Fire-induced pine woodland to shrubland transitions in Southern Europe may promote shifts in soil fertility

Since the mid of the last century, fire recurrence has increased in the Iberian Peninsula and in the overall Mediterranean basin due to changes in land use and climate. The warmer and drier climate projected for this region will further increase the risk of wildfire occurrence and recurrence. Although the impact of wildfires on soil nutrient content in this region has been extensively studied, still few works have assessed this impact on the basis of fire recurrence. This study assesses the changes in soil organic C and nutrient status of mineral soils in two Southern European areas, Várzea (Northern Portugal) and Valencia (Eastern Spain), affected by different levels of fire recurrence and where short fire intervals have promoted a transition from pine woodlands to shrublands. At the short-term (<1year), the amount of soil organic matter was higher in burned than in unburned soils while its quality (represented as labile to total organic matter) was actually lower. In any case, total and labile soil organic matter showed decreasing trends with increasing fire recurrence (one to four fires). At the long-term (>5years), a decline in overall soil fertility with fire recurrence was also observed, with a drop between pine woodlands (one fire) and shrublands (two and three fires), particularly in the soil microsites between shrubs. Our results suggest that the current trend of increasing fire recurrence in Southern Europe may result in losses or alterations of soil organic matter, particularly when fire promotes a transition from pine woodland to shrubland. The results also point to labile organic matter fractions in the intershrub spaces as potential early warning indicators for shifts in soil fertility in response to fire recurrence.

The role of age and exposure to Plasmodium falciparum in the rate of acquisition of naturally acquired immunity: a randomized controlled trial

BACKGROUND

The rate of acquisition of naturally acquired immunity (NAI) against malaria predominantly depends on transmission intensity and age, although disentangling the effects of these is difficult. We used chemoprophylaxis to selectively control exposure to P. falciparum during different periods in infancy and explore the effect of age in the build-up of NAI, measured as risk of clinical malaria.

METHODS AND FINDINGS

A three-arm double-blind randomized placebo-controlled trial was conducted in 349 infants born to Mozambican HIV-negative women. The late exposure group (LEG) received monthly Sulfadoxine-Pyrimethamine (SP) plus Artesunate (AS) from 2.5-4.5 months of age and monthly placebo from 5.5-9.5 months; the early exposure group (EEG) received placebo from 2.5-4.5 months and SP+AS from 5.5-9.5 months; and the control group (CG) received placebo from 2.5-9.5 months. Active and passive case detection (PCD) were conducted from birth to 10.5 and 24 months respectively. The primary endpoint was time to first or only episode of malaria in the second year detected by PCD. The incidence of malaria during the second year was of 0.50, 0.51 and 0.35 episodes/PYAR in the LEG, EEG and CG respectively (p = 0.379 for the adjusted comparison of the 3 groups). The hazard ratio of the adjusted comparison between the LEG and the CG was 1.38 (0.83-2.28, p = 0.642) and that between the EEG and the CG was 1.35 (0.81-2.24, p = 0.743).

CONCLUSIONS

After considerably interfering with exposure during the first year of life, there was a trend towards a higher risk of malaria in the second year in children who had received chemoprophylaxis, but there was no significant rebound. No evidence was found that the age of first exposure to malaria affects the rate of acquisition of NAI. Thus, the timing of administration of antimalarial interventions like malaria vaccines during infancy does not appear to be a critical determinant.

TRIAL REGISTRATION

ClinicalTrials.gov NCT00231452.

Prevalence of the K76T mutation in the putative Plasmodium falciparum chloroquine resistance transporter (pfcrt) gene and its relation to chloroquine resistance in Mozambique

K76T, a mutation in the Plasmodium falciparum chloroquine (CQ) resistance transporter protein, has been implicated in resistance to CQ. A modified 14-day in vivo test to estimate the CQ resistance level was done in southern Mozambique: 21 (42%) of 50 subjects who completed the follow-up were CQ susceptible. Use of msa2-restriction fragment length polymorphism (RFLP) genotyping to differentiate new from recrudescent infections made little difference in the estimated prevalence of resistance. The K76T mutation prevalence was estimated by RFLP-polymerase chain reaction and sequencing, and its relation to parasitological CQ resistance was explored on day 0 samples: 51 of 56 pretreatment samples presented the T76 codon, and it was present in 100% of children with parasitological resistance. T76 also was present in 18 of 23 subjects in whom the infection resolved after CQ treatment. These findings show a high prevalence of the K76T mutation among wild isolates but also suggest additional factors responsible for CQ resistance.