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Mosquito cell lines have been used extensively in research to isolate and propagate arthropod-borne viruses and understand virus-vector interactions. Despite their utility as an in vitro tool, these cell lines are poorly defined and may harbor insect-specific viruses. Accordingly, we screened four commonly-used mosquito cell lines, C6/36 and U4.4 cells from Aedes albopictus, Aag2 cells from Aedes aegypti, and Hsu cells from Culex quinquefasciatus, for the presence of adventitious (i.e. exogenous) viruses. All four cell lines stained positive for double-stranded RNA, indicative of RNA virus replication. We subsequently identified viruses infecting Aag2, U4.4 and Hsu cell lines using untargeted next-generation sequencing, but not C6/36 cells. PCR confirmation revealed that these sequences stem from active viral replication and/or integration into the cellular genome. Our results show that these commonly-used mosquito cell lines are persistently-infected with several viruses. This finding may be critical to interpreting data generated in these systems. Centers for Disease Control and Prevention [U50/CCU116806-01, U01/CK000509-01]; US Department of Agriculture Hatch Funds and Multistate Research Project [CONH00773, NE1443]; National Institute of Health, National Institute of Allergy and Infectious Diseases [AI067380, AI099042]; NIH/NCATS [UL1 TR001082] This work was supported in part by grants from the Centers for Disease Control and Prevention (U50/CCU116806-01 and U01/CK000509-01), the US Department of Agriculture Hatch Funds and Multistate Research Project (CONH00773 and NE1443), and the National Institute of Health, National Institute of Allergy and Infectious Diseases (AI067380, AI099042), and NIH/NCATS (UL1 TR001082).

Productive arbovirus infections require mechanisms to suppress or circumvent the cellular RNA interference (RNAi) pathway, a major antiviral response in mosquitoes. In this study, we demonstrate that two flaviviruses, Dengue virus and Kunjin virus, significantly repress siRNA-mediated RNAi in infected human cells as well as during infection of the mosquito vector Culex quinquefasciatus. Arthropod-borne flaviviruses generate a small structured non-coding RNA from the viral 3′ UTR referred to as sfRNA. Analysis of infections with a mutant Kunjin virus that is unable to generate appreciable amounts of the major sfRNA species indicated that RNAi suppression was associated with the generation of the non-coding sfRNA. Co-immunoprecipitation of sfRNA with RNAi mediators Dicer and Ago2 suggest a model for RNAi suppression. Collectively, these data help to establish a clear role for sfRNA in RNAi suppression and adds to the emerging impact of viral long non-coding RNAs in modulating aspects of anti-viral immune processes.

West Nile virus is similar to most other RNA viruses in that it exists in nature as a genetically diverse population. However, the role of this genetic diversity within natural transmission cycles and its importance to virus perpetuation remain poorly understood. Therefore, we determined whether highly genetically diverse populations are more fit compared to less genetically diverse WNV populations. Specifically, we generated three WNV populations that varied in their genetic diversity and evaluated their fitness relative to genetically marked control WNV in vivo in Culex quinquefasciatus mosquitoes and chickens. Our results demonstrate that high genetic diversity leads to fitness gains in vector mosquitoes, but not chickens.

Corrigendum to “Population variation of West Nile virus confers a host-specific fitness benefit in mosquitoes” [Virology 404 (2010) 89–95] Kelly A. Fitzpatrick , Eleanor R. Deardorff , Kendra Pesko , Doug E. Brackney , Bo Zhang , Edward Bedrick , Pei-Yong Shi , Gregory D. Ebel a,⁎ a Department of Pathology, University of New Mexico School of Medicine, 1 University of New Mexico, MSC-08-4640, Albuquerque, NM 87131, USA b Wuhan Institute of Virology, Chinese Academy of Sciences, Xiao Hong Shan Zhong Qu 14, Wuhan, Hubei 430071, PR China c Division of Epidemiology and Biostatistics, Department of Internal Medicine, University of New Mexico School of Medicine, 1 University of New Mexico, MSC-10-5550, Albuquerque, NM 87131, USA d Novartis Institute for Tropical Diseases, 10, Biopolis Rd. #05-01, Chromos 138670, Singapore

Anopheles gambiae are a major vector of malaria in sub-Saharan Africa. Viruses that naturally infect these mosquitoes may impact their physiology and ability to transmit pathogens. We therefore used metagenomics sequencing to search for viruses in adult Anopheles mosquitoes collected from Liberia, Senegal, and Burkina Faso. We identified a number of virus and virus-like sequences from mosquito midgut contents, including 14 coding-complete genome segments and 26 partial sequences. The coding-complete sequences define new viruses in the order Mononegavirales, and the families Flaviviridae, and Totiviridae. The identification of a flavivirus infecting Anopheles mosquitoes broadens our understanding of the evolution and host range of this virus family. This study increases our understanding of virus diversity in general, begins to define the virome of a medically important vector in its natural setting, and lays groundwork for future studies examining the potential impact of these viruses on anopheles biology and disease transmission.