When will Ebola Burn Out?

[GardenSpider]

Barring an immediate vaccine, (which will take more time than West Africa has no doubt) at what point does a population acquire herd immunity? Does anyone know what the threshold is for ebola? What would this mean for West Africa?

Of course we hope there will be enough new HCW recruits and international troops for the effort to set up clinics, trace and isolate patients to get ahead of the rising wave, but so far that has been disappointing. The numbers differential between our simple arithmetic, (numbers of people on the ground to run interference) and ebola's exponential spread is mind boggling. We're not even playing on the same field. How will we ever get ahead of this?

I've read on FT here: http://www.flutrackers.com/forum/showthread.php?t=228059 that it took 1000 HCW making 19,000 home visits in Nigeria to stop ebola. With untold thousands now infected, what does that suggest in terms of sheer numbers of people on the ground to stop ebola? Is it even possible?

There have been so many alarming predictions like this excerpt from Global Research: http://www.globalresearch.ca/virologist-its-too-late-ebola-will-kill-5-million/5401341 "Jonas Schmidt-Chanasit of the Bernhard Nocht Institute for Tropical Medicine in Hamburg told Germany’s Deutsche Welle that hope is all but lost for the inhabitants of Sierra Leone and Liberia and that the virus will only “burn itself out” when it has infected the entire population and killed five million people. The right time to get this epidemic under control in these countries has been missed,” said Schmidt-Chanasit. “That time was May and June. “Now it is too late.”

Here is a description of the math behind immunity. With Ebola, what criteria determines peak level? http://aeon.co/magazine/health/how-mathematics-can-make-epidemics-history/

snip...

"From influenza to plague, the number of cases in a real epidemic often rises exponentially at first. After a while, the disease reaches a peak level, and then the number of new cases starts to decrease. When McKendrick and Kermack began their research, people generally gave two possible reasons for the decline. Either the epidemic faded away because the infection had become less potent over time, or because there were no susceptible people left – everyone had been infected and either died or become immune.

In their model, McKendrick and Kermack assumed that the pathogen stayed the same throughout the epidemic; the infection did not weaken over time. And yet the model still produced an eventual decline in cases. When the pair compared the model to the 1905 outbreak of plague in Bombay, the predicted number of cases matched the real disease level.

So was the decrease in infection caused by a lack of susceptible people? Apparently not: in the model, there were always some susceptible individuals remaining at the end of the outbreak. McKendrick and Kermack had demonstrated that epidemics don’t necessarily decline because everyone has been infected. They can also end because there aren’t enough infected people left to sustain transmission. Once enough people are immune, infected individuals are unlikely to meet another susceptible person, which means that they generally recover before infecting others."

snip…

Hoping for an ebola-free world.

 

[Ray]

Re: When will Ebola Burn Out?

It won't. Up to 21 day incubation period + travel (bus, car, dirt bike, plane, ship etc) = plenty of human fuel. Best hope vax, meds.

 

[AlaskaDenise]

Re: When will Ebola Burn Out?

Ebola (in general) will never truly "burn out" due to wide genetic variations between strains and not knowing the reservoir host. Past ebola epidemics were halted because of 1) small number of available human hosts, or 2) strict infection control & contact tracing that was done with a manageable population (i.e., sufficient available HCW & other resources). Zoonotic diseases behave differently than those affecting only humans. We'd need a vaccine that would cover all known strains and any newly emerging ones - I expect that's almost as difficult as trying to make a vaccine for HIV.

.

 

[Vibrant62]

Re: When will Ebola Burn Out?

We also do not know the extent of immunity conferred by previous infection: ie does it last a year, a decade, a lifetime?? If immunity only lasts for a short period, reinfection may produce less severe disease, if immunity to it works like flu.... but it would still keep the transmission pool going.

There are so many unanswered questions.

 

[AlaskaDenise]

Re: When will Ebola Burn Out?

We also do not know the extent of immunity conferred by previous infection: ie does it last a year, a decade, a lifetime?? .........There are so many unanswered questions.

Given that most previous outbreaks (except Kikwit, DRC) were in remote areas, can we assume none of that immunity is present in urban areas? Can a person gain immunity when the strains are so genetically different (30-70% by various sources)? The "novel" 2009 H1N1 still made us ill despite prior human immunity of "parts" of its genetic code. However, in influenza all it takes is one small particular mutation to completely change the outcomes, right? With influenza the animal reservoir hosts (wild birds) don't produce novel strains that will infect humans with certainty - most of the many influenza strains in wild birds have never infected humans - but all ebolas (except reston until 2009) infect humans.

.

 

[MHSC]

Re: When will Ebola Burn Out?

?Herd Immunity?: A Rough Guide


http://cid.oxfordjournals.org/content/52/7/911.full

 

[JJackson]

Re: When will Ebola Burn Out?

The answer to the question 'When will it burn out?' if that literally means with out us stopping it first then the answer is not until it has knocked a couple of billion of our population and altered the economic, political and military balances so they are largely unrecognisable.
Burning out may happen in a village, after killing a third of the village, but we can not really afford to wait for it to scale up. It is either do a lot now or a very great more later. If we do not want the whole planet to be forced into a war economy then sooner is better.

Not that that is what I expect to happen. I was just taking the question literally. The current infection rate is under 1% the breaking effect, created by the recovered immune, should become significant once it hits around 40% - so probably not best to rely too heavily on that.

The CAR is probably around 75% (I have seen it described only as 'high' or 'very high'). The CFR is ~70% for this outbreak. Deaths=CFR*CAR*Population. I will leave you to choose a population value 20m or 7,000m and do the math.

