title: Prevalence of Plasmodium falciparum transmission reducing immunity among primary school children in a malaria moderate transmission region in Zimbabwe.
abstract: Malaria continues to cause alarming morbidity and mortality in more than 100 countries worldwide. Antigens in the various life cycle stages of malaria parasites are presented to the immune system during natural infection and it is widely recognized that after repeated malaria exposure, adults develop partially protective immunity. Specific antigens of natural immunity represent among the most important targets for the development of malaria vaccines. Immunity against the transmission stages of the malaria parasite represents an important approach to reduce malaria transmission and is believed to become an important tool for gradual elimination of malaria. Development of immunity against Plasmodium falciparum sexual stages was evaluated in primary school children aged 6-16 years in Makoni district of Zimbabwe, an area of low to modest malaria transmission. Malaria infection was screened by microscopy, rapid diagnostic tests and finally using nested PCR. Plasma samples were tested for antibodies against recombinant Pfs48/45 and Pfs47 by ELISA. Corresponding serum samples were used to test for P. falciparum transmission reducing activity in Anopheles stephensi and An. gambiae mosquitoes using the membrane feeding assay. The prevalence of malaria diagnosed by rapid diagnostic test kit (Paracheck)™ was 1.7%. However, of the randomly tested blood samples, 66% were positive by nested PCR. ELISA revealed prevalence (64% positivity at 1:500 dilution, in randomly selected 66 plasma samples) of antibodies against recombinant Pfs48/45 (mean A 405nm=0.53, CI=0.46-0.60) and Pfs47 (mean A405nm=0.91, CI=0.80-1.02); antigens specific to the sexual stages. The mosquito membrane feeding assay demonstrated measurable transmission reducing ability of the samples that were positive for Pfs48/45 antibodies by ELISA. Interestingly, 3 plasma samples revealed enhancement of infectivity of P. falciparum in An. stephensi mosquitoes. These studies revealed the presence of antibodies with transmission reducing immunity in school age children from a moderate transmission area of malaria, and provide further support to exploit target antigens such as Pfs48/45 for further development of a malaria transmission blocking vaccine.
authors.affiliation: Scientific and Industrial Research and Development Centre, Food and Biomedical Technology Institute, 1574 Alpes Rd., P O Box 6640, Hatcliffe, Harare, Zimbabwe; University of Zimbabwe, Biochemistry Department, P O Box MP 167, Mount Pleasant, Harare, Zimbabwe.
authors.forename: Noah H
authors.initials: NH
authors.lastname: Paul
authors.affiliation: University of Zimbabwe, Biochemistry Department, P O Box MP 167, Mount Pleasant, Harare, Zimbabwe.
authors.forename: Arthur
authors.initials: A
authors.lastname: Vengesai
authors.affiliation: University of Zimbabwe, Biochemistry Department, P O Box MP 167, Mount Pleasant, Harare, Zimbabwe; School of Laboratory Medicine & Medical Sciences, College of Health Sciences, University of KwaZulu Natal, Durban, South Africa.
authors.forename: Takafira
authors.initials: T
authors.lastname: Mduluza
authors.affiliation: University of Zambia School of Medicine and University Teaching Hospital, Department of Paediatrics and Child Health, P.O. Box 50110, Lusaka, Zambia.
authors.forename: James
authors.initials: J
authors.lastname: Chipeta
authors.affiliation: University of Zimbabwe, College of Health Sciences Department of Community Medicine, P O Box MP 167, Mount Pleasant, Harare, Zimbabwe.
authors.forename: Nicholas
authors.initials: N
authors.lastname: Midzi
authors.affiliation: Department of Tropical Medicine, School of Public Health and Tropical Medicine, and Vector Borne Infectious Diseases Research Center, Tulane University, New Orleans, LA 70112, USA.
authors.forename: Geetha P
authors.initials: GP
authors.lastname: Bansal
authors.affiliation: Department of Tropical Medicine, School of Public Health and Tropical Medicine, and Vector Borne Infectious Diseases Research Center, Tulane University, New Orleans, LA 70112, USA. Electronic address: nkumar@tulane.edu.
authors.forename: Nirbhay
authors.initials: N
authors.lastname: Kumar
mesh_terms: D000293:Adolescent; D000818:Animals; D000852:Anopheles / Q000378:metabolism; D000913:Antibodies, Protozoan / Q000276:immunology*; D002648:Child; D055808:Drug Discovery; D004797:Enzyme-Linked Immunosorbent Assay; D005260:Female; D006801:Humans; D007113:Immunity, Innate; D008018:Life Cycle Stages / Q000276:immunology*; D017780:Malaria Vaccines / Q000276:immunology*; D016778:Malaria, Falciparum / Q000453:epidemiology / Q000276:immunology* / Q000517:prevention & control / Q000635:transmission; D008297:Male; D008562:Membrane Glycoproteins / Q000276:immunology*; D010963:Plasmodium falciparum / Q000276:immunology; D016133:Polymerase Chain Reaction; D015995:Prevalence; D015800:Protozoan Proteins / Q000276:immunology*; D015030:Zimbabwe / Q000453:epidemiology
chemical_list: D000913:Antibodies, Protozoan; D017780:Malaria Vaccines; D008562:Membrane Glycoproteins; C526772:Pfs47 protein, Plasmodium falciparum; D015800:Protozoan Proteins; C084847:pfs48-45 protein, Plasmodium falciparum