Infection

The Common Vein copyright 2009

Definition

Infection is defined as colonization of a host by a pathogenic virus or bacteria, leading to inflammation and tissue damage.

Infection is caused by the introduction of pathogenic viruses or bacteria into the body, typically via an open wound. When this occurs the bacteria or viruses quickly begin to use the body’s resources to replicate, leading to an ever-larger population of pathogen and disruption of the body’s normal functioning.  However, viruses and bacteria differ in the means by which they exploit and damage the body and, as a result, infections are classified as either bacterial or viral in nature.

There are many classifications of pathogenic bacteria, each of which may manifest as a different type of infection under different circumstances. Yet they all share a common means of infecting the body that differentiates them from viruses. Pathogenic bacteria are living organisms that invade cells of the body and release toxins that compromise cellular function, sometimes leading to cell death. As a result of this cellular damage, the infected area becomes red, swollen, and tender. This localized pain and inflammation is characteristic of bacterial infections while the presence of pus, a whitish-yellow viscous substance consisting of dead neutrophils, may result, but is not required for a diagnosis of bacterial infection.

Unlike bacteria, viruses are capsules of genetic material that require a living host, as their survival and replication depends upon their ability to invade a host cell and exploit its reproductive machinery. As a result of this invasion, host cells become damaged and sometimes destroyed, leading to either systemic or local infection. Systemic viral infections, such as hepatitis, mononucleosis, and AIDS, are characterized by general malaise, fever, chills, and achiness while local infections, a less common class of viral infection, produce itchiness and/or burning and include such well-known afflictions as herpes and viral conjunctivitis (“pink eye”).

Given the wide variety of pathogenic bacteria and viruses and the array of symptoms they may produce diagnosis of infections is often difficult. However, physical exam, blood work to detect elevated white blood cell counts, and evaluation of a patient’s possible exposure to certain pathogens are all valuable tools.

Imaging techniques are also useful in diagnosing infections, especially those whose symptoms are not apparent or easily detectable during a physical exam. For example, CT scans shown below reveal two brain lesions associated with toxoplasmosis while laporoscopic (?) images of an esophagus reveal the white plaques characteristic of a Candidainfection.

Treatment of bacterial infections is usually accomplished through the use of antibacterial antibiotics. It is important to note, however, that antibiotic therapy is only effective when followed to completion, as antibiotic resistance may result from impartial use of antibiotic prescriptions. Viral infections, on the other hand, are more difficult to treat on the whole. Some such infections, like conunctivitis, may be successfully be treated with antiviral medications. However, other viruses, such as HIV, are virtually unresponsive to conventional treatment and may require intensive rounds of multiple antiviral drugs to be impeded in any way. Finally, treatment and healing of any type of infection may be complicated by immunodeficiency and _____.