Lately, there has been a lot of talk in the news about the MERS outbreak in Asia, but what is MERS and what is a virus really?
What is MERS?
Middle East Respiratory Syndrome or MERS is a viral disease (which means that it CANNOT be treated with antibiotics!). MERS causes respiratory problems, i.e. you get difficulties breathing and cough a lot. Sadly, 30-40 % of the people infected with MERS die.
The exact ways of virus transmission is yet unknown, but coughing someone straight in the face would seem like a bad idea. MERS was firstly identified in Saudi Arabia in 2012, thereof its name.
The virus itself is called Middle East respiratory syndrome coronavirus (MERS-CoV). Corona viruses are a quite large group of viruses including the common cold and the SARS-virus. Viruses have always intrigued me and I think they are one of the weirdest things alive (?).
Viruses – alive, but yet not
Viruses are funny little buggers: alive, but yet not. They have some characteristics of living organisms such as that they carry genetic material, but they lack many other characteristics such as the cell structures, that you can find in even the simplest bacteria, and they have no metabolism of their own. Hence, they are often called “organisms at the edge of life”.
Viruses (or virions) are tiny (20-1000 nm), about 1/100th of the size of your average bacterium and your average bacterium is just a fraction of a human cell. You cannot even see them in a normal light-microscope.
Viruses are completely depending on hijacking a cell to be able to make more viruses (to replicate). They cannot do that on their own. A virus finds a cell and tricks it into letting parts of the virus enter through the cell membrane (sort of the skin of the cell). The virus then marches on to the cell’s own DNA and inserts the viral DNA or RNA and so forces the cell into making more viruses instead of the goodies the cell itself needs. Viruses are like the savants of couch-surfing.To be able to carry out this hijacking, the virus contains several parts: firstly, their genetic material, which can be either DNA or RNA. Secondly, a protein layer (the capsid) that protects the genetic material and thirdly many viruses also have a lipid layer that coats the whole thing when they are outside of cells.
RNA-viruses are the most common ones, but DNA viruses are very common among the groups that attack bacteria (bacteriophages). Some virus-types even spice it up a little with DNA and RNA depending on their life-stage.
Viruses generally have high mutation rates, which means that the nucleotide sequences (the bases: A, G, C, T/U) can change very fast. The nucleotides can change from one to another, become deleted or new nucleotides can even be added to the sequence.
Many of these mutations are silent, meaning that they do not change the amino acid they code for, but sometimes the amino acid does change and this can affect how virulent the virus is (how easy and/or how severe the infection becomes). It can also affect how a virus responds to an antiviral drug. This is one part of the story of why it can be very hard to deal with illnesses such as HIV (Human Immunodeficiency Virus).
An “antigenic shift” occurs when there are major changes in the virus that suddenly makes it very virulent. These large scale events are often due to two processes called recombination or reassortment.Recombination can happen when two or more viruses infect the same cell and the genetic material mixes from the two strains and is then incapsulated into new viruses. The new virus then contains the genetic material from both viruses and can turn out to be quite a nightmare. Think of the bird flu H5N1 for example.
Even if a single virus infects a cell, it can still shuffle around its own genetic material resulting in new characteristics appearing quite frequently. This is called reassortment (viral “sex”).
New virulent strains like MERS-Co (RNA virus) often have a reassortment history. Let’s hope that they soon find a good vaccine and that more efficient treatments are soon available. Working with viruses is a constant fight where your opponent constantly changes.
Dr. Anna of The Imaginarium
Rybicki, EP. The classification of organisms at the edge of life, or problems with virus systematics. S Afr J Sci. 1990;86:182–186.