Molecular Characterization of Usutu Virus Infection by Application of Novel Reporter Viruses

Abstract

The past decade has demonstrated the capacity of emerging viruses to cause global health crises and the necessity of early characterization of these viruses. Arthropod-borne flaviviruses, including dengue viruses (DENVs), West Nile virus (WNV), Zika virus (ZIKV), and yellow fever virus (YFV), are of particular concern, causing over 400 million infections annually. This number is only projected to rise in the absence of further intervention due to rising global temperatures making new environments conducive to mosquito habitation. Some flaviviruses such as DENV and YFV have been extensively characterized, leading to the development of robust vaccines and treatments. Other emerging flaviviruses remain direly understudied, including some that have demonstrated the ability to infect human hosts. One such example is Usutu virus (USUV), an emerging Culex mosquito-borne flavivirus that has been documented to infect several avian and mammalian species. USUV primarily circulates in European countries, having caused mass fatalities in Eurasian blackbird populations. Instances of human infection are typically asymptomatic or associated with mild symptoms; however, neurotropic infection has been observed in immunocompromised hosts. Methods of USUV prevention and treatment have yet to be established and little is known regarding how USUV establishes infection in mammalian hosts. Therefore, we have established a method for the generation and characterization of different USUV reporter viruses, expressing fluorescent (USUV-mScarlet), luminescent (USUV-Nluc) proteins, or flippase recombinase (USUV-Flp). These reporter viruses have utility for identifying the cellular reservoirs of USUV and analyzing the spatio-temporal dynamics of the infection.