Salivary Gland Hypertrophy Virus Research Articles

Comparative Analysis of Salivary Gland Proteomes of Two Glossina Species that Exhibit Differential Hytrosavirus Pathologies.

Glossina pallidipes salivary gland hypertrophy virus (GpSGHV; family Hytrosaviridae) is a dsDNA virus exclusively pathogenic to tsetse flies (Diptera; Glossinidae). The 190 kb GpSGHV genome contains 160 open reading frames and encodes more than 60 confirmed proteins. The asymptomatic GpSGHV infection in flies can convert to symptomatic infection that is characterized by overt salivary gland hypertrophy (SGH). Flies with SGH show reduced general fitness and reproductive dysfunction. Although the occurrence of SGH is an exception rather than the rule, G. pallidipes is thought to be the most susceptible to expression of overt SGH symptoms compared to other Glossina species that are largely asymptomatic. Although Glossina salivary glands (SGs) play an essential role in GpSGHV transmission, the functions of the salivary components during the virus infection are poorly understood. In this study, we used mass spectrometry to study SG proteomes of G. pallidipes and G. m. morsitans, two Glossina model species that exhibit differential GpSGHV pathologies (high and low incidence of SGH, respectively). A total of 540 host proteins were identified, of which 23 and 9 proteins were significantly up- and down-regulated, respectively, in G. pallidipes compared to G. m. morsitans. Whereas 58 GpSGHV proteins were detected in G. pallidipes F1 progenies, only 5 viral proteins were detected in G. m. morsitans. Unlike in G. pallidipes, qPCR assay did not show any significant increase in virus titers in G. m. morsitans F1 progenies, confirming that G. m. morsitans is less susceptible to GpSGHV infection and replication compared to G. pallidipes. Based on our results, we speculate that in the case of G. pallidipes, GpSGHV employs a repertoire of host intracellular signaling pathways for successful infection. In the case of G. m. morsitans, antiviral responses appeared to be dominant. These results are useful for designing additional tools to investigate the Glossina-GpSGHV interactions.

Serotonergic Innervation of the Salivary Glands and Central Nervous System of AdultGlossina pallidipesAusten (Diptera: Glossinidae), and the Impact of the Salivary Gland Hypertrophy Virus (GpSGHV) on the Host

Using a serotonin antibody and confocal microscopy, this study reports for the first time direct serotonergic innervation of the muscle sheath covering the secretory region of the salivary glands of adult tsetse fly, Glossina pallidipes Austen. Reports to date, however, note that up until this finding, dipteran species previously studied lack a muscle sheath covering of the secretory region of the salivary glands. Direct innervation of the salivary gland muscle sheath of tsetse would facilitate rapid deployment of saliva into the host, thus delaying a host response. Our results also suggest that the neuronal and abnormal pattern seen in viral infected glands by the Glossina pallidipes salivary gland hypertrophy virus (GpSGHV) is due to a compensatory increased branching of the neurons of the salivary glands, which is associated with the increased size of the salivary glands in viral infected flies. This study shows for the first time serotonin in the cell bodies of the brain and thoracico-abdominal ganglion in adult tsetse, G. pallidipes Austen (Diptera: Glossinidae). A hypothesis is proposed as to whether innervation of the muscle sheath covering of the secretory region of the salivary glands is present in brachyceran compared with nematoceran dipterans; and, a plea is made that more research is needed to develop a blood feeding model, similar to that in the blow flies, for elucidating the various mechanisms involved in production and deployment of saliva.

Disruption of the salivary gland muscle in tsetse, Glossina pallidipes Austen, as a result of salivary gland hypertrophy virus infection.

