Common Molds and their Impact on Human Health

Molds or fungi can be found in at least small amounts almost anywhere due to their release of tiny spores. Spores can be hazardous to human health and potentially cause allergic reactions, fungal infection (mycosis) or release mycotoxins. Mycotoxins are toxic byproducts (secondary metabolites) produced by fungi.

Health experts indicate that, depending on the type of mold present in a home, the amount and degree of exposure, and the health condition of the occupant, the health effects of mold can range from being insignificant to causing allergic reactions and illness. Pregnant women, infants, the elderly and those with health problems, such as respiratory disease or a weakened immune system, are more at risk when exposed to mold.

The most common types of mold are listed here, alongside their distribution, habitat and human health effects.

  • Absidia are found world-wide, mostly in association with soil and decaying plant debris. They are Small lpyriform shaped sporangia with a characteristic conical shaped columellae and pronounced apophysis, and achieve rapid growth at 400 degrees Celsius. They are a common human pathogen causing pulmonary, rhinocerebral, disseminated, CNS or cutinous zygomycosis.
  • Alternaria  are mostly plant parasites, but a few species are ubiquitous and are also frequently soil borne. Dematiaceous hyphomycete producing chains of darkly pigmented, ovoid to obclavate dictyoconidia, often with short conical or cylindrical beaks. A few species are ubiquitous and are also frequently soil borne but are recognized as causative agents of mycotic keratitis.
  • Aspergillus are commonly found growing on dead leaves, stored grain, compost piles, or in other decaying vegetation and soil. Species are very common in both indoor and outdoor environments. This is in part due to the fact that aspergilli produce vast numbers of small, air-borne spores. They produce enzymes capable of degrading a great variety of organic substrates. A number of species are xerophilic and can thrive in relatively low moisture conditions. In indoor environments, they are found growing on wood, paper, paint, glue, and even dirty metal doors when the humidity is high. The most important clinical species are A. fumigatus, A. flavus, A. terreus, and A. niger. Unlike mycotoxicoses, the primary infection route for aspergillus species is through inhalation. This infection almost always occurs in people with a weakened immune system due to cancer, AIDS, leukemia, organ transplanion or chemotherapy. Aspergillus represent a continuum of symptoms from mild sneezing to fatal systemic infection, are also recognized as causative agents of mycotic keratitis.
  • Aureobasidium pullulans have a world-wide distribution, and are usually isolated as a saprophyte. They produce hyaline blastoconidia simultaneously from the vegetative hyphae, which may also form chains of darkly pigmented, thick-walled arthroconidia. Isolated from skin and nails. However, it has also been reported as a rare causative agent of phaeohyphomycosis, mycotic keratitis and peritonitis in patients on CAPD.
  • Ascospores grow well under a variety of conditions.  Ascospores are microscopic spores which develop during the winter on dead, fallen leaves that were infected the previous season. From budburst onwards, rain triggers the release of ascospores into the air. Ascospores are frequently found indoors on damp substrates. Ascospores are a very large group of spores that contain many genera and species. They are known allergens and these effects vary widely between genus and species of each Ascospore. Toxigenic effects also vary widely within this group.
  • Arthrinium are fungi found in soil and decomposing plant material. It is common in outdoor and indoor environment. The fungus produces one celled dark conidia with a pronounced hyaline rim or germ slit This fungus has been documented in various subcutaneous infections and  should be considered an allergen.  However, they have not been recorded to cause toxin-related diseases to date.
  • Basidiospores  are sexual spores that have been released from the basidium of a fungus. This group of spores is ubiquitous in nature and is mainly found in gardens, forests, and woodlands. Basidiospores are moisture driven as their spores disseminate during rain or in times of high humidity. The presence of these spores at levels greater than those of the outdoor environment may be an indicator of fungal contamination and water damage inside a building. These Spores inside building indicate the dry and brown rot of wood. These spores has been documented to cause hay fever, asthma, eczema,  allergic alveoltis, fatigue, runny nose, sneezing, stuffy nose, plugged ears.
  • Bipolaris/Exserohilum  are either plant pathogens or saprobes in the natural environment. They are known to be allergenic and can also cause fungal sinusitis. Rare cause of mycotic keratitis, subcutaneous, sinusitis, peritonitis in patients on CAPD.
