Opportunistic infection


An opportunistic infection is an infection caused by pathogens that take advantage of an opportunity not normally available, such as a host with a weakened immune system, an altered microbiota, 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, which is seriously debilitated and has lowered resistance to infection, a penetrating injury, or a lack of competition from normal commensals presents an opportunity for the pathogen to infect.

Types of infections

A partial listing of opportunistic organisms includes:
or immunosuppression can be caused by:
The lack of or the disruption of normal vaginal microbiota allows the proliferation of opportunistic microorganisms and will cause the opportunistic infection - bacterial vaginosis.

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 directed against specific infections.

Restoration of immune system

The following may be avoided as a preventative measure to reduce risk of infection:
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:
InfectionWhen to Give ProphylaxisAgent
Pneumocystis jiroveciiCD4 < 200 cells/mm3 or oropharyngeal candidasis TMP-SMX
Toxoplasma gondiiCD4 < 100 cells/mm3 and positive Toxoplasma gondii IgG immunoassayTMP-SMX
Mycobacterium avium complexCD4 < 50Azithromycin

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 immunomodulator.