Demodex Mites – Commensals, Parasites or Mutualistic Organisms?
英文原文
The German dermatologist Gustav Simon is credited with the first description of Demodex mites. He was studying the microanatomical structure of acne vulgaris lesions by examining material expressed from sebaceous follicles under the microscope. He noted structures within this material and was able to identify a worm-like object with a head, legs, and anterior and posterior body parts that made him think this was ‘an animal’ of some sort. Suspicion became certainty when he pressed the object gently between two slides and observed that ‘it moved’! The term Demodex was coined by Richard Owen in 1843 for this genus, borrowing from the Greek the words ‘demo’ (lard) and ‘dex’ (boring worm) to describe the form and location of preference of this organism. The anatomical details were subsequently described by Desch and Nutting. These included (for Demodex folliculorum) 4 pairs of articulated legs, complex mouth parts, genital organs (either penis or vagina), a rudimentary gastrointestinal tract but surprisingly no anus!
对应中文
德国皮肤科医生古斯塔夫·西蒙首次描述了蠕形螨。他通过在显微镜下检查皮脂腺滤泡表达的物质来研究寻常痤疮病变的显微解剖结构。他注意到了这种材料中的结构，并且能够识别出一个像蠕虫一样的物体，它有头、腿和身体的前后部分，这使他认为这是某种“动物”。当他在两张幻灯片之间轻轻按压物体并观察到“它在移动”时，怀疑变成了必然！1843年，理查德·欧文为这个创造了术语“demodex”，借用了希腊语中的“demo”（猪油）和“dex”（蛀虫）来描述这种生物的偏好位置和形式。Desch和Nutting随后描述了解剖细节，包括：（对于毛囊蠕形螨）4对有关节的腿，复杂的口腔部位，生殖器官（阴茎或阴道），一个基本的胃肠道，但令人惊讶的是没有肛门！
英文原文
We now know that 2 mite species (Demodex brevis and D. folliculorum) inhabit normal adult human facial sebaceous follicles. Mites are not found in the skin of newborn infants. Sebaceous follicles are thought to become colonised during later childhood and early adult life by transfer from adult family members. The mites’ life cycle was studied by Spickett by histological and rudimentary in vitro experiments. From a synthesis of this data generated, he proposed that the life cycle of D. folliculorum mites was about 14.5 days. He also demonstrated that all life stages of these mites were negatively phototaxic, that is they were more mobile in a dark environment and relatively inert when bright light was shone on them. However, until optimal in vitro culture techniques and conditions allow Demodex proliferation in the laboratory, the true life cycle of Demodex remains uncertain. Mites are mobile and can travel at a speed of up to 16 mm/h. Mites found from time to time on the skin surface suggest that they emerge from follicles (probably at night to avoid light exposure) and migrate across the surface of the facial skin.
对应中文
我们现在知道有两种螨（皮脂蠕形螨和毛囊蠕形螨）栖息在正常成人面部皮脂腺毛囊中。新生儿皮肤中未发现螨虫；通常认为螨在皮脂腺毛囊的定殖是在儿童后期和成人早期通过成年家庭成员的转移而形成。Spickett通过组织学和初步体外实验研究了螨的生命周期；综合研究数据，他提出毛囊蠕形螨的生命周期约为14.5天。他还证明，这些螨类的所有生命阶段都具有负趋光性的，也就是说，它们在黑暗环境中移动性更强，当强光照射时相对惰性。然而，在最佳的体外培养技术和条件允许蠕形螨在实验室中增殖之前，蠕形螨的真实生命周期仍然不确定。螨类可以移动、速度高达16mm/h。皮肤表面不时发现的螨类表明，它们是从毛囊中冒出来的(可能是为了避免光照)，并在面部皮肤表面迁徙。
英文原文
Mites are known to contain lipase enzymes, to carry bacteria on the surface and they may have endobacteria.
