Comparison and implementation of dissection methods for detecting dog heartworm in mosquito vectors

Dirofilaria immitis (Leidy), a domestic dog parasite, is vectored by mosquitoes. Efficient identification of D. immitis vectors is necessary to target species for vector management. Current mosquito screening methods involve separating abdomens, which contain non-infective parasite stages, from heads/thoraces, which contain the infective stage. This study compared traditional dissection methods with an intact mosquito screening protocol that did not involve dissection. Laboratory-reared Aedes aegypti infected with one of two D. immitis strains were dissected at a timepoint post-bloodfeeding when they would harbor either infective (15-day) or non-infective (1, 48 and 72-hour) nematode lifestages. Uninfected Ae. aegypti were dissected and served as negative controls. DNA was extracted from both dissected (head/thorax and abdomen) and intact mosquitoes of each group and samples were screened for D. immitis with qPCR. Dirofilaria immitis was detected in all head/thorax 15-day post-bloodfed samples of the Missouri (MO) strain indicating successful infection. In the 48 and 72-hour post-bloodfed group, D. immitis was detected in the abdomen and intact samples demonstrating that processing intact samples could produce false positives. Of the 1-hour post-bloodfed group, 90% intact and 30% head/thorax samples had detectable D. immitis, which shows D. immitis presence in the foregut following blood ingestion. Mosquitoes infected with the JYD strain generated similar data. Our study has demonstrated the importance of the dissection step and excluding recently bloodfed mosquitoes in D. immitis surveillance efforts. This study has provided methodological improvements for screening mosquitoes for D. immitis vector incrimination and to improve accuracy of surveillance efforts.