Role of the stable fly as a vector of pig pathogens

A Vetmeduni Vienna study investigated stable flies (Stomoxys calcitrans) from Austrian pig farms for the presence of defined swine pathogens. The findings are published in Microorganisms.

The blood-sucking insect is frequently found on farms and has direct and indirect influences on animal health. Direct influences can include restlessness, pain due to biting, stress, loss of blood, reduced feed intake and lesions of the skin followed by local inflammation and immunosuppression, while indirect effects are due to the transmission of infectious agents.

A research team led by Lukas Schwarz from the University Clinic for Swine at Vetmeduni Vienna, as part of a diploma thesis, examined stable flies from Austrian pig farms for the presence of pathogens such as porcine reproductive and respiratory syndrome virus (PRRSV), porcine circovirus 2 (PCV2), haemotrophic mycoplasmas and cultivable bacterial pathogens. In their pilot study, the researchers also investigated the use of stable flies as a diagnostic matrix to detect pathogens in the ingested pig blood.

“In total, we found 69 different microorganisms 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. Also at seven farms, haemotrophic mycoplasmas were detected in stable flies. PRRSV could not be found in any of the samples, but PCV2 was detected in six farms,” says study director Lukas Schwarz.

The results of the study suggest that stable flies in Austrian pig farms are carriers of several different bacterial species and may also serve as vectors for PCV2 and haemotrophic mycoplasma. Schwarz stresses that more attention should therefore be paid to stable flies and their role as a disease vector in pigs: “Although we cannot evaluate the explicit role of S. calcitrans as a vector, we think that the role of stable flies in disease and pathogen transmission among pigs in Austria is underestimated.”

The researchers also suggest using stable flies as a diagnostic matrix for the detection of PCV2 and haemotrophic mycoplasmas. Schwarz points out, however, that future studies are needed to confirm this possibility and to clarify whether stable flies may also be used as a diagnostic matrix for the detection of PRRSV. They say using stable flies for herd health surveillance would be a cost-effective and humane alternative to blood sampling or other invasive sampling techniques in pigs.

Article: Schwarz, L., Strauss, A., Loncaric, I., Spergser, J., Auer, A., Rümenapf, T., Ladinig, A. (2020). The Stable Fly (Stomoxys calcitrans) as a Possible Vector Transmitting Pathogens in Austrian Pig Farms. Microorganisms, 8(10), E1476, doi: 10.3390/microorganisms8101476

[SOURCE: Vetmeduni Vienna]