对应中文
已知螨虫含有脂肪酶，可在其表面沉积细菌，并可能具有内生细菌。
英文原文
Any potential role of these complex organisms in the biobalance of the skin has been largely ignored. They are regarded by most investigators as simple commensals benefiting from the human sebum in its sheltered ecological follicular niche and without adversely affecting its host, but in animals the pathogenic potential of Demodex species is well documented. Demodectic mange in dogs is a potentially lethal condition, and goats can be similarly affected. Both disorders are caused by a massive proliferation of the normal mite population. In humans there is mounting evidence that Demodex mites, like other cutaneous microflora, may be opportunistic pathogens, that is they have the potential to change status from commensals to parasites (the mites benefit but cause harm to the host) if the host cutaneous environment fa- cilitates their proliferation.
对应中文
在皮肤生物平衡中，这些复杂生物体的任何潜在作用都被忽视了。大多数研究者认为它们是简单的共生体，在其受保护的生态卵泡生态位中受益于人类皮脂，不会对其宿主产生不利影响，但在动物中，蠕形螨物种的致病潜力已得到充分证明。狗身上的蠕形螨病是一种潜在的致命性疾病，山羊也可能受到类似的影响。这两种疾病都是由正常螨类种群的大规模增殖引起的。越来越多的证据表明，蠕形螨和其他皮肤微生物区系一样，可能是机会病原体，也就是说，如果宿主皮肤环境有利于蠕形螨的增殖，它们有可能从共生状态转变为寄生虫(蠕形螨获益，但对宿主造成伤害)。
英文原文
Demodex mite numbers have been repeatedly shown to be increased in patients with rosacea, and a recent report using meta-analysis of previous studies has shown a statistically significant association between Demodex species infestation and the development of rosacea. Rosaceiform dermatitis has been reported following repeated facial application of topical steroids and other immunomodulators with similarly increased numbers of mites recorded. Several other studies have shown that Demodex mite numbers are increased in immunosuppressed patients, children with leukaemia receiving chemotherapy, patients with HIV infection and AIDS, patients undergoing phototherapy and patients on chronic dialysis.
对应中文
既往证据都证明，玫瑰痤疮患者的蠕形螨数量增加。最近一项对先前研究进行荟萃分析的报告显示，在统计上，蠕形螨感染与玫瑰痤疮的发展之间存在显著的相关性。据报道，在反复使用局部类固醇和其他免疫调节剂后，出现了玫瑰痤疮样皮炎，记录到的螨虫数量也同样增加。其他几项研究表明，免疫抑制患者、接受化疗的白血病儿童、艾滋病病毒感染和获得性免疫缺乏综合征患者、接受光疗的患者和慢性透析患者的蠕形螨数量增加。
英文原文
In this issue, Gerber et al. introduce a new clinical setting in which Demodex numbers were found to be increased. In their retrospective study these authors demonstrated increased numbers of D. folliculorum in the cheek region of patients presenting with papulopustular lesions induced by epidermal growth factor receptor inhibitor following therapy for cancer. The authors propose that their findings suggest that epidermal growth factor receptor inhibitor may reduce/impair cutaneous defence mechanisms resulting in increased Demodex proliferation.
对应中文
在本期中，Gerber等人介绍了一种新的临床环境，发现蠕形螨数量增加。在他们的回顾性研究中，这些作者证实，癌症治疗后，表皮生长因子受体抑制剂引起丘疹脓疱病变患者的脸颊区域毛囊蠕形螨数量增加。作者提出，他们的研究结果表明表皮生长因子受体抑制剂可能减少/损害皮肤防御机制，导致蠕形螨数量增加。
英文原文
Our present state of knowledge suggests that Demodex mites normally have a symbiotic relationship with humans. In usual circumstances they appear to live as commensals feeding on their host’s sebum. It is possible in this role that they may even confer a mutualistic host benefit by ingesting bacteria or other organisms in the follicular canal. The host’s innate immune system appears to tolerate the presence of these mites but it may have a ‘culling’ or inhibitory effect on mite proliferation keeping numbers in the canal under control without inducing an inflammatory response. If mite numbers increase to a critical level (possibly causing physical distension of follicles with keratinocyte disruption), they possibly develop a pathogenic role causing host ‘insult’. Thus, cytokine/chemokine release may be initiated, and a humoral immune inflammatory response ensues with clinically visible cutaneous changes. If the follicle is damaged to the point of rupture, a granulomatous ‘foreign-body’ type of reaction subsequently results.
