title: High Rates of Asymptomatic, Sub-microscopic Plasmodium vivax Infection and Disappearing Plasmodium falciparum Malaria in an Area of Low Transmission in Solomon Islands.
abstract: BACKGROUND
  Solomon Islands is intensifying national efforts to achieve malaria elimination. A long history of indoor spraying with residual insecticides, combined recently with distribution of long lasting insecticidal nets and artemether-lumefantrine therapy, has been implemented in Solomon Islands. The impact of these interventions on local endemicity of Plasmodium spp. is unknown.
  
  
  METHODS
  In 2012, a cross-sectional survey of 3501 residents of all ages was conducted in Ngella, Central Islands Province, Solomon Islands. Prevalence of Plasmodium falciparum, P. vivax, P. ovale and P. malariae was assessed by quantitative PCR (qPCR) and light microscopy (LM). Presence of gametocytes was determined by reverse transcription quantitative PCR (RT-qPCR).
  
  
  RESULTS
  By qPCR, 468 Plasmodium spp. infections were detected (prevalence = 13.4%; 463 P. vivax, five mixed P. falciparum/P. vivax, no P. ovale or P. malariae) versus 130 by LM (prevalence = 3.7%; 126 P. vivax, three P. falciparum and one P. falciparum/P. vivax). The prevalence of P. vivax infection varied significantly among villages (range 3.0-38.5%, p<0.001) and across age groups (5.3-25.9%, p<0.001). Of 468 P. vivax infections, 72.9% were sub-microscopic, 84.5% afebrile and 60.0% were both sub-microscopic and afebrile. Local residency, low education level of the household head and living in a household with at least one other P. vivax infected individual increased the risk of P. vivax infection. Overall, 23.5% of P. vivax infections had concurrent gametocytaemia. Of all P. vivax positive samples, 29.2% were polyclonal by MS16 and msp1F3 genotyping. All five P. falciparum infections were detected in residents of the same village, carried the same msp2 allele and four were positive for P. falciparum gametocytes.
  
  
  CONCLUSIONS
  P. vivax infection remains endemic in Ngella, with the majority of cases afebrile and below the detection limit of LM. P. falciparum has nearly disappeared, but the risk of re-introductions and outbreaks due to travel to nearby islands with higher malaria endemicity remains.
authors.affiliation: The Walter & Eliza Hall Institute, Melbourne, Australia; University of Melbourne, Melbourne, Australia.
authors.forename: Andreea
authors.initials: A
authors.lastname: Waltmann
authors.affiliation: National Health Training and Research Institute, Ministry of Health, Honiara, Solomon Islands.
authors.forename: Andrew W
authors.initials: AW
authors.lastname: Darcy
authors.affiliation: Australian Army Malaria Institute, Brisbane, Australia.
authors.forename: Ivor
authors.initials: I
authors.lastname: Harris
authors.affiliation: The Walter & Eliza Hall Institute, Melbourne, Australia; University of Melbourne, Melbourne, Australia.
authors.forename: Cristian
authors.initials: C
authors.lastname: Koepfli
authors.affiliation: National Vector Borne Disease Control Program, Ministry of Health, Honiara, Solomon Islands.
authors.forename: John
authors.initials: J
authors.lastname: Lodo
authors.affiliation: National Health Training and Research Institute, Ministry of Health, Honiara, Solomon Islands.
authors.forename: Ventis
authors.initials: V
authors.lastname: Vahi
authors.affiliation: National Health Training and Research Institute, Ministry of Health, Honiara, Solomon Islands.
authors.forename: David
authors.initials: D
authors.lastname: Piziki
authors.affiliation: Australian Army Malaria Institute, Brisbane, Australia.
authors.forename: G Dennis
authors.initials: GD
authors.lastname: Shanks
authors.affiliation: The Walter & Eliza Hall Institute, Melbourne, Australia; University of Melbourne, Melbourne, Australia.
authors.forename: Alyssa E
authors.initials: AE
authors.lastname: Barry
authors.affiliation: School of Population Health, University of Queensland, Brisbane, Australia.
authors.forename: Maxine
authors.initials: M
authors.lastname: Whittaker
authors.affiliation: Case Western Reserve University, Cleveland, Ohio, United States of America.
authors.forename: James W
authors.initials: JW
authors.lastname: Kazura
authors.affiliation: The Walter & Eliza Hall Institute, Melbourne, Australia; University of Melbourne, Melbourne, Australia; Barcelona Centre for International Health Research (CRESIB), Barcelona, Spain.
authors.forename: Ivo
authors.initials: I
authors.lastname: Mueller
mesh_terms: D000293:Adolescent; D000328:Adult; D000953:Antigens, Protozoan / Q000235:genetics; D002648:Child; D002675:Child, Preschool; D003430:Cross-Sectional Studies; D005260:Female; D006801:Humans; D016778:Malaria, Falciparum / Q000453:epidemiology*; D016780:Malaria, Vivax / Q000453:epidemiology*; D008297:Male; D008542:Melanesia / Q000453:epidemiology; D008853:Microscopy; D010963:Plasmodium falciparum / Q000235:genetics*; D010966:Plasmodium vivax / Q000235:genetics*; D015995:Prevalence; D015800:Protozoan Proteins / Q000235:genetics; D060888:Real-Time Polymerase Chain Reaction; D055815:Young Adult
chemical_list: D000953:Antigens, Protozoan; D015800:Protozoan Proteins; C065974:merozoite surface protein 2, Plasmodium