WHO on Ebola virus transmission

The World Health Organization has issued a situation assessment entitled ‘What we know about transmission of the Ebola virus among humans‘. WHO is rather late entering the transmission discussion which began on 12 September 2014 with the suggestion that Ebola virus transmission could go airborne. WHO is a big organization and moves slowly; nevertheless their voice may reassure those who are not convinced by what virologists have to say. Here are the salient points (voiced here and by many others in the past few weeks).

The Ebola virus is transmitted among humans through close and direct physical contact with infected bodily fluids, the most infectious being blood, faeces and vomit.

Ebola virus disease is not an airborne infection. Airborne spread among humans implies inhalation of an infectious dose of virus from a suspended cloud of small dried droplets.

This mode of transmission has not been observed during extensive studies of the Ebola virus over several decades.

Moreover, scientists are unaware of any virus that has dramatically changed its mode of transmission*. For example, the H5N1 avian influenza virus, which has caused sporadic human cases since 1997, is now endemic in chickens and ducks in large parts of Asia.

That virus has probably circulated through many billions of birds for at least two decades. Its mode of transmission remains basically unchanged.

Speculation that Ebola virus disease might mutate into a form that could easily spread among humans through the air is just that: speculation, unsubstantiated by any evidence.

The last sentence is the key point:

To stop this outbreak, more needs to be done to implement €“ on a much larger scale €“ well-known protective and preventive measures. Abundant evidence has documented their effectiveness

*Sounds familiar?

8 thoughts on “WHO on Ebola virus transmission”

  1. The H5N1 part is the less convincing, since that virus caused clusters of human-to-human transmission in various settings, like Turkey, Azerbaijan, Pakistan, Indonesia, China, Egypt perhaps also in Cambodia although without firm conclusions on route of transmission. More clear the clusters dynamics in Pakistan and Indonesia when close relatives caught the virus from a single individual. H5N1 can acquire the ability to transmit efficiently from human-to-human and the fact it has not achieved this ability so far is not a proof that it can’t. A more fitting example would be appreciated. I think the rabies virus may be a good example, because of some structural similarities with ebov and its ability to spread via particles in some settings (eg. laboratory preparations). Despite this virus is among humans for millennia, its mode of transmission has not changed and remains the same, through saliva of an infected case. But H5N1 is a bad, very bad example: in addition, it was another WHO risk assessment failure…

  2. There is no evidence that H5N1 transmits among humans by aerosol. These clusters of transmission that you list are not well understood and could represent droplet or contact transmission. For you to say that H5N1 can acquire ‘efficient’ human to human transmission is simply wrong. The point remains that no human virus has changed its mode of transmission, and you can pick any number of examples. Continuing to debate this point is not productive.

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  4. I’m sorry to have caused a such bitter response! GOF experiments with H5N1 have been done and were put into spotlight for long time. But I can’t forget the Karo cluster in Sumatra, and the 9 deaths in ten cases among a single family attended the same banquet. This incident was followed-up carefully from the WHO and the initial assessment that the virus may have passed through preparation of food was discarded as the time of onset of illness among various family members did not match the initial case date. But, you are right: unproductive debate. But it remains to be established whether the WHO ”downgrade” level of alertness towards H5N1 is warranted. The virus is alive and well and continue to circulate in poultry at panzootic level. It is a big mistake to leave it overlooked.

  5. The CBSNews web site is reporting that the nurse in Spain who is infected with Ebola owns a dog and the dog is being destroyed as it might be a vector for transmission to humans. Does this make any sense?

  6. “Ebola is not airborne” is not a good choice for dogma. I think anyone here would agree that blood contaminated droplet transmission is possible. We also would disagree that a wide range of droplet sizes are generated by the infected and that the smaller droplets dry out quickly. I recall a study that indicated a proportion of infective Ebola particles could survive drying for as long as 100 minutes, and that infection only requires 1 – 15 live particles. So what we have here are a series of gaussian distributions that suggest dogmatism is ill-advised and that those in droplet contaminated clinical environments should wear respirators or PAPRs to avoid low probability negative outcomes. Whatever you decide to call droplet —> aerosol.

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