Unit of Tropical Medicine, Infectious Disease Department, Hospital Carlos III, 1028029, Madrid, Spain.
Malar J. 2012 Sep 12;11:324. doi: 10.1186/1475-2875-11-324.
Submicroscopic malaria (SMM) can be defined as low-density infections of Plasmodium that are unlikely to be detected by conventional microscopy. Such submicroscopic infections only occasionally cause acute disease, but they are capable of infecting mosquitoes and contributing to transmission. This entity is frequent in endemic countries; however, little is known about imported SMM.The goals of this study were two-fold: a) to know the frequency of imported SMM, and b) to describe epidemiological, laboratorial and clinical features of imported SMM.
A retrospective study based on review of medical records was performed. The study population consisted of patients older than 15 years attended at the Tropical Medicine Unit of Hospital Carlos III, between January 1, 2002 and December 31, 2007. Routinely detection techniques for Plasmodium included Field staining and microscopic examination through thick and thin blood smear. A semi-nested multiplex malaria PCR was used to diagnose or to confirm cases with low parasitaemia.
SMM was diagnosed in 104 cases, representing 35.5% of all malaria cases. Mean age (IC95%) was 40.38 years (37.41-43.34), and sex distribution was similar. Most cases were in immigrants, but some cases were found in travellers. Equatorial Guinea was the main country where infection was acquired (81.7%). Symptoms were present only in 28.8% of all SMM cases, mainly asthenia (73.3% of symptomatic patients), fever (60%) and arthromialgias (53.3%). The associated laboratory abnormalities were anaemia (27.9%), leukopaenia (15.4%) and thrombopaenia (15.4%). Co-morbidity was described in 75 cases (72.1%).
Results from this study suggest that imported SMM should be considered in some patients attended at Tropical Medicine Units. Although it is usually asymptomatic, it may be responsible of fever, or laboratory abnormalities in patients coming from endemic areas. The possibility of transmission in SMM has been previously described in endemic zones, and presence of vector in Europe has also been reported. Implementation of molecular tests in all asymptomatic individuals coming from endemic area is not economically feasible. So re-emergence of malaria (Plasmodium vivax) in Europe may be speculated.
亚微观疟疾（SMM）可定义为密度较低的疟原虫感染，常规显微镜检查不太可能发现。这种亚微观感染偶尔会引起急性疾病，但它们能够感染蚊子并有助于传播。这种情况在流行地区很常见；然而，对于输入性 SMM 知之甚少。本研究的目的有两个：a）了解输入性 SMM 的频率，b）描述输入性 SMM 的流行病学、实验室和临床特征。
回顾性研究基于病历回顾。研究人群为 2002 年 1 月 1 日至 2007 年 12 月 31 日在 Hospital Carlos III 热带医学科就诊的年龄大于 15 岁的患者。疟疾的常规检测技术包括现场染色和厚、薄血涂片的显微镜检查。半巢式多重疟疾 PCR 用于诊断或确认低疟原虫血症的病例。
诊断出 104 例 SMM，占所有疟疾病例的 35.5%。平均年龄（95%置信区间）为 40.38 岁（37.41-43.34），性别分布相似。大多数病例是移民，但也有一些旅行者病例。赤道几内亚是感染的主要来源国（81.7%）。所有 SMM 病例中只有 28.8%出现症状，主要为乏力（有症状患者的 73.3%）、发热（60%）和关节痛（53.3%）。相关的实验室异常包括贫血（27.9%）、白细胞减少（15.4%）和血小板减少（15.4%）。75 例（72.1%）患者合并其他疾病。
本研究结果表明，在热带医学科就诊的一些患者中应考虑输入性 SMM。虽然它通常无症状，但它可能导致来自流行地区的发热或实验室异常。在流行地区已描述了 SMM 传播的可能性，并且在欧洲也已报告了媒介的存在。在所有来自流行地区的无症状个体中实施分子检测在经济上是不可行的。因此，可能推测疟疾（间日疟原虫）在欧洲再次出现。
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