Seroprevalence of Toxoplasma gondii in goats in Hunan province, China

Toxoplasma gondii infections are prevalent in animals and humans worldwide. In the present investigation, the seroprevalence of T. gondii in goats was investigated in Hunan province, subtropical China between March 2014 and December 2015. A total of 1,028 serum samples collected from 14 administrative regions of Hunan province were evaluated by the indirect hemagglutination test (IHAT) for the detection of specific antibodies. Antibodies to T. gondii were detected in 124 serum samples (12%). The T. gondii seroprevalence ranged from 1.7% to 19% among different regions in subtropical China, and the differences were statistically significant (p < 0.01). The results of the present survey indicated that T. gondii infection is prevalent in goats in Hunan, which poses a potential risk for human infection with T. gondii in this province.


Introduction
Toxoplasmosis is a zoonotic parasitic disease caused by Toxoplasma gondii, which infects humans and has a worldwide distribution [20]. It has been estimated that approximately one third of the world's population has been infected with T. gondii [8]. It may cause abortion in pregnant women or occasionally toxoplasmic encephalitis or even death in patients with immune-suppression diseases like AIDS, although almost all infected people are asymptomatic [5]. In addition, T. gondii can also infect almost all warm-blooded animals [15].
In goats, the main clinical signs of toxoplasmosis are abortion and perinatal death, causing huge economic losses to the goat industry worldwide [1,4]. In spite of the high seroprevalence of T. gondii reported in goats around the world [3,6,10], little information is available on the seroprevalence of T. gondii in goats in China [9,18,19,21]. In the People's Republic of China, the goat industry constitutes a large agricultural sector and is important in economic development. In addition, in China, goat meat is the most widely produced and consumed meat. Hunan province is one of the largest producers of goats in China. Although T. gondii infection causes major economic losses in goats, its prevalence in subtropical China might be underestimated and neglected. It has yet to be determined whether T. gondii infection is present in goats in Hunan province, subtropical China. Therefore, investigation of T. gondii infection in goats has important implications for the prevention and control of T. gondii infection in animals and humans in this province of subtropical China.
Given this background and the zoonotic significance of T. gondii, the objective of the present investigation was to examine the seroprevalence (animals-level) of T. gondii infection in goats in Hunan province. The results should provide a foundation for the implementation of control strategies against T. gondii infection in goats in this province and elsewhere.

Materials and methods
Hunan province is situated in the central eastern part of mainland China, between the northern latitudes of 24°38 0 -30°08 0 and eastern longitudes of 108°47 0 -114°15 0 . The surface area is 211,800 square km, with a population of more than 71 million. Hunan's climate is subtropical: January temperatures average 3-8°C while July temperatures average around 27-30°C. The average annual rainfall ranges from 1,200 to 1,700 mm. Hunan province is divided into 14 administrative regions (cities), with the city of Changsha as its capital.
A total of 1,028 blood samples were collected from 54 intensive farms in Hunan province between March 2014 and December 2015. The numbers of goats reared on each farm ranged from approximately 100 to 1,000. The serum samples cover almost the whole Hunan province. Healthy goats were randomly selected for blood samples. Samples were then centrifuged at 1,000 g for 10 min, and the serum was collected, frozen, and stored at À20°C until it was assayed.
Serum samples were tested for antibodies against T. gondii by the indirect hemagglutination test (IHAT) viable kit (NY/T 573-2002, Lanzhou Veterinary Research Institute, Chinese Academy of Agricultural Sciences) according to the manufacturer's instructions. The kit is commercially available and has been used for many years in China to detect specific antibodies to T. gondii in goats and other mammals [7,11,13,17]. The serum samples were identified as positive if an agglutination reaction was seen in wells with dilutions of 1:64 or higher.
A multivariable mixed-effects logistic regression model with the farm as a random effect was used. Other variables were introduced as fixed effects in the model. The data were analyzed statistically using the PASW Statistics 18 program (IBM Corporation, Somers, NY); 95% confidence intervals (CI) were given. The value of p < 0.05 was considered statistically significant in the multivariate analysis.
All animals were handled in strict accordance with good animal practices according to the Animal Ethics Procedures and Guidelines of the People's Republic of China, and the study was approved by the Animal Ethics Committee of Central South University.

Results and discussion
Limited information is available for T. gondii infections in goats in China [9,18,19,21]. No survey of the seroprevalence of T. gondii in goats in tropical China has been reported. IHAT is a simple technique for detecting T. gondii antibodies (IgG and IgM) and has been used extensively in many animals in China [7,11,13,17]. Therefore, the present study used IHAT to detect T. gondii antibodies in goats using a commercially marketed kit.
Female goats (12.4%; 95% CI: 10.3-14.6) had higher T. gondii seroprevalence than males (9.9%; 95% CI: 5.1-14.6) (p > 0.05). This finding indicates that T. gondii infection is more likely in females than males. T. gondii seroprevalence in goats was higher in autumn (15.4%; 95% CI: 11.7-19.1), followed by winter (11.4%; 95% CI: 5.3-17.5), but lower in summer (11.3%; 95% CI: 8.4-14) and spring (1.4%; 95% CI: 0-4.2) ( Table 2). These results suggest that T. gondii infection in goats is prevalent all year round. This is likely to be associated with the moist and warm climate in tropical China, which is favorable for survival of the oocysts [14]. The highest prevalence of T. gondii was found in goats older than 4 years (18.2%; 95% CI: 9.6-26.8), followed by goats < 1 year old (15.8%; 95% CI: 11.1-20.5). T. gondii prevalence in different ages of goats ranged from 8.3% (95% CI: 5.2-11.3) to 18.2% (95% CI: 9.6-26.8) ( Table 2) (p > 0.05). The present study indicated that age is a predisposing factor for T. gondii infection, consistent with results in other animals [12,16]. The seroprevalence of Humans can become infected by T. gondii through ingestion of oocyst-contaminated food, water, or undercooked meat. The present results reveal the presence of T. gondii infection in goats in tropical China, indicating contamination of the environment by T. gondii oocysts, which poses a risk of human infection with T. gondii. As a result, further work is required to assess whether the soil and water on goat farms or in other regions in tropical China are also contaminated by T. gondii oocysts [2]. In addition, toxoplasmosis can lead to abortion, stillbirth, and mummification in pregnant goats [1,4]. However, the present dataset could not determine whether or not T. gondii infection can significantly increase the risk of abortion in goats in tropical China. Therefore, further studies are necessary to investigate a potential effect of T. gondii on reproduction in goats.

Conclusions
The results of the present survey indicate that T. gondii infection is prevalent in goats in subtropical China. Therefore, it is imperative to implement integrated control strategies and measures to prevent and control T. gondii infection in goats. This is the first time that infection with T. gondii in goats has been reported in Hunan province.