Mulberry Pollen
Summary
Mulberry (Morus alba) is a small to mid-sized tree belonging to the genus Morus of the family Moraceae. It is generally found in areas with a subtropical or mild temperate climate and primarily cultivated worldwide to raise silkworms. The pollination period for this tree ranges typically from April to May. According to some studies, mulberry pollen is considered a significant contributor to allergic pollen in the atmosphere. Exposure to its pollen may trigger symptoms like allergic rhinitis, allergic rhino-conjunctivitis, asthma, and, in some rare instances, contact dermatitis in sensitive patients. A cobalamin-independent methionine synthase protein, Mor a 2, has been detected as a significant novel allergen from mulberry pollen. Studies have also detected other allergenic proteins such as profilin, nsLTP (non-specific lipid transfer protein), a ubiquitin-like protein, and a cystatin-like protein from mulberry pollen extract. Significant cross-reactivity between mulberry pollen and other members of the Moraceae family, such as paper mulberry, breadfruit, fig-trees, and jackfruit, has been demonstrated. Cross-reactivity has also been reported with grass pollen and other tree pollens such as olive and alder.
Epidemiology
Worldwide distribution
Pollen grains are considered as one of the causes of allergic reactions in vulnerable populations around the world. Among the Moraceae family, mulberry pollen is considered one of the significant contributors to allergic pollen in Spain. According to a study conducted in Delhi, to determine the prevalence of airborne pollen concentration, the atmosphere's annual average mulberry pollen concentration was reported highest (34.2%) compared to other pollens.
An aeropalynological survey-based study of pollen grains and spores (palynomorphs) in the atmosphere was conducted in Argentina. According to the result, 12 tree pollens like Morus (mulberry), Platanus, Urticaceae, and others contributed more than 1% of the total annual aeroallergen concentration. The arboreal pollen grains from trees such as Morus (mulberry) were reported to contribute more than 68% relative to the total yearly pollen amount of each year. Studies have reported tree pollen from mulberry to be one of the inducers for naso-bronchial allergy in allergic patients.
In a non-randomized cross-sectional Spanish study among 30 patients with allergic rhino-conjunctivitis (ARC), 13 % confirmed positive SPT to mulberry pollen.
A study conducted in Arizona (US) among children with allergic rhinitis exhibited independent association with Bermuda grass and mulberry tree pollen sensitization among subjects of age 11 years. Among the children from the same age group, 23.6% of children with asthma and 18.2% of children with rhinitis reported positive SPT to mulberry pollen.
In the middle-east region, among the tree pollens, the allergenicity rate in allergic patients for mulberry pollen was reported as 7% in Pakistan, 1.4% in Qatar, 19.8% in Turkey.
Route Of Exposure
Main
The main route of exposure for mulberry tree pollen is through inhalation. The inhalation of this pollen allergen causes interaction with cellular IgE antibodies present across the respiratory pathway. This further leads to mast cell degranulation and release of other chemical mediators, resulting in upper respiratory tract symptoms like allergic rhinitis and conjunctivitis.
Clinical Relevance
Aeroallergen-mediated allergic rhinitis and asthma are primary reasons for increased morbidity, health care expenses, and productivity loss in the sensitive population. Such allergic reactions induced by aeroallergens may lead to cognitive impairment, sleep disturbance, and diminished quality of life among impacted children. Exposure to mulberry tree pollen may induce allergic reactions such as asthma, rhinitis, and in rare cases, contact dermatitis among allergic individuals.
Allergic rhinitis
A study was conducted on 48 patients with naso-bronchial allergy to analyze the sensitization rate to various allergens. In this study, 80% of patients with bronchial asthma also suffered from associated AR, while 25% of the AR subjects suffered from associated bronchial asthma. The SPT results showed 6.25% (3/48) positive SPT for mulberry pollen out of total allergens.
Asthma
An aerobiology study was conducted on 1000 patients with asthma or AR in Islamabad (Pakistan). The results revealed positive SPT to various pollens, molds, and house dust in 87.5% of the patients, of which 7% were sensitized to mulberry pollen.
Another study conducted in the US exhibited 23.6% positive SPT to mulberry pollen among children (aged 6 to 11 years) with asthma.
Contact Dermatitis
According to a case report from Spain, a 12-years old child developed symptoms of contact urticaria (itchy erythema and edema of hands and neck region, angioedema of lips and eyelids) after harvesting mulberry leaves. The symptoms disappeared after 2-3 hours. The child was tested positive for SPT and showed specific-IgE to mulberry pollen.
Other topics
Mulberry leaves consumption has demonstrated hypoglycemic and hypolipidemic effects among diabetic patients.
Prevention And Therapy
Prevention strategies
Avoidance
One of the main measures to be taken is to cut down the pollen amount in the respiratory system. During the pollen season, allergic patients are suggested to stay indoors or wear a mask outdoors to keep away from pollen allergens. In worsening conditions, patients might be advised to move to a pollen-free area.
Cross-Reactivity
Some studies have demonstrated significant cross-reactivity between mulberry pollen and other members of the Moraceae family, such as paper mulberry (Broussonetia papyrifera), fig-trees (Ficus species), jackfruit (Artocarpus heterophyllus), and breadfruit (Artocarpus altilis). Mulberry pollen cross-reactivity has also been reported with olive and alder tree pollen.
A study showed IgE-binding inhibition of mulberry pollen extract profilin (14-15 kDa) and nsLTP-10 protein by grass and olive pollen, demonstrating cross-reactivity of profilins with other plant pollens of unrelated family. The study also reported similar inhibition of IgE-binding from Parietaria judaica allergen towards mulberry pollen nsLTP-10 protein.
References
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