Ebola virus has been front-page news recently and the arrival of Dr. Kent Brantley at Emory University Hospital in Atlanta was the first Ebola infected patient to be transported to the U.S. for care. This required a specially equipped air evacuation plane for transport from Liberia to Atlanta and for Emory University Hospital to work with the CDC to set up a special isolation unit for his care. The concern for human to human spread of the virus is highlighted because spread of the virus to health care workers (Dr. Brantley and the U.S. nurse Nancy Writebol being prime examples) is a large part of the reason this is newsworthy.
Ebola virus disease is caused by at least 3 species of viruses in the Ebolavirus genus of the family of viruses called filoviridae. These three species, Bundibugyo evolavirus, Zaire ebolavirus, and Sudan ebolavirus have caused the known large scale Ebola virus disease outbreaks in Africa. Another species called Reston ebolavirus is found in the Phillipines and although it has caused infection in humans it has not been known to be associated with illness or death of humans to date.
Ebola virus disease is an extremely severe illness in most cases. Symptoms typically include high fever and chills, muscle pain and extreme weakness, headache, headache and sore throat. These symptoms are typically followed by severe multisystem disease including kidney and liver failure, rash, gastrointestinal symptoms including vomiting and diarrhea, and often both internal and external bleeding. Death rates in most of the major outbreaks have exceeded 90% although in the current epidemic in Liberia for unknown reasons the death rate at least among the 45 health care workers who have become infected has been somewhat lower.
Ebola virus is believed to have fruit bats as its primary host. In all of the areas where large scale outbreaks have occurred in areas where specific types of fruit bats are common. Other animals, especially other primates including chimpanzees and gorillas have noted, and spread to humans from these animals and others acting as accidental hosts, just as humans are accidental hosts when they become infected by ebola virus.
In West Africa it is believed that humans can become infected when they handle ill or dead infected animals. Then human-to-human spread can occur through contact with infected body fluids of those infected with the virus, either through direct contact or by contact with environmental objects that have become contaminated by virus-containing body fluids or secretions.
Health care workers are at risk in the course of caring for patients with Ebola virus disease. The vomiting, diarrhea and bleeding disorder these patients often exhibit makes avoiding exposure to the virus a challenge even when attempting to use proper protective attire.
The specially designed isolation unit at Emory Hospital in Atlanta where Dr. Bentley is receiving care is undoubtedly using the absolute best safety precautions. Still the risk of transmission of the virus to health care workers is real. This risk of a wider-scale human-to-human outbreak in the U.S. seems exceedingly low, but it is just that risk that I suspect makes the return of Dr. Bentley to Atlanta so newsworthy.
For a more complete discussion of the history of Ebola virus disease and the virology see this WHO article.