  • Cladosporium is one of the most widespread mold. It includes about 40 species naturally found in soil, on decaying plant material and as plant pathogens. Several studies conducted in Europe and North America have shown that Cladosporium spores are present in the outdoor environment throughout the year. However, concentrations are very low in winter. In summer, daily peaks may range from 2,000 to 50,000 spores per cubic meter of air. Concentrations of Cladosporium species in indoor air is influenced by outdoor concentrations and indoor growth sources. C. cladosporioides was reported from acutaneous infection in an immunosuppressed patient. According to the Mayo Clinic, its various strains are some of the most common allergenic mold.
  • Chaetomium is the most common indoor fungal contaminant of moldy damp buildings. It may be found on wet drywall, wall-paper, carpets, window frames, baseboards and plywood. This mold causes many problems of biodeterioration of paper and other cellulose containing material. Chaetomium species are rarely associated with human infections, there are reports of infections involving individuals with weak immune system. Chaetomium globosum is known to produce 2 toxins in moisture damaged buildings, chaetoglobosins A and C. These toxins have the potential to cause illness to building occupants.
  • Curvularia  particularly enjoys cellulose as a substrate, and they can be found growing on wood, decaying plant matter, and living plants. Some colonize grasses and cereal grains, and others can live in the soil. These fungi are gray to black in color, typically darkening with age, and the underside of the colony will be a more pale white to gray. Has been known to cause onychomycosis, ocular keratitis, sinusitis, mycetoma, pneumonia, endocarditis, cerebral abscess, and disseminated infection. Most cases are from immunocompromised patients.
  • Fusarium colonizes continuously wet materials such as soaked wallboard and water reservoirs for humidifiers and drip pans. A common soil fungus and inhabitant on a wide array of plants, this fungi is often found in humidifiers and has been isolated from water-damaged carpets and a variety of other building materials. Human exposure may occur through ingestion of contaminated grains and possibly through the inhalation of spores. Fusarium sp. are frequently involved with eye, skin, and nail infections
  • Myxomycetes are found on decaying logs, stumps and dead leaves (particularly in forested regions). These organisms have both dry and wet spores. Wind disperses the dry fruiting body spores. Myxomycete spores are considered to cause Type 1 allergies (hay fever and asthma) or fungal hypersensitivity reactions.
  • Nigrospora is a filamentous dematiaceous fungus widely distributed in soil, decaying plants, and seeds. It is a unicellular, black, shiny, ovoid to ellipsoidal and horizontally flattened asexual spores (conidia), often with an equatorial colorless line. Although it has been isolated from a few clinical samples, its pathogenicity in man remains uncertain.
  • Penicillium are commonly found in soil, food, cellulose, grains, paint, carpet, wallpaper, interior fiberglass duct insulation, and decaying vegetation. Airborne Penicillium was shown to be significantly associated with lower respiratory infection with children. Scientific evidence has shown that asthma is more prevalent among adults living in damp homes and that asthma is three times more common in adults with mold allergy. Penicillium may cause hypersensitivity pneumonitis, asthma, and allergic alveolitisin susceptible individuals. Penicillium has been isolated from patients with keratitis, ear infections, pneumonia, endocarditis, peritonitis, and urinary tract infections. Penicillium infections are most commonly exhibited in immunosuppressed individuals.
  • Pithomyces  are commonly found on grass and decaying plant material. It has the potential to produce the mycotoxin sporidesmin. Air borne Pithomyces are the sources of allergen, irritant, hypersensitivity pneumonitis, and dermatitis.
  • Stachybotrys are species of black mold that grow well on materials with high cellulose content (such as drywall, ceiling tiles, jute-backed carpets, etc.) and become chronically moist or water-damaged due to water leaks, flooding, excessive humidity, or condensation. Infants under one year old are most at risk if they breathe high levels of Stachybotrys spores for long periods of time. Stachybotrys has been linked to a very rare condition called”pulmonary hemosiderosis” (bleeding of the lungs) in infants from extremely contaminated dwellings. This condition can only occur in thed eveloping lungs of infants, and it does not occur in anyone else. However, other people may develop more general health effects like eye irritations, asthma aggravation, cold-like symptoms, rashes, headaches, fatigue, or an inability to concentrate
  • Ulocladium can be found on gypsum, paper, paint, and straw materials. It requires a large source of water. The most common health effects are allergenic effects and these are generally displayed in the form of Type I allergies. They have been implicated in phaeohyphomycosis and in rare subcutaneous tissue infections. There are no known toxins from this spore at this time.

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