Melaleuca, Cajeput-tree
Route Of Exposure
Other Topics
The melaleuca is a tall-growing tree, native to eastern Australia, Myanmar (Burma), New Guinea, the Solomon Islands, and the East Indies. It is also planted elsewhere in the tropics and is rather common in greenhouses. The species Melaleuca alternifolia, one type of tea tree, is unique to Australia and native to New South Wales.
The melaleuca tree grows 20 to 33 m in height and has a slender crown. The tree is usually single-trunked, but may develop multiple trunks. The most striking feature is its almost pure-white papery bark, peeling off in sheets. The leaves are greyish-green, 4 to 10 cm long, 2 cm wide, and stiff. The leaves are very aromatic.
Melaleuca’s beautiful flowers bloom whitish-pink or purple. They have prominent ivory-white stamens and are produced on bottlebrush-like spikes 16 cm long. Dust-like seeds are enclosed in rounded, tightly clustered, greyish-brown woody capsules produced along the stems. In Australia, melaleuca flowers from October to December; in California and Florida in the USA, from June to November.
The trees grow along creek banks. Some species have weeping foliage; others are stiffer in appearance.
Melaleuca oil (cajeput oil) is distilled from the fresh leaves and twigs. The oil is obtained from several species besides Melaleuca leucadendron. Similar oil, tea tree oil, is usually extracted from a family member, Melaleuca alternifolia. Melaleuca oil is used in medicine and for a variety of other purposes. The principal constituent of the oil is cineol. Solid terpineol is also present, and several aldehydes, such as valeric, butyric and benzoic.
The spongy bark was used by the Aborigines of Australia to make shields and canoes, for roofing, and as timber.
Clinical Relevance
IgE-mediated reactions
Melaleuca pollen can induce asthma, allergic rhinitis and allergic conjunctitivis.
In a study in Darwin, Australia, that correlated daily average ambient pollen and fungal spore concentrations with hospital admissions for allergic respiratory disease, the association was the strongest in the case of Myrtaceae pollen (this being the dominant tree taxa in the region).
In an early study, pollen extracts of the trees Callistemon citrinis (bottlebrush) and melaleuca, as well as of Bahia grass, were analysed for antigenic and allergenic cross-reactivity. Clinical studies demonstrated that 81% of the patients who were skin-test-positive to at least 1 of the pollens were also positive to the other 2.
In a study of the closely-related paperbark tea tree (M. quinquenervia), a 2-year aeroallergen survey and skin-test results from 1 017 subjects were reviewed. Ninety-seven of 1 017 subjects were at 2+ or greater in intradermal tests. One of 6 double-blind nasal challenges and 1 of 4 single-blind bronchial challenges using extract from this tree were positive in subjects with positive skin tests. The study concluded that the paperbark tea tree is not a significant source of aeroallergens.
In a Malaysian study of 200 patients attending a clinic, of the 29.5% who were asthmatic with positive SPT reactions, 21.5% had reactions to 1 or more of the grass pollens, 21.5% to Acacia pollen and 7.5% to melaleuca pollen.
Other reactions
Tea tree oil (melaleuca oil) is an essential oil, distilled predominantly from the leaves of the Australian plant Melaleuca alternifolia. This species is unique to Australia and native to New South Wales. Allergic contact dermatitis to tea tree oil is well recognised and is becoming increasingly common in Australia.
Cross-Reactivity
Extensive cross-reactivity between the different individual species of the genus could be expected.
Clinical studies demonstrated that 81% of the patients who were skin-test-positive to pollen from Callistemon citrinis (bottlebrush), M. leucadendron, or Bahia grass (Paspalum notatum) were also positive to the other 2.
RAST inhibition analysis has demonstrated cross-reactivity between the closely-related Melaleuca quinquenervia and bottlebrush (Callistemon citrinis).
References
- Sweeney M, Hosseiny S, Hunter S, Klotz SD, Gennaro RN, White RS. Immunodetection and comparison of melaleuca, bottlebrush, and bahia pollens. Int Arch Allergy Immunol 1994;105(3):289-96.
- Sam CK, Kesavan-Padmaja, Liam CK, Soon SC, Lim AL, Ong EK. A study of pollen prevalence in relation to pollen allergy in Malaysian asthmatics. Asian Pac J Allergy Immunol 1998;16(1):1-4.
- Hanigan IC, Johnston FH. Respiratory hospital admissions were associated with ambient airborne pollen in Darwin, Australia, 2004-2005. Clin Exp Allergy 2007;37(10):1556-65.
- Stevenson J, Haberle SG, Johnston FH, Bowman DM. Seasonal distribution of pollen in the atmosphere of Darwin, tropical Australia: Preliminary results. Grana 2007;46(1):34-42.
- Stablein JJ, Bucholtz GA, Lockey RF. Melaleuca tree and respiratory disease. Ann Allergy Asthma Immunol 2002;89(5):523-30.
- Stanaland BE, Gennaro RN, Bausher MG, Klotz SD, White RS, Sweeney MJ. Allergenic cross-reactivity between Callistemon citrinis and Melaleuca quinquenervia pollens. Int Arch Allergy Appl Immunol 1988;86(1):35-41.
- Williams JD, Nixon RL, Lee A. Recurrent allergic contact dermatitis due to allergen transfer by sunglasses. Contact Dermatitis 2007;57(2):120-1.
- Morris MC, Donoghue A, Markowitz JA, Osterhoudt KC. Ingestion of tea tree oil (Melaleuca oil) by a 4-year-old boy. Pediatr Emerg Care 2003;19(3):169-71.
- Fritz TM, Burg G, Krasovec M. Allergic contact dermatitis to cosmetics containing Melaleuca alternifolia (tea tree oil) [French] Ann Dermatol Venereol 2001;128(2):123-6.
- Yman L. Botanical relations and immunological cross-reactions in pollen allergy. 2nd ed. Pharmacia Diagnostics AB. Uppsala. Sweden. 1982: ISBN 91-970475-09.