Vector Competence of Northern California Mosquitoes for Dirofilaria immitis (Spirurida: Onchocercidae)

Dirofilaria immitis, commonly known as dog heartworm, is a dangerous filarial nematode that is transmitted by a mosquito vector. Although this parasite is historically localized to regions closer to the equator, the last few decades have experienced an increase in the amount of dog heartworm cases in Northern California, most notably in Lake and San Joaquin Counties. The primary vector of D. immitis in Northern California is Aedes sierrensis, but it is not prevalent enough in some counties to explain the increase in infections. Because of this, more prevalent and abundant species should be assessed for their ability to transmit heartworm. Culex pipiens complex (wild) and Culiseta incidens (laboratory-raised colonies) were chosen as potential vectors during this study due to their ability to meet several key vector criteria, their relative abundance in the areas of interest, and the fact that they habitually take bloodmeals from domestic dogs. Additionally, Ae. sierrensis colonies were used in this study, based on previous knowledge that they are highly competent vectors. Female mosquitoes were infected with 2.5, 5, or 10 mff/ul of D. immitis-infected blood, and decapitated at 15, 18, and 21 days post-infection. Mosquitoes were subsequently tested via qPCR for the presence and relative quantification of D. immitis DNA. We found that Ae. sierrensis and Cx. pipiens complex were both able to support the development of D. immitis to its infective stage, while Cs. incidens was not a competent vector. We also concluded that including a standard curve of known amounts of D. immitis larvae makes it possible to approximate the intensity of the infection in the mosquito. The identification of these important vectors, and the ability to assess infection intensity, may be helpful in the continued vector control efforts in Northern California and beyond