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SLIDESHOW
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Bacteria vs. Virus ( courtecy;- medicine net )
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Can antibiotics treat the flu? Get answers to the most common
questions about viral infections.
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What Is a Virus?
Viruses are small
particles of genetic material (either DNA or RNA) that are surrounded by a
protein coat. Some viruses also have a fatty "envelope" covering.
They are incapable of reproducing on their own. Viruses depend on the organisms
they infect (hosts) for their very survival. Viruses get a bad rap, but they
also perform many important functions for humans, plants, animals, and the
environment. For example, some viruses protect the host against other
infections. Viruses also participate in the process of evolution by
transferring genes among different species. In biomedical research, scientists
use viruses to insert new genes into cells.
What Is a Viral Infection?
A
viral infection is a proliferation of a harmful virus inside the body. Viruses
cannot reproduce without the assistance of a host. Viruses infect a host by
introducing their genetic material into the cells and hijacking the cell’s
internal machinery to make more virus particles. With an active viral
infection, a virus makes copies of itself and bursts the host cell (killing it)
to set the newly-formed virus particles free. In other cases, virus particles
“bud” off the host cell over a period of time before killing the host cell.
Either way, new virus particles are then free to infect other cells. Symptoms
of the viral illness occur as a result of cell damage, tissue destruction, and
the associated immune response.
How Long Are Viral Infections Contagious?
Contagiousness
refers to the ability of a virus to be transmitted from one person (or host) to
another. Viral infections are contagious for varying periods of time depending
on the virus. An incubation period refers to the time between exposure to a
virus (or other pathogen) and the emergence of symptoms. The contagious period
of a virus is not necessarily the same as the incubation period.
Bacteria vs. Virus
Viruses
and bacteria are two types of potentially disease-causing (pathogenic)
particles. Viruses are much smaller than bacteria and can’t reproduce without
the assistance of a host. Bacteria are capable of reproducing on their own. The
symptoms of viral and bacterial illnesses are sometimes similar. A doctor can
determine the underlying cause of an illness based on the patient’s symptoms
and other factors. Lab tests may help clarify whether an illness is due to a
virus, bacteria, or other infectious agent or disease process.
Virus Transmission
Viruses
can be transmitted in a variety of ways. Some viruses can spread through touch,
saliva, or even the air. Other viruses can be transmitted through sexual
contact or by sharing contaminated needles. Insects including ticks and
mosquitoes can act as "vectors," transmitting a virus from one host
to another. Contaminated food and water are other potential sources of viral
infection.
Respiratory Viral
Infections
Respiratory viral
infections affect the lungs, nose, and throat. These viruses are most commonly
spread by inhaling droplets containing virus particles. Examples include:
·
Rhinovirus is the virus that most often causes the
common cold, but there are more than 200 different viruses that can cause
colds. Cold symptoms like coughing, sneezing, mild headache, and sore throat
typically last for up to 2 weeks.
·
Seasonal
influenza is an illness that
affects about 5% to 20% of the population in the US every year. More than
200,000 people per year are hospitalized annually in the US due to
complications of the flu. Flu symptoms are more severe than cold symptoms and
often include body aches and severe fatigue. The flu also tends to come on more
suddenly than a cold.
·
Respiratory
Syncytial Virus (RSV) is an infection
that can cause both upper respiratory infections (like colds) and lower respiratory
infections (like pneumonia and bronchiolitis). It can be very severe in
infants, small children, and elderly adults.
Frequent hand-washing,
covering the nose and mouth when coughing or sneezing, and avoiding contact
with infected individuals can all reduce the spread of respiratory infections.
Disinfecting hard surfaces and not touching the eyes, nose, and mouth can help
reduce transmission as well.
Viral Skin Infections
Viral skin infections
can range from mild to severe and often produce a rash. Examples of viral skin
infections include:
·
Molluscum
contagiosum causes small,
flesh-colored bumps most often in children ages 1 to 10 years old; however,
people of any age can acquire the virus. The bumps usually disappear without
treatment, usually in 6 to 12 months.
