The global rate of heavy metal pollution is rapidly increasing in different habitats. Anopheles malaria vector species appear to tolerate many aquatic habitats with metal pollutants, despite their normal proclivity for 'clean' water (i.e., generally water free of organic matter). Investigations were conducted to establish whether there are biological costs for tolerance to heavy metals in Anopheles gambiae Giles sensu stricto (Diptera: Culicidae), and to assess the potential impact of heavy metal pollution on mosquito ecology. Anopheles gambiae s.s. were selected for cadmium, copper or lead tolerance through chronic exposure of immature stages to solutions of the metals for three successive generations. Biological costs were assessed in the fourth generation by horizontal life table analysis. Tolerance in larvae to cadmium (as cadmium chloride, CdCl2), copper (as copper II nitrate hydrate, (Cu (NO 3 ) 2. 2·5H 2 O) and lead (as lead II nitrate, (Pb (NO 3 ) 2 ), monitored by changes in LC 50 concentrations of the metals, changed from, 6.07, 12.42 and 493.32 μg/L to 4.45, 25.02 and 516.69 μg/L, respectively, after 3 generations of exposure. The metalselected strains had a significantly lower magnitude of egg viability, larval and pupal survivorship, adult emergence, fecundity and net reproductive rate than the control strain. The population doubling times were significantly longer and the instantaneous birth rates lower in most metalselected strains relative to the control strain. Our results suggest that although An. gambiae s.s. displays the potential to develop tolerance to heavy metals, particularly copper, this may occur at a significant biological cost, which can adversely affect its ecological fitness.
Anopheles mosquitoes have been shown to adapt to heavy metals in their natural habitats. In this study we explored the possibility of using Anopheles gambiae sensu stricto as bio-reporters for environmental heavy metal pollution through expressions of their metal responsive metallothionein and α-tubulin genes. The study was undertaken with third instar larvae after selection by cadmium, copper, or lead at LC 30 through five successive generations. Expression levels were determined in the fifth generation by semi quantitative RT-PCR on the experimental and control populations. The data were analyzed using one-way ANOVA. The highest metallothionein (F 3, 11 = 4.574, P = 0.038) and α-tubulin (F 3,11 = 12.961, P = 0.002) responses were observed in cadmium-tolerant treatments. There was significantly higher expression of metallothionein in cadmium or copper treatments relative to the control (P = 0.012), and in cadmium than in lead treatments (P = 0.044). Expressions of α-tubulin were significantly higher in cadmium than in control treatments (P = 0.008). These results demonstrate capacity of An. gambiae s.s. to develop tolerance to increased levels of heavy metal challenge. The results also confirm the potential of heavy metal responsive genes in mosquitoes as possible bio-indicators of heavy metal environmental pollution. How the tolerance and expressions relate to An. gambiae s.s. fitness and vectorial capacity in the environment remains to be elucidated.
Background Despite remarkable success obtained with current malaria vector control strategies in the last 15 years, additional innovative measures will be needed to achieve the ambitious goals for malaria control set for 2030 by the World Health Organization (WHO). New tools will need to address insecticide resistance and residual transmission as key challenges. Endectocides such as ivermectin are drugs that kill mosquitoes which feed on treated subjects. Mass administration of ivermectin can effectively target outdoor and early biting vectors, complementing the still effective conventional tools. Although this approach has garnered attention, development of ivermectin resistance is a potential pitfall. Herein, we evaluate the potential role of xenobiotic pumps and cytochrome P450 enzymes in protecting mosquitoes against ivermectin by active efflux and metabolic detoxification, respectively. Methods We determined the lethal concentration 50 for ivermectin in colonized Anopheles gambiae; then we used chemical inhibitors and inducers of xenobiotic pumps and cytochrome P450 enzymes in combination with ivermectin to probe the mechanism of ivermectin detoxification. Results Dual inhibition of xenobiotic pumps and cytochromes was found to have a synergistic effect with ivermectin, greatly increasing mosquito mortality. Inhibition of xenobiotic pumps alone had no effect on ivermectin-induced mortality. Induction of xenobiotic pumps and cytochromes may confer partial protection from ivermectin. Conclusion There is a clear pathway for development of ivermectin resistance in malaria vectors. Detoxification mechanisms mediated by cytochrome P450 enzymes are more important than xenobiotic pumps in protecting mosquitoes against ivermectin.
