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f47 Garlic

Code f47
LOINC LP169809-2
Family Alliaceae (Liliaceae)
Genus Allium
Species sativum
Route of Exposure Ingestion and Skin contact
Source Material Garlic powder
Latin Name Allium sativum
Other Names Cultivated garlic, Poor Man's treacle
Categories Food Of Plant Origin, Vegetables

Summary

Garlic (Allium sativum) is one of the most common spices used in many cuisines around the world as well as in traditional medicine. Different varieties of garlic are mainly categorized into the hard neck and soft neck variety. Garlic producing countries include Asia, the Mediterranean, Europe and North and South America with China as a leading producer. Allergy to garlic or allium species is extremely rare but should not be underestimated. Owing to the high consumption of garlic around the world, it should be included in the diagnostic food allergy battery. The active properties of garlic are attributed to pungent volatile oil (0.1%) rich in sulfide compounds. The major route of exposure is contact with raw garlic while hypersensitivity is also seen with ingestion or inhalation of garlic dust (secondary exposure route). Garlic is a known type I allergen which also causes allergic contact dermatitis. Clinical manifestations of garlic allergy include a broad spectrum of diseases ranging from gastrointestinal symptoms to contact dermatitis, urticaria, occupational asthma or even anaphylaxis. Clinically relevant allergy to garlic is attributed to the presence of alliin lyase (major allergen) and low molecular weight component diallyl disulfide in raw garlic. These allergens are found to be heat labile and thus cooked garlic shows less allergenicity. These allergens show significant cross-reactivity to other members of Amaryllidaceae family-like onion, leek, shallot and chives. Prevention or avoidance of the food items containing garlic is the best method to reduce or prevent allergenic responses.

Allergen

Nature

Garlic (Allium sativum) is one of the oldest plants used by the family Liliaceae or Amaryllidaceae as traditional medicine. It is a small aromatic annual herb with a very pungent odor (1) similar to onion and used as flavoring agent in cuisines worldwide. The part of the plant used is a small underground bulb, also called as “head” or knob. This is made of sections called clove, each of which remains enclosed in a thin membrane. It possesses elongated, contracted and flat leaves with hermaphrodite flowers. Garlic cloves are used for propagation (2). Onions, leeks, shallot, asparagus and chives are also members of the genus Allium (3).

Habitat

Garlic grows best in sandy loam or loam soil of depth >50 cm and pH 6-7.  Temperature ranging from 16-18ºC and altitude of 1.1-1.5 m above the sea level is suitable conditions for garlic cultivation. It can be grown all year round in different parts of the world. The yield of garlic depends on the optimum irrigation and usually requires rainfall of 350-600 mm during the growth period (2, 4).

Taxonomy

Garlic belongs to the phylum Spermatophyta, and class Monocotyledonae. The genus Allium consists of hundreds of species. As much as 10 different varieties of garlic have been found in different parts of the world based on genetic DNA analysis like A. ursinum, A. vineale, A. oleraceum, A. canadense, A. ampeloprasum, A. odorum, A. fragrans etc. in addition to single clove garlic or pearl garlic found in China. They can be categorized into 2 varieties as hard neck (A. sativum var. ophioscorodon) and soft neck garlic (A. sativum var. sativum) (2). 

 

Taxonomic tree of garlic  (2)  
Domain Eukaryota
Kingdom Plantae
Phylum Spermatophyta
Subphylum Angiospermae
Class Monocotyledonae
Order Asparagales
Family Amaryllidaceae
Subfamily Allioideae
Genus Allium
Species Allium sativum

 

Tissue

The bulbs of garlic are rich in volatile oil consisting of several sulfur-containing compounds including allicin and diallyl disulfide which are found to produce hypersensitive reactions (1, 2, 5, 6)

The most biologically active sulphur containing compound in garlic is allicin. It is lipid soluble and is easily destroyed by heating or cooking. It is the main culprit for the allergic reactions to garlic (1).

Epidemiology

Worldwide distribution

Food allergies are becoming increasingly common throughout the world affecting up to 10% population, more commonly affecting children rather than adults (7). Although, allergy to common spice like garlic is rarely reported it should not be underestimated. Owing to the high consumption of garlic around the world, it should be included in the diagnostic food allergy battery (8). Limited information is available for allergies to the members of Liliaceae family (9). Very few studies have examined the prevalence of spice allergy, especially to garlic. A study with 1092 adult Spanish patients (all patch tested) reported a prevalence of sensitization to diallyl disulfide to be 1.7% (5). A retrospective study in Saudi Arabia with 108 patients already screened for garlic and onion specific IgE antibodies reported garlic and onion specific IgE antibodies in 13.8% of patients (10). Another observational cross-sectional study conducted on 8109 Spanish patients reported food-related allergic symptoms in 11.39% (924 patients) including 2.92% to be sensitized for edible bulbs. Among them, garlic hypersensitivity was found in 17 patients (8). 

The hypersensitivity to garlic is specific to age group as case reports have been found in infants, children as well as adults. A previous study has reported that 4.6% of children and 7.7% of adults were sensitive to Liliaceae vegetables including garlic, onion and chive in skin prick tests (11). 

 

Environmental Characteristics

Living environment

Garlic is usually stored at room temperature with 60-70% humidity and refrigeration should be avoided (2, 4).

Worldwide distribution

Garlic is the oldest cultivated herb and widely used spice in several cuisines around the world; Asian, French and Italian being the major ones. It has originated from Central Asia (2) and is used in India and China for more than 5000 years (12). Garlic producing regions include Asia, the Mediterranean and North and South America,with China as the leading producer (8). Spain is the leading producer country of Garlic in Europe. Other important garlic producing countries reported are Turkey, India, Thailand, Korea Republic, Egypt, etc. (12).

