participants in sports with skin-to-skin contact, and in those with impaired cellular immunity such as HIV-positive individuals.19 Onset of lesions caused by MCV is usually gradual, beginning as a group of minute papules in one or two areas. Individual lesions are discrete, smooth, and may be inflamed but more typically appear as characteristic pearly, flesh-colored, dome-shaped papules with central umbilication12 (see Figure 1). Variation in appearance is common, and the condition may be mistaken for eczema when the lesions are small.
Like its viral relative, variola virus, MCV is specific to humans with no significant animal reservoir,3 although rare isolated cases have been reported in a kangaroo and a horse.10 Molluscum contagiosum virus is cytoplasmically replicating and proliferates within the follicular epithelium. Infected cells grow in size, while cellular organelles are dislocated and eventually obliterated by a large intracytoplasmic inclusion. Rupture and discharge of the virus-packed cells occurs, and debris and MCV accumulate in the central crater-like ostium12 (see Figure 1). Infection is spread by skin-to-skin contact and by autoinoculation. In immunocompetent patients the illness is self-limited and MCV infection generally does not recur,9 however, MCV exhibits an ability to avoid host immune defenses by a variety of complex mechanisms,12 and it is not unusual for lesions to persist and spread, sometimes extensively (see Figure 1b). Diagnosis is based on the appearance of the lesions and can be confirmed by skin biopsy.
Iodine has been used for decades as a topical antiseptic. It is used by activated white blood cells as part of the killing mechanism directed against bacteria and viruses,35,36 and has also been used clinically with limited success by topical application in the treatment of herpes simplex,37 another virus with a large and complex genome. The U.S. Centers for Disease Control recommends iodine for topical antisepsis against MCV on surfaces,39 however, since topically applied iodine does not penetrate the stratum corneum well it has little activity against MC when used alone on intact skin. Only very small quantities of iodine are absorbed through an intact skin,37,38 thus posing little risk of systemic toxicity or effects on thyroid function when topically applied.
Tea Tree Oil (essential oil of Melaleuca alternifolia; fam. Myrtaceae) is a small paper-barked tree indigenous to swampy regions along the north coast of New South Wales and Queensland, Australia. Leaves of the tree were first used medicinally by the Aborigines, and the tree became known by the common name of "tea tree" when Captain Cook and botanist Joseph Banks, investigating local flora (c. 1770), used the leaves of the tree to brew a spicy tea.22 Steam distillation of the leaves yields an essential oil that came into use as a folk remedy as settlers colonized the indigenous portions of Australia, and in more modern times has found use in the cosmetic and perfume industries, as well as a food additive. Modern investigation of TTO properties began in 1925 when Penfold23 extracted the oil and demonstrated antiseptic and anti-bacterial properties. The whole oil exhibits fungicidal activity against skin dermatomycoses22,30,31 and bactericidal activity against a variety of pathogens including methicillin-resistant Staphylococcus aureus.22,23,25 Known toxicity is low.40.41,47 Tea tree oil TTO has been associated with skin sensitization, but at an incidence of less than 0.01%.41
Hausen et al42 studied the influence of light, oxygen, and heat on TTO's ability to induce reaction in TTO-sensitive patients. Fifteen normal constituents or degradation products from TTO were patch tested in otherwise healthy volunteers. Fresh TTO was revealed to be a very weak sensitizing material whereas oxidized TTO was three times stronger. Oxidation and photodegradation of alpha-terpinene in the oil resulted in dramatic increases in the chief sensitizing agent, p-cymene. The authors conclude that the degradation products were the principal sensitizers, and proper handling and storage of the oil were able to minimize this effect.