Background In a recent study using DNA barcoding, we identified the plants fed upon by four Afro-tropical mosquito species that vector dengue, malaria, and Rift Valley fever. Herein, we have expanded on this study by investigating the role of three of the plants, Pithecellobium dulce (Fabaceae), Leonotis nepetifolia (Lamiaceae), and Opuntia ficus-indica (Cactaceae), on the survival, fecundity, and egg viability of the dengue vector Aedes aegypti. Methods We tested these effects using females that received (i) an initial three rations of blood meals and (ii) no blood meal at all. Two controls were included: age-matched females fed on glucose solution with or without an initial blood meal and those fed exclusively on blood meals. Data were collected daily over a 30-day period. The amino acid contents of Ae. aegypti guts and their respective diets were detected by coupled liquid chromatography-mass spectrometry. Results Females fed on P. dulce and an exclusively blood meal diet had a shorter survival than those fed on glucose. On the other hand, females fed on L. nepetifolia survived longer than those fed exclusively on blood meals, whereas those fed on O. ficus-indica had the shortest survival time. With an initial blood meal, females fed on L. nepetifolia laid 1.6-fold more eggs while those fed on the other diets laid fewer eggs compared to those fed exclusively on blood meals. Hatching rates of the eggs laid varied with the diet. Mass spectroscopic analysis of gut contents of mosquitoes exposed to the different diets showed qualitative and quantitative differences in their amino acid levels. Conclusion Our findings highlight the central role of plant nutrients in the reproductive fitness of dengue vectors, which may impact their disease transmission potential.
Background Despite remarkable success obtained with current malaria vector control strategies in the last 15 years, additional innovative measures will be needed to achieve the ambitious goals set for 2030 by the World Health Organization (WHO). New tools will need to address insecticide resistance and residual transmission as key challenges. Endectocides such as ivermectin are drugs that kill mosquitoes which feed on treated subjects. Mass administration of ivermectin can effectively target outdoor and early biting vectors, complementing the still effective conventional tools. Although this approach has garnered attention, development of ivermectin resistance is a potential pitfall. Herein, we evaluate the potential role of xenobiotic pumps and cytochrome P450 enzymes in protecting mosquitoes against ivermectin by active efflux and metabolic detoxification, respectively. Methods We determined the lethal-concentration 50 for ivermectin in colonized Anopheles gambiae, then we used chemical inhibitors and inducers of xenobiotic pumps and cytochrome P450 enzymes in combination with ivermectin to probe the mechanism of ivermectin detoxification. Results Dual inhibition of xenobiotic pumps and cytochromes have a synergistic effect with ivermectin, greatly increasing mosquito mortality. Inhibition of xenobiotic pumps alone had no effect on ivermectin-induced mortality. Induction of xenobiotic pumps and cytochromes may confer partial protection from ivermectin.Conclusion there is a clear pathway for development of ivermectin resistance in malaria vectors. Detoxification mechanisms mediated by cytochrome P450 enzymes are more important than xenobiotic pumps in protecting mosquitoes against ivermectin.
