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Seroprevalence, risk factors and genetic characterization of Toxoplasma gondii in free-range white yaks (Bos grunniens) in China
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VETPAR-7638; No. of Pages 3
Veterinary Parasitology xxx (2015) xxx–xxx
Contents lists available at ScienceDirect
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Short communication
Seroprevalence, risk factors and genetic characterization of Toxoplasma gondii in free-range white yaks (Bos grunniens) in China S.Y. Qin a,b,1 , D.H. Zhou a,1 , W. Cong a,b , X.X. Zhang a,b , Z.L. Lou a,b , M.Y. Yin a,c , Q.D. Tan a,d , X.Q. Zhu a,b,∗ a State Key Laboratory of Veterinary Etiological Biology, Key Laboratory of Veterinary Parasitology of Gansu Province, Lanzhou Veterinary Research Institute, Chinese Academy of Agricultural Sciences, Lanzhou, Gansu Province 730046, PR China b College of Animal Science and Technology, Jilin Agricultural University, Changchun, Jilin Province 130118, PR China c College of Veterinary Medicine, Hunan Agricultural University, Changsha, Hunan Province 410128, PR China d College of Animal Science and Technology, Anhui Agricultural University, Hefei, Anhui Province 230000, PR China
a r t i c l e
i n f o
Article history: Received 24 December 2014 Received in revised form 11 May 2015 Accepted 17 May 2015 Keywords: Toxoplasma gondii Seroprevalence Risk factors Genotype White yak Modified agglutination test (MAT)
a b s t r a c t The objective of this study was to determine the seroprevalence, risk factors and genotypes of Toxoplasma gondii in white yaks (Bos grunniens) in China. A total of 974 serum samples were collected from white yaks in Tianzhu Tibetan Autonomous County (TTAC), Gansu province, northwest China for detecting T. gondii antibodies by the modified agglutination test (MAT), and 414 tissues belonging to 138 white yaks were collected for detecting T. gondii DNA by amplification of B1 gene with a semi-nested PCR. A total of 155 serum samples (15.91%) were seropositive for T. gondii antibodies at a 1:100 cut-off, and 10 DNA samples (7.25%) were positive for the T. gondii B1 gene, which were genetically characterized using multilocus PCR-RFLP. Only one genotype (ToxoDB#9) was identified from two samples with complete genotyping results. Statistically significant differences were not observed between T. gondii seroprevalence and gender, season or pregnancy in the logistic regression analysis (P > 0.05). Ages of white yaks was considered as a main risk factor associated with T. gondii infection. Our results indicated a widespread exposure to T. gondii among white yaks, and revealed the genotype ToxoDB#9 of T. gondii in white yaks for the first time in China. © 2015 Elsevier B.V. All rights reserved.
1. Introduction Toxoplasma gondii can infect humans and almost all warmblooded animals causing serious zoonotic toxoplasmosis (Dubey, 2010). Human infection with T. gondii is through consumption of undercooked meat containing T. gondii cysts, or oocysts shed from infected cats. White yak (Bos grunniens) is a unique yak breed living only in Tianzhu Tibetan Autonomous County (TTAC), Gansu Province, northwest China, which is located in the convergence zone among Qing-Tibet Plateau, Loess Plateau and Inner Mongolian Plateau, and the total number of white yaks is approximately 49,000 (Ma, 2008). Tianzhu White yak has been validated as one of 78 significantly protected species by the Ministry of Agriculture of the People’s Republic of China in 2000 (Niu et al., 2010).
∗ Corresponding author. Tel.: +86 931 8342837; fax: +86 931 8342837. E-mail address: [email protected] (X.Q. Zhu). 1 These authors contributed equally to this work.
Surveys regarding T. gondii infection in black yaks have been reported in some regions of China (Liu et al., 2008, 2011; Wang et al., 2012; Li et al., 2014). However, no information is available concerning T. gondii infection in white yaks in China. The objective of the present survey was to investigate the seroprevalence, assess risk factors and identify genotypes of T. gondii in white yaks in TTAC, China.
2. Materials and methods 2.1. The investigation site The present study was carried out in TTAC which is located between longitude 102◦ 07 to 103◦ 46 east and latitude 36◦ 31 to 37◦ 55 north, in the center of Gansu Province, northwestern China. The average temperature of this region is −8 to 4 ◦ C.
http://dx.doi.org/10.1016/j.vetpar.2015.05.015 0304-4017/© 2015 Elsevier B.V. All rights reserved.
