Research article

Low density parasitaemia, red blood cell polymorphisms and Plasmodium falciparum specific immune responses in a low endemic area in northern Tanzania

Seif Shekalaghe^1,2 , Michael Alifrangis³ , Charles Mwanziva² , Anders Enevold³ , Steve Mwakalinga³ , Humphrey Mkali² , Reginald Kavishe² , Alphaxard Manjurano⁴ , Robert Sauerwein¹ , Chris Drakeley⁴ and Teun Bousema¹

¹  Department of Medical Microbiology, Radboud University Nijmegen Medical Centre, Nijmegen, The Netherlands

²  Kilimanjaro Christian Medical College, Moshi, Tanzania

³  Centre for Medical Parasitology at the Department of International Health, Immunology and Microbiology, University of Copenhagen, and at the Department of infectious Diseases, Copenhagen University Hospital (Rigshospitalet), Copenhagen, Denmark

⁴  Joint Malaria Programme, Moshi, Tanzania; Kilimanjaro Christian Medical Centre, Moshi, Tanzania; Department of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, London, UK

author email corresponding author email

BMC Infectious Diseases 2009, 9:69doi:10.1186/1471-2334-9-69

Published:	21 May 2009

Abstract

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 α⁺-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 α⁺-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 α⁺-thalassaemia was observed.

Conclusion

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 α⁺-thalassaemia.