Latest research from the US gives a clear indication that cockroaches and houseflies do not transmit the SARSCoV-2 virus.
Public health experts know much more about how the SARS-CoV-2 virus spreads between people compared with the beginning of the Covid-19 pandemic. However, research is still ongoing into how the virus spreads indirectly, through contaminated surfaces, animals or insects, in what is known as mechanical transmission. Research published in Journal of Medical Entomology indicates that while houseflies and cockroaches are known vectors of disease, they appear to be incapable of transmitting the SARS-CoV-2 virus in this physical way.
The research team from Texas A&M University in the US had previously discovered that transmission of SARSCoV-2 from humans to pet dogs and cats was occurring in households with confirmed human Covid-19 cases. The same team also determined that houseflies could become infected with the virus in a laboratory setting.
This latest research set out to discover if houseflies and cockroaches could transmit the virus via their bodies and mouthparts within an ordinary household setting, rather than in a laboratory environment.
As part of the study, the researchers set 133 insect traps in 40 homes where at least one resident was confirmed as having Covid-19. In addition, 14 traps were set in seven homes where the family cat or dog had tested positive for the virus.
The traps (a combination of sticky traps and liquid bait traps) collected 1345 insects in total over a three-month period, which included various fly and cockroach species. The insects were tested for presence of the SARS-CoV-2 virus – and all tested negative.
Two scenarios are possible: either the lack of detection of the virus in the insect samples means that the insects were not contaminated by the infected humans/ animals; or the insects were in fact contaminated and the virus degraded before the contents of the traps were analysed.
The results provide evidence that cockroaches are not likely to spread the virus by means of mechanical transmission. Although flies have been shown to be capable of picking up the virus in a hospital with active Covid cases, it seems this is very unlikely to occur in an ordinary domestic environment, even when both humans and pets are actively shedding the virus.
Gabriel Hamer from the Department of Entomology, Texas A&M University, one of the study’s authors, outlined the findings.
“We were sampling insects in homes with recent human Covid-19 cases, some of which also had dogs and cats actively infected with SARS-CoV-2,” he said. “We suspected these were high-risk environments where insects may be able to become contaminated with the virus if they were contacting the infected humans, animals or contaminated surfaces. Instead, we did not detect evidence of the virus in the sampled insects from these homes.
“This study provides more evidence to help narrow down transmission routes of SARS-CoV-2 and evaluates different methods for novel surveillance techniques. It was a team effort that allowed us to rapidly deploy these traps in high-risk settings to directly assess the role of insects in the Covid-19 pandemic.”
Further reading: Roundy, Christopher & Hamer, Sarah & Zecca, Italo & Auckland, L. & Tang, Wendy & Gavranovic, Haley & Swiger, Sonja & Tomberlin, Jeffery & Fischer, Rebecca & Pauvolid-Corrêa, Alex & Hamer, Gabriel. (2022). No Evidence of SARS-CoV-2 Among Flies or Cockroaches in Households Where COVID-19 Positive Cases Resided. Journal of Medical Entomology. 59. 10.1093/jme/tjac055.