对应中文
我们目前的知识表明，蠕形螨通常与人类有共生关系。在通常情况下，它们似乎是以宿主的皮脂为食的共生体。在这种作用下，它们甚至可能通过摄入滤泡管中的细菌或其他有机体而使宿主互惠互利。宿主的先天免疫系统似乎能容忍这些螨类的存在，但它可能对螨类的增殖具有‘剔除’或抑制作用，使螨类的数量保持不变。在不引起炎症反应的情况下，导管处于受控状态。如果螨虫数量增加到一个临界水平（可能导致滤泡的物理膨胀和角质形成细胞的破坏），它们可能会产生致病作用，导致宿主的“损伤”。因此，细胞因子/趋化因子释放可能启动，体液免疫炎症反应随之发生，并伴有临床可见的皮肤变化。如果卵泡损坏到破裂点，随后会出现肉芽肿性“异物”反应。
英文原文
Several factors could allow proliferation of mites to this critical level. For example the particular physical barrier characteristics of an individual’s facial skin may facilitate their increased population. Our preliminary studies have shown that patients with papulopustular rosacea have increased facial pH and reduced skin surface hydration levels. Papulopustular rosacea patients also have abnormal fatty acid composition of their skin surface lipid layer, with increased levels of linoleic acid and myristic acid, as well as reduced levels of specific saturated fatty acids. This type of facial cutaneous microenvironment may prove conducive to mite proliferation. Alternatively, the aberrant innate immune response as previously reported in rosacea patients may facilitate mite multiplication to the point where the humoral response is initiated and cutaneous inflammation results.
对应中文
有几个因素可以使螨类的增殖达到这个临界水平。例如，一个人面部皮肤特殊的屏障特征可能会促进螨类的增加。我们的初步研究表明，丘疹型玫瑰痤疮患者面部pH值升高、皮肤表面水合水平降低，皮肤表面脂层脂肪酸组成也异常，亚油酸和肉豆蔻酸水平升高，特定饱和脂肪酸水平降低。这种面部皮肤微环境可能有利于螨类的增殖。或者，先前在玫瑰痤疮患者中报道的异常的先天免疫反应导致螨虫增殖，引起体液反应启动和皮肤感染的结果。
英文原文
The role of suppression of the host immune response in the facilitation of mite proliferation is suggested by the studies cited above and the publication by Gerber et al. in this issue.
对应中文
上述研究和Gerber等人在本期中发表的文章表明，抑制宿主免疫反应在促进螨虫增殖中起了重要作用。
英文原文
Studies of Demodex mites and their role in healthy skin as well as their potential to cause host damage have the potential to give insight into this complex and important area of cutaneous medicine. It may well be that Demodex mites, like some cutaneous microbes, take on different roles depending on host status, changing from commensals (or even mutuals) to parasites as the host’s defences are altered.
对应中文
对蠕形螨及其在健康皮肤中的作用以及它们引起宿主损害的可能性的研究，有可能深入了解这一复杂而重要的皮肤医学领域。这很可能是由于蠕形螨，就像一些皮肤微生物一样，根据宿主的状态发挥不同的作用，随着宿主防御能力的改变，从共生(甚至互生)变成寄生。
REFERENCES
1.Lacey N, S NR, Powell FC. Demodex mites–commensals, parasitesor mutualistic organisms? Dermatology. 2011;222(2):128-30.