Eilat virus, a unique alphavirus with host range restricted to insects by RNA replication

Abstract

Most alphaviruses and many other arboviruses are mosquito-borne and exhibit a broad host range, infecting many different vertebrates including birds, rodents, equids, humans, and nonhuman primates. Consequently, they can be propagated in most vertebrate and insect cell cultures. This ability of arboviruses to infect arthropods and vertebrates is usually essential for their maintenance in nature. However, several flaviviruses have recently been described that infect mosquitoes but not vertebrates, although the mechanism of their host restriction has not been determined. Here we describe a unique alphavirus, Eilat virus (EILV), isolated from a pool of Anopheles coustani mosquitoes from the Negev desert of Israel. Phylogenetic analyses placed EILV as a sister to the Western equine encephalitis antigenic complex within the main clade of mosquito-borne alphaviruses. Electron microscopy revealed that, like other alphaviruses, EILV virions were spherical, 70 nm in diameter, and budded from the plasma membrane of mosquito cells in culture. EILV readily infected a variety of insect cells with little overt cytopathic effect. However, in contrast to typical mosquito-borne alphaviruses, EILV could not infect mammalian or avian cell lines, and viral as well as RNA replication could not be detected at 37°C or 28°C. Evolutionarily, these findings suggest that EILV lost its ability to infect vertebrate cells. Thus, EILV seems to be mosquito-specific and represents a previously undescribed complex within the genus Alphavirus. Reverse genetic studies of EILV may facilitate the discovery of determinants of alphavirus host range that mediate disease emergence.evolution | Togavirus

Eilat Virus Host Range Restriction Is Present at Multiple Levels of the Virus Life Cycle

“…To extend our previous findings, viral factors responsible for EILV host range restriction at the genomic RNA replication level were investigated (28). The lack of reporter expression following electroporation of synthetically capped EILV genomes suggested a potential role for the 3= UTR, which is critical to alphavirus RNA replication.…”

“…This raises the intriguing possibility that EILV descended from a member of the WEE complex that lost the ability to infect vertebrates as the virus adapted unilaterally to its mosquito host. Several lines of evidence support this hypothesis: (i) antigenic cross-reactivity of EILV with members of WEE complex, SINV, WEEV, and Aura virus (AURAV); (ii) the phylogenetic placement based on the nsP ORF groups EILV within the WEE complex, basal to Whataroa virus (WHATV); and (iii) EILV nsPs and sPs display greater amino acid identity to SINV, WHATV, and AURAV than to other mosquito-borne viruses: nsP1 (71 to 73%), nsP2 (60 to 65%), nsP4 (74 to 77%), capsid (50 to 53%), E1 (49% to 50%), and E2 (40% to 42%) (28). The proposed hypothesis provides an interesting interpretation of these results (28).…”

“…The alphavirus 3= UTR contains a 19-nucleotide (nt) conserved sequence element (CSE) just upstream of the poly(A) tract that serves as a promoter for initiation of negative-strand synthesis and includes binding sites for mosquito and vertebrate proteins that likely facilitate virus replication (32)(33)(34)(35)(36). A previous study showed that the EILV 3= UTR CSE displays considerable sequence identity to that of other mosquitoborne alphaviruses (28). In contrast, the remainder of the EILV 3= UTR shows little sequence or structural identity to SINV ( Fig.…”

Insect-Specific Viruses Detected in Laboratory Mosquito Colonies and Their Potential Implications for Experiments Evaluating Arbovirus Vector Competence

“…This group of viruses is very diverse, representing many different virus families and genera (Togaviridae, Flaviviridae, Bunyaviridae, Rhabdoviridae, Reoviridae, Mesoniviridae, Negevirus) and other still unclassified RNA viruses. [9][10][11][12]14,45,46 Data are lacking on the basic ecology of most insect-specific viruses in nature and their potential effects on mosquito life-history traits and the arboviruses they transmit. When conducting vector competence experiments, investigators should consider screening laboratory mosquito colonies for persistent insectspecific viral infections, and endosymbiotic bacteria, to be aware of potential variables that could alter resulting data sets.…”

“…1 Recent studies have shown that the microbiota of mosquitoes can affect their ability to become infected with and to vector certain pathogens. [2][3][4][5] There is a growing realization that mosquito populations are naturally infected with a wide range of bacteria, 6,7 fungi, 8 and viruses [9][10][11][12][13][14][15] ; and this recognition has raised interest in the potential effects of these microbes on mosquito ecology and on pathogen transmission.…”