. 2004, Wang et al. 2006, Zhou et al. 2008, Pantchev et al. 2010, Xu et al. 2010); however, little is known about Chlamydiaceae prevalence in Tibetan pigs in Tibet, China. The Tibetan pig is a Chinese native pig breed distributed in the southeastern Tibet Plateau and the surrounding areas. During long-term free-range production, Tibetan pigs have evolved adaptions to low temperature and poor food quality (Xin et al. 2011) and, physically possess powerful musculature, with coarse black hair covering the whole body (Zheng 1998). The animal's meat is a sought-after delicacy with a tender texture and high nutritional value. Thus, Tibetan pigs have become an important source of income for Tibetans. Tibetan pigs may also act as a potential risk in the spread of infectious disease. In this context, the objective of the present study was to investigate using a serological approach whether Chlamydiaceae are prevalent in Tibetan pigs in Tibet, China.

Materials and Methods

Results and Discussion

Seventy-one out of 427 serum samples (16.63%, 95% confidence interval [CI] 15.31–17.95) were seropositive for Chlamydiaceae by IHA. Antibody titers were 1:256 in 2, 1:128 in 2, 1:64 in 5, 1:32 in 10, and 1:16 in 52 in the seropositive Tibetan pigs. Of the total of 71 seropositive results, 40 (of 232) samples came from Nyingchi (17.24%, 95% CI 15.40–19.08) and 31 (of 195) originated from Mainling (15.90%, 95% CI 14.02–17.78) (Table 1), although the difference in seroprevalnce between the 2 counties was not statistically significant (p>0.05). As shown in Table 1, the investigation revealed that the prevalences in female and male animals were 17.61% (95% CI 15.22–20.00) and 12.72% (95% CI 11.07–14.37), respectively. Among these positive Tibetan pigs, seroprevalence varied in different age groups, ranging from 0 to 20.61% (95% CI 17.81–23.48) (Table 2).

Surveys of Chlamydiaceae infections in pigs have been performed in many countries (Eggemann et al. 2000, Vanrompay et al. 2004, Pantchev et al. 2010) and some provinces in China (Suo et al. 2005, Luo et al. 2006, Wang et al. 2006, Xian et al. 2007, Zhou et al. 2008, Xu et al. 2010), but little is known about infection with Chlamydiaceae in Tibetan pigs, which are one of the main sources of food and economic activity in Tibet. In this study, the overall seropositivity for Chlamydiaceae exposure was 16.63% (95% CI 15.31–17.95) in Tibetan pigs, which was lower than that of the intensively raised pigs in other provinces of China (Jin et al. 2005, Li 2005, Suo et al. 2005, Luo et al. 2006, Wang et al. 2006, Xian et al. 2007, Zhou et al. 2008, Xu et al. 2010), but higher than that observed in Yunnan province (10.5%) in China (Cao and Zhang 2007). The low seropositivity of Chlamydiaceae in Tibetan pigs may be attributed to higher resistance of Tibetan pigs to the disease compared with pigs from intensive farming systems and inbreeding of Tibetan pigs that could decrease the opportunity of transmission through mating with other populations of pigs.

Among different age groups of Tibetan pigs, a higher prevalence (20.61%, 95% CI 17.81–23.48) was detected in growing pigs (p<0.01), whereas no seroprevalence was detected in breeding boars and sows, possibly due to the limited number of samples. In other reports in China, the seropositivity of Chlamydiaceae in breeding boars and sows from intensive farms was usually more than 30% (Jin et al. 2005, Li 2005, Suo et al. 2005, Luo et al. 2006, Wang et al. 2006, Xian et al. 2007, Zhou et al. 2008, Xu et al. 2010). Further studies of Chlamydiaceae infection in Tibetan pigs should focus on breeding boars and sows.

No statistically significant difference in Chlamydiaceae seroprevalence was observed between female and male Tibetan pigs (p>0.05). However, a tendency for higher prevalence among females was observed. This tendency was also observed in the previous surveys of wild boars in Italy (females, 45.95%; males, 38.8%) (Antonietta et al. 2011) and Germany (females, 83.3%; males, 42.9%) (Helmut et al. 2004) by microimmunofluorescence (MIF) and PCR. Therefore, further studies should be performed to ascertain whether gender is a crucial factor for Chlamydiaceae infection. In this present study, the Chlamydiaceae seropositivity in the 2 counties did not differ significantly (p>0.05), probably because of the use of similar environmental and free-range systems.

Many wild birds (Kaleta and Taday 2003) and ruminants (Cubero-Pablo et al. 2000) can also carry some species of Chlamydiaceae. Cross-species transmission is widespread in chlamydial circulation (Lemus et al. 2010). Whether Tibetan pigs acquired Chlamydiaceae through wild animals interacting with domestic animal husbandry practices in this region could not be assessed based on the present data. Further investigations should study the transmission of Chlamydiaceae in Tibetan pigs, other animals, and humans in Tibet.

In conclusion, the present study demonstrated that there was a 16.63% (95% CI 15.31–17.95) seroprevalence of Chlamydiaceae infection in Tibetan pigs in Tibet, China, which provided baseline data for the effective prevention and control of chlamydiosis in Tibetan pigs in this unique region of the world. To our knowledge, the present report is the first to document the seroprevalence of Chlamydiaceae infection in Tibetan pigs in China.