Faculty of Infectious and Tropical Diseases, London School of Hygiene & Tropical Medicine, WC1E 7HT, London, UK.
Malar J. 2011 Dec 16;10:370. doi: 10.1186/1475-2875-10-370.
In malaria endemic areas, individuals are frequently asymptomatic and may be undetected by conventional microscopy or newer, rapid diagnostic tests. Molecular techniques allow a more accurate assessment of this asymptomatic parasite burden, the extent of which is important for malaria control. This study examines the relative prevalence of sub-microscopic level parasite carriage and clonal complexity of infections (multiplicity of infection) over a range of endemicities in a region of north-eastern Tanzania where altitude is an established proxy of malaria transmission. The PCR prevalence was then compared against other measures of transmission intensity collected in the same area.
This study used 1,121 blood samples collected from a previously conducted cross-sectional malario-metric survey during the short rainy season in 2001 from 13 villages (three at < 600 m, four at 600-1,200 m and six at > 1,200 m in altitude above sea level). Samples were analysed by PCR for carriage of parasites and multiplicity of infection. These data were compared with other measures of transmission intensity collected from the same area.
Parasite prevalence was 34.7% by PCR and 13.6% by microscopy; a 2.5-fold difference in line with other recent observations. This fold difference was relatively consistent at the different altitude bands despite a marked decrease in parasite prevalence with altitude: < 600 m 70.9 vs 28.6, 600-1,200 m 35.5 vs 9.9, > 1,200 m 15.8 vs 5.9. The difference between parasite prevalence by PCR was 3.2 in individuals aged between 15 and 45 years (34.5 vs 10.9) compared with 2.5 in those aged 1-5 (34.0 vs 13.5) though this was not statistically significant. Multiplicity of infection (MOI) ranged from 1.2 to 3.7 and was positively associated with parasite prevalence assessed by both PCR and microscopy. There was no association of MOI and age.Village level PCR parasite prevalence was strongly correlated with altitude, sero-conversion rate and predicted entomological inoculation rate.
Asymptomatic, low density, multi-clone malaria infection was common in this study area. These infections are important as potential contributors to the infectious reservoir of parasites and need to be identified by control programmes especially in this era where malaria elimination is a focus. High throughput standardized PCR approaches are needed to identify individuals who are malaria carriers.
在疟疾流行地区，个体经常无症状，可能无法通过常规显微镜检查或较新的快速诊断检测发现。分子技术可更准确地评估这种无症状寄生虫负担，其程度对疟疾控制很重要。本研究在坦桑尼亚东北部一个疟疾流行地区，研究了一系列流行地区亚微观水平寄生虫携带情况和感染的克隆复杂性（感染倍数）的相对流行率，该地区的海拔是疟疾传播的既定替代指标。然后将 PCR 阳性率与在同一地区收集的其他传播强度测量值进行比较。
本研究使用了 1121 份血液样本，这些样本是在 2001 年短暂雨季期间从坦桑尼亚东北部的 13 个村庄（海拔低于 600 米的 3 个村庄、海拔在 600-1200 米之间的 4 个村庄和海拔高于 1200 米的 6 个村庄）进行的一项先前横断面疟疾计量调查中收集的。通过 PCR 分析样本中寄生虫的携带情况和感染倍数。将这些数据与从同一地区收集的其他传播强度测量值进行比较。
PCR 检测寄生虫的阳性率为 34.7%，显微镜检测为 13.6%；与最近的其他观察结果相比，这一差异高达 2.5 倍。尽管随着海拔的升高寄生虫的阳性率明显下降，但这种倍数差异在不同海拔带相对一致：<600 米为 70.9%比 28.6%，600-1200 米为 35.5%比 9.9%，>1200 米为 15.8%比 5.9%。年龄在 15 至 45 岁之间的个体中，PCR 检测寄生虫的阳性率差异为 3.2（34.5%比 10.9%），而年龄在 1 至 5 岁之间的个体中差异为 2.5（34.0%比 13.5%），尽管这无统计学意义。感染倍数（MOI）范围为 1.2 至 3.7，与通过 PCR 和显微镜评估的寄生虫阳性率呈正相关。MOI 与年龄无相关性。村庄层面的 PCR 寄生虫阳性率与海拔、血清转化率和预测的昆虫接种率呈强相关。
在本研究地区，无症状、低密度、多克隆疟疾感染很常见。这些感染是寄生虫感染储存库的潜在贡献者，需要通过控制方案加以识别，特别是在目前疟疾消除是重点的时代。需要采用高通量标准化 PCR 方法来识别疟疾携带者。
