Development of a Polymerase Chain Reaction Assay to Assess Host Feeding Habits of Culex Mosquitoes in Fort Worth, Texas

Purpose: West Nile Virus (WNV) is endemic to the United States including Texas. The virus occurs in nature in a mosquito-bird-mosquito transmission cycle but mammals including humans can become incidental hosts. Mosquitoes of the genus Culex are considered the primary vector for WNV. The objective of this research is to develop an assay for detecting the presence of mammalian and/or avian DNA in the blood meal contents of blood-fed mosquitoes. Identifying the hosts and any patterns in feeding habits of the vector mosquitoes can provide more information on the natural transmission of West Nile Virus from avian reservoir hosts to Culex mosquito vectors to incidental mammalian hosts. Methods: Mosquitoes were collected weekly using gravid traps and CO2 light traps throughout Fort Worth. DNA was extracted from the abdomens of blood-fed mosquitoes, and the amount of blood meal was recorded. The DNA was amplified by PCR using universal vertebrate primers designed to generate 150-bp (mammals) or 120-bp (birds) 18S rDNA fragments. The PCR products were analyzed using gel electrophoresis. The PCR assay was confirmed using known mammalian and avian samples. Results: A total of 597 blood-fed mosquitoes were collected throughout Fort Worth in 2014. Results were recorded as avian host only, mammalian host only, or both avian and mammalian hosts. More mosquitoes with a blood meal ≤ 1/3 had no host identified compared to those with larger blood meals. Of those with the host identified, most were avian host only (76% of 292 tested with a host identified) followed by both avian and mammalian hosts (23% of 292) and only 2 of the 292 tested that had a host identified had a mammalian host only. Conclusions: The PCR assay using the universal vertebrate primers targeting 18S rDNA is a sensitive method that allows for the detection of both mammalian and avian host DNA in mosquito blood meals including the presence of both mammalian and avian DNA in a single vector blood meal. The assay will be used to analyze blood meal contents from mosquitoes collected in 2015 in addition to those collected in 2014 to identify any trends in feeding habits.