Effectiveness of Coconut Oil Administration on Immunoglobulin E (Ige) Levels in Dogs with Atopic Dermatitis

Fiorell C, Jayanti PD, Dwinata IM, Sudimartini LM and Suartha IN

Published on: 2024-05-16


Atopic dermatitis is a common, chronic and complex skin inflammation involving a combination of genetic factors. Atopic dermatitis is associated with hypersensitivity mediated by IgE, an immunoglobulin that plays a role in allergic mechanisms to environmental allergens. Dogs with atopic dermatitis experience increased levels of IgE in the blood due to an allergic response that occurs in the body which is shown by clinical signs in the form of excessive itching that requires treatment. Treatment of atopic dermatitis is generally carried out with chemical therapy as a symptomatic treatment to reduce itching and skin lesions with pharmacological agents, but drug limitations, high side effects and relatively expensive prices can be the biggest obstacle in the implementation of chemical therapy. Coconut oil is one of the natural ingredients rich in anti-inflammatory, antihistamine, antioxidant, and moisturizing effects that are often used as an alternative symptomatic treatment. This study aims to determine the effect of coconut oil administration on reducing the IgE levels of dogs with atopic dermatitis through the administration of 5 ml of coconut oil orally in the feed every day once and topical application of coconut oil by massage method for 15 minutes every three days for 35 days. The results of the One-way ANOVA test stated that there was no significant difference in IgE levels before and after treatment (P> 0.05), which was characterized by fluctuations in the IgE levels of the five research dogs during treatment.


Dog; Atopic dermatitis; CAD; Coconut oil; Allergy; Itching; IgE


Canine Atopic Dermatitis (CAD) is a common, chronic and complex skin inflammation involving a combination of genetic factors affecting the skin barrier, environmental factors and immunological responses [1]. CAD occurs in dogs due to allergic reactions to most environmental allergens characterized by excessive itching (pruritus) especially on the face, ears and distal extremities [2]. The disease has a genetic predisposition and is associated with hypersensitivity mediated by IgE, an immunoglobulin that plays a role in the mechanism of allergy to environmental allergens [3]. Early clinical signs of CAD are symptoms associated with pruritus (e.g. excessive scratching, chewing, rubbing or licking of the skin) [4]. Immunoglobulin E (IgE) is an antibody produced by the immune system in response to the possible invasion of a foreign substance shown by an allergic response [5]. Individuals who experience allergies or have atopic diseases will produce IgE after exposure to allergens, even at low exposure concentrations [6]. Measurement of IgE levels can be done through blood tests, considering that an increase in blood IgE levels can be a sign that the body is overreacting to an allergen, becoming a marker of allergic disease [7]. Dogs with CAD will experience an increase in blood IgE levels due to an allergic response that occurs in the body which will then be shown by clinical signs in the form of excessive itching that requires treatment. Immunoglobulin E plays a central role in the inflammatory process caused by allergens in various atopic diseases, making it an effective target for therapy in the treatment of various diseases associated with allergic or immunological responses. Treatment of CAD is generally symptomatic with several methods such as identification and avoidance of flare factors (avoidance of allergens, irritants, environmental factors, stress, infections, and hormonal changes), improvement of skin and coat hygiene and care, and reduction of pruritus and skin lesions with pharmacological agents [4, 8]. However, drug limitation, high side effects and relatively expensive price can be the biggest obstacle in the implementation of chemical therapy. Natural ingredient therapy may be one option that can be applied to overcome this problem. Coconut oil is a natural ingredient that is rich in benefits and is often used as an alternative for traditional medicine. Coconut oil contains at least 90% saturated fat, most of which is Medium Chain Triglycerides (MCT). The MCT component itself consists of good fatty acids such as lauric acid, capric acid, caprylic acid, oleic acid, and other acids which are polyunsaturated and monounsaturated fatty acids that are antibacterial, antifungal and antiviral [9]. The saturated fatty acids contained in coconut oil have various beneficial properties, such as lauric acid which is reported to have antimicrobial and antiviral properties [10]. Linoleic acid is reported to have collagen enhancement, skin hydration, and antibacterial functions [10, 11] and palmitic acid is reported to help maintain skin moisture [12]. Coconut oil also contains vitamin E which is useful as an antioxidant, anti-inflammatory, reduces interleukin production, and is good for chronic skin inflammation [13,14]. Several studies show the benefits of using coconut oil on various skin problems in dogs, such as moisturizing itchy and dry dog skin, killing bacteria, helping to repel parasites such as fleas and cage flies, as a treatment for allergies, acne, and scabs, healing wounds, reducing inflammation in the skin, to fight skin fungi such as candida, preventing hair damage, and protecting the skin from UV rays [15-20]. CAD therapy with coconut oil can be done to reduce the severity of pruritus that occurs which is reflected by decreasing blood IgE levels.