Please cite this article in press as: Qin, S.Y., et al., Seroprevalence, risk factors and genetic characterization of Toxoplasma gondii in free-range white yaks (Bos grunniens) in China. Vet. Parasitol. (2015), http://dx.doi.org/10.1016/j.vetpar.2015.05.015
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ARTICLE IN PRESS
VETPAR-7638; No. of Pages 3
S.Y. Qin et al. / Veterinary Parasitology xxx (2015) xxx–xxx
2
Table 1 Seroprevalence and risk factors of Toxoplasma gondii infection in white yaks in Tianzhu Tibetan Autonomous County (TTAC), northwest China by the modified agglutination test (MAT). Factor
Category
No. tested
No. positive
Prevalence (%)
95% CIa
Gender
Male Female
289 685
49 106
16.96 15.47
12.63–21.28 12.77–18.18
Season
Spring Summer Autumn Winter
220 273 231 250
27 56 32 40
12.27 20.51 13.85 16.00
7.94–16.61 15.72–25.30 9.40–18.31 11.46–20.54
Pregnancy
0 1 2 3 4 ≥5
244 109 102 73 53 104
42 21 15 9 8 11
17.21 19.27 14.71 12.33 15.09 10.58
12.48–21.95 11.86–26.67 7.83–21.58 4.78–19.87 5.46–24.73 4.67–16.49
Age (year)b
0 < year ≤ 1 1 < year ≤ 2 2 < year ≤ 3 3 < year ≤ 4 year < 4
115 180 175 128 376
12 23 42 25 53
10.43 12.78 24.00 19.53 14.10
4.85–16.02 7.90–17.66 17.67–30.33 12.66–26.40 10.58–17.61
Total
974
155
15.91
13.62–18.21
a b
95% confidence intervals. This factor is significant in the logistic regression analysis as a risk factor (P < 0.05).
2.2. Serum and tissue samples preparation A total of 974 serum samples were collected randomly from white yaks presented on different farms from June 2013 to April 2014. In addition, 414 tissue samples (138 hearts, 138 livers and 138 lungs) coming from 138 white yaks presented at two local abattoirs were collected between August 2014 and November 2014 for genomic DNA extraction using the TIANamp Genomic DNA kit (TianGen Beijing, China). 2.3. Serological examination and genetic characterization of T. gondii isolates Antibodies to T. gondii were examined using the modified agglutination test (MAT). The detection procedures were carried out as described previously (Costa et al., 2012). Sera with MAT titers of 1:100 or higher were considered positive for T. gondii antibodies (Dubey 2010). DNA samples were examined by a semi-nested PCR targeting the B1 gene, and then genetic characterization of T. gondii isolates from positive samples was conducted with an multilocus PCR-RFLP method, including 11 nuclear loci (i.e., SAG1, 5 - and 3 SAG2, alternative SAG2, SAG3, BTUB, GRA6, c22-8, c29-2, L358, PK1) and an apicoplast locus Apico (Jiang et al., 2014). Genomic DNA samples representing nine reference T. gondii strains (GT1, PTG, CTG, MAS, TgCgCa1, TgCatBr5, TgCatBr64, TgRsCr1 and TgWtdSc40) were used as the positive controls. 2.4. Statistical analysis All the factors (gender, age, pregnancy and sampling season) were studied in a multivariable logistic regression model, and probability (P) value <0.05 was considered as statistically significant between levels within factors and interactions. Odds-ratios (OR) with 95% confidence intervals are calculated. All statistical analyses were performed using SPSS (Release 18.0 standard version, SPSS Inc., Chicago, Illinois). 3. Results and discussion In this study, 15.91% (155/974) of the examined white yaks were seropositive for T. gondii infection by MAT, with titers of 1:100 in 96, 1:200 in 31, 1:400 in 18, 1:800 in 6, 1:1600 in 1, 1:3200 in 1,
1:6400 or higher in 2. Previous studies reported that the seroprevalence of T. gondii in yaks ranged from 8.52% to 35.08% in Qinghai, Tibet and Sichuan provinces, China (Liu et al., 2011; Wang et al., 2012; Li et al., 2014). The differences in seroprevalence among different regions may be due to various detection methods used, ecological and geographical factors including temperature, rainfall, or landscape differences. The T. gondii seroprevalence in white yaks of different genders, pregnancies and ages as well as different sampling seasons is summarized in Table 1. This study found that gender, pregnancies and sampling seasons of examined white yaks were not significant in the