Opportunistic infection

Infections caused by pathogens that take advantage of an opportunity not normally available

Overview

An opportunistic infection is an infection caused by pathogens, such as bacteria, viruses, fungi, or protozoa, that take advantage of an opportunity not normally available. These opportunities can arise due to a weakened immune system, an altered microbiome, or breaches in the body's normal barriers to infection. Opportunistic infections are particularly common in individuals with immunodeficiency, such as those with HIV/AIDS, cancer, or those undergoing immunosuppressive therapy.

Causes

Opportunistic infections occur when the immune system is compromised or when the normal flora of the body is disrupted. Common causes include:

• Immunosuppression: Conditions like HIV/AIDS, chemotherapy, and organ transplantation can weaken the immune system, making the body more susceptible to opportunistic pathogens.
• Antibiotic use: Broad-spectrum antibiotics can disrupt the normal microbiota, allowing opportunistic pathogens to proliferate.
• Chronic diseases: Conditions such as diabetes mellitus and chronic kidney disease can impair immune function.
• Malnutrition: Poor nutrition can weaken the immune system, increasing susceptibility to infections.

Common Opportunistic Pathogens

Bacterial

• Mycobacterium avium complex (MAC) - often affects individuals with advanced HIV/AIDS.
• Clostridioides difficile - can cause severe diarrhea and colitis, especially after antibiotic use.

Viral

• Cytomegalovirus (CMV) - can cause retinitis, colitis, and other systemic infections in immunocompromised individuals.
• Herpes simplex virus (HSV) - can cause severe infections in individuals with weakened immune systems.

Fungal

• Candida albicans - can cause oral thrush and systemic infections.
• Pneumocystis jirovecii - causes Pneumocystis pneumonia (PCP), a common infection in people with HIV/AIDS.

Protozoal

• Toxoplasma gondii - can cause toxoplasmosis, particularly in individuals with HIV/AIDS.

Diagnosis

Diagnosing opportunistic infections involves a combination of clinical evaluation, laboratory tests, and imaging studies. Common diagnostic methods include:

• Blood tests: To detect specific antibodies or antigens.
• Cultures: To identify bacterial or fungal pathogens.
• Imaging: Such as X-rays or CT scans to identify infections in organs like the lungs.
• Biopsy: In some cases, a tissue sample may be needed to identify the pathogen.

Treatment

Treatment of opportunistic infections depends on the specific pathogen and the severity of the infection. Common treatments include:

• Antibiotics: For bacterial infections.
• Antiviral drugs: For viral infections, such as acyclovir for HSV.
• Antifungal medications: Such as fluconazole for fungal infections.
• Antiprotozoal agents: For protozoal infections like sulfadiazine for toxoplasmosis.

Prevention

Preventing opportunistic infections involves:

• Prophylactic medications: Such as trimethoprim-sulfamethoxazole for PCP in HIV patients.
• Vaccinations: To prevent infections like influenza and pneumococcal disease.
• Good hygiene practices: Including handwashing and safe food handling.
• Regular medical check-ups: To monitor immune function and detect infections early.

Related pages

• Immunodeficiency
• HIV/AIDS
• Antibiotic resistance
• Microbiome

• Opportunistic infection
  Opportunistic infection