·
Herpes
simplex virus-1 (HSV-1) is
the common virus that causes cold sores. It’s transmitted through saliva by
kissing or sharing food or drink with an infected individual. Sometimes, HSV-1
causes genital herpes. An estimated 85% of people in the US have HSV-1 by the
time they are in their 60s.
·
Varicella-zoster
virus (VZV) causes itchy,
oozing blisters, fatigue, and high fever characteristic of chickenpox. The
chickenpox vaccine is 98% effective at preventing infection. People who have
had chickenpox (or in extremely rare instances, people who have received the
chickenpox vaccine) are at risk for developing shingles, an illness caused by
the same virus. Shingles can occur at any age, but it occurs most often in
people age 60 or older.
The best way to avoid
viral skin infections is to avoid skin-to-skin contact (especially areas that
have a rash or sores) with an infected individual. Some viral skin infections,
such as varicella-zoster virus, are also transmitted by an airborne route.
Communal showers, swimming pools, and contaminated towels can also potentially
harbor certain viruses.
Foodborne Viral
Infections
Viruses are one of the
most common causes of food poisoning. The symptoms of these infections vary depending
on the virus involved.
·
Hepatitis
A is a virus that
affects the liver for a few weeks up to several months. Symptoms may include
yellow skin, nausea, diarrhea, and vomiting. Up to 15% of infected individuals
experience recurrent illness within 6 months of infection.
·
Norovirus has been reported to be responsible for
outbreaks of severe gastrointestinal illness that happen on cruise ships, but
it causes disease in many situations and locations. About 20 million people in
the U.S. become sick from these highly contagious viruses every year.
·
Rotavirus causes severe, watery diarrhea that can
lead to dehydration. Anyone can get rotavirus, but the illness occurs most
often in babies and young children.
Rotaviruses and
noroviruses are responsible for many (but not all) cases of viral
gastroenteritis, which causes inflammation of the stomach and intestines.
People may use the terms “stomach virus” or “stomach flu” to refer to viral
gastroenteritis, which causes nausea, vomiting, diarrhea, and abdominal pain.
It’s not pleasant to
think about it, but foodborne viral illnesses are transmitted via the
fecal-oral route. This means that a person gets the virus by ingesting virus
particles that were shed through the feces of an infected person. Someone with
this type of virus who doesn’t wash their hands after using the restroom can
transfer the virus to others by shaking hands, preparing food, or touching hard
surfaces. Contaminated water is another potential source of infection.
Sexually Transmitted
Viral Infections
Sexually transmitted
viral infections spread through contact with bodily fluids. Some sexually
transmitted infections can also be transmitted via the blood (blood-borne
transmission).
·
Human
papillomavirus (HPV) is the most common
sexually-transmitted infection in the US. There are many different types of
HPV. Some cause genital warts while others increase the risk of cervical
cancer. Vaccination can protect against cancer-causing strains of HPV.
·
Hepatitis
B is a virus that
causes inflammation in the liver. It’s transmitted through contaminated blood and
bodily fluids. Some people with the virus don’t have any symptoms while others
feel like they have the flu. The hepatitis B vaccine is more than 90% effective
at preventing infection.
·
Genital
herpes is a common
sexually-transmitted infection caused by herpes simplex virus-2 (HSV-2). Herpes
simplex virus-1 (HSV-1), the virus responsible for cold sores, can also
sometimes cause genital herpes. There’s no cure for genital herpes. Painful
sores often recur during outbreaks. Antiviral medications can decrease both the
number and length of outbreaks.
·
Human
immunodeficiency virus (HIV) is a virus that affects certain types of T cells of the
immune system. Progression of the infection decreases the body’s ability to
fight disease and infection, leading to acquired immune deficiency syndrome
(AIDS). HIV is transmitted by coming into contact with blood or bodily fluids
of an infected person.
