Activity of Ivermectin and Its Metabolites against Asexual Blood Stage Plasmodium falciparum and Its Interactions with Antimalarial Drugs.

Ivermectin is an endectocide used widely to treat a variety of internal and external parasites. Field trials of ivermectin mass drug administration for malaria transmission control have demonstrated a reduction of Anopheles mosquito survival and human malaria incidence. Ivermectin will mostly be deployed together with artemisinin-based combination therapies (ACT), the first-line treatment of falciparum malaria. It has not been well established if ivermectin has activity against asexual stage Plasmodium falciparum or if it interacts with the parasiticidal activity of other antimalarial drugs. This study evaluated antimalarial activity of ivermectin and its metabolites in artemisinin-sensitive and artemisinin-resistant P. falciparum isolates and assessed in vitro drug-drug interaction with artemisinins and its partner drugs. The concentration of ivermectin causing half of the maximum inhibitory activity (IC50) on parasite survival was 0.81 µM with no significant difference between artemisinin-sensitive and artemisinin-resistant isolates (P = 0.574). The ivermectin metabolites were 2-fold to 4-fold less active than the ivermectin parent compound (P < 0.001). Potential pharmacodynamic drug-drug interactions of ivermectin with artemisinins, ACT-partner drugs, and atovaquone were studied in vitro using mixture assays providing isobolograms and derived fractional inhibitory concentrations. There were no synergistic or antagonistic pharmacodynamic interactions when combining ivermectin and antimalarial drugs. In conclusion, ivermectin does not have clinically relevant activity against the asexual blood stages of P. falciparum. It also does not affect the in vitro antimalarial activity of artemisinins or ACT-partner drugs against asexual blood stages of P. falciparum.

Ivermectin metabolites reduce Anopheles survival.

Ivermectin mass drug administration to humans or livestock is a potential vector control tool for malaria elimination. The mosquito-lethal effect of ivermectin in clinical trials exceeds that predicted from in vitro laboratory experiments, suggesting that ivermectin metabolites have mosquito-lethal effect. The three primary ivermectin metabolites in humans (i.e., M1 (3″-O-demethyl ivermectin), M3 (4-hydroxymethyl ivermectin), and M6 (3″-O-demethyl, 4-hydroxymethyl ivermectin) were obtained by chemical synthesis or bacterial modification/metabolism. Ivermectin and its metabolites were mixed in human blood at various concentrations, blood-fed to Anopheles dirus and Anopheles minimus mosquitoes, and mortality was observed daily for fourteen days. Ivermectin and metabolite concentrations were quantified by liquid chromatography linked with tandem mass spectrometry to confirm the concentrations in the blood matrix. Results revealed that neither the LC50 nor LC90 values differed between ivermectin and its major metabolites for An. dirus or An. minimus., Additionally, there was no substantial differences in the time to median mosquito mortality when comparing ivermectin and its metabolites, demonstrating an equal rate of mosquito killing between the compounds evaluated. These results demonstrate that ivermectin metabolites have a mosquito-lethal effect equal to the parent compound, contributing to Anopheles mortality after treatment of humans.

Correction: A systematic review and an individual patient data meta-analysis of ivermectin use in children weighing less than fifteen kilograms: Is it time to reconsider the current contraindication?

[This corrects the article DOI: 10.1371/journal.pntd.0009144.].

National survey in Switzerland calls for improved diagnosis and treatment in children with scabies.

AIM OF THE STUDY: The global prevalence of scabies is estimated to be up to 200 million cases annually, with young children particularly affected. In Europe, most cases are thought to originate in migrant populations. Scabies management is challenging in children. To identify knowledge gaps and research needs, we aimed to descriptively evaluate the management of children with scabies by different Swiss healthcare providers. METHODS: An invitation for an anonymous online survey (36 questions) was sent to members of Swiss societies of dermatologists, general practitioners, paediatricians, paediatric dermatologists, paediatric infectious diseases specialists, and tropical medicine specialists, inviting clinicians to participate from 25th May to 8th August 2020. One reminder invitation was sent. Hospital pharmacies and the distributor of permethrin were contacted to report consumption trends of scabicides in 2018 and 2019. RESULTS: The survey was completed by 248 clinicians: 146 (59%) paediatricians, 47 (19%) dermatologists, 28 (11%) general practitioners, 6 (2%) paediatric dermatologists, 13 (5%) paediatric infectious diseases specialists, and 8 (3%) tropical medicine specialists. Most consulted up to 10 scabies cases within a 16-month period, with similar numbers in migrant and Swiss children. Dermoscopy was used by 24% of non-dermatologists. Non-dermatologists did not consider co-treatment of close contacts in up to 59% of cases. While permethrin was the first-line treatment, treatment failures were frequently reported in children aged <5 years. Up to 67% of paediatric dermatologists regularly used oral ivermectin off-label in children weighing <15 kg. None of the paediatric dermatologists, 15% of the dermatologists, and 9% of the non-dermatologists used only one treatment cycle.Scabicide consumption increased. Treatment studies on ivermectin use in children weighing <15 kg had the highest research priority. CONCLUSION: In Switzerland, scabies is a frequent dermatosis in migrant and Swiss children. While accessible, optimal diagnostics are underutilised, and treatment is suboptimal. Permethrin resistance appears to be an increasing problem. Dermatologists regularly use ivermectin off-label in children weighing <15 kg. Treatment studies on ivermectin use in children weighing <15 kg, user-friendly diagnostic tools, new treatment protocols, and child-friendly dosage forms are needed to improve the diagnosis and treatment of children with scabies.

