Seroprevalence and risk factors of Chlamydia abortus infection in Tibetan sheep in Qinghai province, China

doi:10.21203/rs.3.rs-4709091/v1

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Seroprevalence and risk factors of Chlamydia abortus infection in Tibetan sheep in Qinghai province, China

https://doi.org/10.21203/rs.3.rs-4709091/v1

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Background Chlamydia abortus

(C. abortus) is Gram-negative, intracellular bacterium, causing ovine enzootic abortion (OEA). No data about C. abortus infection are available in Tibetan sheep in Qinghai, China.

Result

A total of 1043 Tibetan sheep serum samples were collected from 8 Tibetan sheep flocks in Qinghai, China, then were detected for specific antibodies against C. abortus using a commercial ELISA Kit. The results showed that the overall seroprevalence of C. abortus in Tibetan sheep was 153/1043 (14.7%, 95% confidence interval [CI] 12.5–16.8). The prevalence in female and male Tibetan sheep was 58/421 (13.8%, 95% CI 10.5 ~ 17.1) and 95/622 (15.3%, 95% CI 18.6 ~ 26.6), respectively with no significant difference (P > 0.05). The seroprevalence of antibodies to C. abortus in Tibetan sheep ranged from 10.0 to 21.7% among the eight different areas, and the difference was also without statistical significance [1]. The prevalence among different age groups ranged from 14.0 to 16.5%, with a higher prevalence among 1 to 1.5 years age category.

Conclusion

The results demonstrate the presence of C. abortus infection in Tibetan sheep in Qinghai and its potential impact on public health and the local Tibetan economy. To our knowledge, this is the first seroprevalence survey of C. abortus in Tibetan sheep in Qinghai, China.

Chlamydia abortus

Seroprevalence

Tibetan sheep

C. abortus is an obligate intracellular, gram-negative organism with two phases of elementary body and reticulate body developmental cycles. C. abortus, is widely distributed in the world with strong infectivity and pathogenicity capable of causing, ovine enzootic abortion (OEA) in sheep and goats[2, 3]. It is characterized by abortion in the last 2–3 weeks of pregnancy[4]. In addition, C. abortus infection may cause stillbirth and weak lambs, which usually die within 48 hours. C. abortus is also an important zoonotic pathogen, with most infections occurring among veterinarians, livestock breeders, butchers, and farm workers[5], mainly causing atypical pneumonia in men and miscarriage and pelvic inflammatory disease in women[6, 7]. A case of severe systemic infection and fetal abortion caused by C. abortus in a pregnant woman living on a farm was reported in France in 2020 [8]. The C. abortus infection in sheep has been reported in widely distributed across the globe, serological epidemiology survey revealed that C. abortus is a main reason for the sheep abortion, C. abortus positive rate is 11.1% in Saudi Arabia [9], 13.8% in Egypt [10], 6.6% in Tunisia[11], 9.7% in Iran[12], 33.0% in Spain [13],7.2% in Algeria [3], 33.4% in Italy[14]. The sero-positive rates of Tibetan sheep in Gansu and goat in Hunan of China were 18.65% and 8.45%, respectively [15, 16]. C. abortus infects a wide range of hosts, mainly sheep, but also cattle, pigs, deer, horses, yaks, birds, fur animals, causing significant economic losses to animal husbandry[17, 18].

Tibetan sheep is one of the three coarse sheep breeds in China, and is a unique animal husbandry breed in the Qinghai-Tibet Plateau, mainly distributed in Qinghai, Tibet, Gansu and other areas. Among them, Qinghai Province has the widest distribution, the largest number and the largest proportion, and is known as the "home of Tibetan sheep in China". More than 50 million Tibetan sheep are raised, living between 3000 and 5000 meters above sea level. Tibetan sheep, however, is under threat from many diseases, including contagious pleuropneumonia, peste des petits ruminants, enzootic abortion of ewes caused by C. abortus, toxoplasma and pasteurella disease. C. abortus is an important pathogen of Tibetan sheep, capable of causing abortion in pregnant Tibetan sheep.

The only study which investigated the seroprevalence of C. abortus infection in Tibetan sheep in Gansu, little information is available about the seroprevalence of C. abortus infections in Qinghai in China. Considering the public health and economic importance of C. abortus, the present study was conducted to determine the sero-prevalence of C. abortus in Tibetan sheep population and explore associated risk factors in Qinghai, China.

