Molecular and serological diagnosis of Dirofilaria immitis in companion animals, USA

Abstract

Heartworm Disease (HWD) is caused by the nematode Dirofilaria immitis; a zoonotic infectious agent that affects companion animals and is transmitted by mosquito vectors. The diagnosis of HWD can be achieved by the combination of diagnostic tests, evaluation the presence of circulating antigens derived from adult worms, circulating microfilaria, antibodies, nucleic acids, imaging diagnostics or the demonstration of the parasites during surgical intervention or postmortem examination. The focus of this dissertation is the molecular and serological diagnosis of HWD in companion animals. An extensive literature review is presented in the first chapter. The second chapter described the largest nationwide molecular survey in companion dogs and cats, using convenient samples submitted for molecular diagnostics of Hepatozoon or Feline Infectious Peritonitis. Additionally, a molecular survey for Dirofilaria repens was performed yielding negative results. The molecular prevalence of HW in dogs and cats resembled the reported distribution by the Companion Animal Parasite Council (CAPC) prevalence maps. A third chapter evaluated the presence of antibodies and the novel use of acid treatment as an immune-complex dissociation (ICD) in a large-scale sample pool from apparently healthy companion cats. A prevalence of 3.5% markedly contrasted with the previously reported data. The acid treatment ICD was inconsistent. A detailed quantitative analysis of ICD methods was performed in the fourth chapter, demonstrating the superiority of heat treatment over other ICD methods. The practical application was presented in the fifth chapter, with a marked increase of the prevalence of HW after heat treatment in a nationwide survey on companion dogs. Finally, the sixth chapter compared different diagnostic methods in early HW infection, on samples from experimentally infected dogs. Antigen testing is the test of choice for early HW diagnosis. A novel approach through miRNA deep sequencing and bioinformatics analysis was intended without favorable results. In conclusion, serological and molecular diagnostic techniques for HWD can be improved by optimization of existing protocols and the routine implementation of ICD techniques in cases with inconsistent results.