Understanding Ebola

We have all seen clips on TV of the medical teams in West Africa suiting up with the equivalent of mediaeval full body armour – their only protection against the deadly virus Ebola. Iron Man’s armour has a much simpler task. Last month in Christian Courier, Judith Dinsmore wrote about the devastating consequences of this epidemic.

The World Health Organization is so worried about the danger of this outbreak that they recently took the unprecedented step of permitting doctors to use medicines that have not yet been fully tested. Experimental vaccines are being rushed into production even before we know they are safe and truly effective. This virus is that dangerous.

Epidemiologists at Virginia Tech who are tracking the disease to predict its future suggest that the situation could get much worse and that the spread could be “spiraling out of control.” Depending on our response, the case count of 4,366 on September 7 could, by October 12, be anywhere from 7,861 (if control improves) to 54,895 (if control breaks down). When you read this, these numbers will be out of date, but they indicate how serious the situation is.

The science of an epidemic like this revolves around a number of issues that determine how dangerous it is and what has to be done to control its spread. The West Africa epidemic is not the first Ebola outbreak, but it is unusual in that it has extended into urban areas and become as widespread as it has. Based on past outbreaks, we know a lot about Ebola, and this epidemic is showing characteristics of previous outbreaks.

Severe and infectious  
One number that determines an epidemic’s danger is the mortality associated with the disease. Ebola has a very high mortality rate. In the current epidemic the probability that you will recover if you have the disease is less than 50 percent; in past outbreaks survival has ranged between 75 and 10 percent (25 to 90 percent of infected people die). Ebola is thus very dangerous, especially because we can only treat symptoms; we have no established way to help individuals with the illness.

The second important number is the basic reproduction rate, an indication of how likely the disease is to spread. If you have one case, how many people will be affected? Airborne diseases have a high reproduction rate. Measles, for example, has a reproduction rate of 12 to 18, making it very hard to control, which is why we want all children inoculated against measles. Ebola, in contrast, is currently spread only by direct contact with bodily fluids so has a basic reproduction rate of one to four. If the reproduction rate drops below one, the disorder will eventually die out. Having a population with some degree of immunity, because of a vaccine, natural immunity, or reduced person-to-person contact, lowers the reproduction rate. One of the big fears with Ebola is that it may mutate to a form that can spread in an airborne manner, significantly increasing its reproduction rate. At this point the West Africa Ebola is showing a reproduction rate of just under two, typical for this disease.

The last important number in understanding what will be needed to control and eradicate this epidemic is the time involved in its various stages: incubation period, the time from symptom onset to hospitalization and the time the person is in hospital. For all these numbers this Ebola outbreak is showing typical characteristics of past outbreaks.
It is based on these numbers that predictions of the need and scale of the epidemic are made.

Spreading like wildfire
Scientists have concluded on this basis that if there are no changes in the situation, the number of Ebola cases could double in 15 to 30 days in the three countries involved. If there is a breakdown in control, the number of cases will double faster; if more resources are deployed, the rate of increase will slow down.

Joanne Liu, international president of Doctors Without Borders, says that currently they are overwhelmed by the scale of the epidemic, and a massive deployment of the appropriate resources is urgently needed. She ends her Globe and Mail article, “To put out this fire, we must run into the burning building” (Sept. 15, 2014). From a Christian perspective we need to act rapidly, with great generosity, and with love to help in this situation. Pray fervently for those who are running into this burning building.
 

  • Rudy Eikelboom is a Professor of Psychology, at Wilfrid Laurier University, who has emerged from the dark side of the University after being department chair for 9 years and now teaches behavioural statistics to graduate and undergraduate psychology students. His retirement looms and he is looking forward to doing more writing on the implications of modern science for our Christian faith. Currently, he serves as a pastoral elder at the Waterloo Christian Reformed Church.

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