Ebola: how widespread is natural immunity?

Date: Oct-17-2014 The devastation that the world's worst Ebola outbreak is wreaking in West

Africa is both heart-rending and alarming. Expert projections suggest worse is yet

to come, and with cases now confirmed in the US and Europe, there are rising

concerns that outbreaks may occur on other continents. However, as the virus

continues to infect and kill thousands, it may also be silently immunizing an

unknown number of others.

If immune individuals can be reliably identified, they could be recruited to help with disease control, reducing risk of infection to those who are not immune.

As the latest figures from the World Health Organization (WHO) show, there are

nearly 9,000 cases of Ebola in seven countries: Guinea, Liberia, Nigeria, Senegal,

Sierra Leone, Spain and United States, and nearly 4,500 deaths. The disease has also

taken its toll on healthcare workers, with 427 infected and 236 dead.

Experts predict that the Ebola situation in West Africa is going to get much

worse without a large-scale, prompt global response, as fragile local health systems

collapse under the strain of the disease.

A few weeks ago, using a new prediction model, the US Centers for Disease Control

and Prevention (CDC) estimated that by early 2015, the number of Ebola cases could exceed half a million or more if effective prevention and control measures were not implemented

promptly. The model suggested the number of cases was doubling every 20-40 days.

At a recent news conference in Geneva, Dr. Isabelle Nuttall, WHO Director for

Global Capacities, Alert and Response, said their data shows "cases are doubling

every four weeks," and the disease is "still widespread in Guinea, Liberia and

Sierra Leone."

Ebola projections do not account for effect of immune people

But according to a letter in The Lancet medical journal, there may large

numbers of people in West Africa - as yet unidentified - who are coming into

contact with Ebola but never fall ill or infect others, and who may also be

protected from future infection.

And if the effect such immunity can be confirmed, say the authors, it could have

a significant impact on projections of how widely Ebola will spread. It could also

help contain the outbreak.

They urge public health authorities to carry out a prompt investigation to

establish how commonplace such immunity to Ebola might be. How many people have been

infected without developing symptoms or spreading the disease? And are they likely

to be protected from future outbreaks?

Co-author Dr. Steve Bellan, a postdoctoral researcher in the Department of

Integrative Biology at The University of Texas at Austin, says:

"Ultimately, knowing whether a large segment of the population in the afflicted

regions are immune to Ebola could save lives."

Immune individuals could save lives by helping with disease control

If such individuals can be reliably identified, they could be recruited to help

with disease control, reducing risk of infection to those who are not immune.

"We might not have to wait until we have a vaccine to use immune individuals

to reduce the spread of disease," urges Dr. Bellan. He and his co-authors also note

that:

"Recruitment of such individuals might be preferable to enlistment of survivors
of symptomatic Ebola disease because survivors might experience psychological trauma

or stigmatisation and be fewer in number - in view of the asymptomatic proportions

suggested in previous studies and the low survival rate of symptomatic cases."

The authors say there is evidence from previous Ebola outbreaks that some exposed

people do not develop symptoms, but it is not clear whether it is because they have

developed immunity to the virus.

They conclude that finding out whether naturally immune people exist could make a

big difference to efforts to contain Ebola, and could also affect the accuracy of

projections.

The investigation needs to be as soon as possible, not only in order for any

findings to have the chance to make a difference and save lives in the current

outbreak, but because you can only be sure of finding individuals that are immune

during an outbreak, as the authors explain:

" ... the extent of protective immunity after asymptomatic infection and the
identification of serological markers for protective immunity can only be

definitively addressed in settings with ongoing transmission risk."

Following the recent revelation that a second health care worker has tested positive

for Ebola, and was found to have taken a commercial flight from Cleveland to Dallas

the day before presenting with Ebola symptoms, Medical News Today asks

are the CDC doing enough to stop an Ebola

outbreak in the US?

Written by Catharine Paddock PhD

Not to be reproduced without permission.

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Courtesy: Medical News Today Note: Any medical information available in this news section is not intended as a substitute for informed medical advice and you should not take any action before consulting with a health care professional.