The secretory region of the salivary glands in Glossina pallidipes Austen (Diptera: Glossinidae) is characterized by an external muscle layer. Scanning electron microscopy and transmission electron microscopy investigations provide a detailed description of the longitudinal muscle fibres and a comparison of their structure when affected by salivary gland hypertrophy virus. The virus is responsible for hypertrophy of the salivary glands in symptomatic flies, specifically of the muscle fibres, the cytoarchitecture of which is completely altered. Although observations did not reveal viral particles in the muscle cells of either asymptomatic or symptomatic flies, muscle fibres were enlarged and detached from one another and their associated basement membrane only in symptomatic flies. A decrease in type IV collagen labelling in the basement membrane of the muscles in symptomatic flies is reported and is considered a potential cause of the salivary gland muscle alteration and, possibly, myopathy. The maintenance of an organized muscular layer is essential for the normal secretion of saliva and hence its pathology in symptomatic tsetse flies could affect the normal transmission of the trypanosome that develops inside the salivary gland epithelium. Therefore, a better understanding of the possible role of the virus is essential in order to elucidate its impact on salivary deployment in symptomatic flies.

Microbiome frequency and their association with trypanosome infection in male Glossina morsitans centralis of Western Zambia

Tsetse flies (Diptera: Glossinidae) are considered primary cyclical vectors that transmit pathogenic trypanosomes in Africa. They harbour a variety of microbes including Wolbachia, Sodalis and the salivary gland hypertrophy virus (SGHV) which are all vertically transmitted. Knowledge on tsetse microbiome and their interactions may identify novel strategies for tsetse fly and trypanosomiasis control. Area-wide application of such strategies requires an understanding of the natural microbiome frequency in the different species and subspecies of Glossina in their geographical populations. Consequently, this study determined the prevalence of Sodalis, Wolbachia, SGHV and trypanosome infections in Glossina morsitanscentralis from two sites of Western Zambia. We also explored possible associations of the microbes with trypanosome infections. Male G. morsitanscentralis samples were collected from two sites (Lyoni and Lusinina) in Western Zambia. The age structure of the flies at each site was determined using the wing fray method. DNA was extracted from the samples and analyzed for Wolbachia, Sodalis, SGHV and trypanosome presence using PCR. Associations and measures of associations between trypanosome infection and microbes in the fly were determined. The flies from the two locations (Lusinina, n=45 and Lyoni, n=24) had a similar age structure with their median fray category not being significantly different (p=0.698). The overall prevalence of Wolbachia was 72.5% (95% CI: 61.6–83.3%), Sodalis was 15.9% (95% CI: 7.1–24.8%), SGHV was 31.9% (95% CI: 20.6–43.2%) and Trypanosoma species was 23.2% (95% CI: 13–33.4%). The prevalence of Wolbachia was significantly higher in Lusinina than Lyoni (p=0.000). However this was not the case for Sodalis, SGHV and Trypanosoma species. Despite the low number of flies that were positive for both trypanosome and Sodalis (6; 8.7%), a statistically significant association (p=0.013; AOR 6.2; 95% CI: 1.5–25.8) was observed in G. morsitanscentralis. The study showed that the prevalence of microbiota may vary within the same species of the tsetse depending on the geographical location as was the case of Wolbachia. Further it showed that infection with Sodalis could affect vector competence. The study concludes that Sodalis could be an ideal candidate for symbiont-mediated trypanosomiasis control interventions in G. morsitanscentralis.

Enhancement of the Musca domestica hytrosavirus infection with orally delivered reducing agents

