Posted by Vector and Vector-borne Disease Committee
July 13, 2022
Christopher M Roundy, Sarah A Hamer, Italo B Zecca, Edward B Davila, Lisa D Auckland, Wendy Tang, Haley Gavranovic, Sonja L Swiger, Jeffery K Tomberlin, Rebecca S B Fischer, Alex Pauvolid-Correa, Gabriel Hamer.
Texas A&M University and AgriLife Research, College Station, TX 77843, USA
Journal of Medical Entomology, 30 May 2022, tjac055, https://doi.org/10.1093/jme/tjac055
Author’s Abstract. Flies and other arthropods mechanically transmit multiple pathogens and a recent experimental study demonstrated house flies, Musca domestica L. (Diptera: Muscidae), can mechanically transmit SARS-CoV-2 [Balaraman et al. JME 58: 1948]. The purpose of this study was to explore the possibility of mechanical transmission of SARS-CoV-2 by domestic insects and their potential as a xenosurveillance tool for detection of the virus. Flies were trapped in homes where at least one confirmed human COVID-19 case(s) resided using sticky and liquid-baited fly traps placed inside and outside the home in the Texas counties of Brazos, Bell, and Montgomery, from June to September 2020. Flies from sticky traps were identified, pooled by taxa, homogenized, and tested for the presence of SARS-CoV-2 RNA using quantitative reverse transcription PCR (RT-qPCR). Liquid traps were drained, and the collected fluid similarly tested after RNA concentration. We processed the contents of 133 insect traps from 40 homes, which contained over 1,345 individual insects of 11 different Diptera families and Blattodea. These individuals were grouped into 243 pools, and all tested negative for SARS-CoV-2 RNA. Fourteen traps in seven homes were deployed on the day that cat or dog samples tested positive for SARS-CoV-2 RNA by nasal, oral, body, or rectal samples. This study presents evidence that biting and nonbiting flies and cockroaches (Blattodea) are not likely to contribute to mechanical transmission of SARS-CoV-2 or be useful in xenosurveillance for SARS-CoV-2.
Note: This negative data is good news. Multiple studies have shown that SARS-CoV-2 does not replicate within insects after ingestion, so even experimental mechanical transmission only occurs with a relatively short time period. This combined with a low humoral viremia indicated little risk of biological transmission by biting flies/mosquitoes. The current study showed that even though surfaces may be contaminated with virus within households with infectious persons, the risk of insect acquisition and transmission was undetectable.