Spatial Ecology and Epidemiology Group, Department of Zoology, University of Oxford, Oxford, UK.
PLoS Negl Trop Dis. 2010 Aug 3;4(8):e774. doi: 10.1371/journal.pntd.0000774.
A research priority for Plasmodium vivax malaria is to improve our understanding of the spatial distribution of risk and its relationship with the burden of P. vivax disease in human populations. The aim of the research outlined in this article is to provide a contemporary evidence-based map of the global spatial extent of P. vivax malaria, together with estimates of the human population at risk (PAR) of any level of transmission in 2009.
The most recent P. vivax case-reporting data that could be obtained for all malaria endemic countries were used to classify risk into three classes: malaria free, unstable (<0.1 case per 1,000 people per annum (p.a.)) and stable (> or =0.1 case per 1,000 p.a.) P. vivax malaria transmission. Risk areas were further constrained using temperature and aridity data based upon their relationship with parasite and vector bionomics. Medical intelligence was used to refine the spatial extent of risk in specific areas where transmission was reported to be absent (e.g., large urban areas and malaria-free islands). The PAR under each level of transmission was then derived by combining the categorical risk map with a high resolution population surface adjusted to 2009. The exclusion of large Duffy negative populations in Africa from the PAR totals was achieved using independent modelling of the gene frequency of this genetic trait. It was estimated that 2.85 billion people were exposed to some risk of P. vivax transmission in 2009, with 57.1% of them living in areas of unstable transmission. The vast majority (2.59 billion, 91.0%) were located in Central and South East (CSE) Asia, whilst the remainder were located in America (0.16 billion, 5.5%) and in the Africa+ region (0.10 billion, 3.5%). Despite evidence of ubiquitous risk of P. vivax infection in Africa, the very high prevalence of Duffy negativity throughout Central and West Africa reduced the PAR estimates substantially.
After more than a century of development and control, P. vivax remains more widely distributed than P. falciparum and is a potential cause of morbidity and mortality amongst the 2.85 billion people living at risk of infection, the majority of whom are in the tropical belt of CSE Asia. The probability of infection is reduced massively across Africa by the frequency of the Duffy negative trait, but transmission does occur on the continent and is a concern for Duffy positive locals and travellers. The final map provides the spatial limits on which the endemicity of P. vivax transmission can be mapped to support future cartographic-based burden estimations.
间日疟原虫研究的一个重点是提高我们对风险的空间分布及其与人群间日疟原虫病负担之间关系的认识。本文概述的研究旨在提供一幅当代具有循证医学证据的全球间日疟原虫疟疾空间范围图，并估计 2009 年任何传播水平的人类感染风险（PAR）。
使用所有疟疾流行国家所能获得的最新间日疟原虫病例报告数据，将风险分为三类：无疟疾、不稳定（<0.1 例/每 1000 人/年（p.a.））和稳定（≥0.1 例/每 1000 人/年）间日疟原虫疟疾传播。使用基于寄生虫和病媒生物生物学的温度和干旱数据进一步限制风险区域。利用医学情报来细化报告无传播地区的风险空间范围（例如，大城市和无疟疾岛屿）。然后，通过将分类风险图与调整至 2009 年的高分辨率人口表面相结合，得出每种传播水平下的 PAR。使用这种遗传特征基因频率的独立模型，排除了非洲大量无达菲因子人群对 PAR 总数的影响。据估计，2009 年有 28.5 亿人面临间日疟原虫传播的某种风险，其中 57.1%的人生活在不稳定传播地区。绝大多数（25.9 亿，91.0%）位于中东南亚（CSE），其余分布在美洲（1.6 亿，5.5%）和非洲+地区（1 亿，3.5%）。尽管有证据表明非洲普遍存在间日疟原虫感染风险，但中非和西非广泛存在的无达菲因子现象大大降低了 PAR 估计值。
在一个多世纪的发展和控制之后，间日疟原虫的分布范围仍然比恶性疟原虫更广，是生活在感染风险中的 28.5 亿人中发病率和死亡率的潜在原因，其中大多数人位于中东南亚热带带。由于无达菲因子的存在，非洲的感染概率大大降低，但该疾病在非洲确实存在传播，这是对无达菲因子的当地人以及旅行者的关注。最终地图提供了间日疟原虫传播的地域界限，以便对未来基于地图的疾病负担进行估计。
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