House flies (Musca domestica L.) throughout the world are infected with the salivary gland hypertrophy virus MdSGHV (Hytrosaviridae). Although the primary route of infection is thought to be via ingestion, flies that are old enough to feed normally are resistant to infection per os, suggesting that the peritrophic matrix (PM) is a barrier to virus transmission. Histological examination of the peritrophic matrix of healthy flies revealed a multilaminate structure produced by midgut cells located near the proventriculus. SEM revealed the PM to form a confluent sheet surrounding the food bolus with pores/openings less than 10nm in diameter. TEM revealed the PM to be multilayered, varying in width from 350 to 900nm, and generally thinner in male than in female flies. When flies were fed on the reducing agents dithiothetriol (DTT) or tris (2-caboxyethyl)phosphine hydrochloride (TCEP) for 48h before per os exposure to the virus, infection rates increased 10- to 20-fold compared with flies that did not receive the reducing agent treatments. PM’s from flies treated with DTT and TCEP displayed varying degrees of disruption, particularly in the outer layer, and lacked the electron-dense inner layer facing the ectoperitrophic space. Both drugs were somewhat toxic to the flies, resulting in>40% mortality at doses greater than 10mM (DTT) or 5mM (TCEP). DTT increased male fly susceptibility (55.1% infected) more than that of females (7.8%), whereas TCEP increased susceptibility of females (42.9%) more than that of males (26.2%). The cause for the sex differences in response to oral exposure the reducing agents is unclear. Exposing flies to food treated with virus and the reducing agents at the same time, rather than pretreating flies with the drugs, had no effect on susceptibility to the virus. Presumably, the reducing agent disrupted the enveloped virus and acted as a viricidal agent. In summary, it is proposed that the reducing agents influence integrity of the PM barrier and increase the susceptibility of flies to infection by MdSGHV.

Epidemiology of MdSGHV in Musca Domestica

Musca domestica salivary gland hypertrophy virus (MdSGHV) is a disease that enlarges the salivary glands of Musca domestica (the common house fly), as well as causes infertility in female house flies. An infected female fly will no longer produce or lay eggs and will refuse a male’s mating attempts. Collaborating with the University of Florida’s Entomology and Nematology Department, we have hypothesized that the virus is primarily transmitted through male-male interactions. The constant interaction between males causes damage to the flies’ cuticle. When the virus is present on the cuticle, this damage allows the virus entry into the hemocoel, which subsequently infects the internal organs and in particular the salivary glands. The virus adheres to the fly cuticle at contaminated resting sites and contaminated feeding sites. Infection per os is another possible mode of transmission but insu cient to sustain the virus in the fly population. For females, MdSGHV seems to be transmitted largely per os with random occurrences of cuticular damage that take place at the contaminated food and resting sites. There is no evidence that females exhibit aggressive behavior, or that mating causes cuticular damage. Vertical transmission does not seem to be a mode of transmission. We developed a system of di↵erential equations to model the transmission of MdSGHV for a population of Musca domestica at Florida dairy farms. The model is based on the above understanding of the transmission of the virus together with some other simplifying

A Mathematic Model That Describes Modes of MdSGHV Transmission within House Fly Populations.

In this paper it is proposed that one potential component by which the Musca domestica salivary gland hypertrophy virus (MdSGHV) infects individual flies is through cuticular damage. Breaks in the cuticle allow entry of the virus into the hemocoel causing the infection. Male flies typically have a higher rate of infection and a higher rate of cuticular damage than females. A model for the transmission of MdSGHV was formulated assuming several potential and recognized means of transmission. The model yields results that are in agreement with field data that measured the infection rate in house flies on dairy farms in Florida. The results from this model indicate that MdSGHV will be maintained at a stable rate within house fly populations and support the future use of MdSGHV as a birth control agent in house fly management.

