The prevalence of antibodies to Toxoplasma gondii in horses in Changji Hui Autonomous Prefecture , Xinjiang , northwestern China

Toxoplasmosis is a worldwide zoonosis caused by Toxoplasma gondii, which can infect warm-blooded animals and humans. The present study was performed to investigate the seroprevalence of T. gondii in horses in Xinjiang, northwestern China. A total of 637 blood samples were collected from seven regions in Changji Hui Autonomous Prefecture, Xinjiang in 2011 and assayed for T. gondii antibodies using the modified agglutination test (MAT). Risk factors (age, gender, and region) related to seroprevalence were determined by a multivariate logistic regression analysis. A total of 200 horses (31.4%, 95% CI 27.79–35.00) were seropositive for T. gondii. Age, gender, and region present no association with seroprevalence (p>0.05) in the logistic regression analysis. The results indicated that T. gondii is widely prevalent in horses in Xinjiang, northwestern China, representing a serious threat to animal and human health. Therefore, more careful measures should be performed to control and prevent T. gondii infection in horses from Xinjiang, northwestern China.

The prevalence of Toxoplasma gondii in horses in northwestern China

Introduction
Toxoplasma gondii is an important zoonotic intracellular apicomplexan protozoan that can infect humans and nearly all warm-blooded animals worldwide (DUBEY, 2010;MONTOYA & LIESENFELD, 2004;TENTER et al., 2000;SOUSA et al., 2014;CERRO et al., 2014;BARROS et al., 2014).Humans and animals can be infected mainly through the ingestion of tissue cysts from undercooked or raw meat or through the consumption of food or water contaminated with sporulated oocysts shed by infected felids (KIJLSTRA & JONGERT, 2008).Around the world, approximately one-third of the human population has been infected with T. gondii, and it is estimated that nearly 7.88% of the population in China has been exposed to T. gondii (DUBEY, 2010;ZHOU et al., 2011).Toxoplasmosis is typically asymptomatic in healthy individuals but can cause mortality and morbidity in congenitally infected and immunocompromised patients, such as individuals with AIDS (MONTOYA & LIESENFELD, 2004;BELANGER et al., 1999).
Felids are the only recognised definitive hosts of T. gondii, but humans and virtually all warm-blooded species, including horses, can be intermediate hosts (ELMORE et al., 2010).Horses are widely distributed in the Xinjiang Uygur Autonomous Region, serving as an important means of transportation for the local population.Humans may acquire T. gondii infections by consuming improperly cooked horse meat containing tissue cysts (POMARES et al., 2011).In horses, T. gondii infection is generally subclinical; however, atypical clinical symptoms, including fever, ataxia, retinal degeneration and encephalomyelitis, sometimes appear (DUBEY et al., 1999).In China, although there are several serological surveys for T. gondii infection in horses and some Chinese reports were recently summarised (MIAO et al., 2013;YANG et al., 2013), information on horses remains limited in northwestern China.To the best of our knowledge, there has been only one survey performed in Xinjiang, northwestern China, and it took place more than 10 years ago.In that survey, T. gondii antibodies were assayed by IHA, and no positive sample was observed in the 60 serum samples.The aim of the present survey was to examine the prevalence of antibodies against T. gondii in horses in Xinjiang, northwestern China, providing fundamental data for understanding the main transmission routes between animals and humans, as well as preventing and controlling this disease.

Region and samples
Xinjiang Uygur Autonomous Region is located in northwest China, covering an area of approximately 1,660,000Km 2 and occupying approximately one-sixth of the area of China.The climate in this region is typically temperate and monsoonal continental with an annual precipitation of 150 mm, temperature differences between day and night, and abundant sunshine (yearly sunlight exposure of 2500-35000 h).A total of 637 blood samples were collected from August to December in 2011 in Changji Hui Autonomous Prefecture, Xinjiang.In total, 84, 103, 80, 91, 94, 93 and 92 blood samples were obtained from Miao'ergou, Jimusa'er, Hutubi, Qitai, Manasi, Fukang, and Mulei Kazakh Autonomous County, respectively.Information regarding the age, gender and geographic origin of each horse were obtained.The ages of the horses were classified into four groups: foal (0<age≤1, 129 samples), adolescent (1<age≤5, 118 samples), middle-aged (5<age≤10, 326 samples) and elderly (age>10, 64 samples).In total, 248 of the sampled animals were male, and 389 were female.Blood samples were centrifuged at 3000 × g for 5 min.The separated serum samples were stored at -20°C until use.

Serological assay
T. gondii antibodies were detected in serum samples by the modified agglutination test (MAT) as described previously (DUBEY & DESMONTS, 1987).In brief, serum samples were added to 96-well "U" bottomed polystyrene plates and then diluted twofold from 1:25 to 1:3200.Positive and negative control serums were included in each test, and controversial serums were re-tested.Horse sera with MAT titres of 1:25 or higher were considered positive for T. gondii antibodies based on previous studies (YANG et al., 2013;GARCÍA-BOCANEGRA et al., 2012;ALVARADO-ESQUIVEL et al., 2012).

Statistical analysis
Statistical analysis was performed using SAS [Version 8.0] and SPSS [Release 18.0 standard version].The risk factors (age, gender and region) were analysed using multivariable logistic regression models in SPSS.Differences in the seroprevalence of T. gondii-infected male and female horses, among various age groups and regions, were analysed using a Chi square test with SPSS.A value of P<0.05 was considered statistically significant.

Discussion
Age, gender and region were not significant in the logistic regression analysis (P > 0.05), suggesting that age, gender and region were not crucial factors for T. gondii infection, a finding that was consistent with the results of previous studies (MIAO et al., 2013;YANG et al., 2013).The present study showed that all the regions had T. gondii positive horses, and there were no significant differences among the various regions in Changji Hui Autonomous Prefecture, Xinjiang (P > 0.05).Seroprevalence to T. gondii in male horses (28.6%, 95% CI 23.00-34.26)was lower than that in female horses (33.1%, 95% CI 28.48-37.84).Difference was not significant (p>0.05).Similar findings were reportedin a previous study in Portugal (LOPES et al., 2013).Regarding age group, also no association was observed, however the highest prevalence (35.7%, 95% CI 27.39-43.93)was observed in foals.A relatively lower prevalence was observed in older horses (26.6%, 95% CI 15.74-37.38),which was contrary to the result reported in a previous survey in Tunisia (BOUGHATTAS et al., 2011).
The results of the present study indicated a high prevalence of T. gondii in horses in Changji Hui Autonomous Prefecture, Xinjiang, which may represent a potential source of human infection with T. gondii.Therefore, a more targeted approach to address this problem should be executed to control and prevent T. gondii infection in horses from Xinjiang, northwestern China.

Table 1 .
Seroprevalence of Toxoplasma gondii infection in horses in Changji, Xinjiang Uygur Autonomous Region, northwestern China.