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The effect of age and dietary factors of Anopheles gambiae (Diptera: Culicidae) on the infectivity of natural Plasmodium falciparum parasites was studied. Mosquitoes of various ages (1-3, 4-7 and 8-11 day old) and those fed blood (either single or double meals) and sugar meals were experimentally co-infected with P. falciparum gametocytes obtained from different naturally infected human volunteers. On day 7, midguts were examined for oocyst infection to determine whether mosquito age or diets have significant effects on parasite infectivity. The age of the mosquitoes did not significantly influence the oocyst infection rates (chi2 = 48.32, df = 40, P = 0.172) or oocyst load (# of oocysts/midgut) (P = 0.14) observed. Oocyst load between groups was not significantly different. Similarly, the type of diet (either blood or sugar) did not influence oocyst infection rates (chi2 = 16.52, df = 19, P = 0.622). However, an increase in oocyst infection rates resulted after previous feeding on double blood meals (35%) compared to single blood meals (25%), with comparable oocyst load. These observations are in agreement with those reported in previous studies suggesting that increased mosquito nutritional reserves resulting from increased dietary resources is favorable for malaria infectivity. This field-based study indicates that vector competence of An. gambiae to natural P. falciparum parasites does not vary with age and that nutritional resources acquired prior to an infectious blood meal plays a crucial role in mosquito-parasite relationships.

The effect of age and dietary factors of Anopheles gambiae (Diptera: Culicidae) on the infectivity of natural Plasmodium falciparum parasites was studied. Mosquitoes of various ages (1-3, 4-7 and 8-11 day old) and those fed blood (either single or double meals) and sugar meals were experimentally co-infected with P. falciparum gametocytes obtained from different naturally infected human volunteers. On day 7, midguts were examined for oocyst infection to determine whether mosquito age or diets have significant effects on parasite infectivity. The age of the mosquitoes did not significantly influence the oocyst infection rates (chi2 = 48.32, df = 40, P = 0.172) or oocyst load (# of oocysts/midgut) (P = 0.14) observed. Oocyst load between groups was not significantly different. Similarly, the type of diet (either blood or sugar) did not influence oocyst infection rates (chi2 = 16.52, df = 19, P = 0.622). However, an increase in oocyst infection rates resulted after previous feeding on double blood meals (35%) compared to single blood meals (25%), with comparable oocyst load. These observations are in agreement with those reported in previous studies suggesting that increased mosquito nutritional reserves resulting from increased dietary resources is favorable for malaria infectivity. This field-based study indicates that vector competence of An. gambiae to natural P. falciparum parasites does not vary with age and that nutritional resources acquired prior to an infectious blood meal plays a crucial role in mosquito-parasite relationships.

Spondweni virus (SPONV) and Zika virus are closely related flaviviruses that were first described in Africa in 1952 and 1947, respectively (1). Humans infected by these viruses have similar clinical [...]

Mayaro virus (MAYV; genus Alphavirus, family Togaviridae) is a single-stranded positive RNA virus that was first isolated in Trinidad in 1954 (1) and is one of the viruses that comprise [...]

Abstract Background Malaria caused by Plasmodium falciparum infects roughly 30,000 individuals in Haiti each year. Haiti has used chloroquine (CQ) as a first-line treatment for malaria for many years and as a result there are concerns that malaria parasites may develop resistance to CQ over time. Therefore it is important to prepare for alternative malaria treatment options should CQ resistance develop. In many other malaria-endemic regions, antifolates, particularly pyrimethamine (PYR) and sulphadoxine (SDX) treatment combination (SP), have been used as an alternative when CQ resistance has developed. This study evaluated mutations in the dihydrofolate reductase (dhfr) and dihydropteroate synthetase (dhps) genes that confer PYR and SDX resistance, respectively, in P. falciparum to provide baseline data in Haiti. This study is the first comprehensive study to examine PYR and SDX resistance genotypes in P. falciparum in Haiti. Methods DNA was extracted from dried blood spots and genotyped for PYR and SDX resistance mutations in P. falciparum using PCR and DNA sequencing methods. Sixty-one samples were genotyped for PYR resistance in codons 51, 59, 108 and 164 of the dhfr gene and 58 samples were genotyped for SDX resistance codons 436, 437, 540 of the dhps gene in P. falciparum. Results Thirty-three percent (20/61) of the samples carried a mutation at codon 108 (S108N) of the dhfr gene. No mutations in dhfr at codons 51, 59, 164 were observed in any of the samples. In addition, no mutations were observed in dhps at the three codons (436, 437, 540) examined. No significant difference was observed between samples collected in urban vs rural sites (Welch’s T-test p-value = 0.53 and permutations p-value = 0.59). Conclusion This study has shown the presence of the S108N mutation in P. falciparum that confers low-level PYR resistance in Haiti. However, the absence of SDX resistance mutations suggests that SP resistance may not be present in Haiti. These results have important implications for ongoing discussions on alternative malaria treatment options in Haiti.

