Genetic diversity of the rat lungworm, Angiostrongylus cantonensis, the major cause of eosinophilic meningitis.

Various aspects of the genetics of the rat lungworm, Angiostrongylus cantonensis, are reviewed. This nematode has an XX/XO sex-determination mechanism, with the female having a 2n = 12 (XX) and the male 2n = 11 (XO) chromosome constitution. Allozymes (12 loci) exhibit a low proportion of polymorphic loci (P = .08) and low mean heterozygosity (H = 0.43) in specimens from Hawa'i, and no polymorphism or heterozygosity in specimens from Thailand. The phosphoglucomutase-2 (PGM-2) locus exhibits sex-limited expression, with no detectable enzyme activity in the male worms from either location. Based on the 12 allozyme loci, Nei's genetic distance between the Hawa'i and Thailand isolates is D = 0.03. The p-distance (proportion of nucleotide sites) based on cytochrome c oxidase subunit I (COI) is 3.61% between the Thailand and China isolates as well as between Thailand and Hawa'i isolates, and 0.83% between China and Hawa'i isolates. The partial DNA sequences of the 66 kDa protein gene show a great diversity of haplotypes, indicating both inter- and intra-population variation. Intra-specific sequence variation is also found in the internal transcribed spacer regions. For the small-subunit ribosomal RNA (SSU rRNA) gene, two distinct genotypes have been recorded.