Genetic polymorphism in Dirofilaria immitis.

Dirofilaria immitis is the causative agent of heartworm disease. Reports of macrocyclic lactone inefficacy prompted an investigation of genetic polymorphism in D. immitis. Currently, there is a lack of genetic information for this parasite. Information on baseline levels of genetic heterogeneity in the dog heartworm would have important implications for the possible development of macrocyclic lactone resistance in D. immitis. Genetic variability was investigated to assess the extent of genetic polymorphism in D. immitis populations from the USA (field and laboratory samples) and Japan (field samples). Single nucleotide polymorphisms (SNPs) were investigated in a full-length β-tubulin gene and segments of genes encoding heat shock protein 60 (Hsp60), a P-glycoprotein (Pgp), sarco-endoplasmic reticulum Ca(2+)ATPase (Serca) and phosphofructokinase (PFK). Significant differences in SNP frequencies were found in all genes except PFK. A combined genotype built from two SNPs from β-tubulin, Hsp60, Pgp and Serca was analyzed in the US lab, US field and Japan field samples. Some combined genotypes were unique to each sample group while others were shared between groups. F coefficients calculated for 15 SNPs from β-tubulin, Hsp60, Pgp and Serca were not in equilibrium. Differences in F coefficients were observed between the groups. D. immitis was found to be genetically heterogeneous. This genetic heterogeneity has implication for the development of genetically selected strains of the parasite.