Wild Anopheles funestus Mosquito Genotypes Are Permissive for Infection with the Rodent Malaria Parasite,Plasmodium berghei

Background

Malaria parasites undergo complex developmental transitions within the mosquito vector. A commonly used laboratory model for studies of mosquito-malaria interaction is the rodent parasite, P. berghei. Anopheles funestus is a major malaria vector in sub-Saharan Africa but has received less attention than the sympatric species, Anopheles gambiae. The imminent completion of the A. funestus genome sequence will provide currently lacking molecular tools to describe malaria parasite interactions in this mosquito, but previous reports suggested that A. funestus is not permissive for P. berghei development.

Methods

An A. funestus population was generated in the laboratory by capturing female wild mosquitoes in Mali, allowing them to oviposit, and rearing the eggs to adults. These F1 progeny of wild mosquitoes were allowed to feed on mice infected with a fluorescent P. berghei strain. Fluorescence microscopy was used to track parasite development inside the mosquito, salivary gland sporozoites were tested for infectivity to mice, and parasite development in A. funestus was compared to A. gambiae.

Results

P. berghei oocysts were detectable on A. funestus midguts by 7 days post-infection. By 18–20 days post-infection, sporozoites had invaded the median and distal lateral lobes of the salivary glands, and hemocoel sporozoites were observed in the hemolymph. Mosquitoes were capable of infecting mice via bite, demonstrating that A. funestus supports the complete life cycle of P. berghei. In a random sample of wild mosquito genotypes, A. funestus prevalence of infection and the characteristics of parasite development were similar to that observed in A. gambiae-P. berghei infections.

Conclusions

The data presented in this study establish an experimental laboratory model for Plasmodium infection of A. funestus, an important vector of human malaria. Studying A. funestus-Plasmodium interactions is now feasible in a laboratory setting. This information lays the groundwork for exploitation of the awaited genome sequence of A. funestus.     

Methylene blue as an antimalarial agent

Methylene blue has intrinsic antimalarial activity and it can act as a chloroquine sensitizer. In addition, methylene blue must be considered for preventing methemoglobinemia, a serious complication of malarial anemia. As an antiparasitic agent, methylene blue is pleiotropic: it interferes with hemoglobin and heme metabolism in digestive organelles, and it is a selective inhibitor of Plasmodium falciparum glutathione reductase. The latter effect results in glutathione depletion which sensitizes the parasite for chloroquine action. At the Centre de Recherche en Santé de Nouna in Burkina Faso, we study the combination of chloroquine with methylene blue (BlueCQ) as a possible medication for malaria in endemic regions. A pilot study with glucose-6-phosphate dehydrogenase-sufficient adult patients has been conducted recently.     

Variants of the CD40 ligand gene are not associated with increased susceptibility to tuberculosis in West Africa

Evidence for linkage between tuberculosis and human chromosomal region Xq26 has previously been described. The costimulatory molecule CD40 ligand, encoded by TNFSF5 and located at Xq26.3, is a promising positional candidate. Interactions between CD40 ligand and CD40 are involved in the development of humoral- and cell-mediated immunity, as well as the activation of macrophages, which are the primary host and effector cells for Mycobacterium tuberculosis. We hypothesised that common variation within TNFSF5 might affect susceptibility to tuberculosis disease and, thus, might be responsible for the observed linkage to Xq26. Sequencing 32 chromosomes from a Gambian population identified nine common polymorphisms within the coding, 3 and 5 regulatory sequences of the gene. Six single nucleotide polymorphisms (SNPs) and a 3 microsatellite were genotyped in 121 tuberculosis patients and their available parents. No association with tuberculosis was detected for these variants using a transmission disequilibrium test, although one SNP at –726 showed some evidence of association in males. This finding, however, did not replicate in a separate case control study of over 1,200 West African individuals. We conclude that common genetic variation in TNFSF5 is not likely to affect tuberculosis susceptibility in West Africa and the linkage observed in this region is not due to variation in TNFSF5.Sadly, Professor Steve Bennett passed away in March 2003     