Anopheles bionomics in a malaria endemic area of southern Thailand.

BACKGROUND: Ivermectin mass drug administration (MDA) could accelerate malaria elimination in the Greater Mekong Subregion. This study was performed to characterize the bionomics of Anopheles in Surat Thani province, Thailand. METHODS: Mosquitoes were collected via human landing collections between February and October 2019. Anopheles mosquitoes were morphologically identified to species. Primary Anopheles malaria vectors were dissected to assess parity status, and a subset were evaluated for molecular identification and Plasmodium detection. RESULTS: A total of 17,348 mosquitoes were collected during the study period; of these, 5777 were Anopheles mosquitoes. Morphological studies identified 15 Anopheles species, of which the most abundant were Anopheles minimus (s.l.) (87.16%, n = 5035), An. dirus s.l. (7.05%, n = 407) and An. barbirostris s.l. (2.86%, n = 165). Molecular identification confirmed that of the An. minimus s.l. mosquitoes collected, 99.80% were An. minimus (s.s.) (n = 484) and 0.2% were An. aconitus (n = 1), of the An. dirus (s.l.) collected, 100% were An. baimaii (n = 348), and of the An. maculatus (s.l.) collected, 93.62% were An. maculatus (s.s.) (n = 44) and 6.38% were An. sawadwongporni (n = 3). No Anopheles mosquito tested was Plasmodium positive (0/879). An average of 11.46 Anopheles were captured per collector per night. There were differences between species in hour of collection (Kruskal-Wallis H-test: χ2 = 80.89, P < 0.0001, n = 5666), with more An. barbirostris (s.l.) and An. maculatus (s.l.) caught earlier compared to An. minimus (s.l.) (P = 0.0001 and P < 0.0001, respectively) and An. dirus (s.l.) (P = 0.0082 and P < 0.001, respectively). The proportion of parous An. minimus (s.l.) captured by hour increased throughout the night (Wald Chi-square: χ2 = 17.31, P = 0.000, odds ratio = 1.0535, 95% confidence interval 1.0279-1.0796, n = 3400). Overall, An. minimus (s.l.) parity was 67.68% (2375/3509) with an intra-cluster correlation of 0.0378. A power calculation determined that an An. minimus (s.l.) parity reduction treatment effect size = 34%, with four clusters per treatment arm and a minimum of 300 mosquitoes dissected per cluster, at an α = 0.05, will provide 82% power to detect a significant difference following ivermectin MDA. CONCLUSIONS: The study area in Surat Thani province is an ideal location to evaluate the impact of ivermectin MDA on An. minimus parity.

A systematic review and an individual patient data meta-analysis of ivermectin use in children weighing less than fifteen kilograms: Is it time to reconsider the current contraindication?

BACKGROUND: Oral ivermectin is a safe broad spectrum anthelminthic used for treating several neglected tropical diseases (NTDs). Currently, ivermectin use is contraindicated in children weighing less than 15 kg, restricting access to this drug for the treatment of NTDs. Here we provide an updated systematic review of the literature and we conducted an individual-level patient data (IPD) meta-analysis describing the safety of ivermectin in children weighing less than 15 kg. METHODOLOGY/PRINCIPAL FINDINGS: A systematic review was conducted using the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) for IPD guidelines by searching MEDLINE via PubMed, Web of Science, Ovid Embase, LILACS, Cochrane Database of Systematic Reviews, TOXLINE for all clinical trials, case series, case reports, and database entries for reports on the use of ivermectin in children weighing less than 15 kg that were published between 1 January 1980 to 25 October 2019. The protocol was registered in the International Prospective Register of Systematic Reviews (PROSPERO): CRD42017056515. A total of 3,730 publications were identified, 97 were selected for potential inclusion, but only 17 sources describing 15 studies met the minimum criteria which consisted of known weights of children less than 15 kg linked to possible adverse events, and provided comprehensive IPD. A total of 1,088 children weighing less than 15 kg were administered oral ivermectin for one of the following indications: scabies, mass drug administration for scabies control, crusted scabies, cutaneous larva migrans, myiasis, pthiriasis, strongyloidiasis, trichuriasis, and parasitic disease of unknown origin. Overall a total of 1.4% (15/1,088) of children experienced 18 adverse events all of which were mild and self-limiting. No serious adverse events were reported. CONCLUSIONS/SIGNIFICANCE: Existing limited data suggest that oral ivermectin in children weighing less than 15 kilograms is safe. Data from well-designed clinical trials are needed to provide further assurance.

