Measuring sporadic gastrointestinal illness associated with drinking water - an overview of methodologies.

There is an increasing awareness that drinking water contributes to sporadic gastrointestinal illness (GI) in high income countries of the northern hemisphere. A literature search was conducted in order to review: (1) methods used for investigating the effects of public drinking water on GI; (2) evidence of possible dose-response relationship between sporadic GI and drinking water consumption; and (3) association between sporadic GI and factors affecting drinking water quality. Seventy-four articles were selected, key findings and information gaps were identified. In-home intervention studies have only been conducted in areas using surface water sources and intervention studies in communities supplied by ground water are therefore needed. Community-wide intervention studies may constitute a cost-effective alternative to in-home intervention studies. Proxy data that correlate with GI in the community can be used for detecting changes in the incidence of GI. Proxy data can, however, not be used for measuring the prevalence of illness. Local conditions affecting water safety may vary greatly, making direct comparisons between studies difficult unless sufficient knowledge about these conditions is acquired. Drinking water in high-income countries contributes to endemic levels of GI and there are public health benefits for further improvements of drinking water safety.

Malaria Burden in Pregnancy at Mulago National Referral Hospital in Kampala; Uganda

Pregnancy-associated malaria is a major global health concern. To assess the Plasmodium falciparum burden in pregnancy we conducted a cross-sectional study at Mulago Hospital in Kampala; Uganda. Malaria prevalence by each of three measures-peripheral smear; placental smear; and placental histology was 9(35/391); 11.3(44/389); and 13.9(53/382) respectively. Together; smear and histology data yielded an infection rate of 15.5(59/380) of active infections and 4.5(17/380) of past infections; hence 20had been or were infected when giving birth. A crude parity dependency was observed with main burden being concentrated in gravidae 1 through gravidae 3. Twenty-two percent were afflicted by anaemia and 12.2delivered low birthweight babies. Active placental infection and anaemia showed strong association (OR=2.8) whereas parity and placental infection had an interactive effect on mean birthweight (P=.036). Primigravidae with active infection and multigravidae with past infection delivered on average lighter babies. Use of bednet protected significantly against infection (OR=0.56) whilst increased haemoglobin level protected against low birthweight (OR=0.83) irrespective of infection status. Albeit a high attendance at antenatal clinics (96.8); there was a poor coverage of insecticide-treated nets (32) and intermittent preventive antimalarial treatment (41.5)

Malaria burden in pregnancy at mulago national referral hospital in kampala, Uganda.

Pregnancy-associated malaria is a major global health concern. To assess the Plasmodium falciparum burden in pregnancy we conducted a cross-sectional study at Mulago Hospital in Kampala, Uganda. Malaria prevalence by each of three measures-peripheral smear, placental smear, and placental histology was 9% (35/391), 11.3% (44/389), and 13.9% (53/382) respectively. Together, smear and histology data yielded an infection rate of 15.5% (59/380) of active infections and 4.5% (17/380) of past infections; hence 20% had been or were infected when giving birth. A crude parity dependency was observed with main burden being concentrated in gravidae 1 through gravidae 3. Twenty-two percent were afflicted by anaemia and 12.2% delivered low birthweight babies. Active placental infection and anaemia showed strong association (OR = 2.8) whereas parity and placental infection had an interactive effect on mean birthweight (P = .036). Primigravidae with active infection and multigravidae with past infection delivered on average lighter babies. Use of bednet protected significantly against infection (OR = 0.56) whilst increased haemoglobin level protected against low birthweight (OR = 0.83) irrespective of infection status. Albeit a high attendance at antenatal clinics (96.8%), there was a poor coverage of insecticide-treated nets (32%) and intermittent preventive antimalarial treatment (41.5%).

Default Pathway of var2csa switching and translational repression in Plasmodium falciparum.

Antigenic variation is a subtle process of fundamental importance to the survival of a microbial pathogen. In Plasmodium falciparum malaria, PfEMP1 is the major variable antigen and adhesin expressed at the surface of the infected erythrocyte, which is encoded for by members of a family of 60 var-genes. Peri-nuclear repositioning and epigenetic mechanisms control their mono-allelic expression. The switching of PfEMP1 depends in part on variable transition rates and short-lived immune responses to shared minor epitopes. Here we show var-genes to switch to a common gene that is highly transcribed, but sparsely translated into PfEMP1 and not expressed at the erythrocyte surface. Highly clonal and adhesive P. falciparum, which expressed distinct var-genes and the corresponding PfEMP1s at onset, were propagated without enrichment or panning. The parasites successively and spontaneously switched to transcribe a shared var-gene (var2csa) matched by the loss of PfEMP1 surface expression and host cell-binding. The var2csa gene repositioned in the peri-nuclear area upon activation, away from the telomeric clusters and heterochromatin to transcribe spliced, full-length RNA. Despite abundant transcripts, the level of intracellular PfEMP1 was low suggesting post-transcriptional mechanisms to partake in protein expression. In vivo, off-switching and translational repression may constitute one pathway, among others, coordinating PfEMP1 expression.

