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Quarantine has always been a principal weapon against epidemics: isolate ailing people so they cannot spread illness. Quarantines come in various types, however, which have different effects:

  1. When an individual falls ill they need to be cared for in a facility that minimizes the risk that the virus will be spread to other susceptible people. This is the medical isolation that has been the key to defeating all past Ebola outbreaks. People who are suspected of having Ebola may also be kept isolated from others until their status becomes clear. I’ll call this a precautionary quarantine. A third situation is when a contact of an Ebola patient is cautioned to stay at home, or not to travel, during the 21-day incubation period. I’ll call this a monitoring quarantine.
  2. When an entire neighborhood or region is blocked off, the barrier is referred to by the French term, cordon sanitaire. This may be an urban neighborhood, such as the poor West Point district of Monrovia, or an entire region, such as the remote area at the intersection of Guinea, Liberia and Sierra Leone. Or it may be a de facto cordon sanitaire imposed by the closing of borders and the discontinuance of transport links.
  3. It is also possible to impose a curfew that limits when people can interact outside the home, in the hope that this will reduce transmission.
  4. Finally, Sierra Leone has announced a nationwidewide three-day lock-down, starting September 19, during which everyone will be required to stay home so as to allow a house to house inspection for hidden Ebola patients. [AFP 9/6/14]

Medical isolation is essential and effective, though in West Africa there have been many issues:

  • Some rural “red” villages either doubted that Ebola is real or feared that the doctors brought it. They forced Médecins Sans Frontières/Doctors Without Borders (“MSF”) to withdraw, and in some cases physically blocked road access — a do-it-yourself (reverse) cordon sanitaire! [NYT 7/27/14]  There was no choice but to let the epidemic burn itself out in those villages. I haven’t seen a report of what happened, but it will be illuminating to eventually find out.
  • Urban neighborhoods have resisted siting of Ebola care facilities nearby. Residents of the poor West Point district of Monrovia attacked and ransacked a holding facility [NYT 8/19/14], which lead to the attempted cordon sanitaire around their entire neighborhood described below.
  • People who fear letting ill family members go into Ebola care facilities often try to treat them at home, hiding them from authorities. This increases the risk of infection to home caregivers as well as other family members. Concern about this issue has led Sierra Leone to declare the country-wide lock down described below.
  • There aren’t enough beds in Ebola care facilities, at least in Monrovia. Medical isolation fails if there’s nowhere for people to go. It’s not clear how it will be possible to get on top of this issue since the epidemic is growing exponentially and the construction of facilities — and especially provision of trained staff — is not.

Precautionary quarantines and monitoring quarantines are also essential elements of infection control. The main problem I’ve noticed there is the issue of people breaking quarantine and subsequently infecting some or many other people. The experience of Nigeria is horrific: the outbreak started with one man who broke quarantine in Liberia to fly to Lagos, but it was spread by a series of additional quarantine breakers, one after another. See my earlier post: Arrogance and Privilege Imperil Nigeria’s Attempt to Contain Ebola

On August 1, Guinea, Liberia and Sierra Leone announced a regional cordon sanitaire, to be enforced by their military forces, around the remote area where the outbreak began. The New York Times described it as an infection-control strategy that has not been employed for a century. [NYT 8/12/14] A few days later, however, a writer in the New Republic described as “heartless but effective” a similar cordon sanitaire used in 1995 to control an Ebola outbreak in Zaire. [New Republic 8/14/14] Reuters expressed the concern that the cordon could create abandoned “plague villages.” [Reuters 8/17/14]  The World Food program has been struggling to provide adequate food supplies to 1.3 million people in limited access areas, including classic quarantines as well as cordons sanitaire. [WFP 9/2/14] There has been little mention of the regional cordon sanitaire in recent weeks, perhaps because the battle in the capital cities has taken center stage. The regional cordon may simply become a dead letter if Ebola continues to spread outside it.

