|Lietze, Verena - UNIVERSITY OF FLORIDA|
|Sims, Kelly - UNIVERSITY OF FLORIDA|
|Salem, Tamer - UNIVERSITY OF FLORIDA|
|Boucias, Drion - UNIVERSITY OF FLORIDA|
Submitted to: Journal of Invertebrate Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 19, 2009
Publication Date: February 28, 2009
Citation: Lietze, V.-U., Sims, K.R., Salem, T.Z., Geden, C.J., Boucias, D.G. 2009. Transmission of MdSGHV among adult house flies, Musca domesitca (Diptera: Muscidae), occurs via oral secretions and excreta. Journal of Invertebrate Pathology. 101:49-55. Interpretive Summary: House flies are important pests associated with animals and humans and transmit a wide array of disease organisms. Efforts to manage flies have traditionally relied on chemical insecticides, but flies have become resistant to most insecticides and there is increasing public demand to reduce pesticide use around animals that are used in the production of meat, milk and eggs. Most biological control research on flies has concentrated on targeting fly pupae with parasitic wasps. In contrast, efforts to manage adult flies have been restricted to pathogenic fungi, with mixed results. In this paper, scientists at the University of Florida and USDA-ARS’s Center for Medical, Agricultural and Veterinary Entomology (Gainesville, FL) report on a novel viral disease of adult flies. Studies demonstrated that infected flies began releasing virus particles in their oral secretions at 2 days post-infection and that viremia in these secretions peaked on day 4. Healthy flies became infected when they fed on these secretions, but only when they were exposed as very young flies. In addition to the salivary glands, the crops of the flies also contained virus, and flies became infected when they fed on viremic crop contents. Finally, the feces of infected flies also contained viable virus. The results suggest that this virus may hold potential as a biocontrol agent for flies that could be deployed as either a bait or a surface treatment to fly resting sites.
Technical Abstract: The Musca domestica salivary gland hypertrophy virus (MdSGHV) is a newly characterized, double stranded DNA virus that replicates in the salivary glands of infected adult house flies. Transmission of this non-occluded, enveloped virus within feral populations of M. domestica is believed to be mediated orally via deposition and consumption of saliva, which is a composite of salivary gland secretions and crop contents. In this study, transmission electron micrographs of crops from infected flies showed numerous enveloped virions in the crop lumen adjacent to the cuticular intima as well as on the hemocoel side in close vicinity to muscle cells. However, no replication sites were detected in these tissues. Oral treatments of newly emerged individual flies with viremic salivary gland homogenates, crop homogenates, or gradient-purified virus resulted in an average 44 ± 11% infection. Infection rates did not differ between females and males or between challenged flies that were kept individually and in groups. Using quantitative real-time PCR, MdSGHV DNA was quantified in salivary secretions and excreta obtained from viremic flies. Beginning two days post-infection (dpi), saliva samples collected from individual flies during one feeding event contained detectable numbers of MdSGHV copies. Viral copy numbers increased exponentially until 4 dpi, and from 5-21 dpi each infected fly released an average 1.0 x 106 ± 0.2 x 106 MdSGHV copies per feeding event. Oral transmission experiments showed that the virus released via salivary secretion was infectious when ingested by newly emerged adult flies, resulting in an average 66 ± 10% infection rate. Excreta samples collected over night at 5 dpi from individual infected flies contained an average 6.5 x 105 ± 1.9 x 105 viral copies per sample. Low infection rates (2 ± 3% or 17 ± 8%) were produced when newly emerged flies were challenged with these samples by oral treatments or injection, respectively. In summary, evaluation of the quantity and infectivity of MdSGHV released by individual infected house flies clearly showed that salivation onto a shared food substrate is the main route of natural MdSGHV transmission among adult house flies.