Document Type

MS Thesis

Publication Date



Infection with heartworm (Dirofilaria immitis), is a significant cause of disease in companion animals worldwide. Macrocyclic lactones (MLs) have been the standard treatment for heartworm prevention for the last 25 years. Although widely used and highly effective, recent studies have shown a potential loss of efficacy. Investigations suggest the involvement of a single-nucleotide polymorphisms (SNPs) of a gene encoding a fragment of P-glycoprotein (P-gp) within the Dirofilaria. immitis genome. This reveals a potential relationship between SNP frequencies within the P-gp gene and ML resistance. The prevalence of heartworm infection in the Cumberland Gap Region (CGR) is reported to be 2.73% based on dogs tested at veterinary clinics. This may underrepresent the true prevalence of infection because up to 55% of pet dogs in the area do not receive regular veterinary care. The goal of this study was to obtain a more accurate estimate of the true prevalence of heartworm infection and the microfilaremic status of infected canine hosts and survey the population of D. immitis infecting dogs in the CGR for the existence of the single nucleotide polymorphism within P-glycoprotein and to. We found an overall prevalence in the CGR of 5.04%, higher than what was reported. Additionally, we did not find the GG-GG genotype that is suspected to be involved with ML resistance, but we did find a SNP of GA-GG at the loci of interest.


This thesis is submitted to LMU Institutional Repository by Dr. Charles Faulkner (Major Professor) on behalf of Ms Hailey Watlington (6/25/2024).