Chapter 11 The Imminent Threat of Tropical Viruses: Lessons from the 2014 Ebola Outbreak in Africa

In: Chinese Research Perspectives on the Environment, Volume 9
Author: Xiaohui Shen


While tropical viruses can cause lethal diseases, humans are accountable for unleashing them from the tropical forest. It was precisely human activities of killing wildlife and destroying forests that penetrate the ecological barriers of epidemics and thereafter resulted in the spread of diseases across species. Humanity must contain itself before it can truly learn to co-exist with the nature in harmony.

In March 2014, new Ebola outbreaks swiped Guinea and quickly spread to other African countries such as Sierra Leone, Liberia, Nigeria, Congo-Kinsasha, Senegal, and Mali. According to the latest statistics released by the World Health Organization, the number of people who died of Ebola worldwide had exceeded 10,000 by the end of March 2015, with a total of 25,000 cases of confirmed infection. Three countries in the West Africa region were stricken the most. Due to the difficulty in collecting data from the vast rural area of Africa, the World Health Organization estimates that the actual number of deaths far exceeds the registered number.

This wave of Ebola outbreak was the worst of its kind in history with an accelerating speed of spreading. Many West African countries had to declare a state of emergency. Flights to the epidemic areas were banned and canceled. An ominous air shadowed these tropical African countries as the panic of the virus spread to other countries. Since the epidemic in West Africa was going out of control, the World Health Organization announced that the Ebola outbreak had become a worldwide public emergency and demanded all countries to attach great importance to the development of the pandemic.

1 Three Lethal Viruses from the Tropical Forests in Africa

Viruses are a primitive microscopic organism that is an intermediate form between life and non-life. They are parasites that cannot be “activated” without other cells. A virus is a biological matter yet not completely in life form. It must attack and conquer the host’s cells to reproduce itself. This shows that the virus’s livelihood is extremely “economical,” surviving on resources and energy that entirely come from the host. It is an infective organism that self-replicates with the help of host cells. In the evolutionary processes, viruses generally coexist with the host in peace to obtain a sustainable use of host cell’s resources. However, when viruses spread across species, such equilibrium can often be upset. Moreover, hosts from an alien species may also give in completely to the new viruses. Therefore, in such processes, sudden malignant cell lesions can be intensive enough to destroy the host’s life.

It is estimated that there are at least 320,000 viruses that can infect mammals worldwide. Historically, humans have been struggling with epidemics caused by viruses. In the era of raging infectious diseases, an outbreak of pandemic can significantly impact historical directions. Some scholars point out that, from an epidemiological perspective, Rome was fallen due to malaria; Egypt was destroyed by schistosomiasis; and the Ming and Qing dynasties in China were weakened by the plague. These pandemics led to social chaos which influenced the fate of a civilization. Now, in order to understand the roots of the three major pathogens that are most harmful to modern society, please allow me to draw your attention to Africa.

1.1 Malaria

Malaria is a common human disease that threatens public health in 90 countries around the world. It is a parasitic disease caused by the infection of female Anopheles mosquitoes. More than one-third of the world’s population has been infected with malaria. It is estimated that on an annual basis, the number of people suffering from malaria is 300 to 500 million,1 causing 1.5 to 3.5 million deaths. Most cases of malaria infection and deaths occur in sub-Saharan Africa. During the two years I lived in the West African country Guinea-Bissau which had the highest mortality rate of “brain malaria,” I was infected with malaria twice. Fortunately, I was able to restore health after China’s medical aid team to Africa provided me with timely and effective treatment.

Scientists analyzed some blood samples from wild chimpanzees in Cameroon and found the true source of malaria parasites. They identified eight species of Plasmodium, and the genes of chimpanzee’s Plasmodium is more diverse than that of human Plasmodium, indicating that the malaria is transmitted to humans by the intermediate of the Anopheles mosquito from chimpanzees. Using genetic sequence information, scientists were able to estimate that malaria originated in Africa 65 million years ago, yet it did not spread to areas beyond Africa until 3,300 years ago when it became a global epidemic.

