Acacia Pollen
Summary
Acacia longifolia belonging to the Fabaceae family is a small perennial tree, which is considered an invasive species due to its high seed-producing capability. Its flowering period usually falls during the end of the winter. This tree is native to Africa and Australia and is commonly cultivated globally in sub-tropical regions. This tree is prevalent in Australia, Africa, Arab countries, Malaysia, Africa, Brazil, United States, and Spain. Exposure to A. longifolia can manifest conditions like rhinitis, conjunctivitis, and asthma among allergic individuals. To date, no potential allergens have been identified from A. longifolia. Studies have demonstrated cross-reactivity of Acacia sp. pollen with Salsola kali, Amaranthus retroflexus, Chenopodium album, Kochia scoparia, mesquite, date, and ryegrass pollen.
Epidemiology
Worldwide distribution
Around 40% of allergic individuals are speculated to be impacted by allergies due to pollen. Tree pollinosis is one of the causes of increasing health issues worldwide, especially in arid and subtropical areas. As per studies, around 48% of pollinosis patients belonging to Arab countries were claimed to possess sensitization towards Acacia (wattle) tree pollen.
48.2% of individuals suffering from allergic rhinitis (n = 299) in Ahwaz reported positive skin prick test (SPT) towards A. longifolia pollen extract.
A study was conducted on 200 Malaysian asthmatic patients to analyze whether pollen allergy is associated with the prevalence of pollen in the air. A total of 21.5 % of patients exhibited positive SPT towards Acacia pollen extract.
A cross-sectional study conducted in Australia on 380 school children (with or without asthma) reported positive SPT towards A. longifolia in 12.4% (12/97) of children with asthma and 3.7% (4/107) in healthy children.
A United Arab Emirates (UAE) based study was conducted on 327 patients with ophthalmologic, dermatologic, and respiratory disease (speculated of allergic origin). The study reported 44% of patients to possess a positive family history of asthma. Acacia pollen allergen was claimed to be responsible for exhibiting positive SPT in 25.6% of the study population.
Risk factors
As per a study, a 56-year old female worker, while working majorily with wood from Acacia sp., reported persistent coughing and nocturnal dyspnea (for 3 years). The patient developed prolonged biphasic bronchospasm within 60 minutes of exposure to acacia. Prick test report was found to be positive in this patient for acacia wood.
In certain Mediterranean regions of France and Italy, pollen from mimosa (Acacia floribunda) belonging to the genus Acacia is claimed to be responsible for respiratory allergy. The study reported that 31% (33/106) of floriculturists showed positive SPT towards Acacia floribunda (mimosa).
Route Of Exposure
Main
The route of exposure for acacia pollen allergen is through the inhalation.
Secondary
Gum acacia is a derivative of the acacia senegal tree and is extensively used in lithography, pharmaceutical and cosmetics products. Gum acacia has been claimed to induce asthma upon occupational exposure, and in rare cases, its ingestion may trigger allergic symptoms.
Clinical Relevance
Exposure to A. longifolia pollen may elicit symptoms such as allergic rhinitis, conjunctivitis, and asthma among allergic individuals. According to a study, nasal obstruction was evident among patients with allergic rhinitis. This condition might adversely impact the allergic individuals by compromising the quality of life and sleep while creating an imbalance in their daily life activities (like studying, exercising, and working). Asthma and allergic diseases induced by tree pollens can cause recurrent hospitalization and absence from school among children.
Allergic rhino-conjunctivitis (ARC)
A population-based case-control study was conducted in Central Africa (Rwanda) among 3041 children to estimate the prevalence of vernal kerato-conjunctivitis (VKC). The prevalence of VKC was found to be around 4% (121/3041), and severe VKC was evident in 32.2% (39/121) of children with VKC. The study revealed that 11.9% showed positive SPT and 20.3% exhibited specific positive IgE concentration towards Acacia.
Allergic rhinitis (AR)
According to an Australia based cross-sectional study conducted on 380 school children from suburban and rural region, 12.4% (12/97) within the asthmatic group and 3.7% (4/107) from the healthy children group demonstrated positive SPT response towards Acacia (A. longifolia). Non-significant differences in severity (p= 0.16) were evident, and the tail value from Fisher’s Exact test was reported to be 0.568 for positive SPT towards Acacia among the groups (sub-urban and rural region).
A study was conducted on 206 Malaysian asthmatic patients with and without rhinitis to investigate common aeroallergens' prevalence through SPT. A total of 9.9% (11/111) reported positive SPT towards the Acacia sp. within the rhinitis group.
Prevention And Therapy
Prevention strategies
Avoidance
One of the main measures to be taken is to cut down 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.
Cross-Reactivity
Immunoblot inhibition assays confirmed IgE cross-reactivity of Acacia (A. farnesiana) with Salsola kali, Amaranthus retroflexus, Chenopodium album, Kochia scoparia, and Prosopis juliflora (mesquite).
Cross-reactivity between Australian Acacia sp. and ryegrass (Lolium perenne) was evident.
A study demonstrated A. longifolia (Sydney Golden Wattle) pollen to be cross-reactive with date (Phoenix dactylifera L.) pollen.
References
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