Interactions Between Glossina Pallidipes Salivary Gland Hypertrophy Virus and Tsetse Endosymbionts in Wild Tsetse Populations

BackgroundTherefore, tsetse control is considered an effective and sustainable tactic for the control of cyclically transmitted trypanosomosis in the absence of effective vaccines and inexpensive, effective drugs. The sterile insect technique (SIT) is currently used to eliminate tsetse fly populations in an area-wide integrated pest management (AW-IPM) context in Senegal. For SIT, tsetse mass-rearing is a major milestone that associated microbes can influence. Tsetse flies can be infected with micro-organisms, including the primary and obligate Wigglesworthia glossinidia, the commensal Sodalis glossinidius, and Wolbachia pipientis. In addition, tsetse populations often carry a pathogenic DNA virus, the Glossina pallidipes Salivary Gland Hypertrophy Virus (GpSGHV) that hinders tsetse fertility and fecundity. Interactions between symbionts and pathogens might affect the performance of the insect host. MethodsIn the present study, we assessed the possible interaction of GpSGHV and tsetse endosymbionts under field conditions to decipher the bidirectional interactions in different Glossina species. We determined the co-infection pattern of GpSGHV and Wolbachia in natural tsetse populations. We further analyzed the interaction of both Wolbachia and GpSGHV infection with Sodalis and Wigglesworthia density using qPCR. ResultsThe results indicated that the co-infection of GpSGHV and Wolbachia was most prevalent in Glossina austeni and Glossina morsitans morsitans, with an explicit significant negative correlation between GpSGHV and Wigglesworthia infection. GpSGHV infection levels of more than 104 were not observed when Wolbachia infection was present at high density (>108.5), suggesting a potential protective role of Wolbachia against GpSGHV. ConclusionThe result indicates that Wolbachia infection might protect tsetse fly against GpSGHV and the interactions between the tsetse host and its associated microbes are dynamic, likely species-specific and significant differences may exist between laboratory and field conditions.

Involvement of Follicular Patency in the Ovarian Developmental Block in Virus-infected, MdSGHV, House Flies, Musca domestica (Diptera: Muscidae)

The Musca domestica salivary gland hypertrophy virus (MdSGHV) is known to have marked effects on the female Musca domestica L. (or common house fly) reproductive system, particularly regarding the size and functionality of the ovaries. Examination of the terminal ovarian follicles can help determine if and how MdSGHV mechanistically causes the block in ovarian development. In this study, terminal ovarian follicle lengths were measured and monitored for patency using Trypan blue dye staining. We examined the effect of MdSGHV infection on female house fly ovarian follicles and attempted to rescue the diminished ovarian follicles in MdSGHV-infected house flies through the application of a hormonal treatment (i.e., methoprene). Comparison of patency in control saline-injected females, virus-injected females with no methoprene application, and virus-injected females with topical methoprene application revealed that none of the virus-infected flies showed an increase in terminal follicular length beyond stage 3 follicles (staging according to Adams 1974). Additionally, none showed evidence of patency. In control, saline-injected females, we found the threshold length of the terminal follicles for the onset of patency to be 600 µm. When examined at 48, 72, and 96 h post-eclosion, average follicle length for infected females seldom reached 250 µm and they also failed to display patency. Thus, the virus is somehow involved in shutting down the mechanism involved in follicular patency. The lack of patency in infected follicles may also be one of the determining factors preventing vertical transmission of the pathogen.

Interactions Between Tsetse Endosymbionts and Glossina pallidipes Salivary Gland Hypertrophy Virus in Glossina Hosts

