Thanks to Irene L for tweeting the link to this important post at International SOS Ebola: comments on Ebola as an aerosol virus by Professor John Oxford. Excerpt:
A key virological fact to remember here is that we are dealing with vast populations of Ebola as much as 10 million viruses per micro drop of diarrhoea. These early observations have been well confirmed in the current outbreak. Of necessity with this way of spreading then the number of cases in the community will remain very low and the chain of infection will be easily broken by quarantine of suspects, training of medical staff in Personal Protective Equipment (PPE), good hygiene and a ‘no touch’ technique at funerals of victims and in the community. Evidence from most outbreaks as well as the present one amply confirms this.
As regards the numerical issue, we have to date around 21,000 cases in 12 months in a population of 30 million or so in the countries involved. These are relatively low numbers indeed and do not speak to us of aerosol or air droplet spread.
To give a contrary example of droplets and aerosol spread, in the last week a cornucopia of respiratory viruses have struck in the UK such as influenza, RSV and adenovirus, all spread mainly in the airborne manner and 100,000 persons have been infected over those few days.
I also want to widen the context to other viruses to illustrate that under very special circumstances these minute viruses can take advantage of a unique or unexpected opportunity to spread. We all know that hepatitis B is at a relatively high level in Africa and is spread by sex, blood and birth.
But in an overcrowded family household with lots sharing of towels, toothbrushes and shaving kits, even in the observed absence of blood, the virus can spread. This happens in the UK as well. The reason? The virus, like Ebola, is present in the victim in exceedingly high numbers of greater than 10 million viruses per micro drop of blood.
We never begin to speculate with hepatitis B that it could be spread by coughing, although I have little doubt that amongst the 200 million or so carriers in the world such a transmission has occurred! The virus would certainly be present in mouths with poor tooth hygiene.
Even more relevant is polio. The spread here is faecal/oral via sewage contaminated rivers, swimming pools or, in the family, by poor hand hygiene. But many of the early studies with the live attenuated polio vaccines described the presence of polio virus in saliva from the throat. So again we have well established and documented manner of spreading of a virus by the faecal/oral route, but it is never thought that polio could be spread by coughs and sneezes.
As a final illustration of the ‘just possible’ is rotavirus. This important diarrhoea virus, which incidentally would be expected to have killed more children in West Africa during the last year, compared to Ebola, is again present in stools in exceedingly high quantities. So should a mother casually throw a diarrhoea nappy [diaper] onto the table a few virus particles could spray out as droplets and it is possible that these could be breathed in.
As regards the ‘catch all’ that RNA viruses can mutate, most they do not and the exceptions are influenza and HIV. Polio, rubella, measles, mumps to name a few have not changed in 60 years and Ebola is the same.
Post peak infection curves of the virus always carry a danger
The curve of acquisition of new cases of Ebola, along with figures of death, had peaked in Liberia and Guinea before Christmas: shortly before the arrival of many international groups. This does not mean that their help was unneeded. The contrary is definitely the case. The withdrawal of these trained medical and nursing staff at this precise moment would not be helpful.
The downward running curve of Ebola cases is exceedingly dangerous for two reasons. Firstly the medical staff will be refocused on the other infections in West Africa, malaria, Lassa fever, cholera and enteric pathogens and TB. The declining Ebola cases will make them more easy to miss.
Even more important, these communities themselves will begin to relax and touching and kissing, and funeral habits will start up again.
It took one year to go from one case to 21,000 but now we are not at ground zero with the number of persons currently infected and so outbreaks could start up again from figures way above one! West Africa needs our scientific and medical help for at least the next 6 months and thereafter to train staff for the next outbreak.
Dr. Oxford concludes by writing: "...what these three West African countries really need is international help to build safe water system, sewage, and a health service with well trained doctors and nurses fit for the 21st century. Is this beyond the pale in a world where 500 young people in Europe have volunteered in the last few days to go to Mars on a one way ticket?"