Arbovirus interactions with arthropod hosts

Arboviruses such as dengue or chikungunya are an important source of human disease worldwide. Arbovirus infection of insects such as mosquitoes that transmit these viruses is not a passive event but involves virus spreading through the mosquito, and insect defences trying to limit this spread. How these insect defences function is poorly understood, and the focus of our research.
We use model arboviruses to study antiviral mechanisms in mosquito cells and mosquitoes, but research on human pathogenic viruses such as dengue and chikungunya viruses is being established.
Mosquito antiviral control mechanisms can roughly be separated into those mediated by a process called RNA interference, or antimicrobial pathways usually associated with defence mechanisms against bacterial and fungal infections. We investigate how arbovirus infection initiates these mosquito defence mechanisms, how they are regulated, and how they exert their activity. In addition to studies

Arthropod-borne viruses –arboviruses- of the Flaviviridae, Bunyaviridae and Togaviridae families continue to be an important source of human disease worldwide. Infection of insect vectors such as mosquitoes that transmit arboviruses such as dengue and chikungunya is not a passive event but involves virus replication and spread within the insect vector, and induction of immune responses by the vector to control virus replication and subsequently transmission. We have only recently begun to understand the nature of these antiviral immune responses; of key importance are small RNA-based pathways such as RNA interference (RNAi) but other immune responses do take place.
The main aim of this research programme is to further understand arthropod immune responses to arbovirus infection, in particular in the mosquito, and virus/host interactions. We use model alphaviruses such as Semliki Forest virus (SFV; for which we have a powerful reverse genetics system and an important number of molecular tools available) or replicons derived from alpha- and flaviviruses, but research on human pathogenic viruses such as dengue and chikungunya viruses is being established.

A particular focus of this programme is the RNAi response, and how it is induced and regulated in response to arbovirus infection. The classical RNAi response (also termed exogenous RNAi pathway) is based on degradation of viral double-stranded RNA (dsRNA) replication intermediates into 21 nucleotide siRNAs (also called virus-induced small interfering RNAs, or viRNAs) by a nuclease called Dcr-2; viRNA sequences can be determined by high-throughput sequencing. These viRNAs are integrated into a multiprotein complex called RISC, which uses the viRNAs as guide to find and degrade (through a nuclease called Ago-2) RNAs. Using established cell culture models (live mosquitoes are also available if required), we analyse the nature and properties of viRNAs and cellular small RNAs, as well as molecular mechanisms by which enzymes such as Dcr-2 target viral dsRNA, how this leads to degradation of viral RNAs by RISC, and how these processes are regulated. Other immune signalling pathways and processes (Jak/Stat, phenoloxidase cascade etc.) are also of interest to our research. For dengue virus, we moreover aim to look at all interactions of non-structural proteins with mosquito proteins by using high-throughput screening approaches. This will provide additional insights into virus/mosquito interactions.
We hope that this work will give us new clues as to how these virus/vector interactions function and how they determine transmission (ie. vector competence, the ability of a mosquito to transmit a given virus). With the advent of mosquito transgenesis, work on antiviral immunity and virus/host interactions may also suggest new targets in the vector that can be exploited.
In addition to the projects above, an ongoing project aims to better understand dengue virus transmission and epidemiology in parts of Java, Indonesia. This relates to frequency of transmission and disease, as well as climatic and geographical factors (including entomological studies), and typing of dengue viruses from mosquitoes and patient sera. This part of the programme will further our understanding of the factors involved with dengue transmission and help to inform public health policies in time.