The lung fluke, Paragonimus westermani (Kerbert, 1878), is widely distribut
ed in Asia, and exhibits much variation in its biological properties. Previ
ous phylogenetic studies using DNA sequences have demonstrated that samples
from north-east Asia form a tight group distinct from samples from south A
sia (Philippines, Thailand, Malaysia). Among countries from the latter regi
on, considerable molecular diversity was observed. This was investigated fu
rther using additional DNA sequences (partial mitochondrial cytochrome c ox
idase subunit 1 (COI) and the second internal transcribed spacer of the nuc
lear ribosomal gene repeat (ITS2)) from additional samples of P. westermani
. Phylogenies inferred from these again found three or four groups within P
. westermani, depending on the method of analysis. Populations of P. wester
mani from north-east Asia use snail hosts of the family Pleuroceridae and d
iffer in other biological properties from populations in south Asia (that u
se snail hosts of the family Thiaridae). It is considered that the populati
ons we sampled can be divided into two species, one in north-east Asia and
the other in south Asia.