On August 20, Liberia imposed urban cordons sanitaire on two poor and crowded neighborhoods of Monrovia: West Point and Dolo Town. Hundreds of young men in West Point rioted, throwing rocks at police, who used tear gas and live gunfire to disperse the crowd. [SaharaReporters 8/21/14] Several residents were injured, and a 15-year-old boy died. During the closure there were many stories of evasion, including a couple who bribed a soldier $10 to get out and a man who swam around the cordon each weekday to go to work in a government office. Ten days later the West Point cordon was lifted. [NYT 8/29/14] The West Point cordon would have to be called a failure. Meanwhile Dolo Town had accepted the restriction more calmly, although grumbling was reported three weeks later about continuing to be an “Ebola Jail Town.” [AFP 9/7/14]

Liberia also imposed a nationwide curfew on August 20, from 6 pm to 9 am. [AFP 8/20/14]  There has been a report that nighttime armed burglaries have increased during the curfew. [The New Dawn Liberia 9/8/14] The value of the curfew is debatable. It depends on the importance of urban transmission modes, and how many potential transmission events are prevented by keeping people home at night.

A de facto cordon sanitaire around the entire region has been developing over the past couple of months through a series of border closings and flight suspensions, along with regulations barring entry to ships that had touched at ports in the affected countries. In the past week a plea has been made for flights to continue and for borders to be opened to screened transit. It will become increasingly difficult to get necessary materiel and personnel into the affected countries if transport restrictions aren’t eased.

Most recently, Sierra Leone has announced a three-day nationwide lockdown, starting Sept. 19, during which everyone is expected to stay in their homes, with exceptions only for essential travel. During this period a house-to-house inspection will be conducted to find patients that are being hidden from the authorities. A government spokesman is quoted as saying that, “We intend to ensure that the dreaded disease is checked.” [AFP 9/6/14] MSF has expressed concern that this sort of measure will do more harm than good: “It has been our experience that lockdowns and quarantines do not help control Ebola, as they end up driving people underground and jeopardizing the trust between people and health providers…” But the top U.N. official in Sierra Leone supported the idea. [NYT 9/6/14] My own view is that the idea is daring but a lot could go wrong:

  • Households that are concealing an Ebola patient are likely to resist a thorough inspection, thus frustrating the purpose.
  • Even if a household doesn’t harbor an Ebola patient, it may have some other secret that will lead it to resist inspection.
  • People who are angry anyway will have three full days to sit at home and get angrier and angrier. This could burst out into violence.
  • How will the inspectors distinguish people who just have malaria or colds from people who really do have Ebola?
  • Will the inspectors all be wearing full protective gear, and will they be trained in procedures for putting them on and taking them off? The arrival of a moon-suited team would not be a warm and fuzzy experience, but if they aren’t protected the inspectors themselves could be the next wave of victims.
  • If a lot of patients are found where will they go? I’m not sure about the situation in Sierra Leone, but in Monrovia there aren’t nearly enough beds in Ebola treatment facilities. [WSJ 9/7/14]

All that said, a desperate situation calls for desperate measures. I hope the lockdown works!

 

 

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What can be done? This post will make some suggestions.

1. The first priority is to reduce the rate of transmission through known channels, which I discussed in detail in my previous post, The Ebola Chain Reaction.

Home Caregivers. Education is the first need: people need to know Ebola’s symptoms, then they need to know what to do if someone in their household starts to display them. This is an extremely hard problem. The early symptoms of Ebola — fever, vomiting and diarrhea — are indistinguishable from many other endemic diseases. Every person with a fever can’t be taken immediately to the hospital, and in the meantime the home caregiver is in no position to use any semblance of anti-infection protocol. In a crowded household people share the same spaces for eating, sleeping and every other aspect of life. Practical advice for home caregivers needs to be developed and communicated. That advice should include how a patient can be cared for in the home with reduced risk, when a patient should be taken to a clinic or hospital and how to decontaminate living spaces after a patient has left. But I don’t see how the risk of transmission to other members of a household can be much reduced, especially in poor, crowded housholds.

Healthcare Providers. Sooner or later — hopefully sooner — a symptomatic patient will be brought to a clinic or hospital. Again and again patients have infected multiple hospital staff members, and even forced the hospital to close for decontamination. As the numbers of patients increase this cannot be allowed to continue. Emergency rooms must be organized and staffed so that an Ebola patient can be identified and isolated without endangering staff or other patients. That’s easy to say but really hard to make true. Can we expect emergency room staff to wear bio-hazard suits? Can each patient be kept apart from other patients until they have been assessed? And again the problem arises of distinguishing early stage Ebola from other diseases. A quick, cheap and accurate test is needed to enable healthcare providers to distinguish who does or doesn’t present an Ebola risk. Airports are starting to use infrared detectors to cull out people who are running fevers, but it’s hard to imagine similar gear being deployed to all the relevant hospitals and clinics, and even if someone has a fever a hospital — unlike an airport — can’t just turn the patient away; but knowing who does and doesn’t have a fever might be helpful. And of course healthcare providers need the training and gear necessary to safely care for Ebola patients.

