Acarus siro
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.
Epidemiology
Risk factors
Sensitization to storage mites, including Acarus siro, is an occupational hazard for farm workers and bakers. However, approximately 25% of patients sensitized to storage mites have no relationship with farms or bakeries.
Route Of Exposure
Main
Inhalation.
Secondary
Contact dermatitis, commonly known as (‘grocer’s itch’).
Clinical Relevance
Mites are the sources of potent allergens that sensitize and induce IgE-mediated allergic reactions. Sensitization to storage mites causes rhinitis, asthma and conjunctivitis as well as human acarine dermatitis.
Among 200 patients assessed for rhinitis and/or asthma in an outpatient setting, 123 (61.5%) had sensitization to at least one storage mite. 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%).
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.
Cross-Reactivity
Allergenic cross-reactivity between storage mites and HDMs is well documented; 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.
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.
Aca s 13 (a fatty acid binding protein) may help identify HDM sensitization as 23% of patients tested were sensitized to A. siro.
References
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