Question: How Flaviviridae family of viruses infects vertebrates?

Context:
(WNV) is a neurotropic flavivirus that cycles between mosquitoes and birds but that can also infect humans, horses, and other vertebrate animals. In most humans, WNV infection remains subclinical. However, 20%-40% of those infected may develop WNV disease, with symptoms ranging from fever to meningoencephalitis. A large variety of WNV strains have been described worldwide
can be parasitized by Ixodid ticks, which may be infected with tick-borne pathogens, like Borrelia spp., Babesia spp., Anaplasma, Rickettsia/Coxiella, and tick-borne encephalitis virus. The prevalence of ticks on birds varies over years, season, locality and different bird species. The prevalence of ticks on different species depends mainly on the degree of feeding on the ground. In Europe, the Turdus spp., especially the blackbird, Turdus merula, appears to be most important for harboring ticks. Birds can easily cross barriers, like fences, mountains, glaciers, desserts and oceans, which would stop mammals, and they can move much faster than the wingless hosts. Birds can potentially transport tick-borne pathogens by transporting infected ticks, by being infected with tick-borne pathogens and transmit the pathogens to the ticks, and possibly act as hosts for transfer of pathogens between ticks through co-feeding.
The dengue viruses (DENVs) are mosquito-borne flaviviruses transmitted by infected Aedes mosquitoes. Illness manifests across a clinical spectrum with severe disease characterized by intravascular volume depletion and hemorrhage. Recent estimates on the burden of DENV infection determined that there are 390 million dengue infections per year, three times the current estimate by the WHO
(WNV), an arbovirus maintained in a bird-mosquito enzootic cycle, can infect other vertebrates including humans
(WNV), a mosquito-borne flavivirus in the Japanese encephalitis antigenic group, has caused sporadic outbreaks in humans, horses and birds throughout many of the warmer regions of Europe for at least 20 years. Occasional cases of West Nile encephalitis have also been associated with infected blood transfusions and organ donations
Dengue is the most important vector-borne disease in many different parts of the world and is expanding into other areas of the globe without hindrance. The morbidity and mortality due to dengue complications are increasing globally at an alarming rate. Although transmission of the dengue virus has been documented in well-characterized areas of Pakistan, its incidence in Khyber Pakhtunkhawa has not been characterized
 A rising incidence of acute hepatitis C virus (HCV) in HIV-infected MSM has been observed since 2000 in Europe, Australia, USA and Asia. Transmission appears to occur through the permucosal rather than the more usual parenteral route. Although often multifactorial, permucosal risk factors can be classified as behavioural (sexual practices and mucosally administered drugs) and biological (HIV and sexually transmitted infections). This review will describe the epidemiology of HCV infection in this cohort. Current and future treatment strategies will also be outlined in the context of novel, orally bioavailable, directly acting antiviral therapies
The genus Flavivirus currently consists of approximately 80 single-strand positive-sense RNA viruses. These replicate in a range of hosts including myriad vertebrate, insect, and tick species. As a consequence of this broad host range, the majority of flaviviruses can be propagated in most vertebrate and insect cell cultures. This ability to infect arthropods and vertebrates usually is essential for maintenance of these viruses in nature. But recently, there has been the discovery of a number of flaviviruses that infect mosquitoes but not vertebrates. It remains largely unknown why certain flaviviruses infect vertebrates and mosquitoes while others infect mosquitoes or vertebrates exclusively
Hepatitis C virus (HCV) transmission among people who inject drugs remains a challenging public health problem. We investigated the risk of HCV transmission by analyzing the direct association of HCV with filters, water to dilute drugs, and water containers
 is a mosquito-borne disease caused by four closely related dengue virus (genus Flavivirus)serotypes (DENV-1–4)
 West Nile viruses are enveloped RNA viruses that belong to genus Flavivirus (family Flaviviridae) and are considered important mosquito-borne viral pathogenic agents worldwide
 (JEV) is a mosquito-borne pathogenic flavivirus responsible for acute viral encephalitis in humans
Hepatitis C virus infection (HCV) is not infrequent among haemodialysis patients. Most published reports suggest that patient-to-patient spread, either directly or indirectly, is the most common mode of transmission in renal units
POWV) is a rare tick-borne agent of encephalitis in North America. Historically, confirmed cases occurred mainly in the northeastern United State
(WNV) is a zoonotic arthropod-borne pathogen with continued geographical expansion in Europe. We present and evaluate data on the temporal, spatial and bird species focus of the WNV surveillance programme in dead wild birds in Great Britain 
YFV) is historically one of the most important viruses to affect human populations. Despite the existence of highly effective vaccines for over 70 years, yellow fever remains a significant and re-emerging cause of morbidity and mortality in endemic and high-risk regions of South America and Africa. The virus may be maintained in sylvatic enzootic/epizootic, transitional and urban epidemic transmission cycles with geographic variation in terms of levels of genetic diversity, the nature of transmission cycles and patterns of outbreak activity.