Traditional Funeral Practices. African funeral practices spread infection widely and must be suspended. This is a very difficult problem, since funerals are one of the ways people deal with the powerful emotion of grief. They will resist changes, and unless physically prevented are likely to model the behaviors they have seen and performed in the past. Culturally-specific strategies must be devised and implemented to encourage people to mourn Ebola victims in ways that do not place them at risk of infection.

These three transmission modes are quite capable of keeping the epidemic growing, with an Effective Reproduction Rate (Re) of more than one (as discussed in my last post). Pushing each of them down as low as possible is the first priority.

2. New modes of transmission are possible in the urban environment. Prior outbreaks have all been in rural areas, so there is no past experience with the additional ways Ebola can spread in a city, especially in crowded areas.

The first question is how important any new urban modes of transmission are, i.e. how much of a contribution they make to Re. If any urban mode of transmission is comparable to the known modes it needs to get similar priority, but if urban modes of transmission are more theoretical than real they can be deprioritized. The contact tracing process generates a tremendous amount of information about exactly what kinds of contacts did and did not lead to infection. Contact tracing information from all countries should be collected and analyzed, and conclusions should be shared amongst Ebola fighters. Communications to the public should generally be accurate, but in the public interest may not always be “the whole truth.” Significant modes of urban transmission that are so identified must be countered, if possible.

Even before data is available it makes sense to analyze urban life and make changes that seem logical and have the potential of being cost-effective.

  • Replacing shaking hands with fist bumps is a step in the right direction, although elbow bumps or just bows would be even better. Air kisses between friends and colleagues (if that was ever an African thing) can be suspended for the duration.
  • Situations where people are crowded into direct contact are part of urban life, but present an obvious risk. People can be cautioned to avoid crowds and steps can be taken to reduce crowding in taxis and buses. Update 9/8/14: This chilling item from the Wall Street Journal suggests that taxi drivers and surfaces in taxis could easily become contaminated by bleeding, etc. Ebola patients. [WSJ 9/7/14]
  • While 60% alcohol hand sanitizer is better than nothing the CDC recommendation is to wash hands with soap and water whenever possible. Sanitizer could have an adverse effect if people use it instead of washing. There is also a question of whether alcohol has much effect on the virus anyway. Update 10/7/14: Since Ebola has a lipid coat alcohol-based hand sanitizer should be effective against it. The CDC continues to recommend alcohol-based hand sanitizer (with at least 60% alcohol) when hand washing isn’t possible. [CDC 10/7/14] Bleach is standard for disinfection, but it’s not clear to me whether dipping ones hands in a shared bleach bucket, as is becoming common in some affected cities, is a net benefit.
  • Some offices are taking people’s temperatures when they enter, and asking them to wear it as a badge. The risk of transmission in an office setting would seem to be very low in any case, but if this serves to raise awareness and control anxiety it may be worthwhile.
  • Closing schools initially seems logical, but it imposes social costs and might turn out to be an overreaction. School children are somewhere doing something, probably with other children, when they aren’t in school. It might actually be better to open school, with provisions to minimize physical contact, and perhaps also with a process for taking each student’s temperature as they arrive and sending home anyone with a fever.
  • Other situations in which people put their hands on one another deserve consideration. Massage parlors and sexual contact come to mind. And a panicky post worries about barber shops (not without reason).

Amongst all these possible risks and countermeasures, public communications should focus on the most important transmission modes and the most important countermeasures, based on the best available information at each point. On the other hand, worthless countermeasures, or countermeasures against trivial risks, may be ignored if they afford comfort and don’t unduly draw attention or resources away from more important issues, or lead to a dangerously false sense of security.

3. Superstition, rumors and mistrust must be countered and overcome. The West African Ebola fight has been plagued by these factors from the outset. In addition to the usual superstitions about causes and folk remedies the rumor spread that Ebola was brought by the healthcare personnel who were in fact trying to stop it. MSF had to withdraw from more than two dozen “red villages” because this hostility made them too dangerous. The poor and crowded West Point district of Monrovia attacked and ransacked a quarantine facility that had been sited there. In part this reflected “Ebola denial” which will disappear on its own as the epidemic makes itself felt more widely. But it also reflected mistrust and irrational fear that must be countered.

