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n infection happens when a foreign
organism enters a person's body and causes harm.
The organism uses that person's body
to sustain itself, reproduce, and colonize. These infectious organisms are
known as pathogens. Examples of pathogens include bacteria, viruses, fungi, and
prions. Pathogens can multiply and adapt quickly.
Some infections are mild and barely noticeable, but others
are severe and life-threatening, and some are resistant to treatment. Infection
can be transmitted in a variety of ways.
These include skin
contact, bodily fluids, contact with feces, airborne particles, and touching an
object that an infected person has also touched. How an infection spreads and
its effect on the human body depend on the type of agent.
The immune system is an effective
barrier against infectious agents, but colonies of pathogens
may grow too large for the immune system to fight. At this stage, infections
become harmful.
Many pathogens give off toxins that trigger negative responses from the body.
Many pathogens give off toxins that trigger negative responses from the body.
Fast facts on infection
- Infection
is the effect of a foreign organism in the body.
- Types
of infection include bacterial, fungal, viral, protozoan, parasitic, and
prion disease.
- They
are classified by the type of organism causing the infection.
- Infections
can range from mild inflammation in
one person to an epidemic.
Share on PinterestBacteria
are one type of infectious agent.
Bacteria, viruses, fungi, protozoa, parasites, and prions
are different types of pathogen. They vary in their size, shape, function,
genetic content, and how they act on the body.
For example, viruses are smaller than bacteria, and they can enter a host and take over cells. However, bacteria can survive without a host.
Treatment will depend on the type of pathogen. This article will focus on the most common and deadly types of infection: Bacterial, viral, fungal, and prion.
For example, viruses are smaller than bacteria, and they can enter a host and take over cells. However, bacteria can survive without a host.
Treatment will depend on the type of pathogen. This article will focus on the most common and deadly types of infection: Bacterial, viral, fungal, and prion.
Viral
infections
Share on PinterestThe
common cold is a viral infection.
Viral infections are caused by a virus. Millions of types of
virus are thought to exist, but only 5,000 types have been identified. Viruses contain a small
piece of genetic code. They are protected by a coat of protein and fat.
Viruses invade a host and attach themselves to a cell. As
they enter the cell, they release genetic material. The genetic material forces
the cell to replicate, and the virus multiplies. When the cell dies, it
releases new viruses, and these go on to infect new cells.
Not all viruses destroy their host cell. Some of them change the function of the cell. In this way, viruses
such as human papillomavirus (HPV)
or Epstein-Barr virus (EBV) can lead to cancer by forcing cells to replicate in an
uncontrolled way.
They can also target certain age groups, such as infants or
young children.
A virus may remain dormant for a period before multiplying
again. The person with the virus can appear to have recovered but may get sick
again when the virus reactivates.
Here are some examples of viral infections:
- the common cold, mainly caused
by the rhinovirus, coronavirus, and
adenovirus
- encephalitis and meningitis, caused by
enteroviruses and the herpes viruses
- warts and skin infections,
caused by the human papillomaviruses (HPV) and herpes simplex virus (HSV).
- gastroenteritis, caused by the
novavirus
Other viral conditions include:
- Zika virus
- human immunodeficiency virus (HIV)
- hepatitis
C
- polio
- influenza
- Dengue fever
- H1N1 swine
flu
- Ebola
- Middle East respiratory
syndrome (MERS-CoV)
Antiviral medications help in some cases. They can either
prevent the virus from reproducing or boost the host's immune system.
Antibiotics are not effective against viruses. Using antibiotics against a virus will not stop the virus, and it increases the risk of antibiotic resistance.
Most treatment aims to relieve symptoms while the immune system combats the virus without assistance from medicine.
Antibiotics are not effective against viruses. Using antibiotics against a virus will not stop the virus, and it increases the risk of antibiotic resistance.
Most treatment aims to relieve symptoms while the immune system combats the virus without assistance from medicine.
Bacterial
infections
Bacteria are single-celled microorganisms known as
prokaryotes.
There are estimated to be at least one nonillion bacteria on Earth. A nonillion is a one followed by 30 zeros. Much of Earth's biomass is made up of bacteria.
There are estimated to be at least one nonillion bacteria on Earth. A nonillion is a one followed by 30 zeros. Much of Earth's biomass is made up of bacteria.
Bacteria take three main shapes:
- Spherical: These are usually
the simplest to treat and are known as cocci.
- Rod-shaped: These are called
bacilli.
- Spiral: Coiled bacteria are
known as spirilla. If the coil of a spirillus is particularly tight, they
are known as spirochetes.
Bacteria can live in almost any kind of environment, from
extreme heat to intense cold, and some can even survive in radioactive waste.
There are trillions of strains of bacteria, and few of these cause diseases in humans. Some of them live inside the human body without causing harm, for example in the gut or airways. Some "good" bacteria attack "bad" bacteria and prevent them from causing sickness.
There are trillions of strains of bacteria, and few of these cause diseases in humans. Some of them live inside the human body without causing harm, for example in the gut or airways. Some "good" bacteria attack "bad" bacteria and prevent them from causing sickness.
However, some bacterial diseases are deadly.
