Does biased gene conversion influence polymorphism in the circumsporozoite protein-encoding gene of Plasmodium vivax?

Variation between North Korean and Latin American isolates in the circumsporozoite (CS) protein encoding gene of the human malaria parasite Plasmodium vivax was studied. Polymorphic positions are confined to the central tandemly repeated sequences. Nucleotide substitutions in the tandem repeats produce variants; these substituted positions within the repeat array tend to be conserved between genes. The North Korean CS gene has a short insertion after the repeats encoding a 4-amino acid repeat (Ala-Gly-Gly-Asn) not found in the New World P. vivax genes. This sequence is found both flanking and within the tandem repeats of the CS genes of several strains of the Southeast Asian simian malaria parasite, Plasmodium cynomolgi. The intraspecific conservation of positions of variants within tandem repeat arrays and the interspecific conservation of probably ancestral repeat motifs at the end of these arrays are consistent with the occurrence of nonreciprocal genetic exchanges between the tandem repeats of these genes. However, a striking asymmetry in strand nucleotide composition within the tandem repeats of all CS genes leads us to suggest that biased correction of heteroduplexes formed during recombination plays a role in the evolution of these genes

Seasonal variation in agglutination of Plasmodium falciparum-infected erythrocytes

Abstract. Agglutination and rosette formation are in vitro characteristics of Plasmodium falciparum–infected erythrocytes, which have been associated with host protective immune responses and also with parasite virulence. The present study was carried out in an area of seasonal and unstable malaria transmission in eastern Sudan. Plasma samples were obtained before, during, and after the transmission season from a volunteer cohort of 64 individuals seven years of age and older. These plasmas were assayed for their ability to agglutinate cultured parasitized eryth-rocytes originally obtained from acute malaria infection samples taken from five of the cohort members. Our data show that the capacity of donor plasma samples to agglutinate parasitized cells depended largely on the time of sampling relative to the transmission season, at least within this epidemiologic setting. Thus, although less than half of the pretransmission season samples could agglutinate any of the five lines of cultured parasites, all post-transmission season samples could agglutinate at least one of the parasite lines, with 74 % agglutinating two or more lines. This increase in the agglutination capacity of individual plasma samples after the transmission season occurred essentially regardless of whether an individual had experienced a clinical malaria attack during the transmission season. The study thus confirms the acquisition of agglutinating antibodies following episodes of clinical malaria, but also dem-onstrates that such acquisition can take place in the absence of disease, presumably as a consequence of subclinica

Novel Plasmodium falciparum clones and rising clone multiplicities are associated with the increase in malaria morbidity in Ghanaian children during the transition into the high transmission season

A survey of Plasmodium falciparum infection and clone multiplicity in Ghanaian children was carried out to study the effect of the onset of the malaria transmission season on disease incidence. Fortnightly blood samples were collected from 40 children living in the rural town of Dodowa, between February and August 1998. P. falciparum parasite densities were calculated and PCR genotyping was carried out using the polymorphic MSP-1 and MSP-2 genes as target loci for the estimation of the number of parasite clones in each sample. The average clone number was estimated using maximum likelihood techniques and the minimum number of clones per patient was analysed for the effects of age, sex, season, minimum number of clones per child, level of parasitaemia and parasite genotype. The statistical analysis indicated that the more clones a child carried, the more likely they were to have a clinical malaria episode. This was true after adjusting for age and season effects and for the measured circulating parasitaemia. The probability of clinical disease also increased if the MSP-1 MAD 20 and the MSP-2 FC 27 alleles were present. This longitudinal analysis thus indicates that the probability of a Ghanaian child having a symptomatic malaria episode is positively associated with both increasing numbers and novel types of P. falciparum clones

Voices from an edge. Unsettling the practices of youth voice and participation: arts-based practice in The Blue Room, Manchester

The strengths and limitations of approaches to participatory and democratic practice rooted in voice have been discussed in relation to education and also ‘youth voice’. The paper seeks to make critical connection between the two debates, especially in relation to the persistence of practices of exclusion and marginalisation. Drawing on a two-year participant observation of a creativity-based project in Manchester, UK – The Blue Room – which worked with young men in the city centre who may have been engaged in selling sex, the article asks what it might mean for them to have voice. The widely discussed limitations of neo-liberal accounts of voice and choice are evident in this case, for the extent to which such a way of life can be thought to be freely chosen is a matter of intense debate. The possibility explored in this article is that arts-based strategies of pedagogic engagement might offer (to this group of young people and others) a hopeful (because complex, provisional and in process) form of voice rather than a tokenistic and controlling one

The Plasmodium falciparum var gene transcription strategy at the onset of blood stage infection in a human volunteer.

Item does not contain fulltextThe var genes encode a family of adhesion receptor proteins, Plasmodium falciparum erythrocyte membrane protein 1 (PfEMP1), which profoundly influence malaria pathogenesis. Only a single var gene is transcribed and one PfEMP1 expressed per P.falciparum parasite. Here we present the in vivo transcript distribution of var genes in a P. falciparum-infected non-immune individual and show that the initial expression of PfEMP1 is based on a strategy that allows all or most variants of PfEMP1s to be expressed by the parasite population at the onset of the blood stage infection