The International Limits and Population at Risk of Plasmodium vivax Transmission in 2009

Abstract

BackgroundA 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.MethodologyThe 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 (≥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.ConclusionsAfter 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.

Population genetics of malaria resistance in humans

“…falciparum is the malarial species that is the most important cause of mortality in humans but, in addition, nearly 3 billion people, mainly in Asia and South America, are at risk from another malaria species, P. vivax, which causes chronic disease and deadly complications (Guerra et al, 2010). Three more species, P. ovale, P. malariae and P. knowlesi (Cox-Singh et al, 2008) can also cause malaria in humans.…”

Plasmodium falciparum -like parasites infecting wild apes in southern Cameroon do not represent a recurrent source of human malaria

“…Although the great majority of individuals in Cameroon are Duffy negative (21), it has been proposed that P. vivax persists in west central human populations at a very low frequency (22). Because deep sequencing failed to identify evidence of P. vivax infection in 514 individuals, we considered the possibility that the 454 primers were less efficient in amplifying P. vivax compared with the other Plasmodium species.…”

Broadly neutralizing epitopes in the Plasmodium vivax vaccine candidate Duffy Binding Protein

“…Recent studies show comparable rates of severe malaria and of mortality between P. vivax and Plasmodium falciparum in Southeast Asia (2,3), and frequent clinical manifestations of debilitating symptoms result in high morbidity (4,5). This places a tremendous burden on the healthcare infrastructure (4,5) and imparts hidden costs in the form of decreased economic productivity and standard of living (5).…”