Archives for category: Ebola

A Harvard researcher who tracks Ebola’s evolution remembers being “totally shocked” when he learned that Zaire ebolavirus was behind reports of a mysterious hemorrhagic fever cropping up in Sierra Leone last January. Lassa fever or even the rare Côte d’Ivoire Taï Forest strain of Ebola would have been more logical pathogens according to him, and the question remains:  how exactly did the most lethal form of Ebola – which was previously restricted to Central Africa – suddenly appear thousands of miles away on the edge of West Africa? Researchers may never be able to provide a precise explanation, but they have developed several theories as to how Zaire ebolavirus “jumped” across the continent.

Some background on the basic evolutionary biology of Ebola is necessary to appreciate the mystery presented by this mammoth leap. Moving down the tree of evolutionary similarity, the Filoviridae family encompasses the Ebolavirus genus, of which there are five distinct (known) species: Zaire ebolavirus, Sudan ebolavirus, Reston ebolavirus, Bundibugyo ebolavirus, and Taï Forest ebolavirus. All are found in Africa except for Reston, which has only appeared in a Virginia lab.

Despite widespread reports that the current Ebola outbreak is West Africa’s first instance of the virus, one previous case of Ebola was recorded in the region prior to last December. The case occurred when a female Swiss ethologist contracted the disease while conducting a necropsy on an infected Chimpanzee in the Taï Forest region of Côte d’Ivoire that borders Liberia. She survived what virologists eventually determined to be a separate species of Ebola, and this year’s outbreak in Liberia, Guinea, and Sierra Leone surprisingly has no connection to that species now known as Taï Forest ebolavirus.

The culprit of this year’s outbreak, Zaire ebolavirus has likely circulated in the forests of Central Africa for hundreds of years. The first confirmed case occurred only in 1976 near the Ebola River in Zaire, but based on the virus’s mutation rate, Ebola likely split from Marburg virus – another deadly member of the Filoviridae family – around 800 years ago. Further evidence for the long history of Ebola in Central Africa comes from the virus’s presence in stored samples collected from Gabon primates prior to 1976. Previous cases likely went internationally undetected in part because of long practiced indigenous protocols such as isolating infected people outside of villages in addition to community-wide dietary restrictions during times of unusually severe afflictions (see Matthew Barry’s anthropological research on Ebola).

After 1976, Zaire ebolavirus went eerily quiet but reemerged again in the mid-1990s, beginning a series of semi-annual outbursts that continue to this day in Central Africa (the recent 2014 DRC outbreak is the latest instance and is unconnected to the West Africa outbreak). Contrary to many recent news reports, these sporadic episodes have affected bustling cities (Gulu, Kikwit) and have spread via air travel (from Gabon to South Africa), but the initial index cases have always originated in Central Africa, and the outbreaks have never eclipsed more than a few hundred cases.

The 2014 West African outbreak broke this pattern. Scientists have now traced its origin back to a two year old boy who was likely exposed to fruit bats last December in Guinea, ruling out an immediate cause of an infected person bringing the virus directly from Central Africa.

The connection of fruit bats to an Ebola outbreak is not unusual, and bats have been linked to several other index cases over the years. As a result, bats are the leading suspect for the elusive and long sought “reservoir” animal that asymptomatically harbors the virus between human outbreaks. Tests on thousands of animals in Central Africa have yet to find definitive traces of ebolavirus, perhaps because the virus is also rare amongst animals or else only flares up for short spells.

Even within a single species of Ebola, the virus’s DNA constantly mutates each time it jumps from animal to animal, or animal to human. Thankfully the mutation rate for Ebola is much lower than other RNA viruses such as HIV/AIDS, providing more hope for a sustainable cure. Based on its slow rate of mutation, the genetic structure of the Zaire strain ravishing West Africa seems to have separated from its Central African parent strain of Zaire ebolavirus about a decade ago.

This estimate gives scientists about a ten-year window within which to speculate as to how Zaire ebolavirus ended up in West Africa. Here again, bats present the most likely link.

