Partitiviruses are segmented, multipartite dsRNA viruses that until recently were only known to infect fungi, plants, and protozoans. Metagenomic surveys have revealed that partitivirus-like sequences are also commonly associated with arthropods. One arthropod-associated partitivirus, galbut virus, is common in wild populations of Drosophila melanogaster. To begin to understand the processes that underlie this virus's high global prevalence, we established colonies of wild-caught infected flies. Infection remained at stably high levels over three years, with between 63-100% of individual flies infected. Galbut virus infects fly cells and replicates in tissues throughout infected adults, including reproductive tissues and the gut epithelium. We detected no evidence of horizontal transmission via ingestion but vertical transmission from either infected females or infected males was ∼100% efficient. Vertical transmission of a related partitivirus, verdadero virus, that we discovered in a laboratory colony of Aedes aegypti mosquitoes was similarly efficient. This suggests that efficient biparental vertical transmission may be a feature of at least a subset of insect-infecting partitiviruses. To study the impact of galbut virus infection free from the confounding effect of other viruses, we generated an inbred line of flies with galbut virus as the only detectable virus infection. We were able to transmit infection experimentally via microinjection of homogenate from these galbut-only flies. This sets the stage for experiments to understand the biological impact and possible utility of partitiviruses infecting model organisms and disease vectors. IMPORTANCE Galbut virus is a recently discovered partitivirus that is extraordinarily common in wild populations of the model organism Drosophila melanogaster. Like most viruses discovered through metagenomics, most of the basic biological questions about this virus remain unanswered. We found that galbut virus, along with a closely related partitivirus found in Aedes aegypti mosquitoes, is transmitted from infected females or males to offspring with ∼100% efficiency and can be maintained in laboratory colonies over years. This efficient transmission mechanism likely underlies the successful spread of these viruses through insect populations. We created Drosophila lines that contained galbut virus as the only virus infection and showed that these flies can be used as a source for experimental infections. This provides insight into how arthropod-infecting partitiviruses may be maintained in nature and sets the stage for exploration of their biology and potential utility.

Serpentoviruses are an emerging group of nidoviruses known to cause respiratory disease in snakes and have been associated with disease in other non-avian reptile species (lizards and turtles). This study describes multiple episodes of respiratory disease-associated mortalities in a collection of juvenile veiled chameleons (Chamaeleo calyptratus). Histopathologic lesions included rhinitis and interstitial pneumonia with epithelial proliferation and abundant mucus. Metagenomic sequencing detected coinfection with two novel serpentoviruses and a novel orthoreovirus. Veiled chameleon serpentoviruses are most closely related to serpentoviruses identified in snakes, lizards, and turtles (approximately 40–50% nucleotide and amino acid identity of ORF1b). Veiled chameleon orthoreovirus is most closely related to reptilian orthoreoviruses identified in snakes (approximately 80–90% nucleotide and amino acid identity of the RNA-dependent RNA polymerase). A high prevalence of serpentovirus infection (>80%) was found in clinically healthy subadult and adult veiled chameleons, suggesting the potential for chronic subclinical carriers. Juvenile veiled chameleons typically exhibited a more rapid progression compared to subadults and adults, indicating a possible age association with morbidity and mortality. This is the first description of a serpentovirus infection in any chameleon species. A causal relationship between serpentovirus infection and respiratory disease in chameleons is suspected. The significance of orthoreovirus coinfection remains unknown.

