Swiss Tropical and Public Health Institute, Basel, Switzerland.
PLoS One. 2011 Apr 28;6(4):e19010. doi: 10.1371/journal.pone.0019010.
In malaria endemic areas, most people are simultaneously infected with different parasite clones. Detection of individual clones is hampered when their densities fluctuate around the detection limit and, in case of P. falciparum, by sequestration during part of their life cycle. This has important implications for measures of levels of infection or for the outcome of clinical trials. This study aimed at measuring the detectability of individual P. falciparum and P. vivax parasite clones in consecutive samples of the same patient and at investigating the impact of sampling strategies on basic epidemiological measures such as multiplicity of infection (MOI).
Samples were obtained in a repeated cross-sectional field survey in 1 to 4.5 years old children from Papua New Guinea, who were followed up in 2-monthly intervals over 16 months. At each follow-up visit, two consecutive blood samples were collected from each child at intervals of 24 hours. Samples were genotyped for the polymorphic markers msp2 for P. falciparum and msp1F3 and MS16 for P. vivax. Observed prevalence and mean MOI estimated from single samples per host were compared to combined data from sampling twice within 24 h.
Estimated detectability was high in our data set (0.79 [95% CI 0.76-0.82] for P. falciparum and, depending on the marker, 0.61 [0.58-0.63] or 0.73 [0.71-0.75] for P. vivax). When genotyping data from sequential samples, collected 24 hours apart, were combined, the increase in measured prevalence was moderate, 6 to 9% of all infections were missed on a single day. The effect on observed MOI was more pronounced, 18 to 31% of all individual clones were not detected in a single bleed. Repeated sampling revealed little difference between detectability of P. falciparum and P. vivax.
在疟疾流行地区，大多数人同时感染不同的寄生虫克隆。当它们的密度在检测限附近波动时，以及在疟原虫生命周期的一部分被隔离时，检测单个克隆就会受到阻碍。这对感染水平的测量或临床试验的结果都有重要影响。本研究旨在测量同一患者连续样本中单个疟原虫和间日疟原虫寄生虫克隆的可检测性，并研究采样策略对基本流行病学指标（如感染多重性）的影响。
在巴布亚新几内亚 1 至 4.5 岁儿童中进行了一项重复的横断面现场调查，这些儿童在 16 个月的时间里每两个月随访一次。在每次随访时，每个孩子都在 24 小时的间隔内采集两份连续的血液样本。对样本进行了疟原虫多态性标记物 msp2 和 msp1F3 以及间日疟原虫 MS16 的基因分型。观察到的患病率和从单个样本估计的平均 MOI 与 24 小时内两次采样的组合数据进行了比较。
在我们的数据集中，估计的可检测性很高（0.79[95%置信区间 0.76-0.82]为疟原虫，取决于标记物，0.61[0.58-0.63]或 0.73[0.71-0.75]为间日疟原虫）。当在 24 小时的间隔内收集的连续样本的基因分型数据结合在一起时，测量到的患病率略有增加，在一天内会错过所有感染的 6-9%。对观察到的 MOI 的影响更为明显，在单次采血中未检测到所有个体克隆的 18-31%。重复采样发现疟原虫和间日疟原虫的可检测性之间几乎没有差异。