4. A pattern of quarantine breaking and lying must be broken. Again and again, especially among the privileged classes in Nigeria, people have broken quarantine and/or lied about prior contacts with Ebola cases, thereby putting dozens or hundreds of health care providers and other contacts at risk. (For details see my post, Arrogance and Privilege Imperil Nigeria’s Attempt to Contain Ebola) This reflects arrogance and a habit of getting their own way regardless of consequences to others. The immorality of this behavior — and its dire consequences — must be brought home to everyone, at every level of society. This is culturally-specific but one imagines that achieving this goal might involve use of media and involvement of religious and other thought leaders. It is hard to see how Nigeria — or indeed any society, including developed countries — can control Ebola if a pattern of quarantine breaking and lying like the one we have seen so far should persist.

5. Adequate healthcare facilities are essential to allow Ebola patients to be cared for outside the home, where they are much more likely to pass the virus along to others. The epidemic has consistently outstripped available facilities, and unless there is a marvelous international intervention this seems doomed to continue. Healthcare is also key to minimizing the death rate, which is important as a humanitarian matter even though it is only tangentially relevant to stopping the epidemic. Sadly, there is no possibility of replicating the level of care the two Americans received at Emory, which no doubt contributed to their recoveries. But any lessons learned in developed hospitals about how best to manage Ebola patients should be made available to African healthcare providers. Most important are any recommendations that it might be possible to implement in an overstressed and impoverished facility.

Updated 10/7/14: Here is a new idea that might make an important contribution, even though it’s really distasteful. Sierra Leone plans to build up to 1,000 “makeshift Ebola clinics” that would offer little, if any, treatment. [AP 10/2/14] These “clinics” would really be hospices which would let people die and be safely cremated or buried without infecting their families. It’s dreadful to think of abandoning people who could be saved with minimal care. But just at the moment this may be the least bad alternative, since if the patients die at home they will very likely infect their caretakers and some or all of the other members of their households. If enough of these facilities could be provided, and if people could be persuaded to use them, this could be a game changer.

6. Outsiders must send money, health care and infection control materials, healthcare workers and healthcare trainers. Happily — if far too late — the world finally seems to be waking up to the gravity of the situation, and to its own moral obligation to help, as well as its self-interest in stopping the epidemic before it affects even more countries. Individual readers can find a list of ways to help at the current Ebola Report post. Charity Navigator can help you assess the quality of charities that are fighting the epidemic. Doctors Without Borders USA, for example (the U.S. branch of Médecins Sans Frontières) gets the highest ratings for both use of funds and accountability/transparency.

7. Immunity is the ultimate weapon against disease, and in this case it may be the only way the epidemic can be stopped. Obviously, testing of a vaccine must be given top priority. People who have recovered from Ebola are also an important resource. It might be possible to recruit recovered Ebola patients to play roles in healthcare settings, such as hospital emergency rooms, or in other situations where their immunity could come in handy. Recovered patients may also offer a source of antibodies that could be purified as a serum to help current victims. Mutation is the ultimate weapon of disease, and this could undercut both a vaccine and survivor immunity, but as to this possibility we just have to hope for the best.

Reproduction Rate

The way Ebola spreads is simple: from one person to another. There’s an African animal reservoir — probably fruit bats — from which the virus finds its way into a human being once or twice a year. But from then on the virus is transmitted only through bodily fluids, not via an animal vector such as mosquitoes or fleas. Ebola spreads by a simple chain reaction: each person it infects may infect one or more additional people, and so on. The key is how many susceptible people, on average, each infected person passes the virus on to. This is called the “Effective Reproduction Rate,” or “Re”. (Almost everyone* is initially susceptible to Ebola, but Re will drop proportionately if a substantial portion of the relevant population becomes immune, either by surviving or by receiving some future vaccine. The rate at which the virus would be transmitted in a completely susceptible population, with no immunity, is called the “Basic Reproduction Rate,” or “Ro”.)