These include:
These include:
- cholera
- diphtheria
- dysentery
- bubonic plague
- pneumonia
- tuberculosis
- typhoid
- typhus
Some examples of bacterial infections are:
- bacterial meningitis
- otitis media
- pneumonia
- tuberculosis
- upper respiratory tract
infection
- gastritis
- food poisoning
- eye infections
- sinusitis
- urinary
tract infections
- skin infections
- sexually transmitted diseases
Bacterial infections can be treated with antibiotics, but some
strains become resistant and can survive the treatment.
Fungal
infection
Share on PinterestFungi
reproduce by spreading spores.
A fungus is an often multi-cellular
parasite that can decompose and then absorb organic matter
using an enzyme.
They almost always reproduce through the spreading of
single-celled spores, and the structure of a fungus is normally long and
cylindrical with small filaments branching from the main body. This structure
is known as hypha.
There are approximately 51 million species
of fungus.
Many fungal infections will appear in the upper layers of
the skin, and some progress to the deeper layers. Inhaled fungal spores can
lead to systemic fungal infections, such as thrush, or candidiasis. Systemic
diseases affect the whole body.
The body usually has a population of "good" bacteria
that help to maintain the balance of microorganisms in the intestines, mouth,
vagina, and other parts of the body.
If enough "good" bacteria are destroyed, for
example, by overusing antibiotics, fungi can grow and cause health problems for
the host.
Those with a higher risk of developing a fungal infection
include people who:
- use strong antibiotics for a
long time
- have a weakened immune system,
due, for example, to HIV or AIDS, diabetes, chemotherapy treatment,
and those who have undergone a transplant, as they take medications to
prevent their body from rejecting the new organ
- valley fever, or
coccidioidomycosis
- athlete's foot
- ringworm
- some eye infections
A rash can be an indicator of a fungal infection of the
skin.
Prion
disease
A prion is a protein that contains no genetic material. It
is normally harmless, but if it folds into an abnormal shape, it can become a
rogue agent and affect the structure of the brain or other parts of the nervous
system.
Prions do not replicate or feed on the host but trigger
abnormal behavior in the body's cells and proteins.
Prion diseases are rare, but they progress rapidly, and all
are currently fatal.
Prions cause degenerative brain diseases, such as:
Prions cause degenerative brain diseases, such as:
- bovine spongiform
encephalopathy (BSE), also known as mad cow disease
- Creutzfeldt-Jakob disease (CJD)
Researchers have linked some
cases of Alzheimer's disease to
prion infection.
Other
infections
While the forms of infection mentioned above are the main types,
there are others that can have an effect on the body.
A single-celled organism with a nucleus can cause a protozoan infection. Protozoa commonly
show features similar to animals, such as mobility, and can survive outside of
the human body. They are most commonly transferred by contact with feces.
When they enter the human body, protozoa can also cause
infection. Amebic dysentery is an example of a protozoan infection.
Helminths are larger, multicellular organisms that tend to be
visible to the naked eye when full-grown. This type of parasite includes
flatworms and roundworms. These are also able to infect the human body.
Finally, ectoparasites such
as mites, ticks, lice, and fleas can cause infection by attaching or burrowing
into the skin.
The term can also include blood-sucking arthropods, such as mosquitos, that transmit infection by consuming human blood.
The term can also include blood-sucking arthropods, such as mosquitos, that transmit infection by consuming human blood.
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The cause of an infection is said to be whichever type of
organism has invaded the body.
A particular virus, for example, will be the cause of a
viral infection.
The effects of an infection, such as swelling or a runny
nose, occur as a result of the immune system fighting the invading organism. A
wound filling with pus,
for example, occurs when white blood cells rush to the site of an injury to
combat foreign bacteria.
The symptoms of an infection depend on the organism
responsible as well as the site of the infection.
Viruses target specific cells, such as those in the genitals
or upper respiratory tract. The rabies virus, for
example, targets the nervous system. Some viruses target skin cells, causing
warts. Others target a wider range of cells, leading to various symptoms.
A flu virus can cause a
runny nose, muscle aches, and an upset stomach.
A person with a bacterial infection will often experience
redness and heat, swelling, fever, pain at the site of infection, and swollen
lymph glands. A bacterial infection is less likely to affect a wide area of the
body than a viral one.
A rash can be an indicator of a fungal infection of the
skin.
Common symptoms of prion diseases include brain damage,
memory loss, and cognitive difficulties. They can also trigger the buildup of
plaque in the brain, causing it to waste away.
There is no single way to prevent all infectious diseases,
but the following tips can reduce the risk of transmission:
- Wash your hands often,
especially before and after preparing food and after using the bathroom.
- Clean surface areas and avoid
leaving room-temperature food exposed when cooking.
- Receive any recommended
vaccinations, and keep them up to date.
- Only take antibiotics when
prescribed, and be sure to complete any recommended course even if
symptoms improve earlier than anticipated.
- Disinfect rooms where there may
be high concentrations of bacteria, such as the kitchen and bathroom.
- Practice safe sex by receiving
regular STD checks, using condoms, or abstaining altogether.
- Avoid sharing personal items
such a toothbrushes, combs, razorblades, drinking glasses, and kitchen
utensils.
- Follow a doctor's advice about
traveling or working when you are ill, as you could infect others.
A healthy, active lifestyle can help keep the immune system
strong and able to defend the body against different kinds of infection.
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