are the oldest form of life on Earth. Some types have
existed for billions of years. These single-cell organisms
are invisible to the eye, but they can be seen with
microscopes. Microbes live in the water you drink,
the food you eat, and the air you breathe. Most microbes
are helpful and some even essential, like the billions
of microbes swimming in your intestines to help digest
food and create the essential vitamins our bodies
need. Billions more live naturally in our skin, mouth,
nose, teeth, throat, and urethra. In fact, 95% of
all microbes are not harmful.
There are five types of microbes: bacteria, viruses,
protozoans, fungi, and nematodes (worms).
| Disease Causing Organisms
most abundant organisms on Earth, bacteria live
almost everywhere: in the soil and water, in
plants and animals. Whether they take the form
of spheres, rods or spirals, bacteria consist
of a single cell. Unlike the cells of animals
and plants, bacterial cells lack a nucleus,
but they can carry out all necessary life functions.
Most bacteria are parasites, although a few
manufacture their own food. Some of these parasites
are very helpful -- they aid in many bodily
functions including digestion, and help with
other processes, such as decomposition of soil
and changing of milk into cheese. Disease results,
however, when bacteria multiply rapidly (each
cell simply divides into two identical cells)
and damage or kill human tissue, as in pneumonia
and tuberculosis. Diseases can also produce
toxins that damage or kill human tissue, as
in food poisoning or cholera. Sometimes bacteria
in the body are helpful for a while, and then
something in the body or the bacteria changes,
causing destruction in the host.
far the smallest microbes, viruses can appear
as spirals, 20-sided figures or even more complicated
forms. They consist mainly of genetic material--DNA
or RNA. They are not cells, however, and cannot
carry out life functions on their own. Living
inside the cells of other species, viruses use
the host cells to grow and produce new viral
particles. As they take over genetic material
to reproduce themselves, the host cells often
die. Found in all groups of living things, from
bacteria and fungi to plants and animals, hundreds
of the known viruses can cause many kinds of
infections, chickenpox, measles, flu, colds,
polio, and AIDS. Viruses cannot move by themselves
and must be carried to cells by air currents
and then by body fluids to the cells. Some viruses
may lay dormant for years before becoming active,
as with AIDS. Most diseases come from other
species, for example: smallpox from dogs or
cattle, hemorrhagic fevers from rodents and
monkeys, tuberculosis from cattle and birds,
common cold from horses, and AIDS from African
include yeasts (one-celled), and mushrooms and
molds (multi-celled). Unlike plants, fungi do
not make their own food. Some species of fungi
get their nutrition by breaking down remains
of dead plants or animals. Others are parasites.
Examples of fungal infections include athlete's
foot and ringworm.
microorganisms break down body tissues or absorb
digested food. They can cause anything from
skin infections to internal disorders that can
lead to death. The group called helminths includes
flukes, roundworms, and tapeworms; these are
many-celled animals with developed organs. Among
the numerous types, some are parasites--organisms
that live in or on another species, usually
harming the host species in the process. Because
of their size, parasitic worms grow outside
of cells and can reach an astronomical size
of 30 feet in length.
consist of a single cell that includes a nucleus.
The cell also contains structures that carry
out specific processes needed for life functions.
A diverse and complex group, protozoa range
through many shapes and sizes. They can be parasitic,
needing to live within another organism, or
free-living in moist habitats. The similarity
of inner structures of protozoan and human cells
makes it difficult to treat infections caused
by protozoa. Drugs that may destroy the protozoan
may also destroy human cells. Protozoan infections
include amebic dysentery, malaria, and African
are diseases spread?
disease-causing microbes enter the human body and
stay there for part or all of their life cycle. When
pathogenic microbes spend part of their lives in insects
or other animals before they move to the human body,
they are called vector-borne agents. Some microbes
that live in water are harmful if swallowed, or if
they penetrate the skin. Soil microbes can enter the
human body through a break in the skin or can be inhaled
may be spread in a number of ways:
AND WATER PRECAUTIONS
Typhoid, hepatitis A, polio, traveler's diarrhea
are transmitted by contaminated food and water.
Malaria, dengue fever, Japanese encephalitis, and
yellow fever are transmitted by infected mosquitos.
Tetanus can be contracted from soil and can enter
through broken skin. Parasites are found in soil
and sand contaminated by cat or dog feces.
(coughing and sneezing)
Inluenza, diptheria, meningococcal disease and tuberculosis
are transmitted from person to person through coughing
(sexual activities or blood)
Hepatitus B and AIDS are transmitted by contaminated
needles, syringes, blood and sexual activities.
year, two to three million children die needlessly
for the lack of new vaccines routinely given in North
America, Europe, and Australia. The development and
use of vaccines has reduced and, in some cases, eliminated
many diseases that killed or severely disabled children
and adults just a few generations before. For most
people in the Caribbean today, vaccines are a routine
part of healthcare.
causing organisms have at least two distinct effects
on the body. The first effect is very obvious: we
feel sick, exhibiting symptoms such as fever, nausea,
vomiting, diarrhea, rash, and many others. Although
the second effect is less obvious, it is this effect
that generally leads to eventual recovery from the
infection: the disease causing organism induces an
immune response in the infected host. As the response
increases in strength over time, the infectious agents
are slowly reduced in number until symptoms disappear
and recovery is complete.
are made in several ways. However, all vaccines have
the same general goal - weaken the virus or bacteria
in a way that allows the child to be infected without
developing any symptoms of infection. Vaccines are
made using the same components that are found in the
natural virus or bacteria.