1.2 AIDS

AIDS originates from a virus that attacks human body’s immune system. The complex structure of HIV shows that it has undergone an evolutionary process of natural selection. HIV has 9 genes and is so far the most complicated virus known to human knowledge. While the first case of AIDS infection can be traced back to 1959, the first widely-known AIDS case was found in the United States in 1981. In 1985, the disease was officially dubbed the name of “human immunodeficiency virus” (HIV). In Africa, the geographical distribution of the AIDS population closely matches that of a species of mangabeys,2 yet the infected animals are not killed by the virus. It is said that the hosts of HIV can be traced back to Central Africa in the early 20th century when a hunter entered the tropical forest of Cameroon and killed a chimpanzee. The virus in the chimpanzee’s blood entered the human body through the hunter’s wounds and changed the fate of human beings. HIV has infected at least 65 million people to date, killing about 2 million people each year, and infecting 6,000 new patients every day. AIDS patients in Africa account for more than 70% of the world.

Scientists have two diverse views regarding the origin of AIDS. One perspective is that HIV was originally hosted by human beings since humans evolved from apes millions of years ago, only was discovered and named in recent decades. However, more scholars believe that HIV is not possessed by humans but is caused by cross-species infection of viruses from chimpanzees. After studying the genes of our ancestors, some American scientists believe that since humans and chimpanzees branched out from the evolutionary tree, the two species had sexual relationships for 4 million years and had common offspring. Many scientists also believe that mankind paid a heavy price for such sexual activities with AIDS being one of the worst consequences. Today, the recurrence of AIDS pandemic is fueled by modernity. It has become a disease of civilization and urban lifestyle, which has created an ideal environment for the activation of an ancient virus to spread globally through airplanes.

1.3 Ebola

The Ebola virus is more terrifying than HIV. It is a haunting hemorrhagic plague in Africa. People who have been infected with the Ebola virus rarely survived, with most patients died after one week of initial symptoms. There is still no treatment to cure or prevent Ebola. The deceased victims of the disease have blood coming out of their eyes, ears, and nostrils. Such scenes are particularly chilling. The inner organs of the victims are eventually devoured by the virus, turning into a shapeless slimy paste.

In fact, Ebola is not a new type of infectious disease. It has been popular for centuries in the tropical jungles and grasslands of Central Africa. Ebola had not been well-known because it did not lead to massive deaths previously. The earliest record of the Ebola outbreak was in September 1976, which spread from Sudan to a small town in Zaire called Yambucu (now in Congo-Kinsasha). At the time, this undisclosed yet highly contagious virus ravaged 55 villages and caused 280 deaths. A group of experts from several western countries named the virus after the Ebola River near Yambucu. Since then, there have been more than 30 Ebola outbreaks. Nearly a thousand people died in the 1995 epidemic. Thousands of gorillas also died in Congo and Gabon. After the outbreak of the pandemic, the forest was silent, and the nature was terribly quiet. This time in West Africa, the Ebola eruption was most unusual because it had only happened in the central and eastern parts of Africa. Moreover, none of the incidents had spread as wide as in 2014 with so many cases of infection and death.

The Ebola virus was discovered, but the source of the virus and the route of transmission became a mystery for some time. Ebola is different from diseases like AIDS which causes slow deaths and leaves ample time to reproduce and spread. Ebola uses some animals that carry pathogenies that humans still do not know so well. The reason why the pandemic has not yet caused a pandemic in the world like AIDS and malaria is not that humans have done a perfect job of prevention and control, but because the Ebola virus can kill the victims before it spread. As a result, the virus disappeared with the patient without a trace. As a result, humans found the emergence and disappearance of the disease have been irregular and unpredictable. It is foreseeable that the Ebola epidemic will vanish and recur after hibernation.

