title: Epidemiology of forest malaria in Central Vietnam: the hidden parasite reservoir.
abstract: BACKGROUND
  After successfully reducing the malaria burden to pre-elimination levels over the past two decades, the national malaria programme in Vietnam has recently switched from control to elimination. However, in forested areas of Central Vietnam malaria elimination is likely to be jeopardized by the high occurrence of asymptomatic and submicroscopic infections as shown by previous reports. This paper presents the results of a malaria survey carried out in a remote forested area of Central Vietnam where we evaluated malaria prevalence and risk factors for infection.
  
  
  METHODS
  After a full census (four study villages = 1,810 inhabitants), the study population was screened for malaria infections by standard microscopy and, if needed, treated according to national guidelines. An additional blood sample on filter paper was also taken in a random sample of the population for later polymerase chain reaction (PCR) and more accurate estimation of the actual burden of malaria infections. The risk factor analysis for malaria infections was done using survey multivariate logistic regression as well as the classification and regression tree method (CART).
  
  
  RESULTS
  A total of 1,450 individuals were screened. Malaria prevalence by microscopy was 7.8% (ranging from 3.9 to 10.9% across villages) mostly Plasmodium falciparum (81.4%) or Plasmodium vivax (17.7%) mono-infections; a large majority (69.9%) was asymptomatic. By PCR, the prevalence was estimated at 22.6% (ranging from 16.4 to 42.5%) with a higher proportion of P. vivax mono-infections (43.2%). The proportion of sub-patent infections increased with increasing age and with decreasing prevalence across villages. The main risk factors were young age, village, house structure, and absence of bed net.
  
  
  CONCLUSIONS
  This study confirmed that in Central Vietnam a substantial part of the human malaria reservoir is hidden. Additional studies are urgently needed to assess the contribution of this hidden reservoir to the maintenance of malaria transmission. Such evidence will be crucial for guiding elimination strategies.
authors.affiliation: National Institute of Malariology, Parasitology and Entomology (NIMPE), Hanoi, Vietnam. phamvinht@gmail.com.
authors.forename: Pham Vinh
authors.initials: PV
authors.lastname: Thanh
authors.affiliation: National Institute of Malariology, Parasitology and Entomology (NIMPE), Hanoi, Vietnam. nvhong1982@yahoo.com.
authors.forename: Nguyen
authors.initials: N
authors.lastname: Van Hong
authors.affiliation: Provincial Malaria Station, Tam Ky City, Quang Nam Province, Vietnam. nhivan6@gmail.com.
authors.forename: Nguyen
authors.initials: N
authors.lastname: Van Van
authors.affiliation: Université Catholique de Louvain (UCL), Brussels, Belgium. carine.vanmalderen@uclouvain.be.
authors.forename: Carine
authors.initials: C
authors.lastname: Van Malderen
authors.affiliation: Université Ccatholique de Louvain (UCL), Louvain-la-Neuve, Belgium. valerie.obsomer@uclouvain.be.
authors.forename: Valérie
authors.initials: V
authors.lastname: Obsomer
authors.affiliation: Institute of Tropical Medicine Prince Leopold (ITM), Antwerp, Belgium. arosanas@itg.be.
authors.forename: Anna
authors.initials: A
authors.lastname: Rosanas-Urgell
authors.affiliation: Institute of Tropical Medicine Prince Leopold (ITM), Antwerp, Belgium. kpeeters@itg.be.
authors.forename: Koen Peeters
authors.initials: KP
authors.lastname: Grietens
authors.affiliation: National Institute of Malariology, Parasitology and Entomology (NIMPE), Hanoi, Vietnam. xanguyen60@yahoo.com.
authors.forename: Nguyen Xuan
authors.initials: NX
authors.lastname: Xa
authors.affiliation: Shoklo Malaria Research Unit, Mae Sot, Tak Province, Thailand. Germana@tropmedres.ac.
authors.forename: Germana
authors.initials: G
authors.lastname: Bancone
authors.affiliation: Shoklo Malaria Research Unit, Mae Sot, Tak Province, Thailand. Nongnud@shoklo-unit.com.
authors.forename: Nongnud
authors.initials: N
authors.lastname: Chowwiwat
authors.affiliation: National Institute of Malariology, Parasitology and Entomology (NIMPE), Hanoi, Vietnam. tranthanhduong@hotmail.com.
authors.forename: Tran Thanh
authors.initials: TT
authors.lastname: Duong
authors.affiliation: Institute of Tropical Medicine Prince Leopold (ITM), Antwerp, Belgium. udalessandro@mrc.gm.|Medical Research Council Unit (MRC Unit), Fajara, The Gambia. udalessandro@mrc.gm.
authors.forename: Umberto
authors.initials: U
authors.lastname: D'Alessandro
authors.affiliation: Université Catholique de Louvain (UCL), Brussels, Belgium. niko.speybroeck@uclouvain.be.
authors.forename: Niko
authors.initials: N
authors.lastname: Speybroeck
authors.affiliation: Institute of Tropical Medicine Prince Leopold (ITM), Antwerp, Belgium. aerhart@itg.be.
authors.forename: Annette
authors.initials: A
authors.lastname: Erhart
mesh_terms: D000293:Adolescent; D000328:Adult; D002648:Child; D003430:Cross-Sectional Studies; D005260:Female; D065928:Forests; D006801:Humans; D008288:Malaria / Q000453:epidemiology*; D008297:Male; D012307:Risk Factors; D014744:Vietnam / Q000453:epidemiology; D055815:Young Adult