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.
- 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.
Bacteria 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.
The 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
- Dengue fever
- H1N1 swine flu
- 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.
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.
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.