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• W4291916500 abstract "Vector control tools (VCTs) affect diverse aspects of mosquito biology and are a driver of vector evolution.VCTs change parasite ecology by exposing parasites to insecticides and to vectors with altered genotypes and phenotypes (e.g., lifespan, behaviour, immunity, metabolism, microbiome).Parasite activities are affected by the ways that VCTs alter parasite–vector interactions, and this can drive parasite evolution.Parasite responses to VCTs are likely to include plastic and evolutionary changes to transmission traits expressed during infections in hosts/vectors.Parasite responses could undermine gains made towards malaria elimination and may have knock-on consequences for parasite–host interactions.Knowledge of parasite responses to the selection pressures imposed by VCTs could offer new approaches to reduce disease transmission that are robust to parasite evolution. Insect vectors are responsible for spreading many infectious diseases, yet interactions between pathogens/parasites and insect vectors remain poorly understood. Filling this knowledge gap matters because vectors are evolving in response to the deployment of vector control tools (VCTs). Yet, whilst the evolutionary responses of vectors to VCTs are being carefully monitored, the knock-on consequences for parasite evolution have been overlooked. By examining how mosquito responses to VCTs impact upon malaria parasite ecology, we derive a framework for predicting parasite responses. Understanding how VCTs affect the selection pressures imposed on parasites could help to mitigate against parasite evolution that leads to unfavourable epidemiological outcomes. Furthermore, anticipating parasite evolution will inform monitoring strategies for VCT programmes as well as uncovering novel VCT strategies. Insect vectors are responsible for spreading many infectious diseases, yet interactions between pathogens/parasites and insect vectors remain poorly understood. Filling this knowledge gap matters because vectors are evolving in response to the deployment of vector control tools (VCTs). Yet, whilst the evolutionary responses of vectors to VCTs are being carefully monitored, the knock-on consequences for parasite evolution have been overlooked. By examining how mosquito responses to VCTs impact upon malaria parasite ecology, we derive a framework for predicting parasite responses. Understanding how VCTs affect the selection pressures imposed on parasites could help to mitigate against parasite evolution that leads to unfavourable epidemiological outcomes. Furthermore, anticipating parasite evolution will inform monitoring strategies for VCT programmes as well as uncovering novel VCT strategies. Vector control is one of the most effective methods to curb vector-borne diseases, with insecticide-based interventions predicted to have averted the majority of malaria cases since 2000 [1.Bhatt S. et al.The effect of malaria control on Plasmodium falciparum in Africa between 2000 and 2015.Nature. 2015; 526: 207-211Crossref PubMed Scopus (1617) Google Scholar]. However, because they reduce vector survival and reproduction, the continued and widespread use of chemical-based vector control tools (VCTs) has contributed to the evolution of insecticide resistance (IR) and evasion, particularly in Anopheline mosquito populations (Box 1) [2.Huijben S. Paaijmans K.P. Putting evolution in elimination: winning our ongoing battle with evolving malaria mosquitoes and parasites.Evol. Appl. 2018; 11: 415-430Crossref PubMed Scopus (32) Google Scholar,3.Killeen G.F. et al.Developing an expanded vector control toolbox for malaria elimination.BMJ Glob. Health. 2017; 2e000211Crossref Scopus (75) Google Scholar], and threatens progress towards malaria elimination targets [4.World Health Organisation Global Technical Strategy for Malaria 2016–2030, 2021 Update. WHO, 2021Google Scholar]. It is therefore not surprising that the responses of insect vectors to VCTs receive intensive investigation [5.Carrasco D. et al.Behavioural adaptations of mosquito vectors to insecticide control.Curr. Opin. Insect Sci. 2019; 34: 48-54Crossref PubMed Scopus (54) Google Scholar,6.Ranson H. Lissenden N. Insecticide resistance in African Anopheles mosquitoes: a worsening situation that needs urgent action to maintain malaria control.Trends Parasitol. 