logistic regression analysis (P > 0.05) and left out of the final model. Age of white yaks as a continuous variable was analyzed in the logistic regression model, the results showed that yaks of the 2 < years ≤ 3 years old had a 3 times higher risk of being seropositive compared to yaks of the 0 < years ≤ 1 years old (OR = 3.56, 95% CI = 1.50 − 8.44, P = 0.004), although no significant differences were found between other three age groups compared to the 0 < years ≤ 1 age group (P > 0.05), demonstrating that age is a predisposing factor for T. gondii infection. With the growth of white yaks, the seroprevalence of T. gondii increases, indicating that there may be a cumulative likelihood for exposure to T. gondii infection with age. The reason why the lowest prevalence occurred in white yaks below or equal to one year of age may be that the calves was affected slightly by vertical transmission. By comparison, the adult yaks had more opportunities to contact with food and water contaminated by oocysts shed by infected stray cats under the mode of extensive grazing, as they were more active than the calves and the older living in the grassland. A few previous studies characterized T. gondii isolates in cattle in the world, including Type I or III strains in Switzerland (BergerSchoch et al., 2011), Type II in Brazil (de Macedo et al., 2012) and Type I variant in China (Ge et al., 2014). However, there is no report about genotyping of T. gondii in black yaks, nor white yaks. In this study, 10 samples were detected positive for T. gondii B1 gene but only two positive samples were completely genotyped, due to low DNA concentration. It is interesting that only ToxoDB#9 (Chinese 1) was identified from white yaks, suggesting that this genotype may be the predominant genotype in white yaks, and the genetic diversity of T. gondii may be low in TTAC. To drawn a valid conclusion, more samples should be collected from broader geographical localities of TTAC in the future.
Please cite this article in press as: Qin, S.Y., et al., Seroprevalence, risk factors and genetic characterization of Toxoplasma gondii in free-range white yaks (Bos grunniens) in China. Vet. Parasitol. (2015), http://dx.doi.org/10.1016/j.vetpar.2015.05.015
G Model VETPAR-7638; No. of Pages 3
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The genotype ToxoDB#9 is different from the three predominant lineages (Type I–III), as it may generate moderate or high virulence to mice among different isolates with the same genotype (Wang et al., 2013). Although relevant bioassay in mice was not performed in this study, there is still a risk of humans being infected with this zoonotic strain by consuming white yak meat in the surveyed areas. ToxoDB#9 strains have been reported in a variety of animals and humans from several provinces in China, indicating that it is the major lineage in mainland China (Qin et al., 2014; Cong et al., 2015). In the future, it would be interesting to genotype T. gondii isolates from local Tibetans in TTAC to see if humans share the same genotypes with white yaks. In conclusion, the present study revealed a high T. gondii seroprevalence and identified ToxoDB#9 in white yaks in China for the first time. These findings not only extend the host range for T. gondii, but also indicate a potential public health concern that people are at risk of being infected with T. gondii after consumption of undercooked or raw meat from infected white yaks. Competing interests The authors declare that they have no competing interests. Acknowledgments Project support was provided by the Special Fund for Agroscientific Research in the Public Interest (Grant No. 201303037), the National Natural Science Foundation of China (Grant No. 31228022) and the Science Fund for Creative Research Groups of Gansu Province (Grant No. 1210RJIA006). Laboratoire de ParasitologieMycologie, Centre National de Référence de la Toxoplasmose, Centre de Ressources Biologiques Toxoplasma, Hôpital Maison Blanche, Reims Cédex, France, is thanked for providing the Toxoplasma MAT antigen.
