Persistence and retention of porcine reproductive and respiratory syndrome virus in stable flies (Diptera: Muscidae)

Authors: ROCHON, K - University Of Manitoba; BAKER, R - Iowa State University; ALMOND, G - North Carolina State University; GIMENO, I - North Carolina State University; Perez De Leon, Adalberto - Beto; WATSON, D - North Carolina State University

Submitted to: Journal of Medical Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/13/2015
Publication Date: 9/1/2015
Publication URL: http://handle.nal.usda.gov/10113/62309
Citation: Rochon, K., Baker, R.B., Almond, G.2., Gimeno, I.M., Perez De Leon, A.A., Watson, D.W. 2015. Persistence and retention of porcine reproductive and respiratory syndrome virus in stable flies (Diptera: Muscidae). Journal of Medical Entomology. 52(5):1117-1123.

Interpretive Summary: The stable fly is an economically important pest of livestock. In addition to inflicting a painful bite when blood-feeding, the stable fly can carry certain microbes that cause disease in domestic animals. The full range of disease-causing agents the stable fly can transmit remains to be fully understood. Porcine Reproductive and Respiratory Syndrome virus (PRRSV) affects pigs. Here, the acquisition of PRRSV by the stable fly was assessed through a bloodmeal, and virus persistence in the digestive organs of the fly using virus isolation and molecular techniques. Stable flies were fed blood containing live virus, modified live vaccine virus, and chemically inactivated virus or no virus. Stable flies acquired PRRSV from the bloodmeal and the amount of virus in the flies declined with time, which indicated the virus did not replicate in fly digestive tissues. Active virus was isolated from the flies up to 24h and 96 h post-feeding. Virus isolation results were evaluated by microscopic evaluation of detrimental effects on cells, a fluorescent signal detected with antibodies, and a molecular reaction in a test tube. The fate of PRRSV in the body fluid of flies was examined further following injection through their chest to bypass the midgut barrier. PRRSV injected in this manner was detected in stable flies for 10 days using a quantitative molecular reaction in a test tube. However, detectable quantities of virus declined over time. In contrast to what was observed in the digestive tract, the quantities of injected virus remained at detectable levels in the body fluid of stable flies. Virus levels were as high as ten-thousand times greater in stable fly body fluid when compared to those detected in the digestive tract at the same time point.

Technical Abstract: The acquisition of Porcine Reproductive and Respiratory Syndrome virus (PRRSV) by the stable fly (Stomoxys calcitrans L.) was assessed through a bloodmeal, and virus persistence in the digestive organs of the fly using virus isolation and real-time PCR. Stable flies were fed blood containing live virus, modified live vaccine virus, chemically inactivated virus or no virus. Stable flies acquired PRRSV from the bloodmeal and the amount of virus in the flies declined with time, indicating the virus did not replicate in fly digestive tissues. Active virus was isolated from the flies up to 24 h and 96 h post-feeding. Virus isolation results were evaluated by microscopic evaluation of cytopatic effect, immunofluorescence, and RT-PCR. The fate of PRRSV in the hemolymph of the flies was examined further following intrathoracic injection to bypass the midgut barrier. PRRSV was detected in intrathoracically inoculated adult stable flies for 10 days using quantitative real-time PCR. Detectable quantities of virus over time followed an exponential decay curve. In contrast to what we observed in the digestive tract, detectable virus quantities never fell below 10e5 in the hemolymph of intrathoracically inoculated stable flies. Virus levels were up to 9,500 times greater in the hemolymph when compared to those detected in the digestive tract at the same time point.