Identification of the metabolites of ivermectin in humans.

Mass drug administration of ivermectin has been proposed as a possible malaria elimination tool. Ivermectin exhibits a mosquito-lethal effect well beyond its biological half-life, suggesting the presence of active slowly eliminated metabolites. Human liver microsomes, primary human hepatocytes, and whole blood from healthy volunteers given oral ivermectin were used to identify ivermectin metabolites by ultra-high performance liquid chromatography coupled with high-resolution mass spectrometry. The molecular structures of metabolites were determined by mass spectrometry and verified by nuclear magnetic resonance. Pure cytochrome P450 enzyme isoforms were used to elucidate the metabolic pathways. Thirteen different metabolites (M1-M13) were identified after incubation of ivermectin with human liver microsomes. Three (M1, M3, and M6) were the major metabolites found in microsomes, hepatocytes, and blood from volunteers after oral ivermectin administration. The chemical structure, defined by LC-MS/MS and NMR, indicated that M1 is 3″-O-demethyl ivermectin, M3 is 4-hydroxymethyl ivermectin, and M6 is 3″-O-demethyl, 4-hydroxymethyl ivermectin. Metabolic pathway evaluations with characterized cytochrome P450 enzymes showed that M1, M3, and M6 were produced primarily by CYP3A4, and that M1 was also produced to a small extent by CYP3A5. Demethylated (M1) and hydroxylated (M3) ivermectin were the main human in vivo metabolites. Further studies are needed to characterize the pharmacokinetic properties and mosquito-lethal activity of these metabolites.

Safety, Pharmacokinetics, and Activity of High-Dose Ivermectin and Chloroquine against the Liver Stage of Plasmodium cynomolgi Infection in Rhesus Macaques.

Previously, ivermectin (1 to 10 mg/kg of body weight) was shown to inhibit the liver-stage development of Plasmodium berghei in orally dosed mice. Here, ivermectin showed inhibition of the in vitro development of Plasmodium cynomolgi schizonts (50% inhibitory concentration [IC50], 10.42 µM) and hypnozoites (IC50, 29.24 µM) in primary macaque hepatocytes when administered as a high dose prophylactically but not when administered in radical cure mode. The safety, pharmacokinetics, and efficacy of oral ivermectin (0.3, 0.6, and 1.2 mg/kg) with and without chloroquine (10 mg/kg) administered for 7 consecutive days were evaluated for prophylaxis or radical cure of P. cynomolgi liver stages in rhesus macaques. No inhibition or delay to blood-stage P. cynomolgi parasitemia was observed at any ivermectin dose (0.3, 0.6, and 1.2 mg/kg). Ivermectin (0.6 and 1.2 mg/kg) and chloroquine (10 mg/kg) in combination were well-tolerated with no adverse events and no significant pharmacokinetic drug-drug interactions observed. Repeated daily ivermectin administration for 7 days did not inhibit ivermectin bioavailability. It was recently demonstrated that both ivermectin and chloroquine inhibit replication of the novel severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in vitro Further ivermectin and chloroquine trials in humans are warranted to evaluate their role in Plasmodium vivax control and as adjunctive therapies against COVID-19 infections.

A Roadmap for the Development of Ivermectin as a Complementary Malaria Vector Control Tool.

In the context of stalling progress against malaria, resistance of mosquitoes to insecticides, and residual transmission, mass drug administration (MDA) of ivermectin, an endectocide used for neglected tropical diseases (NTDs), has emerged as a promising complementary vector control method. Ivermectin reduces the life span of Anopheles mosquitoes that feed on treated humans and/or livestock, potentially decreasing malaria parasite transmission when administered at the community level. Following the publication by WHO of the preferred product characteristics for endectocides as vector control tools, this roadmap provides a comprehensive view of processes needed to make ivermectin available as a vector control tool by 2024 with a completely novel mechanism of action. The roadmap covers various aspects, which include 1) the definition of optimal dosage/regimens for ivermectin MDA in both humans and livestock, 2) the risk of resistance to the drug and environmental impact, 3) ethical issues, 4) political and community engagement, 5) translation of evidence into policy, and 6) operational aspects of large-scale deployment of the drug, all in the context of a drug given as a prevention tool acting at the community level. The roadmap reflects the insights of a multidisciplinary group of global health experts who worked together to elucidate the path to inclusion of ivermectin in the toolbox against malaria, to address residual transmission, counteract insecticide resistance, and contribute to the end of this deadly disease.