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(oocysts) and meat from sheep, cattle and pigs in Switzerland. Vet. Parasitol. 177, 290–297. Cong, W., Liu, G.H., Meng, Q.F., Dong, W., Qin, S.Y., Zhang, F.K., Zhang, X.Y., Wang, X.Y., Qian, A.D., Zhu, X.Q., 2015. Toxoplasma gondii infection in cancer patients: prevalence, risk factors, genotypes and association with clinical diagnosis. Cancer Lett. 359, 307–313. Costa, D., Marvulo, M., Silva, J., Santana, S., Magalhães, F., Filho, C.L., Ribeiro, V., Alves, L., Mota, R., Dubey, J., 2012. Seroprevalence of Toxoplasma gondii in domestic and wild animals from the Fernando de Noronha, Brazil. J. Parasitol. 98, 679–680. de Macedo, M.F., de Macedo, C.A., Ewald, M.P., Martins, G.F., Zulpo, D.L., da Cunha, I.A., Taroda, A., Cardim, S.T., Su, C., Garcia, J.L., 2012. Isolation and genotyping of Toxoplasma gondii from pregnant dairy cows (Bos taurus) slaughtered. Rev. Bras. Parasitol. Vet. 21, 74–77. Dubey, J.P., 2010. Toxoplasmosis of Animals and Humans, 2nd ed. CRC Press, Boca Raton, 313 pp. Ge, W., Sun, H., Wang, Z., Xu, P., Wang, W., Mu, G., Wei, F., Liu, Q., 2014. Prevalence and genotype of Toxoplasma gondii infection in cattle from Jilin Province, northeastern China. Vector Borne Zoonotic Dis. 14, 399–402. Jiang, H.H., Qin, S.Y., Wang, W., He, B., Hu, T.S., Wu, J.M., Fan, Q.S., Tu, C.C., Liu, Q., Zhu, X.Q., 2014. Prevalence and genetic characterization of Toxoplasma gondii infection in bats in southern China. Vet. Parasitol. 203, 318–321. Li, K., Gao, J., Shahzad, M., Han, Z., Nabi, F., Liu, M., Zhang, D., Li, J., 2014. Seroprevalence of Toxoplasma gondii infection in yaks (Bos grunniens) on the Qinghai–Tibetan Plateau of China. Vet. Parasitol. 205, 354–356. Liu, J., Cai, J., Zhang, W., Liu, Q., Chen, D., Han, J., Liu, Q., 2008. Seroepidemiology of Neospora caninum and Toxoplasma gondii infection in yaks (Bos grunniens) in Qinghai, China. Vet. Parasitol. 152, 330–332. Liu, Q., Cai, J., Zhao, Q., Shang, L., Ma, R., Wang, X., Li, J., Hu, G., Jin, H., Gao, H., 2011. Seroprevalence of Toxoplasma gondii infection in yaks (Bos grunniens) in northwestern China. Trop. Anim. Health. Prod. 43, 741–743. Ma, C., 2008. Study on sustainable development strategies of Tianzhu white yak industry. Acta Ecol. Anim. Domast. 29, 133–135, in Chinese. Niu, C.E., Zhang, L.P., Gao, Y.Q., Cao, J.M., Liang, C.N., Wei, Y.X., 2010. Study of quality characteristic about fur in Tianzhu white yak. Genet. Breed. 46, 16–18, in Chinese. Qin, S.Y., Cong, W., Liu, Y., Li, N., Wang, Z.D., Zhang, F.K., Huang, S.Y., Zhu, X.Q., Liu, Q., 2014. Molecular detection and genotypic characterization of Toxoplasma gondii infection in bats in four provinces of China. Parasit. Vectors 7, 558. Wang, L., Chen, H., Liu, D., Huo, X., Gao, J., Song, X., Xu, X., Huang, K., Liu, W., Wang, Y., Lu, F., Lun, Z.R., Luo, Q., Wang, X., Shen, J., 2013. Genotypes and mouse virulence of Toxoplasma gondii isolates from animals and humans in China. PLoS One 8, e53483. Wang, M., Wang, Y.H., Ye, Q., Meng, P., Yin, H., Zhang, D.L., 2012. Serological survey of Toxoplasma gondii in Tibetan mastiffs (Canis lupus familiaris) and yaks (Bos grunniens) in Qinghai, China. Parasit. Vectors 5, 35.