Flavocytochrome b2: reactivity of its flavin with molecular oxygen

Flavocytochrome b2, a flavohemoprotein, catalyzes the oxidation of lactate at the expense of the physiological acceptor cytochrome c in the yeast mitochondrial intermembrane space. The mechanism of electron transfer from the substrate to monoelectronic acceptors via FMN and heme b2 has been intensively studied over the years. Each prosthetic group is bound to a separate domain, N-terminal for the heme, C-terminal for the flavin. Each domain belongs to a distinct evolutionary family. In particular, the flavodehydrogenase domain is homologous to a number of well-characterized l-2-hydroxy acid-oxidizing enzymes. Among these, some are oxidases for which the oxidative half-reaction produces hydrogen peroxide at the expense of oxygen. For bacterial mandelate dehydrogenase and flavocytochrome b2, in contrast, the oxidative half-reaction requires monoelectronic acceptors. Several crystal structures indicate an identical fold and a highly conserved active site among family members. All these enzymes form anionic semiquinones and bind sulfite, properties generally associated with oxidases, whereas electron transferases are expected to form neutral semiquinones and to yield superoxide anion. Thus, flavocytochrome b2 is a highly unusual dehydrogenase-electron transferase, and one may wonder how its flavin reacts with oxygen. In this work, we show that the separately engineered flavodehydrogenase domain produces superoxide anion in its slow reaction with oxygen. This reaction apparently also takes place in the holoenzyme when oxygen is the sole electron acceptor, because the heme domain autoxidation is also slow; this is not unexpected, in view of the heme domain mobility relative to the tetrameric flavodehydrogenase core (Xia, Z. X., and Mathews, F. S. (1990) J. Mol. Biol. 212, 837-863). Nevertheless, this reaction is so slow that it cannot compete with the normal electron flow in the presence of monoelectronic acceptors, such as ferricyanide and cytochrome c. An inspection of the available structures of family members does not provide a rationale for the difference between the oxidases and the electron transferases.     

Celecoxib after the onset of reperfusion reduces apoptosis in the amygdala

Reperfused myocardial infarction induces an inflammatory response that is responsible for local and systemic alterations. Among these, apoptosis observed in the amygdala following myocardial infarction has been pointed out as a consequence of such an inflammatory process. We hypothesized that inhibition of the inducible inflammatory enzyme Cox-2 during the reperfusion period may attenuate the apoptotic process in the amygdala. Anaesthetized rats were subjected to left anterior descending coronary artery occlusion for 40 min, followed by reperfusion. The Cox-2 antagonist Celecoxib (3 mg/kg i.p.) was administered 10 min after the onset of the reperfusion period. After 72 h of reperfusion, infarct size was determined and the lateral and medial amygdala were dissected from the brain. Infarct size was similar between untreated and Celecoxib-treated animals (40–45% of the area at risk). Cox-2 expression was significantly reduced in both parts of the amygdala in the Celecoxib group. Apoptosis regression was observed in the amygdala of the Celecoxib group as shown by decreased number of TUNEL positive cells and by decreased of caspase-3 activation. Bax/Bcl-2 ratio was not significantly altered by Celecoxib while Akt activation was increased in the lateral amygdala but not in the medial amygdala. This data indicates that inhibition of Cox-2 by Celecoxib is associated with regression of apoptosis in the amygdala following myocardial infarction.     

B cell analysis of ethnic groups in Mali with differential susceptibility to malaria

ABSTRACT: BACKGROUND: Several studies indicate that people of the Fulani ethnic group are less susceptible to malaria compared to those of other ethnic groups living sympatrically in Africa, including the Dogon ethnic group. Although the mechanisms of this protection remain unclear, the Fulani are known to have higher levels of Plasmodium falciparum-specific antibodies of all Ig classes as compared to the Dogon. However, the proportions of B cell subsets in the Fulani and Dogon that may account for differences in the levels of Ig have not been characterized. METHODS: In this cross-sectional study, venous blood was collected from asymptomatic Fulani (n=25) and Dogon (n=25) adults in Mali during the malaria season, and from P. falciparum-naive adults in the U.S. (n=8). At the time of the blood collection, P. falciparum infection was detected by blood-smear in 16% of the Fulani and 40% of the Dogon volunteers. Thawed lymphocytes were analysed by flow cytometry to quantify B cell subsets, including immature and naive B cells; plasma cells; and classical, activated, and atypical memory B cells (MBCs). RESULTS: The overall distribution of B cell subsets was similar between Fulani and Dogon adults, although the percentage of activated MBCs was higher in the Fulani group (Fulani: 11.07% [95% CI: 9.317 - 12.82]; Dogon: 8.31% [95% CI: 6.378 - 10.23]; P=0.016). The percentage of atypical MBCs was similar between Fulani and Dogon adults (Fulani: 28.3% [95% CI: 22.73 - 34.88]; Dogon: 29.3% [95% CI: 25.06 - 33.55], but higher than U.S. adults (U.S.: 3.0% [95% CI: -0.21 - 6.164]; P<0.001). Plasmodium falciparum infection was associated with a higher percentage of plasma cells among Fulani (Fulani infected: 3.3% [95% CI: 1.788 - 4.744]; Fulani uninfected: 1.71% [95% CI: 1.33 - 2.08]; P=0.011), but not Dogon adults. CONCLUSION: These data show that the malaria-resistant Fulani have a higher percentage of activated MBCs compared to the Dogon, and that P. falciparum infection is associated with a higher percentage of plasma cells in the Fulani compared to the Dogon, findings that may account for the higher levels of P. falciparum antibodies in the Fulani.     

Pneumococci in the African Meningitis Belt: Meningitis Incidence and Carriage Prevalence in Children and Adults

Background

The development of optimal vaccination strategies for pneumococcal conjugate vaccines requires serotype-specific data on disease incidence and carriage prevalence. This information is lacking for the African meningitis belt.

