Mosquito ageing modulates the development, virulence and transmission potential of pathogens

Host age variation is a striking source of heterogeneity that can shape the evolution and transmission dynamic of pathogens. Compared with vertebrate systems, our understanding of the impact of host age on invertebrate–pathogen interactions remains limited. We examined the influence of mosquito age on key life-history traits driving human malaria transmission. Females of Anopheles coluzzii, a major malaria vector, belonging to three age classes (4-, 8- and 12-day-old), were experimentally infected with Plasmodium falciparum field isolates. Our findings revealed reduced competence in 12-day-old mosquitoes, characterized by lower oocyst/sporozoite rates and intensities compared with younger mosquitoes. Despite shorter median longevities in older age classes, infected 12-day-old mosquitoes exhibited improved survival, suggesting that the infection might act as a fountain of youth for older mosquitoes specifically. The timing of sporozoite appearance in the salivary glands remained consistent across mosquito age classes, with an extrinsic incubation period of approximately 13 days. Integrating these results into an epidemiological model revealed a lower vectorial capacity for older mosquitoes compared with younger ones, albeit still substantial owing to extended longevity in the presence of infection. Considering age heterogeneity provides valuable insights for ecological and epidemiological studies, informing targeted control strategies to mitigate pathogen transmission

Plant-mediated effects on mosquito capacity to transmit human malaria

The ecological context in which mosquitoes and malaria parasites interact has received little attention, compared to the genetic and molecular aspects of malaria transmission. Plant nectar and fruits are important for the nutritional ecology of malaria vectors, but how the natural diversity of plant-derived sugar sources affects mosquito competence for malaria parasites is unclear. To test this, we infected Anopheles coluzzi, an important African malaria vector, with sympatric field isolates of Plasmodium falciparum, using direct membrane feeding assays. Through a series of experiments, we then examined the effects of sugar meals from Thevetia neriifolia and Barleria lupilina cuttings that included flowers, and fruit from Lannea microcarpa and Mangifera indica on parasite and mosquito traits that are key for determining the intensity of malaria transmission. We found that the source of plant sugar meal differentially affected infection prevalence and intensity, the development duration of the parasites, as well as the survival and fecundity of the vector. These effects are likely the result of complex interactions between toxic secondary metabolites and the nutritional quality of the plant sugar source, as well as of host resource availability and parasite growth. Using an epidemiological model, we show that plant sugar source can be a significant driver of malaria transmission dynamics, with some plant species exhibiting either transmission-reducing or -enhancing activities

FOLIAGE YIELD, CHEMICAL COMPOSITION AND INTAKE CHARACTERISTICS OF THREE MUCUNA VARIETIES

The effect of variety and fertiliser on foliage yield and chemical composition of the foliage of three mucuna varieties, Mucuna deeringeana, Mucuna cochinchinensis and Mucuna spp. var, Ghana, was studied in an experiment in Burkina Faso in 2005 and 2007. The chemical composition and intake of hay from the same mucuna species were also studied using six Zebu cows per treatment offered 1/3 of their diet as grass hay. The experimental design of the agriculture experiment in both years was a randomised block with 3 mucuna varieties, not fertilised or fertilised with 2 kg DM/m2 of cow manure and with 4 replications. The foliages were harvested when 75% of the plants were flowering both for measuring foliage yield and for making hay. Soil characteristics before and after the experiment, dry matter yields and stem/leaf ratio of the vines were recorded and chemical composition of the foliages analysed. The mean age at harvesting was 57 d for M. spp. var. Ghana that was significantly shorter than for M. deeringeana (63 d) and M. cochinchinensis (81 d). Age at harvesting was not significantly affected by fertilisation. Dry matter yield was significantly lower for M. spp. var. Ghana, 1.71 t/ha for the unfertilised plots, compared to 3.29 and 3.07 t/ha for M. deeringeana and M. cochinchinensis, respectively. Fertilisation with manure more than doubled the yield for all varieties. There was no difference in stem/leaf ratio due to variety or fertiliser. The leaves+petiole fraction was generally heavier than the stem fraction. M. spp. var. Ghana had significantly higher content of crude protein than M. deeringeana and M. cochinchinensis (204, 177 and 150 g/kg DM, respectively). M. cochinchinensis had significantly higher ADF content than M. spp. var. Ghana, 474 and 369 g/kg DM, respectively. M. spp. var. Ghana had the highest CP content (209 g/kg DM), significantly different from M. cochinchinensis (165 g/kg DM) but not from M. deeringeana (192 g/kg DM). M. spp. var. Ghana had the best intake characteristics (4659 g and 3668 g/d for cows and heifers, respectively), but significantly so only for cows. In conclusion, the high foliage yield, the possibility of increasing soil fertility through N fixation and the high nutritive value of the foliage makes mucuna an interesting feed for ruminants even in areas with low soil fertility and a short rainy season

