Low density parasitaemia, red blood cell polymorphisms and Plasmodium falciparum specific immune responses in a low endemic area in northern Tanzania.
BACKGROUND
Low density Plasmodium falciparum infections, below the microscopic detection limit, may play an important role in maintaining malaria transmission in low endemic areas as well as contribute to the maintenance of acquired immunity. Little is known about factors influencing the occurrence of sub-microscopic parasitaemia or the relation with immune responses.We investigated possible associations between the occurrence of sub-microscopic P. falciparum parasite carriage and antibody responses to the asexual stage antigens, G6PD deficiency and alpha+-thalassaemia in 464 subjects from a low endemic area in northern Tanzania.


METHODS
We used samples collected from two cross sectional surveys conducted during dry and wet season in 2005. Submicroscopic parasitaemia was detected by using quantitative nucleic acid sequence based amplification (QT-NASBA). Genotyping for G6PD and alpha+-thalassaemia were performed by high throughput PCR; the prevalence and level of total IgG antibodies against MSP-1, MSP-2 and AMA-1 were determined by ELISA.


RESULTS
Compared to parasite free individuals, individuals carrying sub-microscopic densities of P. falciparum parasites had significantly higher median antibody levels to MSP-1 (p = 0.042) and MSP-2 (p = 0.034) but not to AMA-1 (p = 0.14) while no clear relation between sub-microscopic parasite carriage and G6PD deficiency or alpha+-thalassaemia was observed.


CONCLUSIONS
Our data suggest a role for sub-microscopic parasite densities in eliciting or maintaining humoral immune responses without evidence for a modulating effect of G6PD deficiency or alpha+-thalassaemia.
Shekalaghe
Seif
S
Department of Medical Microbiology, Radboud University Nijmegen Medical Centre, Nijmegen, The Netherlands. sshekalaghe@yahoo.com
Alifrangis
Michael
M
Mwanziva
Charles
C
Enevold
Anders
A
Mwakalinga
Steve
S
Mkali
Humphrey
H
Kavishe
Reginald
R
Manjurano
Alphaxard
A
Sauerwein
Robert
R
Drakeley
Chris
C
Bousema
Teun
T
D000818:Animals; D000913:Antibodies, Protozoan / Q000097:blood*; D000953:Antigens, Protozoan / Q000276:immunology; D002353:Carrier State; D016009:Chi-Square Distribution; D003430:Cross-Sectional Studies; D019353:Endemic Diseases; D004912:Erythrocytes / Q000473:pathology*; D005954:Glucosephosphate Dehydrogenase / Q000235:genetics; D006801:Humans; D016778:Malaria, Falciparum / Q000453:epidemiology / Q000235:genetics / Q000276:immunology / Q000469:parasitology*; D008565:Membrane Proteins / Q000276:immunology; D020066:Merozoite Surface Protein 1 / Q000276:immunology; D018512:Parasitemia / Q000469:parasitology*; D010963:Plasmodium falciparum / Q000276:immunology / Q000502:physiology*; D015995:Prevalence; D015800:Protozoan Proteins / Q000276:immunology; D021161:Self-Sustained Sequence Replication; D018709:Statistics, Nonparametric; D011795:Surveys and Questionnaires; D013636:Tanzania / Q000453:epidemiology; D017085:alpha-Thalassemia / Q000235:genetics
D000913:Antibodies, Protozoan; D000953:Antigens, Protozoan; D008565:Membrane Proteins; D020066:Merozoite Surface Protein 1; D015800:Protozoan Proteins; C090077:apical membrane antigen I, Plasmodium; C065974:merozoite surface protein 2, Plasmodium; D005954:Glucosephosphate Dehydrogenase