title: Characteristic age distribution of Plasmodium vivax infections after malaria elimination on Aneityum Island, Vanuatu.
abstract: Resurgence is a major concern after malaria elimination. After the initiation of the elimination program on Aneityum Island in 1991, microscopy showed that Plasmodium falciparum disappeared immediately, whereas P. vivax disappeared from 1996 onward, until P. vivax cases were reported in January 2002. By conducting malariometric surveys of the entire population of Aneityum, we investigated the age distribution of individuals with parasites during this epidemic in the context of antimalarial antibody levels and parasite antigen diversity. In July 2002, P. vivax infections were detected by microscopy in 22/759 individuals: 20/298 born after the beginning of the elimination program in 1991, 2/126 born between 1982 and 1991, and none of 335 born before 1982. PCR increased the number of infections detected to 77, distributed among all age groups. Prevalences were 12.1%, 16.7%, and 6.0%, respectively (P < 0.001). In November, a similar age pattern was found, but with fewer infections: 6/746 and 39/741 individuals were found to be infected by microscopy and PCR, respectively. The frequencies of antibody responses to P. vivax were significantly higher in individuals born before 1991 than in younger age groups and were similar to those on Malakula Island, an area of endemicity. Remarkably low antigen diversity (h, 0.15) of P. vivax infections was observed on Aneityum compared with the other islands (h, 0.89 to 1.0). A P. vivax resurgence was observed among children and teenagers on Aneityum, an age distribution similar to those before elimination and on islands where P. vivax is endemic, suggesting that in the absence of significant exposure, immunity may persist, limiting infection levels in adults. The limited parasite gene pool on islands may contribute to this protection.
authors.affiliation: Island Malaria Group, Department of Microbiology, Tumor and Cell Biology, Karolinska Institutet, Stockholm, Sweden.
authors.forename: Akira
authors.initials: A
authors.lastname: Kaneko
authors.forename: Luis F
authors.initials: LF
authors.lastname: Chaves
authors.forename: George
authors.initials: G
authors.lastname: Taleo
authors.forename: Morris
authors.initials: M
authors.lastname: Kalkoa
authors.forename: Rie
authors.initials: R
authors.lastname: Isozumi
authors.forename: Renu
authors.initials: R
authors.lastname: Wickremasinghe
authors.forename: Hedvig
authors.initials: H
authors.lastname: Perlmann
authors.forename: Satoru
authors.initials: S
authors.lastname: Takeo
authors.forename: Takafumi
authors.initials: T
authors.lastname: Tsuboi
authors.forename: Shin-ichiro
authors.initials: S
authors.lastname: Tachibana
authors.forename: Masatsugu
authors.initials: M
authors.lastname: Kimura
authors.forename: Anders
authors.initials: A
authors.lastname: Björkman
authors.forename: Marita
authors.initials: M
authors.lastname: Troye-Blomberg
authors.forename: Kazuyuki
authors.initials: K
authors.lastname: Tanabe
authors.forename: Chris
authors.initials: C
authors.lastname: Drakeley
mesh_terms: D000293:Adolescent; D000328:Adult; D017677:Age Distribution; D000953:Antigens, Protozoan / Q000097:blood; D002648:Child; D002675:Child, Preschool; D016054:DNA, Protozoan / Q000032:analysis; D005260:Female; D006801:Humans; D007223:Infant; D016780:Malaria, Vivax / Q000453:epidemiology*; D008297:Male; D008875:Middle Aged; D008969:Molecular Sequence Data; D010966:Plasmodium vivax / Q000235:genetics / Q000302:isolation & purification; D015995:Prevalence; D017422:Sequence Analysis, DNA; D016036:Seroepidemiologic Studies; D009514:Vanuatu / Q000453:epidemiology; D055815:Young Adult
chemical_list: D000953:Antigens, Protozoan; D016054:DNA, Protozoan