All About Infectious Agents (Germs)

Bacteria
These are one celled organisms that are alive and capable of living independently. One of these organisms is a bacterium. Two or more are properly termed bacteria.

Not all bacteria are harmful. Indeed quite a few serve at helping people. Some live in people and cause no harm but produce no benefit. The are most abundant in the mouth, gut and skin

Bacteria are the only living things that live in every possible environment on the earth. The average gram of soil contains roughly 10 BILLION bacteria. Bacteria can live in such odd places as nuclear waste, chlorine beach and sulfuric acid.

They are responsible for such illness such as tuberculosis, bubonic plague, syphilis, leprosy and cholera.

With the use of sulfa drugs, then antibiotics many scientists predicted in the 1960s soon bacterial infections would be a thing of the past. However few people saw the enormous ability for the bacteria to evolve and defeat antibiotics. The development of new antibiotics has been stifled with only three new antibiotics developed since 2000.

Viruses
These are among the most interesting things in nature. Viruses consist of genetic material usually DNA, but some just have RNA. Viruses contain one or the other and not both. This genetic material is contained in a protein shell. Viruses can even infect bacteria. Unlike bacteria, viruses are almost always harmful to the host but there are a few viruses that are benign or cause little problem. A cold sore virus is an example of this.

They are not quite living but they aren't exactly non-living either.

Virologists consider them to be non-living, but a more accurate way to describe them is "potential life."

Viral diseases have been around for ages but it wasn't until the 1930s when they were universally accepted. Filters, which could sceen out bacteria, were commonly used to eliminate bacteria but clearly something else was infecting people and it was smaller than a bacteria. In fact a vaccine for smallpox was developed long before science firmly accepted viruses as fact.

Viruses are tiny, to put this into an analogy if you took a mid sized virus next to a flea, this would be like putting a human being next to Mount Everest, the world's tallest mountain.

Example of Virus diseases include:

Ebola
Chicken Pox
Measles
Flu
Rabies
The Common Cold
Fever Blisters (Cold Sores)
SARS
Lassa Fever

It is suspected viruses may play a role but not directly cause multiple sclerosis and chronic fatigue syndrome.

Viruses have either DNA or RNA

HIV is a retrovirus, as the name suggests, this is do to the fact HIV use RNA for its genetic material while most viruses and all other life forms us DNA as a genetic material.

Viroids
These are infectious agents that exclusively (perhaps with one exception) that infect plants

These agents do not code for proteins and do not have the protein shell of viruses thus are not classed at viruses.

The possible exception is Hepatitis D. This is a strange particle that some virologists class a viroid. Some put it in a class by itself calling it a "delta agent."

Delta Agent
This causes Hepatitis-D and Labrea fever, which is now considered to be a sub type of Hepatitis-D. This agent can only replicate in the presence of Hepatitis-B. Thus the vaccine that protects against Hepatitis-B also protects against Hepatitis-D.

The delta agent differs from a virus in that it does not have a protein shell but it does code for a single protein, so it isn't usually classed as a viroid.

Prion
This is the agent best known for causing Mad Cow Disease. This is not universally accepted however. About 15% of medical researchers believe that it is not a prion but rather an unusual unidentified virus that is not yet identified

Prions are unusual in that they contain no genetic material. They are a protein. It is thought the prion is a protein that is mis-folded. Proteins in the body are folded in a certain way, however it is thought when the prion comes in contact with other protein it causes these normally folded proteins to mis-fold. This newly mis-folded protein now continues the cycle and makes other normally folded proteins mis-fold and this causes the illness

The acceptance of prions is controversial because an infectious agent without any genetic material is completely new. Because it contains no genetic material it cannot be killed by ultraviolet light or other methods such as heating. And because it is a protein like every other protein in your body, just mis-folded, the body's immune system doesn't view it as a foreign object so does noting to destroy it.

Fungi
Once classed as plants, biologists now have them in their own Kingdom called heterotrophs. They are now thought to be closer to animals than plants. But whatever the relationship is, in addition to some being highly poisonous, some fungi cause disease. Though some, such as edible mushrooms and yeast are obviously helpful.

Examples of disease caused by funji include: athlete's foot, ringworm, yeast infections and in plants Dutch elm disease.

Protozoa
These are simple single celled organisms, they posses the ability to move independently. They are neither animals nor plants and put into their own kingdom called Protista. They share this kingdom with some kinds (but not all kinds) of algae and various kinds of molds. They are vital in the role that they control many type of bacteria.

Protozoa also cause several diseases in plants and animals. Most notably of these is malaria. Other diseases caused to humans are African sleeping sickness, amoebic dysentery, chagas' disease, giardiasis, leishmaniasis, malaria, primary amoebic meningoencephalitis (PAM) and vaginitis.

What is an epidemic?
An epidemic is traditionally defined as when three in ten people (33%) in a given area are sick with the same illness. However this has been modified to become when a lot, but not a majority of people, in a given area are sick with the same area.

What is a pandemic?
A pandemic is traditionally defined as when nine out of every ten people (90%) has the same illness. Today it has be redefined to mean a majority (over 50%) a given population has the same illness?

That is confusing what's an "area" defined as?
It can be anything you want it to be. The terms epidemic and pandemic are simply relative. Here is an example using the traditional definitions.

Chicago has 2,800,000 people

Let's say 2,600,000 people in the city of Chicago have the flu.

We take 2,800,000 and divide it by 2,600,000 and we get about 93%.

This means in the city of Chicago 93% of the people are sick with the flu. So we say the flu is "pandemic" in Chicago. That is because more than 90% of the total population of an given area, in this case Chicago, has the flu.

But now let's consider this:

Illinois has about 12,750,000 people

Let's say in the entire state of Illinois 4,500,000 million have the flu. That would 2,600,000 in Chicago plus 1,900,000 elsewhere in the state for a total of 4,500,000.

So we take 12,750,000 and divide it by 4,500,000 and get 35%. So in the entire state of Illinois the flu is epidemic. It's epidemic because it's over 33% but less than 90%.

See the difference? The same flu is "pandemic" to Chicago, but "epidemic" to Illinois.

It's all relevant.


What is an endemic?
This is the word used to descirbe an area which a given illness has always been present in low levels and the people living in that area have some sort of total or low level immunity to that disease.

For instance in West Africa malaria is endemic. Most people in that area have some immunity to it. So when they get malaria, it is a very mild case or they never know they had it.

In this case a lot of West Africans in that area have one copy of a gene that protects them from malaria by making the disease less severe to them. Africans from other areas and Europeans and Asians lack this gene so if they go to West Africa and get Malaria, it can be deadly.

However the downside to this is, if the West Africans get the gene from both parents not just one parent, the develop sickle cell anemia.


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