Since the April outbreak of Ebola virus infection in Africa, I have been asked by a concerned public to allay concerns about the risk of Ebola for Americans. I also have been asked why this and other terrifying viruses seem to emerge from places like Africa on a regular basis to threaten us with illness and destruction. I hope to answer these questions in this article.
For those of you who have not followed the African outbreak of Ebola virus in the news media, I can tell you that the illness caused by Ebola virus is riveting. Since the current outbreak started late in April, 121 of 160 patients have died, and the epidemic is not yet over.
[However, the World Health Organization announced Thursday that the virus' spread appeared to have stopped. It gave the death toll as 164 of 211 known victims.]
The virus and the illness it causes are worthy of some description. Ebola is a member of the family of viruses called filovirus. These are thin molecular tubes seen as long looped or bent threads under the powerful electron microscope. If they enter cells of the body, they multiply exuberantly, destroying these cells and packing them with crystals of Ebola virus.
A person infected with Ebola usually first complains of an abrupt, splitting headache followed by high fever and by pain in muscles and joints. Knife-like chest and abdominal pains may occur early, and the patient rapidly becomes so sick and exhausted that he or she cannot climb out of bed. As a result of the fever and severe watery diarrhea that develops, the patient becomes depleted of salt and water, causing even more weakness. A raised or splotchy red rash develops about a week after the onset of the illness, growing for three to four days. After this, the flesh may peel off in places like a snake shedding its skin.
After one week, the blood of most patients fails to clot, and they begin to bleed. This is why the illness is called Ebola hemorrhagic fever. Patients bleed into their lungs and cough up blood clots. They bleed into their intestines and vomit blood and pass black bloody stools. They bleed from the nose, gums and vagina. They bleed into their skin, developing bruises, and the whites of their eyes turn blood red. They ooze blood from needle puncture sites and from ordinary cuts. The majority of such patients, about one in four or up to nine of 10 depending on the virus subtype, die in one to two weeks after massive blood loss, death of internal organs and shock. It is easy to understand why emerging viruses of such virulence are attention-getters.
But one must remember that not all infected persons die, and many may not even get sick. Like most viral infections, some individuals with Ebola undoubtedly resist even the most virulent varieties of the virus. But we don't know how many people can resist, nor how they do this. Resistance could be a matter of low doses of infecting virus, a change in the virus itself which weakens it, or immunity of the infected individual to the virus. Surprisingly, antibody surveys in Africa reveal that many people have been infected with Ebola in the past, up to 21 percent of some populations in Central Africa, for example. So obviously, most people infected do not die, but we do not know how many will remain well or how many will become sick.
We know that humans can be infected by innocuous Ebola viruses. For example, six years ago some animal handlers in Virginia were infected by Ebola virus spread from infected monkeys imported from the Philippines, but the handlers had not become sick, whereas the monkeys died. (How monkeys from the Philippines got Ebola is a mystery.) One wonders if such "weakened" viruses account for some of the anti-Ebola antibodies found in perfectly healthy Africans.
What triggered the current outbreak of Ebola virus in Zaire? The virus was first identified 19 years ago, when the disease broke out simultaneously in southern Sudan and northern Zaire. The virus in fact is named after a Zairian river.
No clinical case was confirmed for 15 years in Africa. Where had the virus been lurking all these years? Small or large mammals, biting insects or even plants are all possible incubators of the virus, allowing it to go into hibernation. We simply do not know the environmental reservoir, but there must be one because viruses cannot live and replicate by themselves outside of living cells.
I'm hopeful that we will eventually discover the haunts of Ebola virus, because until we do, it will be nearly impossible to prevent or control it. Teams of African, European and American investigators are actively searching out the origins of the current Zairian epidemic.