Matherials and Methods

Study Animals

The dogs used in this study were 5 dogs with CAD with H-0 (day before treatment) as control. The dogs used as research objects are local Balinese dog breeds or called Balinese village dogs aged 3-5 months. The object of research has a variety of pruritus severity, where the object of research used has a complex lesion with moderate lesion scoring based on the lesion scoring guide by Cahyaniarta et al. (2019) [21].

Study Design

This study is a Pre-Experimental study to observe pre and post treatment changes. This study only applied one treatment with six sampling times, where all five samples received the same treatment, namely oral and topical administration of coconut oil (massage) for 35 days. Based on the calculation of the number of samples according to Goh (2008) [22], the number of samples used was 5 samples of atopic dermatitis dogs considered sufficient to conduct this study. Sampling was done once a week, with day 0 as the control sample, then day 7, 14, 21, 28, and 35 as the treatment sample. The location of dog maintenance and sampling was carried out at the Animal Hospital, with the address Jalan Raya Sesetan Gg. Markisa No.6, South Denpasar, Denpasar City. The separation of blood and serum samples was carried out at the Biomedical Laboratory of the Faculty of Veterinary Medicine, Udayana University. Examination of blood IgE levels was carried out at the Veterinary Immunology Laboratory, Faculty of Veterinary Medicine, Udayana University.

Sample Collection

Serum sample is collected by collecting 2 ml blood sample from each of the five dogs from the cephalica antebrachii lateralis or saphenous vein using a sterile syringe and collected in a Plain Red Top Blood Tube Vacutainer. Each sample will be centrifuged using a centrifuge at 1,500 rpm, causing the various blood components to separate based on their respective densities. Examination of IgE levels in blood, serum samples will be tested using Canine IgE ELISA Kit Cat.No E0208Ca. The stages of checking IgE levels using the kit begin with the preparation of all reagents, standard solutions, and samples at room temperature before use. The stage continues by adding samples and ELISA reagents to each well on the test plate, where at this stage, 50μl of standard solution is added to the standard well, 40μl of sample and 10μl of anti-IgE antibody to the sample well, and 50μl of streptavidin-HRP to the sample and standard wells. The plate was then covered and incubated for 1 hour at 37°C. The plate was then washed 5 times to remove unbound substances with 0.35ml of washing solution for 30 seconds to 1 minute for each wash. The plate is then graded on tissue paper or other absorbent material. This was followed by adding substrate solutions A and B to each well, with 50μl of each substrate to each well, then the plate was covered with a fresh cover and incubated for 10 minutes at 37°C in darkness. After the incubation was completed, read the optical density (OD) value using a microplate reader set at 450 nm within 10 minutes after the addition of the stop solution.

Data Analysis

Data from the blood IgE level examination were analyzed using computer software specifically for curve fitting. Data on optical density (OD) values and concentrations according to the standards collected were processed using Microsoft Excel spread sheet for making graphs of IgE levels, then processed using SPSS application for data analysis. The data in the form of a curve was then observed to see a decrease in the IgE levels of each sample using the One-Way ANOVA test. This test was conducted to determine the significance difference between the group means.


The results obtained from serum examination of IgE levels in five dogs with CAD after oral and topical administration of coconut oil for 35 days showed that at week 0 (before treatment), the five dogs sample showed an average IgE level of 524.1 uL ± 147.072, and experienced changes in weeks 1-5 (after treatment). The decrease occurred in week 1 with an average IgE level of 401.7 uL ± 90.198 and week 2 with an average IgE level of 375.3 uL ± 64.631. The increase then occurred in week 3 with an average of 474.9 uL ± 181,760, followed by week 4 with an average of 496.5 uL ± 111,957, and continued to increase until week 5 with an average of 576.3 uL ± 232,513.

