VIRAL INFECTION
Labels Viral Infections
- Definition.
- How Are Viruses Different from Bacteria?
- How Do Viruses Infect the Body?
- How Long Do Viral Infections Last?
- How Do Viruses Cause Illness?
- Diagnosis & Treatment.
- Prevention.
Showing posts with label Viral Infections. Show all posts
Showing posts with label Viral Infections. Show all posts
Labels Viral Infections
DEFINITION
Viral infections occur when viruses enter cells in the body and begin
reproducing, often causing illness. Viruses are tiny germs that can reproduce
only by invading a living cell.
reproducing, often causing illness. Viruses are tiny germs that can reproduce
only by invading a living cell.
How Are Viruses Different from Bacteria?
Viruses are far smaller than bacteria. They are so small that they could not
be seen until the electron microscope was invented in the 1940s. Unlike
most bacteria, viruses are not complete cells that can function on their
own. They cannot convert carbohydrates to energy, the way that bacteria
and other living cells do. Viruses depend on other organisms for energy
Moreover, viruses cannot reproduce unless they get inside a living cell.
Most viruses consist only of tiny particles of nucleic acid (the material
that makes up genes) surrounded by a coat of protein. Some have an outer
envelope as well.
Thousands of viruses There are thousands of viruses, and in humans
they cause a wide range of diseases. For instance, rhinoviruses cause colds,
influenza viruses cause flu, adenoviruses* cause various respiratory problems,
and rotaviruses cause gastroenteritis. Polioviruses can make their
way to the spinal cord and cause paralysis, whereas coxsackieviruses
(sometimes written as Coxsackie viruses) and echoviruses* sometimes
infect the heart or the membranes surrounding the spinal cord or lungs.
Herpesviruses cause cold sores, chickenpox, and genital herpes, which is
a sexually transmitted disease. Other viruses cause a variety of conditions
from measles and mumps to AIDS.
The body’s defense system Most viruses do not cause serious
diseases and are killed by the body’s immune system*—its network of
natural defenses. In many cases, people never even know they have been
infected. But unlike bacteria, which can be killed by antibiotics, most
viruses are not affected by existing medicines. Fortunately, scientists have
been able to make vaccines, which help the body develop natural defenses
to prevent many viral infections.
be seen until the electron microscope was invented in the 1940s. Unlike
most bacteria, viruses are not complete cells that can function on their
own. They cannot convert carbohydrates to energy, the way that bacteria
and other living cells do. Viruses depend on other organisms for energy
Moreover, viruses cannot reproduce unless they get inside a living cell.
Most viruses consist only of tiny particles of nucleic acid (the material
that makes up genes) surrounded by a coat of protein. Some have an outer
envelope as well.
Thousands of viruses There are thousands of viruses, and in humans
they cause a wide range of diseases. For instance, rhinoviruses cause colds,
influenza viruses cause flu, adenoviruses* cause various respiratory problems,
and rotaviruses cause gastroenteritis. Polioviruses can make their
way to the spinal cord and cause paralysis, whereas coxsackieviruses
(sometimes written as Coxsackie viruses) and echoviruses* sometimes
infect the heart or the membranes surrounding the spinal cord or lungs.
Herpesviruses cause cold sores, chickenpox, and genital herpes, which is
a sexually transmitted disease. Other viruses cause a variety of conditions
from measles and mumps to AIDS.
The body’s defense system Most viruses do not cause serious
diseases and are killed by the body’s immune system*—its network of
natural defenses. In many cases, people never even know they have been
infected. But unlike bacteria, which can be killed by antibiotics, most
viruses are not affected by existing medicines. Fortunately, scientists have
been able to make vaccines, which help the body develop natural defenses
to prevent many viral infections.
How Do Viruses Infect the Body?
Viruses can enter the human body through any of its openings, but most
often they use the nose and mouth. Once inside, the virus attaches itself
to the outside of the kind of cell it attacks, called a host cell. For example,
a rhinovirus attacks cells in the nose, whereas an enterovirus binds to cells
in the stomach and intestines. Then the virus works its way through the
host cell’s outer membrane.
After entering the cell, the virus begins making identical viruses from
the host cell’s protein. These new viruses may make their way back out
through the host cell’s membrane, sometimes destroying the cell, and then
attacking new host cells. This process continues until the body develops
enough antibodies* and other defenses to defeat the viral invaders.
Not all viruses attack only one part of the body, causing what is called
a localized infection. Some viruses spread through the bloodstream or
the nerves, attacking cells throughout the body. For instance, HIV*, the
human immunodeficiency virus that causes AIDS*, attacks certain cells
of the immune system that are located throughout the body.
often they use the nose and mouth. Once inside, the virus attaches itself
to the outside of the kind of cell it attacks, called a host cell. For example,
a rhinovirus attacks cells in the nose, whereas an enterovirus binds to cells
in the stomach and intestines. Then the virus works its way through the
host cell’s outer membrane.
