Earlier this month, the World Health Organization, blamed for a slow response to last year's massive Ebola epidemic in West Africa, declared this year’s rapidly spreading Zika outbreak in the Western hemisphere a "public health emergency of international concern." Meanwhile, in January, Ebola claimed two more victims in Sierra Leone, just after the official announcement of the end of a long epidemic that claimed over 11,000 lives in West Africa.
Given the many emerging infections we have experienced—including HIV, Ebola, and pandemic influenza—why did Ebola and Zika catch us so unprepared? Both have been known threats for decades. In each case, the first outbreak was initially discounted. Before the reports of neurological effects, Zika, a mosquito-borne virus that came to Brazil from Polynesia only two years ago and had been circulating in Africa for far longer, was considered a mild disease and little cause for concern. By contrast, Ebola's lethality has been legendary since it was first identified in 1976. But when the recent West African Ebola epidemic was first recognized, in March of 2014, pleas for reinforcements by Médecins Sans Frontières (Doctors Without Borders/MSF), the first international organization to respond, went unheeded by the international community. Hospitals and Ebola treatment units, overflowing with victims, were forced to turn many away.
For Ebola, after months of indecision, the international community mounted a massive response. Billions of dollars were pledged, the largest amount ever, much of it for building new Ebola treatment units. After the new treatment units were built, there were many reports of the buildings standing empty due to a lack of patients. History suggests that these units are also unlikely to enhance the weak health-care infrastructure, and may well stay empty due to the stigma of having housed Ebola patients.
Public health prevention offers tested, cost-effective ways to protect us so we're not always playing catch-up after an epidemic has already gained momentum.
Certainly, an Ebola epidemic on this scale was unprecedented and, to many observers and civilians, inconceivable. There is no cure for Ebola, and there was no vaccine available at the time, so treatment—essentially intensive care—becomes essential to the immediate response, and serves to prevent further spread by separating the infected from the uninfected. Recent advances in care have reduced the Ebola fatality rate from 90 percent to about 50 percent, but treatment is extremely resource-intensive. For example, MSF had 248 international and 2,800 locally hired staff in the affected areas, and operated a total of 549 treatment beds.
Despite these heroic efforts, however, there was a fundamental disconnect. Treating patients after the fact is far less effective than prevention, but public health—the heart of prevention—was largely missing from the response, especially in the crucial early stages of the outbreak. The main exception in the Ebola response was contact tracing, working back through the chain of known patients' contacts to identify others who were exposed so that they can be evaluated and treated. Even so, for most of the epidemic, 50 to 80 percent of the new patients had not previously appeared on any contact list, meaning that many Ebola victims were being missed.
Public health is much more than just vaccines. It uses a panoply of preventive measures to identify and reduce causes of disease at the population level. A prime example is public health surveillance, the reporting and identification of cases and the analysis of relevant data.
Surveillance can give early warning of a new disease (such as Zika in Brazil last year) or warn of increases in a disease already present. It was to improve global early warning that, in 1994, we started ProMED (the Program for Monitoring Emerging Diseases, a free, publicly available resource on the Internet for reporting and discussion of unusual disease outbreaks). Public health can then follow up on surveillance findings through epidemiologic investigation to analyze the patterns of disease in a population, possible causes, and the mechanisms of disease spread. This is being done now, at last, with Zika.
One of the classic examples of the power of this approach is Dr. John Snow's work on cholera in Victorian London. Snow, using techniques of public health detective work that today's epidemiologists would recognize, showed that cholera was carried in the water, and that water from a different source could greatly reduce the risk of catching the disease. Other key public health actions involve the community in safeguarding their own health, including health education (often through community leaders), hygiene and sanitation, and mosquito control. These should be participatory activities so that they also empower and strengthen communities.
Past experience with these and similar infections often seems forgotten in the midst of the crisis. People continue to insist that we need more treatment and vaccines, but public health prevention offers tested, cost-effective ways to protect us so we're not always playing catch-up after an epidemic has already gained momentum. Unlike a vaccine, which works for a single disease and can take months or years to develop, good public health also protects against the future epidemics still waiting in the wings, and can be applied anywhere.
We hear a lot about Zika now, but one mosquito, Aedes aegypti, is the primary vector (transmitter) of numerous viruses in addition to Zika, including yellow fever, dengue, and Chikungunya, all of which have been considered, at various times, more serious than Zika. Controlling this mosquito would by itself ameliorate all these disease threats. Ironically, in South America, control of Aedes aegypti was largely successful earlier in the 20th century (with great expenditure of effort), only to be abandoned once the immediate threat receded.
These public health measures are inexpensive in comparison with the cost of containing the last Ebola outbreak, or Zika, and would forestall much of the anxiety and suffering caused by these outbreaks. Many of the components of a strong global public health system already exist, but need to be made into a cohesive system and sustained. We have better tools than ever, including rapid worldwide communications, and new diagnostic and preventive technologies. Ebola is only one of many outbreaks that caught us unprepared, and, as Zika demonstrated, we can expect many more. Zika was on nobody's radar screen as a potential public health emergency. Such experiences remind us that we can't yet predict the next devastating epidemic, but we know it will occur. To save ourselves from another explosive epidemic like Ebola and Zika, and whatever comes next, we must learn to use public health effectively as our first line of defense.