t9 Olive Pollen

The Olive trees are evergreen. The trunk is large and bears several branches with cascading twigs (1). There are nearly 3000 varieties of the olive tree.  

Olives thrive best in dry summer seasons. Olives are abundant in North America (especially in California and Arizona along with Mexico), South America (Chile, Peru, and Argentina), Africa, China, Japan, and Australia. They are used as ornamental trees for landscaping purposes in parks as well as along the sides of the roads in urban cities.

The flowering season for Olive is usually between May and June. Pollen from the Olive tree is the most significant allergy-causing agent in the region of the Mediterranean basin. In Spain, the second most prevalent cause of allergy after grasses is Olive.

The pollination period for Olive pollens is between Mid-April and June-end in Spain and Italy.

Plants from the Oleaceae family are widely used as ornamental plants and trees in cities. Since the flowering season of each of these genera differs, the urban dwellers who are sensitized to olive pollen may present allergenic reactions during the winter (resulting from pollens of ash), the spring (due to allergens from olive pollen), and early summers (as a result of privet pollens).

The allergen triggers AR and asthma in patients sensitive to this allergen. As patients with olive pollen allergy show polysensitization (often due to cross-reactivity within its own species), identifying the primary allergen causing the sensitization is essential. Changes in climate and sensitization spectrum of an individual must be recognized so that the exposure to pollens can be prevented as the patient may avoid visiting areas with Olive trees.

The main marker for primary allergy against Olive pollen is Ole e 1. Olive shows cross-reactivity with other genera, including privet, ash, and lilac in the Oleaceae family. The cross-reactivity between Olive and Ash is so extensive that Ole e 1 acts as a very good marker allergen for diagnosing allergy against ash pollen. 

Nature

The Olive tree grows to a height of 8-15m. The tree grows at a slow pace and retains green leaves throughout the year. Olive trees are a long-lived species; they can live up to 1000 years. The trunk is large and bears several branches with cascading twigs (1). Olive's most useful genotypes are selected based on characteristics of bigger fruits, higher fruit set, and higher oil content, and are cultivated by vegetative propagation (2). Olive's flowering season is usually between May and June (3). There are nearly 3000 varieties of the olive tree (4).

Habitat

The Olive trees require warm, dry summers and rainy, cool winters. Olive can grow on many soil types; however, sandy loam soils are the best for Olives. Olives can also tolerate drought. Olives also thrive along the edges of cultivations or abandoned orchards (1).

Taxonomy

Worldwide distribution

Pollen from the Olive tree is the most significant allergy-causing pollen in the region of the Mediterranean basin (6-10). In Southern Europe, pollen from Olive trees forms the most significant cause of Type-I respiratory allergy after grass pollen allergens (3). Olive pollen accounts for the majority of cases of pollinosis in Mediterranean countries. In many Spain and Italy provinces, Olive tree pollen is the primary cause of pollinosis (4). In the South-West Mediterranean and some North America regions, Olive pollen allergens form the most significant cause of respiratory allergy (9, 11).

In Spain, the second most prevalent cause of allergy after grasses is Olive (4, 12). The annual pollen counts of Olive in Southern Spain are twice as high as those in Central Spain and eight times higher than in Northern Spain. In Northern Spain, the concentration and potency of Olive pollen were lower than those in the Mediterranean countries (6). In olive-growing areas, high sensitization to olive has been observed. A total of 58% of people in Toledo, 78% in Ciudad Real, and almost 97% population in Jaen are sensitized to pollen from Olive trees in Spain (10). Another study in Spain found that out of 195 patients in the age range of 14-76 years, with pollen allergy and suffering from rhinitis and/or asthma, 53% were monosensitized to Olive tree pollens (13). The sensitization for Olive pollens was the highest (16.5%) amongst all tree allergens in 532 children with allergic symptoms and age less than 15 years from 21 primary care centers in Italy and Spain (14). Olive was the least sensitizing agent amongst Parietaria, dust mites, grass pollen, and Olive pollens for 462 elderly allergic patients in Campania (Southern Italy) (15).

Out of 952 allergic patients (of age 41 years) from Monchengladbach (North Rhine-Westphalia) and Munich (Bavaria) in Germany, 26% of patients were allergic to Olive pollens. The percentage of patients with Olive allergy was two times higher in Bavaria than in NRW (p= 0.000) (8).

In Northern Greece, Olive pollen was the least sensitizing allergen affecting 231 (14.71%) out of 675 school-going children in the age range of 6-17 years (16).

Risk factors

There is a significant variation in the pollination period of Olea, depending on the geographical location. The pollination period for Olive pollens is between Mid-April and June-end in Spain and Italy (4). During the pollination period, there is an increase in the number of allergic individuals and individuals with severe symptoms due to the rise in pollen production (4).

The cross-reactivity between seasonal allergens may cause allergic reactions throughout the year in individuals sensitized to pollen from the Oleaceae family. As a result, aggravation of the allergic response induced by Olive during winters or spring could be due to allergens of the Ligustrum genus during summers. Thus chronic symptoms in patients are sensitized to pollen allergens from the Oleaceae family (17).