Interwoven Biology of the Tsetse Holobiont

Microbial symbionts can be instrumental to the evolutionary success of their hosts. Here, we discuss medically significant tsetse flies (Diptera: Glossinidae), a group comprised of over 30 species, and their use as a valuable model system to study the evolution of the holobiont (i.e., the host and associated microbes). We first describe the tsetse microbiota, which, despite its simplicity, harbors a diverse range of associations. The maternally transmitted microbes consistently include two Gammaproteobacteria, the obligate mutualists Wigglesworthia spp. and the commensal Sodalis glossinidius, along with the parasitic Alphaproteobacteria Wolbachia. These associations differ in their establishment times, making them unique and distinct from previously characterized symbioses, where multiple microbial partners have associated with their host for a significant portion of its evolution. We then expand into discussing the functional roles and intracommunity dynamics within this holobiont, which enhances our understanding of tsetse biology to encompass the vital functions and interactions of the microbial community. Potential disturbances influencing the tsetse microbiome, including salivary gland hypertrophy virus and trypanosome infections, are highlighted. While previous studies have described evolutionary consequences of host association for symbionts, the initial steps facilitating their incorporation into a holobiont and integration of partner biology have only begun to be explored. Research on the tsetse holobiont will contribute to the understanding of how microbial metabolic integration and interdependency initially may develop within hosts, elucidating mechanisms driving adaptations leading to cooperation and coresidence within the microbial community. Lastly, increased knowledge of the tsetse holobiont may also contribute to generating novel African trypanosomiasis disease control strategies.

Tsetse fly microbiota: form and function

Tsetse flies are the primary vectors of African trypanosomes, which cause Human and Animal African trypanosomiasis in 36 countries in sub-Saharan Africa. These flies have also established symbiotic associations with bacterial and viral microorganisms. Laboratory-reared tsetse flies harbor up to four vertically transmitted organisms—obligate Wigglesworthia, commensal Sodalis, parasitic Wolbachia and Salivary Gland Hypertrophy Virus (SGHV). Field-captured tsetse can harbor these symbionts as well as environmentally acquired commensal bacteria. This microbial community influences several aspects of tsetse's physiology, including nutrition, fecundity and vector competence. This review provides a detailed description of tsetse's microbiome, and describes the physiology underlying host-microbe, and microbe-microbe, interactions that occur in this fly.

Correlation between structure, protein composition, morphogenesis and cytopathology of Glossina pallidipes salivary gland hypertrophy virus

The Glossina pallidipes salivary gland hypertrophy virus (GpSGHV) is a dsDNA virus with rod-shaped, enveloped virions. Its 190 kb genome contains 160 putative protein-coding ORFs. Here, the structural components, protein composition and associated aspects of GpSGHV morphogenesis and cytopathology were investigated. Four morphologically distinct structures: the nucleocapsid, tegument, envelope and helical surface projections, were observed in purified GpSGHV virions by electron microscopy. Nucleocapsids were present in virogenic stroma within the nuclei of infected salivary gland cells, whereas enveloped virions were located in the cytoplasm. The cytoplasm of infected cells appeared disordered and the plasma membranes disintegrated. Treatment of virions with 1 % NP-40 efficiently partitioned the virions into envelope and nucleocapsid fractions. The fractions were separated by SDS-PAGE followed by in-gel trypsin digestion and analysis of the tryptic peptides by liquid chromatography coupled to electrospray and tandem mass spectrometry. Using the MaxQuant program with Andromeda as a database search engine, a total of 45 viral proteins were identified. Of these, ten and 15 were associated with the envelope and the nucleocapsid fractions, respectively, whilst 20 were detected in both fractions, most likely representing tegument proteins. In addition, 51 host-derived proteins were identified in the proteome of the virus particle, 13 of which were verified to be incorporated into the mature virion using a proteinase K protection assay. This study provides important information about GpSGHV biology and suggests options for the development of future anti-GpSGHV strategies by interfering with virus-host interactions.

The Antiviral Drug Valacyclovir Successfully Suppresses Salivary Gland Hypertrophy Virus (SGHV) in Laboratory Colonies of Glossina pallidipes

