Alicia Arnott; Alyssa E Barry; John C Reeder

“ One of the fundamental factors governing transmission and immunity is parasite diversity. An understanding of parasite population genetic structure is necessary to understand the epidemiology, diversity, distribution and dynamics of natural P. vivax populations. In addition, studying the population structure of genes under immune selection also enables investigation of the dynamic interplay between transmission and immunity, which is crucial for vaccine development. ”

“ In order to enable accurate comparisons of genetic diversity of global P. vivax populations, a standardized approach to microsatellite genotyping is required, similar to that implemented for investigation of P. falciparum [59] . However, there remain a number of challenges and limitations to developing such an approach. Selection of both the appropriate number and length of microsatellites to be used for genotyping is crucial to obtain accurate results [ [23] . Increasing the number of markers investigated increases the likelihood of detecting multiple clone infections. ”

“ Porous land borders between malaria endemic countries, specifically throughout Southeast Asia and the Middle East, are potential barriers to the successful implementation of malaria elimination campaigns [68] , [70] . Migration of infected individuals resulting in importation of Plasmodium spp. and subsequent transmission by local vectors has contributed to the global spread of malaria [71] . Migration of infected individuals may seriously confound containment of P. vivax, as individuals can be unaware of their infection status due to long incubation periods. ”

“ As biomarkers do not currently exist to determine whether recurrent P. vivax parasitaemia is due to reactivation of liver hypnozoites, genotyping is used to identify whether recurrent episodes of P. vivax infection are the result of re-infection with a new clone or recrudescence/relapse of an existing drug-resistant clone [76] , [77] . The basis for this approach is that genetic diversity is sufficient to be able to distinguish between strains using a panel of diverse markers [ [75] . ”

“ The Malaria Eradication Research Agenda (malERA) Consultative Group on Basic Science and Enabling Technologies recently reported that no campaign for malaria control or elimination can proceed without a comprehensive knowledge of disease epidemiology and host-parasite-vector interactions, and how these interactions are affected by intensified intervention measures [ [18] . ”

“ The unique biology of P. vivax is likely to be responsible for the apparent paradox of multiple clone infection in a low transmission setting. The latent hypnozoite stage of the P. vivax lifecycle increases the likelihood of superinfection with a second clone, potentially resulting in the reactivation of heterologous hypnozoites and an increased likelihood of meiotic recombination, ultimately increasing genetic diversity within the population [2] , [25] . ”

“ Following reports of increasing P. vivax genetic diversity in Korea [73] , Choi and colleagues used genotyping to successfully distinguish between autochthonous and imported P. vivax cases, identifying that the imported infections originated in neighbouring Asian countries. Imported infections also pose a risk in non-endemic regions of endemic countries. Many South American countries are geographically heterogeneous with regard to malaria transmission, and imported cases can result in serious illness and death amongst non-immune populations [74] . ”

“ Abstract Traditionally, infection with Plasmodium vivax was thought to be benign and self-limiting, however, recent evidence has demonstrated that infection with P. vivax can also result in severe illness and death. Research into P. vivax has been relatively neglected and much remains unknown regarding the biology, pathogenesis and epidemiology of this parasite. ”

“ Genotyping to determine the multiplicity of infection (MOI) can be performed using either one or two markers that are extremely polymorphic, or a larger number of less polymorphic genome-wide markers. Currently, regions of the genome containing polymorphic repeat sequences, such as microsatellites or surface antigen genes, are the markers of choice for doing this. Microsatellite markers are short, tandem, one to six nucleotide repeats, found frequently throughout the genome and are typically, selectively neutral. ”

“ Not only useful in the context of molecular epidemiology studies, identifying and managing multiple clone infections may have additional public health implications, as increasing, or high levels of multiple clone P. vivax infections may drive increases in parasite virulence and fitness, as parasite clones compete for both resources within the infected host and survival against antimalarial interventions [19] . ”

“ Gunawardena and colleagues reported diversity of the MS16 microsatellite was far higher amongst Sri Lankan P. vivax strains compared to strains collected in Ethiopia, despite a higher rate of polyclonal infections detected amongst the Ethiopian samples tested [29] (Table 1) . A similarly high level of MS16 diversity was observed by Koepfli and colleagues, reporting that more clones were detected using MS16, compared with the MSP1-f3 marker amongst strains from Papua New Guinea (PNG) , due to a greater likelihood of clones sharing the same MSP1-f3 allele [62] . ”

“ McCutchan, TF & Su, XZ (2008) , Local adaptation and vector-mediated population structure in Plasmodium vivax malaria, vol. 25, pp. 1245–1252, 10.1093/molbev/msn07318385220 JoyDAGonzalez-CeronLCarltonJMGueyeAFayMMcCutchanTFSuXZ, pmid:18385220, DOI 10.1093/molbev/msn073 ↑ Sutton, PL; Neyra, V; Hernandez, JN & Branch, OH (2009) , Plasmodium falciparum and Plasmodium vivax infections in the Peruvian Amazon: propagation of complex, multiple allele-type infections without super-infection, vol. ”