  • If, on average, each infected person passes the virus on to just one other susceptible person (Re is one) the epidemic will continue at a steady rate, neither growing nor dying out. This is called an “endemic” disease. The total number of cases grows, but the rate at which new cases occur stays the same.
  • If Re is less than one the epidemic will die out, slowly or rapidly depending on where the number falls between one and zero.
  • If Re is more than one the epidemic will mushroom until some factor pushes that number back down below one. The rate of growth will depend on how big this number is, but the epidemic will relentlessly accelerate so long as Re is greater than one. This is “exponential” or “explosive” growth.

The only way to stop an epidemic is to push Re down below one. Of course it’s also best to get as close to zero as possible as rapidly as possible, but so long as Re is less than one the disease will eventually die out.

Forty Years of Rural Outbreaks

Ebola outbreaks have so far always started in rural areas, with the likely suspect usually being some sort of bush meat, typically bats or monkeys.

Home caregivers are very likely to be infected, so at the outset an Re of at least one is almost assured. Other family members and visitors are also at risk. This mode of transmission can be greatly reduced by caring for patients, as soon as they become infectious, in a facility that follows rigorous infection-control procedures. This approach has worked for Médecins Sans Frontières (“MSF”) in all prior outbreaks. (Lugubriously, this form of transmission may also be reduced when patients aren’t cared for by anyone, either because they are the last member of a family or because they are put out of the house when they fall ill.)

Healthcare providers are especially vulnerable, particularly in the early stage of the outbreak. The initial symptoms of Ebola are similar to those of many other less-infectious diseases, so the first wave of sufferers typically walk in to clinics or hospitals and are examined and cared for like other patients. Not only are doctors and nurses likely to become infected, but before the outbreak is recognized they may pass infection on to other patients. This is tragic, and definitely helped the current outbreak get a foothold, but it may ultimately not be an important element of Re. For one thing, MSF has shown that rigorous procedures and high-quality anti-infection suits can essentially eliminate this risk. As of a recent report, no MSF employees had become infected in the West African outbreak, though many other healthcare providers have been. For another, hospitals and clinics may be closed when they have become contaminated, and patients may stop going there for any illnesses once the risk of Ebola infection becomes known. The collapse of the health care system has many adverse effects, but the silver lining is the fact that people who don’t go to a hospital at all can’t either transmit or acquire Ebola there.

African funeral practices have played a big role in amplifying Re.

  • The body of someone who dies is traditionally hand-washed by members of the family. This almost guarantees that the washers will be infected.
  • Mourners at a traditional funeral may touch and even kiss the body. This can infect many people, who bring the virus with them when they return home. The entire outbreak in Sierra Leone, for example, has been traced to fourteen women who attended a single traditional healer’s funeral in Guinea. [NYT]
  • Finally, those who bury the body are at high risk unless infection-control procedures are used.

It is obviously essential to stop these funeral practices, since one victim can infect a huge number of other people this way. Again, MSF has been able to do this in the villages affected by previous Ebola outbreaks by working with local chiefs and explaining the situation to the villagers.

The impact of funeral practices on Re is affected by the mortality rate. In prior outbreaks up to 90% of those infected died, so almost all had the potential to infect many others through their funerals. In West Africa only about half seem to be dying, so the impact of funerals is somewhat reduced. This effect is swamped, however, by the large number of potential infections from one traditional funeral. Even though the reduced mortality rate makes funerals somewhat less important it is still essential to bring traditional funeral practices to a stop if Re is to be reduced below one.

In more than a dozen rural outbreaks over nearly forty years Re has been decisively driven below one, and the outbreak stopped, by rigorous infection control, contact-tracing and quarantine. The support of local communities was obtained by personal contact and education.

New Complications in West Africa

The West African outbreak, however, presents a very different picture. The health care systems in the affected countries had been damaged by years of civil war as well as profound poverty. This is the first time Ebola has appeared in any of these countries, so they were slow to recognize it and unfamiliar with the steps needed to contain it. Whatever the reasons, the virus was able to spread for several months before being recognized, and the consequences have been tragic.

