title: Multiple-clone activation of hypnozoites is the leading cause of relapse in Plasmodium vivax infection.
abstract: BACKGROUND
  Plasmodium vivax infection is characterized by a dormant hepatic stage, the hypnozoite that is activated at varying periods of time after clearance of the primary acute blood-stage, resulting in relapse. Differentiation between treatment failure and new infections requires characterization of initial infections, relapses, and clone multiplicity in vivax malaria infections.
  
  
  RESULTS
  Parasite DNA obtained from primary/relapse paired blood samples of 30 patients with P. vivax infection in Brazil was analyzed using 10 molecular markers (8 microsatellites and MSP-1 blocks 2 and 10). Cloning of PCR products and genotyping was used to identify low-frequency clones of parasites. We demonstrated a high frequency of multiple-clone infections in both primary and relapse infections. Few alleles were identified per locus, but the combination of these alleles produced many haplotypes. Consequently, the majority of parasites involved in relapse showed haplotypes that were distinct from those of primary infections. Plasmodium vivax relapse was characterized by temporal variations in the predominant parasite clones.
  
  
  CONCLUSIONS
  The high rate of low frequency alleles observed in both primary and relapse infections, along with temporal variation in the predominant alleles, might be the source of reported heterologous hypnozoite activation. Our findings complicate the concept of heterologous activation, suggesting the involvement of undetermined mechanisms based on host or environmental factors in the simultaneous activation of multiple clones of hypnozoites.
authors.affiliation: Laboratory of Malaria, Centro de Pesquisas René Rachou - Fiocruz Minas, Belo Horizonte, Minas Gerais, Brazil.
authors.forename: Flávia Carolina F
authors.initials: FC
authors.lastname: de Araujo
authors.forename: Antônio Mauro
authors.initials: AM
authors.lastname: de Rezende
authors.forename: Cor Jesus F
authors.initials: CJ
authors.lastname: Fontes
authors.forename: Luzia Helena
authors.initials: LH
authors.lastname: Carvalho
authors.forename: Cristiana F
authors.initials: CF
authors.lastname: Alves de Brito
mesh_terms: D000328:Adult; D000483:Alleles; D000962:Antimalarials / Q000008:administration & dosage; D001938:Brazil; D002908:Chronic Disease; D005260:Female; D005787:Gene Frequency; D005838:Genotype; D006239:Haplotypes; D006790:Host-Parasite Interactions / Q000235:genetics / Q000276:immunology; D006801:Humans; D016780:Malaria, Vivax / Q000097:blood / Q000188:drug therapy / Q000235:genetics / Q000469:parasitology; D008297:Male; D020066:Merozoite Surface Protein 1 / Q000235:genetics; D018895:Microsatellite Repeats / Q000235:genetics; D008875:Middle Aged; D010966:Plasmodium vivax / Q000235:genetics / Q000378:metabolism / Q000472:pathogenicity; D012008:Recurrence; D017211:Treatment Failure; D055815:Young Adult
chemical_list: D000962:Antimalarials; D020066:Merozoite Surface Protein 1