Emmonsia parva
 | This article may be too technical for most readers to understand. (January 2015) |
| Emmonsia parva | |
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| Kingdom: | Fungi |
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| Genus: | Emmonsia |
| Species: | Emmonsia parva
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Emmonsia parva (formerly Chrysosporium parvum) is a filamentous,
Ecology
Emmonsia parva, E. crescens, and E. pasteuriana together comprise the genus Emmonsia,
Growth and morphology
The fungus is dimorphic growing in two distinct forms.
Pathogenicity
Transmission
The main route of infection is inhalation of airborne spores through the respiratory pathway.[8] This can occur in both healthy and immunocompromised individuals, however a disseminated infection is more common in the latter.[8] After inhalation the conidia switch to their adiaspore state, triggered by the temperature increase within the body. These develop without replicating in the alveoli of the lung.[2] Transmission can originate directly from the soil or through an animal reservoir such as mice or bats.[2]
Infection
Adiaspiromycosis, caused by E. parva may lead to pulmonary disease. It is termed an infection, but better described as a bodily reaction to foreign material,[3] invoking various cellular processes within the circulatory and immune systems. Once the adiaspore is formed it finds a place to localize in the alveoli and implants somewhere in the tissue in that section.[2] At this site the spores become calcified which causes a slight localized reaction involving inflammation.[2] Lung function may be obstructed at this stage. The body mounts a multicellular immune response to the presence of these adiaspores leading to the formation of noncaseating granulomas.[2]
The onset of adiaspiromycosis is dependent on the level of exposure to conidia. The disease is self-limiting so the onset of symptoms is determined by the amount of conidia inhaled.[8] Low level exposure induces little to no clinical symptoms, while a greater dosage risks development of pulmonary disease. This is referred to as acute pulmonary adiaspiromycosis, primary progressive pulmonary adiaspiromycosis or disseminated pulmonary adiaspiromycosis. It is characterized by widespread lesions caused by granulomas within both lungs. There are 3 forms of manifestation:
- A single granuloma[8]
- A cluster of granulomas in a localized region[8]
- Widespread bilateral granulomatous disease[8]
The onset of symptoms is dependent on 2 factors: the dosage of conidia [10] and the immune status of the host.[4] Usually infection is asymptomatic with pulmonary disease developing very rarely.[2] Fatality rates are low. If however the level of spores inhaled is sufficient or the immune system of the host is adequately compromised clinical symptoms may develop which include coughing, dyspnea, low-grade fever, weight loss and conjunctivitis including blurred vision, photophobia and ocular pain.[2][8] Within the sclera, white, opaque nodules develop in conjunction with local edema or hyperemia. This opacification may extend to other distal parts of the eye such as the limbus and angular corneal opacities.[2] Granulomas also form in the anterior chamber. However purulent conjunctival discharge and hemorrhaging were not observed as opposed to conjunctivitis brought on by viral or bacterial infection.[2]
Diagnosis
Adiaspiromycosis is histopathologically diagnosed. Three criteria must be met for accurate diagnosis:
- Dissemated nodular lesions in both lungs.[2]
- Manifested systemic and respiratory symptoms[2]
- Presence of adiaspores within granulomas in the lung[2]
The adiaspores must be identified as E. parva in culture media or sequencing to separate the infection from E. crescens. Periodic acid–Schiff (PAS) stains can be used to observe the thick-walled adiaspores in tissue regions.[2] Sequencing can be used as a tool to discriminate the fungus from its close relative, the genus Blastomyces.[9] The target is the D2 variable domain found in the large subunit of nuclear rRNA at the 5' end.[2] This region has sufficient variability between the two species. To differentiate between separate Emmonsia species the internal transcribed spacer (ITS) can be targeted.[2] Also the size of the spores varies considerably with E. parva having smaller ones.
Treatment
The onset of adiaspiromycosis is rarely serious and is self-limiting[4] so often no treatment is required and the body clears the spores on its own. Fluconazole (FLC), AmB, and ketoconazole [4][8] have proven to be therapeutic in progressive or serious infection. Oral intraconazole (ITC) is also an effective aid. Surgical resection may be a last resort if fungal infection persists.[8]
Epidemiology
Exposure to soil and dust is a major route of infection so manual labor in regions with high levels of each can lead to an increased risk of inhalation. As a result, adiaspiromycosis is reported more commonly in men then in women.[5] In most cases exposure is asymptomatic. Cases have been reported in immunocompromised individuals such as those diagnosed with AIDS.[5] There has been only one reported case of E. pasteuriana infection and it occurred in an AIDS patient who had disseminated open wounds.[8] Cleaning, working or playing in areas inhabited by small mammals such as mice or bats may increase risk of infection.[2] Farmers, greenhouse workers or those involved in construction are also at a greater risk of exposure.[8]
References
- ISBN 9780124828506.
- ^ ISBN 9781439812402.
- ^ ISBN 9780124158955.
- ^ ISBN 9780521509954.
- ^ ISBN 9781405170567.
- ^ ISBN 9780520013445.
- ^ ISBN 9780723432371.
- ^ ISBN 9780470177914.
- ^ PMID 9738044.
- ^ ISBN 978-0824706838.