Table 1: Mean IgE Levels of Five Dogs with CAD Before and After Oral and Topical Administration of Coconut Oil.


Levels (uL/ml)

Duration of Administration (Week)








524,1 ± 147,072a

401,7 uL ± 90,198a

375,3 uL ± 64,631a

474,9 uL ± 181,760a

496,5 uL ± 111,957a

576,3 uL ± 232,513a

In the curve shown in Figure 1: it can be seen that there are fluctuations in IgE levels before and after treatment. A decrease in IgE levels occurred in week 1 and 2 after coconut oil administration, but there was a gradual increase in the IgE levels of dog’s sample in weeks 3 to 5. One-way ANOVA test results stated that there was no significant difference in IgE levels before and after treatment (P> 0.05).


Canine Atopic Dermatitis (CAD) or Atopic Dermatitis in dogs is a chronic skin disease characterized by high itchiness of the skin characterized by damage to epidermal barrier function and skin inflammation [23]. As a disease classified as a type 1 hypersensitivity allergic reaction mediated by IgE, the main step in the treatment of atopic dermatitis is to reduce or control inflammatory reactions, pruritus, and skin lesions produced by the immune system with 524,1 401,7 375,3 474,9 496,5 576,3 0 100 200 300 400 500 600 700 W-0 W-1 W-2 W-3 W-4 W-5 Mean IgE Levels of the Five Dogs Sample During Coconut Oil Administration pharmacological agents [4]. About 80% of AD patients show elevated serum IgE levels characterized by high itching symptoms [24]. Therefore, decreased itch response is a subjective marker of decreased IgE levels in the blood. In weeks 1 and 2, there was a decrease in the average IgE levels in the five dogs’ sample from week 0. This can occur due to the effectiveness of coconut oil content which is useful as an anti-inflammatory and antihistamine agent in reducing inflammation and relieving pruritus symptoms that occur in the five dogs’ sample. Oral and topical administration of coconut oil by massage is effective in supporting skin health and function as a component of the external immune system that protects the body from pathogens and other foreign bodies. The content of medium chain fatty acids (MCT) such as lauric acid and capric acid in coconut oil has been shown to have anti-inflammatory functions [19]. Lauric acid is a precursor of monolaurin which has been shown to regulate immune cell proliferation and has antimicrobial properties [25, 26]. With oral and topical coconut oil treatment, lauric acid found in coconut oil is absorbed by the body, producing monolaurin compounds that help fight infection by disrupting the cell membrane of pathogenic microorganisms [27]. This will then support the process of cell proliferation to fight pathogens, decrease inflammation and pruritus response, resulting in a decrease in IgE levels as antibodies that appear in allergic responses in atopic dermatitis. This can then be seen directly through clinical signs of decreased pruritus response and severity of pruritus as a subjective marker of decreased IgE levels in the blood. Pruritus severity is a difficult parameter to measure in both humans and animals, where in dogs, the use of itch evaluation monitoring has not been fully validated and its usefulness in the practical world is still very limited [28]. Changes in scratching habitus in sampled dogs are difficult to detect in their entirety, given that assessment of variability is subjective and observations must be made thoroughly for 24 hours to ascertain the scratching nature of the dog, which is considered difficult for experimental designs. Therefore, the results of the hair and skin inspection of the five dogs sample became a subjective parameter for the decrease in itch response at weeks 1 and 2, which was indicated by the improvement of the skin and hair due to the decrease in scratching response. At week 0, the five dogs sample showed poor skin quality conditions, where all five dogs sample had dry skin accompanied by macroscopic lesions such as crusts, scales, erythema, macules, papules, hyperpigmentation, and linchenfication. Changes in skin quality can then be observed in weeks 1 and 2, where the five dogs sample showed an improvement in skin quality characterized by a decrease in pruritus, which is characterized by the fall of crusts and scales, reduced erythema, reduced macules and papules, reduced hyperpigmentation and linchenfication, and hair growth. Topical and oral administration of coconut oil was effective in improving the skin barrier function of the five dogs’ sample in weeks 1 and 2, which was characterized by improved skin quality. In addition to the decrease in IgE levels due to improved skin quality through anti-inflammatory effects, the improved skin quality of the five dogs’ sample in weeks 1 and 2 was also supported by the effectiveness of coconut oil in maintaining skin moisture and lipid balance. By maintaining skin lipid balance, coconut oil, which functions as a moisturizer, can help reduce skin sensitivity and allergic responses. Applying moisturizers to the skin has