How is it possible to even hope for an ebola epidemic of this current size to remain contained to a relatively small part of Africa?

Question

As of 2014-09-14 at least 5347 cases of ebola have been identitied. Some estimates are much higher. While experts are sounding the alarm to try to get sufficient resources to contain the outbreak, some people are also speaking very hopefully about containment to roughly the current affected area. This article puts the risk of the outbreak reaching the United States as low as 3%. I'm not an expert in the field, but it seems like there are almost countless ways in which an increased number of cases increases the risk of further exponential growth. It's encouraging to hear that in countries with better healthcare, death rates would likely be much lower, but at this point, isn't it inevitable that the outbreak will run its course as a global pandemic?

For example, which of these possibilities is just my imagination, or likely so improbable that we don't need to worry about it?

1. Scared carriers not yet showing symptoms sneak or force their way across boarders to unaffected regions.

2. Objects, food, or water touched by the infected go unnoticed until they end up leaving the containment zone.

3. If it can jump from bats or monkeys, thousands of infected humans increase points of contact to create vectors into other species, perhaps one that will travel unnoticed far beyond the containment zone.

4. After months of the same security precautions day in and day out, airport checkpoints, and other points of entry become lazy, and let infected through.

With numbers as high as they are, and possibly higher than we even know, is this really containable at all?

Answer 1

This is too long for a comment, so my thoughts about this here. The CDC Director said a few days ago after a visit in Africa "The window of opportunity is closing".

1. This can happen. However, you are not getting contagious unless you show symptoms. This is different in other diseases like chicken pox or measles where you spread the virus before showing symptoms. So there has to be a lot of awareness. Also doctors need to be very careful with patients showing these symptoms. This is most likely one of the main reasons for the wide spreading of the disease.

2. Same problem as in 1. Theoretically this is easy to prevent, but in a situation of chaos this can cause problems. But since infected people which show symptoms will not handle large amounts of food, this is most likely less of a problem.

3. Every crossing of a species-barrier is a rare event. Double-crossings are even less likely. So I don't think this is a problem. Besides this, we already have to independent Ebola outbreaks which has never happened before. One is the one in West-Africa, the other one is happening in the Democratic Republic of Congo. Both are independent cross-overs.

4. This can cause problems. The advantage of the first world is that we have functional health care systems. They allow better care for the persons and also better isolation of contact persons. I think it is unlikely that it would spread widely. The perspective will be different, if the virus makes the jump into the densely populated regions in South-East Asia. There a lot of people live closely together, this can cause real problems. Fortunately for us the virus is not highly contagious. To infect yourself you need unprotected contact to the body fluids (blood, stool, feces, sweat etc.) of infected persons.

Answer 2

I'm not an expert in the field, but it seems like there are almost countless ways in which an increased number of cases increases the risk of further exponential growth. It's encouraging to hear that in countries with better healthcare, death rates would likely be much lower, but at this point, isn't it inevitable that the outbreak will run its course as a global pandemic?

I don't think it is inevitable. The current strain has a high virulency, high mortality, but low transmissibility. It does not infect until the patient shows symptoms, but by most of that time she/he will be unable to move and spread the infection because of the 39°C degree fever. Only the people nursing the patient, e.g. family members, workers in the healthcare system, are in danger. So it spreads slowly compared to other diseases and that's why it is easy to quarantine and prevent. If it does not change attitude due to a mutation or anything else, I think we can avoid a more serious pandemic, at least I hope so.

There is an already existing model for an older strain available here: Understanding the dynamics of Ebola epidemics.

Scared carriers not yet showing symptoms sneak or force their way across boarders to unaffected regions.

I have the impression by listening and reading news, that most of the people know nothing about ebola in Africa, or they don't really care, because they cannot read, or they have bigger problems e.g. starving. For example Sierra Leone is one of the poorest countries in the world. They cannot move so easily, because travel requires money. So I think this is possible, but unlikely. If it happens, the infected person cannot spread the disease fast, because she/he will be unable to move after showing the symptoms. So she/he can be quarantined.

Objects, food, or water touched by the infected go unnoticed until they end up leaving the containment zone.

I think in the current case this is unlikely either. But if a food contains virions, it does not necessary cause disease, e.g. microwave oven, or long shipment - usual by fruits like banana - can inactivate it.

If it can jump from bats or monkeys, thousands of infected humans increase points of contact to create vectors into other species, perhaps one that will travel unnoticed far beyond the containment zone.

Well, it needed 8 changes to fully adapt to guinea pigs. (It was possible to infect these animals, but the outcome was not lethal.) The virions contain 19kb of RNA, and the mutation rate is 2.0 x 10^-3 substitutions per site per year. Now I am not an expert of genetics (I always hated it), but as far as I understand it is possible to rougly estimate the risk based on this data. I guess it would take decades to adapt to another species, so it is not a fast process.

• 2013 - Animal models for Ebola and Marburg virus infections

  Comparative sequence analysis of the complete genomes of the GP-adapted EBOV and wild-type virus showed 8 nucleotide differences, which led to 5 amino acid substitutions; single amino acid mutations in NP and L and 3 mutations in VP24 (Volchkov et al., 2000). Using a reverse genetics approach, it was shown that VP24 had a critical role in the pathogenesis and the amino acid changes in VP24 were essential to achieve EBOV virulence in guinea pigs.

• 2013 - Ebola virus infection inversely correlates with the overall expression levels of promyelocytic leukaemia (PML) protein in cultured cells

  Ebola virus belongs to the family of negative strand RNA viruses (Mononegavirales) and together with the Marburg virus are the two known species of the Filoviridae family 1. Electron microscopy of Ebola virions produced in cell culture have shown them to be pleomorphic, appearing as either 6-shaped, circular or as long filamentous (and sometimes branched) forms with a length up to 14,000 nm and a uniform diameter of 80 nm 2. The 19 kb single-stranded RNA genome encodes seven viral proteins: the membrane associated (matrix) proteins VP24 and VP40, the viral glycoproteins, GP (that forms the 10 nm long peplomers) and sGP (non-structural secreted form), the characteristic helical ribonucleocapsid that consists of the nucleoprotein (NP), VP30, VP35 and the L-protein that forms a RNA-dependent RNA polymerase 1.

• wikipedia - Ebola virus

  Sequencing of 99 different Ebola isolates from patients in the 2014 West African outbreak of Ebola showed the virus to be rapidly mutating,[15] with a mutation rate of 2.0 x 10-3 substitutions per site per year making it as fast changing as seasonal influenza.[16] This is likely to represent rapid adaptation to human hosts as the virus is repeatedly passed from human to human (as opposed to usually being passed between fruit bats and only occasionally crossing over into humans), and may pose challenges for the development of a vaccine to the virus.[17][18]

After months of the same security precautions day in and day out, airport checkpoints, and other points of entry become lazy, and let infected through.

I don't think security works this way. Btw currently we have the technique to filter out people showing symptoms, for instance with IR detectors looking for elevated body temperature. We have e.g. ELISA for checking IgM or the presence of the virus itself in blood tests. So if these measures are needed, I think we will apply them. Currently they are not needed, according to CDC there were only 5 cases outside Africa.