People can reduce the
risk of getting a sexually-transmitted viral infection by abstaining from sex
or only having sex while in a monogamous relationship with someone who does not
have a sexually-transmitted infection. Using a condom decreases, but doesn’t
entirely eliminate, the risk of acquiring a sexually-transmitted infection.
Minimizing the number of sexual partners and avoiding intravenous drug use are
other ways to reduce the risk of acquiring sexually-transmitted and bloodborne
viral infections.
Other Viral Infections
Viruses are abundant in
the world and cause many other infections ranging from mild to
life-threatening.
·
Epstein-Barr
virus (EBV) is a type of
herpes virus that’s associated with fever, fatigue, swollen lymph nodes, and an
enlarged spleen. EBV is a very common virus that causes mononucleosis
("mono"). More than 90% of adults have been infected with this
“kissing disease” that is spread primarily through saliva.
·
West
Nile virus (WNV) is a virus that’s
most commonly transmitted by infected mosquitos. Most people (70% to 80%) with
WNV don’t have any symptoms while others develop a fever, headache, and other
symptoms. Less than 1% of people with WNV develop inflammation of the brain
(encephalitis) or inflammation of the tissue surrounding the brain and spinal
cord (meningitis).
·
Viral
meningitis is an inflammation
of the lining of the brain and spinal cord that causes headache, fever, stiff
neck, and other symptoms. Many viruses can cause viral meningitis, but a group
of viruses called enteroviruses are most often to blame.
Antiviral Medication and Other Treatment
Many
viral infections resolve on their own without treatment. Other times, treatment
of viral infections focuses on symptom relief, not fighting the virus. For
example, cold medicine helps alleviate the pain and congestion associated with
the cold, but it doesn’t act directly on the cold virus.
There
are some medications that work directly on viruses. These are called antiviral
medications. They work by inhibiting the production of virus particles. Some
interfere with the production of viral DNA. Others prevent viruses from
entering host cells. There are other ways in which these medications work. In
general, antiviral medications are most effective when they’re taken early on
in the course of an initial viral infection or a recurrent outbreak. Different
kinds of antiviral medications may be used to treat chickenpox, shingles,
herpes simplex virus-1 (HSV-1), herpes simplex virus-2 (HSV-2), HIV, hepatitis
B, hepatitis C, and influenza.
Viruses and Cancer
Viruses insert
themselves into host cell DNA in order to make more virus particles. Cancer is
a disease that occurs as the result of mutations or alterations to DNA. Because
viruses affect the DNA of host cells, viruses are known to contribute to
several different types of cancer. Viruses known to increase the risk of cancer
include:
·
Epstein-Barr virus (EBV)
for nasopharyngeal cancer, Burkitt lymphoma, Hodgkin’s lymphoma, and stomach
cancer
·
Hepatitis B and
hepatitis C for liver cancer
·
Human immunodeficiency
virus (HIV) for Kaposi sarcoma, invasive cervical cancer, lymphomas, and other
cancers
·
Human T-lymphotrophic
virus-1 (HTLV-1) for T-cell leukemia/lymphoma (ATL)
·
Human papilloma virus
(HPV) for cervical cancer
·
Merkel cell polyomavirus
(MCV) for a rare skin cancer called Merkel cell carcinoma
Viral Illness Prevention
Vaccines
can reduce the risk of acquiring some viral illnesses. Vaccines are available
to help protect against the flu, hepatitis A, hepatitis B, chickenpox, herpes
zoster (shingles), cancer-causing strains of human papillomavirus (HPV),
measles/mumps/rubella (MMR), polio, rabies, rotavirus, and other viruses.
Vaccines
vary in effectiveness and in the number of doses required to confer protection.
Some vaccines require booster shots t
Reviewed by Robert Cox, MD on Friday, July 01, 2016
Viral Infection Types,
Treatment, and Prevention
This tool does not
provide medical advice
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