Malaria early in the first pregnancy: Potential impact of iron status

Background and Aims: Low iron stores may protect from malaria infection, therefore improving iron stores in early pregnancy in line with current recommendations could increase malaria susceptibility. To test this hypothesis we compared iron biomarkers and red cell indices in nulliparae and primigravidae who participated in a randomized controlled trial of long-term weekly iron supplementation. Methods: Cross-sectional and longitudinal data analysis from a randomized controlled trial of long-term weekly iron supplementation in rural Burkina Faso. Malaria parasitaemia was monitored and biomarkers and red cell indices measured at study end-points: plasma ferritin, transferrin receptor (sTfR), zinc protoporphyrin, hepcidin, sTfR/log10 ferritin ratio, body iron, haemoglobin, red cell distribution width; mean corpuscular haemoglobin concentration/volume, and C-reactive protein. Correlation coefficients between biomarkers and red cell indices were determined. A regression correction approach based on ferritin was used to estimate iron body stores, allowing for inflammation. Body iron differences were compared between nulliparae and primigravidae, and the association determined of iron biomarkers and body iron stores with malaria. Results: Iron and haematological indices of 972 nulliparae (mean age 16.5 years) and 314 primigravidae (median gestation 18 weeks) were available. Malaria prevalence was 54.0% in primigravidae and 41.8% in nulliparae (relative risk 1.28, 95% CI 1.13-1.45, P<0.001), anaemia prevalence 69.7% and 43.4% (P<0.001), and iron deficient erythropoiesis (low body iron) 8.0% and 11.7% (P=0.088) respectively. Unlike other biomarkers the sTfR/log10 ferritin ratio showed no correlation with inflammation as measured by CRP. Most biomarkers indicated reduced iron deficiency in early pregnancy, with the exception of haemoglobin. Body iron increased by 0.6 to 1.2 mg/kg in early gestation, did not differ by malaria status in nulliparae, but was higher in primigravidae with malaria (6.5 mg/kg versus 5.0 mg/kg; relative risk 1.53, 95% CI 0.67-2.38, P<0.001). Conclusion: In primigravidae, early pregnancy haemoglobin was not a good indicator of requirement for iron supplementation, which could be detrimental given the association of better iron status with increased malaria infection. Trial Registration: clinicaltrials.gov:NCT01210040. Until placed in a public repository, data relating to the current study can be requested from the corresponding author and will be made available following an end user data agreement and sponsor approval

Data from: Plant-mediated effects on mosquito capacity to transmit human malaria

The ecological context in which mosquitoes and malaria parasites interact has received little attention, compared to the genetic and molecular aspects of malaria transmission. Plant nectar and fruits are important for the nutritional ecology of malaria vectors, but how the natural diversity of plant-derived sugar sources affects mosquito competence for malaria parasites is unclear. To test this, we infected Anopheles coluzzi, an important African malaria vector, with sympatric field isolates of Plasmodium falciparum, using direct membrane feeding assays. Through a series of experiments, we then examined the effects of sugar meals from Thevetia neriifolia and Barleria lupilina cuttings that included flowers, and fruit from Lannea microcarpa and Mangifera indica on parasite and mosquito traits that are key for determining the intensity of malaria transmission. We found that the source of plant sugar meal differentially affected infection prevalence and intensity, the development duration of the parasites, as well as the survival and fecundity of the vector. These effects are likely the result of complex interactions between toxic secondary metabolites and the nutritional quality of the plant sugar source, as well as of host resource availability and parasite growth. Using an epidemiological model, we show that plant sugar source can be a significant driver of malaria transmission dynamics, with some plant species exhibiting either transmission-reducing or -enhancing activities

