Wall pellitory
Allergen
Summary
Parietaria officinalis (P.officinalis), also known as wall pellitory, is a wind-pollinated, perennial plant that commonly grows in the shade of the walls with a height of about 30-100 cm. This species (Parietaria) possesses a prolonged pollination period, which starts during the beginning of spring and continues till summer. Additionally, a second shorter pollination period has also been reported, initiating from the end of August till October. The plant can grow in waste places and rocks. This weed pollen is predominantly found in Italy, Southern and Western Europe, North Africa, United States, Croatia, and Australia. P.officinalis pollen can trigger conditions like rhinitis, asthma, conjunctivitis, and seasonal hay fever. The allergen Par o 1 from P.officinalis pollen has been identified and listed in the IUIS database. P.officinalis pollen exhibits cross-reactivity with P. judaica, house-dust mites, birch, mugwort, and olive pollen.
Epidemiology
Worldwide distribution
Pollen from P. officinalis (wall pellitory) has been identified as one of the primary allergens responsible for pollinosis in western and southern Europe. A US-based prospective study identified 22.6% (31/137) as the frequency of positive response towards pellitory (weed) pollen among the study population. An Italy-based retrospective study on 793 respiratory allergic patients (6-85 years) confirmed 32.4% (108/333) of the patients were sensitized towards P. officinalis pollen. A cross-sectional study in Indonesia involving 106 respiratory allergic patients (19-59 years old) has reported 4.7% (5/106) of the study population to possess IgE-mediated sensitivity towards wall pellitory pollen. A retrospective Turkey-based study conducted on 7492 patients (with AR and/or asthma; 16-82 years) reported 2.4% (182/7492) as the prevalence of P. officinalis pollen-mediated sensitization among the study population.
Route Of Exposure
Main
The route of exposure for wall pellitory pollen is through inhalation.
Clinical Relevance
The pollination season of P. officinalis has been found to be usually prolonged, along with a high pollination level. Therefore, sensitive patients have been reported to experience severe symptoms during this period. Exposure to P. officinalis weed pollen has been reported to elicit conditions such as rhinitis, asthma, conjunctivitis, and seasonal hay fever.
Rhinitis, asthma, and conjunctivitis
A retrospective study conducted on respiratory allergic patients revealed wall pellitory as one of the sensitizing allergens. As per the study, patients sensitized towards wall pellitory pollen exhibited conditions like rhinitis (39.9%; 114), asthma (78%; 223), and conjunctivitis (94.1%; 269). A retrospective study reported 25% (71/284) of the allergic conjunctivitis patients to exhibit positive skin prick test towards P. officinalis pollen. The study further claimed that sensitization towards seasonal allergens like P. officinalis could lead to pollen-mediated allergies.
Prevention And Therapy
Avoidance
One of the main measures to be taken is to reduce the amount of pollen in the respiratory system. During pollen season, allergic patients are suggested to stay indoors or wear a mask outdoors to keep away from pollen allergens. In worsening conditions, patients may be advised to move to a non-pollen area.
Allergen immunotherapy
In a study conducted on 26 allergic rhinitis patients, sublingual immunotherapy containing P. officinalis exhibited significant improvement in conditions like sneezing (p=0.005), nasal itching (p=0.003), rhinorrhoea (p=0.008), and nasal congestion (p=0.003).
Cross-Reactivity
P. officinalis (wall pellitory) pollen has also been found to exhibit cross-reactivity with house-dust mites (D. farina, D. pteronyssinus), birch, mugwort, and olive pollen. Moreover, cross-reactivity between P. judaica and P. officinalis pollen extract has also been reported by a study.
References
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