Serological survey of Toxoplasma gondii in Tibetan mastiffs (Canis lupus familiaris) and yaks (Bos grunniens) in Qinghai, China

Background Toxoplasma gondii is an amphixenosis which has extensive hosts. In recent years, the prevalence of T. gondii in China has been reported, while little is known on the survey of T. gondii infection in northwest China, especially in yaks (Bos grunniens) and Tibetan mastiffs (Canis lupus familiaris). The current study survey the infection of T. gondii in Tibetan mastiffs and yaks in Qinghai Province, China. Methods The indirect hemagglutination test (IHAT) was used to examine T. gondii antibodies in 1 795 serums, including 192 Tibetan mastiffs and 1603 yaks in Qinghai Province, China. Results In this study, the seroprevalence of T. gondii infection was 8.52%. Twenty (10.42%) of 192 serums of Tibetan mastiffs and 133 (8.30%) of 1603 serums of yaks were seropositive. The seroprevalence of T.gondii infection in Tibetan mastiffs in breeding farm (1.08%) was lower than that in the field (19.19%), and the difference was statistically significant (P <0.05). The seroprevalence of antibodies to T.gondii in yaks ranged from 5.45% to 13.28% among the four different areas. The seroprevalence in different age groups were determined with apparent association. Conclusions The results indicated that T.gondii infection was prevalent in Tibetan mastiffs and yaks, which have implications for public health in this region. To our knowledge, this is the first seroprevalence survey of Tibetan mastiffs infected by T. gondii in The People’s Republic of China.


Background
Toxoplasma gondii, an obligate intracellular protozoan parasite, is one of the common parasitic infections of man and other warm-blooded animals [1][2][3], which may cause fetal diseases with severe problems, such as abortion, encephalitis, mental retardation and blindness in congenital cases [2]. There are two main routes of infection of T.gondii: through the ingestion of uncooked and raw infected meat, and through the ingestion of the oocysts present in the environment, from the faeces of infected cats [1,4].
Recently, the seroprevalence of T. gondii infection in yaks (Bos grunniens) have been reported in Qinghai Province, northeast of Tibetan Plateau [5,6], while little is known about the infection of T. gondii in Tibetan mastiffs (Canis lupus familiaris), living in high altitude and cold plateaus (over 3000 m above sea level). Tibetan mastiff is a canine species, known as the oldest and most ferocious dog in the world and has been introduced and domesticated into many other countries as pet.
The objectives of the present study were to investigate seroprevalence of T. gondii infection in yaks, as well as in Tibetan mastiffs from Qinghai Province, northwestern China. The control toxoplasmosis of yaks and Tibetan mastiffs reared on farms should be paid more attention to in China.

The sites investigated
The  Table 3, the investigation revealed that the prevalence in female animals was 7.86%, and 17.31% in male animals, but the difference was not statistically significant (P >0.05).
A total of 133 serum samples of yaks were seropositive (8.30%). The four counties in Qinghai Province which were tested were all infected by T.gondii ( Table 2). The seroprevalence in male and female yaks was 7.99% and 8.57% (Table 2), but the difference was not statistically significant (P >0.05). As shown in Table 4, the investigation revealed the antibody titers of T.gondii infection in yaks and the prevalence in the age group of ≤1 year was 12.71%, 5.51% in 1-3 years, 9.11% in 4-5 years, and 17.91% in >5 years, and the difference was statistically significant (P <0.05).

Discussion
Nearly one third of the global human population has been reported infected by T.gondii, but only a small percentage of exposed people show obvious clinical symptoms [7]. By far, toxoplasmosis has been confirmed to occur in dogs [8]. Tibetan mastiffs feed on the uncooked and raw meat, which lead to high potential to be infected by T.gondii. Limited knowledge about the T.gondii infection in Tibetan mastiffs in China is available. In the present study, the seropositivity of Tibetan mastiffs' serum samples (10.42%) was considered higher compared to the results in pet dogs in other provinces and cities of China [9][10][11][12][13]. Indeed, the special geographic environment may also contribute to the high seropositivity. However, the prevalence is lower  The present investigation showed that the overall seropositivity was 8.30% in yaks, which was lower than Qumalai, Nangqian, Zadou, Zhiduo [6] and in a study performed partial areas in Qinghai Province [5], but higher than Tianjun [6]. As we know, yaks free-graze in the pasture, living together with other wild and domesticated animals, which have more chances to ingest T.gondii oocysts through the fecal-oral route. Among the four investigated areas, a higher seropositivity of T.gondii was found in Yushu county, compared with the other three counties (P <0.05). The higher seroprevalence of T.gondii in Yushu is also possibly due to the special geographic environment as explained previously.
A higher prevalence of infection was detected in females when comparing the gender of yaks, but the difference was not statistically significant (P >0.05). The comparison of the ages of yaks showed higher infection in group aged >5 years old ( Table 4). Because of long-term pasture with other animals, older yaks have had more opportunities to be in contact with food contaminated with oocysts. The group of yaks ≤1 year old was ranked as the second highest prevalence of T.gondii. The acquisition by the fetus with T. gondii infection during female bovine pregnancy is also considered as an important factor of contamination. So it may be an indicator of the infection rate of congenital T. gondii in yaks. Although attempts to isolate T. gondii from seropositive cattle were often unsuccessful [18], and a study showed that viable tissue cysts can remain in cattle for up to 1 191 days [19]. So the infected yaks may be an important source of infection for other animals and humans in China.
The meat of yak is mainly consumed by people and other carnivorous animals in Qinghai Province, and under certain condition, it is consumed raw or undercooked. The prevalence of antibodies to T.gondii may affect infection rates in other hosts in the same region, and it was primarily confirmed by epidemiological studies of seropositivity between Tibetan mastiffs and yaks in Yushu and Wulan. In the Tibet plateau, Tibetan mastiffs and yaks are pastured together in the field. Tibetan mastiffs feed on the meat of yaks. Sometimes, the aborted fetuses of these herbivores, instead of deep burial or burning down, were also the food of Tibetan mastiffs. So in this study, the seropositivity of T.gondii in Tibetan mastiffs and yaks in Yushu (P >0.05) and Wulan (P >0.05) has no statistically significant difference, while Tibetan mastiffs in the field were significant higher than those in the breeding farms (P <0.05).

Conclusions
In conclusion, these findings demonstrated Tibetan mastiffs and yaks in Qinghai are exposed to T.gondii infection, and yaks posed a potential risk of human contamination with T. gondii. To our knowledge, this is the first seroprevalence survey of Tibetan mastiffs infected by T. gondii in mainland China. It is necessary to carry out measures to prevent and control T. gondii infection in Tibetan mastiffs and yaks.