Interspecies Airborne Transmission of Ebola

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Ebola virus (EBOV) causes a deadly hemorrhagic fever. The symptoms initially resemble a very bad case of influenza, but they progress to include a rash, splotchy purple skin, and internal and external bleeding. Blood loss is not the primary cause of death, however. Instead, death is due to circulatory shock from low blood pressure and other complications. Experimental treatments are being developed, but currently, there is no official regimen.

There are 5 known species of Ebola: Bundibugyo, Ivory Coast, Reston, Sudan, and Zaire. All of them can cause illness and/or death in humans, with the exception of Reston (which was partially the subject of the bestselling book The Hot Zone). As of May 2012, the World Health Organization reported 21 major outbreaks of Ebola since 1976. Zaire Ebola tends to be the most deadly, with case-fatality rates as high as 90%.

For people, the primary route of transmission is via direct contact with infected humans or animals or their fluids. Airborne transmission was considered theoretically possible, but not a major route of transmission.

That might change now.

Reporting in a new study in Scientific Reports, researchers infected pigs with Zaire Ebola. (In pigs, Zaire Ebola causes a respiratory tract infection, but it is not lethal.) They were placed in close proximity to, but not in direct contact with, four cynomolgus macaques (crab-eating monkeys) located in stacked cages. (See photo.) After 9 days, all the pigs cleared the infection. The monkeys did not fare as well. They all became infected with Ebola virus and were euthanized.

Furthermore, the authors also detected Ebola RNA in air samples taken from the laboratory.

While the results could not conclusively demonstrate that the monkeys weren't infected via some other route (e.g., by touching an infected saliva droplet and rubbing their eyes), other evidence -- including post-mortem analyses -- strongly suggest airborne transmission. 

The authors conclude that farms and other settings which house animals together could be sites of interspecies transmission of Ebola. And of course, their finding suggests that animal-to-human and human-to-human transmission of Ebola can happen through the air.

A couple of things to keep in mind: First, it is very likely that Ebola has always had this ability. However, since most cases of Ebola in humans probably occurred via direct contact, airborne transmission played only a minor role. Second, the pigs and monkeys were housed together for several days, and it is very likely that prolonged exposure is required for airborne transmission.

So, it's not time to panic. But, if you are the panicky type, then definitely don't watch this movie.

Source: Hana M. Weingartl, Carissa Embury-Hyatt, Charles Nfon, Anders Leung, Greg Smith & Gary Kobinger. "Transmission of Ebola virus from pigs to non-human primates." Scientific Reports 2, Article number: 811. November 15, 2012. doi:10.1038/srep00811

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