References Berger-Schoch, A.E., Herrmann,C, Schares, G., Müller, N., Bernet, D., Gottstein, B., Frey, C.F., 2011. Prevalence and genotypes of Toxoplasma gondii in feline faeces
Please cite this article in press as: Qin, S.Y., et al., Seroprevalence, risk factors and genetic characterization of Toxoplasma gondii in free-range white yaks (Bos grunniens) in China. Vet. Parasitol. (2015), http://dx.doi.org/10.1016/j.vetpar.2015.05.015
ARTICLE IN PRESS
VETPAR-7638; No. of Pages 3
Veterinary Parasitology xxx (2015) xxx–xxx
Contents lists available at ScienceDirect
Veterinary Parasitology journal homepage: www.elsevier.com/locate/vetpar
Short communication
Seroprevalence, risk factors and genetic characterization of Toxoplasma gondii in free-range white yaks (Bos grunniens) in China S.Y. Qin a,b,1 , D.H. Zhou a,1 , W. Cong a,b , X.X. Zhang a,b , Z.L. Lou a,b , M.Y. Yin a,c , Q.D. Tan a,d , X.Q. Zhu a,b,∗ a State Key Laboratory of Veterinary Etiological Biology, Key Laboratory of Veterinary Parasitology of Gansu Province, Lanzhou Veterinary Research Institute, Chinese Academy of Agricultural Sciences, Lanzhou, Gansu Province 730046, PR China b College of Animal Science and Technology, Jilin Agricultural University, Changchun, Jilin Province 130118, PR China c College of Veterinary Medicine, Hunan Agricultural University, Changsha, Hunan Province 410128, PR China d College of Animal Science and Technology, Anhui Agricultural University, Hefei, Anhui Province 230000, PR China
a r t i c l e
i n f o
Article history: Received 24 December 2014 Received in revised form 11 May 2015 Accepted 17 May 2015 Keywords: Toxoplasma gondii Seroprevalence Risk factors Genotype White yak Modified agglutination test (MAT)
a b s t r a c t The objective of this study was to determine the seroprevalence, risk factors and genotypes of Toxoplasma gondii in white yaks (Bos grunniens) in China. A total of 974 serum samples were collected from white yaks in Tianzhu Tibetan Autonomous County (TTAC), Gansu province, northwest China for detecting T. gondii antibodies by the modified agglutination test (MAT), and 414 tissues belonging to 138 white yaks were collected for detecting T. gondii DNA by amplification of B1 gene with a semi-nested PCR. A total of 155 serum samples (15.91%) were seropositive for T. gondii antibodies at a 1:100 cut-off, and 10 DNA samples (7.25%) were positive for the T. gondii B1 gene, which were genetically characterized using multilocus PCR-RFLP. Only one genotype (ToxoDB#9) was identified from two samples with complete genotyping results. Statistically significant differences were not observed between T. gondii seroprevalence and gender, season or pregnancy in the logistic regression analysis (P > 0.05). Ages of white yaks was considered as a main risk factor associated with T. gondii infection. Our results indicated a widespread exposure to T. gondii among white yaks, and revealed the genotype ToxoDB#9 of T. gondii in white yaks for the first time in China. © 2015 Elsevier B.V. All rights reserved.
1. Introduction Toxoplasma gondii can infect humans and almost all warmblooded animals causing serious zoonotic toxoplasmosis (Dubey, 2010). Human infection with T. gondii is through consumption of undercooked meat containing T. gondii cysts, or oocysts shed from infected cats. White yak (Bos grunniens) is a unique yak breed living only in Tianzhu Tibetan Autonomous County (TTAC), Gansu Province, northwest China, which is located in the convergence zone among Qing-Tibet Plateau, Loess Plateau and Inner Mongolian Plateau, and the total number of white yaks is approximately 49,000 (Ma, 2008). Tianzhu White yak has been validated as one of 78 significantly protected species by the Ministry of Agriculture of the People’s Republic of China in 2000 (Niu et al., 2010).
∗ Corresponding author. Tel.: +86 931 8342837; fax: +86 931 8342837. E-mail address: [email protected] (X.Q. Zhu). 1 These authors contributed equally to this work.
Surveys regarding T. gondii infection in black yaks have been reported in some regions of China (Liu et al., 2008, 2011; Wang et al., 2012; Li et al., 2014). However, no information is available concerning T. gondii infection in white yaks in China. The objective of the present survey was to investigate the seroprevalence, assess risk factors and identify genotypes of T. gondii in white yaks in TTAC, China.
