Type:
Whole Allergen
Whole Allergen
w14 Common Pigweed
w14 Common Pigweed Scientific Information
Display Name:
Common Pigweed
Route of Exposure:
Inhalation
Family:
Amaranthaceae
Species:
Amaranthus retroflexus
Latin Name:
Amaranthus retroflexus
Other Names:
Redroot Pigweed
Summary
Common Pigweed (Amaranthus retroflexus) is an insect and wind-pollinated plant that grows 20 to 150 cm in height. It is commonly known as an allergenic weed worldwide due to its capability to produce enormous number of pollen. This plant is abundantly found in pasturelands, farming fields, and grounds. The pollination period of this plant starts in August and lasts until October. It is extensively found in countries like Saudi Arabia, India, Iran, the US, Australia, etc. Pigweed pollen sensitivity may vary across geographical regions, depending on the tested population's diversity. It is considered one of the primary risk factors responsible for inducing respiratory allergies (like allergic rhinitis, allergic rhino-conjunctivitis, and asthma) in sensitive individuals. Pigweed pollen allergens Ama r 1 and Ama r 2 have been identified and listed in the IUIS database. Additionally, Ama r 3, a polcalcin allergenic protein from this pollen, has also been recognized by a study. Pigweed pollen has exhibited cross-reactivity with pollen from other species like lamb’s quarters, Russian thistle, Mesquite, Needle bush, and Burning bush.
Allergen
Nature
Common pigweed (Amaranthus retroflexus) belongs to the Amaranthaceae family. It is a monoecious (having both male and female flowers in the same part) plant. It pollinates through wind and insect (1, 2). The plant is dense to moderately covered with hair and can grow up to a height of 20 to 150 cm. The stem is usually straight, reddish at the base, and can be either be single or branched. This plant's leaves are broad, oval-shaped, grey-green, and 2 to 15 cm in length. The leaves possess prominent veins with hairs on the lower surface. The flowers are small, spiny, and arranged in terminal and axillary inflorescences. These inflorescences are silver-green with erect or flexible tip (3, 4). The blooming season for this plant ranges from August to October. Due to abundant pollen production quantities, it is now considered one of the most allergenic weeds globally (5).
Habitat
Common pigweed is an annual weed generally found in considerable quantities in open fields or lands used for farming or grassland areas (5). In Canada, common pigweed is found in 1000 meters elevated areas (6).
Taxonomy
| Taxonomic tree of Common pigweed (7) | |
|---|---|
| Domain | Eukaryota |
| Kingdom | Plantae |
| Phylum | Spermatophyta |
| Subphylum | Angiospermae |
| Class | Dicotyledonae |
| Order | Caryophyllales |
| Family | Amaranthaceae |
| Genus | Amaranthus |
| Species | Amaranthus retroflexus |
| Taxonomic tree of Common pigweed (7) |
|---|
Tissue
The pollen grains of pigweed have a cytoplasm, which is encapsulated by a thin layer called intine. Outside this layer, there is another layer called exine. The pigweed pollen diameter is about 17.8 to 22 micrometers in size (2).
Epidemiology
Worldwide distribution
The Amaranthaceae family pollens have been determined as a major cause of pollinosis in countries of the northern hemisphere like Asia, Europe, and the US. Specifically, common pigweed pollen from the Amaranthus genus is considered a major cause of respiratory allergy in the semi-desert regions around the world (8).
In an aeroallergen study conducted on 299 allergic rhinitis patients in Ahvaz, Iran, weed pollen was the most prevalent (89%) outdoor allergen. Among the weed allergens, 70.9% of the patients showed positive skin prick test (SPT) and total IgE to pigweed allergen (9).
A US-based study conducted on 562 military children (≤18 years) with rhinitis underwent SPT with an 8-test screening panel (various allergen mixes) (n=209) or a 51-aeroallergen standard panel (n=345). 8 patients were excluded from the study based on positive diluent or negative histamine control. 80.3% (277/345) of the patients showed positive SPT towards at least 1 aeroallergen. 27% of the 345 patients exhibited positive SPT towards pigweed allergen. (10).
In a retrospective review conducted in Northern Mexico on 247 allergic patients to determine the prevalence of hypersensitivity to common allergens, 5.4% of the individuals were found sensitive to pigweed pollen (11).
According to an aeroallergen sensitization study conducted in Thailand on 100 patients with allergic rhinitis, 16% of them showed positive SPT to pigweed allergen (12).