2016; 32: 187-196Abstract Full Text Full Text PDF PubMed Scopus (505) Google Scholar]. However, remarkably little attention has been paid to how VCTs alter parasite–vector–host interactions and how parasites are responding to the selection pressures imposed by the consequences of VCTs.Box 1Vector responses to insecticide-based VCTsMechanisms of resistanceInsecticide target-site mutations reduce insecticide toxicity by causing structural modifications to target proteins, and include knockdown resistance mutations (kdr) in the para sodium channel gene (pyrethroid/DDT resistance), an Rdl gene mutation (dieldrin resistance), and an acetylcholinesterase enzyme (ace-1) mutation (organophosphate and carbamate resistance) [15.Alout H. et al.Interactive cost of Plasmodium infection and insecticide resistance in the malaria vector Anopheles gambiae.Sci. Rep. 2016; 629755Crossref PubMed Scopus (46) Google Scholar]. Increased metabolism and clearance via overexpression of detoxification gene families, including cytochrome P450-associated monooxygenases (P450s), glutathione S-transferases (GSTs), and carboxylesterases, enhance insecticide detoxification [33.Ingham V.A. et al.Transcriptomic analysis reveals pronounced changes in gene expression due to sub-lethal pyrethroid exposure and ageing in insecticide resistance Anopheles coluzzii.BMC Genomics. 2021; 22: 337Crossref PubMed Scopus (6) Google Scholar]. Other mechanisms include reducing insecticide penetration via a thicker cuticle [75.Balabanidou V. et al.Cytochrome P450 associated with insecticide resistance catalyzes cuticular hydrocarbon production in Anopheles gambiae.Proc. Natl. Acad. Sci. U. S. A. 2016; 113: 9268-9273Crossref PubMed Scopus (206) Google Scholar], and sequestration by chemosensory proteins in the legs [76.Ingham V.A. et al.A sensory appendage protein protects malaria vectors from pyrethroids.Nature. 2020; 577: 376-380Crossref PubMed Scopus (87) Google Scholar].Insecticide exposureDue to insecticide decay and insecticide resistance (IR) mechanisms, exposure to sublethal insecticide doses occur. In the short term, this stimulates changes to detoxification and redox metabolism gene expression [30.Ingham V.A. et al.Integration of whole genome sequencing and transcriptomics reveals a complex picture of the reestablishment of insecticide resistance in the major malaria vector Anopheles coluzzii.PLoS Genet. 2021; 17e1009970Crossref PubMed Scopus (8) Google Scholar,33.Ingham V.A. et al.Transcriptomic analysis reveals pronounced changes in gene expression due to sub-lethal pyrethroid exposure and ageing in insecticide resistance Anopheles coluzzii.BMC Genomics. 2021; 22: 337Crossref PubMed Scopus (6) Google Scholar], and reduces host-seeking and blood feeding [20.Thiévent K. et al.The interaction between permethrin exposure and malaria infection affects the host-seeking behaviour of mosquitoes.Malar. J. 2019; 18: 79Crossref PubMed Scopus (9) Google Scholar,77.Glunt K.D. et al.Empirical and theoretical investigation into the potential impacts of insecticide resistance on the effectiveness of insecticide-treated bed nets.Evol. Appl. 2018; 11: 431-441Crossref PubMed Scopus (30) Google Scholar]. Longer term effects include reduced survival of both IR and insecticide-susceptible (IS) mosquitoes [77.Glunt K.D. et al.Empirical and theoretical investigation into the potential impacts of insecticide resistance on the effectiveness of insecticide-treated bed nets.Evol. Appl. 2018; 11: 431-441Crossref PubMed Scopus (30) Google Scholar,78.Viana M. et al.Delayed mortality effects cut the malaria transmission potential of insecticide-resistant mosquitoes.Proc. Natl. Acad. Sci. U. S. A. 2016; 113: 8975-8980Crossref PubMed Scopus (67) Google Scholar], but lifespan is not affected in some highly resistant populations [79.Hughes A. et al.Anopheles gambiae populations from Burkina Faso show minimal delayed mortality after exposure to insecticide-treated nets.Parasit. Vectors. 