Generation of cross-protective antibodies against Plasmodium falciparum sequestration by immunization with an erythrocyte membrane protein 1-duffy binding-like 1 alpha domain.

The Plasmodium falciparum erythrocyte membrane protein 1 (PfEMP1) is an important virulence factor on the surface of infected erythrocytes. Naturally acquired antibodies to PfEMP1 expressed by parasites causing severe malaria are suggested to be protective and of major interest for the development of a vaccine against severe disease. In this study, the PfEMP1 expressed by a parasite clone displaying a multiadhesive phenotype associated with severe malaria was well recognized by sera of malaria semi-immune children. The efficiency of the Duffy binding-like 1 alpha (DBL1 alpha) domain of this PfEMP1 was therefore, alone or in combination with two additional DBL1 alpha domains, evaluated as a potential vaccine candidate using both a rodent model and a primate model. Antibodies against the DBL1 alpha domain were generated by immunization with recombinant DBL1 alpha-Semliki Forest virus particles and recombinant protein and analyzed in vitro. The immunized animals were challenged in vivo with various parasite strains or clones. Immunization with the PfEMP1-DBL1 alpha domain abolished the PfEMP1-dependent sequestration of the homologous strain in immunized rats and substantially inhibited parasite adhesion in immunized monkeys. Protection against sequestration of heterologous parasite strains was also confirmed by direct or indirect challenge in the rat model. These results strongly support the use of the DBL1 alpha domain in the development of a vaccine targeting severe malaria.

Nonimmune immunoglobulin binding and multiple adhesion characterize Plasmodium falciparum-infected erythrocytes of placental origin.

The harmful effects of pregnancy-associated malaria (PAM) are engendered by the heavy sequestration of Plasmodium falciparum-parasitized RBCs in the placenta. It is well documented that this process is mediated by interactions of parasite-encoded variant surface antigens and placental receptors. A P. falciparum erythrocyte membrane protein 1 variant, VAR2CSA, and the placental receptor chondroitin sulfate A (CSA) are currently the focus of PAM research. A role for immunoglobulins (IgG and IgM) from normal human serum and hyaluronic acid as additional receptors in placental sequestration have also been suggested. We show here (i) that CSA and nonimmune IgG/IgM binding are linked phenotypes of in vitro-adapted parasites, (ii) that a VAR2CSA variant shown to bind CSA also harbors IgG- and IgM-binding domains (DBL2-X, DBL5-epsilon, and DBL6-epsilon), and (iii) that IgG and IgM binding and adhesion to multiple receptors (IgG/IgM/HA/CSA) rather than the exclusive binding to CSA is a characteristic of fresh Ugandan placental isolates. These findings are of importance for the understanding of the pathogenesis of placental malaria and have implications for the ongoing efforts to develop a global PAM vaccine.

Molecular aspects of malaria pathogenesis.

Plasmodium falciparum being the most lethal plasmodiae is still a major cause of the disease burden and mortality in malaria endemic areas. Due to the wide spread drug resistance in combination with poor socio-economic situation in the vast majority of the endemic countries, malaria is today a great global challenge. The scientific community is, however, progressing. The 23 Mb genome of P. falciparum has been decoded and publicly available. Data of transcriptional profiling at certain developmental stages have already been generated. More than 50% of P. falciparum genes are transcribed constitutively in all the developmental stages of parasite life cycle. Functional disruption of these genes might have implications for parasite growth and development. Available microarray data indicate that P. falciparum preferentially expresses rif and stevor gene families at gametocyte and sporozoite stages while var genes are predominantly expressed at the erythrocytic stage. Gene regulation mechanisms of the variant gene families in P. falciparum are still not understood though some regulatory elements have been proposed. The occurrence of severe malaria is determined by both parasite and human host factors. Sequestration and antigenic variation are two of the evasion mechanisms utilized by P. falciparum in order to escape the human host defences. Understanding the molecular mechanisms underlying these phenomena is of a major importance and interest in malaria research. Here, we summarize and highlight the recent progress in molecular aspects of severe malaria.