Antibody response dynamics to the Plasmodium falciparum conserved vaccine candidate antigen, merozoite surface protein-1 C-terminal 19kD (MSP1-19kD), in Peruvians exposed to hypoendemic malaria transmission.
BACKGROUND
In high-transmission areas, developing immunity to symptomatic Plasmodium falciparum infections requires 2-10 years of uninterrupted exposure. Delayed malaria-immunity has been attributed to difficult-to-develop and then short-lived antibody responses.


METHODS
In a study area with <0.5 P. falciparum infections/person/year, antibody responses to the MSP1-19kD antigen were evaluated and associations with P. falciparum infections in children and adults. In months surrounding and during the malaria seasons of 2003-2004, 1,772 participants received > or =6 active visits in one study-year. Community-wide surveys were conducted at the beginning and end of each malaria season, and weekly active visits were completed for randomly-selected individuals each month. There were 79 P. falciparum infections with serum samples collected during and approximately one month before and after infection. Anti-MSP1-19kD IgG levels were measured by ELISA.


RESULTS
The infection prevalence during February-July was similar in children (0.02-0.12 infections/person/month) and adults (0.03-0.14 infections/person/month) and was negligible in the four-month dry season. In children and adults, the seroprevalence was maintained in the beginning (children = 28.9%, adults = 61.8%) versus ending malaria-season community survey (children = 26.7%, adults = 64.6%). Despite the four-month non-transmission season, the IgG levels in Plasmodium-negative adults were similar to P. falciparum-positive adults. Although children frequently responded upon infection, the transition from a negative/low level before infection to a high level during/after infection was slower in children. Adults and children IgG-positive before infection had reduced symptoms and parasite density.


CONCLUSIONS
Individuals in low transmission areas can rapidly develop and maintain alphaMSP1-19kD IgG responses for >4 months, unlike responses reported in high transmission study areas. A greater immune capacity might contribute to the frequent asymptomatic P. falciparum infections in this Peruvian population.
Torres
Katherine J
KJ
Department of Medicine, Division of Infectious Disease, University of Alabama, Alabama, Birmingham, USA. kathjess2000@yahoo.com
Clark
Eva H
EH
Hernandez
Jean N
JN
Soto-Cornejo
Katherine E
KE
Gamboa
Dionicia
D
Branch
OraLee H
OH
D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000818:Animals; D000913:Antibodies, Protozoan / Q000097:blood*; D002648:Child; D002675:Child, Preschool; D019353:Endemic Diseases / Q000517:prevention & control; D004797:Enzyme-Linked Immunosorbent Assay; D006801:Humans; D007074:Immunoglobulin G / Q000097:blood; D007223:Infant; D017780:Malaria Vaccines / Q000276:immunology*; D016778:Malaria, Falciparum / Q000453:epidemiology / Q000517:prevention & control* / Q000635:transmission; D020066:Merozoite Surface Protein 1 / Q000276:immunology*; D008875:Middle Aged; D010568:Peru / Q000453:epidemiology; D010963:Plasmodium falciparum / Q000276:immunology*; D015995:Prevalence; D016036:Seroepidemiologic Studies
D000913:Antibodies, Protozoan; D007074:Immunoglobulin G; D017780:Malaria Vaccines; D020066:Merozoite Surface Protein 1
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