2020; 13: 17Crossref PubMed Scopus (23) Google Scholar]. Furthermore, older mosquitoes are more susceptible to insecticides [80.Jones C.M. et al.Aging partially restores the efficacy of malaria vector control in insecticide-resistant populations of Anopheles gambiae s.l. from Burkina Faso.Malar. J. 2012; 11: 24Crossref PubMed Scopus (56) Google Scholar].Methods for evasionAvoidance is an alternative to coping with insecticides and occurs by blood foraging less frequently or at times of day when hosts are not protected by bed nets [5.Carrasco D. et al.Behavioural adaptations of mosquito vectors to insecticide control.Curr. Opin. Insect Sci. 2019; 34: 48-54Crossref PubMed Scopus (54) Google Scholar], in the early evening [81.Thomsen E.K. et al.Mosquito behavior change after distribution of bednets results in decreased protection against malaria exposure.J. Infect. Dis. 2017; 215: 790-797PubMed Google Scholar], or early morning [82.Moiroux N. et al.Changes in Anopheles funestus biting behavior following universal coverage of long-lasting insecticidal nets in benin.J. Infect. Dis. 2012; 206: 1622-1629Crossref PubMed Scopus (218) Google Scholar]. ITNs target anthropophilic species that bite indoors at night, rather than less specialist feeders that bite at any time of day and/or outdoors. Thus, sustained ITN use is associated with increased outdoor biting [83.Russell T.L. et al.Increased proportions of outdoor feeding among residual malaria vector populations following increased use of insecticide-treated nets in rural Tanzania.Malar. J. 2011; 10: 80Crossref PubMed Scopus (429) Google Scholar] and resting [84.Kreppel K.S. et al.Emergence of behavioural avoidance strategies of malaria vectors in areas of high LLIN coverage in Tanzania.Sci. Rep. 2020; 1014527Crossref PubMed Scopus (27) Google Scholar], as well as seeking a higher proportion of blood meals from non-human vertebrate hosts [84.Kreppel K.S. et al.Emergence of behavioural avoidance strategies of malaria vectors in areas of high LLIN coverage in Tanzania.Sci. Rep. 2020; 1014527Crossref PubMed Scopus (27) Google Scholar,85.Ndenga B.A. et al.Malaria vectors and their blood-meal sources in an area of high bed net ownership in the western Kenya highlands.Malar. J. 2016; 15: 76Crossref PubMed Scopus (43) Google Scholar].Further considerationsIdentifying the genetic basis and heritability of IR traits is challenging for complex behaviours such as a biting time-of-day, habitat choice, and host preference, but some behavioural resistance strategies are heritable [86.Govella N.J. et al.Heritability and phenotypic plasticity of biting time behaviors in the major African malaria vector Anopheles arabiensis.bioRxiv. 2021; (Published online May 17, 2021. https://doi.org/10.1101/2021.05.17.444456)Google Scholar,87.Main B.J. et al.The genetic basis of host preference and resting behavior in the major African malaria vector, Anopheles arabiensis.PLoS Genet. 2016; 12e1006303Crossref PubMed Scopus (55) Google Scholar]. In general, mechanisms conferring resistance are costly when expressed in the absence of insecticides. For example, biochemical resistance is associated with costs across both larval and adult stages [27.Tchouakui M. et al.Cytochrome P450 metabolic resistance (CYP6P9a) to pyrethroids imposes a fitness cost in the major African malaria vector Anopheles funestus.Heredity (Edinb). 2020; 124: 621-632Crossref PubMed Scopus (15) Google Scholar,88.Nkahe D.L. et al.Fitness cost of insecticide resistance on the life-traits of a Anopheles coluzzii population from the city of Yaoundé, Cameroon [version 2; peer review: 2 approved, 1 not approved].Wellcome Open Res. 2020; 5: 171Crossref PubMed Scopus (10) Google Scholar, 89.Assogba B.S. et al.The ace-1 locus is amplified in all resistant Anopheles gambiae mosquitoes: fitness consequences of homogeneous and heterogeneous duplications.PLoS Biol. 2016; 14e2000618Crossref PubMed Scopus (43) Google Scholar, 90.Otali D. et al.Increased production of mitochondrial reactive oxygen species and reduced adult life span in an insecticide-resistant strain of Anopheles gambiae.Bull. Entomol. Res. 2014; 104: 323-333Crossref PubMed Scopus (19) Google Scholar], including reduced fecundity and lifespan, differing across vector genotypes and resistance mechanisms [15.Alout H. et al.Interactive cost of Plasmodium infection and insecticide resistance in the malaria vector Anopheles gambiae.Sci. Rep. 2016; 629755Crossref PubMed Scopus (46) Google Scholar,16.Okoye P.N. et al.Relative developmental and reproductive fitness associated with pyrethroid resistance in the major southern African malaria vector, Anopheles funestus.Bull. Entomol. Res. 2007; 97: 599-605Crossref PubMed Scopus (40) Google Scholar]. Trade-offs may limit avoidance; changes to biting time-of-day affect reproductive schedule [39.O’Donnell A.J. et al.Time-of-day of blood-feeding: effects on mosquito life history and malaria transmission.Parasit. Vectors. 