Mangrove community structure and regeneration potential on a rapidly expanding,river delta in Java

Key message

Mangroves in rapidly expanding Southeast Asian river deltas form floristically simple zones dominated by a few highly regenerative species adaptable or tolerant to rapid sedimentation and extensive river flooding.

Abstract

The size class distribution, community composition and spatial structure of five representative mangrove forests in the rapidly expanding Cimanuk river delta on Java were determined. These deltaic forests are species-poor (eight true mangrove species) and spatially segregated into three distinct floristic zones: (1) a fringing, low intertidal zone co-dominated by Avicennia marina and A. officinalis, with less abundant Bruguiera parviflora, Rhizophora apiculata, and R. mucronata; (2) a zone transitional between the low and mid intertidal in which Avicennia and Rhizophora spp. co-dominate; and (3) a mid intertidal zone dominated by R. mucronata and R. apiculata. Numerically dominated by seedlings (52,500–73,500 seedlings ha^?1) and saplings (5,268–5,660 saplings ha^?1), all five forests are relatively young and actively regenerating. Positive correlations of tree stem diameter and tree height with soil organic matter and P concentrations, salinity, the soil C/N ratio, pH, and silt/clay composition highlight the importance of soil factors in sustaining forest growth. The low diversity and relative structural simplicity of these rapidly growing and regenerating forests may be attributed to adaptation or tolerance to flooding and the rapid sedimentation and seaward expansion of the delta.     

Filariasis Attenuates Anemia and Proinflammatory Responses Associated with Clinical Malaria: A Matched Prospective Study in Children and Young Adults

Background

Wuchereria bancrofti (Wb) and Mansonella perstans (Mp) are blood-borne filarial parasites that are endemic in many countries of Africa, including Mali. The geographic distribution of Wb and Mp overlaps considerably with that of malaria, and coinfection is common. Although chronic filarial infection has been shown to alter immune responses to malaria parasites, its effect on clinical and immunologic responses in acute malaria is unknown.

Methodology/Principal Findings

To address this question, 31 filaria-positive (FIL+) and 31 filaria-negative (FIL−) children and young adults, matched for age, gender and hemoglobin type, were followed prospectively through a malaria transmission season. Filarial infection was defined by the presence of Wb or Mp microfilariae on calibrated thick smears performed between 10 pm and 2 am and/or by the presence of circulating filarial antigen in serum. Clinical malaria was defined as axillary temperature ≥37.5°C or another symptom or sign compatible with malaria infection plus the presence of asexual malaria parasites on a thick blood smear. Although the incidence of clinical malaria, time to first episode, clinical signs and symptoms, and malaria parasitemia were comparable between the two groups, geometric mean hemoglobin levels were significantly decreased in FIL− subjects at the height of the transmission season compared to FIL+ subjects (11.4 g/dL vs. 12.5 g/dL, p<0.01). Plasma levels of IL-1ra, IP-10 and IL-8 were significantly decreased in FIL+ subjects at the time of presentation with clinical malaria (99, 2145 and 49 pg/ml, respectively as compared to 474, 5522 and 247 pg/ml in FIL− subjects).

Conclusions/Significance

These data suggest that pre-existent filarial infection attenuates immune responses associated with severe malaria and protects against anemia, but has little effect on susceptibility to or severity of acute malaria infection. The apparent protective effect of filarial infection against anemia is intriguing and warrants further study in a larger cohort.     

Combining hydrology and mosquito population models to identify the drivers of rift valley Fever emergence in semi-arid regions of west Africa

Background

Rift Valley fever (RVF) is a vector-borne viral zoonosis of increasing global importance. RVF virus (RVFV) is transmitted either through exposure to infected animals or through bites from different species of infected mosquitoes, mainly of Aedes and Culex genera. These mosquitoes are very sensitive to environmental conditions, which may determine their presence, biology, and abundance. In East Africa, RVF outbreaks are known to be closely associated with heavy rainfall events, unlike in the semi-arid regions of West Africa where the drivers of RVF emergence remain poorly understood. The assumed importance of temporary ponds and rainfall temporal distribution therefore needs to be investigated.