Ivermectin as a novel complementary malaria control tool to reduce incidence and prevalence: a modelling study.

BACKGROUND: Ivermectin is a potential new vector control tool to reduce malaria transmission. Mosquitoes feeding on a bloodmeal containing ivermectin have a reduced lifespan, meaning they are less likely to live long enough to complete sporogony and become infectious. We aimed to estimate the effect of ivermectin on malaria transmission in various scenarios of use. METHODS: We validated an existing population-level mathematical model of the effect of ivermectin mass drug administration (MDA) on the mosquito population and malaria transmission against two datasets: clinical data from a cluster- randomised trial done in Burkina Faso in 2015 wherein ivermectin was given to individuals taller than 90 cm and entomological data from a study of mosquito outcomes after ivermectin MDA for onchocerciasis or lymphatic filariasis in Burkina Faso, Senegal, and Liberia between 2008 and 2013. We extended the existing model to include a range of complementary malaria interventions (seasonal malaria chemoprevention and MDA with dihydroartemisinin-piperaquine) and to incorporate new data on higher doses of ivermectin with a longer mosquitocidal effect. We consider two ivermectin regimens: a single dose of 400 µg/kg (1 × 400 µg/kg) and three consecutive daily doses of 300 µg/kg per day (3 × 300 µg/kg). We simulated the effect of these two doses in a range of usage scenarios in different transmission settings (highly seasonal, seasonal, and perennial). We report percentage reductions in clinical incidence and slide prevalence. FINDINGS: We estimate that MDA with ivermectin will reduce prevalence and incidence and is most effective in areas with highly seasonal transmission. In a highly seasonal moderate transmission setting, three rounds of ivermectin only MDA at 3 × 300 µg/kg (rounds spaced 1 month apart) and 70% coverage is predicted to reduce clinical incidence by 71% and prevalence by 34%. We predict that adding ivermectin MDA to seasonal malaria chemoprevention in this setting would reduce clinical incidence by an additional 77% in children younger than 5 years compared with seasonal malaria chemoprevention alone; adding ivermectin MDA to MDA with dihydroartemisinin-piperaquine in this setting would reduce incidence by an additional 75% and prevalence by an additional 64% (all ages) compared with MDA with dihydroartemisinin-piperaquine alone. INTERPRETATION: Our modelling predictions suggest that ivermectin could be a valuable addition to the malaria control toolbox, both in areas with persistently high transmission where existing interventions are insufficient and in areas approaching elimination to prevent resurgence. FUNDING: Imperial College Junior Research Fellowship.

Safety, Pharmacokinetics, and Mosquito-Lethal Effects of Ivermectin in Combination With Dihydroartemisinin-Piperaquine and Primaquine in Healthy Adult Thai Subjects.

Mass administration of antimalarial drugs and ivermectin are being considered as potential accelerators of malaria elimination. The safety, tolerability, pharmacokinetics, and mosquito-lethal effects of combinations of ivermectin, dihydroartemisinin-piperaquine, and primaquine were evaluated. Coadministration of ivermectin and dihydroartemisinin-piperaquine resulted in increased ivermectin concentrations with corresponding increases in mosquito-lethal effect across all subjects. Exposure to piperaquine was also increased when coadministered with ivermectin, but electrocardiograph QT-interval prolongation was not increased. One subject had transiently impaired liver function. Ivermectin mosquito-lethal effect was greater than predicted previously against the major Southeast Asian malaria vectors. Both Anopheles dirus and Anopheles minimus mosquito mortality was increased substantially (20-fold and 35-fold increase, respectively) when feeding on volunteer blood after ivermectin administration compared with in vitro ivermectin-spiked blood. This suggests the presence of ivermectin metabolites that impart mosquito-lethal effects. Further studies of this combined approach to accelerate malaria elimination are warranted.

Safety of oral ivermectin during pregnancy: a systematic review and meta-analysis.

