Inventory of potential vectors of trypanosoma and infection rate of the Tsetse fly in the National Park of Ivindo, Gabon

Background: Trypanosoma’s vectors distribution is poorly investigated in Gabon, where  Trypanosomiasis historical foci exist. Thus, an active detection of Trypanosoma sp transmission needs to be assessed.Objectives: The present study aims to identify potential vectors of Trypanosoma sp and to evaluate the infection rate of the Tsetse fly in an area of Gabon.Methods: An entomological survey was conducted in the National Park of Ivindo in May 2012 using Vavoua traps. All captured insects were identified. Tsetse were dissected and organs were  microscopically observed to detect the presence of Trypanosoma sp.Results: 247 biting flies known as vectors of Trypanosomiasis were caught including 189 tsetse flies, 32 Tabanid and 26 Stomoxys. Tsetse flies had the highest bulk densities per trap per day (ADT = 3 tsetse / trap / day), while the lowest density was found among Stomoxys (ADT= 0.41 Stomoxys / trap / day). The infection rate of flies was 6.3%. Infectious organs were midguts and to a lesser extent salivary glands and proboscis.Conclusion: The presence of Tsetse infected by Trypanosoma highlights an existing risk of trypanosomiasis infection in the National Park of Ivindo.Keywords: Tsetse fly, Tabanids, vector, Stomoxys, biodiversity, trypanosomiasis

Evidence of decline of malaria in the general hospital of Libreville, Gabon from 2000 to 2008

BACKGROUND: Substantial decline in malaria transmission, morbidity and mortality has been reported in several countries where new malaria control strategies have been implemented. In Gabon, the national malaria policy changed in 2003, according to the WHO recommendations. The trend in malaria morbidity was evaluated among febrile children before and after their implementation in Libreville, the capital city of Gabon. METHODS: From August 2000 to December 2008, febrile paediatric outpatients and inpatients, under 11 years of age, were screened for malaria by microscopic examination at the Malaria Clinical Research Unit (MCRU) located in the largest public hospital in Gabon. Climatic data were also collected. RESULTS: In total, 28,092 febrile children were examined; those under five years always represented more than 70%. The proportion of malaria-positive slides was 45% in 2000, and declined to 15% in 2008. The median age of children with a positive blood smear increased from 24(15-48) to 41(21-72) months over the study period (p < 0.01). Rainfall patterns had no impact on the decline observed throughout the study period. CONCLUSION: The decrease of malaria prevalence among febrile children during the last nine years is observed following the introduction of new strategies of malaria cases management, and may announce epidemiological changes. Moreover, preventive measures must be extended to children older than five years

A novel malaria vaccine candidate antigen expressed in Tetrahymena thermophila

Development of effective malaria vaccines is hampered by the problem of producing correctly folded Plasmodium proteins for use as vaccine components. We have investigated the use of a novel ciliate expression system, Tetrahymena thermophila, as a P. falciparum vaccine antigen platform. A synthetic vaccine antigen composed of N-terminal and C-terminal regions of merozoite surface protein-1 (MSP-1) was expressed in Tetrahymena thermophila. The recombinant antigen was secreted into the culture medium and purified by monoclonal antibody (mAb) affinity chromatography. The vaccine was immunogenic in MF1 mice, eliciting high antibody titers against both N- and C-terminal components. Sera from immunized animals reacted strongly with P. falciparum parasites from three antigenically different strains by immunofluorescence assays, confirming that the antibodies produced are able to recognize parasite antigens in their native form. Epitope mapping of serum reactivity with a peptide library derived from all three MSP-1 Block 2 serotypes confirmed that the MSP-1 Block 2 hybrid component of the vaccine had effectively targeted all three serotypes of this polymorphic region of MSP-1. This study has successfully demonstrated the use of Tetrahymena thermophila as a recombinant protein expression platform for the production of malaria vaccine antigens

An expanded global inventory of allelic variation in the most extremely polymorphic region of Plasmodium falciparum merozoite surface protein 1 provided by short read sequence data.

BACKGROUND: Within Plasmodium falciparum merozoite surface protein 1 (MSP1), the N-terminal block 2 region is a highly polymorphic target of naturally acquired antibody responses. The antigenic diversity is determined by complex repeat sequences as well as non-repeat sequences, grouping into three major allelic types that appear to be maintained within populations by natural selection. Within these major types, many distinct allelic sequences have been described in different studies, but the extent and significance of the diversity remains unresolved. METHODS: To survey the diversity more extensively, block 2 allelic sequences in the msp1 gene were characterized in 2400 P. falciparum infection isolates with whole genome short read sequence data available from the Pf3K project, and compared with the data from previous studies. RESULTS: Mapping the short read sequence data in the 2400 isolates to a reference library of msp1 block 2 allelic sequences yielded 3815 allele scores at the level of major allelic family types, with 46% of isolates containing two or more of these major types. Overall frequencies were similar to those previously reported in other samples with different methods, the K1-like allelic type being most common in Africa, MAD20-like most common in Southeast Asia, and RO33-like being the third most abundant type in each continent. The rare MR type, formed by recombination between MAD20-like and RO33-like alleles, was only seen in Africa and very rarely in the Indian subcontinent but not in Southeast Asia. A combination of mapped short read assembly approaches enabled 1522 complete msp1 block 2 sequences to be determined, among which there were 363 different allele sequences, of which 246 have not been described previously. In these data, the K1-like msp1 block 2 alleles are most diverse and encode 225 distinct amino acid sequences, compared with 123 different MAD20-like, 9 RO33-like and 6 MR type sequences. Within each of the major types, the different allelic sequences show highly skewed geographical distributions, with most of the more common sequences being detected in either Africa or Asia, but not in both. CONCLUSIONS: Allelic sequences of this extremely polymorphic locus have been derived from whole genome short read sequence data by mapping to a reference library followed by assembly of mapped reads. The catalogue of sequence variation has been greatly expanded, so that there are now more than 500 different msp1 block 2 allelic sequences described. This provides an extensive reference for molecular epidemiological genotyping and sequencing studies, and potentially for design of a multi-allelic vaccine

