Volume 34, Issue 1, Winter 2015

The Mysteries of Ebola

Probing the Connections

By BCI Staff


Editors’ note

The outbreak of Ebola in West Africa has been devastating. While Senegal and Nigeria have contained their outbreaks, the situation remains grim in Guinea, Liberia and Sierra Leone—though the rate of infection has begun dropping in Liberia. As of early December, at least 15,000 individuals had contracted the disease and more than 5,000 had died. Mali is the latest African country to report cases. All previous known outbreaks were in Central Africa; this is the first documented outbreak in West Africa. Because several species of fruit bats in Central Africa and Asia have been found to possess antibodies to the disease, scientists believe bats are a natural reservoir for the virus, which apes, forest antelopes, porcupines and humans can catch from eating fruit or other foods contaminated by bat saliva or droppings, or by touching their mouths or eyes after touching a surface contaminated by droppings or saliva. Our hearts go out to the victims of this terrible tragedy.

In the end, we may never know how it began.

Image courtesy of the World Health OrganizationIt was in March when the mysterious illness affecting a small region of Guinea was identified as Ebola. Although West Africa has a native strain of the virus, the strain from which people in Guinea were dying appears to be a variant of Zaire ebolavirus, known previously only from outbreaks in Central Africa, more than 2,000 miles to the east.

The current outbreak, by far the largest since the disease was first identified in 1976 in Central Africa near the Ebola River, seems to have started in the village of Meliandou in Guéckédou Prefecture, Guinea, with the death of a 2-year-old boy in December 2013. His mother, sister and grandmother also became fatally ill. People infected by those victims and a local health care worker—Ebola spreads by physical contact with bodily fluids—then carried the disease to other villages. Health care workers responding early to the crisis were particularly hard hit, with 419 contracting Ebola and 233 dying before protective clothing, strong disinfectants and improved procedures for working with infected individuals were widely available.

Since then, Ebola has spread to five other African countries, and infected health care and aid workers returning to Europe and the United States have spread Ebola to several European and American nurses who have treated these individuals. In Guinea, Liberia and Sierra Leone, the disease continued to spread rapidly due in part to the common West African practice of touching and washing the body of the deceased.

Doctors Without Borders, which was already working in Guinea on other diseases, speculated the young Guinean child—“Patient Zero” in the parlance of epidemiology—had gotten the disease directly from local fruit bats, noting that bats are routinely hunted in the area as “bushmeat.”

This did not explain, however, if and how Zaire ebolavirus jumped 2,000 miles from Central Africa. New questions arose while old ones lingered: Had an infected fruit bat from Central Africa flown that distance and been caught and eaten? Had its droppings or saliva contaminated a piece of fruit eaten by a person, pig, porcupine, forest antelope or primate? Did Zaire ebolavirus travel to West Africa in another way, possibly via Guinea’s underground trade in primates and bushmeat?

And regardless of how Ebola made this journey, when exactly did it arrive? In April The New England Journal of Medicine reported the Ebola striking West Africa may represent a previously undiscovered strain that may have been circulating in West Africa for some time. This theory received support in a September article in Science: Researchers studying genetic variation over time of Zaire ebolavirus believe this variant may have found its way from Central Africa to Guinea as early as 2004. How it did so remains unknown. Extensive field research and testing of West African fruit bats and other animals routinely consumed as bushmeat may be needed before the likeliest routes of transmission are known.

The origins of four previous outbreaks of Ebola, all in Central Africa, are equally obscure. The truth is, the study of zoonotic disease—maladies that can jump from wild animals to humans—remains a young science. Predicting Ebola outbreaks remains elusive, although scientists are working towards this goal. Dr. Kevin Olival, a disease ecologist with EcoHealth Alliance, says a concerted, multidisciplinary effort is needed to better characterize the diversity and distribution of Ebola viruses in wildlife. “Then we must overlay this with risky human behaviors, like bushmeat hunting, that are likely to lead to viral spillover,” he notes.

When the epidemic is finally contained, the world will be a different place. The world’s leading health care systems and international health agencies have had their shortcomings exposed. The lack of funding to bring trial vaccines to market for heretofore-obscure diseases must be addressed. In the hardest-hit countries—Guinea, Liberia and Sierra Leone—the social and economic consequences are already profound. The fragile economies of these countries have been seriously damaged, as international travel and trade with those countries have all but disappeared. The grieving, angry and fearful survivors of Ebola will demand answers and assurances from governments that have few of either to give.

What Is Ebola?

Ebola is a hemorrhagic (i.e., causing internal bleeding) fever caused by a virus in the Filoviridae family. It is a severe, often fatal disease in humans and gorillas, chimpanzees and monkeys. Five strains of the disease have been identified, one of which does not infect humans. Symptoms appear two to 21 days after exposure, according to the World Health Organization. At first, it seems much like a flu—headache, fever, and aches and pains. Sometimes there is also a rash; diarrhea and vomiting follow. In more than half of all cases, Ebola takes a severe turn, causing victims to hemorrhage. Death is usually caused by blood vessels deep in the body leaking fluid, causing blood pressure to fall so low that the heart, kidneys, liver and other organs begin to fail.

