Reasons to Calm Down About Ebola

Reasons to Calm Down About Ebola

 

Nigeria has contained Ebola, with a health system that is better than Liberia’s but below developed-world standards.

By F. Landis MacKellar  and Jose G. Siri  in the Wall Street Journal

 

The Ebola epidemic ravaging Liberia, Sierra Leone and Guinea is unlikely to become a global pandemic, though an international response is critical. The isolated cases in the U.S., Spain and elsewhere are to be expected, but as long as public-health systems act with alacrity, this should not lead to new outbreaks.

Ebola is not particularly successful in humans by viral standards. HIV, to take a familiar example, has been killing more than a million people a year for almost two decades. Ebola has hitherto caused only small, localized outbreaks. This is likely because Ebola is not adapted to human hosts, but is introduced into populations on rare occasions, when people come into close contact with its natural reservoirs—thought to be bats and possibly other wildlife. Since the virus didn’t evolve with humans, it wreaks havoc on our bodies but achieves only limited success in propagating itself.

A virus’s goal is to survive, which means infecting as many new hosts as possible. There are a number of ways to do this. One is to be highly transmissible, jumping from individual to individual through proximity or casual contact. Think influenza, which causes its hosts to spew massive numbers of infectious airborne particles. Another way is to cause only minor disease, but to remain infectious over long periods. Cold sores, for example, are caused by the herpes simplex virus and are lifelong.

Ebola does neither. The period of transmission begins only after symptoms appear. There is no evidence for airborne transmission, and while sexual transmission is possible, it is not likely a major route of infection. Images of health workers in alien-looking protective gear spread fear and anxiety, but Ebola is not very contagious. Transmission requires direct contact with bodily fluids. The reason to use hazmat suits is not the probability of contagion; it is that, if you are infected, the probability of death is high.

There are straightforward epidemiological models that can help us understand Ebola and forecast its spread. A handful of parameters can describe an epidemic: the length of the infectious period before recovery or death and the contact rate between individuals, for example. The bottom-line figure, however, is the effective reproduction number: the average number of new infections arising from a single infected individual. If greater than one, the epidemic widens; if held below one, the epidemic dies out.

Right now, most estimates place this number in West Africa between 1.5 and 2, meaning that Ebola continues to increase exponentially. The U.S. Centers for Disease Control and Prevention estimated in late September that ending the epidemic will require 70% of the infectious population to be placed in medically supervised isolation units, or settings where the likelihood of transmission is similarly reduced. That is unlikely to be achieved soon. Every month of delay in reaching that target will result in tens of thousands of additional deaths, the CDC warns.

Why is the scale of this Ebola outbreak so unlike what we have seen before? How did it escape public-health systems, created in large part to contain infectious disease? Two factors can help explain.

The first, depressing factor is that Ebola did not need to elude public health systems—there were none to speak of in Liberia, Sierra Leone or Guinea. According to a 2014 report from the World Health Organization, per capita government health spending in 2011 was $18 in Liberia, $13 in Sierra Leone and $7 in Guinea. In the U.S., it was $4,047. Households are too poor to fill the gap with private expenditure and there are limits to how much international aid programs and charity can do.

The second factor is urbanization. Previous Ebola outbreaks—all in rural and relatively isolated areas—were amenable to familiar tactics including, for example, rapid deployment of field hospitals, isolation of cases identified through contact tracing, and careful burial practices.

But West Africa, like other parts of the world, has experienced galloping urbanization, in both capital cities and the hinterlands. Urban lifestyles make contact tracing more difficult, creating risk factors different from those in previous outbreaks. For example, the WHO warned of the danger of Ebola infection from unsterilized public transport in Monrovia, a fairly novel concern for health workers. Urban poverty can be deeper and more desperate than rural poverty, and infrastructure and services in cities are often lacking.

Globalization has made international disease transmission easier, but it is unlikely to lead to large-scale global propagation in this case. For Ebola, the barriers to global spread are high. Highly infectious people are desperately sick; they will not be boarding airplanes. Travelers entering this stage after reaching their destinations will be identified and isolated by properly functioning health systems.

Nigeria provides an edifying example. The collapse of Liberian-American Patrick Sawyer in Lagos’s busy international airport on July 20 was the nightmare scenario—Ebola unleashed in a crowded venue, in a teeming megacity of the developing world. But rapid, well-coordinated action on the part of the Nigerian government averted disaster, and that West African nation’s incipient outbreak has been contained, despite a health system below developed-world standards.

Misjudgments are possible, as when Ebola patient Thomas Eric Duncan was turned away from a Dallas hospital, and subsequently died on Oct. 8. Protective protocols can be insufficient or break down, as was the case for health-care workers who cared for Duncan and for a nurse’s assistant who contracted Ebola in Spain. But as the threat of Ebola importation becomes more widely understood, health-care professionals and facilities are better prepared with each passing day. What the public should understand is this: Vigilance and decisive action can halt Ebola’s spread even under adverse circumstances.

Mr. MacKellar, senior associate at the Population Council, is co-editor of Population and Development Review. Mr. Siri is a research fellow at the United Nations University International Institute for Global Health.