Potential impact of host immunity on malaria treatment outcome in Tanzanian children infected with Plasmodium falciparum

<p>Abstract</p> <p>Background</p> <p>In malaria endemic areas children may recover from malaria after chemotherapy in spite of harbouring genotypically drug-resistant <it>Plasmodium falciparum</it>. This phenomenon suggests that there is a synergy between drug treatment and acquired immunity. This hypothesis was examined in an area of moderately intense transmission of <it>P. falciparum </it>in Tanzania during a drug trail with sulphadoxine-pyrimethamine (SP) or amodiaquine (AQ).</p> <p>Methods</p> <p>One hundred children with uncomplicated malaria were treated with either SP or AQ and followed for 28 days. Mutations in parasite genes related to SP and AQ-resistance as well as human sickle cell trait and alpha-thalassaemia were determined using PCR and sequence-specific oligonucleotide probes and enzyme-linked immunosorbent assay (SSOP-ELISA), and IgG antibody responses to a panel of <it>P. falciparum </it>antigens were assessed and related to treatment outcome.</p> <p>Results</p> <p>Parasitological or clinical treatment failure (TF) was observed in 68% and 38% of children receiving SP or AQ, respectively. In those with adequate clinical and parasitological response (ACPR) compared to children with TF, and for both treatment regimens, prevalence and levels of anti-Glutamate-rich Protein (GLURP)-specific IgG antibodies were significantly higher (P < 0.001), while prevalence of parasite haplotypes associated with SP and AQ resistance was lower (P = 0.02 and P = 0.07, respectively). Interestingly, anti-GLURP-IgG antibodies were more strongly associated with treatment outcome than parasite resistant haplotypes, while the IgG responses to none of the other 11 malaria antigens were not significantly associated with ACPR.</p> <p>Conclusion</p> <p>These findings suggest that GLURP-specific IgG antibodies in this setting contribute to clearance of drug-resistant infections and support the hypothesis that acquired immunity enhances the clinical efficacy of drug therapy. The results should be confirmed in larger scale with greater sample size and with variation in transmission intensity.</p

Prozone in malaria rapid diagnostics tests: how many cases are missed?

<p>Abstract</p> <p>Background</p> <p>Prozone means false-negative or false-low results in antigen-antibody reactions, due to an excess of either antigen or antibody. The present study prospectively assessed its frequency for malaria rapid diagnostic tests (RDTs) and <it>Plasmodium falciparum </it>samples in an endemic field setting.</p> <p>Methods</p> <p>From January to April 2010, blood samples with <it>P. falciparum </it>high parasitaemia (≥ 4% red blood cells infected) were obtained from patients presenting at the Provincial Hospital of Tete (Mozambique). Samples were tested undiluted and 10-fold diluted in saline with a panel of RDTs and results were scored for line intensity (no line visible, faint, weak, medium and strong). Prozone was defined as a sample which showed no visible test line or a faint or weak test line when tested undiluted, and a visible test line of higher intensity when tested 10-fold diluted, as observed by two blinded observers and upon duplicate testing.</p> <p>Results</p> <p>A total of 873/7,543 (11.6%) samples showed <it>P. falciparum</it>, 92 (10.5%) had high parasitaemia and 76 were available for prozone testing. None of the two Pf-pLDH RDTs, but all six HRP-2 RDTs showed prozone, at frequencies between 6.7% and 38.2%. Negative and faint HRP-2 lines accounted for four (3.8%) and 15 (14.4%) of the 104 prozone results in two RDT brands. For the most affected brand, the proportions of prozone with no visible or faint HRP-2 lines were 10.9% (CI: 5.34-19.08), 1.2% (CI: 0.55-2.10) and 0.1% (CI: 0.06-0.24) among samples with high parasitaemia, all positive samples and all submitted samples respectively. Prozone occurred mainly, but not exclusively, among young children.</p> <p>Conclusion</p> <p>Prozone occurs at different frequency and intensity in HRP-2 RDTs and may decrease diagnostic accuracy in the most affected RDTs.</p