2. Materials and methods 2.1. The investigation site The present study was carried out in TTAC which is located between longitude 102◦ 07 to 103◦ 46 east and latitude 36◦ 31 to 37◦ 55 north, in the center of Gansu Province, northwestern China. The average temperature of this region is −8 to 4 ◦ C.
http://dx.doi.org/10.1016/j.vetpar.2015.05.015 0304-4017/© 2015 Elsevier B.V. All rights reserved.
Please cite this article in press as: Qin, S.Y., et al., Seroprevalence, risk factors and genetic characterization of Toxoplasma gondii in free-range white yaks (Bos grunniens) in China. Vet. Parasitol. (2015), http://dx.doi.org/10.1016/j.vetpar.2015.05.015
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VETPAR-7638; No. of Pages 3
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Table 1 Seroprevalence and risk factors of Toxoplasma gondii infection in white yaks in Tianzhu Tibetan Autonomous County (TTAC), northwest China by the modified agglutination test (MAT). Factor
Category
No. tested
No. positive
Prevalence (%)
95% CIa
Gender
Male Female
289 685
49 106
16.96 15.47
12.63–21.28 12.77–18.18
Season
Spring Summer Autumn Winter
220 273 231 250
27 56 32 40
12.27 20.51 13.85 16.00
7.94–16.61 15.72–25.30 9.40–18.31 11.46–20.54
Pregnancy
0 1 2 3 4 ≥5
244 109 102 73 53 104
42 21 15 9 8 11
17.21 19.27 14.71 12.33 15.09 10.58
12.48–21.95 11.86–26.67 7.83–21.58 4.78–19.87 5.46–24.73 4.67–16.49
Age (year)b
0 < year ≤ 1 1 < year ≤ 2 2 < year ≤ 3 3 < year ≤ 4 year < 4
115 180 175 128 376
12 23 42 25 53
10.43 12.78 24.00 19.53 14.10
4.85–16.02 7.90–17.66 17.67–30.33 12.66–26.40 10.58–17.61
Total
974
155
15.91
13.62–18.21
a b
95% confidence intervals. This factor is significant in the logistic regression analysis as a risk factor (P < 0.05).
2.2. Serum and tissue samples preparation A total of 974 serum samples were collected randomly from white yaks presented on different farms from June 2013 to April 2014. In addition, 414 tissue samples (138 hearts, 138 livers and 138 lungs) coming from 138 white yaks presented at two local abattoirs were collected between August 2014 and November 2014 for genomic DNA extraction using the TIANamp Genomic DNA kit (TianGen Beijing, China). 2.3. Serological examination and genetic characterization of T. gondii isolates Antibodies to T. gondii were examined using the modified agglutination test (MAT). The detection procedures were carried out as described previously (Costa et al., 2012). Sera with MAT titers of 1:100 or higher were considered positive for T. gondii antibodies (Dubey 2010). DNA samples were examined by a semi-nested PCR targeting the B1 gene, and then genetic characterization of T. gondii isolates from positive samples was conducted with an multilocus PCR-RFLP method, including 11 nuclear loci (i.e., SAG1, 5 - and 3 SAG2, alternative SAG2, SAG3, BTUB, GRA6, c22-8, c29-2, L358, PK1) and an apicoplast locus Apico (Jiang et al., 2014). Genomic DNA samples representing nine reference T. gondii strains (GT1, PTG, CTG, MAS, TgCgCa1, TgCatBr5, TgCatBr64, TgRsCr1 and TgWtdSc40) were used as the positive controls. 2.4. Statistical analysis All the factors (gender, age, pregnancy and sampling season) were studied in a multivariable logistic regression model, and probability (P) value <0.05 was considered as statistically significant between levels within factors and interactions. Odds-ratios (OR) with 95% confidence intervals are calculated. All statistical analyses were performed using SPSS (Release 18.0 standard version, SPSS Inc., Chicago, Illinois). 3. Results and discussion In this study, 15.91% (155/974) of the examined white yaks were seropositive for T. gondii infection by MAT, with titers of 1:100 in 96, 1:200 in 31, 1:400 in 18, 1:800 in 6, 1:1600 in 1, 1:3200 in 1,
1:6400 or higher in 2. Previous studies reported that the seroprevalence of T. gondii in yaks ranged from 8.52% to 35.08% in Qinghai, Tibet and Sichuan provinces, China (Liu et al., 2011; Wang et al., 2012; Li et al., 2014). The differences in seroprevalence among different regions may be due to various detection methods used, ecological and geographical factors including temperature, rainfall, or landscape differences. The T. gondii seroprevalence in white yaks of different genders, pregnancies and ages as well as different sampling seasons is summarized in Table 1. This study found that gender, pregnancies and sampling seasons of examined white yaks were not