Background Malaria is transmitted when infected Anopheles mosquitoes take a blood meal. During this process, the mosquitoes inject a cocktail of bioactive proteins that elicit antibody responses in humans and could be used as biomarkers of exposure to mosquito bites. This study evaluated the utility of IgG responses to members of the Anopheles gambiae D7 protein family as serological markers of human–vector contact. Methods The D7L2, D7r1, D7r2, D7r3, D7r4 and SG6 salivary proteins from An. gambiae were expressed as recombinant antigens in Escherichia coli. Antibody responses to the salivary proteins were compared in Europeans with no prior exposure to malaria and lifelong residents of Junju in Kenya and Kitgum in Uganda where the intensity of malaria transmission is moderate and high, respectively. In addition, to evaluate the feasibility of using anti-D7 IgG responses as a tool to evaluate the impact of vector control interventions, we compared responses between individuals using insecticide-treated bednets to those who did not in Junju, Kenya where bednet data were available. Results We show that both the long and short forms of the D7 salivary gland antigens elicit a strong antibody response in humans. IgG responses against the D7 antigens reflected the transmission intensities of the three study areas, with the highest to lowest responses observed in Kitgum (northern Uganda), Junju (Kenya) and malaria-naïve Europeans, respectively. Specifically, the long form D7L2 induced an IgG antibody response that increased with age and that was lower in individuals who slept under a bednet, indicating its potential as a serological tool for estimating human–vector contact and monitoring the effectiveness of vector control interventions. Conclusions This study reveals that D7L2 salivary antigen has great potential as a biomarker of exposure to mosquito bites and as a tool for assessing the efficacy of vector control strategies such as bednet use. Graphical abstract
Background In a recent study using DNA barcoding, we identified the plants fed upon by four Afro-tropical mosquito species that vector dengue, malaria, and Rift Valley fever. Herein, we have expanded on this study by investigating the role of three of the plants Pithecellobium dulce (Fabaceae), Leonotis nepetifolia (Lamiaceae), and Opuntia ficus-indica (Cactaceae) on survival, fecundity, and egg viability of the dengue vector Aedes aegypti. Methods We tested these effects using females that received a) an initial three rations of bloodmeal, and b) received no bloodmeal at all. Two controls were included; age-matched females fed on glucose solution with or without initial bloodmeal, and those fed exclusively on bloodmeal. Data was collected daily over a 30-day period. The amino acid content of Ae. aegypti guts and the amino acid content of their respective diets was detected by coupled liquid chromatography – mass spectrometry. Results Females fed on P. dulce and exclusive bloodmeal had a shorter survival than those fed on glucose. On the other hand, females fed on L. nepetifolia survived longer than those fed exclusively on bloodmeal, whereas those fed on O. ficus-indica had the shortest survival time. With initial bloodmeal, females fed on L. nepetifolia laid 1.6-fold more eggs while those fed on the other diets laid fewer eggs, compared to those fed exclusively on bloodmeal. Hatching rates of the eggs laid varied with the diet. Mass spectroscopic analysis of gut contents of mosquitoes exposed to the different diets showed qualitative and quantitative differences in their amino acid levels. Conclusion Our findings highlight the central role of plant nutrients in the reproductive fitness of dengue vectors which may impact their disease transmission potential.
Background: In a recent study using DNA barcoding, we identified the plants fed upon by four Afro-tropical mosquito species that vector dengue, malaria, and Rift Valley fever. Herein, we have expanded on this study by investigating the role of three of the plants Pithecellobium dulce (Fabaceae), Leonotis nepetifolia (Lamiaceae), and Opuntia ficus-indica (Cactaceae) on survival, fecundity, and egg viability of the dengue vector Aedes aegypti. Methods: We tested these effects using females that received a) an initial three rations of bloodmeal, and b) received no bloodmeal at all. Two controls were included; age-matched females fed on glucose solution with or without initial bloodmeal, and those fed exclusively on bloodmeal. Data was collected daily over a 30-day period. The amino acid content of Ae. aegypti guts and the amino acid content of their respective diets was detected by coupled liquid chromatography – mass spectrometry.Results: Females fed on P. dulce and exclusive bloodmeal had a shorter survival than those fed on glucose. On the other hand, females fed on L. nepetifolia survived longer than those fed exclusively on bloodmeal, whereas those fed on O. ficus-indica had the shortest survival time. With initial bloodmeal, females fed on L. nepetifolia laid 1.6-fold more eggs while those fed on the other diets laid fewer eggs, compared to those fed exclusively on bloodmeal. Hatching rates of the eggs laid varied with the diet. Mass spectroscopic analysis of gut contents of mosquitoes exposed to the different diets showed qualitative and quantitative differences in their amino acid levels. Conclusion: Our findings highlight the central role of plant nutrients in the reproductive fitness of dengue vectors which may impact their disease transmission potential.
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