Abstract Background The origin of highly competent malaria vectors has been linked to productive larval habitats in the field, but there isn't solid quantitative or qualitative data to support it. To test this, the effect of larval habitat soil substrates on larval development time, pupation rates and vector competence of Anopheles gambiae to Plasmodium falciparum were examined. Methods Soils were collected from active larval habitats with sandy and clay substrates from field sites and their total organic matter estimated. An. gambiae larvae were reared on these soil substrates and the larval development time and pupation rates monitored. The emerging adult mosquitoes were then artificially fed blood with infectious P. falciparum gametocytes from human volunteers and their midguts examined for oocyst infection after seven days. The wing sizes of the mosquitoes were also measured. The effect of autoclaving the soil substrates was also evaluated. Results The total organic matter was significantly different between clay and sandy soils after autoclaving (P = 0.022). A generalized liner model (GLM) analysis identified habitat type (clay soil, sandy soil, or lake water) and autoclaving (that reduces presence of microbes) as significant factors affecting larval development time and oocyst infection intensities in adults. Autoclaving the soils resulted in the production of significantly smaller sized mosquitoes (P = 0.008). Autoclaving clay soils resulted in a significant reduction in Plasmodium falciparum oocyst intensities (P = 0.041) in clay soils (unautoclaved clay soils (4.28 ± 0.18 oocysts/midgut; autoclaved clay soils = 1.17 ± 0.55 oocysts/midgut) although no difference (P = 0.480) in infection rates was observed between clay soils (10.4%), sandy soils (5.3%) or lake water (7.9%). Conclusion This study suggests an important nutritional role for organic matter and microbial fauna on mosquito fitness and vector competence. It shows that the quality of natural aquatic habitats of mosquito larvae may influence malaria parasite transmission potential by An. gambiae. This information can be important in targeting larval habitats for malaria control.

Abstract Background Studies on Plasmodium falciparum gametocyte development and dynamics have almost exclusively focused on patients treated with antimalarial drugs, while the majority of parasite carriers in endemic areas are asymptomatic. This study identified factors that influence gametocytaemia in asymptomatic children in the absence and presence of pyrimethamine-sulphadoxine (SP) antimalarial treatment. Methods A cohort of 526 children (6 months – 16 years) from western Kenya was screened for asexual parasites and gametocytes and followed weekly up to four weeks. Children with an estimated parasitaemia of ≥1,000 parasites/μl were treated with SP according to national guidelines. Factors associated with gametocyte development and persistence were determined in untreated and SP-treated children with P. falciparum mono-infection. Results Gametocyte prevalence at enrolment was 33.8% in children below five years of age and decreased with age. In the absence of treatment 18.6% of the children developed gametocytaemia during follow-up; in SP-treated children this proportion was 29.8%. Age, high asexual parasite density and gametocyte presence at enrolment were predictive factors for gametocytaemia. The estimated mean duration of gametocytaemia for children below five, children from five to nine and children ten years and above was 9.4, 7.8 and 4.1 days, respectively. Conclusion This study shows that a large proportion of asymptomatic untreated children develop gametocytaemia. Gametocytaemia was particularly common in children below five years who harbor gametocytes for a longer period of time. The age-dependent duration of gametocytaemia has not been previously shown and could increase the importance of this age group for the infectious reservoir.