Opportunistic infections can be caused by a wide variety of different types of pathogens. These infections can be caused by viral, bacterial, fungal, as well as parasitic pathogens. A partial list of opportunistic pathogens and their associated effects are as follows:
Bacteria • Atopobium vaginae is an anaerobic bacterium recognized for its role in the development of
bacterial vaginosis (BV). •
Clostridioides difficile (formerly known as
Clostridium difficile) is a bacteria that is known to cause gastrointestinal infection and diarrhea. It is typically associated with being the most common
hospital acquired infection. •
Cutibacterium acnes (formerly Propionibacterium acnes) can act as an opportunistic agent in infections associated with implanted medical devices, forming biofilms. • Extraintestinal pathogenic Escherichia coli (ExPEC) are
E. coli strains that can lead to diseases beyond the gut, notably urinary tract infections (UTIs), meningitis, and bacteremia (bloodstream infections). • Haemophilus influenzae is a bacterium implicated in causing illnesses such as meningitis, epiglottitis which can obstruct airways, pneumonia, otitis media affecting the ear, sinusitis involving the sinuses, and potentially leading to complications like mastoiditis, parameningeal abscess, and pericarditis. •
Klebsiella pneumoniae, a member of a group including pathogens, can be responsible for various infections in hospitalized individuals as it is frequently isolated from hospital admissions and the broader group (
Enterobacteriaceae) is known to cause diverse infections. •
Legionella pneumophila is a bacterium that causes
Legionnaire's disease, a
respiratory infection. •
Mycobacterium avium complex (MAC) is a group of two bacteria,
M. avium and
M. intracellulare, that typically
co-infect, leading to a lung infection called
mycobacterium avium-intracellulare infection. •
Mycobacterium tuberculosis is a species of bacteria that causes
tuberculosis, a respiratory infection. •
Pseudomonas aeruginosa is a bacterium that can cause respiratory infections. It is frequently associated with
nosocomial infections and
cystic fibrosis which can lead to organ dysfunctions and shortened life expectancy. •
Salmonella is a
genus of bacteria that is known to cause gastrointestinal infections causing an inflammatory response accompanied with fever and diarrhea. •
Staphylococcus aureus is a bacterium known to cause skin infections and
sepsis, among other pathologies. Notably,
S. aureus has evolved several
drug-resistant strains, including
MRSA. • Stenotrophomonas maltophilia has emerged as a challenging nosocomial agent frequently associated with respiratory tract infections like pneumonia and exacerbations in individuals with COPD, and can also cause bacteremia, particularly linked to central lines in vulnerable patients. •
Streptococcus pneumoniae is a bacterium that causes respiratory infections as well as
meningitis and
bacteremia.'''''' •
Streptococcus pyogenes (also known as group A
Streptococcus) is a bacterium that can cause a variety of conditions, including
impetigo and
strep throat, as well as other illnesses.
Fungi •
Aspergillus is a fungus, commonly associated with respiratory infection. •
Candida albicans is a species of fungus that is a part of the normal human microbiome. It acts as a commensal unless there is a change in concentrations. It can be associated with various conditions such as
oral thrush and gastrointestinal infection. •
Coccidioides immitis is a fungus known for causing
coccidioidomycosis, more commonly known as Valley Fever. • Cryptococcus gattii: This emerging fungal pathogen can cause severe and often fatal infections, manifesting as pulmonary disease and meningitis in both immunocompromised and immunocompetent individuals. •
Cryptococcus neoformans is a fungus that causes
cryptococcosis, which can lead to pulmonary infection as well as nervous system infections, like
meningitis. • Dematiaceous (pigmented) molds: These fungi are responsible for a range of diseases including
phaeohyphomycosis,
chromoblastomycosis,
eumycotic mycetoma, invasive sinusitis, and allergic fungal sinusitis; cerebral infections can also occur. • Fusarium species: These fungi can cause
hyalohyphomycosis, particularly in immunocompromised individuals, as well as
mycotic keratitis and
onychomycosis. • Hyaline (non-pigmented) molds (e.g.,
Acremonium,
Paecilomyces,
Scopulariopsis species): This group encompasses various molds, including
Fusarium spp. causing hyalohyphomycosis, mycotic keratitis, and onychomycosis, as well as commonly causing pneumonia, sinusitis, and cutaneous lesions that may disseminate in neutropenic patients;
Scedosporium spp. associated with sinusitis and pneumonia;
Lomentospora prolificans causing a varied range of infections and disseminated disease;
Scopulariopsis spp. and
Acremonium spp. linked to sinopulmonary diseases;
