“七彩”霉菌:美艳绝伦的致命威胁

仅供医学专业人士阅读参考
美丽身影背后留下的却是临床诊治的困难重重。
“日出江花红胜火,春来江水绿如蓝”、“赤橙黄绿青蓝紫,谁持彩练当空舞”……自古以来,缤纷的色彩多用于形容美好的事物;但在感染领域,美艳惊人的“七彩”却代表着一种致命的威胁——霉菌感染。
目前世界各国仍深陷于新冠疫情的影响中,其中印度已然成为“七彩”霉菌的温床[1-2]。而这些“彩色”霉菌感染患者预后极差:约60%的黑木耳病(毛霉病)患者眼球被摘除;白木耳病(曲霉病)患者出现肠道严重溃烂/坏疽;黄木耳病(未命名的真菌病)导致患者脓液渗出、开放伤口缓慢愈合、营养不良、器官衰竭并最终坏死[1-2]。此外,“彩色”霉菌感染患者病死率极高;有报道称,侵袭性曲霉病和毛霉病患者病死率分别可达70%和100%[3]
在我国,尽管目前尚未有如此丰富的“彩色”霉菌感染病例报道,但高危患者数量的增加、广谱抗生素的应用、对曲霉感染的预防等因素导致近年来毛霉病患者数量不断上升,已引起临床关注[4]

实际临床中,这些“美丽身影”藏匿于哪些患者中?它们的背后隐藏着哪些令人悚然的凶险?我们应如何应对这些“彩色”霉菌的挑战?

“美丽但凶险”的曲霉

感染病死率高,诊治方法存在诸多不足

曲霉可呈现黑色、黄色、绿色、红色等多种不同颜色,而患者一旦感染此种“美艳”的曲霉后,病死率将显著增加。当前诊断水平有限,且现有治疗药物存在多种不足;未来如何更好地管理侵袭性曲霉病仍有待更多深入研究与探讨。

1.高危患者群不断扩大,耐药问题日渐突出

免疫功能低下是侵袭性曲霉病的重要危险因素。血液恶性肿瘤、异基因造血干细胞移植、实体器官移植等与侵袭性曲霉病的发生密切相关[5]。医疗技术的进步使高危人群发生改变:接受靶向药物治疗的患者已成为新型高危人群[6-7]。既往报道,接受依布替尼治疗的慢性淋巴细胞白血病和原发性中枢神经系统淋巴瘤患者中,侵袭性曲霉病发病率达39%[8];另一项研究中,接受依布替尼治疗且并发侵袭性真菌病的患者中,77.3%为曲霉病[9]

我国真实世界数据显示肺真菌病病因中,曲霉病发病率呈显著增加趋势[10]烟曲霉是最常见的菌种,其次为黄曲霉、土曲霉、黑曲霉等[11]。既往曲霉对伏立康唑、伊曲康唑、两性霉素B和棘白菌素类药物的敏感率均较高[12];但随着唑类药物的大量应用,唑类耐药(甚至泛唑类耐药)曲霉(烟曲霉)检出率日益增多[13-15]

侵袭性曲霉病显著延长患者住院时间、增加经济负担、增加死亡风险。有报道称,侵袭性曲霉病患者病死率可达70%以上[16-19];耐药菌则进一步加剧了临床治疗失败率[20]

图1:侵袭性曲霉病患者病死率[17-19]

面对日渐增多的侵袭性曲霉病患者,哪些技术可协助临床早期识别?针对不断加重的耐药问题,现有抗真菌药物是否可有效应对?除曲霉外,近年来不断出现的毛霉病应如何管理?既往罕见的真菌近年来是否仍罕见?

2.亟待更准确的诊断及更强效的治疗

无菌部位培养、组织核酸检测是确诊侵袭性曲霉病的标准,但诊断敏感率低、周转时间长。CT检查、G/GM试验、PCR检测均是临床重要方法,但存在一定的局限性[21]

1、CT检查:疾病不同阶段表现是从非特征性的气道病变(如支气管周围实变影、支气管扩张征、树芽征和毛玻璃样等)逐渐演变为特征性的血管侵袭(如晕轮征、新月征、空洞等)[22-24],且非特征性气道病变也较常见[25]

图2:侵袭性肺曲霉病患者CT改变[25]

2、G/GM试验:血G/GM试验具有较高的诊断价值;但不同临界值(0.5、1.0及1.5)的GM试验检测敏感性及特异性无显著差异,且不同标准会导致漏诊或接受不必要的治疗和检测[26]

3、PCR检测:PCR诊断的敏感性及特异性可达90%以上[27];但不同实验室的敏感性和特异性相差较大,且存在假阳性情况[28]

面对诊断方法的局限性,早期经验治疗仍是目前侵袭性曲霉病的主要治疗策略。伏立康唑并不能完全满足临床实践中的需求。有报道称:伏立康唑治疗侵袭性曲霉病的42天和90天病死率为32%和42%;重症患者病死率显著更高,达61%和68%[29]。究其原因可能为:

1、安全性的影响:伏立康唑的肝毒性、环糊精可能导致的肾毒性、中枢神经毒性、光敏性导致的皮肤反应、视觉影响等影响药物的应用[30]

