Infections are one of the most common types of diseases that afflicts humans. It is caused by a number of different infectious agents that are in our environment – from the air around us, to our water supply, foods that we eat, surfaces within our home and even on or within our bodies. Everyday the immune system is constantly working to fight off these infectious agents but sometimes it is overwhelmed and an infection arises.
What Causes an Infection?
Infections are caused by different biological agents, most of which are living. This includes:
Bacteria, protozoa and fungi need nutrition to survive, can reproduce on their own, can grow and change, and are able to adapt the environment it is within. They are therefore said to be living entities or microorganisms (microscopic organisms). Unlike the others, viruses are not considered to be living because it is a protein particle that only carries genetic material (DNA or RNA) but does not meet any of the other characteristics of life.
Read more about an infection.
The living microbes (bacteria, protozoa, fungi) either directly damage and consume living tissue in an infection or it produces toxins that injure and even destroy living tissue. These microbes also multiply on or inside the host’s body with the injury worsening over time, especially if there is no medical treatment or if the immune system is not able to counteract it.
Viruses on the other hand inject their genetic material within the host cells. This then forces the cell to produce more of the virus as well as disrupts the cell’s normal processes and eventually results in cellular death. Sometimes the components of viruses or its byproducts that are produced by the host cell are toxic and damages the cell. It is also possible for some viruses to lie relatively dormant within a cell but transform the cell in a way that it damages other cells or is killed by the immune system.
How To Spot An Infection
Infectious agents cause tissue damage and as a result there will be inflammation. This is the body’s response to tissue damage and it is intended to minimize any further damage or tissue death. Inflammation is not specific to infections. It can occur with any tissue injury, such as a physical, electromagnetic or chemical injury. Inflammation also increases the amount of immune cells at the infected site which can then neutralize the threat, which is useful for infections in particular.
Read more about inflammation.
The signs of inflammation include:
Another feature of an infection that may not always be obvious is loss of function. For example, an extensively inflamed finger may not be able to move or feel sensations as it normally would. It is important to stress that these features of inflammation can occur with any cause of tissue damage and not just an infection.
Signs and Symptoms
Apart from the signs and symptoms discussed below, there may also be additional symptoms depending on the area that is infected. For example, urinary tract infections (UTIs) may also present with frequent urination whereas a throat infection may cause bad breath. However, in most cases there will be characteristic signs that are indicative of an infection.
As mentioned, inflammation is the body’s response to tissue injury. A host of chemicals and immune cells play a role in mediating inflammation. This leads to pain, swelling, heat, redness and sometimes loss of function of the infected area. Heat and redness may not always be detectable except when inflammation occurs on or near to the body surface. Swelling may also not be visible yet still detectable within the body by its effects on surrounding organs.
The inflammatory process causes blood vessels at the site to widen so that more immune cells and other required components carried by blood can be brought to the area. This causes redness of the affected areas since blood has a characeristic red color and there is more flowing at the affected site. There is also heat radiating from the site as blood carries heat from the inner core to the surface. The blood vessels become leaky and fluid escapes into the tissue spaces which is seen as swelling.
Chemicals released from the damaged tissue as well as chemicals released from immune cells that migrate to the area stimulate the pain receptors. This causes the sensation of pain that it typically felt with inflammation anywhere in the body. All of these symptoms may be localized when the infection is isolated to one area of the body or it may be generalized if the infection is throughout the body (systemic).
Pus is the fluid composed of cellular debris, dead and living microbes, the body’s immune cells, sometimes blood and fluid from the site of the infection. It is not always present or detectable but is commonly seen with infections on the skin surface that have not been properly treated in the early stages. It has a yellow to yellow-brown appearance and with certain types of infections it may even be green. Pus may also have a foul odor.
Fever is a well known sign of an infection. Most of us immediately think of an infection when a fever is detected. There are instances where the body temperature may be raised even without an infection being present. A fever is defined as a body temperature above 98.6ºF (37°C) but it is usually not considered to be significant until it exceeds 100.4°F (38°C).
A fever is one of the body’s mechanisms to combat an infection. This process is in itself not dangerous but if the body temperature rises too high then hyperthermia can cause complications and even death. To some extent the intensity of the fever is a reflection of the severity of the infection. However, it is important to note that in some infections, like certain types of gastroenteritis, there may be no fever present.
Malaise is a general feeling of being unwell. It occurs with most types of systemic infections but is less common with localized infections, unless the infectious agent and/or its toxins enter the bloodstream. Malaise is not a realiable sign of an infection as it occurs with many other non-infectious diseases. Therefore malaise should be considered in conjunction with other signs of an infection, like a fever and the signs of inflammation.