2019; 12: 301Crossref PubMed Scopus (16) Google Scholar] and may cause ‘jet lag’ between feeding rhythms and other circadian-regulated processes, such as detoxification and immune responses [38.Rund S.S.C. et al.Daily rhythms in mosquitoes and their consequences for malaria transmission.Insects. 2016; 7: 14Crossref PubMed Scopus (52) Google Scholar], increasing susceptibility to insecticides at certain times of day [91.Balmert N.J. et al.Time-of-day specific changes in metabolic detoxification and insecticide resistance in the malaria mosquito Anopheles gambiae.J. Insect Physiol. 2014; 64: 30-39Crossref PubMed Scopus (55) Google Scholar]. Furthermore, blood meals from non-preferred host species reduce mosquito fitness [36.Lyimo I.N. et al.The impact of host species and vector control measures on the fitness of African malaria vectors.Proc. R. Soc. B Biol. Sci. 2013; 280: 20122823Crossref PubMed Scopus (21) Google Scholar], due to differences in haematological properties [51.Emami S.N. et al.The transmission potential of malaria-infected mosquitoes (An.gambiae-Keele, An.arabiensis-Ifakara) is altered by the vertebrate blood type they consume during parasite development.Sci. Rep. 2017; 740520Crossref Scopus (15) Google Scholar]. Mechanisms of resistance Insecticide target-site mutations reduce insecticide toxicity by causing structural modifications to target proteins, and include knockdown resistance mutations (kdr) in the para sodium channel gene (pyrethroid/DDT resistance), an Rdl gene mutation (dieldrin resistance), and an acetylcholinesterase enzyme (ace-1) mutation (organophosphate and carbamate resistance) [15.Alout H. et al.Interactive cost of Plasmodium infection and insecticide resistance in the malaria vector Anopheles gambiae.Sci. Rep. 2016; 629755Crossref PubMed Scopus (46) Google Scholar]. Increased metabolism and clearance via overexpression of detoxification gene families, including cytochrome P450-associated monooxygenases (P450s), glutathione S-transferases (GSTs), and carboxylesterases, enhance insecticide detoxification [33.Ingham V.A. et al.Transcriptomic analysis reveals pronounced changes in gene expression due to sub-lethal pyrethroid exposure and ageing in insecticide resistance Anopheles coluzzii.BMC Genomics. 2021; 22: 337Crossref PubMed Scopus (6) Google Scholar]. Other mechanisms include reducing insecticide penetration via a thicker cuticle [75.Balabanidou V. et al.Cytochrome P450 associated with insecticide resistance catalyzes cuticular hydrocarbon production in Anopheles gambiae.Proc. Natl. Acad. Sci. U. S. A. 2016; 113: 9268-9273Crossref PubMed Scopus (206) Google Scholar], and sequestration by chemosensory proteins in the legs [76.Ingham V.A. et al.A sensory appendage protein protects malaria vectors from pyrethroids.Nature. 2020; 577: 376-380Crossref PubMed Scopus (87) Google Scholar]. Insecticide exposure Due to insecticide decay and insecticide resistance (IR) mechanisms, exposure to sublethal insecticide doses occur. In the short term, this stimulates changes to detoxification and redox metabolism gene expression [30.Ingham V.A. et al.Integration of whole genome sequencing and transcriptomics reveals a complex picture of the reestablishment of insecticide resistance in the major malaria vector Anopheles coluzzii.PLoS Genet. 2021; 17e1009970Crossref PubMed Scopus (8) Google Scholar,33.Ingham V.A. et al.Transcriptomic analysis reveals pronounced changes in gene expression due to sub-lethal pyrethroid exposure and ageing in insecticide resistance Anopheles coluzzii.BMC Genomics. 