Assessment of Stomoxys calcitrans (Diptera: Muscidae) as a vector of porcine reproductive and respiratory syndrome virus

Survival of Porcine Reproductive and Respiratory Syndrome Virus (PRRSV) in the Environment

Porcine reproductive and respiratory syndrome (PRRS) is one of the most economically important diseases of swine, with losses due to poor reproductive performance and high piglet and growing pig mortality. Transmission of porcine reproductive and respiratory syndrome virus (PRRSV) may occur by both direct and indirect routes; the latter includes exposure to PRRSV-contaminated fomites, aerosols, and arthropod vectors. This review has collected available data on the ex-vivo environmental stability and persistence of PRRSV in an effort to highlight important sources of the virus and to determine the role of environmental conditions on the stability of the virus, especially temperature. The ex-vivo settings include fomites (solid, porous, and liquid fomites), insects, people, and pork meat, as well as the role of environmental conditions on the stability of the virus, especially temperature.

The Stable Fly (Stomoxys calcitrans) as a Possible Vector Transmitting Pathogens in Austrian Pig Farms

This pilot study aimed to investigate stable flies from Austrian pig farms for the presence of defined swine pathogens, such as porcine reproductive and respiratory syndrome virus (PRRSV), porcine circovirus 2 (PCV2), hemotrophic mycoplasmas in ingested blood and/or body parts and bacteria on the surface of the flies. Furthermore, the use of stable flies as a diagnostic matrix for the detection of pathogens in the ingested pig blood should be investigated. In total, 69 different microorganisms could be found on the surface of tested S. calcitrans from 20 different pig farms. Escherichia coli was the most common bacterium and could be found on flies from seven farms. In seven farms, hemotrophic mycoplasmas were detected in stable flies. PRRSV could not be found in any of the samples of these 20 farms but PCV2 was detected in six farms. Whether the stable fly can be used as a matrix to monitor the health status cannot be accurately determined through this study, especially in regard to PRRSV. Nevertheless, it might be possible to use the stable fly as diagnostic material for defined pathogens like Mycoplasma suis and PCV2.

Persistence and Retention of Porcine Reproductive and Respiratory Syndrome Virus in Stable Flies (Diptera: Muscidae)

We investigated the acquisition of porcine reproductive and respiratory syndrome (PRRS) virus by the stable fly (Diptera: Muscidae; Stomoxys calcitrans (L.)) through a bloodmeal, and virus persistence in the digestive organs of the fly using virus isolation and quantitative reverse-transcription PCR (qRT-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 virus did not replicate in fly digestive tissues. Virus RNA was recovered from the flies fed live virus up to 24 h postfeeding using virus isolation techniques and 96 h using qRT-PCR. We further examined the fate of PRRSV in the hemolymph of the flies following intrathoracic injection to bypass the midgut barrier. PRRSV was detected in intrathoracically inoculated adult stable flies for 10 d using qRT-PCR. In contrast to what we observed in the digestive tract, detectable virus quantities in the intrathoracically inoculated stable flies followed an exponential decay curve. The amount of virus decreased fourfold in the first 3 d and remained stable thereafter, up to 10 d.