Many species of tsetse flies are infected with a virus that causes salivary gland hypertrophy (SGH) symptoms associated with a reduced fecundity and fertility. A high prevalence of SGH has been correlated with the collapse of two laboratory colonies of Glossina pallidipes and colony maintenance problems in a mass rearing facility in Ethiopia. Mass-production of G. pallidipes is crucial for programs of tsetse control including the sterile insect technique (SIT), and therefore requires a management strategy for this virus. Based on the homology of DNA polymerase between salivary gland hypertrophy virus and herpes viruses at the amino acid level, two antiviral drugs, valacyclovir and acyclovir, classically used against herpes viruses were selected and tested for their toxicity on tsetse flies and their impact on virus replication. While long term per os administration of acyclovir resulted in a significant reduction of productivity of the colonies, no negative effect was observed in colonies fed with valacyclovir-treated blood. Furthermore, treatment of a tsetse colony with valacyclovir for 83 weeks resulted in a significant reduction of viral loads and consequently suppression of SGH symptoms. The combination of initial selection of SGHV-negative flies by non-destructive PCR, a clean feeding system, and valacyclovir treatment resulted in a colony that was free of SGH syndromes in 33 weeks. This is the first report of the use of a drug to control a viral infection in an insect and of the demonstration that valacyclovir can be used to suppress SGH in colonies of G. pallidipes.

Prevalence and genetic variation of salivary gland hypertrophy virus in wild populations of the tsetse fly Glossina pallidipes from southern and eastern Africa

The Glossina pallidipes salivary gland hypertrophy virus (GpSGHV) is a rod-shaped, non-occluded double-stranded DNA virus that causes salivary gland hypertrophy (SGH) and reduced fecundity in the tsetse fly G. pallidipes. High GpSGHV prevalence (up to 80%) makes it impossible to mass-rear G. pallidipes colonies for the sterile insect technique (SIT). To evaluate the feasibility of molecular-based GpSGHV management strategies, we investigated the prevalence and genetic diversity of GpSGHV in wild populations of G. pallidipes collected from ten geographical locations in eastern and southern Africa. Virus diversity was examined using a total sequence of 1497 nucleotides (∼1% of the GpSGHV genome) from five putative conserved ORFs, p74, pif1, pif2, pif3 and dnapol. Overall, 34.08% of the analyzed flies (n=1972) tested positive by nested PCR. GpSGHV prevalence varied from 2% to 100% from one location to another but phylogenetic and gene genealogy analyses using concatenated sequences of the five putative ORFs revealed low virus diversity. Although no correlation of the virus diversity to geographical locations was detected, the GpSGHV haplotypes could be assigned to one of two distinct clades. The reference (Tororo) haplotype was the most widely distributed, and was shared by 47 individuals in seven of the 11 locations. The Ethiopian haplotypes were restricted to one clade, and showed the highest divergence (with 14–16 single nucleotide mutation steps) from the reference haplotype. The current study suggests that the proposed molecular-based virus management strategies have a good prospect of working throughout eastern and southern Africa due to the low diversity of the GpSGHV strains.

Implications of Microfauna-Host Interactions for Trypanosome Transmission Dynamics in Glossina fuscipes fuscipes in Uganda

Tsetse flies (Diptera: Glossinidae) are vectors for African trypanosomes (Euglenozoa: kinetoplastida), protozoan parasites that cause African trypanosomiasis in humans (HAT) and nagana in livestock. In addition to trypanosomes, two symbiotic bacteria (Wigglesworthia glossinidia and Sodalis glossinidius) and two parasitic microbes, Wolbachia and a salivary gland hypertrophy virus (SGHV), have been described in tsetse. Here we determined the prevalence of and coinfection dynamics between Wolbachia, trypanosomes, and SGHV in Glossina fuscipes fuscipes in Uganda over a large geographical scale spanning the range of host genetic and spatial diversity. Using a multivariate analysis approach, we uncovered complex coinfection dynamics between the pathogens and statistically significant associations between host genetic groups and pathogen prevalence. It is important to note that these coinfection dynamics and associations with the host were not apparent by univariate analysis. These associations between host genotype and pathogen are particularly evident for Wolbachia and SGHV where host groups are inversely correlated for Wolbachia and SGHV prevalence. On the other hand, trypanosome infection prevalence is more complex and covaries with the presence of the other two pathogens, highlighting the importance of examining multiple pathogens simultaneously before making generalizations about infection and spatial patterns. It is imperative to note that these novel findings would have been missed if we had employed the standard univariate analysis used in previous studies. Our results are discussed in the context of disease epidemiology and vector control.

