Swiss Tropical and Public Health Institute, Basel, Switzerland.
University of Basel, Basel, Switzerland.
J Infect Dis. 2020 Feb 3;221(4):598-607. doi: 10.1093/infdis/jiz420.
Accurate quantification of female and male gametocytes and sex ratios in asymptomatic low-density malaria infections are important for assessing their transmission potential. Gametocytes often escape detection even by molecular methods, therefore ultralow gametocyte densities were quantified in large blood volumes.
Female and male gametocytes were quantified in 161 PCR-positive Plasmodium falciparum infections from a cross-sectional survey in Papua New Guinea. Ten-fold concentrated RNA from 800 µL blood was analyzed using female-specific pfs25 and male-specific pfmget or mssp qRT-PCR. Gametocyte sex ratios from qRT-PCR were compared with those from immunofluorescence assays (IFA).
Gametocytes were identified in 58% (93/161) P. falciparum-positive individuals. Mean gametocyte densities were frequently below 1 female and 1 male gametocyte/µL by qRT-PCR. The mean proportion of males was 0.39 (95% confidence interval, 0.33-0.44) by pfs25/pfmget qRT-PCR; this correlated well with IFA results (Pearsons r2 = 0.91; P < .001). A Poisson model fitted to our data predicted 16% P. falciparum-positive individuals that are likely to transmit, assuming at least 1 female and 1 male gametocyte per 2.5 µL mosquito bloodmeal.
Based on model estimates of female and male gametocytes per 2.5 µL blood, P. falciparum-positive individuals detected exclusively by ultrasensitive diagnostics are negligible for human-to-mosquito transmission.Estimating the transmission potential of ultralow-density malaria infections informs interventions. Almost all infections with ≥1 female and male gametocyte per 2.5 µL mosquito bloodmeal, and thus with highest likelihood of contributing to human-to-mosquito transmission, were detectable by standard molecular diagnostics.
准确量化无症状低密度疟疾感染中的雌性和雄性配子体以及性别比例对于评估其传播潜力非常重要。配子体即使通过分子方法也常常无法检测到，因此，在大量血液中定量超低密度配子体。
对巴布亚新几内亚一项横断面研究中的 161 例聚合酶链反应（PCR）阳性间日疟原虫感染进行了雌性和雄性配子体定量。使用女性特异性 pfs25 和男性特异性 pfmget 或 mssp qRT-PCR 分析来自 800µL 血液的十倍浓缩 RNA。qRT-PCR 检测的配子体性别比例与免疫荧光分析（IFA）进行比较。
在 161 例疟原虫阳性个体中，有 58%（93/161）确定存在配子体。通过 qRT-PCR 检测，常常见到低于 1 个雌性和 1 个雄性配子体/µL 的配子体密度。pfs25/pfmget qRT-PCR 检测的平均雄性比例为 0.39（95%置信区间，0.33-0.44）；这与 IFA 结果相关性良好（Pearson r2 = 0.91；P<0.001）。根据我们的数据拟合泊松模型预测，假设每 2.5µL 蚊血餐中至少有 1 个雌性和 1 个雄性配子体，有 16%的疟原虫阳性个体可能传播。
基于每 2.5µL 血液中雌性和雄性配子体的模型估计，仅通过超灵敏诊断检测到的疟原虫阳性个体对于蚊传的可能性微不足道。估计超低密度疟疾感染的传播潜力有助于干预措施的实施。几乎所有每 2.5µL 蚊血餐中至少有 1 个雌性和 1 个雄性配子体的感染，并且最有可能导致人-蚊传播，都可以通过标准分子诊断检测到。