One theory picked up by those with a taste for primitiving Africa, postulates that Africans’ supposed appetite for bat meat (and bush meat in general) has led to the illegal smuggling of infected bats or chimpanzees from Central Africa to West Africa. While it is true that infected primates acted as vectors for bringing Reston ebolavirus to the US and Marburg virus to Germany, there is no evidence of an elaborate black market for bush meat criss-crossing Africa. Assuming a thriving bush meat trade is to misunderstand the driving factor behind wild game consumption in Africa: poverty. West Africans don’t import chimpanzees and bats from Central Africa as exotic delicacies—hungry villagers hunt small game in the forest to add protein to their diets, as other forms of meat are often prohibitively expensive. The average annual income in Guinea is $416 (World Bank).

A more likely scenario for Ebola’s jump involves the long distance migration of bats. Bats are unique amongst mammals in their ability to fly, and recent research tracking their flight patterns has uncovered that they often travel hundreds of miles a year in search of insects. Just about everything about bats from their migration routes to their immune systems is notoriously understudied.

According to the few published studies, scientists know that there are “metapopulations” of bats – separate colonies (whose members can run into the millions) that interact on some level. In other words, large populations of bats come into contact with other large populations of bats at the fringes of their territories or as they migrate, allowing pathogens to pass between them. Along such a metapopulation network, Zaire ebolavirus could have worked its way up the coast of West Africa. Preliminary positive tests for Zaire ebolavirus in bats found in Ghana – about halfway between the DRC and Guinea – support this theory of a gradual passing on of Ebola.

One factor that complicates this picture of bat-born Ebola is the fact that human outbreaks seem to only occur in regions of Africa where large primates are found. This remains a puzzling mystery, but one possible explanation floated is that Ebola needs to be – in a sense – shaken back and forth between bats and non-human primates before it mutates into a form that can be picked up by humans. An intriguing theory and time will tell if index cases eventually do emerge from areas without non-human primates.


Here‘s a pretty good map of Ebola cases throughout Africa that I just came across. It was created using Ersi Story Maps software and what makes it useful is its simple and straightforward design, which allows the user to run through a timeline of known Ebola cases while the map zooms in to show their location. It would have been nice if the creator had included more information on each outbreak (such as which species it was and a little bit of background on the outbreak), but it’s still a very useful representation of Ebola’s spatial distribution in Africa. 

Here’s a single PDF of the entire “Ebola’s History” series: Ebola’s_History

I’ve finally finished what sprawled into an eight part series “summarizing” the history of Ebola. This project, which was originally supposed to be a quick summary in order to contextualize the current outbreak in West Africa, in the end turned into a far more ambitious undertaking, but I hope it succeeded in compiling some useful information on Ebola’s long-span history from medical, media, and social science sources, and is as straight forward and accessibly written as I intended it to be. Thanks for reading and check back soon for more posts on my time in Lagos.


Sculpture at Makerere University, Uganda (Mark Duerksen, 2011)

This is the final post in an eight part series on the history of Ebola. For immediate information about how to help prevent the further spread of Ebola and keep yourself safe please consult and share the Ebola Facts website.

As we are well aware, this year the two-decade trend of isolated outbreaks in Central Africa every few years has been broken by a much larger and more prolonged series of cases in West Africa. The outbreak began when a two-year-old child in southeastern Guinea contracted the most deadly species of the virus (Zaire ebolavirus) in early December last year, putting into motion the initially slow and then progressively faster spread of the virus to Liberia, Sierra Leone, and now Nigeria. Unlike the past twenty year’s string of Central African outbreaks that were each unique and separate despite initial speculation otherwise, this year’s West African outbreak does seem to be the result of a single index case followed by human-to-human transmission. Here’s a good time-lapse map of that transmission through West Africa. Summaries of the specifics of this year’s outbreak are widely available online, so I won’t go into too much detail here, but I will offer a few pieces of analysis based on the history I’ve covered in the previous posts.