2021; 22: 337Crossref PubMed Scopus (6) Google Scholar], and reduces host-seeking and blood feeding [20.Thiévent K. et al.The interaction between permethrin exposure and malaria infection affects the host-seeking behaviour of mosquitoes.Malar. J. 2019; 18: 79Crossref PubMed Scopus (9) Google Scholar,77.Glunt K.D. et al.Empirical and theoretical investigation into the potential impacts of insecticide resistance on the effectiveness of insecticide-treated bed nets.Evol. Appl. 2018; 11: 431-441Crossref PubMed Scopus (30) Google Scholar]. Longer term effects include reduced survival of both IR and insecticide-susceptible (IS) mosquitoes [77.Glunt K.D. et al.Empirical and theoretical investigation into the potential impacts of insecticide resistance on the effectiveness of insecticide-treated bed nets.Evol. Appl. 2018; 11: 431-441Crossref PubMed Scopus (30) Google Scholar,78.Viana M. et al.Delayed mortality effects cut the malaria transmission potential of insecticide-resistant mosquitoes.Proc. Natl. Acad. Sci. U. S. A. 2016; 113: 8975-8980Crossref PubMed Scopus (67) Google Scholar], but lifespan is not affected in some highly resistant populations [79.Hughes A. et al.Anopheles gambiae populations from Burkina Faso show minimal delayed mortality after exposure to insecticide-treated nets.Parasit. Vectors. 2020; 13: 17Crossref PubMed Scopus (23) Google Scholar]. Furthermore, older mosquitoes are more susceptible to insecticides [80.Jones C.M. et al.Aging partially restores the efficacy of malaria vector control in insecticide-resistant populations of Anopheles gambiae s.l. from Burkina Faso.Malar. J. 2012; 11: 24Crossref PubMed Scopus (56) Google Scholar]. Methods for evasion Avoidance is an alternative to coping with insecticides and occurs by blood foraging less frequently or at times of day when hosts are not protected by bed nets [5.Carrasco D. et al.Behavioural adaptations of mosquito vectors to insecticide control.Curr. Opin. Insect Sci. 2019; 34: 48-54Crossref PubMed Scopus (54) Google Scholar], in the early evening [81.Thomsen E.K. et al.Mosquito behavior change after distribution of bednets results in decreased protection against malaria exposure.J. Infect. Dis. 2017; 215: 790-797PubMed Google Scholar], or early morning [82.Moiroux N. et al.Changes in Anopheles funestus biting behavior following universal coverage of long-lasting insecticidal nets in benin.J. Infect. Dis. 2012; 206: 1622-1629Crossref PubMed Scopus (218) Google Scholar]. ITNs target anthropophilic species that bite indoors at night, rather than less specialist feeders that bite at any time of day and/or outdoors. Thus, sustained ITN use is associated with increased outdoor biting [83.Russell T.L. et al.Increased proportions of outdoor feeding among residual malaria vector populations following increased use of insecticide-treated nets in rural Tanzania.Malar. J. 2011; 10: 80Crossref PubMed Scopus (429) Google Scholar] and resting [84.Kreppel K.S. et al.Emergence of behavioural avoidance strategies of malaria vectors in areas of high LLIN coverage in Tanzania.Sci. Rep. 2020; 1014527Crossref PubMed Scopus (27) Google Scholar], as well as seeking a higher proportion of blood meals from non-human vertebrate hosts [84.Kreppel K.S. et al.Emergence of behavioural avoidance strategies of malaria vectors in areas of high LLIN coverage in Tanzania.Sci. Rep. 2020; 1014527Crossref PubMed Scopus (27) Google Scholar,85.Ndenga B.A. et al.Malaria vectors and their blood-meal sources in an area of high bed net ownership in the western Kenya highlands.Malar. J. 2016; 15: 76Crossref PubMed Scopus (43) Google Scholar]. Further considerations Identifying the genetic basis and heritability of IR traits is challenging for complex behaviours such as a biting time-of-day, habitat choice, and host preference, but some behavioural resistance strategies are heritable [86.Govella N.J. et al.Heritability and phenotypic plasticity of biting time behaviors in the major African malaria vector Anopheles arabiensis.bioRxiv. 2021; (Published online May 17, 2021. https://doi.org/10.1101/2021.05.17.444456)Google Scholar,87.Main B.J. et al.The genetic basis of host preference and resting behavior in the major African malaria vector, Anopheles arabiensis.PLoS Genet. 2016; 12e1006303Crossref PubMed Scopus (55) Google Scholar]. In general, mechanisms conferring resistance are costly when expressed in the absence of insecticides. For example, biochemical resistance is associated with costs across both larval and adult stages [27.Tchouakui M. et al.Cytochrome P450 metabolic resistance (CYP6P9a) to pyrethroids imposes a fitness cost in the major African malaria vector Anopheles funestus.Heredity (Edinb). 