Biochemical genetic relationship of Thailand and Hawaii isolates of Parastrongylus cantonensis (Nematoda: Angiostrongylidae)

Abstract

The genetic relationship of the Thailand and Hawaii isolates (strains) of the rat lungworm Parastrongylus (=Angiostrongylus) cantonensis was investigated by gene-enzyme systems using vertical polyacrylamide slab gel electrophoresis. Six gene-enzyme systems were successfully determined, with each being represented by two presumptive loci. Glucose phosphate dehydrogenase, glucose phosphate isomerase, lactate dehydrogenase, malate dehydrogenase and malic enzyme were monomorphic at both loci, and the respective bands exhibited similar mobility in both isolates implying absence of genetic variation. Of the two phosphoglucomutase loci, the faster-moving locus (PGM-1) was polymorphic in the Hawaii isolate, represented by two alleles, the faster-moving, less common Pgm-1A(allele frequency = 0.36 ± 0.03) and the slower-moving, more common Pgm-1B(allele frequency = 0.64), with heterozygosity of 0.43. PGM-1 was monomorphic in the Thailand isolate, represented by the faster-moving Pgm-1Aallele. The slower-moving PGM-2 locus was invariant, with a single band of enzyme activity, in the female worms of both the Thailand and Hawaii isolates. There was no detectable enzyme activity at this PGM-2 locus in the male worms of both isolates. The non-expression or 'null' PGM-2 phenotype in the male worms was presumed to be sex-limited. Based on the six gene-enzyme systems with a total of 12 presumptive loci, it can be concluded that the Thailand and Hawaii isolates of P. cantonensis are genetically very similar, with a genetic distance of D = 0.03. The very low proportion of polymorphic loci (P = 0.08) in the Hawaii isolate and its absence in the Thailand isolate may be attributed to founder effect (a special type of genetic drift). © 2007 Elsevier Ltd. All rights reserved.