IMG_5260Matt Ridley gets it all wrong for The Times

First there’s a need to correct a couple of pieces of misinformation that continue to circulate with this year’s outbreak. A more minor error is that this is not in fact the first time that there has been a West African case of Ebola as many news outlets have reported. Previously a zoologist working in Cote d’Ivoire caught the Tai Forest species of the virus and then fully recovered in Switzerland. Second and more importantly, the virus has not been previously restrained to only rural, remote areas of Central Africa. As we’ve seen, two of the deadliest previous outbreaks occurred when the virus struck the relatively large cities and regional hubs of Kikwit and Gulu. These Central African cities might not have quite the same level of road infrastructure linking them to other urban centers as West African cities do (although I know plenty of people board buses every day in Gulu bound for several cities and countries), but these two cases do provide a precedent for urban outbreaks of Ebola. And although these previous urban outbreaks were incredibly deadly, the cities were able to eventually contain the virus’s spread within a matter of months. So, in searching for a reason why this year’s outbreak has spread so far and killed so many, the answer is not as simple as stating that this is the first time the virus has appeared in an urbanized setting.

Other explanations have included the slow recognition and response time of international medical teams. Again, a look at the history of the virus shows that response time is not a unique factor in considering why this outbreak is so much worse. In the cases of the 1976 Sudan and Zaire outbreaks and several subsequent episodes, international teams were slow to recognize the virus’s appearance and did not arrive on the scene until after the local communities had already contained the spread of the virus. This fact suggests that one reason for the extent and deadliness of this year’s outbreak might be partly found in the local community’s responses. As Hewlett observed in Gulu, the DRC, and Gabon, many communities in Central Africa possess long practiced social procedures such as quarantine and modified burial practices that they employ when their communities recognize that they are dealing with an especially virulent affliction. I do not know if communities in West Africa have similar procedures, but it would not be surprising if they don’t due to the fact that they’re not used to seeing diseases like Ebola, or alternatively that they did previously possess similar response techniques but that the long civil wars in Liberia and Sierra Leone destroyed that local knowledge as violence and insecurity ripped communities apart.

Whatever the cause(s) behind the severity of this year’s outbreak, the fact is Zaire ebolavirus’s path through West Africa has been more deadly than all previous Ebola cases combined, and I have to admit that when I initially heard that the virus had arrived in Lagos—the impetus for this series of posts—I feared that Ebola might finally find in the fast life, international networks, and rancid infrastructure of Sub-Saharan Africa’s largest city what HIV/AIDS found in the reused medical needles, sex trade, and migrant networks of 1970s Kinshasa and Brazzaville—that is, the lethal mixture of social and environmental conditions that would allow the virus to eventually explode into a global epidemic.


Trash disposal in Lagos (Mark Duerksen 2014)

Being a Central African originating RNA virus linked to primates and transmitted through body fluids, comparisons of Ebola to HIV/AIDS were bound to occur. However there are several important differences that will likely yet prevent Ebola from boiling into an epidemic the way HIV/AIDS did. The first significant difference is the length of time from infection to fatality (or recovery for 10-60% of Ebola patients). HIV can hole up and multiply inside an infected person’s immune system for months, years, or even a decade, slowly destroying T-cells until it has killed so many that doctors consider the person to have developed AIDS. Over these months or years while HIV festers into AIDS, a person with HIV may be completely asymptomatic, but all the while still able spread the virus through sexual contact or blood transfusions. This slow and silent development timeline means that an HIV carrier might not even realize that he or she has become infected for years or even a decade and all the while be transmitting the virus to numerous people, allowing HIV to creep into a critical mass of carriers before it is even detected. This quiet buildup of an infected mass of people is exactly what happened for decades in Central Africa, and by the time doctors “discovered” HIV/AIDS, it was already an epidemic throughout the region.

Ebola on the other hand asymptomatically incubates for a few days or up to a few weeks, during which time the victim cannot transmit the virus to another person. Once symptoms develop after the incubation period, the patient’s health declines quickly and death is then generally a matter of days away, leaving only a very small window to further spread the virus (although it can still be contracted from infected corpses, so that is an additional concern and why burial practices are crucial to containing Ebola). One important note here is that those who recover from Ebola can still transmit the virus through semen or possibly breast milk for a number of weeks. While Ebola is easier to transmit during its small contagious window than HIV/AIDS is during its prolonged window, Ebola still has a low transmission rate,[1] requiring direct contact with infected bodily fluids, and the virus cannot be transmitted through the air the way respiratory diseases can be. Despite the horrific extent and fatality numbers of Ebola in West Africa, the virus will likely burn itself out due to its short contagious window (although it might take severe quarantine and curfew measures as we’re now seeing in West Africa) before it ever reaches a critical, completely uncontrollable mass in the way HIV did.