The ironic thing is if we really did nothing the population least scathed would probably be hunters and consumers of fruit bats, and bush meat more generally. They are the population most likely to have some immunity.

 

[Vibrant62]

Re: When will Ebola Burn Out?

JJackson. I agree with regard to numbers, but if immunity is short lived and several infections are required before full immunity is acquired, those numbers could be higher over a decade.

one query I do have though - what do you mean by a 'war economy'? Please could you define this?

Many thanks

 

[JJackson]

Re: When will Ebola Burn Out?

what do you mean by a 'war economy'?

The UK switched to a War Economy in the second World War. Everybody was switched to weapons manufacture, food production or some other function directly related to the war effort. The vast majority of other business lost their labour and shut down for the duration.
In this case I guess we would all be making PPE, drips, body bags, growing food or digging graves.

 

[Vibrant62]

Re: When will Ebola Burn Out?

Definitely growing food in the UK... our food security is appalling. We import @50% of our needs.

 

[JJackson]

Re: When will Ebola Burn Out?

Definitely growing food in the UK... our food security is appalling. We import @50% of our needs.

That's fine then, we would lose the other half anyway. A little black humor in a discussion of the absurd.

 

[Vibrant62]

Re: When will Ebola Burn Out?

necessary when looking at such dark possibilities... it keeps us sane or something close to!!

 

[AnnaLisa]

Re: When will Ebola Burn Out?

I don't see a real impediment to it spreading right now. We are putting a lot of faith in contact tracing. I'm very concerned about what happens when it gets to regions where there is minimal health infrastructure, and no realistic way to trace. :/

After this case in Spain, I am a bit worried how well we will do caring for patients in more developed areas as well.

Left pondering.....

 

[Vibrant62]

Re: When will Ebola Burn Out?

I think the bottom line is:-

Ebola wont burn out in any harmless way, and it would be extremely foolish to hope or expect it to.

This is why the world is acting, the question is if the world is acting fast enough, and if enough is being done right now.

 

[GardenSpider]

Re: When will Ebola Burn Out?

I don't see a real impediment to it spreading right now. We are putting a lot of faith in contact tracing. I'm very concerned about what happens when it gets to regions where there is minimal health infrastructure, and no realistic way to trace. :/

After this case in Spain, I am a bit worried how well we will do caring for patients in more developed areas as well.

Left pondering.....

I couldn't agree more. From the outset, the news on ebola has been incredibly frustrating; from the sluggish response to the outbreak at its inception, to the world sitting on its hands during the critical months, to the raging fire that ebola has become putting the world at risk. For ebola, it's been the perfect storm.

On the bright side, ebola could galvanize the world and force a type of cooperation we haven't seen since WWII, but I think we are still waiting for that.

I too am left pondering. The comments here are insightful and chilling. We will find the perfect solution to this perfect storm, albeit may take a while. Perhaps by this time next year, we'll all be getting our ebola vaccine!

 

[GardenSpider]

Re: When will Ebola Burn Out?

Here is an interesting comment from Peter Jahrling;
A top scientist worries that Ebola has mutated to become more contagious
http://www.vox.com/2014/10/13/6959087/ebola-outbreak-virus-mutated-airborne

JB: There have been worries that Ebola can become a pandemic like HIV and spread around the world. Even Tom Frieden, director of the Centers for Disease Control and Prevention, was recently saying as much. Your thoughts?

PJ: The mode of transmission is different between the two viruses. Ebola causes an acute infection which you either die from or you're immune, you don't carry the virus for long periods of time. Whereas with AIDS, a lot of people transmitting AIDS didn't know they have it. Before we had a triple cocktail therapy, AIDS was lethal with the exception of a few people who were not susceptible. Long term AIDS was hotter than Ebola. My gut feeling is that Ebola is going to burn out in human populations.

JB: Why are you optimistic about this epidemic burning out?

PJ: In this epidemic, it would appear that there have been multiple introductions [of the virus from animals to humans]. It's not all person to person transmission. It's coming from animals again and again. [This means people need to be near potential animal hosts ? believed to be fruit bats endemic to Africa ? to get the virus.] Now there are all these different strains. That could also mean the virus is more mutable. We can't yet say. I think it's unlikely that this thing is going to perpetuate in humans.

 

[Lizw]

Re: When will Ebola Burn Out?

Here is an interesting comment from Peter Jahrling;
A top scientist worries that Ebola has mutated to become more contagious
http://www.vox.com/2014/10/13/6959087/ebola-outbreak-virus-mutated-airborne

JB: There have been worries that Ebola can become a pandemic like HIV and spread around the world. Even Tom Frieden, director of the Centers for Disease Control and Prevention, was recently saying as much. Your thoughts?

PJ: The mode of transmission is different between the two viruses. Ebola causes an acute infection which you either die from or you're immune, you don't carry the virus for long periods of time. Whereas with AIDS, a lot of people transmitting AIDS didn't know they have it. Before we had a triple cocktail therapy, AIDS was lethal with the exception of a few people who were not susceptible. Long term AIDS was hotter than Ebola. My gut feeling is that Ebola is going to burn out in human populations.

JB: Why are you optimistic about this epidemic burning out?

PJ: In this epidemic, it would appear that there have been multiple introductions [of the virus from animals to humans]. It's not all person to person transmission. It's coming from animals again and again. [This means people need to be near potential animal hosts ? believed to be fruit bats endemic to Africa ? to get the virus.] Now there are all these different strains. That could also mean the virus is more mutable. We can't yet say. I think it's unlikely that this thing is going to perpetuate in humans.

There is a thread already on this interview, and I'll reiterate what I said there. I think he is entirely wrong in his assertion that repeated animal contacts are responsible for any significant amount of infection.