Pig Ascaris: an important source of human ascariasis in China.

The aim of the present study is to detect the frequency and distribution of cross infection and hybridization of human and pig Ascaris in China. Twenty high polymorphic microsatellite loci were selected to screen 258 Ascaris worms from humans and pigs from six provinces in China. The software programs Structure, Baps and Newhybrids were used to determine the case of cross infection and hybridization of human and pig Ascaris. Results showed that cross infection was detected in all sampled locations and of the total 20 cross infection cases, 19 were indentified as human infections by pure-bred pig type Ascaris in contrast to only one case of pig infection by pure-bred human type Ascaris. Similar to the findings in cross infection, hybrid Ascaris was also detected in all locations and both host species and most of hybrids (95%) were detected from human host. The distribution of cross infection and hybrids showed significant difference between the two host species and among three categories of genotype in terms of G1, G2 and G3, and also between the south and north regions (for hybrids only). The results strongly suggest pig Ascaris as an important source of human ascariasis in endemic area where both human and pig Ascaris exist. In consideration of current control measures for human ascariasis targeting only infected people, it is urgently needed to revise current control measures by adding a simultaneous treatment to infected pigs in the sympatric endemics. The knowledge on cross transmission and hybridization between human and pig Ascaris is important not only for public health, but also for the understanding of genetic evolution, taxonomy and molecular epidemiology of Ascaris.