Methods for Measuring Natural Dengue Transmission from Humans to Mosquitoes
PI: Amy Morrison (UC Davis) and Louis Lambrechts (Institut Pasteur)
Co-PI: Kanya Long (Andrews University), Thomas Scott (UC Davis)
This proposal represents a first step in assessing- through accurate, field-relevant measures- the extent of heterogeneity in DENV infectiousness to mosquitoes among naturally infected people. This study will establish a rigorous methodology and gain preliminary data in preparation for future studies. Additionally, the study will detennine key epidemiological parameters including the threshold of infection (the minimum viremia required to infect mosquitoes) and 50% oral infectious dose (01050, or viremia resulting in 50% infected mosquitoes) for DENV in Ae. aegypti under natural transmission conditions, provide the first demonstration that people with inapparent DENV infection can contribute to transmission, and establish the validity and acceptability of these methods. Because allowing mosquitos to feed directly on people is potentially objectionable to the community and to institutional review boards (IRB) it is critical to evaluate methodological alternatives. The hypothesis is that indirec, artificial feeding methods an be used as a viable second option when direct feeding is not possible or desirable. The aims of this study are 1) to evaluate the efficiency of direct and indirect feeding methods for infecting field-derived Ae. aegypti mosquitoes with DENV; 2) to demonstrate that people with inapparent DENV infections can transmit virus to mosquitoes; and 3) to ascertain community attitudes about allowing mosquitoes to feed directly on DENV infected people. To accomplish these aims, ongoing passive and active febrile surveillance studies will be leveraged to identify clinically apparent dengue cases that can participate in mosquito feeding protocols and can trigger contact cluster investigations that effectively capture individuals positive for DENV antigen or RNA by NS1 or PCR, including inapparent or mild disease cases, for enrollment in feeding protocols. Viremic participantswill provide tubes of blood with no additive and with EDTA for exposure to mosquitoes in an artificial feeder and will have mosquitoes feed directly on their arms or legs. Mosquitoes will be held for 14 days in a secure insectary. Heads and bodies will be tested for DENV infection and dissemination by PCR, and virus in heads quantified by FFA and qPCR. This data will provide critical information necessary to predict the impact of vaccine and vector control interventions and to determine the contribution of inapparent and mild infections to DENV transmission, addressing one of the largest knowledge gaps in our understanding of DENV epidemiology.