Tsetse flies are the sole cyclic vector for trypanosomosis, the causative agent for human African trypanosomosis or sleeping sickness and African animal trypanosomosis or nagana. Tsetse population control is the most efficient strategy for animal trypanosomosis control. Among all tsetse control methods, the Sterile Insect Technique (SIT) is one of the most powerful control tactics to suppress or eradicate tsetse flies. However, one of the challenges for the implementation of SIT is the mass production of target species. Tsetse flies have a highly regulated and defined microbial fauna composed of three bacterial symbionts (Wigglesworthia, Sodalis and Wolbachia) and a pathogenic Glossina pallidipes Salivary Gland Hypertrophy Virus (GpSGHV) which causes reproduction alterations such as testicular degeneration and ovarian abnormalities with reduced fertility and fecundity. Interactions between symbionts and GpSGHV might affect the performance of the insect host. In the present study, we assessed the possible impact of GpSGHV on the prevalence of tsetse endosymbionts under laboratory conditions to decipher the bidirectional interactions on six Glossina laboratory species. The results indicate that tsetse symbiont densities increased over time in tsetse colonies with no clear impact of the GpSGHV infection on symbionts density. However, a positive correlation between the GpSGHV and Sodalis density was observed in Glossina fuscipes species. In contrast, a negative correlation between the GpSGHV density and symbionts density was observed in the other taxa. It is worth noting that the lowest Wigglesworthia density was observed in G. pallidipes, the species which suffers most from GpSGHV infection. In conclusion, the interactions between GpSGHV infection and tsetse symbiont infections seems complicated and affected by the host and the infection density of the GpSGHV and tsetse symbionts.

The Effect of the Musca domestica Salivary Gland Hypertrophy Virus on Food Consumption in Its Adult Host, the Common House Fly (Diptera: Muscidae)

The Musca domestica salivary gland hypertrophy virus (MdSGHV) substantially enlarges the house fly’s salivary glands and prevents or delays ovarian development in its adult host, but the effect that MdSGHV has on the house fly’s food consumption is currently unknown. Using house flies from a laboratory-reared colony, we evaluated the effect of MdSGHV infection on food consumption over a 7-d period. Both treatment (virus-infected) and control (saline-injected) flies were provided with a choice of 8% sucrose solution and 4% powdered milk solution to determine food preferences. Quantities of each solution consumed were measured every 24 h for each fly to measure food consumptions. Infected house flies were shown to consume less overall of both solutions than house flies injected with saline. The largest consumption discrepancy was seen between female house flies. Healthy female flies with developing ovaries continued to consume a sugar and protein diet, whereas infected female flies fed predominantly on a sugar diet. Additionally, infected male and female flies consumed significantly lower quantities of protein and sucrose than control flies. This suggests that MdSGHV has a negative consumption effect (e.g., hunger, starvation) on its host. Thus, differences in food consumption of infected and control flies probably represent differences in the nutritional requirements of flies resulting from viral infection.

The discovery, distribution and diversity of DNA viruses associated with Drosophila melanogaster in Europe

Drosophila melanogaster is an important model for antiviral immunity in arthropods, but very few DNA viruses have been described in association with the Drosophilidae. This has limited the opportunity to use natural host-pathogen combinations in experimental studies, and may have biased our understanding of the Drosophila virome. Here we describe fourteen DNA viruses detectable by metagenomic analysis of 6.5 thousand pool-sequenced Drosophila, sampled from 47 European locations between 2014 and 2016. These include three new Nudiviruses, a new and divergent Entomopox virus, a virus related to Leptopilina boulardi filamentous virus, and a virus related to Musca domestica salivary gland hypertrophy virus. We also find an endogenous genomic copy of Galbut virus, an RNA Partitivirus, segregating at very low frequency. Remarkably, we show that Vesanto virus, a small DNA virus previously described as a Bidnavirus, may be composed of up to 12 segments and represents a new lineage of segmented DNA viruses. Only two of the DNA viruses, Kallithea virus (Nudiviridae) and Vesanto virus (Bidna-virus like) are common, being found in 2% or more of wild flies. The other viruses are rare, with many likely to be represented by a single infected fly in the collection. We find that virus prevalence in Europe reflects that seen in publicly-available datasets, with Kallithea virus and Vesanto virus being commonly detectable in data from wild-caught flies and large population cages, and the others being rare or absent. These analyses suggest that DNA viruses are generally rarer than RNA viruses in D. melanogaster, and may be less likely to persist in laboratory cultures. Our findings go some way to redress the earlier bias toward RNA virus studies in Drosophila, and lay the foundation needed to harness the power of Drosophila as a model system for the study of DNA viruses.