Pathogenic fungi are
fungi that cause disease in humans or other
organisms. Approximately 300 fungi are known to be pathogenic to humans. Markedly more fungi are known to be pathogenic to
plant life than those of the
animal kingdom. The study of fungi pathogenic to humans is called "medical mycology". Although fungi are
eukaryotic, many pathogenic fungi are
microorganisms.
The study of fungi and other organisms pathogenic to plants is called
plant pathology
Plant pathology (also phytopathology) is the scientific study of diseases in plants caused by pathogens (infectious organisms) and environmental conditions (physiological factors). Organisms that cause infectious disease include fungi, oom ...
.
''Candida''
''Candida'' species cause infections in individuals with deficient immune systems.
Th1-type cell-mediated immunity
Cell-mediated immunity or cellular immunity is an immune response that does not involve antibodies. Rather, cell-mediated immunity is the activation of phagocytes, antigen-specific cytotoxic T-lymphocytes, and the release of various cytokines ...
(CMI) is required for clearance of a fungal infection.
''
Candida albicans
''Candida albicans'' is an opportunistic pathogenic yeast that is a common member of the human gut flora. It can also survive outside the human body. It is detected in the gastrointestinal tract and mouth in 40–60% of healthy adults. It is usu ...
'' is a kind of diploid
yeast that commonly occurs among the human
gut microflora
Gut microbiota, gut microbiome, or gut flora, are the microorganisms, including bacteria, archaea, fungi, and viruses that live in the digestive tracts of animals. The gastrointestinal metagenome is the aggregate of all the genomes of the gut m ...
. ''C. albicans'' is an
opportunistic pathogen
An opportunistic infection is an infection caused by pathogens (bacteria, fungi, parasites or viruses) that take advantage of an opportunity not normally available. These opportunities can stem from a variety of sources, such as a weakened immune ...
in humans. Abnormal over-growth of this fungus can occur, particularly in
immunocompromised
Immunodeficiency, also known as immunocompromisation, is a state in which the immune system's ability to fight infectious diseases and cancer is compromised or entirely absent. Most cases are acquired ("secondary") due to extrinsic factors that a ...
individuals.
''C. albicans'' has a
parasexual cycle
The parasexual cycle, a process restricted to fungi and single-celled organisms, is a nonsexual mechanism of parasexuality for transferring genetic material without meiosis or the development of sexual structures. It was first described by Italian ...
that appears to be stimulated by environmental stress.
Other species of ''Candida'' may be pathogenic as well, including ''
Candida stellatoidea,
C. tropicalis,
C. pseudotropicalis,
C. krusei,
C. parapsilosis,'' and ''
C. guilliermondii.''
''Aspergillus''
The most common pathogenic species are ''
Aspergillus fumigatus
''Aspergillus fumigatus'' is a species of fungus in the genus ''Aspergillus'', and is one of the most common ''Aspergillus'' species to cause disease in individuals with an immunodeficiency.
''Aspergillus fumigatus'', a saprotroph widespread in ...
'' and ''
Aspergillus flavus
''Aspergillus flavus'' is a saprotrophic and pathogenic fungus with a cosmopolitan distribution. It is best known for its colonization of cereal grains, legumes, and tree nuts. Postharvest rot typically develops during harvest, storage, and/or ...
''. Aspergillus flavus produces
aflatoxin
Aflatoxins are various poisonous carcinogens and mutagens that are produced by certain molds, particularly ''Aspergillus'' species. The fungi grow in soil, decaying vegetation and various staple foodstuffs and commodities such as hay, sweetco ...
which is both a toxin and a
carcinogen
A carcinogen is any substance, radionuclide, or radiation that promotes carcinogenesis (the formation of cancer). This may be due to the ability to damage the genome or to the disruption of cellular metabolic processes. Several radioactive substa ...
and which can potentially contaminate foods such as nuts. ''Aspergillus fumigatus'' and ''
Aspergillus clavatus
''Aspergillus clavatus'' is a species of fungus in the genus ''Aspergillus'' with conidia dimensions 3–4.5 x 2.5–4.5 μm. It is found in soil and animal manure. The fungus was first described scientifically in 1834 by the French mycologist ...
'' can cause
allergic
Allergies, also known as allergic diseases, refer a number of conditions caused by the hypersensitivity of the immune system to typically harmless substances in the environment. These diseases include hay fever, food allergies, atopic dermati ...
disease. Some ''Aspergillus'' species cause disease on grain crops, especially
maize, and synthesize
mycotoxin
A mycotoxin (from the Greek μύκης , "fungus" and τοξίνη , "toxin") is a toxic secondary metabolite produced by organisms of kingdom Fungi and is capable of causing disease and death in both humans and other animals. The term 'mycotoxin' ...
s including
aflatoxin
Aflatoxins are various poisonous carcinogens and mutagens that are produced by certain molds, particularly ''Aspergillus'' species. The fungi grow in soil, decaying vegetation and various staple foodstuffs and commodities such as hay, sweetco ...
