Molecular Detection of Toxoplasma gondii in the Slaughter Sheep and Goats from Shandong Province,Eastern China

Introduction

T oxoplasma gondii, an obligate intracellular pathogen, is the causative agent of toxoplasmosis (Zhou et al. 2011, Jones et al. 2012). Nearly one-third of the human population is exposed to this parasite (Weiss et al. 2009). Most human infections are asymptomatic but at times the parasite can cause devastating diseases. For example, toxoplasmosis can cause focal brain lesions, coma, and even death in HIV-infected patients (Basavaraju 2016). In addition, this parasite can cause ocular diseases and mental retardation in congenitally infected children (Jones et al. 2018).

In animals, T. gondii infection can not only cause serious reproductive and economic losses, but also result in the potential threat to the public health, since infection is mainly transmitted in humans by consuming uncooked meat or raw milk containing toxoplasma organisms (Schurer et al. 2016). A number of surveys of T. gondii infection in farm animals around the world have confirmed that meat from sheep or goats is one of the most important sources of infection (Bártová et al. 2009, Dubey 2009a, Kamani et al. 2010). In China, some studies have shown the seroprevalence of T. gondii infection in sheep ranged from 4.4% to 29.8% (Liu et al. 2010, Wu et al. 2011, Yang et al. 2013). The prevalence of T. gondii infection in goats has also been investigated in some areas in China, which ranges from 4.96% to 16.3% (Zhao et al. 2011, Xu et al. 2014, Miao et al. 2015, Li et al. 2016).

Previously studies showed that the seroprevalence of toxoplasma infection in children (Qingdao and Weihai, China) and psychiatric patients (Weihai, China) from Shandong province were very high (15.13% and 17.30%, respectively) and logic regression showed that T. gondii infection was associated with raw/undercooked meat (Cong et al. 2015, Meng et al. 2015). However, there have been few reports of T. gondii infection in farm animals, especially sheep and goats in the cities of Weihai, Rizhao, and Yantai (Shandong province, eastern China). Therefore, the objective of this study was to investigate the prevalence of T. gondii infection in the above mentioned areas in Shandong province, eastern China, and the results would help to explore the potential risks for human infection and provide a foundation for the prevention and control of T. gondii infection in farm sheep and goats in these areas and elsewhere.

Materials and Methods

Results and Discussion

Mutton is the main ingredient of hot pots, dumpling, and kebabs in China, and the consumption of undercooked meat containing T. gondii tissue cysts would pose a health risk. Limited information for T. gondii infections in sheep and goats is available in Shandong province, eastern China. The seminested PCR targeting T. gondii B1 gene is a simple technique for detecting T. gondii DNA and has been successfully applied in many investigations of T. gondii infection (Dubey et al. 1996, Muller et al. 1996, Remington et al. 2004). As shown in Table 1, 47 sheep samples and 25 goat samples were found to be T. gondii positive, and the overall prevalence was 10.73% (47/438) and 9.84% (25/254), respectively. Studies in different parts of China have reported different positive rates. In Heilongjiang province, the prevalence in goats and sheep was 3.8% and 3.0%, respectively (Wang et al. 2011). The overall seroprevalence of T. gondii in sheep in Liaoning province was 4.4% (Yang et al. 2013). In Gansu and Qinghai, two northwestern provinces, the prevalence in sheep was 20.3% and 21.33%, respectively (Liu et al. 2015, Yin et al. 2015). Throughout the world, data on the prevalence in sheep and goats show big variations. A study from Portugal found T. gondii antibodies in 33.6% of sheep and 18.5% of goats (Lopes et al. 2013). Another study from Italy found that 49.9% (937/1876) of sheep were seropositive for T. gondii by ELISA tests (Vesco et al. 2007). Serum samples from 600 sheep were randomly collected in South Africa, and the T. gondii seroprevalence was found to be 5.6% (indirect fluorescent antibody) and 4.3% (ELISA), respectively (Samra et al. 2007).

Many factors could affect the prevalence, including climates, animal age, techniques, sample sizes, and even the breed of sheep. In a report from Ghana, sheep and goats sampled from the Coastal Savannah and the Forest zones had a higher seropositivity than that from drier Guinea Savannah zone (Van der Puije et al. 2000). (Kamani et al. 2010) reported that in a survey of 372 sheep and 372 goats from three geopolitical zones of Borno state, Nigeria, and farm location was a factor associated with seropositivity. A study from Pakistan found the animal age as a risk factor associated with T. gondii infection in sheep and goats (Ramzan et al. 2009).

The prevalence of T. gondii in Weihai, Rizhao, and Yantai was 11.69% (36/308), 10.64 (15/141), and 8.64% (21/243), respectively. The difference was not statistically significant (p > 0.05). Supermarket and rural market were selected for T. gondii examination, and the prevalence was 6.84% (29/424) in the supermarkets and 16.04% (43/268) in the rural markets, with significant difference between the two types of markets (p < 0.05) (Table 1). It is noteworthy that the prevalence in farm animals (8.48%) was significantly lower than that in domesticated animals (19.05%) (p > 0.05). Cats are the definitive hosts during the T. gondii life cycle and can transmit the resistant oocysts to the environment when they defecate (Dubey 2009b). The high prevalence in the rural markets and domesticated animals is due to the free-range farming in rural areas, where the livestock have easy access to contaminated water or soil. Some studies have been conducted and showed that T. gondii oocysts were widely distributed in the soil, especially at the areas used as defecation sites by cats (Afonso et al. 2008, Lass et al. 2009). Previous studies showed that lambs fed 20 oocysts each became infected, and adult sheep developed fever and none of them died after given an oral dose of T. gondii oocysts (Buxton et al. 1991, Esteban-Redondo and Innes 1998). Further studies need to be conducted to evaluate the relationship between soil contamination and T. gondii infection in sheep and goats in the aforementioned districts in this study.

In conclusion, this study showed that T. gondii infection is highly prevalent in Shandong province, China. The risk factors significantly associated with T. gondii prevalence are market and the pasturing system on the farms. Therefore, it is necessary to implement integrated strategies, including intensive breeding and efficient management measures, to prevent and control T. gondii infection in sheep and goats in the study regions.