Ebola returns

Everyone’s talking about Ebola these-days, as if it’s the height of fashion. Notably in the media at the moment is the Paula Cafferkey case. One particular headline that drew my attention was along the lines of “[Paula Cafferkey] contracts Ebola again”; a statement that seems to have shocked the nation. I thought I’d take this opportunity therefore to explain a little about Ebola and what a virus actually does; I hope to highlight this headline is slightly misleading to an unknowing reader.

Viruses enter cells through many methods. Every virus adopts a different method of entry; hence exposure to one virus will not protect you from alternative infections. Ebola is a filovirus, meaning it is able to form filamentous particles that contain its RNA (a single stranded variation of the well-known DNA double helix). These particles can then spread around a host to infect alternative sites. Ebola virus enters through specific receptors on host cells; upon attachment, this stimulates the host cell to suck the virus inside.

Viruses are typically lazy; they are not capable of self-replication so must rely on their host in order to replicate. Every virus encodes proteins that allow it to hijack a host cell. Luckily for Ebola, its RNA is single stranded and this form acts as a perfect template for viral protein formation (confused? see video). For us, the problem arises here. Once a virus has been replicated, traditionally it can only be completely removed upon death of the infected host cell.

As Ebola RNA acts as the perfect template for replication, viral proteins can form quickly. These proteins quickly overwhelm the immune system, before it can generate a response to fight off the infection. Some individuals (the lucky ones), are naturally equipped with antibodies which can slow down viral spread.  Most of us however, need to make do with the current recommended treatments for Ebola; aka the wait-it-out drug, alongside other experimental treatments to alleviate symptoms. These do a grand job, or not in the case of Paula Cafferkey.

The current Ebola strain circulating is a new Zaire strain (ZEBOV). ZEBOV is a sneaky opponent, with its ability to hide in special areas of the body known as “immuno-privileged sites” (a phrase for areas that are concealed from the immune system). Ebola has recently been shown to be capable of surviving for up to 9 months in recovered patients sperm. ZEBOV can remain hidden in areas such as these, until an opportunity arises for it to replicate again. The host then experiences a second potentially fatal wave of infection, whilst ZEBOV demonstrates it has not yet learnt to be subtle in its ways.

The Symptoms of Ebola

ZEBOV can be considered a diva. Instead of remaining inconspicuous, Ebola causes a storm inside its host; mass inflammation, bleeding, nausea, diarrhoea and shock symptoms. Although our body makes a feeble attempt at fighting off the infection, symptoms arguably facilitate viral spread; enabling viral particles to infect those in close proximity.

Viruses essentially want to replicate to the point where everyone is infected. The human genome now contains around 100,000 pieces of permanent retroviral DNA; making up an estimated 5-8% of the total size. Consequently ZEBOV is potentially in the early stages of its evolution. Unless it quickly loses its fatality however, it is unlikely to reach the permanent infection stage. (Which is good news for us, but not for those who are already infected!).

Cartoon

To return to my initial point; Cafferkey did not “contract” the virus again. A more accurate headline would perhaps describe the virus as recurrent or capable of reactivation, after undefined periods of latency in immuno-privileged sites. Until ZEBOV evolves to become less aggressive, our immune systems will continue to react dangerously; threatening virus and host survival. We can only hope that preventative treatments and therapies begin to emerge, or that Mother Nature kindly favours a less virulent strain. Despite this, the ZEBOV outbreak in West Africa is currently under control, again supporting that fatal pathogens are usually short-lived. Conclusively, the presence of persistent ZEBOV DNA in humans remains a frightening prospect. The importance of continual patient monitoring should not be overlooked.

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