Department of Medical Parasitology and Infection Biology, Swiss Tropical and Public Health Institute, Basel, Switzerland.
University of Basel, Basel, Switzerland.
Malar J. 2019 Apr 29;18(1):149. doi: 10.1186/s12936-019-2787-x.
Malaria is endemic in Tanzania with majority of clinical cases caused by Plasmodium falciparum. Additionally, Plasmodium malariae and Plasmodium ovale spp. are also present and clinical manifestations caused by these infections are not well described. Clinical episodes caused by P. malariae infections are often characterized by a relatively mild illness with a low number of parasites, which can persist for long periods. In this report, two cases of P. malariae infections that were identified during a clinical trial evaluating the P. falciparum malaria vaccine candidate, PfSPZ Vaccine are described. The two participants were followed up and monitored for clinical and laboratory parameters to assess vaccine safety providing the opportunity to study clinical manifestations of P. malariae over 4 months.
Two young, healthy Tanzanian men infected with low density asexual blood stage P. malariae diagnosed by quantitative polymerase chain reaction (qPCR) are described. Retrospective analysis of collected and stored blood samples revealed that the two volunteers had constant asexual blood stage parasitaemia for more than 4 months. During the 132 days of infection, the volunteers' vital signs, body temperature and serum biochemistry all remained within normal ranges. Haematological abnormalities, which were transiently outside normal ranges, were regarded as not clinically significant. During this time period, four consecutive evaluations of blood samples by thick blood smear microscopy conducted by an experienced microscopist were all negative, indicating the presence of low-density sub-microscopic infections.
The two cases of P. malariae infections presented here confirm the ability of this Plasmodium species to persist at low density in the human host for extended time periods without causing clinical symptoms. The presented data also demonstrate that clinical study sites in malaria endemic regions need to have a strong malaria diagnostic infrastructure, including the ability of capturing sub-microscopic parasitaemia and differentiation of Plasmodium species. Trial registration ClinicalTrials.gov: NCT02613520, https://clinicaltrials.gov/ct2/show/NCT02613520 , Registered: November 24th 2015, Enrolment of the first participant to the trial: December 15th 2015, Trial was registered before the first participant was enrolled.
坦桑尼亚存在疟疾流行，多数临床病例由恶性疟原虫引起。此外，还存在间日疟原虫和卵形疟原虫，其引起的临床表现尚未明确。由间日疟原虫感染引起的临床发作通常表现为病情相对较轻，寄生虫数量较少，且可长期持续。本报告描述了在评估恶性疟原虫疟疾疫苗候选物 PfSPZ 疫苗的临床试验中发现的两例间日疟原虫感染。对这两名参与者进行了随访和临床及实验室参数监测，以评估疫苗安全性，为研究间日疟原虫的临床表现提供了 4 个月的机会。
描述了两例年轻健康的坦桑尼亚男性，通过定量聚合酶链反应（qPCR）诊断为低密度无性血期间日疟原虫感染。对收集和储存的血液样本进行回顾性分析表明，这两名志愿者的无性血期寄生虫血症持续了 4 个月以上。在感染的 132 天内，志愿者的生命体征、体温和血清生化指标均在正常范围内。短暂超出正常范围的血液学异常被认为无临床意义。在此期间，由经验丰富的显微镜检查师连续进行了 4 次血涂片显微镜检查，均为阴性，提示存在低密度亚微观感染。
本报告中的两例间日疟原虫感染病例证实了该疟原虫种在人类宿主中以低密度持续存在并延长时间而不引起临床症状的能力。所提供的数据还表明，疟疾流行地区的临床研究地点需要具有强大的疟疾诊断基础设施，包括捕获亚微观寄生虫血症和区分疟原虫种的能力。
ClinicalTrials.gov：NCT02613520，https://clinicaltrials.gov/ct2/show/NCT02613520，注册日期：2015 年 11 月 24 日，第一例参与者入组日期：2015 年 12 月 15 日，试验在第一例参与者入组前已注册。