.
Aspergillosis is the group of diseases caused by ''Aspergillus''. The symptoms include fever, cough, chest pain or breathlessness. Usually, only patients with weakened
immune systems or with other
lung conditions are susceptible.
The spores of ''
Aspergillus fumigatus
''Aspergillus fumigatus'' is a species of fungus in the genus ''Aspergillus'', and is one of the most common ''Aspergillus'' species to cause disease in individuals with an immunodeficiency.
''Aspergillus fumigatus'', a saprotroph widespread in ...
'' are ubiquitous in the atmosphere. ''A. fumigatus'' is an opportunistic pathogen. It can cause potentially lethal invasive infection in immunocompromised individuals.
''A. fumigatus'' has a fully functional sexual cycle that produces cleistothecia and
ascospores
An ascus (; ) is the sexual spore-bearing cell produced in ascomycete fungi. Each ascus usually contains eight ascospores (or octad), produced by meiosis followed, in most species, by a mitotic cell division. However, asci in some genera or s ...
.
''Cryptococcus''
''
Cryptococcus neoformans
''Cryptococcus neoformans'' is an encapsulated yeast belonging to the class Tremellomycetes and an obligate aerobe that can live in both plants and animals. Its teleomorph is a filamentous fungus, formerly referred to ''Filobasidiella neoformans ...
'' can cause a severe form of
meningitis
Meningitis is acute or chronic inflammation of the protective membranes covering the brain and spinal cord, collectively called the meninges. The most common symptoms are fever, headache, and neck stiffness. Other symptoms include confusion or ...
and meningo-encephalitis in patients with
HIV
The human immunodeficiency viruses (HIV) are two species of ''Lentivirus'' (a subgroup of retrovirus) that infect humans. Over time, they cause acquired immunodeficiency syndrome (AIDS), a condition in which progressive failure of the immune ...
infection and
AIDS
Human immunodeficiency virus infection and acquired immunodeficiency syndrome (HIV/AIDS) is a spectrum of conditions caused by infection with the human immunodeficiency virus (HIV), a retrovirus. Following initial infection an individual ma ...
. The majority of ''Cryptococcus'' species live in the soil and do not cause disease in humans. ''
Cryptococcus neoformans
''Cryptococcus neoformans'' is an encapsulated yeast belonging to the class Tremellomycetes and an obligate aerobe that can live in both plants and animals. Its teleomorph is a filamentous fungus, formerly referred to ''Filobasidiella neoformans ...
'' is the major human and animal pathogen. ''
Papiliotrema laurentii'' and ''
Naganishia albida'', both formerly referred to ''
Cryptococcus
''Cryptococcus'' is a genus of fungi in the family Cryptococcaceae that includes both yeasts and filamentous species. The filamentous, sexual forms or teleomorphs were formerly classified in the genus ''Filobasidiella'', while ''Cryptococcus'' ...
'', have been known to occasionally cause moderate-to-severe disease in human patients with compromised immunity. ''
Cryptococcus gattii
''Cryptococcus gattii'', formerly known as ''Cryptococcus neoformans'' var. ''gattii'', is an encapsulated yeast found primarily in tropical and subtropical climates. Its teleomorph is ''Filobasidiella bacillispora'', a filamentous fungus belongi ...
'' is endemic to tropical parts of the continent of Africa and Australia and can cause disease in non-immunocompromised people.
Infecting ''C. neoformans'' cells are usually phagocytosed by
alveolar macrophage
An alveolar macrophage, pulmonary macrophage, (or dust cell) is a type of macrophage, a professional phagocyte, found in the airways and at the level of the alveoli in the lungs, but separated from their walls.
Activity of the alveolar macrophag ...
s in the lung.
The invading ''
C. neoformans'' cells may be killed by the release of oxidative and nitrosative molecules by these macrophages.
However some ''C. neoformans'' cells may survive within the macrophages.
The ability of the pathogen to survive within the macrophages probably determines latency of the disease, dissemination and resistance to
antifungal
An antifungal medication, also known as an antimycotic medication, is a pharmaceutical fungicide or fungistatic used to treat and prevent mycosis such as athlete's foot, ringworm, candidiasis (thrush), serious systemic infections such as cryp ...
agents. In order to survive in the hostile intracellular environment of the macrophage, one of the responses of ''C. neoformans'' is to
upregulate
In the biological context of organisms' production of gene products, downregulation is the process by which a cell decreases the quantity of a cellular component, such as RNA or protein, in response to an external stimulus. The complementary pro ...
genes employed in responses to
oxidative stress
Oxidative stress reflects an imbalance between the systemic manifestation of reactive oxygen species and a biological system's ability to readily detoxify the reactive intermediates or to repair the resulting damage. Disturbances in the normal r ...
.
