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

Institute for Human Infections and Immunity and Department of Pathology, University of Texas Medical Branch, Galveston, TX 77555.
Proceedings of the National Academy of Sciences (Impact Factor: 9.67). 08/2012; 109(36):14622-7. DOI: 10.1073/pnas.1204787109
Source: PubMed


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.

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Available from: Gustavo Palacios, Feb 20, 2015
    • "Similarly, the second, third and fourth unique groups of viruses, also initially identified from the cohort of mosquitoes collected in Cote d'Ivoire, do not replicate in vertebrate cells and phylogenetically could not be assigned to an established bunyavirus genus (Marklewitz et al., 2015, 2013). Viruses that appear only to replicate in a mosquito vector, without the requirement for vertebrates as part of their transmission cycle, have also been identified in other arbovirus families (Cook et al., 2006; Crabtree et al., 2003; Hoshino et al., 2007; Nasar et al., 2012). Recent analysis of these viruses is providing valuable information on the evolution and genetic divergence of individual viral species, and molecular determinants of transmissibility and pathogenesis. "
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    • "The family Togaviridae also includes the genus Rubivirus (Büchen-Osmond, 2006). There are 31 currently recognized alphavirus species that divide into eight phylogenetic groupings with SINV being the type species (Forrester et al., 2012; Nasar et al., 2012). The relatively recent discovery of aquatic alphaviruses that infect fish and Southern Elephant Seal virus, which is likely transmitted by a louse species (La Linn et al., 2001; Villoing et al., 2000; Weston et al., 1999), and the presence of these viruses in basal positions in reported phylogenies suggests an aquatic/oceanic origin for the terrestrial alphaviruses (Forrester et al., 2012). "
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    • "Our in vitro results with heterologous superinfecting viruses do not support this hypothesis. The SINV nsP2/3 cleavage site is identical to that of EILV and its nsP1/2 site differs only by one amino acid; consequently there should be greater exclusion of SINV than of WEEV, whose nsP cleavage sites display greater sequence divergence (Fig. 5) (Nasar et al., 2012). Superinfection with SINV and WEEV resulted in almost identical levels of reduction in virus production and delays in replication kinetics (Figs. 5 and 6). "
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