Aging reduces the accuracy of self-reported walking limitation in patients with vascular-type claudication

BACKGROUND: The published correlations between treadmill performance and the Walking Impairment Questionnaire (WIQ) score are generally fair. We hypothesized that the slope of the relationship of maximal treadmill walking time to WIQ would be lower in older than in younger patients, resulting in (1) a fair correlation in the population considered as a whole and (2) different cutoff points of the WIQ score to predict the ability to complete 5 minutes of treadmill walking in different age groups. METHODS: A 9-month prospective study was performed among patients referred for vascular-type claudication. Patients were divided into three age groups by years: 70 (group 3, n = 77). Patients self-completed the WIQ, which was corrected with a nurse, if necessary, and then completed a treadmill test. We calculated the correlation coefficient and slope of the relationship between the WIQ and maximal treadmill walking time. We used receiver operating characteristics curve analysis to estimate the accuracy of the WIQ score to determine the ability of the patients to complete 5 minutes of treadmill walking. RESULTS: Differences in slopes were significant between groups 1 vs 2 (P = .02), 2 vs 3 (P < .002), and 1 vs 3 (P < .001). The R(2) for the regression lines also tended to decrease but was only significant between two extremes (1 vs 2, P = .11; 2 vs 3, P = .07; 1 vs 3, P < .001). In patients aged <60 years (group 1), a WIQ score of 47 predicted the ability to complete a 5-minute test on treadmill with 86.8% accuracy (area under the receiver operating characteristics curve, 0.906; P < .001). The accuracy in predicting treadmill results from the WIQ score was fair in group 2 and nonsignificant in group 3. CONCLUSIONS: Prediction of treadmill walking capacity from the WIQ score should account for age. The TransAtlantic Inter-Society Consensus suggests that self-reported limitation has an equal weight as measured walking distance in the treatment choices and follow-up of patients with peripheral arterial disease. The WIQ should probably be used with caution in clinical routine, and constant-load treadmill testing is probably not the ideal candidate in elderly patients. New or adapted tools are likely needed in such patients but remain to be studied

Effect of sugar treatment on the sporozoite index and EIP.

<p>(a) Sporozoite index (± 95% CI), expressed as the proportion of mosquitoes exposed to an infectious blood meal and having disseminated sporozoites in their head/thoraces, over 2 replicates and using a total of 4 gametocyte carriers. Numbers in brackets indicate, for each sugar treatment, the total number of mosquitoes analyzed with PCR on 14 days post infection (dpi). Different letters above the bars denote statistically significant differences based on multiple pair-wise post-hoc tests. (b) Survivorship of malaria-exposed mosquitoes for each sugar treatment over 2 replicates, and using a total of 4 gametocyte carriers. Survival was recorded twice a day from 1 to 14 dpi. (c) Sporozoite index (± 95% CI) over time and using a total of 2 gametocyte carriers. *p<0.05; **p < 0.01, NS: non-significant difference between sugar treatment</p

Effect of sugar treatment on the early development of <i>P</i>. <i>falciparum</i>, and on the survival and fecundity of malaria-exposed <i>Anopheles coluzzii</i>.

<p>(a) Infection rate (± 95% CI), expressed as the proportion of mosquitoes exposed to an infectious blood meal and harboring at least one oocyst in their midgut, over 4 replicates and using a total of 7 gametocyte carriers. Numbers in brackets indicate the total number of mosquitoes dissected 7 days post infection (dpi) for each sugar treatment. Different letters above the bars denote statistically significant differences based on multiple pair-wise post-hoc tests. (b) Infection intensity (± se), expressed as the mean number of developing oocysts in the guts of infected females, over 4 replicates and using a total of 7 gametocyte carriers. Numbers in brackets indicate the total number of infected mosquitoes for each sugar treatment. Different letters above the bars denote statistically significant differences based on multiple pair-wise post-hoc tests. (c) Survivorship of malaria-exposed mosquitoes for each sugar treatment over 4 replicates and using a total of 7 gametocyte carriers. Survival was recorded twice a day from 1 to 7 dpi. (d) Egg incidence (± 95% CI) of malaria-exposed mosquitoes, expressed as the proportion of mosquito females carrying fully matured eggs inside their ovaries on 7 dpi for each sugar treatment and infection status.</p