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An opportunistic infection is an infection caused by bacterial, viral, fungal, or protozoan pathogens that take advantage of a host with a weakened immune system or an altered microbiota (such as a disrupted gut flora). Many of these pathogens do not cause disease in a healthy host that has a normal immune system. A compromised immune system, however, 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. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「opportunistic infection」の詳細全文を読む スポンサード リンク
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