An Insect Nidovirus Emerging from a Primary Tropical Rainforest

Zirkel, Florian; Kurth, Andreas; Quan, Phenix-Lan; Briese, Thomas; Ellerbrok, Heinz; Pauli, Georg; Leendertz, Fabian H.; Lipkin, W. Ian; Ziebuhr, John; Drosten, Christian; Junglen, Sandra

CAVV is the first mosquito nidovirus and represents the prototype species of a family in the order Nidovirales that includes features distinct from those established for the Arteriviridae, Roniviridae, and Coronaviridae. Based on morphology, conserved genome motifs, and phylogenetic relationship, CAVV cannot be assigned to one of the established nidovirus families. Further investigations are required to elucidate further details of the CAVV replication apparatus and structural protein functions. It is unknown whether CAVV infection is restricted to mosquitoes or if transmission to other hosts, potentially vertebrates, occurs. It is interesting that CoV has not been detected in insects, but that the typical reservoir hosts-bats for alpha-and beta-CoV and birds for gamma-CoV-are largely insect feeding. Common ancestors of CAVV and CoV may thus have been insect borne and have diverged after independent host switches to bats and birds. This is in contrast to earlier proposals suggesting acquisition of gamma-CoV by birds from bats via raptors (57) but in agreement with hypotheses that emphasize CoV phylogeny and ecological considerations (58) . Moreover, it has been suspected from epidemiological observations that a link between ToV and insects may exist (59) . Even though it has not been confirmed that these viruses are carried by insects, the epidemiological implications of insects suggest at least ecologically relevant contact between the virus and its host. An ancestral existence of nidoviruses in arthropods is also supported by the phylogeny of the Nidovirales CAVV included; phylogenetically basal RoV is hosted by crustaceans, which, like mosquitoes, belong to the phylum Arthropoda. An arthropod host at the root of the Nidovirales tree would provide a parsimonious explanation for host associations of several of the known Nidovirales.