After entering the cell, the virus begins making identical viruses from
the host cell’s protein. These new viruses may make their way back out
through the host cell’s membrane, sometimes destroying the cell, and then
attacking new host cells. This process continues until the body develops
enough antibodies* and other defenses to defeat the viral invaders.
Not all viruses attack only one part of the body, causing what is called
a localized infection. Some viruses spread through the bloodstream or
the nerves, attacking cells throughout the body. For instance, HIV*, the
human immunodeficiency virus that causes AIDS*, attacks certain cells
of the immune system that are located throughout the body.
How Long Do Viral Infections Last?
In most types of viral infection, the immune system clears the virus from
the body within days to a few weeks. But some viruses cause persistent or
latent* infections, which can last for years. In these cases, a person may
get infected and seem to recover or may not be aware of being infected
at all. Then years later, the illness occurs again, or symptoms start for the
first time. Viruses that can cause latent infections include herpesviruses,
Hepatitis B and C viruses, and HIV.
the body within days to a few weeks. But some viruses cause persistent or
latent* infections, which can last for years. In these cases, a person may
get infected and seem to recover or may not be aware of being infected
at all. Then years later, the illness occurs again, or symptoms start for the
first time. Viruses that can cause latent infections include herpesviruses,
Hepatitis B and C viruses, and HIV.
How Do Viruses Cause Illness?
Viruses can cause illness by destroying or interfering with the functioning
of large numbers of important cells. Sometimes, as mentioned earlier, the
cell is destroyed when the newly created viruses leave it. Sometimes the
virus keeps the cell from producing the energy it needs to live, or the virus
upsets the cell’s chemical balance in some other way. Sometimes the virus
seems to trigger a mysterious process called “programmed cell death” or
apoptosis (ap-op-TO-sis) that kills the cell.
Some persistent or latent viral infections seem to transform cells into
a cancerous state that makes them grow out of control. It has been estimated
that 10 to 20 percent of cancers are caused by viral infections.
The most common are liver cancer caused by persistent infection with
hepatitis B or hepatitis C virus and cancer of the cervix (the bottom of a
woman’s uterus or womb), both of which are linked to certain strains of
the human papillomavirus.
Sometimes a viral illness is caused not by the virus itself, but by the
body’s reaction to it. The immune system may kill cells in order to get rid
of the virus that is inside them. This process can cause serious illness if
the cells being killed are very important to the body’s functioning, such as
those in the lungs or central nervous system, or if the cells cannot reproduce
quickly enough to replace the ones being destroyed.
of large numbers of important cells. Sometimes, as mentioned earlier, the
cell is destroyed when the newly created viruses leave it. Sometimes the
virus keeps the cell from producing the energy it needs to live, or the virus
upsets the cell’s chemical balance in some other way. Sometimes the virus
seems to trigger a mysterious process called “programmed cell death” or
apoptosis (ap-op-TO-sis) that kills the cell.
Some persistent or latent viral infections seem to transform cells into
a cancerous state that makes them grow out of control. It has been estimated
that 10 to 20 percent of cancers are caused by viral infections.
The most common are liver cancer caused by persistent infection with
hepatitis B or hepatitis C virus and cancer of the cervix (the bottom of a
woman’s uterus or womb), both of which are linked to certain strains of
the human papillomavirus.
Sometimes a viral illness is caused not by the virus itself, but by the
body’s reaction to it. The immune system may kill cells in order to get rid
of the virus that is inside them. This process can cause serious illness if
the cells being killed are very important to the body’s functioning, such as
those in the lungs or central nervous system, or if the cells cannot reproduce
quickly enough to replace the ones being destroyed.
DIAGNOSIS & TREATMENT
Symptoms Symptoms vary widely, depending on the virus and the
organs involved. Many viruses, like many bacteria, cause fever, and either
respiratory symptoms (coughing and sneezing) or intestinal symptoms
(nausea, vomiting, diarrhea). Viral illnesses often cause high fevers in
young children, even when the illnesses are not dangerous.
Diagnosis Some viral infections, such as influenza, the common
cold, and chickenpox, are easily recognized by their symptoms and no
lab tests are needed. For many others, such as viral hepatitis, AIDS,
and mononucleosis, a blood sample is analyzed for the presence of specific
antibodies to the virus. If present, these antibodies help confirm
the diagnosis. In some cases, a virus may be grown in the laboratory,
using a technique called tissue culture*, or identified by its nucleic
acid, using a technique called polymerase chain reaction (PCR). Tests
such as tissue culture or PCR are used when antibody tests are not
precise enough or when the actual amount of a virus in the body must
be determined.