Only by locating the origin of the virus and verifying the media and channels of its infection, we could be able to take measures to cut off the origins of the disease and permanently control the epidemic. Scientists believe that the origin of the Ebola virus may be a kind of wild animal that has no direct contact with humans. It is very likely another kind of animal that has direct contact with humans acts as an intermediate host and transmits the virus from the original host to the crowd. This theory is able to explain the sudden appearance and disappearance of Ebola in the past decades. To test such hypothesis, scientists from various countries in Africa have examined mosquitoes, bugs, mice, pigs, cows, monkeys, bats, and deer. In 1996, scientists captured and analyzed 48,000 animals in the Central African Republic alone. However, they didn’t find any substantial evidence.

2 A Bane of Disturbing Wildlife

In 2014, after the first outbreak of the Ebola epidemic in four countries in West Africa, 17 European and African experts in tropical diseases, ecology and anthropology formed a research team to investigate and trace the origin of the Ebola virus. They performed animal testing near a small mountain village in remote eastern Guinea, where the first outbreak of Ebola was recorded in December 2013. Scientists discovered that at the time, a two-year-old child was bitten by a fruit bat that had been infected with the Ebola virus. The boy then transmitted the virus to his mother, both of whom died within a week. Later, as the Ebola virus spread with the crowds who came to attend the funeral, it spread farther and farther and expanded.

Previously, although scientists have discovered that bats are the main carriers of the Ebola virus, it was rare to observe cases of infection from bats to humans. The Ebola outbreak was caused, in many cases, by eating infected wild animals. In the Congo rainforest and its surrounding areas, chimpanzee meat is an integral part of the dietary structure of indigenous peoples, and chimpanzees rush to eat young children from time to time. In a sense, it may be said that the food chain relationship in tropical Africa is as old as prehistoric.

In January 1995, a farmer from the outskirts of Kikwit in Zaire died of hemorrhagic fever. The epidemic quickly spread, killing 245 people in 4 months, including 60 medical staff. However, the investigation of the Ebola virus host by scientists discovered nothing. In February 1996, in a small remote village Mayibout at the junction of Gabon and Zaire, 18 people fell sick at the same time. Before the illness, they were believed to slaughter a chimpanzee who died in the jungle and ate it as a meal. Scientists later noticed that the chimpanzees were dying due to Ebola infection. Subsequently, they also discovered Ebola virus in samples of three large fruit bats. At this point, after more than ten years of field research, scientists finally traced the hosts and intermediate hosts of the Ebola virus.

We have also concerns over the diet of people living in Gabon and Cameroon. Locals eat most kinds of wildlife they hunt. In the bazaar of Congo (Brazzaville), we have seen monkeys being slaughtered and roasted for sale. In Gabon, people chopped off the heads of black colobus and make them into barbecue items; and in Guinea, bat soups and smoked bats were local delicacies; not to mention the common hobby of indigenous people in African jungles: eating chimpanzees and gorillas. Therefore, such trade of “bush meat” has directly led to the spread of waves of various diseases across species to humans. When people are eating these wild animals, the viruses carried in them entered the human body and are in fact engulfing humans too.

Chimpanzees, gorillas, and monkeys are all hosts for the Ebola virus, while bats are intermediate hosts for spreading the virus. In Guinea in March 2014, it was bats that caused a major outbreak of the Ebola virus. Studies have shown that the level of metabolism of bats can increase 15 times when they are flying (compared with birds which only increase 2 times). As their metabolism level soars, the body temperature of bats rises. Increased body temperature can stimulate many immune responses in mammals and produce more antibodies. Bats are able to reduce the toxicity of various viruses in the body through their mechanism of continuous high fever. As a result, bats have become highly-effective repositories of viruses, and their ability to retain mobility while carrying the viruses enables them to become highly-effective spreaders of viruses.