13Partitiviruses are segmented, multipartite dsRNA viruses that until recently were only known to 14 infect fungi, plants, and protozoans. Metagenomic surveys have revealed that partitivirus-like 15 sequences are also commonly associated with arthropods. One arthropod-associated partitivirus, 16 galbut virus, is extraordinarily common in wild populations of Drosophila melanogaster fruit 17 flies. To begin to understand the processes that underlie this virus's high global prevalence, we 18 established colonies of wild-caught infected flies. Infection remained at stably high levels over 19 three years, with between 63-100% of individual flies infected. Galbut virus infects fly cells and 20 replicates in tissues throughout infected adults, including reproductive tissues and the gut 21 epithelium. We detected no evidence of horizontal transmission via ingestion but vertical 22 transmission from either infected females or infected males was ~100% efficient. Vertical 23 transmission of a related partitivirus, verdadero virus, that we discovered in a laboratory colony 24 of Aedes aegypti mosquitoes was similarly efficient. This suggests that efficient biparental 25 vertical transmission may be a feature of at least a subset of insect-infecting partitiviruses. To 26 study the impact of galbut virus infection free from the confounding effect of other viruses, we 27 generated an inbred line of flies with galbut virus as the only detectable virus infection. We were 28 able to transmit infection experimentally via microinjection of homogenate from these galbut-29 only flies. This sets the stage for experiments to understand the biological impact and possible 30 utility of partitiviruses infecting important model organisms and disease vectors.31 32 Keywords: 33 Drosophila melanogaster, Aedes aegypti, galbut virus, verdadero virus, partitivirus, arthropod, 34 vertical transmission, metagenomics, virus discovery, virome. 35 36 Importance 37 38Galbut virus is a recently discovered partitivirus that is extraordinarly common in wild 39 populations of the model organism Drosophila melanogaster. Like most viruses discovered 40 through metagenomics, most of the basic biological questions about this virus remain 41 unanswered. We found that galbut virus, along with a closely related partitivirus found in Aedes 42 aegypti mosquitoes, is transmitted from infected females or males to offspring with ~100% 43 efficiency and can be maintained in laboratory colonies over years. This represents one of the 44 most efficient means of virus transmission described, and likely underlies the successful spread 45 of these viruses through insect populations. We created Drosophila lines that contained galbut 46 virus as the only virus infection and showed that these flies can be used as a source for 47 experimental infections. This provides insight into how arthropod-infecting partitiviruses may be 48 maintained in nature and sets the stage for exploration of their biology and potential utility. 49 50 51 52Metagenomic surveys of wild organisms have...

Galbut virus (family Partitiviridae) infects Drosophila melanogaster and can be transmitted vertically from infected mothers or infected fathers with near perfect efficiency. This form of super-Mendelian inheritance should drive infection to 100% prevalence, and indeed, galbut virus is ubiquitous in wild D. melanogaster populations. However, on average, only about 60% of individual flies are infected. One possible explanation for this is that a subset of flies are resistant to infection. Although galbut virus-infected flies appear healthy, infection may be sufficiently costly to drive selection for resistant hosts, thereby decreasing overall prevalence. To test this hypothesis, we quantified a variety of fitness-related traits in galbut virus-infected flies from two lines from the Drosophila Genetic Reference Panel (DGRP). Galbut virus-infected flies had no difference in average lifespan and total offspring production compared to their uninfected counterparts. Galbut virus-infected DGRP-517 flies pupated and eclosed faster than their uninfected counterparts. Some galbut virus-infected flies exhibited altered sensitivity to viral, bacterial, and fungal pathogens. The microbiome composition of flies was not measurably perturbed by galbut virus infection. Differences in phenotype attributable to galbut virus infection varied as a function of fly sex and DGRP strain, and differences attributable to infection status were dwarfed by larger differences attributable to strain and sex. Thus, galbut virus infection does produce measurable phenotypic changes, with changes being minor, offsetting, and possibly net-negative.

Bluetongue virus (BTV) is an arthropod-borne, segmented double-stranded RNA virus that can cause severe disease in both wild and domestic ruminants. BTV evolves via several key mechanisms, including the accumulation of mutations over time and the reassortment of genome segments.Additionally, BTV must maintain fitness in two disparate hosts, the insect vector and the ruminant. The specific features of viral adaptation in each host that permit host-switching are poorly characterized. Limited field studies and experimental work have alluded to the presence of these phenomena at work, but our understanding of the factors that drive or constrain BTV's genetic diversification remains incomplete. Current research leveraging novel approaches and whole genome sequencing applications promises to improve our understanding of BTV's evolution, ultimately contributing to the development of better predictive models and management strategies to reduce future impacts of bluetongue epizootics.