Plants from the Oleaceae family are widely used as ornamental plants and trees in cities. Since the flowering season of each of these genera differs, the urban dwellers who are sensitized to Olive pollen may present allergenic reactions during the winter (resulting from pollens of ash), the spring (due to allergens from olive pollen), and early summers (as a result of privet pollens) (3). 

Living environment

Olives thrive best in dry summer seasons (18). Olives are used as ornamental trees for landscaping purposes in parks and along the sides of the roads in urban cities (1, 11).

Worldwide distribution

The olive tree is native to Asia Minor. It propagated to the Mediterranean region and was later introduced into North America (especially in California and Arizona along with Mexico), South America (Chile, Peru, and Argentina), South Africa, and Australia (4, 19). It was also popularized in North Africa. In the present day, Olive trees are also found in China and Japan. In many Spain and Italy provinces, the cultivation of the olive tree is very intensive (4).

Main

Pollens from Olive trees are pollinated mainly by birds (1). Olive tree pollens enter the body via the upper airways (6).

Allergic rhinitis (AR)

AR developing from Olive pollens varies greatly with geographical location (12, 19). Sensitization to Olive pollen is seen in nearly 70% of patients with respiratory symptoms in the Mediterranean regions (20). Seasonal respiratory allergy is most frequently caused by pollens from Olive trees in the Mediterranean area(20). Specific nasal responses to Olive pollen allergens have been shown in Local Allergic Rhinitis (LAR) (9).

Asthma

Among a total of 277 children between the ages of 6 and 14 years, with bronchial asthma in South Jordan, 18% were sensitized to Olive pollen (21). Out of 545 Turkish patients between the ages of 30 and 49, diagnosed with AR and/or asthma, 33.2% of patients were sensitized to Olive pollen. More number of patients with mild asthma were sensitized to Olive pollen (52%) compared to moderate and severe asthma patients (22).

Other diseases

Apart from specific symptoms (like rhino-conjunctivitis and asthma), pollen allergies also cause sleep disorders, fatigue, depression, and impaired cognition in allergic patients. These symptoms increase during pollen season and decrease life quality in allergic patients (23, 24).

Other topics

Pollinosis resulting from Olive pollens depends significantly on the rise in pollen counts (4). An increase in the production of Olives increases the concentration of Olive pollens, which in turn may increase the allergic sensitization and also the severity of symptoms of allergic respiratory disease (8). This impacts the sensitization of patients to different allergens. The allergens that may be minor for a population residing in areas of low-pollen counts may prove to be major allergens in regions with increased pollen counts (4).

Allergen immunotherapy (AIT)

As patients with Olive pollen allergy show polysensitization, identifying the primary allergen causing the sensitization is extremely important for a proper AIT as molecular diagnosis changes the indication for AIT (25, 26).

Prevention strategies

Since the period of pollination of Olive differs according to climate and geography, changes in climate and sensitization spectrum of an individual must be recognized so that the exposure to pollens can be prevented by instructing the patient to avoid visiting areas with Olive trees. Also, the adoption of proper diagnostic measures and the development and administration of specific immunotherapy will help prevent Olive allergy as much as possible (8).

Avoidance

Pollen calendars demonstrate the diversity of pollen aeroallergens of a particular area along with the duration and intensity of the pollen season for each type of allergen. This is important as it will enable the patients allergic to pollens, decrease their exposure on days when the pollen counts are high, either by taking the necessary precautions or by planning their outdoor activities carefully (10).  

Allergenic molecules

The following allergenic molecules from Olive have been characterized (4, 27):

1. Ole e 1
2. Ole e 2
3. Ole e 3
4. Ole e 4
5. Ole e 5
6. Ole e 6
7. Ole e 7
8. Ole e 8
9. Ole e 9
10. Ole e 10
11. Ole e 11
12. Ole e 36kD.
13. Ole e 13 (found in raw olive)  (17)
14. Ole e 14 (low IgE activity) (17).

Ole e 1 makes up more than 10% of pollen's overall protein content in the main varieties of the Olive tree. However, the fruit, leaf, and stem lack Ole e 1 (12). 

Biomarkers of severity

The main marker for primary allergy against Olive pollen is Ole e 1. The prevalence of sensitization to Ole e 1 amongst patients allergic to Olive ranges from approximately 70 to more than 80% (12, 28).

Cross-reactivity

Olive shows cross-reactivity amongst different genera in the Oleaceae family, including Ash and Privet (17, 19). Widespread cross-reactivity is seen between Olive and ash to the extent that Ole e 1 works as a very good marker allergen for diagnosing allergy against ash pollen (20).   

Ole e 1-specific IgE in the serum of patients sensitized to Olive pollens inhibits cross-reactivity of pollens from Oleaceae family with those of non-Oleaceae families (12).

Olive also presents cross-reactivity with Privet pine, Birch, Mugwort, and Cypress (18).

Author: Turacoz Healthcare Solutions

Reviewer: Dr. Magnus Borres

Last reviewed: October  2020