Bats are hosts of many deadly diseases and viruses. It is due to the destruction of their natural habitats, bats have to approach human settlements and live in fruit trees and trees with flourishing branches. Of all the different kinds of bats, the fruit bats are the most dangerous kind. They will leave the virus on the peel and flesh of the fruit through their saliva and urine. People who eat these virus-infected fruits will be infected.

Bats are mammals with an ancient ancestry. Their superior flying capability has enabled them to acquire a vast mobility space and to contact with a large number of plants and animals. This increases the possibilities to spread the pathogens they carry. While bats can carry as many as 61 kinds of viruses that can cause human diseases, they themselves are immune from the symptoms and therefore are particularly scary. Once the viruses are transmitted to humans, they will create a storm of plague that spreads and cause deaths everywhere.

American medical historian Howard Michael, author of The Story of Pestilences3 points out that humans have not yet learned the right way to live in harmony with nature. Some viruses that have been hibernating for thousands of years are constantly being awakened by the enhanced ability of humans to conquer nature. In particular, since the era of agricultural and industrial civilization, the continuous and intense development of the wilderness has exposed humans to more viruses than ever before. Those diseases that were isolated in the depths of the jungles were “discovered” one by one by humans. When humans destroy the ecological barriers that block the disease, the viruses have successfully crossed the boundaries of the species. The war between ethnic groups or countries, as well as population migration, colonization, trade, and tourism, further spread the epidemic diseases to all corners of the human life circle.

It is worth noting that, since the colonial era, the spread of plagues is often across continents as well as across the colonists and indigenous peoples. For instance, smallpox was originally only popular in the Old World, including European, Asian and African continents. However, when European colonists landed in America, they brought many kinds of infectious diseases with them to indigenous people whose immune system was not prepared for those diseases. The most lethal kind was smallpox. The ancient Aztec Empire in the Mexican region suffered from a loss of population from 25 million to 3 million within less than 50 years due to the smallpox plague brought by 300 colonists of Spain. The survivors lost their morale to fight and a powerful empire had fallen. After the plague eradicated the Aztec Empire, it continued to advance southward and also destroyed the Mayan civilization. Due to the smallpox epidemic, the ancient Inca civilization that existed in Peru and neighboring countries today was also easily conquered by 180 Spanish colonists. The European colonists, with or without intention, spread smallpox to the aboriginals in North America. Under the ravages of the smallpox virus, several major aboriginal tribes shrank from millions to only a few thousand people, some even completely died out. Before coming into contact with the colonists, there were 20 million to 30 million inhabitants throughout the Americas. By the 16th century, only 1 million people survived.

By the mid-17th century, nature took the revenge on the colonists. Slaves from Africa brought malaria and yellow fever to the Americas. Europeans there were apparently more susceptible to these two tropical diseases than local aboriginals.

Today, while AIDS is still rampant and Ebola is surging, the spread of the viruses has been significantly accelerated by modern means of transportation. People who live thousands of miles away across the oceans can be connected by a single flight. In this long-running fight against the viruses, the world will share the same fate. It is hard for any nation or ethnicity to be exempted from the epidemics.

3 We Share the Same Health Prospects across the World

The fight between viruses and humanity can easily make us overlook the other side of the story—microbiological organisms play a vital role in the global ecosystem. It is widely known that the saprophytic bacteria that keep our biosphere clean by decomposing the decaying corpses of plants and animals and releasing essential nitrogen back into the soil for plant growth. Microorganisms transform the energy and material on this planet to keep the vibrancy of their circulation, which sustains the continuity and the health of animals and plants. Without these microorganisms, all types of ecosystems in the world will be suffocated by the junks they produce themselves.

The human body can also be seen as a self-contained “ecosystem.” The healthy operation of this ecosystem also depends on the participation of microorganisms. Large volumes of bacteria co-existed in the human body including skin, mouth, and stomach, contributing to daily life activities. The symbiosis of humans and bacteria benefit from the variety and volume of bacteria. Although only a small portion of bacteria is harmful to human health, their destructive power is astonishing. As Nobel Prize laureate Joshua Lederberg4 said, “Nothing guarantees that we can always win in the natural evolutional competition between viruses and humans.” Despite the advancement in science and technology to get out of such race, humans are still far away from becoming a super species that is not constrained by any biological mechanisms. Humans have strived hard to improve their own life quality but nothing fundamental changed. The natural laws are far more powerful compared with human social laws.

