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The germ theory of disease

Your immune system protects you from bugs: harmful micro-organisms. These are tiny living organisms that can infect and sicken us. There are many types, including:  viruses, bacteria, fungi, protozoa.  It might surprise you to know that it is a very modern idea that germs – another word for bugs – cause disease.  The germ theory has only been widely accepted since the second half of the 19th century, and is still not accepted by some.

Please allow me an arithmetic deviation. When was the 19th century?  Our calendar starts with Jesus.  A century is 100 years, so we describe the first 100 years after His birth as the first century.  So the 19th century are the years from 1800 to 1899, or the 1800s.  In 2016, we are living in the 21st century: science fiction for me,  growing up in mid-20th century.

Wikipedia tells me that germ theory was originally proposed by Girolamo Fracastoro in the year 1546. (I wonder if there has been adequate credit given to earlier Chinese or Greek thinking.  Most ideas can be found in these classical sources,   confirming the biblical verse that ‘there is nothing new under the sun’. ) The microscope was only developed in the 16th century, and it was not till 1676 that  Antonie van Leeuwenhoek discovered micro-organisms.  He had developed a microscope with up to 300 times magnification and  discovered red blood cells and spermatozoa (or sperm, if you remember where you come from).

The role of micro-organisms, or bugs, in causing disease remained controversial until medical science advanced. As these bugs are too small to be seen, they were not discovered until we had microscopes.  Viruses are much smaller than bacteria, and cannot be seen with a light microscope.  An electron microscope  allows us to see viruses, but we can also see the effect of viruses on the cells they infect on a lab dish.  The first virus was only isolated in 1898, influenza virus in 1933.

The cartoon above shows the key features of the influenza virus: the two proteins that it uses to get into and out of the cell it infects and takes over, preparing billions of copies of itself in the infected cells.  Below, you can see these two proteins as well as the 8 strands of its genetic code, each coding for the proteins that make up the virus.  Influenza is an RNA virus, meaning its code is made of RiboNucleic Acid.  In contrast, bacteria and humans use DNA, or DeoxyRiboNucleic Acid, as our genetic code, in each of our cells.

 

influenza-virion1

The influenza virus 

Source: http://www.twiv.tv/virus-structure/  where you can see other types of virus.

Our understanding of the immune system is even more recent than of bugs.  Many different types of viruses cause disease; and even more so for bacteria. For most viruses, including influenza the symptoms we get are not from the infection itself, but from the body’s attempt to remove an invader that has breached the initial defence barriers of skin, gut, or vagina.  This is why many viruses will cause an influenza-like illness.

Other viruses, like measles, polio, or Ebola each have distinctive patterns of illness, that still is the reflection of the battle between the virus and the specific tissues that that virus has a propensity to attack. In addition to an acute infection, some vaccines can be carried for a long time to be reactivated as shingles or cancer. hepatitis B and human papilloma virus cause cancer of the liver and cervical cancer, respectively.

The immune system does not only protect us from these infections, but we can teach the immune system so that it can defeat an infection before it sickens us.  But to understand the immune system, we first need to understand cells….

 

 

 

 

Diversion on dates:

So, was Jesus born in Year zero or one? Probably neither, but in 4BC – which means four years before Christ is born, so how can that be?  The problem was this new calendar, called Annus Domini (AD) , was not established till some hundreds of years later.    The issue of whether to choose zero or one as the starting point is a computer coding question too.  Are you 0-day or 1-day old on the day your are born?  The zero itself was not born till seventh century India, around 650 AD (7th century), though did not reach Europe till the 12th century I hope by now you will recognise is the seventh century after His birth.  And that in 2016, we are living in the 21st century.  Can you believe it?

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