Route of Exposure

Main

Skin contact of raw garlic can typically affect thumb, index and middle fingertips leading to contact dermatitis (13). Allicin being a membrane-permeable compound can enter the cells and may produce toxicity (1).

Secondary

Ingestion of garlic and also the inhalation of garlic dust and even garlic bulb vapor can cause dermatitis, rhinitis, asthma, urticaria, or gastrointestinal symptoms (8, 14).

Detection

Allergic rhinitis

Three cases of allergic rhinitis (AR) in adults were reported due to occupational exposure to garlic. All three patients lately developed asthma preceded by AR as an allergic response due to exposure to garlic or garlic powder. The patients were symptomatic when in contact with garlic and remain symptomless without garlic contact (15).

Asthma

Bronchial asthma was reported very early due to occupational exposure of garlic dust. Certain studies have reported scattered cases of asthma as an allergic response to garlic (8, 10). An epidemiological study of 150 spice mill workers for analyzing specific exposure to garlic and chili pepper allergens demonstrated their association with asthma or probable obstructive lung disease. The study reported the prevalence of spice-dust-related asthma-like symptoms in 17% of workers. Sensitization to garlic was seen among 19% of workers and among them, 13% was monosensitized to garlic and 6% cosensitized to chili pepper (16).

Atopic Dermatitis

Pandhi et al. (2020) evaluated 100 Indian hand eczema patients for clinical subtype and pattern of contact sensitization to various allergens causing hand eczema. Exposure to garlic was found to be the etiological reason in 9% of patients with allergic contact dermatitis to be the most common clinical pattern of hand eczema (17).

Other diseases

Allergic contact dermatitis is considered to be the most common allergic reaction with garlic. A study evaluating 1092 patients for patch tests to diallyl disulfide revealed 19 patients with a positive test with hands as the most frequently affected site. This study revealed sensitivity to diallyl disulfide to be more common in females than males (5). The study to screen food allergy on 108 Saudi patients showed several allergic symptoms in sensitized individuals like urticaria in 5, gastrointestinal symptoms in 5, contact dermatitis in 3 and asthma in 2 patients. (10). Another study on 8109 Spanish patients presented hypersensitivity reactions to 44 aeroallergens and food allergens including garlic and onion. The hypersensitive symptoms to garlic majorly included chronic diarrhea and dyspepsia along with asthma and pulpitis in index fingers and thumb of left hand (8).

Anaphylaxis after oral intake of garlic is extremely rare (9), Treudler, Reuter (18) There was a reported case of anaphylaxis in an allergic 48-year old man (with seasonal AR and gastroesophageal reflux) after ingestion of raw garlic. He had a history of generalized urticaria, angioedema and vomiting after ingestion of garlic sauce and also urticaria, angioedema and hypotension after ingestion of tzatziki (yoghurt, garlic, olive oil, vinegar, cucumber and pepper). IgE binding assay identified alliinase as the major causative allergen in addition to 8 other proteins which may be responsible for an allergenic response (18). An unusual case of anaphylaxis in a 16-month old male infant is also reported and is attributed to the consumption of garlic flavored yogurt. The patient presented with diffuse erythema, itching, swelling of the eyelids and lip, vomiting, cough, and wheezing and was diagnosed as anaphylaxis. The sensitization of infants may be through breast milk or during pregnancy as the mother testified to consume garlic containing food during pregnancy.(9).

Other topics

The array of garlic induced skin reactions are varied in different patients. Few studies reported irritant contact dermatitis on exposure to garlic (19, 20). Pemphigus was also reported attributing to garlic as a dietary factor (21).

Prevention and Therapy

Prevention strategies

Avoidance

Avoiding garlic containing food items can control allergenic asthma or contact dermatitis.

Susceptible individuals when having contact with raw garlic or accidental ingestion of garlic can lead to a wide array of symptoms ranging from gastrointestinal symptoms to urticaria, dermatitis, asthma or even anaphylaxis (3, 9, 14, 18). The possible way to avoid developing such garlic allergic symptoms is to carefully choose the food items without garlic (22). A study in the UK has shown that consumers have a good understanding of food allergies and are concerned about their own food allergy management practices which include avoiding the allergen by checking food labels (23).

 

Molecular Aspects

Allergenic molecules

Allergenicity to garlic is thought to be due to the presence of sulfur compounds. The major allergen identified in garlic is alliin lyase with a molecular weight of 56 kDa (6, 8, 9) This is reported to be present in raw garlic and when heated for 5 min, is degraded to small fragments of 10 kDa (14).

Garlic is a known type I allergen and also causes allergic contact dermatitis. Garlic is found to contain several low molecular weight type IV contact allergens like diallyl disulfide, allicin, and allyl propyl disulfide (5). The allergen diallyl disulfide in garlic is thought to be responsible for finger-pulp dermatitis (thumb, index and middle fingertips) when garlic is held for chopping (5, 13).

A pool of sera of 17 sensitized patients to garlic showed IgE binding to two proteins of molecular weights about 12 and 60 kDa with 60 kDa protein showing higher intensity to garlic. Moreover, immunodetection revealed an association between the symptoms and specific lipid transfer proteins (LTPs) to garlic but no cross-reactivity with other LTPs in peach and wheat (Mediterranean diet) (8).

Cross-reactivity

Widespread cross-reactivity among different members of the Liliaceae family has been described. Alliin lyase, a major garlic allergen, was found homologous to alliin lyases found in onion, leek and shallot from the same family (6). Allergic cross-reactivity has also been shown among members of the Liliaceae family and grass pollen antigens (8).

Compiled By

Author: Turacoz Healthcare Solutions

Reviewer: Dr. Fabio Iachetti

 

Last reviewed: November  2020

References
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