m8 Setomelannoma rostrata Helminthosporum haledes Exserohilum rostratum

m8 Setomelannoma rostrata Helminthosporum haledes Exserohilum rostratum Scientific Information

Type:

Whole Allergen

Display Name:

Setomelannoma rostrata Helminthosporum haledes Exserohilum rostratum

Allergen code:

Family:

Pleosporaceae

Species:

Rostratum

Route of Exposure:

Inhalation

Latin Name:

Setomelannoma rostrata Helminthosporum haledes Exserohilum rostratum

Summary

Setomelanomma rostrata/Heminthosporum haledes/Exserohium rostratum are members of the Bipolaris complex, which has been the subject of some taxonomical confusion. Fungal species from this group are ubiquitous in the environment and are mainly plant pathogens. However, a few species cause mycotic fungal disease in humans, mainly in immunosuppressed patients. Exserohilum spp. are predominantly found in tropical and subtropical regions. Heminthosporum and Exserohilum spp. – specific allergens can cause asthma, allergic rhinitis, and sinusitis. However, there are no recognized allergens currently described.

Allergen

Nature

S. rostrata, H. haledes and E. rostratum are closely related members of the Pleosporaceae taxonomical family. They are part of the Bipolaris complex that comprises the Bipolaris, Drechslera, Helmintosporium, and Exserohilum genera. Bipolaris complex fungi have been a source of confusion in the literature due to morphological similarities of the conidia, which are pigmented, cylindrical and typically pseudoseptate (1). E. rostratum has previously been known as Helminthosporum rostratum, Bipoloris rostrata and Drechslera rostrata (1).

The majority of the nearly 25 species belonging to the Exserohilum genus are plant pathogens (2, 3). However, three species from this genus are pathogenic to humans (E. rostratum, E. longirostratum, E. mcginnisii) and cause cutaneous, corneal, and systemic mycoses in patients with immunosuppression. E. rostratum is a dematiaceous mold, forms dark gray colonies with a “cottony” texture, and melanized, septate hyphae with long, brown-colored, fusiform conidia of approximately 30-80 µm (2, 3). In 2012, E. rostratum was the causative pathogen of 753 infections and 64 deaths in an outbreak of iatrogenic infection caused by contaminated methylprednisolone (2).

Taxonomy

*Taxonomic tree of Exoserohilum rostratum* (4)**
Domain	Eukaryote
Kingdom	Fungi
Phylum	Ascomycota
Class	Dothideomycetes
Order	Pleosporales
Family	Pleosporaceae
Genus	Exoserohilum

Epidemiology

Worldwide distribution

Exserohium species are ubiquitous in the environment and have a geographical distribution mainly limited to the tropics and subtropical regions (3). A study from India reported a prevalence of sensitization to Helminthosporm spp., as detected by skin prick test, of 1.9% amongst a cohort of patients with atopy (5). A study from the Midwestern USA also reported sensitization rate (of allergen-specific IgE) to H. haledes of 5% (6).

Route of Exposure

Main

Exposure to the E. rostratum allergen is thought to be through the inhalational route. It has been demonstrated that approximately 13% (+/- 2.4%) of E. rostratum spores release allergen before germination. The same study also showed a significant increase in the percentage of spores releasing allergen after germination (89.9% +/- 2.7%; P<0.01). It has been proposed that a significant factor in exposure is related to the ability of fungal spores to germinate in the respiratory tract (7).

Clinical Relevance

Helminthosporum spp. are known to be a cause of allergic rhinitis and asthma (1). Furthermore, Exserohilum spp. are reportedly the cause of allergic bronchopulmonary disease (7). There is also a body of evidence in the literature, mainly as case reports, that Exserohilum spp. are a cause of chronic allergic fungal sinusitis. Although it should be noted that in some of these reports, no skin testing or allergen-specific IgE assay was undertaken (3).

Molecular Aspects

Allergenic molecules

Currently, there are no allergens specific to S. rostrata, H. haledes or E. rostratum recognized by the WHO-IUIS Allergen Nomenclature Sub-Committee. However, Drechslera spp. have been demonstrated to produce allergen. Furthermore, at least four allergen-specific IgE-binding proteins have been identified in Bipolaris extracts.

Cross-reactivity

A study from Southern China found that in patients with allergic bronchopulmonary aspergillosis and Aspergillus fumigatus-sensitized patients with asthma, H. Haledes-specific IgE levels correlated with total A. fumigatus-specific IgE (r_s= 0.585, P < .05), which was consistent with the findings of a previous Swedish study. This suggests cross-reactivity of H. halodes with the A. fumigatus allergen. However, no significant correlation was found with the A. fumigatus components Asp f 1, Asp f 2, Asp f 3, Asp f 4 or Asp f 6 (8).

Compiled By

Author: RubyDuke Communications

Reviewer: Dr. Christian Fischer

Last reviewed: February 2022

References

Levetin E, Horner WE, Scott JA, Barnes C, Baxi S, Chew GL, et al. Taxonomy of Allergenic Fungi. The Journal of Allergy and Clinical Immunology: In Practice. 2016;4(3):375-85.e1.
Reedy JL, Negoro PE, Feliu M, Lord AK, Khan NS, Lukason DP, et al. The Carbohydrate Lectin Receptor Dectin-1 Mediates the Immune Response to Exserohilum rostratum. Infect Immun. 2017;85(3).
Alajmi S, Koratum RM, Khan Z, Ahmad S, Jeragh A, Ibrahim H, et al. Allergic Fungal Sinusitis Caused by Exserohilum rostratum and Literature Review. Mycopathologia. 2019;184(1):89-96.
Life Co. Exserohilum rostratum (Drechsler) K.J. Leonard & Suggs 2021 [cited 2022 10.01.22]. Available from: https://www.catalogueoflife.org/data/taxon/3DQLF.
Dey D, Mondal P, Laha A, Sarkar T, Moitra S, Bhattacharya S, et al. Sensitization to Common Aeroallergens in the Atopic Population of West Bengal, India: An Investigation by Skin Prick Test. International Archives of Allergy and Immunology. 2018;178:1-6.
Benninger MS, Daly T, Graffmiller K. Positivity rates of in vitro inhalant/respiratory and food allergy tests in the northern midwestern United States. Ear Nose Throat J. 2018;97(9):296-322.
Green BJ, Mitakakis TZ, Tovey ER. Allergen detection from 11 fungal species before and after germination. J Allergy Clin Immunol. 2003;111(2):285-9.
Luo W, Hu H, Wu Z, Wei N, Huang H, Zheng P, et al. Molecular allergen sensitization of Aspergillus fumigatus between allergic bronchopulmonary aspergillosis and A fumigatus-sensitized asthma in Guangzhou, Southern China. J Clin Lab Anal. 2020;34(10):e23448.