BACKGROUND: About 3·7 billion doses of ivermectin have been distributed in mass drug administration (MDA) campaigns globally over the past 30 years. At 10-100 times higher than current human doses, ivermectin is a known teratogen in mammals. During these campaigns with recommended doses, pregnant women might be inadvertently exposed. We therefore aimed to evaluate the existing evidence for serious and non-serious adverse events after ivermectin exposure in pregnant women. METHODS: For this systematic review and meta-analysis, we searched relevant databases and trial registry platforms on July 15, 2018, for randomised controlled trials (RCTs) and observational studies that reported adverse events in pregnant women. We did not use language or date restrictions. Outcomes of interest were spontaneous abortions, stillbirths, congenital anomalies, and neonatal death (serious adverse events), as well as maternal morbidity, preterm births, and low birthweight (adverse events). The risk of bias was assessed using the Newcastle-Ottawa Scale for observational studies and the Cochrane Risk of Bias Tool for RCTs. We did the meta-analysis of observational studies and RCTs separately. The quality of evidence was assessed using the GRADE approach. The study protocol is registered with PROSPERO, protocol CRD42016046914. FINDINGS: We identified 147 records, of which only five observational studies and one RCT were included for quantitative analysis; these studies were published between 1990 and 2008, and were done in six African countries. 893 women with 899 pregancy outcomes were included, of whom 496 pregnant women (500 pregnancy outcomes) received ivermectin inadvertently during MDA campaigns in the observational studies and 397 pregnant women (399 pregnancy outcomes) purposely received ivermectin as part of the open-label RCT. No study reported neonatal deaths, maternal morbidity, preterm births, or low birthweight. It is unclear whether exposure to ivermectin during pregnancy increases the risk of spontaneous abortions and stillbirths (odds ratio [OR] 1·15 [95% CI 0·75-1·78] with very low certainty of evidence for the four observational studies and 0·62 [0·18-2·14] with very low certainty of evidence for the RCT) or congenital anomalies (OR 1·69 [95% CI 0·83-3·41] with very low certainty of evidence for the five observational studies and 1·10 [0·07-17·65] with very low certainty of evidence for the RCT). INTERPRETATION: There is insufficient evidence to conclude on the safety profile of ivermectin during pregnancy. Treatment campaigns should focus additional efforts on preventing inadvertent treatment of pregnant women. FUNDING: Unitaid.

Promising approach to reducing Malaria transmission by ivermectin: Sporontocidal effect against Plasmodium vivax in the South American vectors Anopheles aquasalis and Anopheles darlingi.

BACKGROUND: The mosquito resistance to the insecticides threatens malaria control efforts, potentially becoming a major public health issue. Alternative methods like ivermectin (IVM) administration to humans has been suggested as a possible vector control to reduce Plasmodium transmission. Anopheles aquasalis and Anopheles darlingi are competent vectors for Plasmodium vivax, and they have been responsible for various malaria outbreaks in the coast of Brazil and the Amazon Region of South America. METHODS: To determine the IVM susceptibility against P. vivax in An. aquasalis and An. darlingi, ivermectin were mixed in P. vivax infected blood: (1) Powdered IVM at four concentrations (0, 5, 10, 20 or 40 ng/mL). (2) Plasma (0 hours, 4 hours, 1 day, 5, 10 and 14 days) was collected from healthy volunteers after to administer a single oral dose of IVM (200 µg/kg) (3) Mosquitoes infected with P. vivax and after 4 days was provided with IVM plasma collected 4 hours post-treatment (4) P. vivax-infected patients were treated with various combinations of IVM, chloroquine, and primaquine and plasma or whole blood was collected at 4 hours. Seven days after the infective blood meal, mosquitoes were dissected to evaluate oocyst presence. Additionally, the ex vivo effects of IVM against asexual blood-stage P. vivax was evaluated. RESULTS: IVM significantly reduced the prevalence of An. aquasalis that developed oocysts in 10 to 40 ng/mL pIVM concentrations and plasma 4 hours, 1 day and 5 days. In An. darlingi to 4 hours and 1 day. The An. aquasalis mortality was expressively increased in pIVM (40ng/mL) and plasma 4 hours, 1, 5 10 and 14 days post-intake drug and in An. darlingi only to 4 hours and 1 day. The double fed meal with mIVM by the mosquitoes has a considerable impact on the proportion of infected mosquitoes for 7 days post-feeding. The oocyst infection prevalence and intensity were notably reduced when mosquitoes ingested blood from P. vivax patients that ingested IVM+CQ, PQ+CQ and IVM+PQ+CQ. P. vivax asexual development was considerably inhibited by mIVM at four-fold dilutions. CONCLUSION: In conclusion, whole blood spiked with IVM reduced the infection rate of P. vivax in An. aquasalis and An. darlingi, and increased the mortality of mosquitoes. Plasma from healthy volunteers after IVM administration affect asexual P. vivax development. These findings support that ivermectin may be used to decrease P. vivax transmission.

What does not kill it makes it weaker: effects of sub-lethal concentrations of ivermectin on the locomotor activity of Anopheles aquasalis.