Methodology/Principal Findings

A hydrological model is combined with a mosquito population model to predict the abundance of the two main mosquito species (Aedes vexans and Culex poicilipes) involved in RVFV transmission in Senegal. The study area is an agropastoral zone located in the Ferlo Valley, characterized by a dense network of temporary water ponds which constitute mosquito breeding sites.The hydrological model uses daily rainfall as input to simulate variations of pond surface areas. The mosquito population model is mechanistic, considers both aquatic and adult stages and is driven by pond dynamics. Once validated using hydrological and entomological field data, the model was used to simulate the abundance dynamics of the two mosquito species over a 43-year period (1961–2003). We analysed the predicted dynamics of mosquito populations with regards to the years of main outbreaks. The results showed that the main RVF outbreaks occurred during years with simultaneous high abundances of both species.

Conclusion/Significance

Our study provides for the first time a mechanistic insight on RVFV transmission in West Africa. It highlights the complementary roles of Aedes vexans and Culex poicilipes mosquitoes in virus transmission, and recommends the identification of rainfall patterns favourable for RVFV amplification.     

Des-A-ring benzothiadiazines: inhibitors of HCV genotype 1 NS5B RNA-dependent RNA polymerase

In our program to discover non-nucleoside, small molecule inhibitors of genotype 1 HCV polymerase, we investigated a series of promising analogs based on a benzothiadiazine screening hit that contains an ABCD ring system. After demonstrating that a methylsulfonylamino D-ring substituent increased the enzyme potency into the low nanomolar range, we explored a minimum core required for activity by truncating to a three-ring system. Described herein are the syntheses and structure-activity relationship of a set of inhibitors lacking the A-ring of an ABCD ring system. We observed that small aromatic rings and alkenyl groups appended to the 5-position of the B-ring were optimal, resulting in inhibitors with low nanomolar potencies.     

Identification of halosalicylamide derivatives as a novel class of allosteric inhibitors of HCV NS5B polymerase

Halosalicylamide derivatives were identified from high-throughput screening as potent inhibitors of HCV NS5B polymerase. The subsequent structure and activity relationship revealed the absolute requirement of the salicylamide moiety for optimum activity. Methylation of either the hydroxyl group or the amide group of the salicylamide moiety abolished the activity while the substitutions on both phenyl rings are acceptable. The halosalicylamide derivatives were shown to be non-competitive with respect to elongation nucleotide and demonstrated broad genotype activity against genotype 1-3 HCV NS5B polymerases. Inhibitor competition studies indicated an additive binding mode to the initiation pocket that is occupied by the thiadiazine class of compounds and an additive binding mode to the elongation pocket that is occupied by diketoacids, but a mutually exclusive binding mode with respect to the allosteric thumb pocket that is occupied by the benzimidazole class of inhibitors. Therefore, halosalicylamides represent a novel class of allosteric inhibitors of HCV NS5B polymerase.     

Prostacyclin production by rat aorta "in vitro" is increased by the combined action of dipyridamole plus pentoxifylline

The present study evaluates the effect of dipyridamole and pentoxifylline, individually and in combination, on PGI2-like production and arachidonic acid metabolism of rat aorta "in vitro". Pentoxifylline 100 microM and dipyridamole 92 and 184 microM increased PGI2-like activity, as measured by the platelet aggregation inhibitory capacity of the aortic ring incubates, by 71%, 46% and 60% respectively; a greater increase in PGI2-like activity was observed with the combination of the drugs than when they were used separately. This effect was observed even at the lowest doses assayed. In fact, dipyridamole 9.2 microM plus pentoxifylline 1 microM increased the PGI2-like activity by 30% while the individual increase was 4.5% and 10.6% respectively. To obtain more information on the effect of the dipyridamole-pentoxifylline combination on arachidonic acid metabolism, arteries were incubated with (1-14C) arachidonic acid, and the 6-keto-PGF1 alpha and PGE2 quantified. Dipyridamole 92 microM plus pentoxifylline 1 and 10 microM increased 6-keto-PGF1 alpha and PGE2 production by about 30% and 48% respectively while the combination with pentoxifylline 100 microM increased the 6-keto-PGF1 alpha 76.5% and the PGE2 50%. The possible biological effect and therapeutic implications of increased PGI2 production by the arteries due to the dipyridamole-pentoxifylline combination remains to be ascertained.