Mechanical transmission of SARS-CoV-2 by house flies

Abstract

Background Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is a recently emerged coronavirus that is the causative agent of the coronavirus disease 2019 (COVID-19) pandemic. COVID-19 in humans is characterized by a wide range of symptoms that range from asymptomatic to mild or severe illness including death. SARS-CoV-2 is highly contagious and is transmitted via the oral–nasal route through droplets and aerosols, or through contact with contaminated fomites. House flies are known to transmit bacterial, parasitic and viral diseases to humans and animals as mechanical vectors. Previous studies have shown that house flies can mechanically transmit coronaviruses, such as turkey coronavirus; however, the house fly’s role in SARS-CoV-2 transmission has not yet been explored. The goal of this work was to investigate the potential of house flies to mechanically transmit SARS-CoV-2. For this purpose, it was determined whether house flies can acquire SARS-CoV-2, harbor live virus and mechanically transmit the virus to naive substrates and surfaces. Methods Two independent studies were performed to address the study objectives. In the first study, house flies were tested for infectivity after exposure to SARS-CoV-2-spiked medium or milk. In the second study, environmental samples were tested for infectivity after contact with SARS-CoV-2-exposed flies. During both studies, samples were collected at various time points post-exposure and evaluated by SARS-CoV-2-specific RT-qPCR and virus isolation. Results All flies exposed to SARS-CoV-2-spiked media or milk substrates were positive for viral RNA at 4 h and 24 h post-exposure. Infectious virus was isolated only from the flies exposed to virus-spiked milk but not from those exposed to virus-spiked medium. Moreover, viral RNA was detected in environmental samples after contact with SARS-CoV-2 exposed flies, although no infectious virus was recovered from these samples. Conclusions Under laboratory conditions, house flies acquired and harbored infectious SARS-CoV-2 for up to 24 h post-exposure. In addition, house flies were able to mechanically transmit SARS-CoV-2 genomic RNA to the surrounding environment up to 24 h post-exposure. Further studies are warranted to determine if house fly transmission occurs naturally and the potential public health implications of such events.

Domestic Filth Flies in New Haven, Connecticut: A Case Study on the Effects of Urbanization and Climate Change by Comparing Fly Populations after 78 Years

“…SARS-CoV-2 was first detected in New Haven in March 2020, nine months after the current fly survey began. While the World Health Organization considers the flies' role in the transmission of the virus to again be incidental [129] research is starting to emerge demonstrating that flies are capable of transmitting SARS-CoV-2 and that infected flies are present in field samples from infected communities [130,131]. As the pandemic continues across the US and the world, an increase in fly surveys should be anticipated, providing the impetus to generate further comparative studies of domestic filth flies.…”

Environmental factors influencing the transmission of the coronavirus 2019: a review

“…The flies need to acquire the virus from a contaminated surface and afterward harbor it on their gut or body surfaces to transmit it mechanically. The study results indicated that flies do not play a significant role in transmitting SARS-CoV-2 to humans and animals (Balaraman et al 2021a , b ).…”

“…It was tested whether mosquitoes are susceptible to SARS-CoV-2 by an oral route of infection, which was not previously evaluated. The study concluded that insects do not play an essential role in transmitting SARS-CoV-2 to humans (Balaraman et al 2021a , b ).…”

Zoonotic and Reverse Zoonotic Transmissibility of SARS-CoV-2

“…Recent studies demonstrated that SARS-CoV-2 replication was not supported in biting midges ( Culicoides sonorensis ) and mosquitoes ( Aedes aegypti, Aedes albopictus, Culex pipiens, Culex quinquefasciatus , and Culex tarsalis ), suggesting that these species are unable to be biological vectors of SARS-CoV-2 ( Balaraman et al, 2021a ; Fortuna et al, 2021 ; Huang et al, 2020c ). However, it has been demonstrated that houseflies ( Musca domestica ) can acquire and harbor infectious SARS-CoV-2 for up to 24 hours post-exposure ( Balaraman et al, 2021b ).…”

“…It was reported that rodents and arthropods were involved in the mechanical transmission of the turkey coronavirus and SARS-CoV during the SARS epidemic ( Calibeo-Hayes et al, 2003 ; Reuben et al, 2020 ). Experimental studies showed that houseflies were able to mechanically transmit SARS-CoV-2 genomic RNA to the surrounding environment up to 24 h post-exposure ( Balaraman et al, 2021b ). Some of the United States’ common rodents, such as fox squirrels ( Sciurus niger ), Wyoming ground squirrels ( Urocitellus elegans ), house mice ( Mus musculus ), and black-tailed prairie dogs ( Cynomys ludovicianus ), are not susceptible to SARS-CoV-2 infection ( Bosco-Lauth et al, 2021 ).…”