BACKGROUND: Malaria remains a major public health concern. Vector control measures based solely on insecticide treated nets (ITNs) and indoor residual spraying (IRS) have demonstrated not to be feasible for malaria elimination. It has been shown that ivermectin affects several aspects of Anopheles species biology. Along the Latin American seacoast, Anopheles aquasalis Curry plays an important role in malaria transmission. The observation of mosquitoes locomotor activity under laboratory conditions can reveal details of their daily activity rhythms, which is controlled by an endogenous circadian clock that seems to be influenced by external signals, such as light and temperature. In this study, we assessed basal locomotor activity and the effects of ivermectin on locomotor activity of the American malaria vector, An. aquasalis. METHODS: Adult females of Anopheles aquasalis used in experiments were three to five days post-emergence. Blood from one single subject was used to provide mosquito meals by membrane feeding assays. Powdered ivermectin compound was used to achieve different concentrations of drug as previously described. Fully engorged mosquitoes were individually placed into glass tubes and provided with 10% sucrose. Each tube was placed into a Locomotor Activity Monitor (LAM). The LAMs were kept inside an incubator under a constant temperature and a 12:12 h light:dark cycle. The average locomotor activity was calculated as the mean number of movements performed per mosquito in the period considered. Intervals of time assessed were adapted from a previous study. One-way ANOVA tests were performed in order to compare means between groups. Additionally, Dunnett's method was used for post-hoc pairwise means comparisons between each group and control. Stata software version 13 was used for the analysis. RESULTS: Anopheles aquasalis showed a nocturnal and bimodal pattern for mosquitoes fed both control blood meals and sub-lethal concentrations of ivermectin. In this species, activity peaks occurred at the beginning of the photophase and scotophase in the control group. The nocturnal activity is evident and higher just after the evening peak and maintains basal levels of locomotion throughout the scotophase. In the entire group analysis, locomotor activity means of experimental sets were significantly lower than control for each period of time evaluated. In the survival group, the locomotor activity means of all treatment sets were lower than control mosquitoes for all intervals of time when both the whole period and scotophase were assessed. When the middle of scotophase was evaluated, means were significantly lower for LC15 and LC25, but not LC5. For the beginning of photophase period, significant differences were detected only between control and LC5. When both the photophase and scotophase were assessed alone, no significant differences were found. Mean locomotor activity was significantly lower for dead group when compared to survival group for all experimental sets when whole period, photophase, and scotophase were assessed. CONCLUSIONS: Ivermectin seems to decrease locomotor activity of An. aquasalis at sub-lethal concentrations. The effects on locomotor activity increase according at higher ivermectin concentrations and are most evident during the whole scotophase as well as in the beginning and in the end of this phase, and sub-lethal effects may still be observed in the photophase. Findings presented in this study demonstrate that sub-lethal ivermectin effects reduce mosquito locomotor activity, which could diminish vectorial capacity and therefore the malaria transmission.

Ivermectin susceptibility, sporontocidal effect, and inhibition of time to re-feed in the Amazonian malaria vector Anopheles darlingi.

BACKGROUND: Outdoor malaria transmission hinders malaria elimination efforts in the Amazon region and novel vector control tools are needed. Ivermectin mass drug administration (MDA) to humans kills wild Anopheles, targets outdoor-feeding vectors, and can suppress malaria parasite transmission. Laboratory investigations were performed to determine ivermectin susceptibility, sporontocidal effect and inhibition of time to re-feed for the primary Amazonian malaria vector, Anopheles darlingi. METHODS: To assess ivermectin susceptibility, various concentrations of ivermectin were mixed in human blood and fed to An. darlingi. Mosquito survival was monitored daily for 7 days and a non-linear mixed effects model with Probit analysis was used to calculate lethal concentrations of ivermectin that killed 50% (LC50), 25% (LC25) and 5% (LC5) of mosquitoes. To examine ivermectin sporonticidal effect, Plasmodium vivax blood samples were collected from malaria patients and offered to mosquitoes without or with ivermectin at the LC50, LC25 or LC5. To assess ivermectin inhibition of mosquito time to re-feed, concentrations of ivermectin predicted to occur after a single oral dose of 200 µg/kg ivermectin were fed to An. darlingi. Every day for 12 days thereafter, individual mosquitoes were given the opportunity to re-feed on a volunteer. Any mosquitoes that re-blood fed or died were removed from the study. RESULTS: Ivermectin significantly reduced An. darlingi survivorship: 7-day-LC50 = 43.2 ng/ml [37.5, 48.6], -LC25 = 27.8 ng/ml [20.4, 32.9] and -LC5 = 14.8 ng/ml [7.9, 20.2]. Ivermectin compound was sporontocidal to P. vivax in An. darlingi at the LC50 and LC25 concentrations reducing prevalence by 22.6 and 17.1%, respectively, but not at the LC5. Oocyst intensity was not altered at any concentration. Ivermectin significantly delayed time to re-feed at the 4-h (48.7 ng/ml) and 12-h (26.9 ng/ml) concentrations but not 36-h (10.6 ng/ml) or 60-h (6.3 ng/ml). CONCLUSIONS: Ivermectin is lethal to An. darlingi, modestly inhibits sporogony of P. vivax, and delays time to re-feed at concentrations found in humans up to 12 h post drug ingestion. The LC50 value suggests that a higher than standard dose (400-µg/kg) is necessary to target An. darlingi. These results suggest that ivermectin MDA has potential in the Amazon region to aid malaria elimination efforts.

