Insect-transmitted vertebrate viruses: Flaviviridae

Abstract

SUMMARYThe Flaviviridae include almost 70 viruses, nearly half of which have been associated with human disease. These viruses are among the most important arthropod-borne viruses worldwide and include dengue, yellow fever, and Japanese encephalitis viruses. Morbidity and mortality caused by these viruses vary, but collectively they account for millions of encephalitis, hemorrhagic fever, arthralgia, rash, and fever cases per year. Most of the members of this family are transmitted between vertebrate hosts by arthropod vectors, most commonly mosquitoes or ticks. Transmission cycles can be simple or complex depending on the hosts, vectors, the virus, and the environmental factors affecting both hosts and viruses. Replication of virus in invertebrate hosts does not seem to result in any significant pathology, which suggests a close evolutionary relationship between virus and vector. Another example of this relationship is the ability of these viruses to grow in invertebrate ceil culture, where replication usually results in a steady state, persistent infection, often without cytopathic effect. Yields of virus from insect cell culture vary but are generally similar to yields in vertebrate cells. Replication kinetics are comparable between insect and vertebrate ceil lines, despite differences in incubation temperature. Both vertebrate and insect cell culture systems continue to play a significant role in flavivirus isolation and the diagnosis of disease caused by these agents. Additionally, these culture systems permit the study of flavivirus attachment, penetration, replication, and release from cells and have been instrumental in the production and characterization of live-attenuated vaccines. Both vertebrate and insect cell culture systems will continue to play a significant role in basic and applied flavivirus research in the future.

Ocular Manifestations of Emerging Flaviviruses and the Blood-Retinal Barrier

“…Flaviviruses consist of more than 90 RNA-enveloped viruses out of which 30 can cause severe disease in humans and animals. Most members of the family are arthropod-borne and are transmitted to the host by mosquitos or ticks [ 1 ]. The genus flavivirus contains several members which continue to be of global concern such as mosquito-borne Dengue virus (DENV 1–4), West Nile Virus (WNV), Japanese Encephalitis virus (JEV), Yellow fever virus (YFV), Zika virus (ZIKV), Murray Valley Encephalitis Virus (MVEV), Kyasanur Forest Disease virus (KFDV), St. Louis Encephalitis Virus (SLEV) (Fenner’s Veterinary Virology, 5th ed, 2017) along with Tick-borne Encephalitis Virus (TBEV).…”

“…Conformational changes lead to fusion of the host and viral membrane, facilitating the release of the viral genomic RNA. The polypeptide is co- and post-translationally processed by host signalases and virus encoded serine proteases to translate into the ten viral proteins: three structural proteins (Envelope (E), Capsid (C), Pre-Membrane (PrM)) and seven non-structural proteins (NS1, NS2A, NS2B, NS3, NS4A, NS4B and NS5) [ 1 ].…”

NS4/5 mutations enhance flavivirus Bamaga virus infectivity and pathogenicity in vitro and in vivo

“…The emergence of flaviviruses as pathogens may be linked to the naturally high rate of mutations in the genome of RNA viruses, due to the low proof-reading efficiency of the RNA-dependent RNA polymerase [5]. Indeed, flaviviruses are positive-sense, single-stranded RNA viruses with a genome of approximately 11 kilobases (kb), contained in an enveloped icosahedral nucleocapsid [6,7]. The viral RNA contains an open reading frame (ORF) coding for a single polyprotein that is co-and post-translationally cleaved into three structural (capsid (C), membrane precursor (prM) / membrane (M) and envelope (E)), seven non-structural (NS) proteins and the 2K peptide (NS1, NS2A, NS2B, NS3, NS4A, 2K, NS4B, and NS5) [8,9].…”

A New Clade of Insect-Specific Flaviviruses from Australian Anopheles Mosquitoes Displays Species-Specific Host Restriction

“…The genus Flavivirus (family Flaviviridae ) comprises enveloped, positive-sense single-stranded RNA viruses with a genome of approximately 10 to 11 kb contained in an icosahedral nucleocapsid ( 1 – 3 ). The viral RNA has 5′ and 3′ untranslated regions (UTRs) flanking a single open reading frame (ORF) coding for a single polyprotein composed of three structural proteins (capsid, membrane precursor/membrane, and envelope) and seven nonstructural proteins (NS1, NS2A, NS2B, NS3, NS4A, NS4B, and NS5) ( 4 ).…”