Infectious Diseases
Disease
and the Immune System
An
infectious or communicable disease is one that can be transmitted from person to
person, from an infected animal or from the environment to the person.
Illness results when the bacteria, viruses or other agents invade and
multiply in the host (the person's body) and as a result cause specific
diseases. Illness and the
development of resulting disease depend primarily on the bacteria, virus or
other agents and on the reaction of the body's immune system.
Basically, bacteria or viruses can invade the body without causing the
signs and symptoms of disease if the body's immune system responds adequately.
Only when the bacteria or virus overpower the immune system do the signs
and symptoms of disease develop.
When
bacteria enter the body, they attack normal cells by secreting toxins that
damage or kill the cells and by competing with the cells for nutrients.
Bacteria are self-contained, living cells that reproduce rapidly if not
checked by the immune system or appropriate medication.
Viruses are not capable of reproducing until they have entered a host
cell. The virus has a protective
outer coating that enables it to bind securely to host cells; once the virus has
penetrated the cell's lining, the coating dissolves, allowing the virus to alter
cellular function as it attacks from inside the cell.
When the cell regenerates itself, it reproduces a cell that has been
genetically altered by the virus.
Obviously,
the immune system has to fight bacteria and viruses in two different ways.
With a bacterial infection, the body's B-lymphocytes recognize the
bacteria and produce antibodies-proteins that search out and kill the bacteria.
B-lymphocytes can fulfill the same immune response to viruses only while
the viruses are still free floating in the bloodstream.
Once a virus invades a cell, the B-lymphocytes become ineffective.
To kill the virus, they also have to kill the body's own cell that is
serving as host. Because the
B-lymphocytes are incapable of this type of action, the immune system calls up
its second line of defense, the T-lymphocytes, which can identify and destroy
cells occupied by viruses.
The
function of the immune system and its production of antibodies is what enable
researchers to identify disease. If
a study of a patient's blood shows that antibodies to a certain illness are
present, the physician can be certain that the patient has either been exposed
to the illness or developed it.
Transmission
of Disease
The
spread of disease depends on the ability of the infecting organism to survive
outside its source. A source may be
an infected person, an animal, an insect or even an inert object.
Transmission also depends on the ability of the infecting organism to
move from one place to another. There
are four general routes of transmission:
1.
Contact
transmission is the most common mode for infection disease.
Simply stated, an infected person comes into contact with a non-infected
person and transmits the disease. Contact
transmission can be either direct or indirect. Direct transmission involves
direct physical contact between two people.
A person may touch the weeping lesions of chickenpox, for example, and
become infected. Direct transmission
also involves droplet contact, where sneezing, coughing or talking contaminates
the air with droplets. Cold and flu
viruses are most commonly spread by droplet contact.
Even with droplet contact, the contact must be direct, since droplets
generally do not travel more than 12 feet from the source.
Indirect transmission occurs when an infected person spreads the
infection to an inanimate object, and a non-infected person touches or otherwise
comes into contact with the infected object.
Equipment and instruments often spread disease as can soil, air, insects,
food, milk and water.
2.
Airborne
transmission is much like droplet contact but it is more diffused.
Droplets that are sneezed, coughed or otherwise sprayed into the air
evaporate but the residue remains in the air for long periods of time.
Airborne dust particles pick up some of these bacteria or other disease
causing organisms and air currents help to spread them over a wide area.
The disease-causing organisms then are inhaled by or come to rest on a
susceptible person who is subsequently infected.
3.
Vehicle
transmission is when the infective agents are introduced directly by a
"vehicle" or something that carries the infective agent.
A person may drink contaminated water or may eat contaminated food or it
also could occur as a result of the injection of contaminated blood or
contaminated drugs.
4.
Vector
transmission occurs when an animal provides the route of transmission to a
person such as an infected tick causing Rocky Mountain spotted fever or an
infected mosquito transmitting malaria.
Human
Immunodeficiency Virus (HIV)
One
of the most terrifying and difficult infectious diseases currently posing a
health hazard is acquired immunodeficiency syndrome, or AIDS.
This disease is commonly referred to as Human Immunodeficiency Virus or
HIV. The first isolated cases were
reported among previously healthy young homosexual men in 1981.
Within a few years, the disease had spread globally.
Unfortunately,
it is extremely difficult to get an accurate picture of the HIV situation.
The incubation period is unknown but may be as long as 10 years, so
researchers say that millions of Americans may be infected without knowing it
and, therefore, may be spreading the disease in alarming proportions.
