Low infectivity of Plasmodium falciparum gametocytes to Anopheles gambiae following treatment with sulfadoxine-pyrimethamine in Mali

Sulfadoxine-pyrimethamine (SP) treatment increases the rate of gametocyte carriage and selects SP resistance-conferring mutations in Plasmodium falciparum dihydrofolate reductase (DHFR) and dihydropteroate synthase (DHPS), raising concerns of increased malaria transmission and spread of drug resistance. In a setting in Mali where SP was highly efficacious, we measured the prevalence of DHFR and DHPS mutations in P. falciparum infections with microscopy-detected gametocytes following SP treatment, and used direct feeding to assess infectivity to Anopheles gambiae sensu lato. Children and young adults presenting with uncomplicated malaria were treated with SP or chloroquine and followed for 28 days. Gametocyte carriage peaked at 67% 1 week after treatment with a single dose of SP. Those post-SP gametocytes carried significantly more DHFR and DHPS mutations than pre-treatment asexual parasites from the same population. Only 0.5% of 1728 mosquitoes fed on SP-treated gametocyte carriers developed oocysts, while 11% of 198 mosquitoes fed on chloroquine-treated gametocyte carriers were positive for oocysts. This study shows that in an area of high SP efficacy, although SP treatment sharply increased gametocyte carriage, the infectiousness of these gametocytes to the vector may be very low. Accurate and robust methods for measuring infectivity are needed to guide malaria control interventions that affect transmission.     

Evidence for divergent selection between the molecular forms of <Emphasis Type="Italic">Anopheles gambiae</Emphasis>: role of predation

Background  

The molecular forms of Anopheles gambiae are undergoing speciation. They are characterized by a strong assortative mating and they display partial habitat segregation. The M form is mostly found in flooded/irrigated areas whereas the S form dominates in the surrounding areas, but the ecological factors that shape this habitat segregation are not known. Resource competition has been demonstrated between species undergoing divergent selection, but resource competition is not the only factor that can lead to divergence.     

Increase of malaria attacks among children presenting concomitant infection by Schistosoma mansoni in Senegal

Background

Parasites incur periodic mutations which must ultimately be eliminated to maintain their genetic integrity.

Methods

It is hypothesised that these mutations are eliminated not by the conventional mechanisms of competition between parasites in different hosts but primarily by competition between parasites within the same infection.

Results

This process is enhanced by the production of a large number of parasites within individual infections, and this may significantly contribute to parasitic virulence.

Conclusions

Several features of the most virulent human malaria parasite Plasmodium falciparum can usefully be re-interpreted in this light and lend support to this interpretation. More generally, it constitutes a novel explanation for the evolution of virulence in a wider range of microparasites.     

Distribution spatio-temporelle de la faune de phlébotomes en zones urbaine et périurbaine de Bamako,Mali

Au Mali la leishmaniose cutanée (LC) est bien décrite en milieu rural, mais sa transmission n’est pas encore établie en milieu urbain. L’objectif de l’étude était de décrire la faune phlébotomienne à Bamako et dans ses environs. Les pièges CDC et adhésifs servaient à collecter les phlébotomes en 2011 et 2012 à Bamako. Les pièges étaient placés dans le district de Bamako répartis en 30 zones (200 m × 200 m) à l’aide des images de satellite SPOT-5. La délimitation des zones était basée sur les facteurs écologiques (relief, hydrographie, couverture végétale) et anthropologiques (nature des maisons, dépôts d’ordure). Les pièges étaient placés en 2011 à Sotuba, zone périurbaine, puis à Donéguébougou et Banambani, deux villages environnants de Bamako. Au total 122 phlébotomes étaient collectés 27 (22,13 %) à Banambani, 12 (9,83 %) à Donéguébougou, 2 (1,63 %) à Sotuba et 81 (66,39 %) à Bamako. La densité des phlébotomes en novembre était plus élevée, avec 48 spécimens capturés (39,3 %), que celle d’avril, mai et décembre (p ≥ 0,001). A Bamako, les zones 6 et 28 étaient associées aux densités les plus élevées de phlébotomes respectivement 32 (26,22 %) et 23 (18,85 %) (p ≤ 0,005). Les résultats suggèrent que le genre Phlebotomus n’était pas présent à Bamako, et que la densité des vecteurs variait en fonction des zones et des mois.     

Direct evidence of lower viral replication rates in vivo in human immunodeficiency virus type 2 (HIV-2) infection than in HIV-1 infection

Studies have shown that human immunodeficiency virus type 2 (HIV-2) is less pathogenic than HIV-1, with a lower rate of disease progression. Similarly, plasma viral loads are lower in HIV-2 infection, suggesting that HIV-2 replication is restricted in vivo in comparison to that of HIV-1. However, to date, in vivo studies characterizing replication intermediates in the viral life cycle of HIV-2 have been limited. In order to test the hypothesis that HIV-2 has a lower replication rate in vivo than HIV-1 does, we quantified total viral DNA, integrated proviral DNA, cell-associated viral mRNA, and plasma viral loads in peripheral blood samples from groups of therapy-na?ve HIV-1-infected (n = 21) and HIV-2-infected (n = 18) individuals from Dakar, Senegal, with CD4(+) T-cell counts of >200/microl. Consistent with our previous findings, total viral DNA loads were similar between HIV-1 and HIV-2 and plasma viral loads were higher among HIV-1-infected individuals. Proportions of DNA in the integrated form were also similar between these viruses. In contrast, levels of viral mRNA were lower in HIV-2 infection. Our study indicates that HIV-2 is able to establish a stable, integrated proviral infection in vivo, but that accumulation of viral mRNA is attenuated in HIV-2 infection relative to that in HIV-1 infection. The differences in viral mRNA are consistent with the differences in plasma viral loads between HIV-1 and HIV-2 and suggest that lower plasma viral loads, and possibly the attenuated pathogenesis of HIV-2, can be explained by lower rates of viral replication in vivo.     