Information courtesy of the World Health Organization

Though several medications are being rushed to trial, there is no vaccine or definitive cure for Ebola. Patients brought to treatment centers are kept hydrated, nourished and treated for other infections as needed in hopes that the body’s immune system can eventually overcome the disease, as it does in about half of the patients receiving medical attention in the current outbreak. Virologists also believe some people are immune: A 2010 study in the Central Africa nation of Gabon found 15 percent of the population had antibodies to Ebola. Immunity may be conferred, ironically, by having gotten low doses of the virus by eating infected fruit or monkeys or bats that are undercooked, according to researchers at the Universities of Texas, Tulane University and the International Center for Medical Research in Gabon. But it remains a hypothesis.

The virus is spread through direct contact (through broken skin or mucous membranes) with the blood or other body fluids of a person who is sick with Ebola, or with objects (like needles) that have been contaminated with the virus. There is no evidence Ebola can be spread through the air or water.

Until the current outbreak, highly contagious Ebola was thought to be confined to Central Africa. This is the first known outbreak in West Africa, and it far surpasses the scale of the previous four large outbreaks.

Scientists believe people risk infection when they or their domestic livestock, like pigs, consume raw fruits contaminated by the saliva or droppings of one of three species of fruit bats in Africa found to have antibodies to Ebola.

This fact has led scientists to believe that these bats are a natural reservoir for the disease, but to date, no live Ebola virus has been found in any bats. But given this background and because apes and other primates consume large quantities of fruit, they also are at risk of contracting Ebola, as are some ungulates. Hunting and consuming primates and bats as bushmeat is another risky behavior West African governments have sought to curb early in the current epidemic.

Still, the fact remains: When Ebola will appear, and the exact reasons why, cannot yet be predicted. Far more remains unknown than known.

Separating Fact from Fiction

In times of crisis, however, it’s human nature to want answers, and the scientific uncertainties underlying this devastating epidemic make it more difficult to dispel widespread fear and anger in the affected countries. Because only 50 percent of people survive and return home from hospitals, many infected individuals have shunned treatment centers, leading to greater spread of the disease. Those who think health care workers bring the disease with them have even driven doctors and nurses out of villages. It also has been difficult in some rural areas even to track the disease, due to the belief that saying the word, “Ebola” would bring it on. An early but widespread rumor that Ebola was a medical hoax further hampered public cooperation. Conversely, those seeking medical treatment have often been turned away, given the very small number of hospital beds in these countries. Sierra Leone took the dramatic step in October of admitting as much and began providing families with protective clothes and gloves to take care of family members at home.

Given the terrible impact of this tragedy, it may seem callous in the extreme to ask, “What does this outbreak mean for bats?” But the health of bats and humans in the tropics are inextricably linked. Bats control insects, pollinate crops and help maintain the health and diversity of tropical forests in Africa, as elsewhere. As those forests disappear and humans increasingly encroach on the last remaining habitats for bats and all other wild animals—and in some cases eat these animals—the potential for zoonotic disease to jump to humans increases substantially.

Given what we currently know about Ebola, the indiscriminate, widespread killing of bats would probably do little to make people safer, and perhaps would have the opposite effect if displaced bats are driven to seek out new roosts. But given the scale of the current crisis and its heavy toll on human life and well-being, a determined and coordinated effort to exterminate bats throughout West Africa may occur. Nigeria, which limited its outbreak to 19 people infected by a man who flew there from Liberia, has begun exterminating bats near government buildings.

As the crisis recedes, BCI and its public health partners will advocate for African governments to embrace a “One Health” approach (see related sidebar below) to minimizing the chances for future outbreaks. We also may help fund research to answer some of the key questions surrounding bats and their possible role in the current epidemic, as well as explore whether better understanding the immune system of tropical fruit bats could lead to better control measures in the future (read “Can Bats Help?” on page 11 for more on this topic).

In the more immediate future, banning consumption and sale of bushmeat, cracking down on the illegal wildlife trade, and reducing human encroachment into parks and preserves and other important natural areas would all be important steps forward. But in some of Africa’s poorest countries, these could prove tall tasks.

Can Bats Help?

Beyond their more well-known research associations with sonar and radar technology, bats have been the subject of many scientific studies over the years. At the Centre for Irish Bat Research, the genetic code of bats, some species of which can live for more than 40 years, is being used to study aging in humans. The anti-coagulating agent in the saliva of vampire bats has been used to create medicines that aid the recovery of stroke victims.

Now, some researchers are hoping bats can help us learn more about Ebola.

In addition to being a suspected reservoir for Ebola, bats are believed to be natural hosts for the viruses that cause Marburg, Nipah, SARS and MERS. As far as scientists are aware—and more research is needed—the immune systems of some species of bats may be providing some level of protection to bats against these viruses.

Answering questions about the immune system of tropical fruit bats might contribute to the development of control measures against the spread of diseases like Ebola, says Professor Janusz Paweska, head of the Special Pathogens Unit at the Centre for Emerging and Zoonotic Diseases at the National Institute for Communicable Diseases in Johannesburg, South Africa.

Ten researchers, including Paweska, identified Ebola antibodies in three fruit bat species in 2005. In 2011, he was part of a research team that visited Luebo in the Democratic Republic of Congo (DRC) to study one of the identified species, the hammer-headed bat (find out more about this species on page 6). In 2007 and 2008, the Luebo region was hit by two outbreaks of Ebola.

Understanding how deadly viruses like Ebola and the similarly fatal Marburg virus circulate in reservoir hosts is one of “the most hunted treasures in modern biology,” Paweska says. “If we could understand the bat immune system and how it counteracts the replication or the growth of these very dangerous viruses, we might take some lessons from there and apply them to the development of antivirals or vaccines,” he adds.

 

 
 
 

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