2020; 124: 621-632Crossref PubMed Scopus (15) Google Scholar,88.Nkahe D.L. et al.Fitness cost of insecticide resistance on the life-traits of a Anopheles coluzzii population from the city of Yaoundé, Cameroon [version 2; peer review: 2 approved, 1 not approved].Wellcome Open Res. 2020; 5: 171Crossref PubMed Scopus (10) Google Scholar, 89.Assogba B.S. et al.The ace-1 locus is amplified in all resistant Anopheles gambiae mosquitoes: fitness consequences of homogeneous and heterogeneous duplications.PLoS Biol. 2016; 14e2000618Crossref PubMed Scopus (43) Google Scholar, 90.Otali D. et al.Increased production of mitochondrial reactive oxygen species and reduced adult life span in an insecticide-resistant strain of Anopheles gambiae.Bull. Entomol. Res. 2014; 104: 323-333Crossref PubMed Scopus (19) Google Scholar], including reduced fecundity and lifespan, differing across vector genotypes and resistance mechanisms [15.Alout H. et al.Interactive cost of Plasmodium infection and insecticide resistance in the malaria vector Anopheles gambiae.Sci. Rep. 2016; 629755Crossref PubMed Scopus (46) Google Scholar,16.Okoye P.N. et al.Relative developmental and reproductive fitness associated with pyrethroid resistance in the major southern African malaria vector, Anopheles funestus.Bull. Entomol. Res. 2007; 97: 599-605Crossref PubMed Scopus (40) Google Scholar]. Trade-offs may limit avoidance; changes to biting time-of-day affect reproductive schedule [39.O’Donnell A.J. et al.Time-of-day of blood-feeding: effects on mosquito life history and malaria transmission.Parasit. Vectors. 2019; 12: 301Crossref PubMed Scopus (16) Google Scholar] and may cause ‘jet lag’ between feeding rhythms and other circadian-regulated processes, such as detoxification and immune responses [38.Rund S.S.C. et al.Daily rhythms in mosquitoes and their consequences for malaria transmission.Insects. 2016; 7: 14Crossref PubMed Scopus (52) Google Scholar], increasing susceptibility to insecticides at certain times of day [91.Balmert N.J. et al.Time-of-day specific changes in metabolic detoxification and insecticide resistance in the malaria mosquito Anopheles gambiae.J. Insect Physiol. 2014; 64: 30-39Crossref PubMed Scopus (55) Google Scholar]. Furthermore, blood meals from non-preferred host species reduce mosquito fitness [36.Lyimo I.N. et al.The impact of host species and vector control measures on the fitness of African malaria vectors.Proc. R. Soc. B Biol. Sci. 2013; 280: 20122823Crossref PubMed Scopus (21) Google Scholar], due to differences in haematological properties [51.Emami S.N. et al.The transmission potential of malaria-infected mosquitoes (An.gambiae-Keele, An.arabiensis-Ifakara) is altered by the vertebrate blood type they consume during parasite development.Sci. Rep. 2017; 740520Crossref Scopus (15) Google Scholar]. Just like drugs or vaccines, VCTs are an ecological perturbation that decreases parasite fitness by reducing vectorial capacity (the rate at which a vector can transmit a pathogen from a currently infectious case; Box 2) [7.MacDonald G. Epidemiological basis of malaria control.Bull. World Health Organ. 1956; 15: 613-626PubMed Google Scholar]. History illustrates that attempts to reduce the survival and/or transmission of parasites/pathogens are readily met with counter-evolution. For example, malaria parasites have evolved resistance against all classes of antimalarial drugs [8.Hyde J.E. Drug-resistant malaria.Trends Parasitol. 2005; 21: 494-498Abstract Full Text Full Text PDF PubMed Scopus (148) Google Scholar], and can alter life history traits (see Glossary) to partially compensate for fitness lost due to drug treatment [9.Schneider P. et al.Adaptive plasticity in the gametocyte conversion rate of malaria parasites.PLoS Pathog. 2018; 14e1007371Crossref Scopus (34) Google Scholar]. Parasites transmitted via vectors targeted by VCTs face diverse perturbations to their ecology (reviewed in [10.Rivero A. et al.Insecticide control of vector-borne diseases: when is insecticide resistance a problem?.PLoS Pathog. 