significant in the logistic regression analysis (P > 0.05) and left out of the final model. Age of white yaks as a continuous variable was analyzed in the logistic regression model, the results showed that yaks of the 2 < years ≤ 3 years old had a 3 times higher risk of being seropositive compared to yaks of the 0 < years ≤ 1 years old (OR = 3.56, 95% CI = 1.50 − 8.44, P = 0.004), although no significant differences were found between other three age groups compared to the 0 < years ≤ 1 age group (P > 0.05), demonstrating that age is a predisposing factor for T. gondii infection. With the growth of white yaks, the seroprevalence of T. gondii increases, indicating that there may be a cumulative likelihood for exposure to T. gondii infection with age. The reason why the lowest prevalence occurred in white yaks below or equal to one year of age may be that the calves was affected slightly by vertical transmission. By comparison, the adult yaks had more opportunities to contact with food and water contaminated by oocysts shed by infected stray cats under the mode of extensive grazing, as they were more active than the calves and the older living in the grassland. A few previous studies characterized T. gondii isolates in cattle in the world, including Type I or III strains in Switzerland (BergerSchoch et al., 2011), Type II in Brazil (de Macedo et al., 2012) and Type I variant in China (Ge et al., 2014). However, there is no report about genotyping of T. gondii in black yaks, nor white yaks. In this study, 10 samples were detected positive for T. gondii B1 gene but only two positive samples were completely genotyped, due to low DNA concentration. It is interesting that only ToxoDB#9 (Chinese 1) was identified from white yaks, suggesting that this genotype may be the predominant genotype in white yaks, and the genetic diversity of T. gondii may be low in TTAC. To drawn a valid conclusion, more samples should be collected from broader geographical localities of TTAC in the future.
Please cite this article in press as: Qin, S.Y., et al., Seroprevalence, risk factors and genetic characterization of Toxoplasma gondii in free-range white yaks (Bos grunniens) in China. Vet. Parasitol. (2015), http://dx.doi.org/10.1016/j.vetpar.2015.05.015
G Model VETPAR-7638; No. of Pages 3
ARTICLE IN PRESS S.Y. Qin et al. / Veterinary Parasitology xxx (2015) xxx–xxx
The genotype ToxoDB#9 is different from the three predominant lineages (Type I–III), as it may generate moderate or high virulence to mice among different isolates with the same genotype (Wang et al., 2013). Although relevant bioassay in mice was not performed in this study, there is still a risk of humans being infected with this zoonotic strain by consuming white yak meat in the surveyed areas. ToxoDB#9 strains have been reported in a variety of animals and humans from several provinces in China, indicating that it is the major lineage in mainland China (Qin et al., 2014; Cong et al., 2015). In the future, it would be interesting to genotype T. gondii isolates from local Tibetans in TTAC to see if humans share the same genotypes with white yaks. In conclusion, the present study revealed a high T. gondii seroprevalence and identified ToxoDB#9 in white yaks in China for the first time. These findings not only extend the host range for T. gondii, but also indicate a potential public health concern that people are at risk of being infected with T. gondii after consumption of undercooked or raw meat from infected white yaks. Competing interests The authors declare that they have no competing interests. Acknowledgments Project support was provided by the Special Fund for Agroscientific Research in the Public Interest (Grant No. 201303037), the National Natural Science Foundation of China (Grant No. 31228022) and the Science Fund for Creative Research Groups of Gansu Province (Grant No. 1210RJIA006). Laboratoire de ParasitologieMycologie, Centre National de Référence de la Toxoplasmose, Centre de Ressources Biologiques Toxoplasma, Hôpital Maison Blanche, Reims Cédex, France, is thanked for providing the Toxoplasma MAT antigen.
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Please cite this article in press as: Qin, S.Y., et al., Seroprevalence, risk factors and genetic characterization of Toxoplasma gondii in free-range white yaks (Bos grunniens) in China. Vet. Parasitol. (2015), http://dx.doi.org/10.1016/j.vetpar.2015.05.015