Emergence of Ancylostoma caninum parasites with the benzimidazole resistance F167Y polymorphism in the US dog population.

BACKGROUND

Anthelmintic resistance to benzimidazole has been detected in the canine hookworm, Ancylostoma caninum. Benzimidazole resistance is believed to have developed originally in greyhounds, but has also been detected in non-greyhound pet dogs. The aim of this study was to validate a probe-based allele-specific real-time PCR tests for the F167Y polymorphism on the β-tubulin isotype-1 gene and to determine the geographic distribution.

METHODS

Allele-specific real-time PCR tests were established and validated to detect the codon 167 polymorphism in the Ancylostoma caninum β-tubulin isotype-1gene. Additionally, real-time PCR tests were validated for Ancylostoma spp. and Uncinaria stenocephala. Two nucleic acid extraction protocols were validated including mechanical disruption of parasite structures in stool. The frequency of the F167Y single nucleotide polymorphism (SNP) was determined in hookworm confirmed stool samples. Samples with the resistant 167Y genotype were confirmed by β-tubulin gene sequencing and allele frequencies were determined.

RESULTS

The Ancylostoma spp. and A. caninum F167Y allele-specific real-time PCR tests were highly sensitive and specific when tested against synthetic DNA, spiked samples, and characterized parasites. Using an optimized total nucleic acid extraction protocol, 54 of 511 (10.6%) were found to contain the benzimidazole resistance allele. All 55 samples containing hookworms with the resistance mutation were confirmed by β-tubulin gene sequencing. The majority of resistant hookworms (44 resistant, 183 tested; 24.4%) originated from Florida, five from California (103 tested, 4.9%), three from Idaho (40 tested, 7.5%), two from Nevada (22 tested, 9.1%), and one sample from Hawaii (13 tested, 7.7%). Resistant genotypes were found in 14 different dog breeds including eight in Greyhounds. Allele-frequency determination revealed resistance allele frequencies between 1 and 100% with 58% above 50%.

CONCLUSIONS

This data strongly supports recent findings of benzimidazole resistant canine hookworms present throughout the general US pet dog population.