As per a study in Iran, 68.8 % of the total participating patients (n=306) and 85.6% of the atopic patients suffering from allergic rhinitis showed positive SPT and total IgE towards pigweed allergen in a study conducted in Iran (13).
Environmental Characteristics
Worldwide distribution
Common pigweed pollen is prevalent worldwide in various climatic conditions. It is one of the most allergenic weeds and considered a major risk factor for the development of respiratory allergy in temperate as well as dry areas such as Saudi Arabia, India, Iran, Kuwait and western parts of the United States, and the tropical regions of Africa, Australia, and the Mediterranean countries (2, 5, 6). It is also found in Pakistan, China, Russia, and Canada (4).
Route of Exposure
Main
The main route of exposure for common pigweed pollen is the airway (9, 13).
Clinical Relevance
Aeroallergens such as pollens are the primary reason for the development of allergic rhinitis. Allergic reaction induced by allergenic pollen such as pigweed pollen is characterized by sneezing, itching, runny nose, and nasal congestion. Allergic rhinitis, as well as asthma, are considered the most common allergic conditions. They are regarded as a significant public health issue throughout the world. They also pose a significant burden on the patients' quality of life and further leads to increase in cost of healthcare treatment (13, 14).
Allergic rhinitis (AR) and allergic rhino-conjunctivitis (ARC)
In an Iranian study conducted on 306 AR patients to determine the prevalence of various aeroallergens, 74% (226/306) of these patients were also suffering from ARC. The study revealed weed species as the most prevalent category of aeroallergen. As per the survey, positive SPT to pigweed was seen among 85.6% of the atopic individuals with AR (13).
Asthma
A prospective study was conducted on 189 patients who have asthma, AR, and ARC in Venezuela. 83.6% had moderate severity among 49 of the patients who have asthma. The results showed serum IgE antibodies to common pigweed in 8.6% of the patients' sera (14).
Another cross-sectional study was conducted on 1700 schoolchildren in Saudi Arabia. 27.5% (n=468) children among them were diagnosed with bronchial asthma and 20.8% (n=353) had 12-month nocturnal cough (severe asthma). Among these, 3.2% with bronchial asthma and 2% with severe asthma had sensitization to common pigweed allergen (15).
Prevention and Therapy
Allergen immunotherapy
In a study conducted on 51 patients with ARC, sublingual immunotherapy containing pigweed showed significant improvement (p< 0.05) while controlling allergic symptoms (17).
Prevention strategies
Avoidance
Avoiding exposure to a particular allergen can be the first step towards allergic rhinitis management (13).
One of the main measures that can be taken is to cut down the pollen amounts in the respiratory system. During pollen season, allergic patients are suggested to stay indoors or wear masks outdoors to keep away from pollen allergens. In worsening conditions, patients may be recommended to move or live in a non-pollen area (16).
Molecular Aspects
Allergenic molecules
Major allergens such as Ama r 1 and Ama r 2 have been identified and listed in the IUIS database for common pigweed pollen showing positive sensitization rates in patients with respiratory allergy (5, 18, 19). A polcalcin allergen Ama r 3 has also been identified from common pigweed in immunoblot analysis with a molecular weight of 10 kDa (8). Common weed allergens that have been recognised in the IUIS database have been listed in the table below (19).
| Allergen | Biochemical Name | Molecular Weight (kDa) | Allergenicity |
|---|---|---|---|
| Ama r 1 | Ole e 1-like protein | 18 (19) | A study conducted on 26 patients with respiratory allergy and seasonal rhinitis, 38.46% specific-IgE sensitivity was found to Ama r 1 (5). |
| Ama r 2 | Profilin | 14 (19) | A study conducted on 12 patients with respiratory allergy (AR and ARC) showed that 33% of patients sensitized to common pigweed reacted with Ama r 2 (18). |
| Allergen | Biochemical Name | Molecular Weight (kDa) | Allergenicity |
|---|
Biomarkers of severity
Ama r 2 (profilin) is considered a relevant marker allergen from common pigweed pollen (20).
Cross-reactivity
Studies have demonstrated extensive cross-reactivity between common pigweed and other allergenic species of the Amaranthaceae family such as lamb’s quarters (White goosefoot- Chenopodium album), Russian thistle (Saltwort- Salsola kali-pestifer) and Burning bush (Kochia scoparia) (5).
Cross-reactivity also exists between common pigweed and some unrelated allergenic species like Mesquite (Prosopis juliflora) and Needle bush (Acacia farnesiana) (5).