Perhaps the most optimism-inspiring difference between HIV/AIDS and Ebola is the two viruses’ rates of mutation. While both likely simmered in the forests of Central Africa long before scientists officially detected and classified them, Ebola’s genetic structure has hardly changed since the first confirmed cases in 1976 while HIV/AIDS has mutated incredibly rapidly, making treatment for HIV/AIDS much more difficult to square with virus’s continually changing configuration. Ebola’s steady genetic structure makes the prospects for a cure much more promising, and as we’ve seen with the initial success of ZMapp, cures seem to be on the horizon. Now we just have to hope treatments can be produced and distributed asap because, while Ebola is not likely to become a global epidemic, it is causing untold suffering in West Africa that we likely won’t realize the true extent of for some time yet. Ebola’s destructive path through West Africa includes not only the direct victims of the virus, but also those caught in the clashes between soldiers enforcing quarantines and those trying to flee its path, survivors who are now shunned by their communities, communities that no longer trust doctors and hospitals, businesses and entire economies that have taken a massive hit, and medical infrastructure throughout the region that has been depleted, abandoned, and looted, causing other illnesses to proliferate in the absence of treatment facilities. Still it is worth noting the statistics on HIV/AIDS and other deadly diseases deaths per day dwarf Ebola deaths in the Ebola-affected countries–a reminder that those preventable diseases also require immediate attention and that serious long term work to repair medical infrastructure and communities’ relations with medical personnel will be imperative to West Africans’ health once this outbreak can be contained.

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(image source)

[1] Daniel G Bausch, et al., “Assessment of the Risk of Ebola Virus Transmission from Bodily Fluids and Fomites,” Journal of Infectious Disease, 196(), S142-S147. Available online:

As social scientists studied communities affected by the slew of outbreaks that swept through Central Africa in the 1990s and 2000s, virologists began to wonder if the unprecedented number of cases were somehow connected. Initially they developed a theory that a single Ebola outbreak from a single index case was slowly simmering and spreading through Zaire (and then DRC), Gabon, Congo, CAR, Sudan, and Uganda. The reality that the outbreaks included several species of the virus and a multiple suspected index cases connected mostly to the handling of animal carcasses squashed the theory of a single outbreak, but still the question remained, why this sudden and prolonged string of separate and distinct outbreaks?

Scientists next looked for larger environmental patterns that might connect the Central African cases. Most outbreaks of Ebola occur in between the dry and wet seasons, but there has been speculation that broader climatic event might be connected to the sustained spike in cases. The 1976 simultaneous outbreaks of separate species only a few hundred miles from each other also points to an environmental occurrence activating the virus and allowing it to jump from the reservoir to monkeys and humans. Scientists have been studying satellite photographs of the Congo Basin from the past few decades in an attempt to detect any environmental changes that overlap spatially with flare ups of Ebola. These studies have found that especially arid dry seasons disrupt the ecosystem in the jungle, leading animals to move beyond their normal confines in search of food and water, which results in increased human-animal contact.[1] If this is accurate, global warming has serious implications for Ebola outbreaks.

