Pre-treatment of canine plasma with heat, rather than acid, efficiently enhances Dirofilaria immitis antigen detection

Evaluation of diagnostic techniques for early detection of heartworm in experimentally infected dogs: identification of Dirofilaria immitis-derived microRNA in the initial 28 weeks post-inoculation

BACKGROUND

Dirofilaria immitis, commonly known as heartworm (HW), is a parasitic nematode transmitted by various mosquito species, leading to heartworm disease (HWD) in dogs. Diagnosis of HW typically involves antigen or microfilariae detection, or visualization of adult worms through imaging or post mortem examination. Polymerase chain reaction (PCR) and micro RNA (miRNA) detection have been explored for HW diagnosis.

METHODS

Three dogs, previously experimentally infected with HW, underwent blood sampling every 4 weeks for 7 months. Samples were assessed for antigen presence after heat treatment, PCR amplification, and microfilaria examination using Giemsa-stained thick smears. Additionally, whole blood aliquots underwent miRNA deep sequencing and bioinformatic analysis.

RESULTS

Heartworm antigen was detectable after heat treatment at 20 weeks post-inoculation and via PCR at 24 weeks, with microfilariae observed in peripheral blood smears at 28 weeks. However, deep miRNA sequencing revealed that the miRNA candidate sequences are not consistently expressed before 28 weeks of infection.

CONCLUSIONS

While ancillary molecular methods such as PCR and miRNA sequencing may be less effective than antigen detection for detecting immature larval stages in an early stage of infection, our experimental findings demonstrate that circulating miRNAs can still be detected in 28 weeks post-infection.

Heat Treatment Augments Antigen Detection of Dirofilaria immitis in Apparently Healthy Companion Dogs (3.8% to 7.3%): Insights from a Large-Scale Nationwide Survey across the United States

BACKGROUND

Heartworm disease (HWD) is a vector-borne disease caused by the filarial nematode Dirofilaria immitis. Low antigen levels caused by immune complex formation preclude HWD diagnosis. Heat treatment is an immune complex dissociation technique used to enhance antigen detection. Only a few studies have reported the benefits of heat treatment in nationwide surveys.

METHODS

To investigate the impact of heat treatment on the seroprevalence of HWD in companion dogs in the USA, serum samples (n = 3253) were analyzed for D. immitis antigen (DiroCHEK®, Zoetis) without and with heat treatment of the samples.

RESULTS

Compared to sera without heat treatment, heat treatment significantly increased overall prevalence from 3.8% (123/3253) to 7.3% (237/3253) (p < 10-4), expanding antigen detection from 32 to 39 of the 48 states and Washington District of Columbia included in this study.

CONCLUSIONS

This study represents the largest nationwide survey of HW antigen detection in dogs in the US applying heat treatment to canine sera. The heat treatment used herein has the advantage of requiring a low volume of serum, making it optimal for use in routine diagnosis. Heat treatment should be used routinely by reference laboratories and veterinary clinics in patients with a negative initial test.