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Research answers public health concerns about virus transmission – ScienceDaily


According to a recently published article by Texas A&M AgriLife Research scientists, insects such as biting flies and cockroaches do not spread the COVID-19 pathogen to humans.

Chris Roundy, Ph.D., a graduate student in the Department of Entomology at the time of the study, removes flies from a sticky trap. (Texas A&M AgriLife photo by Gabe Hammer)

Public health experts and officials know much more about the spread of COVID-19, but concerns remain about how the virus spreads indirectly from person to person through contaminated surfaces, animals or insects.

Insects are known to spread many infectious diseases to humans, so assessing the role of insects in the potential transmission of SARS-CoV-2 was a priority in the early stages of the COVID-19 pandemic, according to study co-author Gabriel Hamer, Ph.D., an AgriLife Research entomologist in the Texas A&M Department of Entomology. .

The article “No evidence of SARS-CoV-2 among flies and cockroaches in households with positive cases of COVID-19” was published in Journal of Medical Entomology covers the project and the findings of the team.

The team included Gabriel Hamer, Sarah Hamer, PhD, DVM, assistant professor of epidemiology at the Texas A&M College of Veterinary and Biological Sciences, and assistance from research assistants and graduate students and other faculty in the Department of Entomology in the College of Agriculture and Life Sciences and the School of Public Health. health. The lead author, Chris Roundy, Ph.D., was a graduate student in the Department of Entomology at the time and is now with the Colorado Department of Health and Environment.

“We sampled insects in homes with recent human cases of COVID-19, some of which also had dogs and cats actively infected with SARS-CoV-2,” said Gabriel Hammer. “We suspected that this was a high-risk environment where insects could contract the virus when they came into contact with infected people, animals or contaminated surfaces. Instead, we found no evidence of the virus in the insect samples from these homes. .”

Previous work by a research team funded by the Centers for Disease Control and Prevention found that transmission of SARS-CoV-2 from humans to domestic dogs and cats occurred in households with confirmed human cases of COVID-19. More recently, the team also studied the transmission of SARS-CoV-2 among white-tailed deer in Texas.

Testing flies and cockroaches for COVID-19

Scientists, including the Texas A&M COVID-19 and Pets Project team, have found that animals such as cats and dogs are susceptible to SARS-CoV-2 infection and can shed the infectious virus. But less was understood about potential transmission via insects, particularly through mechanical transmission of contaminated mouthparts.

A member of the Texas A&M AgriLife Research team takes samples from one of dozens of sticky traps. The samples were part of a study to determine whether flies and cockroaches can spread SARS-CoV-2. (Texas A&M AgriLife photo by Gabe Hammer)

Previous experimental studies by other researchers showed that both infectious virus and viral RNA could be detected in houseflies after exposure to SARS-CoV-2 in the laboratory. AgriLife Research’s field study found no evidence that these insects acquired SARS-CoV-2 RNA in natural domestic conditions.

Mechanical transmission involves transmitting the pathogen to humans through infectious particles on insect body parts, Hamer said. Biological transmission involves the pathogen entering the insect and then growing and multiplying before transmission via the insect’s saliva or feces.

Hamer said most vector-borne pathogens, such as West Nile virus in mosquitoes, are spread biologically. But flies that don’t bite can mechanically transmit bacteria like salmonella.

As part of the investigation, Hamer and other AgriLife Research scientists processed the contents of 133 insect traps in 40 homes that each had at least one confirmed human case of COVID-19. From June to September 2020, sticky traps collected more than 1,345 individual insects representing 11 different species of flies and roaches.

Insects were tested using reverse transcription quantitative PCR. Fluid in additional trap types was also tested after RNA concentration. Individual insects were grouped into 243 groups, and all of them tested negative for SARS-CoV-2.

Fourteen traps in seven homes were placed in homes on the same day that dog and cat samples tested positive for the virus, further increasing the possibility of the insects coming into contact with infected animals or surfaces.

The study provides evidence that biting and non-biting flies and roaches cannot spread the virus through mechanical transmission or be useful as a surveillance tool to track SARS-CoV-2 transmission.

“This study provides additional evidence to help narrow the transmission pathways of SARS-CoV-2 and evaluates different methods for new surveillance methods,” Hamer said. “It was a team effort that allowed us to rapidly deploy these traps in high-risk environments to directly assess the role of insects in the COVID-19 pandemic.”

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