Paecilomyces variotii causing sinopulmonary disease; and
Penicillium species implicated in necrotizing esophagitis and disseminated infections. •
Histoplasma capsulatum is a species of fungus known to cause
histoplasmosis, which can present itself with an array of symptoms, but often involves respiratory infection. • Lomentospora prolificans: This fungus can cause a remarkably varied range of infections and disseminated disease, including
keratitis,
mycotic aneurysms,
external otitis, sinusitis,
peritonitis, onychomycosis, and
esophagitis. •
Pseudogymnoascus destructans (formerly known as
Geomyces destructans) is a fungus that causes
white-nose syndrome in
bats. •
Microsporidia is a group of fungi that infect species across the
animal kingdom, one species of which can cause
microsporidiosis in immunocompromised human hosts. •
Pneumocystis jirovecii (formerly known as
Pneumocystis carinii) is a fungus that causes
pneumocystis pneumonia, a respiratory infection. • Rhodotorula species: These yeasts can cause
fungemia, often linked to central venous catheter use, as well as localized infections including
meningitis, skin infections, ocular infections, peritonitis, and prosthetic joint infections. • Zygomycetes (e.g.,
Mucor,
Rhizopus,
Absidia): This group can cause infections like
rhinocerebral mucormycosis, and
Mucor has been associated with respiratory infections; specifically,
Absidia corymbifera is considered a human pathogen. ===
Protozoa === •
Cryptosporidium is a
protozoan that causes the condition
Cryptosporidiosis. This condition affects the
gastrointestinal tract. •
Toxoplasma gondii is a protozoan, known for causing
toxoplasmosis which is known to lead to impairment of the brain.
Viruses • Adenovirus is known to cause various illnesses, including lower respiratory tract infections, pneumonia, acute respiratory diseases, epidemic
keratoconjunctivitis affecting the eyes, acute hemorrhagic cystitis of the bladder, and
gastroenteritis affecting the digestive system. •
LCMV causes lymphocytic choriomeningitis disease and death in immunocompromised organ-transplant patients. •
HSV is considered a member of the human herpesvirus family and is most frequently associated with
immunocompromisation diseases and
JAK inhibitors. •
Cytomegalovirus is considered a member of the human herpesvirus family and is most frequently associated with respiratory infection. • Hepatitis B Virus (HBV) can lead to acute liver infection manifesting as anicteric hepatitis, icteric hepatitis, or fulminant hepatitis, and chronic infection can progress to an asymptomatic carrier state, chronic hepatitis, cirrhosis of the liver, and
hepatocellular carcinoma. Severe liver damage can result in complications like
jaundice,
hepatic encephalopathy,
ascites, gastrointestinal bleeding, and
coagulopathy. • Hepatitis C Virus (HCV) infection can become chronic, leading to liver damage that can progress to
cirrhosis,
portal hypertension, hepatic decompensation with encephalopathy, and hepatocellular carcinoma. • Influenza Virus is responsible for seasonal flu epidemics and can be categorized into types affecting various hosts, such as avian (bird) flu, canine (dog) flu, swine (pig)/variant flu, and can cause pandemic flu, all generally resulting in respiratory illnesses. • Human Metapneumovirus (HMPV) commonly causes upper and lower respiratory tract infections, with symptoms such as cough, mucous production, fever, and dyspnea, and can lead to more severe conditions like pneumonia and
bronchiolitis. • Human Papillomavirus (HPV) is the initiating force behind multiple conditions, including cutaneous and anogenital
warts, which in some cases can progress to various carcinomas. •
Human polyomavirus 2 (also known as JC virus) is known to cause
progressive multifocal leukoencephalopathy (PML) which affects the central nervous system. •
Human herpesvirus 8 (also known as Kaposi sarcoma-associated herpesvirus) is a virus associated with
Kaposi sarcoma, a type of skin cancer. • Human T-cell leukemia virus type 1 (HTLV-1) causes a chronic lifelong infection that can lead to general immunosuppression,
uveitis affecting the eyes, dermatitis of the skin, pneumonitis in the lungs, adult T-cell leukemia, and HTLV-1 associated myelopathy also known as tropical spastic paraparesis. • Parainfluenza Virus commonly causes upper and lower respiratory illnesses with symptoms similar to the common cold, such as fever, runny nose, cough, sneezing, and sore throat, and can also cause more serious illnesses in children including
croup, bronchitis, and bronchiolitis. • SARS-CoV-2 is the virus that causes
Coronavirus Disease 2019 (
COVID-19), with symptoms that can include fever, cough, fatigue, muscle or body aches, headache, new loss of taste or smell, sore throat, congestion or runny nose, nausea or vomiting, and diarrhea. •
Varicella-Zoster Virus causes Shingles. == Opportunistic infections and HIV/AIDS ==