I remember watching the Outbreak with Dustin Hoffman many years ago and seeing how the scientists in the movie worked on an extremely dangerous virus type in their super protective space suits. I told my parents I wanted to work on viruses like they did. They looked at me with horror. I did become a scientist, but my research interests developed differently though my fascination for viruses remained unchanged. Nevertheless, after accumulating all that scientific knowledge and having a kid of my own I can now understand why my parents were afraid. Some viruses really are dangerous.
Viruses exist on the borderlines of life. Scientists have been discussing whether viruses are living organisms or not, because they cannot function and reproduce on their own outside a host organism. Viruses have a small number of genes in their genome and they cannot produce the proteins they need to survive by themselves. Smart as they are, viruses hijack the cellular machinery of their hosts to make many copies of their own genome and the proteins required to assemble new viruses (a process called the viral replication). This way they ensure the survival of their own kind and they invade their host.
We usually don’t worry so much about common viruses such as the rhinovirus that causes the ordinary cold or the norovirus that causes mild nausea and diarrhea, because a week or so at home with a gentle treatment is usually sufficient to get back on our feet. Yet the world has seen some real strong viruses that have killed millions of people. Smallpox, which has killed up to 30% of those infected including several queens and kings in Europe, still threatened 60% of the population worldwide by 1967 when a global vaccination campaign was launched by the World Health Organization (WHO).1 Smallpox has been the first disease to be declared eradicated globally since 1980. On the other hand, HIV remains a major global threat as it has claimed more than 34 million lives so far and it continues to infect more than 1 million people every year.2
Viruses have been on earth since before human beings have evolved into their current form. It’s like a never-ending fight between these microscopic creatures and our immune systems. Every time we encounter a virus our immune system fights back and acquires immunity against that particular virus – Well, that is, unless the virus targets the immune system itself like HIV does-. Unfortunately for us, viruses do not stay the same: the key to their power is their rapid evolution rate.
As they move from human to human, viruses accumulate mutations in their genome, which sometimes leads to the generation of a new type of the same virus (so called ‘strain’ of a virus). The nature of the viral genome plays a big role in this strain generation. Some viral genomes evolve easier than the others though the nature of transmission is also effective. The longer and easier a virus type moves from host to host, the more likely it is to evolve into a new strain. For example, the influenza (flu) virus spreads through the air easily, infecting many people during a typical flu season, and meanwhile, accumulates mutations. This is why new strains of influenza come up very often and why there is a new vaccine every year.
Wondering what scientists are doing to help us fight with these ancient and clever enemies?
They charge viruses from many different angles: they investigate the functions of the viral genes, they investigate how a virus invades a cell and then spreads to others, they investigate the physical structure of the viruses, they investigate host factors that play a role in viral infection, they investigate potential anti-viral drugs and vaccines…the list goes on.
Here is a brilliant recent example of virus research.
The Avian influenza (bird flu) virus cannot replicate itself in human cells. Therefore, transmission of this virus from birds to humans is rare, but when it happens it’s an outbreak. Scientists knew from previous work that birds had something that the virus used to replicate itself. To find that ‘something’, they bashed the chicken genome into pieces and put each piece into mammalian cells. They found that one chicken gene helped the virus to replicate efficiently.3 Now, there is a human version of this gene, but the bird virus cannot use it. However, viruses change. When the Avian influenza virus adapts itself to use the human version of this gene, it spreads from birds to humans. Disrupting the interaction between the virus and this gene may provide a way to control an Avian influenza outbreak.
We need to keep in mind that nothing in biology works solely in one way or the other, it’s always a combination of different factors and routes involved. Viruses use all sorts of combinations of strategies to escape from our immune systems. So are scientists in our war against the viruses.
In a follow-up post, I will talk about real world outbreaks with a real world scientist’s personal account of the Ebola outbreak in West Africa. Stay tuned.
If you would like to read more about viruses:
This article from Scientific American talks about the discussion whether viruses are alive or not and also has a section on the enigmatic “giant” viruses.
Here is a cool video that shows how a flu virus invades a human cell.
1 Smallpox WHO fact sheet. Available Online from: https://web.archive.org/web/20070921235036/http://www.who.int/mediacentre/factsheets/smallpox/en/ [Accessed 10.02.2016]
2 HIV WHO fact sheet. Available online from: http://www.who.int/mediacentre/factsheets/fs360/en/ [Accessed 10.02.2016]
3 LONG, J. S. et al. 2016. Species difference in ANP32A underlies influenza A virus polymerase host restriction. Nature, 529, 101-104. Pubmed: 26738596
Featured image “Influenza virus” by dream designs from freedigitalphotos.net