House Flies Can Spread Coronavirus
Dr. Robert E. Lee

Note - Once again we are proud to be first to present more of Dr. Lee's frontline research and information regarding the SARS epidemic and its dynamics. He deserves worldwide recognition for his numerous personal contributions and citations of other key data and information as below. - ed

Avian Dis 2003 Jan-Mar;47(1):149-53 Mechanical transmission of turkey coronavirus by domestic houseflies (Musca domestica Linnaeaus). Calibeo-Hayes D, Denning SS, Stringham SM, Guy JS, Smith LG, Watson DW. Department of Entomology, College of Agriculture and Life Sciences, North Carolina State University, Raleigh, NC 27695, USA.

Domestic houseflies (Musca domestica Linnaeaus) were examined for their ability to harbor and transmit turkey coronavirus (TCV). Laboratory-reared flies were experimentally exposed to TCV by allowing flies to imbibe an inoculum comprised of turkey embryo-propagated virus (NC95 strain). TCV was detected in dissected crops from exposed flies for up to 9 hr postexposure; no virus was detected in crops of sham-exposed flies. TCV was not detected in dissected intestinal tissues collected from exposed or sham-exposed flies at any time postexposure. The potential of the housefly to directly transmit TCV to live turkey poults was examined by placing 7-day-old turkey poults in contact with TCV-exposed houseflies 3 hr after flies consumed TCV inoculum. TCV infection was detected in turkeys placed in contact with TCV-exposed flies at densities as low as one fly/bird (TCV antigens detected at 3 days post fly contact in tissues of 3/12 turkeys); however, increased rates of infection were observed with higher fly densities (TCV antigens detected in 9/12 turkeys after contact with 10 flies/bird). This study demonstrates the potential of the housefly to serve as a mechanical vector of TCV. PMID: 12713170

Am J Vet Res 1983 Nov;44(11):2078-82 Identification of porcine transmissible gastroenteritis virus in house flies (Musca domestica Linneaus). Gough PM, Jorgenson RD.

Transmissible gastroenteritis (TGE) virus was detected in house flies (Musca domestica Linneaus) by staining with specific fluorescent antibody. The flies were collected within a swine confinement facility in which TGE was enzootic. Laboratory-reared flies were infected experimentally with TGE virus and the virus was recovered from the insects for 72 hours after infection. The TGE virus was identified both by the fluorescent antibody technique and by isolation in cell culture. The nature of plaque formation in cell monolayers inoculated with the virus passaged through flies changed from a large plaque (4 mm or greater in diameter) to a small plaque (1 mm in diameter) over the period. Large plaques were observed early after infection and were attributed to TGE virus mechanically carried by the flies. Small plaques occurred 8 to 12 hours after infection and were considered to be produced by virus replicated in the dipterous cell. PMID: 6316821

So, Jeff, it is my reasonable guess that SARS coronavirus can be spread by house flies for between 3 and 72 hours after a fly has come into contact with SARS coronavirus as is likely to happen if a fly lands on any infected human waste/body fluids. You will note that, for turkey coronavirus, it is sufficient to have one single infected fly land on a bird and the bird can become infected. It is a reasonable infection-control policy, as summer approaches and flies begin flying, for any infected nation to institute fly abatement programs immediately and for individual citizens of infected nations to be concerned about and proactive about preventing contact with flies.

This is going to be a challenging summer in Asia. As flies (and perhaps other insects?) are likely to spread the disease in the summer and the virus appears to spread by close human contact in the winter and summer it is not likely that SARS coronavirus will display any seasonality. Once flies begin flying, I anticipate there will be an increase in SARS cases particularly in areas where flies have access to human waste/body fluids and subsequent access to humans.

This is a really troublesome finding and does not bode well for quarantine effectiveness. How does a nation protect itself from flies?