Wednesday 29th January 2020

Infectious Diseases

From common cold to AIDS

Sub 30 Minute Test For Infectious Diseases

Infectious diseases are diseases caused by a pathogen agent, i.e. a germ. These diseases are called infectious or transmissible or communicable diseases because the pathogen organism can travel from one person (or other animal) to another, thus spreading the disease. It is a parasitic relationship, in which the germ is the parasite and the body in which it lives is the host.

The most common types of germs are viruses and bacteria. Viruses are among the simplest living organisms. They are subcellular organisms and, since the cell is the elementary unit of life, viruses need a cell in which to live in order to survive, hence they need a host. Bacteria are monocellular beings, i.e. composed of only one cell, and they belong to the vegetable kingdom. Some bacteria are beneficial to human beings, others are causing illness.

Among infectious diseases are many childhood diseases, but others can be contracted by adults too. Common cold, flu (influenza), measles, German measles (rubella), mumps, scarlet fever, smallpox, chickenpox, polio (poliomyelitis), whooping cough (pertussis), diphtheria, pneumonia, meningitis, malaria, yellow fever, lockjaw (tetanus), scabies, leprosy, plague, rabies, cholera, SARS, syphilis, gonorrhea, chlamydia, anthrax, salmonellosis, TB (tuberculosis), as well as many others, are all infectious diseases. AIDS is also a communicable disease, caused by a particular type of virus, a retrovirus, HIV. Some infectious diseases are sexually transmitted, and are called venereal diseases.

Historically, infectious diseases have been some of humanity's worst enemies. Epidemics of plague, the black death, decimated entire human populations in past centuries.

We don't live at such high risk of fatal diseases from infection any more. What has caused this improvement and consequent lengthening of our lifespan? Better living conditions with heightened hygienic measures and vaccines have both played a role in the eradication of some infectious diseases which were great killers.

Some people attribute more importance to hygiene and other people to vaccinations. But most historians agree that some infectious diseases had already been vanquished or almost disappeared before vaccination programmes were started, due to the introduction of hygienic measures particularly in high-density-population cities, along with improved nutrition and lifestyle.

This does not mean that vaccines are to be dismissed. Even today they are responsible for producing what is called "herd immunity", which is a situation in which so many people have been immunised to a particular disease-causing organism through mass vaccination that the germ has been virtually wiped out.

Since their introduction there have always been controversies surrounding vaccines, and today is no exception. Perhaps the idea of inoculating somebody with a germ, albeit a weakened or dead form of it in order to develop immunity to it, seems so counterintuitive as a kind of prevention that some people find it difficult to see any good in it or even actively fear it.

The recent case of the huge furore over the MMR (measles-mumps-rubella) vaccine in Britain, which lasted 9 years from 1998 to 2007 with a mastodontic media coverage, at one point involving a debate over whether the UK Prime Minister of the time, Tony Blair, had had his newborn baby Leo vaccinated or not, is an example of how powerful the anti-vaccination feeling and how organized the anti-vaccine lobby are.

We will cover the thorny issue of vaccines also in this section of the site.


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Photo accompanying the article Atlas Genetics by Montage Communications made available under an Attribution-ShareAlike 2.0 Generic (CC BY-SA 2.0).