The RTS,S/AS01B malaria vaccine warrants comparative field trials with RTS,S/AS02A to determine the best formulation for the protection of children and infants. The association between complete protection and immune responses is a potential tool for further optimization of protection. Trial registration. ClinicalTrials.gov identifier NCT00075049.

The gene for the circumsporozoite (CS) protein of Plasmodium falciparum has been cloned and its nucleotide sequence determined. The gene encodes a protein of 412 amino acids as deduced from the nucleotide sequence. The protein contains 41 tandem repeats of a tetrapeptide, 37 of which are Asn-Ala-Asn-Pro and four of which are Asn-Val-Asp-Pro. Monoclonal antibodies against the CS protein of Plasmodium falciparum were inhibited from binding to the protein by synthetic peptides of the repeat sequence. The CS protein of Plasmodium falciparum and the CS protein of a simian malaria parasite, Plasmodium knowlesi, have two regions of homology, one of which is present on either side of the repeat. One region contains 12 of 13 identical amino acids. Within the nucleotide sequence of this region, 25 of 27 nucleotides are conserved. The conservation of these regions in parasites widely separated in evolution suggests that they may have a function such as binding to liver cells and may represent an invariant target for immunity.

Abstract. Determining malaria vector species and age is crucial to measure malaria risk. Although different in ecology and susceptibility to control, the African malaria vectors Anopheles gambiae sensu stricto and An. arabiensis are morphologically similar and can be differentiated only by molecular techniques. Furthermore, few reliable methods exist to estimate the age of these vectors, which is a key predictor of malaria transmission intensity. We evaluated the use of nearinfrared spectroscopy (NIRS) to determine vector species and age. This non-destructive technique predicted the species of field-collected mosquitoes with approximately 80% accuracy and predicted the species of laboratory-reared insects with almost 100% accuracy. The relative age of young or old females was predicted with approximately 80% accuracy, and young and old insects were predicted with ≥ 90% accuracy. For applications where rapid assessment of the age structure and species composition of wild vector populations is needed, NIRS offers a valuable alternative to traditional methods.

Abstract. Nine monoclonal antibodies (MAbs) developed against Plasmodium vivax (Grassi & Feletti) salivary gland sporozoites were evaluated for use in an enzyme‐linked immunosorbent assay (ELISA), using sporozoites developed in Anopheles dims Peyton & Harrison An.gambiae Giles and An.maculatus Theobald. Four of the antibodies were unsuitable due to the low sensitivity of the resulting assays or the requirement for high concentrations of capture antibody. An additional two MAbs were rejected because they resulted in assays with high background absorbance, attributed to self‐binding. Of the three remaining MAbs, the use of Navy vivax sporozoite (NVS) 3 resulted in an ELISA with the highest sensitivity and the lowest concentration requirement for capture antibody. Assay sensitivity varied with sporozoite strain indicating possible quantitative epitope heterogeneity. None of the MAbs cross‐reacted with the heterologous sporozoites tested by immunofluorescence antibody assay (IFA). The IFA activity was not an indicator of ELISA sensitivity. The use of MAb NVS 3 in a standardized ELISA method resulted in an assay 10 times more sensitive than reported previously for P. vivax sporozoites, with a detection limit of fewer than 100 sporozoites per mosquito.

No abstract

Abstract. We present evidence that a parasite with characteristics of Plasmodium vivax is being transmitted among Duffy blood group-negative inhabitants of Kenya. Thirty-two of 4,901 Anopheles gambiae and An. funestus (0.65%) collected in Nyanza Province were ELISA positive for the P. vivax circumsporozoite protein VK 247. All positives were found late in the rainy season, when An. funestus predominated, and disproportionately many were found at a single village. A P. vivax specific sequence of the SSU rRNA gene was amplified from three of six ELISA-positive mosquitoes. Erythrocytes from 31 children, including 9 microscopically diagnosed as infected with P. vivax, were negative by flow cytometry for the Fy3 or Fy6 epitopes, which indicate Duffy blood group expression. A DNA fragment specific for the C terminus of the gene for P. vivax merozoite surface protein 1 (MSP-1) was amplified from the blood of four of these children and subsequently sequenced from two.

Vector incrimination studies were conducted from April 2003 to February 2005 at three riverine villages 1.5 km to 7.0 km apart, along the Matapi River, Amapa State, Brazil. A total of 113,117 mosquitoes were collected and placed in pools of

Phenotypic heterogeneity in the repetitive portion of a human malaria circumsporozoite (CS) protein, a major target of candidate vaccines, has been found. Over 14% of clinical cases of uncomplicated Plasmodium vivax malaria at two sites in western Thailand produced sporozoites immunologically distinct from previously characterized examples of the species. Monoclonal antibodies to the CS protein of other P. vivax isolates and to other species of human and simian malarias did not bind to these nonreactive sporozoites, nor did antibodies from monkeys immunized with a candidate vaccine made from the repeat portion of a New World CS protein. The section of the CS protein gene between the conserved regions I and II of a nonreactive isolate contained a nonapeptide repeat, Ala-Asn-Gly-Ala-Gly-Asn-Gln-Pro-Gly, identical at only three amino acid positions with published nonapeptide sequences. This heterogeneity implies that a P. vivax vaccine based on the CS protein repeat of one isolate will not be universally protective.