Latin name: Chaetomium globosum
Source material: Spores and mycelium
Common names: Yeast
A mould, which may result in allergy symptoms in sensitised individuals.
Chaetomium is a dematiaceous, filamentous fungus belonging to a large genus of saprobic ascomycetes found in soil, air, plant debris, dung, straw, paper, bird feathers, and seeds. (1) More than 100 species have been described, the most common ones being C. atrobrunneum, C. funicola, C. globosum, and C. strumarium. C. globosum is the most frequently encountered species. (2) Several are very common in indoor environments (C. elatum, C. globosum, C. murorum). (3) Most grow best at between 25 and 35°C. (3) Most species cause degradation of cellulose-rich substrates, such as some components of soil, straw or wood. The fungus requires a cellulose-rich medium for sporulation, and growth of Chaetomium globosum is often stimulated in the presence of Aspergillus fumigatus, which excretes such compounds as sugar phosphates and phospho-glyceric acid. (2)
Chaetomium colonies grow rapidly. They have a cottony appearance and are initially white in colour, the mature colonies becoming grey to olive, and later sometimes tan to red or brown to black. Microscopically, C. globosum has distinctive small brown ‘lemon’ or ‘football’-shaped ascospores. The spores, formed inside the fruiting bodies, are forced out of openings and spread by wind, insects, and water splash.
One species, C. piluliferum, produces an extensive Botryotrichum asexual state that is often detected growing on building materials. (3) Some species are known to produce mycotoxins, including the chaetoglobosin and chaetomin toxins produced by C. globosum. (4, 5) Sterigmatocystin is produced by rare species. Other compounds produced (which may not be mycotoxins in the strictest sense) include a variety of mutagens. (6)
Some species are thermophilic and neurotropic in nature, (7, 8) in particular C. atrobrunneum, C. strumarium and C. perlucidum. (5) The ability of these species to grow at elevated temperatures may contribute to their neurotropic potential.
Chaetomium species are commonly found on paper products, wood and natural fibre textiles (such as jute-backed carpets, canvas, etc.). They are also common in natural environments on a variety of plant material, and are frequently isolated from natural substrata and seen at low levels in outside air.
C. globosum has been reported to be one of the top 12 species of microfungi isolated from North American wallboard. (9) C. globosum has also been found in kitchens and bathrooms, and in wallpaper, mattresses and carpets. (10) Water leakage through roofs, rising damp, and defective plumbing installations have been reported to be the main sources for water damage with subsequent mould growth. Materials most susceptible to mould attacks were water-damaged, aged organic cellulose-containing materials such as wood, jute, wallpaper, and cardboard, in which the moulds most frequently encountered were Penicillium (68%), Aspergillus (56%), and Chaetomium (22%). (11)
Chaetomium spp. have been found in the atmosphere of Karachi City (12) and even in the desert environment of Saudi Arabia, where these fungi were found inhabiting household environments including bedrooms, drawing rooms, living rooms, kitchens and bathrooms. (13) They have also been isolated from the dust of air-conditioners (14) and homes in Nigeria, (15) and from the homes of asthmatics in the USA. (16)
Occupational exposure, which could result in allergy, may occur from handling black pepper, white pepper, Brazil nuts, (17) and cashew kernels. (18, 19) These fungi have also been shown to be present in tobacco samples. (20) Chaetomium spp. (in particular C. thermophilum) have been shown to be present in combine harvester wheat and sorghum dust and in the atmosphere of their hay sites. (21) This fungus may also be present in anise and fennel seeds, as reported in a study from Egypt. (22)
No allergens have yet been characterised. However, two potential allergens have been isolated. The gene for a 46-kDa endochitinase has been cloned. (23) Its allergenic potential was not evaluated. A small heat-shock protein gene (hsp22.4) has also been cloned, with an estimated molecular mass of 22.4 kDa. (24)
The allergenic potential of this species or other species in the genus has not been well studied. However, because the types of clinical symptoms caused by the various species differ considerably, a common allergen (though possible) cannot be deduced, and therefore neither can cross-reactivity between species. Whether all members of the genus may result in allergic reactions or not can also not be deduced.
Anecdotal evidence suggests that hypersensitivity reactions – in particular, IgE-mediated reactions – to the Chaetomium genus, especially C. globosum, may induce symptoms of asthma and/or hypersensitivity pneumonitis in sensitised individuals; however, no studies have been reported to date. It appears that organisms in the genus rarely induce IgE-mediated reactions in sensitised individuals, but whether this impression is the result of limited research or of the actual low allergenic potential of the fungi is not clear. Whether few or many or all members of the genus can result in allergic reactions cannot be deduced; a conservative view is probably reasonable, as the types of non-IgE clinical reactions vary considerably among the various species. This is in spite of Chaetomium species producing airborne spores that are often found in spore counts.
In a study in Sao Paulo, Brazil, evaluating sensitisation in 201 patients with asthma and/or allergic rhinitis to 42 airborne fungi using skin specific IgE tests, 15 were shown to be sensitised to Chaetomium. (25)
The prevalence of sensitisation to common indoor fungal species in an atopic population was examined in West Virginia, USA. All 102 patients with symptoms consistent with allergic rhinitis or asthma were evaluated for immunoglobulin IgE reactivity to a panel of skin-prick test (SPT) reagents used for routine allergy testing and for an additional six fungi that are common indoor contaminants. Of this group, 68% had at least one positive skin test. The most prevalent positive SPTs were to dust mites, cats, vernal grass, and short ragweed. Twenty-one percent (21 of 102) were skin-test positive to at least one fungal extract, of which 12 of 21 (58%) showed sensitivity to one or more of the newly tested species; most notably Trichoderma viride (8%), Chaetomium globosum (7%), Paecilomyces variotii (7%), and Acremonium strictum (6%). The authors suggested that cross-reactivity with other fungi may partially explain these results. (26)
Whether fungi may contribute to increased severity of asthma or not was investigated in a group of patients hospitalised as a result of exacerbation of asthma. Skin-prick tests, with standard aeroallergens of airborne allergens (including grass, tree, Dermatophagoides pteronyssinus, Dermatophagoides farinae, feather, and cat and dog fur) and a panel of mould allergens, were performed in 105 asthmatic patients and controls. Sensitivity to A. pullulans was significantly associated with more severe asthma. Sensitisation to Helminthosporium was associated with an increased number of asthma exacerbations that required hospitalisation. Twenty-two percent were sensitised to C. globosum. (27)
Although Chaetomium species are rarely implicated in human disease, their spectrum of mycoses includes onychomycosis, (28, 29, 30) sinusitis, (2) empyema, (31) pneumonia, (32, 33) and fatal disseminated cerebral disease in immunocompromised hosts (34, 35, 36) and intravenous drug users. (5) The majority of reports have involved patients with hematologic malignancies and/or immunosuppression secondary to bone marrow or solid organ transplantation. (37, 38)
Chaetomium spp. are among the fungi that cause infections referred to (as a group) as phaeohyphomycosis. (39) Fatal deep mycoses due to Chaetomium atrobrunneum have been reported in an immunocompromised host. Brain abscess, peritonitis and cutaneous lesions may also develop due to Chaetomium spp. (9, 10, 40)
In rare cases, some species can be agents of opportunistic invasive disease. (41, 42) C. globosum is one of these, being the most common species isolated in at least 9 clinical cases of infection, (43) including peritonitis as a complication in peritoneal dialysis. (44)
Compiled by Dr Harris Steinman.
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