Down-expressed GLT-1 in PSD astrocytes inhibits synaptic formation of NSC-derived neurons in vitro

Little is known about the effect of astroglial GLT-1 of post-stroke depression (PSD) rat model on the function of neural stem cells (NSCs). This study aimed to investigate whether astroglial GLT-1 of PSD rats affect differentiation of NSCs from neonatal rat hippocampus and synaptic formation of NSC-derived neurons. Astrocytes were isolated from the left hippocampus of normal adult SD rats and PSD rats. A lentiviral vector was used to silence the expression of GLT-1 in astrocytes of PSD rats. NSCs were respectively co-cultured with normal (control), PSD, and GLT-1 silenced astrocytes for 7 days. GLT-1, GFAP, MAP2, Synaptophysin (SYN), glutamate (Glu) and glutamine (Gln) were respectively measured by qRT-PCR, western blot, immunofluorescence and efficient mass spectrometry (MS). PSD astrocytes increased the number of NSC-derived astrocytes, but inhibited the expression of GLT-1 of NSC-derived astrocytes and synapses of NSC-derived neurons. On the basis of the low expression of GLT-1 in PSD astrocytes, we further silenced GLT-1 in PSD astrocytes. Interestingly, GLT-1 silenced PSD astrocytes more obviously inhibited synapses of NSC-derived neurons, but increased the number of NSC-derived neurons and reversed the expression of GLT-1 in NSC-derived astrocytes. At the same time, concentration of glutamate in the medium elevated, and glutamine in the medium gradually reduced. In NSC-derived neurons and astrocytes, glutamate metabolism was also affected by changed GLT-1. Down-expressed GLT-1 in PSD astrocytes stimulated NSCs differentiating into astrocytes, but inhibiting the formation of functional synapses by influencing glutamate metabolism in vitro.     

LRP1 loss in airway epithelium exacerbates smoke-induced oxidative damage and airway remodeling

The LDL receptor-related protein 1 (LRP1) partakes in metabolic and signaling events regulated in a tissue-specific manner. The function of LRP1 in airways has not been studied. We aimed to study the function of LRP1 in smoke-induced disease. We found that bronchial epithelium of patients with chronic obstructive pulmonary disease and airway epithelium of mice exposed to smoke had increased LRP1 expression. We then knocked out LRP1 in human bronchial epithelial cells in vitro and in airway epithelial club cells in mice. In vitro, LRP1 knockdown decreased cell migration and increased transforming growth factor β activation. Tamoxifen-inducible airway-specific LRP1 knockout mice (club Lrp1^?/?) induced after complete lung development had increased inflammation in the bronchoalveolar space and lung parenchyma at baseline. After 6 months of smoke exposure, club Lrp1^?/? mice showed a combined restrictive and obstructive phenotype, with lower compliance, inspiratory capacity, and forced expiratory volume_0.05/forced vital capacity than WT smoke-exposed mice. This was associated with increased values of Ashcroft fibrotic index. Proteomic analysis of room air exposed-club Lrp1^?/? mice showed significantly decreased levels of proteins involved in cytoskeleton signaling and xenobiotic detoxification as well as decreased levels of glutathione. The proteome fingerprint created by smoke eclipsed many of the original differences, but club Lrp1^?/? mice continued to have decreased lung glutathione levels and increased protein oxidative damage and airway cell proliferation. Therefore, LRP1 deficiency leads to greater lung inflammation and damage and exacerbates smoke-induced lung disease.     

An effective method to purify Plasmodium falciparum DNA directly from clinical blood samples for whole genome high-throughput sequencing

Highly parallel sequencing technologies permit cost-effective whole genome sequencing of hundreds of Plasmodium parasites. The ability to sequence clinical Plasmodium samples, extracted directly from patient blood without a culture step, presents a unique opportunity to sample the diversity of "natural" parasite populations in high resolution clinical and epidemiological studies. A major challenge to sequencing clinical Plasmodium samples is the abundance of human DNA, which may substantially reduce the yield of Plasmodium sequence. We tested a range of human white blood cell (WBC) depletion methods on P. falciparum-infected patient samples in search of a method displaying an optimal balance of WBC-removal efficacy, cost, simplicity, and applicability to low resource settings. In the first of a two-part study, combinations of three different WBC depletion methods were tested on 43 patient blood samples in Mali. A two-step combination of Lymphoprep plus Plasmodipur best fitted our requirements, although moderate variability was observed in human DNA quantity. This approach was further assessed in a larger sample of 76 patients from Burkina Faso. WBC-removal efficacy remained high (<30% human DNA in >70% samples) and lower variation was observed in human DNA quantities. In order to assess the Plasmodium sequence yield at different human DNA proportions, 59 samples with up to 60% human DNA contamination were sequenced on the Illumina Genome Analyzer platform. An average ~40-fold coverage of the genome was observed per lane for samples with ≤ 30% human DNA. Even in low resource settings, using a simple two-step combination of Lymphoprep plus Plasmodipur, over 70% of clinical sample preparations should exhibit sufficiently low human DNA quantities to enable ~40-fold sequence coverage of the P. falciparum genome using a single lane on the Illumina Genome Analyzer platform. This approach should greatly facilitate large-scale clinical and epidemiologic studies of P. falciparum.