In fact, researchers estimate that for every diagnosed case of HIV, there
are at least 50 undiagnosed Americans with the disease.
What
is AIDS or HIV?
AIDS
(or HIV) is a disease that renders the immune system ineffective.
The AIDS virus enters the body and affects the immune system's
T-lymphocytes. As discussed earlier,
the T-lymphocytes identify and destroy cells that are occupied by viruses.
There
are actually two types of T-lymphocytes.
1.
The
"Helper" T-lymphocytes stimulate the immune system to combat disease.
2.
The
"Suppressor" T-lymphocytes tell the immune system to shut down when
its work no longer is needed.
In
the normal body, there are about twice as many helper T-lymphocytes as
suppressor T-lymphocytes. The AIDS
virus kills the helper T-lymphocytes and renders the remaining ones ineffective.
The body no longer can recognize and respond to foreign cells, like
viruses and cancer cells, and as a result no longer can fight disease.
There
are four categories in which a person that tests positive for HIV can be
diagnosed.
1.
Asymptomatic
HIV Infection occurs when an individual tests positive for HIV but does not
present any symptoms of opportunistic non-life threatening or life threatening
infections.
2.
Symptomatic HIV
Infection occurs when an individual tests positive for HIV and presents symptoms
of opportunistic infections not considered life threatening.
Symptoms can include fever over 100 degrees, night sweats, weight loss of
greater than 10 percent or 15 pounds, persistent diarrhea, debilitating fatigue
and persistent lymph gland problems. These
symptoms must last longer than three weeks and be accompanied by laboratory
confirmation of a number of abnormalities, including a reduced number of
T-lymphocytes and an abnormal helper/suppressor T-lymphocyte ratio.
3.
Severe Immune
Depression occurs when an individual tests positive for HIV and presents with a
T-cell count of fewer than 200.
4.
AIDS occurs
when an individual tests positive for HIV and presents symptoms of opportunistic
infections considered life threatening. These
infections usually do not occur among people with healthy immune systems or
produce a very mild illness when the immune system is functioning, as it should.
These infections often include various forms of pneumonia and/or cancer.
Transmission
A
person who is ill with AIDS and asymptomatic HIV can transmit HIV.
The virus is extremely fragile and unable to survive very long outside
the human body, so it cannot be transmitted casually.
Researchers have confirmed that the only way HIV can be transmitted is by
intimate contact with the body fluids of an infected individual even though the
infected individual may not have any symptoms.
Body fluids include blood, semen, vaginal secretions and breast milk.
While
HIV has been found in saliva, there have been no documented cases of the disease
being passed solely through kissing. HIV
cannot be transmitted by shaking hands, coughing, sneezing, sharing meals,
sharing eating utensils or any other casual contact.
You cannot get HIV from toilet seats, towels, office equipment or any
other object casually handled by infected persons.
More
than two-thirds of individuals infected with HIV in the United States
are believed to have acquired the virus through sexual contact.
Studies show that both men and women can transmit HIV to their partners,
although female-to-male transmission is much less common in this country.
The chances of becoming infected with HIV become greater the more sexual
partners a person has.
Use
of an infected needle is also a major source of infection.
Those who most often share needles, such as intravenous drug users and
athletes who inject steroids, are at highest risk.
Tattooing
also may have caused an infection, and some cases, may have occurred in
poverty-stricken areas where needles are reused for medical or immunization
purposes.
Prior
to 1985, blood donated by infected persons was passed to non-infected persons,
causing transmission of HIV. Particularly
at risk were hemophiliacs who, because of their increased needs, must receive
donated plasma that is pooled from as many as several thousand donors at a time.
Others receiving blood transfusions following surgery or trauma also
became infected. Since 1985, donated
blood has been carefully screened to prevent infected blood from being given in
hospitals or other settings. In
addition, blood used for hemophiliacs is heated - treated to destroy HIV.
Not
everyone infected by HIV will develop AIDS, but they still are capable of
transmitting the virus to others regardless of whether they themselves have
signs or symptoms.
Commitment
to Safety
Every
Darien-Woodridge Fire Protection District EMS provider is committed to safety
and a consciousness about the transmission of disease.
They work with an attitude of protecting both themselves and the public.
While working with a patient, paramedics and EMTs wear latex gloves, eye protection and masks. After each patient, the linen is always changed on the gurneys and the equipment is disinfected. Hypodermic needles always are disposed of in a Sharps container, which is a rigid-walled puncture-resistant container.