Study area

This study involved 8 regions throughout Qinghai Province in China, respectively (Fig. 1). Qinghai Province is located in the western part of China, the roof of the world in the northeast of the Qinghai-Tibet Plateau. Qinghai is the birthplace of the Yangtze River, Yellow River and Lancang River, so it is called "the source of rivers", also known as "the source of three rivers", known as the "water tower of China" reputation. The geographical position of Qinghai Province is between 89°35'-103°04' east longitude and 31°36'-39°19' north latitude, which is more than 1,200 kilometers long from east to west, and more than 800 kilometers wide from north to south. The total area of Qinghai Province is 722,300 square kilometers, accounting for one thirteenth of the total area of China. Qinghai province has an average elevation of 3,000 meters above sea level.

Samples

A total of 1043 blood samples were collected randomly from 8 regions in Qinghai Province in the autumn of 2023, including Xining City (n = 120), Haidong City (n = 160), Haibei Prefecture (n = 125), Haixi Prefecture (n = 119), Hainan Prefecture (n = 200), Huangnan Prefecture (n = 80), Yushu Prefecture (n = 120), Guoluo Prefecture (n = 119), including 421 females and 622. The blood samples were placed at room temperature for 4 h and quickly transferred to the laboratory, and centrifuged at 3000 g for 10 minutes to obtain sera that were stored at -80 ℃ until use.

Detection of C. abortus antibodies

Anti-C. abortus IgG antibodies were detected with ELISA kits according to the manufacturer's instructions (ID Screen® Chlamydophila abortus Indirect Multi-species, IDVET Innovative Diagnostics, Montpellier, France). The optical density (OD) was measured at 450 nm by an ELISA microplate reader (Multiskan™ FC, Thermo Fisher Scientific™, USA). Signal to noise ratio was calculated according to the following formula:

S/P (%) = 100 × (OD sample / OD positive control)

Where S: tested sample, P: positive control.

Sera samples with S/P ratios higher than 60% were considered positive.

The differences in infection rate based on location, genders and age groups of Tibetan sheep were analyzed by Chi-square test in SPSS (Statistical Analysis System, Version 22.0). Values of P < 0.05 were considered statistically significant.

In this study, Of the 1043 serum samples, 153/1043 (14.7%, 95% CI 12.5–16.8) were positive for C. abortus including 58/421 (13.8%, 95% CI 10.5 ~ 17.1) female Tibetan sheep and 95/622 (15.3%, 95% CI 18.6–22.6) male Tibetan sheep (Table 1), the difference, however, was not statistically significant (P > 0.05). Antibodies against C. abortus in Tibetan sheep varied from 10.0–21.7% among the different regions but the difference was not statistically significant (P > 0.05) (Table 2). The seroprevalence among the different age groups ranged from 14.0–16.5% (Table 3) and was higher in the 1 to 1.5 years category, but was not significantly different (P > 0.05).

Table 1

Prevalence of *Chlamydia abortus* infection in Tibetan sheep by gender in Qinghai Province, China.
Gender	No. of tested samples	No. of positive samples	Prevalence % (95% CI)	P value
Female	421	58	13.8(10.5 ~ 17.1)	0.503
Male	622	95	15.3(18.6 ~ 26.6)
Total	1043	153	14.7(12.5 ~ 16.8)

Table 2

Prevalence of *Chlamydia abortus* infection in Tibetan sheep by areas in Qinghai Province, China.
Area	o. of tested samples	No. of positive samples	Prevalence % (95% CI)	P value
Xining	120	12	10.0(4.6 ~ 15.4)	0.087
Haidong	160	21	13.1(7.9 ~ 18.4)
Haibei	125	23	18.4(11.6 ~ 25.2)
Haixi	119	15	12.6(6.6 ~ 18.6)
Hainan	200	22	11.0(6.7 ~ 15.3)
Huangnan	80	12	15.0(7.2 ~ 22.8)
Yushu	120	26	21.7(14.3 ~ 29.0)
Guoluo	119	22	18.5(11.5 ~ 25.5)
Total	1043	153	14.7(12.5 ~ 16.8)

