Data from: Blood-stage parasitaemia and age determine Plasmodium falciparum and P. vivax gametocytaemia in Papua New Guinea

A better understanding of human-to-mosquito transmission is crucial to control malaria. In order to assess factors associated with gametocyte carriage, 2083 samples were collected in a cross-sectional survey in Papua New Guinea. Plasmodium species were detected by light microscopy and qPCR and gametocytes by detection of pfs25 and pvs25 mRNA transcripts by reverse-transcriptase PCR (qRT-PCR). The parasite prevalence by PCR was 18.5% for Plasmodium falciparum and 13.0% for P. vivax. 52.5% of all infections were submicroscopic. Gametocytes were detected in 60% of P. falciparum-positive and 51% of P. vivax-positive samples. Each 10-fold increase in parasite density led to a 1.8-fold and 3.3-fold increase in the odds of carrying P. falciparum and P. vivax gametocytes. Thus the proportion of gametocyte positive and gametocyte densities was highest in young children carrying high asexual parasite densities and in symptomatic individuals. Dilution series of gametocytes allowed absolute quantification of gametocyte densities by qRT-PCR and showed that pvs25 expression is 10-20 fold lower than pfs25 expression. Between 2006 and 2010 parasite prevalence in the study site has decreased by half. 90% of the remaining infections were asymptomatic and likely constitute an important reservoir of transmission. However, mean gametocyte densities were low (approx. 1-2 gametocyte/μL) and it remains to be determined to what extent low-density gametocyte positive individuals are infective to mosquitos.

深入阐明人蚊传播机制，对于疟疾防控工作至关重要。为明确与配子体（gametocyte）携带相关的影响因素，研究团队在巴布亚新几内亚开展横断面调查，共采集2083份样本。研究采用光学显微镜与实时荧光定量PCR（qPCR）检测疟原虫属（Plasmodium）物种，并通过逆转录实时荧光定量PCR（qRT-PCR）检测pfs25与pvs25 mRNA转录本，以判定配子体携带状态。经qPCR检测，恶性疟原虫（Plasmodium falciparum）的感染率为18.5%，间日疟原虫（P. vivax）为13.0%。所有感染病例中，52.5%为亚显微感染。在恶性疟原虫检测阳性的样本中，60%可检出配子体；间日疟原虫阳性样本的配子体检出率为51%。寄生虫载量每提升10倍，宿主携带恶性疟原虫与间日疟原虫配子体的优势分别升高1.8倍与3.3倍。因此，配子体检出率与配子体载量最高的群体，为携带高红细胞内无性期寄生虫载量的幼儿，以及有症状感染者。通过构建配子体稀释梯度系列，研究可通过qRT-PCR实现配子体载量的绝对定量，结果显示pvs25的表达量较pfs25低10~20倍。2006年至2010年间，研究区域的寄生虫感染率下降了50%。剩余感染病例中90%为无症状感染，这类人群极有可能构成重要的疟疾传播储备库。但研究测得的配子体平均载量较低（约1~2个配子体/微升），低密度配子体阳性个体对蚊虫的感染能力究竟可达何种程度，仍有待进一步探明。