Ivermectin susceptibility and sporontocidal effect in Greater Mekong Subregion Anopheles.

BACKGROUND: Novel vector control methods that can directly target outdoor malaria transmission are urgently needed in the Greater Mekong Subregion (GMS) to accelerate malaria elimination and artemisinin resistance containment efforts. Ivermectin mass drug administration (MDA) to humans has been shown to effectively kill wild Anopheles and suppress malaria transmission in West Africa. Preliminary laboratory investigations were performed to determine ivermectin susceptibility and sporontocidal effect in GMS Anopheles malaria vectors coupled with pharmacokinetic models of ivermectin at escalating doses. METHODS: A population-based pharmacokinetic model of ivermectin was developed using pre-existing data from a clinical trial conducted in Thai volunteers at the 200 µg/kg dose. To assess ivermectin susceptibility, various concentrations of ivermectin compound were mixed in human blood meals and blood-fed to Anopheles dirus, Anopheles minimus, Anopheles sawadwongporni, and Anopheles campestris. Mosquito survival was monitored daily for 7 days and a non-linear mixed effects model with probit analyses was used to calculate concentrations of ivermectin that killed 50% (LC50) of mosquitoes for each species. Blood samples were collected from Plasmodium vivax positive patients and offered to mosquitoes with or without ivermectin at the ivermectin LC25 or LC5 for An. dirus and An. minimus. RESULTS: The GMS Anopheles displayed a range of susceptibility to ivermectin with species listed from most to least susceptible being An. minimus (LC50 = 16.3 ng/ml) > An. campestris (LC50 = 26.4 ng/ml) = An. sawadwongporni (LC50 = 26.9 ng/ml) > An. dirus (LC50 = 55.6 ng/ml). Mosquito survivorship results, the pharmacokinetic model, and extensive safety data indicated that ivermectin 400 µg/kg is the ideal minimal dose for MDA in the GMS for malaria parasite transmission control. Ivermectin compound was sporontocidal to P. vivax in both An. dirus and An. minimus at the LC25 and LC5 concentrations. CONCLUSIONS: Ivermectin is lethal to dominant GMS Anopheles malaria vectors and inhibits sporogony of P. vivax at safe human relevant concentrations. The data suggest that ivermectin MDA has potential in the GMS as a vector and transmission blocking control tool to aid malaria elimination efforts.

Filling gaps on ivermectin knowledge: effects on the survival and reproduction of Anopheles aquasalis, a Latin American malaria vector.

BACKGROUND: Strategies designed to advance towards malaria elimination rely on the detection and treatment of infections, rather than fever, and the interruption of malaria transmission between mosquitoes and humans. Mass drug administration with anti-malarials directed at eliminating parasites in blood, either to entire populations or targeting only those with malaria infections, are considered useful strategies to progress towards malaria elimination, but may be insufficient if applied on their own. These strategies assume a closer contact with populations, so incorporating a vector control intervention tool to those approaches could significantly enhance their efficacy. Ivermectin, an endectocide drug efficacious against a range of Anopheles species, could be added to other drug-based interventions. Interestingly, ivermectin could also be useful to target outdoor feeding and resting vectors, something not possible with current vector control tools, such as impregnated bed nets or indoor residual spraying (IRS). RESULTS: Anopheles aquasalis susceptibility to ivermectin was assessed. In vivo assessments were performed in six volunteers, being three men and three women. The effect of ivermectin on reproductive fitness and mosquito survivorship using membrane feeding assay (MFA) and direct feeding assay (DFA) was assessed and compared. The ivermectin lethal concentration (LC) values were LC50 = 47.03 ng/ml [44.68-49.40], LC25 = 31.92 ng/ml [28.60-34.57] and LC5 = 18.28 ng/ml [14.51-21.45]. Ivermectin significantly reduced the survivorship of An. aquasalis blood-fed 4 h post-ingestion (X 2 [N = 880] = 328.16, p < 0.001), 2 days post-ingestion (DPI 2) (X 2 [N = 983] = 156.75, p < 0.001), DPI 7 (X 2 [N = 935] = 31.17, p < 0.001) and DPI 14 (X 2 [N = 898] = 38.63, p < 0.001) compared to the blood fed on the untreated control. The average number of oviposited eggs per female was significantly lower in LC5 group (22.44 [SD = 3.38]) than in control (34.70 [SD = 12.09]) (X 2 [N = 199] = 10.52, p < 0.001) as well as the egg hatch rate (LC5 = 74.76 [SD = 5.48]) (Control = 81.91 [SD = 5.92]) (X 2 [N = 124] = 64.24, p < 0.001). However, no differences were observed on the number of pupae that developed from larvae (Control = 34.19 [SD = 10.42) and group (LC5 = 33.33 [SD = 11.97]) (X 2 [N = 124] = 0.96, p > 0.05). CONCLUSIONS: Ivermectin drug reduces mosquito survivorship when blood fed on volunteer blood from 4 h to 14 days post-ingestion controlling for volunteers' gender. Ivermectin at mosquito sub-lethal concentrations (LC5) reduces fecundity and egg hatch rate but not the number of pupae that developed from larvae. DFA had significantly higher effects on mosquito survival compared to MFA. The findings are presented and discussed through the prism of malaria elimination in the Amazon region.

