Table of Contents

Whole Allergen

d70 Acarus siro

d70 Acarus siro Scientific Information

Type:

Whole Allergen

Display Name:

Acarus siro

Allergen code:

d70

Family:

Acaridae

Species:

Acarus siro

Route of Exposure:

Inhalation (1)

Source Material:

Mite feces

Latin Name:

Acarus siro

Other Names:

Flour mite, grain mite

Summary

Acarus siro is one of the Acaridae family of storage mites, known commonly as the ‘flour’ or ‘grain’ mite. Traditionally associated with occupational exposure in rural workers, storage mites have been more recently linked with non-occupational sensitization in urban environments, causing contact dermatitis, rhinoconjunctivitis and asthma. A. siro is the most common species of mite contaminating food and is primarily found in stored cereal products, but has also been reported in other foodstuffs such as meat, pulses, dried fruit and cheese. Importantly, A. siro is also found in the home, in soft furnishings, mattresses and pet beds, where house dust mites (HDM) are characteristically found. Allergenic cross-reactivity between storage mites and HDMs is well documented.

Allergen

Nature

Acarus siro is mainly found in stored cereal-based food products, such as grain and flour (1), but has also been found in other food products, including cheese (2) (3), meat, pulses, dried fruit, tea and spices (4).

Of 571 UK shop-bought cereal-based food products, 21% were contaminated with storage mites. After home storage for 6 weeks, 38% of 421 food samples contained storage mites (1).

Storage mites are also found in the home; mattresses, soft furnishings, pets and pet bedding are all sources of storage mites (1).

Taxonomy

*Taxonomic tree of Acarus siro* (5)**
Domain	Eukaryota
Kingdom	Metazoa
Phylum	Arthropoda
Subphylum	Chelicerata
Class	Arachnida
Subclass	Acari
Order	Astigmata
Family	Acaridae
Genus	Acarus

Tissue

Mite feces are the most relevant source of allergens (6).

Epidemiology

Risk factors

Sensitization to storage mites, including Acarus siro, is an occupational hazard for farm workers (7) and bakers (1). However, approximately 25% of patients sensitized to storage mites have no relationship with farms or bakeries (1).

Environmental Characteristics

Worldwide distribution

Acarus siro is more common in temperate regions, as these meet its preferred physical conditions, but can be found worldwide (4).

Route of Exposure

Main

Inhalation (1).

Secondary

Contact dermatitis, commonly known as (‘grocer’s itch’) (2).

Clinical Relevance

Mites are the sources of potent allergens that sensitize and induce IgE-mediated allergic reactions (8). Sensitization to storage mites causes rhinitis, asthma and conjunctivitis (8) as well as human acarine dermatitis (2).

Among 200 patients assessed for rhinitis and/or asthma in an outpatient setting, 123 (61.5%) had sensitization to at least one storage mite (9). Patients with storage mite sensitization had the following disease characteristics: rhinitis (96.7%), asthma (46.3%), rhinitis and asthma (43.1%), conjunctivitis (25.2%) and atopic dermatitis (9.8%) (9).

When compared with non-allergic participants without asthma, sensitization to A. siro is associated with increased odds of having nasal allergies without asthma, and of having asthma with nasal allergies, but is not associated with having asthma without nasal allergies (1).

Molecular Aspects

Allergenic molecules

Table adapted from Allergome.org (10)

Allergen	Type	Mass (kDa)
Aca s 1	Cysteine protease	37.3
Aca s 10	Tropomyosin	33
Aca s 13	Fatty acid binding protein	14.7
Aca s 2	NPC2 family	14.6
Aca s 3	Serine protease	27.8
Aca s 4	Amylase	58
Aca s 7	Unknown	23
Aca s 8	Glutathione S-transferase	27.4

Allergens in storage mites are proteins with a variety of functions, including fatty acid-binding proteins, tropomyosin and paramyosin homologues, apoliphorine-like proteins, alfa tubulines and other allergens, such as group 2, 5 and 7 allergens. In particular, the allergen Aca s 13 (a fatty acid binding protein) reacted with serum from 23% of patients sensitized to A. siro (11).

