Characterization of the repertoire diversity of the Plasmodium falciparum stevor multigene family in laboratory and field isolates

BACKGROUND: The evasion of host immune response by the human malaria parasite Plasmodium falciparum has been linked to expression of a range of variable antigens on the infected erythrocyte surface. Several genes are potentially involved in this process with the var, rif and stevor multigene families being the most likely candidates and coding for rapidly evolving proteins. The high sequence diversity of proteins encoded by these gene families may have evolved as an immune evasion strategy that enables the parasite to establish long lasting chronic infections. Previous findings have shown that the hypervariable region (HVR) of STEVOR has significant sequence diversity both within as well as across different P. falciparum lines. However, these studies did not address whether or not there are ancestral stevor that can be found in different parasites. METHODS: DNA and RNA sequences analysis as well as phylogenetic approaches were used to analyse the stevor sequence repertoire and diversity in laboratory lines and Kilifi (Kenya) fresh isolates. RESULTS: Conserved stevor genes were identified in different P. falciparum isolates from different global locations. Consistent with previous studies, the HVR of the stevor gene family was found to be highly divergent both within and between isolates. Importantly phylogenetic analysis shows some clustering of stevor sequences both within a single parasite clone as well as across different parasite isolates. CONCLUSION: This indicates that the ancestral P. falciparum parasite genome already contained multiple stevor genes that have subsequently diversified further within the different P. falciparum populations. It also confirms that STEVOR is under strong selection pressure

Chronic infection during placental malaria is associated with up-regulation of cycloxygenase-2

<p>Abstract</p> <p>Background</p> <p>Placental malaria (PM) is associated with poor foetal development, but the pathophysiological processes involved are poorly understood. Cyclooxygenase (COX) and lipoxygenase (LOX) which convert fatty acids to prostaglandins and leukotrienes, play important roles in pregnancy and foetal development. COX-2, currently targeted by specific drugs, plays a dual role as it associates with both pre-eclampsia pathology and recovery during infection. The role of COX during PM was questioned by quantifying at delivery COX-1, COX-2, 15-LOX, and IL-10 expression in two groups of malaria infected and uninfected placenta.</p> <p>Methods</p> <p>Placental biopsies were collected at delivery for mRNA isolation and quantification, using real time PCR.</p> <p>Results</p> <p>COX-2 and IL-10 mRNAs increased mainly during chronic infections (nine- and five-times, respectively), whereas COX-1 transcripts remained constant. COX-2 over-expression was associated with a higher birth weight of the baby, but with a lower rate of haemoglobin of the mother. It was associated with a macrophage infiltration of the placenta and with a low haemozoin infiltration. In the opposite way, placental infection was associated with lower expression of 15-LOX mRNA. A high degree of haemozoin deposition correlates with low birth weight and decreased expression of COX-2.</p> <p>Conclusion</p> <p>These data provide evidence that COX-2 and IL-10 are highly induced during chronic infection of the placenta, but were not associated with preterm delivery or low birth weight. The data support the involvement of COX-2 in the recovery phase of the placental infection.</p

Geographic Structuring of the Plasmodium falciparum Sarco(endo)plasmic Reticulum Ca2+ ATPase (PfSERCA) Gene Diversity

Artemisinin, a thapsigargin-like sesquiterpene has been shown to inhibit the Plasmodium falciparum sarco/endoplasmic reticulum calcium-ATPase PfSERCA. To collect baseline pfserca sequence information before field deployment of Artemisinin-based Combination therapies that may select mutant parasites, we conducted a sequence analysis of 100 isolates from multiple sites in Africa, Asia and South America. Coding sequence diversity was large, with 29 mutated codons, including 32 SNPs (average of one SNP/115 bp), of which 19 were novel mutations. Most SNP detected in this study were clustered within a region in the cytosolic head of the protein. The PfSERCA functional domains were very well conserved, with non synonymous mutations located outside the functional domains, except for the S769N mutation associated in French Guiana with elevated IC50 for artemether. The S769N mutation is located close to the hinge of the headpiece, which in other species modulates calcium affinity and in consequence efficacy of inhibitors, possibly linking calcium homeostasis to drug resistance. Genetic diversity was highest in Senegal, Brazil and French Guiana, and few mutations were identified in Asia. Population genetic analysis was conducted for a partial fragment of the gene encompassing nucleotide coordinates 87-2862 (unambiguous sequence available for 96 isolates). This supported a geographic clustering, with a separation between Old and New World samples and one dominant ancestral haplotype. Genetic drift alone cannot explain the observed polymorphism, suggesting that other evolutionary mechanisms are operating. One possible contributor could be the frequency of haemoglobinopathies that are associated with calcium dysregulation in the erythrocyte

