557-562 Wang SK.pmd

Toxoplasmosis is caused by the intracellular protozoan Toxoplasma gondii. It is anopportunistic zoonosis in warm-blooded animals and humans, with a worldwide distribution. Toxoplasma gondii dense granule protein 16 (TgGRA16) can modulate some functions in host cells and is considered a significant virulent factor of the parasite. The present study reports sequence variation in TgGRA16 gene among T. gondii strains from different hosts and geographical locations, and the construction of phylogenetic relationships of these T. gondii strains based on sequences of TgGRA16, and analysis of B cell epitopes in TgGRA16. Our results showed that all TgGRA16 gene sequences were 1518 bp and the C+G contents ranged from 52.17% to 52.59%. Sequence variation in the TgGRA16 gene was 0-1.51%. Phylogenetic analysis revealed that TgGRA16 gene sequence could not be used to differentiate the different T. gondii genotypes. Six B cell epitopes were predicted in TgGRA16. These results indicated that TgGRA16 gene is not an ideal marker for studying genetic relationships of T. gondii isolates, but may represent a good vaccine candidate against toxoplasmosis. Toxoplasmosis, a zoonotic disease with a worldwide distribution, is caused by the obligate intracellular pathogen Toxoplasma gondii. This parasite can infect all warmblooded animals and humans (Dubey, 2010; Zhou et al., 2011; Robert-Gangneux et al., 2012). Toxoplasma gondii infection in humans is usually asymptomatic or presents only mild symptoms in immune-competent individuals (Montoya et al., 2004). However, toxoplasmosis in immune-compromised patients or pregnant women may lead to psychiatric disorders, abortion, stillbirth and some other serious health problems or even death (Trees et al., 2005; Mwambe et al., 2013; Khademvatan et al., 2014). In animals, toxoplasmosis may result in abortion and neonatal loss especially in goats and sheep, which cause great economic losses to the livestock industry (Dubey et al., 2005; Dubey, 2010). Toxoplasma gondii infections in humans are acquired mainly through ingestion of cysts in undercooked or raw meat or ingestion of water or food contaminated with sporulated oocysts (Hill et al., 2002, 2013). Nearly one third of the world’s population is reported to be seropositive for T. gondii (Dubey, 2008). However, chemical drugs cannot completely eliminate T. gondii from infected hosts or prevent the parasite from reactivation (Coombs et al., 2002; Innes,