Cross-reactivity

Allergenic cross-reactivity between storage mites and HDMs is well documented (1); in a European Community Respiratory Health Survey, 8% of people were found to be sensitized to HDMs and 10% to storage mites. Among those patients with storage mite sensitization, 44% were also sensitized to HDM (1).

Another study reported that 84% (n/N=274/310) of patients sensitive to house dust mites were also sensitive to storage mites; 73% (n/N=227/310) of patients were sensitized to all three species of storage mite studied (Lepidoglyphus destructor, Tyrophagus putrescentiae and A. siro). In this study, none of the patients tested positive for A. siro alone. Approximately 70% of patients undergoing skin prick tests (SPTs) had negative skin reactions to A. siro; additionally, the positive SPT observed measured between 3-12 mm, with a very small percentage measuring >12 mm. When A. siro-specific IgE were measured in the participating patients, 25% had a negative result (12).

Aca s 13 (a fatty acid binding protein) may help identify HDM sensitization as 23% of patients tested were sensitized to A. siro (11).

Compiled By

Author: RubyDuke Communications

Reviewer: Dr. Christian Fischer

Last reviewed:May 2022

References

Jõgi NO, Kleppe Olsen R, Svanes C, Gislason D, Gislason T, Schlünssen V, et al. Prevalence of allergic sensitization to storage mites in Northern Europe. Clin Exp Allergy. 2020;50(3):372-82.
Mullen GR, Oconnor BM. Chapter 26 - Mites (Acari). In: Mullen GR, Durden LA, editors. Medical and Veterinary Entomology (Third Edition): Academic Press; 2019. p. 533-602.
Mullen GR, Oconnor BM. 23 - MITES (Acari). In: Mullen G, Durden L, editors. Medical and Veterinary Entomology. San Diego: Academic Press; 2002. p. 449-516.
Trematerra P, Throne J. CHAPTER 5 - Insect and Mite Pests of Durum Wheat. In: Sissons M, Abecassis J, Marchylo B, Carcea M, editors. Durum Wheat (Second Edition): AACC International Press; 2012. p. 73-83.
CABI. Acarus siro (flour mite) Wallingford, UK2021 [cited 2021 6.12.21]. Available from: https://www.cabi.org/isc/datasheet/2522.
Erban T, Rybanska D, Harant K, Hortova B, Hubert J. Feces Derived Allergens of Tyrophagus putrescentiae Reared on Dried Dog Food and Evidence of the Strong Nutritional Interaction between the Mite and Bacillus cereus Producing Protease Bacillolysins and Exo-chitinases. Frontiers in Physiology. 2016;7.
Solarz K, Pająk C. Risk of exposure of a selected rural population in South Poland to allergenic mites. Part II: acarofauna of farm buildings. Experimental and Applied Acarology. 2019;77(3):387-99.
van Hage-Hamsten M, Johansson SGO. Storage mites. Experimental & Applied Acarology. 1992;16(1):117-28.
Marques ML, Rezende I, Cunha I, Gouveia J, Rodrigues Dos Santos F, Falcão I, et al. Allergic sensitization to storage dust mites: a prospective study of patients with respiratory allergy. Eur Ann Allergy Clin Immunol. 2020.
Allergome. Acarus siro 2021 [cited 2021 6.12.21]. Available from: http://www.allergome.org/script/search_step2.php.
Fernández-Caldas E, Iraola V, Carnés J. Molecular and biochemical properties of storage mites (except Blomia species). Protein Pept Lett. 2007;14(10):954-9.
Vidal C, Chomón B, Pérez-Carral C, González-Quintela A. Sensitization to Lepidoglyphus destructor, Tyrophagus putrescentiae, and Acarus siro in patients allergic to house dust mites (Dermatophagoides spp.). J Allergy Clin Immunol. 1997;100(5):716-8.