Discovery of a novel double-stranded DNA virus associated with ant labial gland disease reveals its long-term interaction with ants

Large double-stranded DNA (dsDNA) viruses have been shown to have a wide host range in insects. However, their infection in ants has not yet been described. In this study, we report the identification of a novel filamentous virus, Camponotus japonicus labial gland disease virus (CjLGDV), from the enlarged labial glands of Camponotus japonicus . Transmission electron microscopy revealed numerous non-enveloped nucleocapsids in the nuclei and enveloped envelopment intermediates in the cytoplasm of infected gland cells. Genome sequencing analysis showed that CjLGDV possesses a circular dsDNA genome of 142 kb. Comparative analysis identified a closely related virus from Anoplolepis gracilipes, which was named Anoplolepis gracilipes labial gland disease virus (AgLGDV). CjLGDV and AgLGDV have common genomic characteristics and key conserved genes with the viral members in the order Lefavirales , class Naldaviricetes , as well as additional genes uniquely shared with Apis mellifera filamentous virus (AmFV) and AmFV-like virus (AmFLV). Phylogenetic analysis places CjLGDV and AgLGDV in a distinct lineage within Naldaviricetes , probably representing two members of a novel virus family distantly related to AmFV and AmFLV. By mining public databases, LGDV-related endogenous viral elements were identified in the genomes of multiple ant species, suggesting widespread viral gene integration and a deep evolutionary association between these viruses and their ant hosts. Collectively, our findings reveal a previously unrecognized group of ant-infecting viruses that represents a new viral family within the order Lefavirales , class Naldaviricetes . IMPORTANCE Ants, as highly eusocial insects, play vital roles in ecosystems worldwide. While numerous RNA viruses have been documented in ants, no double-stranded DNA (dsDNA) virus has previously been confirmed to infect them. Labial gland disease, reported for decades, lacks a clearly defined cause until now. Here, we identify and characterize a large filamentous dsDNA virus, Camponotus japonicus labial gland disease virus (CjLGDV), from the swollen labial gland of C. japonicus , and a closely related Anoplolepis gracilipes labial gland disease virus in A. gracilipes . Phylogenetic and genomic analyses of the two viruses support the establishment of a new viral family within the order Lefavirales , class Naldaviricetes . The discovery of endogenous viral elements related to CjLGDV in multiple ant genomes suggests the historical infection of CjLGDV-like viruses in ants. These findings broaden the known host range of naldaviricetes and shed new light on the diversity, evolution, and host interaction of large dsDNA viruses in arthropods.