Several new elements have complicated the relatively simple pattern of previous outbreaks:

  1. Ignorance, superstition and rumor have frustrated efforts to apply the established protocol, both in certain rural villages and in poor urban neighborhoods, notably the West Point district of Monrovia. Health care personnel have had to withdraw completely from a dozen “red villages” in Guinea where residents fear that MSF and Red Cross are causing Ebola rather than seeking to control it.[NYT] People have been hiding Ebola victims instead of letting them go into isolation wards.
  2. The uncontrolled spread of Ebola into several big cities raises the risk of additional modes of transmission, such as physical contact in taxis, buses and crowds, and contamination of shared surfaces.
  3. The number of patients has overwhelmed available isolation facilities.
  4. In several cases people who had been exposed to Ebola, or were already ill, have nevertheless chosen to travel, thus putting many others at risk. [Ebola Strategy 2014-08-31]  Some people have also lied about potential exposure to gain admission to hospitals, thus risking infection to doctors, nurses, staff and other patients.

The consequence has been that Re appears to be at least one in Guinea and Sierra Leone, and more like 1.5 in Liberia. An excellent article in Science projects a tripling to around 10,000 cases by September 24, and hundreds of thousands in subsequent months, with no end in sight so long as Re stays so high. [Science 2014-08-31].

The only way to stop the outbreak is to identify and implement a suite of feasible measures that together push and hold the Effective Reproduction Rate (Re) below one. It is of course also important as a humanitarian concern to provide the best possible care for those who fall ill, but care has no effect on the rate at which the virus spreads except to the extent that it implies reduction of potentially infective contacts.

The outbreak has naturally segmented itself to some degree, into rural and urban areas, and by country. A couple of attempts at quarantine barriers, called cordons sanitaire, have attempted to segment it further, with mixed success. (I plan to discuss this in a future post.) To the extent that segmentation works it may be possible to stop the outbreak using different suites of infection-reduction measures in different segments. In particular, relatively well-organized countries such as Nigeria and Senegal may well be able to bring their own smaller outbreaks under control using the standard protocol of contact tracing, monitoring and quarantine, even if the epidemic continues to grow uncontrollably in, say, Liberia.

Wild Cards

The current situation is bad enough without worrying about how it could get worse, but there are a few uncertainties that it’s useful to keep in mind.

Ebola is mutating rapidly,[Washington Post 2014-08-28] and it’s possible that the virus could change in ways that increase its infectiousness, especially through the air. That would be very problematic, to put it mildly.

An animal transmission vector might emerge, particularly in places where bodies are not promptly disposed of.

Sexual transmission might become significant in a promiscuous segment of the population, such as a subset of gay men. Not only could an infected person pass the virus on to multiple sexual partners, but this could also happen after recovery, since Ebola is found in the semen of recovered patients for up to seven weeks. [Who Fact Sheet]

Secondary effects of the outbreak could disrupt infection-reduction measures or even destabilize affected regions. The most immediate risk is a breakdown in food supplies, but one could also imagine breakdowns in other public services. Public disorder has broken out in several places, and this could continue or worsen. In the middle term the weak economies of the affected countries will be further damaged by disruption of internal and foreign trade. Also, the breakdown of the health care systems in these countries may facilitate epidemics of other diseases.

At the bottom of Pandora’s Box there is hope:

A safe and effective vaccine could bring the outbreaks to a fairly quick end. Indeed, this may be the only real hope of doing so.

Possible Preexisting Immunity A subsequent New York Times article raises the possibility that some portion of East Africans are already immune to Ebola. [NYT 9/5/14] The article cites a 2010 study in Gabon, which had had four Ebola outbreaks from 1994 to 2002. The study found Ebola antibodies in 15% of the population, ranging from 34% in some remote villages to 3% on the coast. The investigator speculated that many of the antibodies resulted from low-level exposures that weren’t sufficient to cause illness. This is interesting because it might afford a large pool of people who are already immune, who might be able to take on hazardous jobs with less personal risk, and who might be able to donate curative antibodies. There are several cautions, however:

  1. Immunity is to a particular strain.
  2. It’s not clear what level of antibodies is protective in humans.
  3. While an injection of antibodies might help an infected person fight off the disease it would not function like a vaccine to generate long-term immunity.
  4. Levels of exposure in Gabon, which had a long history of Ebola outbreaks, might be higher than in the countries currently affected.
  5. The epidemic is currently most worrisome in coastal cities, where antibodies would probably be lowest.
  6. Whatever preexisting immunity existed in remote villages wasn’t sufficient to keep Ebola from getting a foothold there.
  7. Sophisticated techniques are needed to test for antibodies.

More Information:
[Measuring Disease Dynamics in Populations: Characterizing the Likelihood of Control, Johns Hopkins]

[Exponential Growth and the Legend of Paal Paysam]