Treatment Viruses cannot be treated with the antibiotics that kill bacteria.
Fortunately, a few drugs, such as ribavirin and acyclovir, can control
the spread of viral invaders without destroying host cells. Intense research
to find better treatments for AIDS led to development of many drugs
that help fight the virus. Unfortunately, as of 2009, none of these drugs
was able to treat viral infections as effectively as antibiotics treat bacterial
infections.
organs involved. Many viruses, like many bacteria, cause fever, and either
respiratory symptoms (coughing and sneezing) or intestinal symptoms
(nausea, vomiting, diarrhea). Viral illnesses often cause high fevers in
young children, even when the illnesses are not dangerous.
Diagnosis Some viral infections, such as influenza, the common
cold, and chickenpox, are easily recognized by their symptoms and no
lab tests are needed. For many others, such as viral hepatitis, AIDS,
and mononucleosis, a blood sample is analyzed for the presence of specific
antibodies to the virus. If present, these antibodies help confirm
the diagnosis. In some cases, a virus may be grown in the laboratory,
using a technique called tissue culture*, or identified by its nucleic
acid, using a technique called polymerase chain reaction (PCR). Tests
such as tissue culture or PCR are used when antibody tests are not
precise enough or when the actual amount of a virus in the body must
be determined.
Treatment Viruses cannot be treated with the antibiotics that kill bacteria.
Fortunately, a few drugs, such as ribavirin and acyclovir, can control
the spread of viral invaders without destroying host cells. Intense research
to find better treatments for AIDS led to development of many drugs
that help fight the virus. Unfortunately, as of 2009, none of these drugs
was able to treat viral infections as effectively as antibiotics treat bacterial
infections.
PREVENTION
Hygiene and sanitation The first step in preventing the spread
of viral infections is simply to practice good hygiene. Doing so involves
washing the hands often, and eating only food that has been prepared
properly. It also involves building and maintaining facilities for getting rid
of sewage safely and for providing clean drinking water.
Vaccination Another important preventive measure is immunizing
people against viruses. Immunization involves giving people vaccines that
stimulate the immune system to make antibodies, proteins that target a
specific germ. Vaccines to prevent hepatitis B, polio, mumps, measles,
rubella (German measles), and chickenpox are usually given to babies and
young children in the United States. Vaccines also can prevent influenza
and hepatitis A.
Vaccines are useful only against certain kinds of viruses. For example,
the polioviruses that cause poliomyelitis (polio), a great crippler of children
in the past, are few in number and relatively stable. So it was possible
in the 1950s to make a vaccine that protects children from getting polio
(although the illness still occurs in the developing world where fewer children
are vaccinated). By contrast, influenza viruses change in minor ways
every few years and in a major way about every ten years, so a flu vaccine
is useful for only a year or two.
One reason a vaccine for the common cold has never been developed
is that there are at least a hundred different rhinoviruses that cause colds,
and as of 2009 it had not been possible to make a vaccine that works
against all of them. A similar problem with HIV, which has many different
and fast-changing strains (variations), is one of several reasons why
progress toward an AIDS vaccine was slow.
of viral infections is simply to practice good hygiene. Doing so involves
washing the hands often, and eating only food that has been prepared
properly. It also involves building and maintaining facilities for getting rid
of sewage safely and for providing clean drinking water.
Vaccination Another important preventive measure is immunizing
people against viruses. Immunization involves giving people vaccines that
stimulate the immune system to make antibodies, proteins that target a
specific germ. Vaccines to prevent hepatitis B, polio, mumps, measles,
rubella (German measles), and chickenpox are usually given to babies and
young children in the United States. Vaccines also can prevent influenza
and hepatitis A.
Vaccines are useful only against certain kinds of viruses. For example,
the polioviruses that cause poliomyelitis (polio), a great crippler of children
in the past, are few in number and relatively stable. So it was possible
in the 1950s to make a vaccine that protects children from getting polio
(although the illness still occurs in the developing world where fewer children
are vaccinated). By contrast, influenza viruses change in minor ways
every few years and in a major way about every ten years, so a flu vaccine
is useful for only a year or two.
One reason a vaccine for the common cold has never been developed
is that there are at least a hundred different rhinoviruses that cause colds,
and as of 2009 it had not been possible to make a vaccine that works
against all of them. A similar problem with HIV, which has many different
and fast-changing strains (variations), is one of several reasons why
progress toward an AIDS vaccine was slow.
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