What does Zika virus look like?
Viruses are small
Very small. Smaller than a speck of dust, smaller than a germ like E coli. Between 20 and 300nm [there are one million nanometers in a millimeter]. So we can't just take a photo of them.
Here are some 3D renderings of viruses such as this one: Hepatitis C
Viruses can only survive deep in body tissues, usually inside cells. If we could film viruses in the blood stream they would be like flotsam washing along the arteries and veins, dwarfed by thousands of giant red cells and a few even larger white cells. But we can't. Light microscopes can only reach a resolution of 200nm so even a giant virus is a minute dot.
But the electron microscope has a resolution of 50pm [there are a thousand picometers in one nanometer]. The problem is that the smallest electron microscope is about the size of a PC. Here it is:
So it won't fit inside any living body. As a result for transmission electron microscopy you need to:
You'll be familiar with the resulting gray scale em photos like this:
It looks spherical and transparent. There is no colour. The only way we can see coloured images is by adding stains to the sample. And the only way we can see the 3D structure of the virus is by using a scanning electron microscope, which can work with thicker sections but you may have to:
This image of Zika virus homing in on a human embryo [much reduced in size is particularly unsettling:
It looks like a studio portrait, with two lights from above and a backlight helping it standing out from the monotone background.
But it is nothing of the sort. It's made-up.
Viruses can only survive deep in body tissues, usually inside cells. If we could film viruses in the blood stream they would be like flotsam washing along the arteries and veins, dwarfed by thousands of giant red cells and a few even larger white cells. But we can't. Light microscopes can only reach a resolution of 200nm so even a giant virus is a minute dot.
But the electron microscope has a resolution of 50pm [there are a thousand picometers in one nanometer]. The problem is that the smallest electron microscope is about the size of a PC. Here it is:
So it won't fit inside any living body. As a result for transmission electron microscopy you need to:
- Take a sample
- bring it to the lab
- fix the structure with formaldehyde
- freeze it quickly in liquid ethane and keep it frozen
- take fine slices
- place the sample in a vacuum
- direct electron beams at the sample
You'll be familiar with the resulting gray scale em photos like this:
Here is our first sight of Zika virus in frozen section.
It looks spherical and transparent. There is no colour. The only way we can see coloured images is by adding stains to the sample. And the only way we can see the 3D structure of the virus is by using a scanning electron microscope, which can work with thicker sections but you may have to:- bathe the sample in electron dense solution
- dry it
- freeze fracture it to examine the broken off edge
- embed it with epoxy resin
- blow metal vapour such as platinum across it to create shadows
- take an imprint of the structures with carbon vapour
- stain it with heavy metals: lead, tungsten or uranium
As you can imagine, any of these processes may interfere with the sample to cause artefacts. So it's necessary to compare the results of several different methods to get an accurate picture.
Since viruses are essentially colourless, artificial colour is added in the staining process or in illustrating the virus structure in order to make it visible. It's guesswork:
From these sudies we know that Zika virus has a smooth surface but develops projections when it is attacked by acid inside the cell. The projections are exaggerated in some illustrations to create a more beautiful/sinister image:
This image of Zika virus homing in on a human embryo [much reduced in size is particularly unsettling:
For me, the image which best captures the structure of Zika is this diagram:
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