shown anti-neural growth effects in animal models with acute dry skin [29]. Nerve anti-growth effects on the skin can have a significant impact on the management of pruritus or itching in skin conditions such as atopic dermatitis. When nerves in the skin overgrow or become more sensitive, this can result in intense itching sensations. By applying coconut oil as a skin moisturizer, the moisturizing effect can help reduce nerve overgrowth or reduce nerve sensitivity in the skin. This is in line with a study conducted by Evangelista et al. (2014) [23], in which the study showed that topical administration of coconut oil in pediatric patients aged 1-13 years with mild to moderate atopic dermatitis for 8 weeks can improve SCORAD (SCORing Atopic Dermatitis) scores, reduce TEWL (Transpidermal Water Loss) scores, increase skin moisture, and reduce pruritus values. The decrease in pruritus can be explained by the concomitant improvement in skin barrier function. Disruption of the skin barrier due to coconut oil application is effective in altering epidermal innervation and increasing nerve density in the skin due to the moisturizing effect of coconut oil. Topical administration of coconut oil was shown to be helpful in maintaining skin lipid balance which is essential for healthy skin barrier function [18]. Another study demonstrated the effect of coconut oil in reducing SCORAD index values and showed in vitro antibacterial activity against S. aureus in adults with atopic disease [30]. The antimicrobial properties that coconut oil also contains can help reduce the growth of bacteria and fungi on the skin that can aggravate atopic dermatitis. By reducing secondary infections and skin irritation, the administration of coconut oil to dogs with CAD may help reduce excessive immune responses and IgE production, supporting the reduction of IgE levels. In addition to lauric acid and capric acid, the antioxidant compounds such as vitamin E and polyphenols in coconut oil also help protect skin cells from oxidative damage associated with allergic reactions and inflammation, supporting the reduction in IgE levels that occurred in the second and third weeks. In weeks 3, 4, and 5, there was an increase in the average IgE levels in the five dogs’ sample. This is most likely due to the adaptation and tolerance of the dogs with CAD to the effects of coconut oil. This phenomenon could include a re-regulation of the immune response or tolerance to the components of coconut oil, causing a re-increase in IgE production due to the administration of coconut oil with continuous exposure to the same dose and frequency for 35 days. According to Vashinta and Berrigan in Anesthesiology Core Review (2014) [31], there are several mechanisms that explain tolerance to a drug after repeated exposure, where a drug may develop more than one type of tolerance, namely dispositional tolerance (metabolic), tolerance of reduced responsiveness (pharmacodynamic), and behavioral tolerance (contextspecific). In the context of coconut oil, the tolerance that occurs is a dispositional (metabolic) tolerance due to repeated oral use of coconut oil that reduces the amount of coconut oil available in the body of dogs suffering from atopic dermatitis. The underlying pharmacokinetic process involves increased elimination of coconut oil due to increased metabolic enzyme activity triggered by repeated oral use of coconut oil. The increase in IgE production in weeks 3, 4, and 5 can also occur due to the lack of effectiveness of the compound content in coconut oil in suppressing the allergic response of the immune system directly, considering that until now, the treatments used for immunological disorders are almost all empirical in origin, where in most cases of immunological diseases (including allergies), immunosuppressive drugs are used to have a direct effect in suppressing the immune system [32]. During the treatment period, dogs can still be exposed to additional allergens from the surrounding environment. The environment plays an important role in the development and exacerbation of atopic dermatitis through exposure to allergens and other environmental factors that can affect the immune system and increase IgE levels [33]. Environmental factors related to where dogs live, such as air humidity, temperature, or pollution levels, can also affect skin health and IgE levels. Although control of the cleanliness of the rearing environment has been carried out, this cannot rule out the possibility of additional allergen exposure from the rearing environment. This exposure is likely to be the cause of increased IgE production, even if the symptoms of atopic dermatitis begin to decrease due to topical or oral administration of coconut oil. The cause of the re-increase in IgE levels in weeks 3, 4 and 5 is likely to be the result of a combination of the above factors. The complex interaction between these factors may affect the dog's immune response and alter the dynamics of IgE levels during the treatment period.