Ultrastructure of the salivary glands of non-infected and infected glands in Glossina pallidipes by the salivary glands hypertrophy virus

Light, scanning electron, and transmission electron microscopy analyses were conducted to examine the morphology and ultrastructure of the salivary glands of Glossina pallidipes. Three distinct regions, each with a characteristic composition and organization of tissues and cells, were identified: secretory, reabsorptive and proximal. When infected with the salivary gland hypertrophy (SGH) virus, glands showed a severe hypertrophy, accompanied by profound changes in their morphology and ultrastructure. In addition, the muscular fibers surrounding the secretory region of the glands were disrupted. The morphological alterations in the muscular tissue, caused by viral infection, could be an important aspect of the pathology and may shed light on the mode of action of the SGH virus. Results were discussed with regard to the potential effect of viral infection on normal salivation and on the ability of infected tsetse flies to transmit a trypanosome parasite.

Intercommunity effects on microbiome and GpSGHV density regulation in tsetse flies

Tsetse flies have a highly regulated and defined microbial fauna made of 3 bacterial symbionts (obligate Wigglesworthia glossinidia, commensal Sodalis glossinidius and parasitic Wolbachia pipientis) in addition to a DNA virus (Glossina pallidipes Salivary gland Hypertrophy Virus, GpSGHV). It has been possible to rear flies in the absence of either Wigglesworthia or in totally aposymbiotic state by dietary supplementation of tsetse’s bloodmeal. In the absence of Wigglesworthia, tsetse females are sterile, and adult progeny are immune compromised. The functional contributions for Sodalist are less known, while Wolbachia cause reproductive manupulations known as cytoplasmic incompatibility (CI). High GpSGHV virus titers result in reduced fecundity and lifespan, and have compromised efforts to colonize flies in the insectary for large rearing purposes. Here we investigated the within community effects on the density regulation of the individual microbiome partners in tsetse lines with different symbiotic compositions. We show that absence of Wigglesworthia results in loss of Sodalis in subsequent generations possibly due to nutritional dependancies between the symbiotic partners. While an initial decrease in Wolbachia and GpSGHV levels are also noted in the absence of Wigglesworthia, these infections eventually reach homeostatic levels indicating adaptations to the new host immune environment or nutritional ecology. Absence of all bacterial symbionts also results in an initial reduction of viral titers, which recover in the second generation. Our findings suggest that in addition to the host immune system, interdependencies between symbiotic partners result in a highly tuned density regulation for tsetse’s microbiome.

Salivary gland hypertrophy virus of house flies in Denmark: prevalence, host range, and comparison with a Florida isolate

House flies (Musca domestica) infected with Musca domestica salivary gland hypertrophy virus (MdSGHV) were found in fly populations collected from 12 out of 18 Danish livestock farms that were surveyed in 2007 and 2008. Infection rates ranged from 0.5% to 5% and averaged 1.2%. None of the stable flies (Stomoxys calcitrans), rat-tail maggot flies (Eristalis tenax) or yellow dung flies (Scathophaga stercoraria) collected from MdSGHV-positive farms displayed characteristic salivary gland hypertrophy (SGH). In laboratory transmission tests, SGH symptoms were not observed in stable flies, flesh flies (Sarcophaga bullata), black dump flies (Hydrotaea aenescens), or face flies (Musca autumnalis) that were injected with MdSGHV from Danish house flies. However, in two species (stable fly and black dump fly), virus injection resulted in suppression of ovarian development similar to that observed in infected house flies, and injection of house flies with homogenates prepared from the salivary glands or ovaries of these species resulted in MdSGHV infection of the challenged house flies. Mortality of virus-injected stable flies was the highest among the five species tested. Virulence of Danish and Florida isolates of MdSGHV was similar with three virus delivery protocols, as a liquid food bait (in sucrose, milk, or blood), sprayed onto the flies in a Potter spray tower, or by immersiion in a crude homogenate of infected house flies. The most effective delivery system was immersion in a homogenate of ten infected flies/ml of water, resulting in 56.2% and 49.6% infection of the house flies challenged with the Danish and Florida strains, respectively.