2010; 6e1001000Crossref PubMed Scopus (250) Google Scholar]). In the short term, at the start of a control programme, parasites experience a dramatic drop in the health, abundance, and lifespan of vectors, and in the longer term, parasites encounter vectors that have altered genotypes and phenotypes, as well as alternative vector species.Box 2R0, vectorial capacity and transmission dynamicsR0, also known as the Ross-MacDonald equation, describes the expected number of infected hosts generated from a single infected host in a completely susceptible population. It is defined using the equation [92.Smith D.L. et al.Ross, Macdonald, and a theory for the dynamics and control of mosquito-transmitted pathogens.PLoS Pathog. 2012; 8e1002588Crossref Scopus (332) Google Scholar]:R0=ma2bc−lnprpv[I] The equation for vectorial capacity derives from the above. It excludes r, the daily rate that each human recovers from infection because it contains the purely entomological concepts of R0 [92.Smith D.L. et al.Ross, Macdonald, and a theory for the dynamics and control of mosquito-transmitted pathogens.PLoS Pathog. 2012; 8e1002588Crossref Scopus (332) Google Scholar]:V=ma2bc−lnppv[II] Density of vectors per vertebrate hosts (m). Transmission is positively correlated to the number of vectors per host and is shaped by the reproductive output of vector species and how this interacts with environmental factors.Human-biting rate (a). The rate that humans are bitten varies across vector species due to species specificity in host preference and whether preference depends on the availability of different kinds of host [93.Takken W. Verhulst N.O. Host preferences of blood-feeding mosquitoes.Annu. Rev. Entomol. 2013; 58: 433-453Crossref PubMed Scopus (371) Google Scholar].Vector competence (bc). The proportion of bites by an infectious mosquito that infect a human (b) and the probability that a mosquito becomes infected after biting an infected human (c) make up vector competence [94.Cator L.J. et al.The role of vector trait variation in vector-borne disease dynamics.Front. Ecol. Evol. 2020; 8: 189Crossref PubMed Scopus (27) Google Scholar]. The ability of a parasite to survive within the vector during development into the form which is infective to a new human host reflects the combined effects of parasite infectivity to vectors and vector susceptibility [95.Lefèvre T. et al.Non-genetic determinants of mosquito competence for malaria parasites.PLoS Pathog. 2013; 9e1003365Crossref PubMed Scopus (85) Google Scholar].Duration of parasite extrinsic incubation period (EIP) (v). The time it takes for the parasite to develop from the point of ingestion to the form infective to a new human host is shaped by parasite intrinsic factors [96.Ohm J.R. et al.Rethinking the extrinsic incubation period of malaria parasites.Parasit. Vectors. 2018; 11: 178Crossref PubMed Scopus (56) Google Scholar] as well as environmental temperature [97.Shapiro L.L.M. et al.Quantifying the effects of temperature on mosquito and parasite traits that determine the transmission potential of human malaria.PLoS Biol. 2017; 15e2003489Crossref PubMed Scopus (117) Google Scholar] and resource availability within the vector [64.Shaw W.R. et al.Plasmodium development in Anopheles: a tale of shared resources.Trends Parasitol. 2022; 38: 124-135Abstract Full Text Full Text PDF PubMed Scopus (10) Google Scholar]. Because v and p interact exponentially, small changes in EIP can dramatically affect vectorial capacity.Daily probability of adult survival (p). The EIP lasts for a long proportion of vector lifespan, and transmission requires that the vector survives throughout this period.All vectorial capacity parameters (even including m) are a product of how parasites and vectors interact and are subject to alteration by VCTs. Based on observations in the literature, Table I illustrates potential impacts of the consequences of VCTs on these parameters. Increases are denoted by ‘+’, reductions are denoted by ‘–’, and scenarios that are yet to be investigated or for where specific details matter and general principles are unlikely are indicated by ‘?’. Particularly noteworthy is that the effects of VCTs on parasite contributions to vectorial capacity are largely unknown.Table IThe consequences of VCT use and their potential effect on" @default.
• W4291916500 created "2022-08-16" @default.
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• W4291916500 date "2022-10-01" @default.
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• W4291916500 title "Vector control: agents of selection on malaria parasites?" @default.
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