Methods

We conducted hospital-based surveillance of acute bacterial meningitis in an urban and rural population of Burkina Faso during 2007–09. Cerebrospinal fluid was evaluated by polymerase chain reaction for species and serotype. In 2008, nasopharyngeal swabs were obtained from a representative population sample (1 month to 39 years; N = 519) and additional oropharyngeal swabs from 145 participants. Swabs were evaluated by culture.

Results

Annual pneumococcal meningitis incidence rates were highest among <6-month-old (58/100,000) and 15- to 19-year-old persons (15/100,000). Annual serotype 1 incidence was around 5/100,000 in all age groups. Pneumococcal carriage prevalence in nasopharyngeal swabs was 63% among <5-year-old children and 22% among ≥5-year-old persons, but adding oropharyngeal to nasopharyngeal swabs increased the estimated carriage prevalence by 60%. Serotype 1 showed high propensity for invasive disease, particularly among persons aged ≥5 years.

Conclusions

Serotype 1 causes the majority of cases with a relatively constant age-specific incidence. Pneumococcal carriage is common in all age groups including adults. Vaccination programs in this region may need to include older target age groups for optimal impact on disease burden.     

Divergent cell signaling after short-term intensified endurance training in human skeletal muscle

Endurance training represents one extreme in the continuum of skeletal muscle plasticity. The molecular signals elicited in response to acute and chronic exercise and the integration of multiple intracellular pathways are incompletely understood. We determined the effect of 10 days of intensified cycle training on signal transduction in nine inactive males in response to a 1-h acute bout of cycling at the same absolute workload (164 +/- 9 W). Muscle biopsies were taken at rest and immediately and 3 h after the acute exercise. The metabolic signaling pathways, including AMP-activated protein kinase (AMPK) and mammalian target of rapamycin (mTOR), demonstrated divergent regulation by exercise after training. AMPK phosphorylation increased in response to exercise ( approximately 16-fold; P < 0.05), which was abrogated posttraining (P < 0.01). In contrast, mTOR phosphorylation increased in response to exercise ( approximately 2-fold; P < 0.01), which was augmented posttraining (P < 0.01) in the presence of increased mTOR expression (P < 0.05). Exercise elicited divergent effects on mitogen-activated protein kinase (MAPK) pathways after training, with exercise-induced extracellular signal-regulated kinase (ERK) 1/2 phosphorylation being abolished (P < 0.01) and p38 MAPK maintained. Finally, calmodulin kinase II (CaMKII) exercise-induced phosphorylation and activity were maintained (P < 0.01), despite increased expression ( approximately 2-fold; P < 0.05). In conclusion, 10 days of intensified endurance training attenuated AMPK, ERK1/2, and mTOR, but not CaMKII and p38 MAPK signaling, highlighting molecular pathways important for rapid functional adaptations and maintenance in response to intensified endurance exercise and training.     

Frontiers: skeletal muscle sodium pump regulation: a translocation paradigm

The skeletal muscle sodium pump plays a major role in the removal of K(+) ions from the circulation postprandial, or after a physical activity bout, thereby preventing the development of hyperkalemia and fatigue. Insulin and muscle contractions stimulate Na(+)-K(+)-ATPase activity in skeletal muscle, at least partially via translocation of sodium pump units to the plasma membrane from intracellular stores. The molecular mechanism of this phenomenon is poorly understood. Due to the contradictory reports in the literature, the very existence of the translocation of Na(+)-K(+)-ATPase to the skeletal muscle cell surface is questionable. This review summarizes more than 30 years work on the skeletal muscle sodium pump translocation paradigm. Furthermore, the methodological caveats of major approaches to study the sodium pump translocation in skeletal muscle are discussed. An understanding of the molecular regulation of Na(+)-K(+)-ATPase in skeletal muscle will have important clinical implications for the understanding of the development of complications associated with the metabolic syndrome, such as cardiovascular diseases or increased muscle fatigue in diabetic patients.     

Profil parasitologique de deux formes de schistosomiase (formes urinaire et intestinale) dans dix sites du Burkina Faso (pays d’Afrique sub-saharienne)

In spite of great progress in schistosomiasis control during the last decade in Burkina Faso, this disease remains a public health concern in the country. Indeed, our study consisted of the analysis of parasitological data related to Schistosoma haematobium and Schistosoma mansoni and in malacological investigations. The prevalence rate of Schistosoma haematobium varies from 3.3% to 50.4% and from 3.3% to 39.1% for Schistosoma mansoni, but only in the western part of Burkina Faso. Schoolboys are more infested than girls, but the phenomenon is reversed in adults. Biomphalaria pfeifferi, Bulinus truncatus, Bulinus senegalensis and Bulinus globosus were collected during this study. Thus, the behavioral factors as well as the dynamics and the distribution of the intermediate mollusks play a major role in the persistence of the disease.