Trichinella spiralis: genetic evidence for synanthropic subspecies in sylvatic hosts

Isolates of the nematode genus Trichinella from sylvatic hosts differ in their potential to reproduce in domestic swine. The structure of the genomic DNA from 13 sylvatic isolates from North America and 5 pig isolates, 4 from North America and 1 from Asia, was examined and correlated with the infectivity of the isolate for domestic pigs. DNA restriction fragment length differences, identified by ethidium bromide staining and by hybridization with 32P-labeled ribosomal RNA, served as molecular markers to classify each isolate. All 5 pig isolates and 8 of 13 sylvatic isolates had a high infectivity and reproductive capacity in pigs. All isolates that were highly infectious for pigs regardless of host origin had similar DNA characteristics and were classified operationally as T. spiralis spiralis (pig) and those of the second group as T. spiralis ssp. A DNA clone of repetitive DNA from T. s. spiralis, pBP2, was selected from a library of genomic DNA in plasmid pUC8. When used as a probe, pBP2 hybridized only to the DNA of T. s. spiralis isolates, thus making it a useful diagnostic reagent to predict whether new isolates are highly infectious for pigs (i.e., T. s. spiralis). These results show that T. s. spiralis occurs in wild mammals and this should be considered a serious obstacle to efforts to eradicate trichinellosis from domestic swine.