The haploid nuclei of ''C. neoformans'' can undergo nuclear fusion (
karyogamy) to become diploid. These diploid nuclei may then undergo
meiosis, including
recombination, resulting in the formation of haploid
basidiospore
A basidiospore is a reproductive spore produced by Basidiomycete fungi, a grouping that includes mushrooms, shelf fungi, rusts, and smuts. Basidiospores typically each contain one haploid nucleus that is the product of meiosis, and they are pr ...
s that are able to disperse.
Meiosis may facilitate
repair
The technical meaning of maintenance involves functional checks, servicing, repairing or replacing of necessary devices, equipment, machinery, building infrastructure, and supporting utilities in industrial, business, and residential installa ...
of ''C. neoformans'' DNA in response to macrophage challenge.
''Histoplasma''
''
Histoplasma capsulatum
''Histoplasma capsulatum'' is a species of dimorphic fungus. Its sexual form is called ''Ajellomyces capsulatus''. It can cause pulmonary and disseminated histoplasmosis.
''H. capsulatum'' is "distributed worldwide, except in Antarctica, but ...
'' can cause
histoplasmosis
Histoplasmosis is a fungal infection caused by '' Histoplasma capsulatum''. Symptoms of this infection vary greatly, but the disease affects primarily the lungs. Occasionally, other organs are affected; called disseminated histoplasmosis, it can ...
in humans, dogs and cats. The fungus is most prevalent in the Americas, India and southeastern Asia. It is endemic in certain areas of the
United States. Infection is usually due to inhaling contaminated air.
''Pneumocystis''
''
Pneumocystis jirovecii'' (or Pneumocystis carinii) can cause a form of
pneumonia in people with weakened
immune systems, such as premature children, the elderly and
AIDS
Human immunodeficiency virus infection and acquired immunodeficiency syndrome (HIV/AIDS) is a spectrum of conditions caused by infection with the human immunodeficiency virus (HIV), a retrovirus. Following initial infection an individual ma ...
patients.
''Stachybotrys''
''
Stachybotrys chartarum'' or "black mold" can cause respiratory damage and severe headaches. It frequently occurs in houses and in regions that are chronically damp.
Host defense mechanisms
Endothermy
Mammalian
endothermy and homeothermy are potent nonspecific defenses against most fungi. A comparative genomic study found that in opportunistic fungi there are few if any specialised virulence traits consistently linked to opportunistic pathogenicity of fungi in humans apart from the ability to grow at 37 °C.
Barrier tissues
The
skin,
respiratory tract,
gastrointestinal tract, and the
genital-urinary tract induced inflammation are common bodily regions of fungal infection.
Immune response
Studies have shown that hosts with higher levels of
immune response cells such as
monocytes/
macrophages,
dendritic cells, and
invariant natural killer (iNK) T-cells exhibited greater control of fungal growth and protection against systemic infection.
Pattern recognition receptors (PRRs) play an important role in inducing an immune response by recognizing specific fungal pathogens and initiating an immune response.
In the case of mucosal
candidiasis
Candidiasis is a fungal infection due to any type of '' Candida'' (a type of yeast). When it affects the mouth, in some countries it is commonly called thrush. Signs and symptoms include white patches on the tongue or other areas of the mouth ...
, the cells that produce
cytokine IL-17 are extremely important in maintaining
innate immunity
The innate, or nonspecific, immune system is one of the two main immunity strategies (the other being the adaptive immune system) in vertebrates. The innate immune system is an older evolutionary defense strategy, relatively speaking, and is the ...
.
Link to extremotolerance
A comprehensive comparison of distribution of
opportunistic pathogens
An opportunistic infection is an infection caused by pathogens ( bacteria, fungi, parasites or viruses) that take advantage of an opportunity not normally available. These opportunities can stem from a variety of sources, such as a weakened immun ...
and stress-tolerant fungi in the fungal tree of life showed that
polyextremotolerance and opportunistic pathogenicity consistently appear in the same fungal orders and that the co-occurrence of opportunism and
extremotolerance (e.g.
osmotolerance and
psychrotolerance) is statistically significant. This suggests that some adaptations to stressful environments may also promote fungal survival during the infection.
See also
*
List of human diseases associated with infectious pathogens
*
Microbiology
*
Microsporidia
Microsporidia are a group of spore-forming unicellular parasites. These spores contain an extrusion apparatus that has a coiled polar tube ending in an anchoring disc at the apical part of the spore. They were once considered protozoans or pr ...
*
Mycology
*
Plant pathology
Plant pathology (also phytopathology) is the scientific study of diseases in plants caused by pathogens (infectious organisms) and environmental conditions (physiological factors). Organisms that cause infectious disease include fungi, oom ...
*
Plague Inc.
References
Further reading
*
External links
Ecmm.eu: Official European Confederation of Medical Mycology website
{{Fungi classification, state=collapsed
.
Fungi and humans
Fungus common names
Mycology