The salivary secretome of the tsetse fly Glossina pallidipes (Diptera: Glossinidae) infected by salivary gland hypertrophy virus.

BackgroundThe competence of the tsetse fly Glossina pallidipes (Diptera; Glossinidae) to acquire salivary gland hypertrophy virus (SGHV), to support virus replication and successfully transmit the virus depends on complex interactions between Glossina and SGHV macromolecules. Critical requisites to SGHV transmission are its replication and secretion of mature virions into the fly's salivary gland (SG) lumen. However, secretion of host proteins is of equal importance for successful transmission and requires cataloging of G. pallidipes secretome proteins from hypertrophied and non-hypertrophied SGs.Methodology/Principal FindingsAfter electrophoretic profiling and in-gel trypsin digestion, saliva proteins were analyzed by nano-LC-MS/MS. MaxQuant/Andromeda search of the MS data against the non-redundant (nr) GenBank database and a G. morsitans morsitans SG EST database, yielded a total of 521 hits, 31 of which were SGHV-encoded. On a false discovery rate limit of 1% and detection threshold of least 2 unique peptides per protein, the analysis resulted in 292 Glossina and 25 SGHV MS-supported proteins. When annotated by the Blast2GO suite, at least one gene ontology (GO) term could be assigned to 89.9% (285/317) of the detected proteins. Five (∼1.8%) Glossina and three (∼12%) SGHV proteins remained without a predicted function after blast searches against the nr database. Sixty-five of the 292 detected Glossina proteins contained an N-terminal signal/secretion peptide sequence. Eight of the SGHV proteins were predicted to be non-structural (NS), and fourteen are known structural (VP) proteins.Conclusions/SignificanceSGHV alters the protein expression pattern in Glossina. The G. pallidipes SG secretome encompasses a spectrum of proteins that may be required during the SGHV infection cycle. These detected proteins have putative interactions with at least 21 of the 25 SGHV-encoded proteins. Our findings opens venues for developing novel SGHV mitigation strategies to block SGHV infections in tsetse production facilities such as using SGHV-specific antibodies and phage display-selected gut epithelia-binding peptides.

Impact of House Fly Salivary Gland Hypertrophy Virus (MdSGHV) on a Heterologous Host, Stomoxys calcitrans

The effect of Musca domestica salivary gland hypertrophy virus (MdSGHV) on selected fitness parameters of stable flies, Stomoxys calcitrans (L.), was examined in the laboratory. Virus-injected stable flies of both genders suffered substantially higher mortality than control flies. By day 9, female mortality was 59.3 +/- 10.1% in the virus group compared with 23.7 +/- 3.7% in the controls; mortality in virus-injected males was 78.1 +/- 3.1% compared with 33.3 +/- 9.3% for controls. Fecundity of control flies on days 6-9 was 49-54 eggs deposited per live female per day (total, 8,996 eggs deposited), whereas virus-injected flies produced four to five eggs per female on days 6-7 and less then one egg per female per day thereafter (total, 251 eggs). Fecal spot deposition by virus-injected flies was comparable to controls initially but decreased to approximately 50% of control levels by day 4 after injection; infected flies produced only 26% as many fecal spots as healthy flies on days 6 and 7. None of the virus-injected stable flies developed symptoms of salivary gland hypertrophy. Quantitative real-time polymerase chain reaction demonstrated virus replication in injected stable flies, with increasing titers of virus genome copies from one to four days after injection. MdSGHV in stable flies displayed tissue tropism similar to that observed in house fly hosts, with higher viral copy numbers in fat body and salivary glands compared with ovaries. Virus titers were approximately 2 orders of magnitude higher in house fly than in stable fly hosts, and this difference was probably due to the absence of salivary gland hypertrophy in the latter species.