Compiled By
Author: Turacoz Healthcare Solutions
Reviewer: Dr. Christian Fischer
Last reviewed: January 2021
References
- W Bond GD, R Turner. The biology and non-chemical control of Common Amaranth (Amaranthus retroflexus L.) HDRA. 2007.
- Franssen AS, Skinner D, Al-Khatib K, Horak M, editors. Pollen morphological differences in Amaranthus species and interspecific hybrids2001.
- Tekiela D. Amaranthus species A current and emerging threat in Wyoming. 2017.
- redroot pigweed Amaranthus retroflexus L. [Internet]. 2011. Available from: https://accs.uaa.alaska.edu/wp-content/uploads/Amaranthus_retroflexus_BIO_AMRE.pdf.
- Morakabati P, Assarehzadegan MA, Khosravi GR, Akbari B, Dousti F. Cloning and Expression of Ama r 1, as a Novel Allergen of Amaranthus retroflexus Pollen. J Allergy (Cairo). 2016;2016:4092817.
- Costea M, Weaver SE, Tardif FJ. The biology of Canadian weeds. 130. Amaranthus retroflexus L., A. powellii S. Watson and A. hybridus L. Canadian Journal of Plant Science. 2004;84(2):631-68.
- CABI. Common Pigweed (Amaranthus retroflexus) 2019 [21-12-2020]. Available from: https://www.cabi.org/isc/datasheet/4652.
- Vakili Moghaddam M, Fallahpour M, Mohammadi M, Rasi Varaee FS, Mokhtarian K, Khoshmirsafa M, et al. Identification of polcalcin as a novel allergen of Amaranthus retroflexus pollen. Allergol Immunopathol (Madr). 2019;47(4):357-64.
- Assarehzadegan M-A, Shakurnia A, Amini A. The most common aeroallergens in a tropical region in Southwestern Iran. World Allergy Organ J. 2013;6(1):7-.
- Calabria CW, Dice J. Aeroallergen sensitization rates in military children with rhinitis symptoms. Ann Allergy Asthma Immunol. 2007;99(2):161-9.
- Ramos Morín CJ, Canseco González C. [Hypersensitivity to common allergens in the central region of Coahuila]. Rev Alerg Mex. 1993;40(6):150-4.
- Pumhirun P, Towiwat P, Mahakit P. Aeroallergen sensitivity of Thai patients with allergic rhinitis. Asian Pac J Allergy Immunol. 1997;15(4):183-5.
- Fereidouni M, Hossini RF, Azad FJ, Assarehzadegan MA, Varasteh A. Skin prick test reactivity to common aeroallergens among allergic rhinitis patients in Iran. Allergol Immunopathol (Madr). 2009;37(2):73-9.
- Sánchez-Borges M, Capriles-Hulett A, Torres J, Ansotegui-Zubeldia IJ, Castillo A, Dhersy A, et al. Diagnosis of allergic sensitization in patients with allergic rhinitis and asthma in a tropical environment. Rev Alerg Mex. 2019;66(1):44-54.
- Alqahtani J, Asaad A, Awadalla N, Mahfouz A. Environmental Determinants of Bronchial Asthma among Saudi School Children in Southwestern Saudi Arabia. International Journal of Environmental Research and Public Health. 2016;14:22.
- Xie Z-J, Guan K, Yin J. Advances in the clinical and mechanism research of pollen induced seasonal allergic Asthma. American journal of clinical and experimental immunology. 2019;8(1):1.
- Morris MS, Lowery A, Theodoropoulos DS, Duquette RD, Morris DL. Quality of Life Improvement with Sublingual Immunotherapy: A Prospective Study of Efficacy. Journal of Allergy. 2012;2012:253879.
- Tehrani M, Sankian M, Assarehzadegan MA, Falak R, Noorbakhsh R, Moghadam M, et al. Identification of a new allergen from Amaranthus retroflexus pollen, Ama r 2. Allergol Int. 2011;60(3):309-16.
- WHO/IUIS. Redroot Pigweed 2019 [04-12-2020]. Available from: http://www.allergen.org/search.php?allergensource=Amaranthus+retroflexus.
- Gadermaier G, Stemeseder T, Hemmer W, Hawranek T. Marker Allergens of Weed Pollen: Basic Considerations and Diagnostic Benefits in Routine Clinical Practice. 2017. p. 227-40.
