Wednesday, July 30, 2014

The Nature of Ebola

Ebola is a filamentous, RNA virus; of the five known species, four cause disease in humans.  Fruit bats appear to be the natural host (carrier) of ebola virus; they are unaffected by the virus but animals or humans that handle or consume bats, are bitten by them or consume fruit that they had partially eaten may become infected.  The index case in human outbreaks appears to most often result from that person having handled or consumed an infected animal (rather than having acquired the virus directly from a bat).  The virus has an affinity for endothelial cells, monocytes and hepatocytes (liver cells) where it begins to replicate; a flu-like illness generally develops within two weeks of exposure though the incubation period varies from 2 to 25 days.

The flu-like symptoms gradually worsen, leading to multi-organ failure and death in 50-90% of infected humans; coagulopathy leads to bleeding in the skin, GI tract and mucous membranes in half of the cases.  Transmission between humans, first documented in the Sudan and Congo outbreaks of 1976, is by contact with bodily fluids (saliva, blood, vomitus, stool, tears, sexual secretions, etc.); to date, transmission via respiratory droplets has not been documented.  The current ebola outbreak in West Africa is the largest documented by the World Health Organization to date and its potential spread to Nigeria via an infected traveler raises the specter of a more widespread outbreak.

At this time, there is no specific anti-viral therapy and an ebola vaccine is not yet available; supportive care (IV fluids, artificial ventilation, nutrition, blood pressure support, etc.) is currently the only medical option, placing healthcare workers at significant risk.  Prevention is the key, including education regarding contact with fruit bats, wild game and sick humans.  Since the human death rate is very high, a reservoir of infection does not develop within human populations; however, since the incubation period may be as long as 3 weeks, the disease may be spread before the infected individual is symptomatic.  An additional concern is the recent finding that male survivors of ebola may retain the virus in their semen and might infect sexual partners long after their illness subsides.