Tsetse Salivary Gland Hypertrophy Virus: Hope or Hindrance for Tsetse Control?

Many species of tsetse flies (Diptera: Glossinidae) are infected with a virus that causes salivary gland hypertrophy (SGH), and flies with SGH symptoms have a reduced fecundity and fertility. The prevalence of SGH in wild tsetse populations is usually very low (0.2%–5%), but higher prevalence rates (15.2%) have been observed occasionally. The successful eradication of a Glossina austeni population from Unguja Island (Zanzibar) using an area-wide integrated pest management approach with a sterile insect technique (SIT) component (1994–1997) encouraged several African countries, including Ethiopia, to incorporate the SIT in their national tsetse control programs. A large facility to produce tsetse flies for SIT application in Ethiopia was inaugurated in 2007. To support this project, a Glossina pallidipes colony originating from Ethiopia was successfully established in 1996, but later up to 85% of adult flies displayed symptoms of SGH. As a result, the colony declined and became extinct by 2002. The difficulties experienced with the rearing of G. pallidipes, epitomized by the collapse of the G. pallidipes colony originating from Ethiopia, prompted the urgent need to develop management strategies for the salivary gland hypertrophy virus (SGHV) for this species. As a first step to identify suitable management strategies, the virus isolated from G. pallidipes (GpSGHV) was recently sequenced and research was initiated on virus transmission and pathology. Different approaches to prevent virus replication and its horizontal transmission during blood feeding have been proposed. These include the use of antiviral drugs such as acyclovir and valacyclovir added to the blood for feeding or the use of antibodies against SGHV virion proteins. In addition, preliminary attempts to silence the expression of an essential viral protein using RNA interference will be discussed.

The genome of Oryctes rhinoceros nudivirus provides novel insight into the evolution of nuclear arthropod-specific large circular double-stranded DNA viruses

The Oryctes rhinoceros nudivirus (OrNV) is a dsDNA virus with enveloped, rod-shaped virions. Its genome is 127,615bp in size and contains 139 predicted protein-coding open reading frames (ORFs). In-depth genome sequence comparisons revealed a varying number of shared gene homologues, not only with other nudiviruses (NVs) and baculoviruses, but also with other arthropod-specific large dsDNA viruses, including the so-called Monodon baculovirus (MBV), the salivary gland hypertrophy viruses (SGHVs) and white spot syndrome virus (WSSV). Nudivirus genomes contain 20 baculovirus core gene homologues associated with transcription (p47, lef-8, lef-9, lef-4, vlf-1, and lef-5), replication (dnapol and helicase), virus structure (p74, pif-1, pif-2, pif-3, 19kda/pif-4, odv-e56/pif-5, vp91, vp39, and 38K), and unknown functions (ac68, ac81, and p33). Most strikingly, a set of homologous genes involved in peroral infection (p74, pif-1, pif-2, and pif-3) are common to baculoviruses, nudiviruses, SGHVs, and WSSV indicating an ancestral mode of infection in these highly diverged viruses. A gene similar to polyhedrin/granulin encoding the baculovirus occlusion body protein was identified in non-occluded NVs and in Musca domestica SGHV evoking the question of the evolutionary origin of the baculovirus polyhedrin/granulin gene. Based on gene homologies, we further propose that the shrimp MBV is an occluded member of the nudiviruses. We conclude that baculoviruses, NVs and the shrimp MBV, the SGHVs and WSSV share the significant number of conserved genetic functions, which may point to a common ancestry of these viruses.