O'nyong nyong Virus Molecular Determinants of Unique Vector Specificity Reside in Non-Structural Protein 3

Abstract

O'nyong nyong virus (ONNV) and Chikungunya virus (CHIKV) are two closely related alphaviruses with very different infection patterns in the mosquito, Anopheles gambiae. ONNV is the only alphavirus transmitted by anopheline mosquitoes, but specific molecular determinants of infection of this unique vector specificity remain unidentified. Fifteen distinct chimeric viruses were constructed to evaluate both structural and non-structural regions of the genome and infection patterns were determined through artificial infectious feeds in An. gambiae with each of these chimeras. Only one region, non-structural protein 3 (nsP3), was sufficient to up-regulate infection to rates similar to those seen with parental ONNV. When ONNV non-structural protein 3 (nsP3) replaced nsP3 from CHIKV virus in one of the chimeric viruses, infection rates in An. gambiae went from 0% to 63.5%. No other single gene or viral region addition was able to restore infection rates. Thus, we have shown that a non-structural genome element involved in viral replication is a major element involved in ONNV's unique vector specificity.

Author Summary

O'nyong nyong virus (ONNV) is unique in that it is the only alphavirus, and one of few viruses in general, to be transmitted to humans by the bite of an anopheline mosquito. The genetics responsible for this unique vector specificity would be useful information in helping to develop antivirals, vaccines, and other methods for interrupting virus transmission. Previous research using other arboviruses has shown that specific viral genomic regions, amino acid sequences, or even single nucleotide mutations can have a profound effect on virus growth, infection, and virulence characteristics. Using chimeric viruses that substitute a gene from one virus with a gene from a closely related virus is a proven method of evaluating the relative contribution of each gene to a given phenotype. Our study analyzed both structural and non-structural regions of the ONNV genome using chimeric viruses and artificially infected Anopheles gambiae mosquitoes. When ONNV non-structural protein 3 (nsP3) replaced nsP3 from chikungunya virus in one of the chimeric viruses, infection rates in An. gambiae went from 0% to 63.5%. No other single gene or viral region addition was able to restore infection rates. That ONNV nsP3 is largely responsible for ONNV's unique ability to infect An. gambiae is especially interesting since the exact mechanisms and functions of this highly-variable protein remain poorly understood.