Abstract

An opportunistic infection is an infection caused by pathogens (bacteria, viruses, fungi, or protozoa) that take advantage of an opportunity not normally available, such as a host with a weakened immune system, an altered microbiota (such as a disrupted gut flora), or breached integumentary barriers. Many of these pathogens do not cause disease in a healthy host that has a normal immune system. However, a compromised immune system, a penetrating injury, or a lack of competition from normal commensals presents an opportunity for the pathogen to infect.

Causes

Immunodeficiency or immunosuppression can be caused by:

- Malnutrition

- Fatigue

- Recurrent infections

- Immunosuppressing agents for organ transplant recipients

- Advanced HIV infection

- Chemotherapy for cancer

- Genetic predisposition

- Skin damage

- Antibiotic treatment leading to disruption of the physiological microbiome, thus allowing some microorganisms to outcompete others and become pathogenic (e.g. disruption of intestinal flora may lead to "Clostridium difficile" infection

- Medical procedures

- Pregnancy

- Ageing

- Leukopenia (i.e. neutropenia and lymphocytopenia)

The lack of or the disruption of normal vaginal flora allows the proliferation of opportunistic microorganisms and will cause the opportunistic infection - bacterial vaginosis.

Types of infections

A partial listing of opportunistic organisms includes:

- "Aspergillus" sp.

- "Candida albicans"

- "Clostridium difficile"

- "Coccidioides immitis"

- "Cryptococcus neoformans"

- "Cryptosporidium"

- "Cytomegalovirus"

- "Geomyces destructans" (bats)

- "Histoplasma capsulatum"

- "Isospora belli"

- "Polyomavirus JC polyomavirus", the virus that causes Progressive multifocal leukoencephalopathy.

- "Kaposi's Sarcoma caused by Human herpesvirus 8 (HHV8)", also called Kaposi's sarcoma-associated herpesvirus (KSHV)

- "Legionnaires' Disease (Legionella pneumophila)"

- "Microsporidium"

- "Mycobacterium avium complex (MAC) (Nontuberculosis Mycobacterium)"

- "Mycobacterium tuberculosis"

- "Pneumocystis jirovecii", previously known as "Pneumocystis carinii" f. "hominis"

- "Pseudomonas aeruginosa"

- "Salmonella"

- "Staphylococcus aureus"

- "Streptococcus pneumoniae"

- "Streptococcus pyogenes"

- "Toxoplasma gondii"

Prophylaxis (Prevention)

Since opportunistic infections can cause severe disease, much emphasis is placed on measures to prevent infection. Such a strategy usually includes restoration of the immune system as soon as possible, avoiding exposures to infectious agents, and using antimicrobial medications ("prophylactic medications") directed against specific infections.

Prophylaxis (Prevention) | Prophylactic medications

Individuals at higher risk are often prescribed prophylactic medication to prevent an infection from occurring. A patient's risk level for developing an opportunistic infection is approximated using the patient's CD4 T-cell count and sometimes other markers of susceptibility. Common prophylaxis treatments include the following:

Treatment

Treatment depends on the type of opportunistic infection, but usually involves different antibiotics.

Veterinary treatment

Opportunistic infections caused by Feline Leukemia Virus and Feline immunodeficiency virus retroviral infections can be treated with Lymphocyte T-Cell Immune Modulator.