Efficacy of Permethrin Treated Bed Nets Against Leishmania major Infected Sand Flies.

Insecticide treated nets (ITNs) are a potential tool to help control sand flies and prevent Leishmaniasis. However, little is currently known about the response of Leishmania infected sand flies to ITNs. In this study, Phlebotomus duboscqi sand flies were infected with the parasite Leishmania major. Infected and noninfected sand flies were then evaluated against permethrin treated and untreated bed nets in a laboratory assay that required sand flies to pass through suspended netting material to feed on a mouse serving as an attractive host. The number of sand flies passing through the nets and blood feeding was recorded. There was not a significant difference in the ability of infected or noninfected sand flies to move through treated or untreated nets. Fewer sand flies entered the permethrin treated nets compared to the untreated nets, indicating that permethrin creates an effective barrier. The results show that in addition to reducing the nuisance bites of noninfected sand flies, ITNs also protect against Leishmania infected sand flies and therefore can play in key role in reducing the rates of Leishmaniasis. This study is important to the Department of Defense as it continues to develop and field new bed nets to protect service members.

Establishment of the Ivermectin Research for Malaria Elimination Network: updating the research agenda.

The potential use of ivermectin as an additional vector control tool is receiving increased attention from the malaria elimination community, driven by the increased importance of outdoor/residual malaria transmission and the threat of insecticide resistance where vector tools have been scaled-up. This report summarizes the emerging evidence presented at a side meeting on "Ivermectin for malaria elimination: current status and future directions" at the annual meeting of the American Society of Tropical Medicine and Hygiene in New Orleans on November 4, 2014. One outcome was the creation of the "Ivermectin Research for Malaria Elimination Network" whose main goal is to establish a common research agenda to generate the evidence base on whether ivermectin-based strategies should be added to the emerging arsenal to interrupt malaria transmission.

Efficacy and safety of the mosquitocidal drug ivermectin to prevent malaria transmission after treatment: a double-blind, randomized, clinical trial.

BACKGROUND: Artemisinin combination therapy effectively clears asexual malaria parasites and immature gametocytes but does not prevent posttreatment malaria transmission. Ivermectin (IVM) may reduce malaria transmission by killing mosquitoes that take blood meals from IVM-treated humans. METHODS: In this double-blind, placebo-controlled trial, 120 asymptomatic Plasmodium falciparum parasite carriers were randomized to receive artemether-lumefantrine (AL) plus placebo or AL plus a single or repeated dose (200 µg/kg) of ivermectin (AL-IVM1 and AL-IVM2, respectively). Mosquito membrane feeding was performed 1, 3, and 7 days after initiation of treatment to determine Anopheles gambiae and Anopheles funestus survival and infection rates. RESULTS: The AL-IVM combination was well tolerated. IVM resulted in a 4- to 7-fold increased mortality in mosquitoes feeding 1 day after IVM (P < .001). Day 7 IVM plasma levels were positively associated with body mass index (r = 0.57, P < .001) and were higher in female participants (P = .003), for whom An. gambiae mosquito mortality was increased until 7 days after a single dose of IVM (hazard rate ratio, 1.34 [95% confidence interval, 1.07-1.69]; P = .012). Although we found no evidence that IVM reduced Plasmodium infection rates among surviving mosquitoes, the mosquitocidal effect of AL-IVM1 and AL-IVM2 resulted in 27% and 35% reductions, respectively, in estimated malaria transmission potential during the first week after initiation of treatment. CONCLUSIONS: We conclude that IVM can be safely given in combination with AL and can reduce the likelihood of malaria transmission by reducing the life span of feeding mosquitoes. CLINICAL TRIALS REGISTRATION: NCT0160325.