Based on the results of the study, it can be concluded that oral and topical administration of coconut oil is not effective in causing a decrease in total IgE levels in dogs with CAD. Adaptation and tolerance of the body of dogs with CAD to the effect of coconut oil plays an important role in the lack of effectiveness of coconut oil administration, accompanied by reregulation of immune responses or tolerance to coconut oil components. Further research is needed to compare the effect of coconut oil on the IgE levels of dogs with CAD through oral administration with topical administration separately to see the effectiveness of each treatment.


Ethical Clearance

Ethical clearance was obtained from the Institute for Research and Community Service, Veterinary Medicine of Udayana University with contract number B/206/UN14.2.9/PT.01.04/2023.

Funding and Acknowedgement

The authors express gratitude for the monetary assistance provided the Institute for Research and Community Service, Veterinary Medicine of Udayana University with contract number B/206/UN14.2.9/PT.01.04/2023.


  1. Wollenberg A, Thomsen SF, Lacour JP, Jaumont X and Lazarewicz S. Targeting immunoglobulin E in atopic dermatitis: A review of the existing evidence. World Allergy Organization Journal. 2021; 14: 100519.
  2. Mueller RS. A Systematic Review of Allergen Immunotherapy, A Successful Therapy for Canine Atopic Dermatitis and Feline Atopic Skin Syndrome. Journal of the American Veterinary Medical Association. 2023; 261: S30-S35.
  3. Halliwell R. Revised nomenclature for veterinary allergy. Veterinary Immunology and Immunopathology.2006; 114(3–4), 207-208.
  4. Olivry T, DeBoer DJ, Favrot C, Jackson HA, Mueller RS, Nuttal T and Prelaud P. Treatment of canine atopic dermatitis: 2015 updated guidelines from the International Committee on Allergic Diseases of Animals (ICADA). BMC Veterinary Research. 2015; 11: 210.
  5. Hayes K. How Immuoglobulin E (IgE) Functions in Your Body: an Antibody Involved in the Allergic Response. 2023.
  6. Weber MB, Petry V, Weis L, Mazzotti NG and Cestari TF. 2004. Evaluating the Relation Between Pruritus, Serum IgE Levels and Severity of Clinical Manifestations in Atopic Dermatitis Patients. an Bras Dermatol. 2005; 80: 245-8
  7. Heyworth-Smith D, Campbell P. Laboratory Diagnosis of Allergy. QML Pathology Newsletter, Brisbane. 2017.
  8. Olivry T, DeBoer DJ, Favrot C, Jackson HA, Mueller RS, Nuttal T and Prelaud P. Treatment of canine atopic dermatitis: 2015 updated guidelines from the International Committee on Allergic Diseases of Animals (ICADA). BMC Veterinary Research. 2015; 11: 210.
  9. Reisen J. 2017. Coconut Oil for Dogs: Is it Really Good for Them? American Kennel Club. New York.
  10. Sulastri E, Mappiratu M and Sari AK. Uji Aktivitas Antibakteri Krim Asam Laurat Terhadap Staphylococcus Aureus Atcc 25923 dan Pseudomonas Aeruginosa ATCC 27853. GALENIKA Journal of Pharmacy. 2016; 2: 59-67.
  11. Nagata C, Nakamura K and Wada K. Association of dietary fat, vegetables, and antioxidant micronutrients with skin aging in Japanese women. British Journal of Nutrition. 2010; 103: 1493-1498.
  12. Maulidha F and Dewajeni H. Pemilihan Jenis Minyak Dalam Pembuatan Sabun Mandi Cair Dengan Metode Hot Process. Distilat. 2022; 8: 876-882.
  13. Tsoureli-Nikita E, Hercogova J, Lotti T and Menchini G. Evaluation of dietary intake of vitamin E in the treatment of atopic dermatitis: a study of the clinical course and evaluation of the immunoglobulin E serum levels. International Journal of Dermatology. 2002; 41: 146-150.
  14. Kato E, Sasaki Y and Takahashi N. Sodium dl-alpha-tocopheryl-6-O-phosphate inhibits PGE (2) production in keratinocytes induced by UVB, IL-1beta, and peroxidants. Bioorganic and Medicinal Chemistry. 2011; 19: 6348-6355.
