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The Effects of Midgut Serine Proteases on Dengue Virus Type 2 Infectivity of Aedes aegypti

Dengue viruses (DENV) cause significant morbidity and mortality worldwide and are transmitted by the mosquito Aedes aegypti. Mosquitoes become infected after ingesting a viremic bloodmeal, and molecular mechanisms involved in bloodmeal digestion may affect the ability of DENV to infect the midgut. We used RNA interference (RNAi) to silence expression of four midgut serine proteases and assessed the effect of each RNAi phenotype on DENV-2 infectivity of Aedes aegypti. Silencing resulted in significant reductions in protease mRNA levels and correlated with a reduction in activity except in the case of late trypsin. RNA silencing of chymotrypsin, early and late trypsin had no effect on DENV-2 infectivity. However, silencing of 5G1 or the addition of soybean trypsin inhibitor to the infectious bloodmeals significantly increased midgut infection rates. These results suggest that some midgut serine proteases may actually limit DENV-2 infectivity of Ae. aegypti.

Received January 16, 2008. Accepted for publication May 18, 2008.

Acknowledgments: We thank Erik Powers for his assistance with mosquito rearing, dissections, and plaque titrations, Cynthia Meredith for maintaining the insectaries, and Dr. James Zumbrunnen for his help with the statistical analysis.

Financial support: These studies were funded by the National Institute of Health (AI-25489) and the Fellowship Training Program (T01/CCT822307) provided by the Centers for Disease Control and Prevention.

^* Address correspondence to Doug E. Brackney, Department of Pathology, University of New Mexico School of Medicine, 1 University of New Mexico, Albuquerque, NM 87131. E-mail: dbrackney{at}salud.unm.edu

Authors’ addresses: Doug E. Brackney, Department of Pathology, University of New Mexico School of Medicine, 1 University of New Mexico, Albuquerque, NM 87131, Tel: 505-272-3326, E-mail: dbrackney{at}salud.unm.edu. Brian D. Foy and Ken E. Olson, Arthropod-borne Infectious Disease Laboratory, Colorado State University, 1692 Campus Delivery, Fort Collins, CO 80523.