The existence of the viruses also reveals that the structure of the food chain (or “biological chain” in a more precise term) is not a pyramidal linear one but an interlocking network. The mutual food supply relationships between different species are by no means a simplified unidirectional one as “big fish eats small fish, small fish eats shrimps.” In fact, the biological chain consisted of a very complex network which facilitates the circulation of energy, material, and information within this “web of life.” This forms an interesting network that features interdependence, mutual constraints, and co-evolution. Thus, it is not accurate to say that humans and predators stay at the top of the pyramid of food chains. Human beings are actually an “unwilling” node in the food chain or ecological chain. They are both “consuming” and “being consumed.” Regardless of how greedy mankind seizes natural resources by their hegemony gained over millions of years of evolution, attempting to fill their endless desires, they themselves cannot escape the destiny of being consumed by the decomposers of nature. In fact, they are already slowly “consumed” by bacteria and viruses while they are still alive. This is precisely how mother nature achieves her “fairness” and “justice” through the web of life.

When we learned that the biological chain (including the food chain) is an interlocking network system, and the relationships between organisms are both mutually dependent and restrictive, and all species are equal in a way, we would understand that mankind’s attempt to “eliminate” certain species that are “harmful” to the interest of themselves is essentially a short-sighted move to tear the web of life. A temporary solution to the current problem will lead to bigger and more problems. For instance, when people learn that bats are the carriers of Ebola virus and will cause major outbreaks, what measures will be taken? The usual practice is to vigorously eliminate this wild animal that acts as an intermediate host. However, the result of doing so will simply lead to another “ecological disaster”—particularly considering the fact that it is bats that pollinate crops and eat large amounts of mosquitoes. The drastic decrease of the population of bats will inevitably lead to failures of growing crops and controlling mosquitoes, causing famine and the spread of mosquito-mediated tropical diseases such as dengue fever and malaria, etc. Any missing link in the biological chain may cause an unexpected chain reaction. In the face of the epidemic, human beings are more likely to benefit from restraining ourselves instead of attacking others.

In the biosphere, microorganisms including pathogenic viruses are a link between various organisms or different species. Biologists believe that it is the inevitable result of natural selection and evolution. When the ecosystem is relatively stable, the viruses will be lurking in the hosts. Conversely, any disturbance in an ecological perspective, mainly human interference including deforestation and wildlife hunting, can cause the spread of pathogens across species and triggers epidemics.

The tropical rainforest is an unrivaled vast gene bank of diverse species, and possibly also the largest gene bank of viruses since the diversity of the virus is also an integral part of biodiversity. Humans cannot and need not eliminate all viruses. All we need to do is to learn how to co-exist with viruses to maximize their benefits and minimize their harms, so that the virus can, like other living things, benefit all humanity.


The author Xiaohui Shen is a committee member of the National Committee of the Chinese People’s Biosphere and senior engineer of the State Forestry Administration in China. He has long been engaged in the research, writing and environmental protection of protected areas, forests, wetlands, desertification, and wildlife conservation biology. At the time of the Ebola outbreak in 2014, Xiaohui Shen was in West Africa and wrote this article based on his in-depth research of the issue.


Translator notes: the original article was 30,000 to 500 million which could be a typo.


Strictly speaking, mangabeys are monkeys instead of apes claimed by the author.


Translator notes: I was not able to find the original English version of the book, neither any historian who has the name Howard Michael. However it was published in Chinese by Shanghai Academy of Social Sciences Press in 2003.


Translator notes: The author misspelled the name of this Nobel laureate and I was not able to find the original version of the quotes.


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