Table 3

Prevalence of *Chlamydia abortus* infection in Tibetan sheep by age in Qinghai Province, China.
Age group	No. of tested samples	No. of positive samples	Prevalence % (95% CI)	P value
0 ~ 0.5	254	36	14.2(9.9 ~ 18.5)	0.939
0.5 ~ 1	611	89	14.6(11.8 ~ 17.4)
1 ~ 1.5	121	20	16.5(9.9 ~ 23.1)
1.5 ~ 2	57	8	14.0(5.0 ~ 23.1)
Total	1043	153	14.7(12.5 ~ 16.8)

In the present study, the C. abortus seroprevalence in male and female Tibetan sheep was 15.3% and 13.8%, respectively. However, there was no significant difference in the prevalence in female and male Tibetan sheep (P > 0.05), which was consistent with the results of Tibetan sheep in Gansu[16], goat in Hunan, sheep and goat in Eastern Saudi Arabia, sheep and goat in Iran[9, 19]. The same results have been observed in studies on other animal species such as the yaks in Qinghai Province and Tibet, Tibetan pigs in Tibet, China[20–22]. These findings suggested that gender might not be a key factor in C. abortus infection in Tibet sheep populations.

Qinghai is located in western China, in the northeast of the Qinghai-Tibet Plateau on the roof of the world, with an average elevation of more than 3,000 meters. High altitude is the most important ecological challenge for Tibetan sheep. Our results revealed that antibodies against C. abortus in Tibetan sheep varied from 10.0–21.7% between regions. The highest seroprevalence for C. abortus was in Yushu, the highest altitude area in Qinghai Province. The results showed that there was a certain geographical distribution of C. abortus infection in Qinghai Province, which might be related to the altitude.

The seroprevalence of antibodies against C. abortus was not statistically different among age categories, a higher prevalence (16.5%) was detected in the 1 to 1.5 year age category. This pattern of age-related seroprevalence has also been observed in previous surveys of Black-Boned Sheep in China, ewes in Tunisia and sheep in Iran[11, 19, 23]. However, this is different from the previous research results of Tibetan sheep in Gansu Province, which showed that age was an important risk factor, according to the staff of the local veterinary station, most Tibetan sheep were slaughtered before the age of 1 year. The main sample collection in this study mainly focused on Tibetan sheep before the age of 1 year, so different research results may be related to age groups.

Qinghai Province, as the "home of Tibetan sheep in China", C. abortus should have enough attention, formulate scientific and effective measures to prevent and reduce economic losses caused by the disease for Tibetan sheep industry. In Tibetan sheep breeding process, C. abortus should be built into the immunization program. Vaccination against of C. abortus can control the transmission of C. abortus at the source, reduce its speed, prevent infection. The C. abortus infection in Tibetan sheep should be timely treatment, strengthen daily management measures, to do the daily disinfection work, cut off the route of transmission of the disease.

To our knowledge, the present report is the first to document the seroprevalence of C. abortus infection in Tibetan sheep in Qinghai, China. This study showed existence of C. abortus antibodies in Tibetan sheep, and the seroprevalence of 14.7% in Tibetan sheep in Qinghai, China. These findings further demonstrate the need for surveillance of C. abortus together with the rest of the reproductive pathogens in Tibetan sheep.

Ethics approval and consent to participate

The animal study was reviewed and approved by the Animal Ethics Procedures and Guidelines of the People’s Republic of China and Research Ethics Committee of Qinghai University (No. SL-2023043).

Consent for publication

Not applicable.

Competing interests

The authors declare that they have no competing interests.

Funding

This study was supported by grants from the Open Project of State Key Laboratory of Plateau Ecology and Agriculture, Qinghai University (2023-ZZ-06)

Author Contribution

Fan Lei carried out the methodology and drafted the manuscript. Te Ba provided the samples and data collection.Jia-li Yu and Ya-qian Niu conducted the statistical analyses.Lin Liang revised the manuscript.

Data availability

Please contact the authors for data requests.

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Seroprevalence and risk factors of Chlamydia abortus infection in Tibetan sheep in Qinghai province, China

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Background Chlamydia abortus

Result

Conclusion

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Background

Materials and Methods

Study area

Samples

Results

Discussion

Conclusion

Declarations

Funding

Author Contribution

Data availability

References

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