THE scale of the ongoing outbreak of the Ebola virus in western Africa has taken health-care workers, scientists, policymakers - in fact, everyone - by surprise. Prior to this outbreak, the largest number of human cases in a single outbreak was just over 400. In this outbreak, it is now more than 7,000.

The identification of Mr Thomas Duncan, the first person diagnosed in the United States, who later died, and Spanish nurse Teresa Romero Ramos, who became the first case of human-to-human transmission of the virus outside Africa, has raised questions about whether the virus can be contained in countries outside Africa.

The Ebola virus is a disease of contact; it is transferred from person to person by the exchange of bodily fluids (blood, faeces and vomit) from someone who is showing symptoms of the disease. And it is likely that there will be further cases imported via infected individuals travelling back from West Africa. A recent study suggested that there was a 25 per cent to 70 per cent chance of the virus reaching France by the end of this month and between 15 per cent and 25 per cent for the United Kingdom in the same timeframe. Other research last month said there was only a 10 per cent chance of a case being identified in the US that month. Soon afterwards, Mr Duncan presented himself at his local hospital.

The global network of flights certainly makes it more likely that further cases will be imported into countries, in addition to those already affected. However, given the heightened awareness, and the time these countries have had to prepare for this scenario - and stronger public health infrastructure - they are more likely to be able to limit the transmission of the virus.

Act fast, act local

THERE has been lots of discussion about why this outbreak is so much larger than previously. Some of the reasons suggested are: that there has been only one previously documented case of human infection with the Ebola virus in West Africa (the virus has primarily caused human infections in central and eastern Africa) so health workers in this region had little experience in dealing with Ebola outbreaks; that there was a delayed response by the local and international public health agencies; poor health-care infrastructure due to civil war or lack of investment - the list can go on.

All outbreaks prior to this one in West Africa have been controlled through the implementation and strict maintenance of basic public health strategies - early diagnosis and isolation of infected individuals, provision of appropriate protective equipment for medical staff, contact tracing and education and awareness campaigns targeting the local population. But in the case of the current outbreak, the virus was able to spread in the highly dense and mobile population before these measures could be put in place.

Breaking transmission

IF YOU can break the transmission, you can control the outbreak. These measures have already proved successful. An infected Liberian who travelled to Nigeria imported the virus, which spread to 19 individuals but was quickly contained due to the implementation of the strategies above. This was possibly thanks to a health-care surveillance infrastructure in Nigeria that is used to monitor for cases of polio. These facilities and personnel were successfully mobilised to limit the spread of the Ebola virus. Nigeria has not seen any new cases since Aug 31 and will be declared Ebola-free tomorrow if no further cases are detected.

Given the scale of this outbreak, it is likely that further measures will be needed, such as the use of experimental treatments and the fast-tracked development of vaccines and therapeutic drugs, as senior experts concluded at a meeting convened by the World Health Organisation in Geneva last month. It is anticipated that there could be a limited roll-out of vaccines and drugs to health-care workers in the region by the start of next year.

Going airborne?

THE other issue that has been at the forefront of people's minds is whether the virus could mutate to become airborne. The honest answer is this is highly unlikely but we cannot rule it out.

A recent report in the journal Science noted that there have been changes to the virus' genetic code during this outbreak but this is only to be expected, due to the nature in which the virus replicates. There is no evidence that these mutations have led to the virus becoming airborne. If we look for examples of better studied viruses that mutate, such as influenza and the human immunodeficiency virus, we have known about these viruses for a long time and monitored the accumulation of mutations within their genomes.

While the rate of mutations has been prolific, these viruses have not changed the mechanism by which they are transmitted. In fact, there is no evidence any virus has changed its mode of transmission due to naturally occurring mutations in its genomes.

The writer is Senior Lecturer in Medical Microbiology at the University of Westminster. This article first appeared in The Conversation (http://theconversation.com), a website which carries analysis by academics and researchers in Australia and Britain.