Antibiotic susceptibility profile of Streptococcus pneumoniae isolated from acute respiratory infection in Dakar: a cross sectional study

Streptococcus pneumoniae is a pathogen causing pneumonia, meningitis, otitis and bacteraemia. Nowadays, S. pneumoniae is developing antibacterial resistance, particularly for those with reduced susceptibility to penicillin. The objective of this study was to assess the susceptibility profile of S. pneumoniae strains isolated from acute respiratory infections (ARIs) in children younger than 5 years of age in Dakar, Senegal. S. pneumoniae strains were isolated from broncho-alveolar lavages (BALs), nasopharyngeal swabs, and middle ear secretion from children in the Paediatric Department of Abass Ndao University Teaching Hospital and Paediatric Department of Roi Baudouin Hospital in Dakar, Senegal. The strains were cultivated on Columbia agar supplemented with 5% of horse blood and gentamicin (6 mg/L). Antibiotic susceptibility testing was performed using E-test method. A total of 34 strains of S. pneumoniae were isolated and identified in this study, among them 7 strains (20.58%) showed penicillin-resistance. Antibiotics such as amoxicillin/clavulanic acid (MIC90=0.036 μg/mL), cefuroxim (MIC90=0.38 μg/mL), cefixim (MIC90=1.5 μg/mL), as well as macrolides (azithromycin MIC90=1.5 μg/mL, clarithromycin MIC90=0.125 μg/mL) and fluoroquinolone (levofloxacin MIC90=1 μg/mL, ofloxacin MIC90=2 μg/mL) were mostly active. However, all S. pneumoniae strains were resistant to sulfamethoxazole/trimethoprim (MIC90: 32 μg/mL). Except of S. pneumoniae strains penicillin-resistance or reduced susceptibility, most strains were susceptible to β-lactams antibiotics commonly used in ARI treatment. Continuous surveillance of antimicrobial resistance patterns of pneumococcus strains is still crucial for effective control of ARIs in children

The Plasmodium falciparum STEVOR Multigene Family Mediates Antigenic Variation of the Infected Erythrocyte

Modifications of the Plasmodium falciparum–infected red blood cell (iRBC) surface have been linked to parasite-associated pathology. Such modifications enable the parasite to establish long-lasting chronic infection by evading antibody mediate immune recognition and splenic clearance. With the exception of the well-demonstrated roles of var-encoded PfEMP1 in virulence and immune evasion, the biological significance of other variant surface antigens (rif and stevor) is largely unknown. While PfEMP1 and RIFIN have been located on the iRBC surface, recent studies have located STEVOR at the iRBC membrane where it may be exposed on the erythrocyte surface. To investigate the role of STEVOR in more detail, we have developed antibodies against two putative STEVOR proteins and used a combination of indirect immunofluorescence assays (IFA), live IFA, flow cytometry, as well as agglutination assays, which enable us to demonstrate that STEVOR is clonally variant at the surface of schizont stage parasites. Crucially, expression of different STEVOR on the surface of the iRBC changes the antigenic property of the parasite. Taken together, our data for the first time demonstrate that STEVOR plays a role in creating antigenic diversity of schizont stage parasites, thereby adding additional complexity to the immunogenic properties of the iRBC. Furthermore, it clearly demonstrates that to obtain a complete understanding of how parasite-induced pathology is linked to variation on the surface of the iRBC, focusing the interactions of multiple multigene families needs to be considered