Ebola can spread by air in cold, dry weather common to the U.S. but not West Africa, presenting a “possible, serious threat” to the public, according to two studies by U.S. Army scientists.
After successfully exposing monkeys to airborne Ebola, which “caused a rapidly fatal disease in 4-5 days,” scientists with the U.S. Army Medical Research Institute of Infectious Diseases (USAMRIID) concluded Ebola can spread through air but likely hasn’t in Equatorial Africa because the region is too warm, with temperatures rarely dropping below 65°F.
“We… demonstrated aerosol transmission of Ebola virus at lower temperature and humidity than that normally present in sub-Saharan Africa,” the 1995 study entitled Lethal Experimental Infections of Rhesus Monkeys by Aerosolized Ebola Virus reported. “Ebola virus sensitivity to the high temperatures and humidity in the thatched, mud, and wattle huts shared by infected family members in southern Sudan and northern Zaire may have been a factor limiting aerosol transmission of Ebola virus in the African epidemics.”
“Both elevated temperature and relative humidity have been shown to reduce the aerosol stability of viruses.”
The study also referred to the 1989 Ebola outbreak at a primate quarantine facility in Reston, Va., in which the virus rapidly spread between unconnected rooms.
“While infections in adjacent cages may have occurred by droplet contact, infections in distant cages suggests aerosol transmission, as evidence of direct physical contact with an infected source could not be established,” the study added.
It is interesting to note this outbreak occurred in December 1989, when temperatures in Reston were usually below freezing, and it’s unlikely the indoor temperature in the vast quarantine facility was much higher.
A 2012 study also by the USAMRIID, which exposed monkeys to an airborne filovirus similar to Ebola, reached a similar conclusion to the 1995 study.
“There is no strong evidence of secondary transmission by the aerosol route in African filovirus outbreaks; however, aerosol transmission is thought to be possible and may occur in conditions of lower temperature and humidity which may not have been factors in outbreaks in warmer climates,” the study entitled A Characterization of Aerosolized Sudan Virus Infection in African Green Monkeys, Cynomologus Macaques and Rhesus Macaques stated.
The study pointed out that filoviruses, which include Ebola and the Sudan virus used in this particular study, have stability in aerosol form comparable to influenza.
“Filoviruses in aerosol form are therefore considered a possible, serious threat to the health and safety of the public,” it added.
And the Pentagon took this threat of airborne filoviruses so seriously that it organized a Filovirus Medical Countermeasures Workshop with the Department of Health and Human Services in 2013.
“The DoD seeks a trivalent filovirus vaccine that is effective against aerosol exposure and protective against filovirus disease for at least one year,” the executive summary of the workshop stated.
The Pentagon’s concern with airborne Ebola runs contrary to health officials who claim the disease can’t spread through coughing and sneezing, but according to the Army studies, that may only be true in tropical climates.
“How much airborne transmission will occur will be a function of how well Ebola induces coughing and sneezing in its victims in cold weather climates,” the web site potlblog.com suggested. “Coughing and nasal bleeding are both reported symptoms in Africa, so the worst should be expected.”