2、药物间相互作用的影响:与CYP450酶间复杂的作用导致伏立康唑与其它多种药物存在显著的相互作用(如:质子泵抑制剂、他汀类药物、华法林、他克莫司、西罗莫司、环孢素等),从而影响药物的应用[31-32]

3、耐药率的增加:国外数据显示:烟曲霉对唑类药物耐药率显著增加,甚至达20%;耐药率的增加与临床治疗失败密切相关[15,20]

针对侵袭性曲霉病的流行病学及诊治挑战,亟待一种更强效、更安全的药物进行管理;目前多种新型抗真菌药物正在不断研发中,以期进一步改善患者预后。

“谈之色变”的毛霉:

高病死率及致残率,现有诊治技术极为有限

毛霉病常见表现为鼻子和舌头变色、视力模糊、呼吸困难、口腔内黑色病变等,因此又称“黑木耳病”。近年来毛霉病报道例数不断增加,甚至已成为疫情期间的重要侵袭性真菌病类型。高致死率及致残率也使其成为全球的关注热点。

患者数量不断增加,病死率及致残率高

毛霉属于接合菌门真菌,毛霉科中的毛霉属、根霉属、根毛霉属、犁头霉属均可导致毛霉病。预估全球毛霉病发病率为0.005-1.7/百万人;其中,印度毛霉病患病率为14/10万人,是发达国家的80倍,且发病率呈增加趋势[33-34]。多种因素与毛霉病的发生密切相关;在我国,肺接合菌病多见于糖尿病、HIV 感染、病毒性肝炎、长期使用糖皮质激素/免疫抑制剂等患者[35-36]

图3:我国接合菌病患者基础疾病分布[36]

鼻-眼-脑、肺是毛霉病常见感染部位[37],且不同基础疾病患者的感染部位存在差异[35]

图4:毛霉病感染部位分布[35,37]

毛霉病进展迅速,除非及时进行手术和抗真菌治疗,否则毛霉病患者病情会迅速恶化并最终死亡,其病死率可高达96%[35]。毛霉病患者初始一般表现为头疼、流鼻血、咳血、视力模糊等,随疾病进展可扩散至大脑,增加死亡风险[38]。因此,临床治疗时,为防止疾病进一步扩散,常选择手术摘除眼球、剥离鼻窦等[38]

图5:毛霉病患者病死率[35]

临床诊断面临诸多挑战,可用药物极为有限

无菌部位镜检是毛霉病的重要诊断工具,但其灵敏度取决于标本来源及质量;且制备样本时毛霉丝易受损,减少生长,导致阳性率低[39]。反晕轮征是毛霉病患者的特征性表现,但临床中毛霉病影像学表现呈多样化,且常为非特征性表现,如:肺叶和节段性实变、结节或肿块、毛玻璃样影等[40]。G/GM试验阳性有助于排除毛霉病,但阴性结果对诊断无价值。PCR是目前诊断毛霉病的重要手段,全血、血清、血浆、肺泡灌洗液、尿液等多种标本均可使用,且敏感性高[39]

不仅诊断困难,毛霉病的治疗药物选择也极为有限。目前最新欧洲医学真菌学联盟(ECMM)指南主要推荐两性霉素B脂质体作为初始治疗方案[41]。此外,艾沙康唑已获FDA批准用于治疗成人毛霉病,ECMM指南推荐肾功能受损患者初始选择艾沙康唑治疗;泊沙康唑虽具有抗毛霉活性但尚未被批准用于毛霉病的治疗[37,41]

此外,毛霉病患者的抗真菌治疗一般需几周至几个月[42];长疗程治疗期间患者的依从性及耐受性下降,从而对临床疗效产生一定影响。

针对日益严峻的毛霉病,临床应充分掌握目前可用抗真菌药物的特性,依据患者基础情况及疾病进展制订适当方案。此外,新型药物的研发及诊断技术的探讨仍是未来毛霉病管理的重要发展方向。

其它罕见真菌:同样不容忽视

“彩色”真菌不仅只有曲霉和毛霉,其它罕见真菌同样具有极高的危险性。镰刀菌好发于免疫功能低下患者,尤其血液系统恶性肿瘤、造血干细胞移植、实体器官移植受者等[43]。镰刀菌感染患者病死率较高,其90天病死率可达91.3%[44]。马尔尼菲篮状菌好发于HIV感染患者,亚洲地区HIV患者中的发病率为0.3%-15%;马尔尼菲篮状菌感染患者病死率约8%-40%[45]。球孢子菌病、组织胞浆菌病等地方性真菌病,既往报道主要发生于美国及西半球等地区,但近年来研究发现其流行区域可能已超出公认的边界,甚至已出现在亚洲地区,需引起临床重视[46-47]

面对罕见真菌感染的严峻挑战,早期识别此类患者并给予适当的经验治疗极为重要;在有限的药物选择情况下,综合患者基础特点、真菌流行病学现状及药物基本特性将有助于临床中合理选择适当抗真菌药物。此外,未来亟待更多新型、高效的检测手段及新型抗真菌药物,以进一步改善患者预后。

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