Serological markers to measure recent changes in malaria at population level in Cambodia.
BACKGROUND
Serological markers for exposure to different Plasmodium species have recently been used in multiplex immunoassays based on the Luminex technology. However, interpretation of the assay results requires consideration of the half-life of specific antibodies against these markers. Therefore, the aim of the present study was to document the half-life of malaria specific serological makers, as well as assessing the sensitivity of these markers to pick up recent changes in malaria exposure.


METHODS
A recently developed multiplex immunoassay was used to measure the intensity of antibody (Ab) responses against 19 different Plasmodium specific antigens, covering different human malaria parasites and two vector saliva antigens. Therefore, 8439 blood samples from five cross-sectional surveys in Ratanakiri, Cambodia, were analysed. These involve a random selection from two selected surveys, and an additional set of blood samples of individuals that were randomly re-sampled three, four or five times. A generalized estimating equation model and linear regression models were fitted on log transformed antibody intensity data.


RESULTS
Results showed that most (17/21) Ab-responses are higher in PCR positive than PCR negative individuals. Furthermore, these antibody-responses follow the same upward trend within each age group. Estimation of the half-lives showed differences between serological markers that reflect short- (seasonal) and long-term (year round) transmission trends. Ab levels declined significantly together with a decrease of PCR prevalence in a group of malaria endemic villages.


CONCLUSIONS
For Plasmodium falciparum, antibodies against LSA3.RE, GLURP and Pf.GLURP.R2 are most likely to be a reflexion of recent (range from 6 to 8 months) exposure in the Mekong Subregion. PvEBP is the only Plasmodium vivax Ag responding reasonably well, in spite of an estimated Ab half-life of more than 1 year. The use of Ab intensity data rather dichotomizing the continuous Ab-titre data (positive vs negative) will lead to an improved approach for serological surveillance.
Department of Biomedical Sciences, Institute of Tropical Medicine, Antwerp, Belgium. kkerkhof@itg.be.|Department of Biomedical Sciences, University of Antwerp, Antwerp, Belgium. kkerkhof@itg.be.
Karen
http://orcid.org/0000-0002-2208-9902
K
Kerkhof
Department of Biomedical Sciences, Institute of Tropical Medicine, Antwerp, Belgium.|Department of Biology, University of Antwerp, Antwerp, Belgium.
Vincent
V
Sluydts
Department of Biomedical Sciences, Institute of Tropical Medicine, Antwerp, Belgium.|Department of Biomedical Sciences, University of Antwerp, Antwerp, Belgium.
Laura
L
Willen
Molecular Epidemiology Unit, Institut Pasteur du Cambodge, Phnom Penh, Cambodia.
Saorin
S
Kim
Molecular Epidemiology Unit, Institut Pasteur du Cambodge, Phnom Penh, Cambodia.
Lydie
L
Canier
National Centre for Parasitology, Entomology and Malaria Control, Phnom Penh, Cambodia.
Somony
S
Heng
Division of Malaria Research, Proteo-Science Center, Ehime University, Matsuyama, Japan.
Takafumi
T
Tsuboi
National Centre for Parasitology, Entomology and Malaria Control, Phnom Penh, Cambodia.
Tho
T
Sochantha
National Centre for Parasitology, Entomology and Malaria Control, Phnom Penh, Cambodia.
Siv
S
Sovannaroth
Molecular Epidemiology Unit, Institut Pasteur du Cambodge, Phnom Penh, Cambodia.
Didier
D
Ménard
Department of Biomedical Sciences, Institute of Tropical Medicine, Antwerp, Belgium.|Department of Biomedical Sciences, University of Antwerp, Antwerp, Belgium.
Marc
M
Coosemans
Department of Biomedical Sciences, Institute of Tropical Medicine, Antwerp, Belgium. ldurnez@itg.be.
Lies
L
Durnez
D000293:Adolescent; D000328:Adult; D000913:Antibodies, Protozoan / Q000097:blood*; D000917:Antibody Formation; D002160:Cambodia / Q000453:epidemiology; D002648:Child; D002675:Child, Preschool; D003430:Cross-Sectional Studies; D005260:Female; D006207:Half-Life; D006801:Humans; D007223:Infant; D008288:Malaria / Q000453:epidemiology* / Q000276:immunology*; D008297:Male; D008875:Middle Aged; D000072138:Mosquito Vectors / Q000276:immunology*; D010963:Plasmodium falciparum / Q000276:immunology*; D010966:Plasmodium vivax / Q000276:immunology*; D055815:Young Adult
D000913:Antibodies, Protozoan
Half life; Malaria; Malaria transmission; Serological markers