  15. Agero AL and Verallo-Rowell VM. A randomized double-blind controlled trial comparing extra virgin coconut oil with mineral oil as a moisturizer for mild to moderate xerosis. Dermatitis: Contact, Atopic, Occupational, Drug. 2004; 15: 109–116.
  16. Yang D, Pornpattananangkul D, Nakatsuji T, Chan M, Carson D, Huang CM and Zhang L. The antimicrobial activity of liposomal lauric acids against Propionibacterium acnes. Biomaterials. 2009; 30: 6035-6040.
  17. Zhu JJ, Cermak SC, Kenar JA., Brewer G, Haynes KF, Boxler D, et al. Taylor D.B. Better than DEET Repellent Compounds Derived from Coconut Oil. Scientific Reports. 2018; 8: 14053.
  18. Nevin KG and Rajamohan T. Effect of Topical Application of Virgin Coconut Oil on Skin Components and Antioxidant Status during Dermal Wound Healing in Young Rats. Skin Pharmacology and Physiology. 2010; 23: 290–297.
  19. Intahphuak S, Khonsung P and Panthong A. Anti-inflammatory, analgesic, and antipyretic activities of virgin coconut oil. Pharmaceutical Biology. 2010; 48: 151-157.
  20. Ogbolu DO, Oni AA, Daini OA and Oloko AP. In Vitro Antimicrobial Properties of Coconut Oil on Candida Species in Ibadan, Nigeria. Journal of Medicinal Food. 2009; 10: 384-387.
  21. Cahyaniarta IKC, Suartha IN, and Sudimartini LM. Perubahan Lesi Makroskopis pada Anjing Penderita Dermatitis Setelah Pengobatan Minyak Mimba dan Minyak Kelapa Murni. Indonesia Medicus Veteriner. 2019; 8: 791-797.
  22. Goh, Y. M. 2008. Experimental design and sample size issue in laboratory animal experiment. In Workshop on the Care and Use of Laboratory Animal Research. Surabaya.
  23. Evangelista MT, Abad-Casintahan F and Lopez-Villafuerte L. The effect of topical virgin coconut oil on SCORAD index, transepidermal water loss, and skin capacitance in mild to moderate pediatric atopic dermatitis: a randomized, double-blind, clinical trial. International journal of dermatology. 2014; 53: 100-108.
  24. Furue M, Chiba T, Tsuji G, Ulzii D, Kido-Nakahara M, Nakahara T and Kadono T. Atopic dermatitis: immune deviation, barrier dysfunction, IgE autoreactivity and new therapies, Allergology Internationa. 2017; 66: 398-403.
  25. Witcher KJ, Novick RP, Schlievert PM. Modulation of immune cell proliferation by glycerol monolaurate. Clin Diagn Lab Immunol. 1996; 3: 10-13.
  26. Bergsson G, Steingrímsson O and Thormar H. Bactericidal effects of fatty acids and monoglycerides on Helicobacter pylori. Int J Antimicrob Agents. 2002; 20: 258-262.
  27. Pereira CC, Da Silva MA, Langone MA. Enzymatic synthesis of monolaurin. Appl Biochem Biotechnol. 2004; 113–116: 433-445.
  28. Hill PB, DeBoer DJ. The ACVD Task Force on Canine Atopic Dermatitis (IV): Environmental Allergens. Veterinary Immunology and Immunopathology.2001; 81: 169-186.
  29. Kapoor S and Saraf S. Assessment of viscoelasticity and hydration effect of herbal moisturizers using bioengineering techniques. Pharmacogn Mag 2010; 6: 298-304.
  30. Verallo-Rowell VM, Dillague KM and Syah-Tjundawan BS. Novel antibacterial and emollient effects of coconut and virgin olive oils in adult atopic dermatitis. Dermatitis 2008; 19: 308-315.
  31. Vashishta R and Berrigan MJ. Drug tolerance and tachyphylaxis. Freeman BS and Berger JS. (Eds.). Anesthesiology Core Review: Part One Basic Exam. McGraw-Hill Education.
  32. Janeway CA, Travers P, Walport M and Schlomchik MJ. Immunobiology: The Immune System in Health and Disease (5th edition). New York: Garland Science. 2001.
  33. Kantor R and Silverberg JI. Environmental risk factors and their role in the management of atopic dermatitis. Expert Review of Clinical Immunology. 2017; 13: 15-26.