Detection and Determination of Toxoplasma gondii Seroprevalence in Native Korean Goats ( Capra hircus coreanae )

Introduction

T oxoplasma gondii is an obligate intracellular protozoan parasite capable of infecting most warm-blooded animals. Although this parasite causes asymptomatic infections in immunocompetent individuals, it could cause severe and life-threatening disease in immunocompromised people (Tenter et al. 2000). T. gondii has a worldwide distribution associated with the localization of felid family members, which serve as definitive hosts (Sharif et al. 2007, Kamani et al. 2010). Toxoplasmosis is regarded as one of the most prevalent zoonoses, and one-third of the world's population is believed to have had exposure to the parasite (Tenter et al. 2000, Hill et al. 2006).

Toxoplasmosis can be transmitted by ingestion of raw or undercooked meat containing T. gondii tissue cysts, consumption of fresh vegetables or water contaminated with oocysts, or vertically by transmission across the placenta (Dubey 1996, Dubey and Lindsay 2006). Congenital toxoplasmosis is a major cause of abortion and stillbirth in farm livestock, especially sheep and goats, resulting in significant economic losses to the livestock industry (Buxton 1998).

Several serological tests are available for detection of Toxoplasma infection in both humans and animals (Dubey and Lindsay 2006). These include the Sabin–Feldman dye test, indirect hemagglutination assay (IHA), indirect fluorescent antibody test (IFAT), latex agglutination test (LAT), enzyme-linked immunosorbent assay (ELISA), and modified agglutination test (MAT). ELISA was found to be less prone to interlaboratory variation because reading was automated and provided reliable results in identification of serum antibodies against T. gondii and was appropriate for use in epidemiological surveys of Toxoplasma infection in goats (Figueiredo et al. 2001, Hill et al. 2006, Opsteegh et al. 2010).

Seroprevalence of T. gondii infection in goats has been shown to vary, ranging from 0% to 77% among different countries and regions within a country (Tenter et al. 2000, Jittapalapong et al. 2005, Ramzan et al. 2009, Zhang et al. 2010). Native Korean goat (Capra hircus coreanae) is the only breed of goat that is indigenous to Korea; the number of registered native Korean goats is approximately 562,000 (KOSIS 2005). These goats are raised mainly for meat and for use as a natural health supplement. Although T. gondii is considered one of the most important zoonotic protozoa, there is a scarcity of reports on caprine toxoplasmosis in Korea (Youn 2009). Therefore, the purpose of the current study was to detect T. gondii infection and to determine the seroprevalence of the pathogen in native Korean goats.

Materials and Methods

Study area and goat population

The sampling area was divided into three geographical regions (northern, central, and southern) of Korea according to the administrative boundary and the latitude (Fig. 1). The entire study area lies between 34°20′ and 37°11′ North latitude and between 126°07′ and 129°19′ East longitudes with a mean annual temperature of 13.6°C and mean annual precipitation of 1500 mm. The study population consisted of approximately 14,800 goats in 60 herds distributed throughout the entire country. The farming system is semi-intensive, where goats are kept under confinement with a limited grazing time and freedom to move in confinement. Goats are raised for up to 3 years before slaughter for meat. Male goats are usually put on the market after being raised for 1–1.5 years, whereas females are put on the market after being raised for 2 years for gestation.

OPEN IN VIEWER

FIG. 1.

Study areas: Regions of origin of the goat sera samples tested for the presence of anti–T. gondii immunoglobulin G (IgG) antibodies.

Results and Discussion

Among the 610 serum samples analyzed, 31 (5.1%) were found to be seropositive for anti–T. gondii IgG antibodies (Table 1). The result observed in the current study is lower than that of caprine toxoplasmosis reported in Brazil (46.0% by IFAT and 43.0% by ELISA; Carneiro et al. 2009) and Bulgaria (59.8% by IHAT; Prelezov et al. 2008). In addition, the seroprevalence rates reported in other Asian countries like China (31.7% by ELISA and 26.7% by MAT), Thailand, and Pakistan (27.9% and 25.5% by LAT, respectively) were found to be higher than those of the current study (Jittapalapong et al. 2005, Ramzan et al. 2009, Zhang et al. 2010). Our result was also below the previously estimated global average prevalence of 31% (Fayer 1981). However, a lower seroprevalence (4.6%) than that of the current study, based on ELISA, was reported in Nigeria (Kamani et al. 2010). Differences among various countries might be attributed to differences in ecological zones, diagnostic methods used, climate or the number, and spread of final hosts (cats and other felids) in the study areas.

Our findings showing a lower prevalence than the global average suggest the presence of a relatively low number of feral and owned free-roaming cats in the study areas (Dubey and Livingston 1986). In addition, the confined movement and limited grazing farm management system that reduces exposure of goats to an environment contaminated with infectious cat-shed oocysts could have aided in prevention of infection with T. gondii. However, an increase in both the number of feral cats and the prevalence of T. gondii in feral and owned free-roaming cats in large cities of Korea has been reported (Kim et al. 2008, Lee et al. 2011). Considering the potential of a single cat to excrete 10 million resistant oocysts contaminating the environment daily (Lee et al. 2011), the current result could be indicative of the potential risk. In addition, among the 60 herds examined in this study, 23 (38.3%; 95% CI 27.1–51.0) tested positive for anti–T. gondii antibodies (Table 1).

Similar seroprevalence of T. gondii infection was observed between the two age groups of goats (p>0.05) (Table 1). This result was contrary to findings reported in previous studies, which suggest that a longer period of exposure to different risk factors may account for a greater prevalence of toxoplasmosis in adult goats (Figueiredo et al. 2001, Jittapalapong et al. 2005, Carneiro et al. 2009).

Although T. gondii occurs throughout the year, changes in prevalence according to season were investigated. Similar seroprevalence was observed during both the warm (April to September) and cold (October to March) seasons, with no significant difference (Table 1). This finding differs from results obtained from a study conducted in Nigeria in which T. gondii infection was more common during the warm and humid season than during the cold or hot dry season (Kamani et al. 2010). Warm and moist environments favor survival of oocysts outside the host, thus increasing the seroprevalence of T. gondii. Similarities in regional seroprevalence observed in the current study could be due to a lack of variation in weather conditions among most regions of Korea and similarities in management systems of the farms from which the samples were collected.

In conclusion, the current study is the first to evaluate the seroprevalence of anti–T. gondii antibodies in native Korean goats. The results demonstrated that T. gondii infection has a nationwide distribution among goats in Korea. Therefore, implementation of integrated control strategies that are vigilant enough to limit and stop the risks of contamination and transmission from felids such as feral cats as well as measures for prevention and control of T. gondii infection within the goats to prevent human infection during eating of raw or undercooked goat meat for medicinal purposes is recommended.