is a systemic arthropod-borne viral disease of major global public health importance. At least 2.5 billion people who live in areas of the world where dengue occurs are at risk of developing dengue fever (DF) and its severe complications, dengue hemorrhagic fever (DHF) and dengue shock syndrome (DSS). 
 is a mosquito-transmitted infection that poses significant global health risks for travelers and individuals living in the tropics and subtropics.
(WNV) (Flaviviridae: Flavivirus) is transmitted from mosquitoes to birds, but can cause fatal encephalitis in infected humans.
West Nile virus (WNV) is a member of the genus Flavivirus within the Japanese encephalitis antigenic complex. The enzootic virus cycle involves transmission between avian hosts and ornithophilic mosquitoes, whereas humans and horses are considered dead-end hosts
 four major flavivirus clades are transmitted by mosquitoes, ticks, directly between vertebrates or directly between arthropods, respectively, but the molecular determinants of mode of transmission in flaviviruses are unknown. 
 Tick-borne encephalitis virus (TBEV), one of the most prevalent arboviruses in Europe and in many parts of Asia. Transmission of TBEV to humans usually occurs by bite of an infected tick or rarely by ingestion of unpasteurized milk products of infected livestock. 
Most alphaviruses and flaviviruses survive in nature by replicating alternately in a vertebrate host and a hematophagous arthropod (mosquitoes or, for some flaviviruses, ticks). Arthropod vectors acquire the viral infection by biting a viremic host, and after an extrinsic incubation period during which the virus replicates in the vector's tissues, they transmit virus through salivary secretions to another vertebrate host
Western Hemisphere have drawn attention to West Nile virus (WNV) as an international public health problem. Of particular concern has been the ability for the virus to cause outbreaks of disease in highly populated urban centers. Incrimination of Australian mosquito species is an essential component in determining the receptivity of Australia to the introduction and/or establishment of an exotic strain of WNV and can guide potential management strategies. Based on vector competence experiments and ecological studies, we suggest candidate Australian mosquito species that would most likely be involved in urban transmission of WNV, along with consideration of the endemic WNV subtype, Kunjin

Answer: A wide range of about 500 different viruses is transmitted by arthropods such as ticks, mosquitoes and sandflies. These arboviruses multiply in the arthropod vector, and for each virus there is a natural cycle involving vertebrates (various birds or mammals) and arthropods. The virus enters the arthropod when the latter takes a blood meal from the infected vertebrate, and passes through the gut wall to reach the salivary gland where replication takes place. Once this has occurred, 1–2 weeks after ingesting the virus, the arthropod becomes infectious, and can transmit the virus to another vertebrate during a blood meal. Certain arboviruses that infect ticks are also transmitted directly from adult tick to egg (transovarial transmission), so that future generations of ticks are infected without the need for a vertebrate host.