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Dirofilaria immitis is a mosquito-borne parasite that causes dog heartworm disease, effecting over 100,000 dogs in the United States each year (CAPC - Parasite Prevalence Maps., 2021). Increased disease reports are commonly attributed to an increase in the local mosquito vector population. Since 2013, dog heartworm disease cases have increased by approximately 21% in the United States as reported by the American Heartworm Society. During the same time, invasive mosquitoes belonging to the genus Aedes have been found in Southern California and spread to other areas. The purpose of our research was to determine the prevalence of Dirofilaria immitis (D. immitis), the parasite that causes dog heartworm, in invasive Aedes aegypti and Aedes albopictus and in native Culiseta incidens. The Greater Los Angeles Mosquito and Vector Control District (GLAMVCD) collected Aedes mosquitoes and placed them into pools of 10-50 mosquitoes, separated by species and location collected. These pools were sent to the University of California at Davis for viral testing of West Nile virus, Zika, Chikungunya, Dengue and western equine encephalomyelitis. Pools negative for these viruses were then sent to the Thiemann laboratory for D. immitis-specific testing by polymerase chain reaction (PCR). Culiseta incidens mosquitoes were sent directly to the Thiemann laboratory at the University of the Pacific, where heads/thoraces were separated from the abdomen and placed into pools. The heads/thoraces were tested by PCR to specifically test for infective stage L3 filarial larvae. Dirofilaria immitis was detected in all three mosquito species tested. Of the 403 pools tested and 153 locations, D. immitis was detected across 12 cities. Aedes aegypti was collected in the highest number (n=4017) with a minimum infection rate (MIR) of 1.982, Aedes albopictus (MIR = 4.292) was least sampled (n=233), and the MIR for Culiseta incidens (n=1740) was 2.874. All Ae. aegypti positive pools were found between August-October of 2018 although more mosquitoes were collected in 2019. Culiseta incidens pools were only collected between April and June of 2019, with all infected pools detected in June of 2019. Temporal variations require further assessment to better understand filarial prevalence in Southern California. |