Another study that may lend further support to the environmental activation hypothesis was conducted in 2010 when scientists examined the genomes of living African bats and rodents and found ancient “fragments” of filoviruses in their genomes. Through recent advances in the fascinating subfield of paleovirology the researchers were able to estimate that filoviruses are likely tens of millions of years old based on the genetic remnants of the disease shared by the mammals coupled with the scientists’ knowledge of the mammals’ shared evolutionary trees. If rodents and bats have carried filoviruses for tens of millions of years as they migrated across the world, it’s no surprise that strains of Ebola exist in both Sub-Saharan Africa and the Philippines. The study goes on to suggest that other rodents, marsupials, and bats may carry yet unknown forms of filoviruses in the Americas.[2] The fact that we’ve only seen the virus pass from reservoir to human in Central Africa and the Philippines, lends credence to the idea that it is something particular to the Central African environment (that the Philippines may share) that is “activating” or allowing the virus to jump from the reservoir to larger mammals. Could global warming activate latent filoviruses in other regions of world? [Or, alternatively perhaps other New World strains are similar to the Reston species in that they don’t cause human illness when spread to humans and therefore haven’t been detected yet.]

As promising as the research has been into detecting an environmental link, in focusing on identifying climatic trends connecting the past twenty years of outbreaks, scientists have neglected to consider the often-horrific human history of Central Africa as a potential source of explanation for the string of outbreaks. In the aftermath of the Rwandan civil war and 1994 genocide, the deadliest conflict since World War II unfolded across Central Africa, killing over four million people, displacing many millions more, and dragging in soldiers from throughout the region. The First and Second Congo Wars have not received nearly as much scholarly attention as they require, but books such as Africa’s World War written by Gerard Prunier begin to document the devastating bloodbath that occurred as troops from Rwanda and Uganda marched across lawless Zaire to evict Mobutu from his rotting seat of power in Kinshasa. Two decades later, the conflict continues to this day with fighting between Kagame’s Rwanda and rebel groups such as M23 in eastern DRC. Additionally South Sudan has suffered its own bloody history that persists despite independence from northern Sudan, and the Lord’s Resistance Army has terrorized Northern Uganda/CAR for many years, displacing numerous people.


Charcoal mural in an IDP camp near Gulu, Uganda (Mark Duerksen, 2009)

The result of the countless armed conflicts in Central Africa has been an upheaval of societies across region, causing an increased likelihood of human exposure to Ebola as starving refugees and soldiers turned to bush meat while they roamed through the Congo’s dense forests, and as they displaced animals by burning and logging forests, which may have put primates in greater contact with both humans and the reservoir. It would be interesting to see what further spatial research tracing the conflict and the virus over the past 20 years might reveal.

Scientists’ omission of the deadliest conflict since WWII from their causal considerations and the dismal results of the ethics review of Ebola research (previous post) suggests a troubling trend where scientists studying Ebola in reality know very little about the region and the people affected by the virus.

[1] Stephen Pincock, “Seeing Ebola from Space,” The Scientist, May 1, 2006. Available online:

[2] Derek J Taylor, et al., “Filoviruses are ancient and integrated into mammalian genomes,” BMC Evolutionary Biology, 10(2010), 1471-2148.

In 1994 the Ebola’s eerie silence was broken when it reappeared in Gabon and Cote d’Ivoire. The single human case in Cote d’Ivoire occurred when a 34-year-old female Swiss ethologist contracted the disease while conducting a necropsy on a chimp that had died from a suspected outbreak of Ebola amongst a troupe of Chimpanzees in the Tai Forest near Liberia. Once symptoms appeared, physicians quickly transferred her to Switzerland where she soon made a full recovery without infecting anyone else (a precedent for the two Americans with Ebola currently being transferred back to the US). [1] This solitary case is significant because it is the only known human instance of Tai ebolavirus, and, prior to 2014, was the only known Ebola case in West Africa despite many news agencies reporting that this year’s outbreak is the first West African Ebola episode.

In Central Africa, the three chimpanzee-linked cases that occurred in Gabon between 1994 and 1995 were all relatively isolated, each infecting less than 60 people, but one victim did travel to Johannesburg where he infected a nurse who died days later without further passing on the disease.[2] This episode provides a precedent for fears that the 2014 outbreak may travel far beyond the initial index case via international air travel, however the case was quickly contained to a single transmission.

[1] Tara Waterman, “Ebola Cote d’Ivoire Outbreaks,” Stanford Honors Thesis, 1999. Online:

[2] Xavier Pourrut et al., “The natural history of Ebola virus in Africa,” Microbes and Infection, 7(2005), 1005-1014. Online: