bims-mosdis Biomed News
on Mosquito Distribution and Disease
Issue of 2020‒02‒09
thirty-five papers selected by
Richard Halfpenny
Staffordshire University

  1. Rev Panam Salud Publica. 2020 ;44 e7
    Viveiros-Rosa SG, Regis EG, Santos WC.
      Objective: To identify studies on the competence of Culex mosquitoes as vectors for the transmission of Zika virus (ZIKV) around the globe.Methods: We performed an integrative review to identify relevant articles on specific experiments to determine whether Culex mosquitoes are vectors for ZIKV. The sources we used for our research were the Brazilian Periódicos CAPES electronic portal (MEDLINE/PubMed, ScienceDirect Journals, Nature Publishing Group, SciELO, Springer Link, and 250 other databases) and gray literature.
    Results: We identified 344 studies, of which 36 were considered for this review. In 8 studies, infection in salivary glands of Culex quinquefasciatus, Culex restuans, Culex tarsalis, and Culex coronator was detected. Cx. quinquefasciatus was the most studied among those confirmed as potential ZIKV vectors, and only strains of Asian lineages (THA/2014/SV0127-14; SZ01 (2016)) and American lineages (BRPE243 (2015); PRVABC59 (2015)) can infect the salivary glands of Culex mosquitoes. The tested African strains (MR766 and DAK AR 41525) were unable to infect salivary glands.
    Conclusions: There is still a lack of compelling evidence that indicates Culex spp. are a competent ZIKV vector, but they should remain a target for further monitoring studies, especially regarding ZIKV transmission to other species. Furthermore, studies should not be limited to studying whether their salivary glands are infected.
    Keywords:  Culex.; Public health; Zika virus; mosquito vectors
  2. PLoS One. 2020 ;15(2): e0220753
    Jones R, Kulkarni MA, Davidson TMV, , Talbot B.
      BACKGROUND: Three arthropod-borne viruses (arboviruses) causing human disease have been the focus of a large number of studies in the Americas since 2013 due to their global spread and epidemiological impacts: Zika, dengue, and chikungunya viruses. A large proportion of infections by these viruses are asymptomatic. However, all three viruses are associated with moderate to severe health consequences in a small proportion of cases. Two mosquito species, Aedes aegypti and Aedes albopictus, are among the world's most prominent arboviral vectors, and are known vectors for all three viruses in the Americas.OBJECTIVES: This review summarizes the state of the entomological literature surrounding the mosquito vectors of Zika, dengue and chikungunya viruses and factors affecting virus transmission. The rationale of the review was to identify and characterize entomological studies that have been conducted in the Americas since the introduction of chikungunya virus in 2013, encompassing a period of arbovirus co-circulation, and guide future research based on identified knowledge gaps.
    METHODS: The preliminary search for this review was conducted on PubMed (National Library of Health, Bethesda, MD, United States). The search included the terms 'zika' OR 'dengue' OR 'chikungunya' AND 'vector' OR 'Aedes aegypti' OR 'Aedes albopictus'. The search was conducted on March 1st of 2018, and included all studies since January 1st of 2013.
    RESULTS: A total of 96 studies were included in the scoping review after initial screening and subsequent exclusion of out-of-scope studies, secondary data publications, and studies unavailable in English language.
    KEY FINDINGS: We observed a steady increase in number of publications, from 2013 to 2018, with half of all studies published from January 2017 to March 2018. Interestingly, information on Zika virus vector species composition was abundant, but sparse on Zika virus transmission dynamics. Few studies examined natural infection rates of Zika virus, vertical transmission, or co-infection with other viruses. This is in contrast to the wealth of research available on natural infection and co-infection for dengue and chikungunya viruses, although vertical transmission research was sparse for all three viruses.
  3. Vet World. 2019 Nov;12(11): 1729-1734
    Mulyaningsih B, Umniyati SR, Hadisusanto S, Edyansyah E.
      Background and Aim: Studies to determine abundance, distribution, species composition, and mosquito interactions are very important in understanding the risk of disease transmission to implement appropriate mosquito management in endemic areas. Lymphatic filarial worms are one of the parasites that are contracted and/or transmitted by mosquitoes when sucking the blood of infected humans or animals and then biting others. This research was conducted to study the abundance, species composition, mosquito biting cycles, density and periodicity of mosquitoes caught in Lubuk Pauh Village, Bulang Tengah Suku Ulu, Musi Rawas, South Sumatera, Indonesia, which is an endemic area of zoonotic Brugia malayi.Materials and Methods: The mosquito collection was done in July 2018 using the human landing collection method for 11 h from 18.00 pm to 5.00 am Western Indonesian Time. The catching of mosquitoes was done both indoors and outdoors, and mosquitoes were identified under a dissecting microscope using an identification key to confirm their species. Detection of B. malayi larvae in mosquitoes was confirmed by dissection and polymerase chain reaction methods.
    Results: The caught mosquitoes consisted of four species: Armigeres subalbatus, Culex quinquefasciatus, Culex vishnui, and Mansonia uniformis. Based on the Shannon-Wiener index, Lubuk Pauh Village has low mosquito species diversity (0.210). Ar. subalbatus was the dominant mosquito in Lubuk Pauh Village with dominance number 95.08, and it had the most frequent activity in each of periods of indoor and outdoor collection, with the highest density (man-hour density) at 18.00-19.00 (51.750). B. malayi infective stage larvae were not found in all mosquito species caught.
    Conclusion: Existence of Ar. subalbatus, Cx. quinquefasciatus, and Ma. uniformis in Lubuk Pauh Village which is an endemic area of B. malayi shows that the area is at risk of lymphatic filariasis transmission.
    Keywords:  Armigeres subalbatus; Brugia malayi; Musi Rawas; South Sumatera; lymphatic filariasis
  4. Acta Trop. 2020 Feb 03. pii: S0001-706X(19)31669-9. [Epub ahead of print] 105386
    Ferreira-de-Lima VH, Câmara DCP, Honório NA, de Lima-Camara TN.
      Aedes (Stegomyia) albopictus is a mosquito originating from the Asian continent, which was detected in the Americas in 1985 and Brazil in 1986. Due to its rapid expansion throughout Brazil, this species has already been reported in 26 of the 27 federative units of Brazil. In this review, we evaluate some of the biological, epidemiological and ecological characteristics of Ae. albopictus through critical analysis of their importance in the pathogen transmission dynamics, since its first record in the country. We show that immature forms of this species are frequently found in artificial breeding sites whereas females exhibit anthropophilic behavior despite its eclecticism on blood feeding. In addition, Ae. albopictus shows advantages in interspecific competition with Ae. aegypti for both immature and adult stages. Taking together, these aspects as well as its vector competence indicate that Ae. albopictus could act as a bridge vector between sylvatic and urban pathogen transmission cycles. We conclude by pointing to the need of continuous surveillance of Ae. albopictus in Brazil and raise several questions that still need to be answered.
    Keywords:  Aedes albopictus; Arbovirus; Bioecological; Brazil; Vector
  5. J Med Entomol. 2020 Feb 05. pii: tjaa009. [Epub ahead of print]
    Goenaga S, Chuchuy A, Micieli MV, Natalini B, Kuruc J, Kowalewski M.
      Since the last yellow fever (YF) outbreak was detected in Argentina in 2009, vector surveillance and studies of arbovirus infections are carried out intermittently specifically in areas where nonhuman primates of the Alouatta genus are present. We report in these areas of Corrientes province the detection of Haemagogus leucocelaenus (Dyar and Shannon) (Diptera: Culicidae) and Sabethes albiprivus (Theobald) (Diptera: Culicidae), both species involved in the forest YF cycle, and also the presence of Aedes albopictus (Skuse) in new areas in Argentina, which represents the southernmost citation for this species in South America. Aedes albopictus, a mosquito species native to Asia, was reported for the first time in Argentina in 1998, in Misiones province. Since then, no other report has indicated the extension of the distribution of this mosquito. This report shows the importance of performing continual entomological and arboviruses surveillance and highlights the impact that could result from the expansion of Ae. albopictus across Argentina.
    Keywords:  arbovirology; mosquito borne diseases; surveillance
  6. J Insect Physiol. 2020 Feb 04. pii: S0022-1910(19)30318-X. [Epub ahead of print] 104019
    Felipe Ramírez-Sanchez L, Camargo C, Avila FW.
      Aedes aegypti is the primary vector of several arboviruses that impact human health including the dengue, Zika, and yellow fever viruses. The potential of Ae. aegypti females to transmit viruses is enhanced by mating-induced behavioral and physiological changes that increase female host-seeking behaviors, blood-feeding frequency and longevity. The mating-induced changes are due to female receipt of male seminal fluid proteins (SFPs) during copulation. SFPs also inhibit female re-mating-re-mating incidence is significantly reduced in the initial hours after mating and nearly absent after 24 h. Males, however, are not limited in the number of females they can inseminate and are able to mate with multiple females in succession. As successive mating depletes SFPs, we examined parameters of fertility and re-mating incidence in females after mating with recently mated males. Males of two Ae. aegypti strains (Colombian and Thai) were mated five consecutive times and fecundity, resulting larvae and hatch percentage in each female of the mating sequence was assessed. In both strains, we found that males can mate three times in succession without impacting fertility in their mates. However, significant declines in fecundity, resulting larvae, and hatch percentage were observed after a third mating. Male size influenced female fecundity and fertility as mates of small males showed further reductions compared to mates of big males after mating consecutively. Seven days after the consecutive mating assays, the re-mating rate of females mated fifth in succession was significantly increased (Colombian strain: 33%; Thai strain: 48%) compared to females mated first (0% in both strains). Re-mating incidence was further increased in small, Thai strain males where 82% of fifth mated females re-mated compared to 0% of first mated females. Finally, we show that regardless of male size, mates of experimental males were similarly fertile to mates of control males when mated for a sixth time 48 h after the consecutive mating assays, showing that males recover fertility after 2 d. Our results show that male sexual history influences fertility and re-mating incidence of Ae. aegypti females.
    Keywords:  Fecundity; Fertility; Re-mating; Reproduction; Seminal fluid proteins
  7. Int J Environ Health Res. 2020 Feb 03. 1-11
    Kroner DG, Plunkett P, Lydy MJ.
      The present study examined how dimensions of perceived risk contributed to mosquito avoidance behaviors in a flood-prone area. Mosquito avoidance behaviors were classified into proactive (i.e. used repellant sources) and withdrawal/reactive (i.e. reduced outside activities) behaviors. After controlling for level of mosquito bites, increased scores for above normal perceived risk were associated with withdrawal/reactive avoidance behaviors; whereas, increased scores for normal perceived risk were associated with proactive avoidance behaviors. Efforts to improve mosquito avoidance behaviors should distinguish the type of perceived risk and the type of avoidance behavior. Greater congruence between perceived risk (i.e. normal risk of mosquito-borne illnesses) and avoidance behaviors (i.e. planning avoidance behaviors) will increase the effectiveness of education programs for disease prevention.
    Keywords:  Environmental health education; West Nile Virus; risk; rural
  8. Vector Borne Zoonotic Dis. 2020 Feb 04.
    Turell MJ, Cohnstaedt LW, Wilson WC.
      Rift Valley fever virus (RVFV) causes severe disease in domestic ungulates (cattle, goats, and sheep) and a febrile illness in humans (with ∼1% case fatality rate). This virus has been spreading geographically, and there is concern of it spreading to Europe or the Americas. Environmental temperature can significantly affect the ability of mosquitoes to transmit an arbovirus. However, these effects are not consistent among viruses or mosquito species. Therefore, we evaluated the effect of incubation temperatures ranging from 14°C to 30°C on infection and dissemination rates for Culex tarsalis and Aedes taeniorhynchus allowed to feed on hamsters infected with RVFV. Engorged mosquitoes were randomly allocated to cages and placed in incubators maintained at 14°C, 18°C, 22°C, 26°C, or 30°C. Although infection rates detected in Cx. tarsalis increased with increasing holding temperature, holding temperature had no effect on infection rates detected in Ae. taeniorhynchus. However, for both species, the percentage of mosquitoes with a disseminated infection after specific extrinsic incubation periods (4, 7, 10, 14, 17, or 21 days) increased with increasing incubation holding temperature, even after adjusting for the apparent increase in infection rate in Cx. tarsalis. The effects of environmental factors, such as ambient temperature, need to be taken into account when developing models for viral persistence and spread in nature.
    Keywords:  Rift Valley fever; incubation period; transmission
  9. Viruses. 2020 Jan 27. pii: E147. [Epub ahead of print]12(2):
    Amoa-Bosompem M, Kobayashi D, Murota K, Faizah AN, Itokawa K, Fujita R, Osei JHN, Agbosu E, Pratt D, Kimura S, Kwofie KD, Ohashi M, Bonney JHK, Dadzie S, Sasaki T, Ohta N, Isawa H, Sawabe K, Iwanaga S.
      Entomological surveillance is one of the tools used in monitoring and controlling vector-borne diseases. However, the use of entomological surveillance for arboviral infection vector control is often dependent on finding infected individuals. Although this method may suffice in highly endemic areas, it is not as effective in controlling the spread of diseases in low endemic and non-endemic areas. In this study, we examined the efficiency of using entomological markers to assess the status and risk of arbovirus infection in Ghana, which is considered a non-endemic country, by combining mosquito surveillance with virus isolation and detection. This study reports the presence of cryptic species of mosquitoes in Ghana, demonstrating the need to combine morphological identification and molecular techniques in mosquito surveillance. Furthermore, although no medically important viruses were detected, the importance of insect-specific viruses in understanding virus evolution and arbovirus transmission is discussed. This study reports the first mutualistic relationship between dengue virus and the double-stranded RNA Aedes aegypti totivirus. Finally, this study discusses the complexity of the virome of Aedes and Culex mosquitoes and its implication for arbovirus transmission.
    Keywords:  Aedes aegypti; Culex spp.; Ghana; cryptic species; dengue virus; insect-specific virus; mosquito virome; totivirus; virus-virus interaction
  10. Sci Total Environ. 2020 Jan 25. pii: S0048-9697(20)30462-9. [Epub ahead of print]715 136952
    Buxton M, Cuthbert RN, Dalu T, Nyamukondiwa C, Wasserman RJ.
      Free-range cattle rearing in arid landscapes contributes profoundly to ecosystem degradation. Cattle dung nutrification in aquatic habitats potentially shapes species diversity and abundance due to resource availability. These nutrient-enriched environments may increase oviposition by mosquitoes and influence proliferation of disease vectors. Here, we examined mosquito larval abundance of Culex pipiens pipiens (culicine) and an unidentified Anopheles (anopheline) species across different concentration treatments of nutrient (cattle dung) loadings (T1-T4; 1 g L-1, 2 g L-1, 4 g L-1 and 8 g L-1, respectively) in a randomised outdoor mesocosm experiment. The experiment was run for two weeks post-dung inoculation (Day 7 to 21), with mosquito larvae collected (Day 14 and 21), identified and quantified. Higher dung nutrient concentrations significantly increased mosquito larval abundance relative to dung-free controls. Culicine larvae were 26-times more abundant than anopheline on average. Higher dung concentrations also tended to promote more rapid development in larval mosquitoes. With no colonisation by mosquito larvae in the control treatments, we conclude that the input of dung in aquatic ecosystems promotes vector development and abundance with the potential to increase risk of mosquito-borne infections. We therefore recommend sustainable management policies that tackle likely ecological disservices attributable to free-ranging livestock communities.
    Keywords:  Anopheles; Arid landscapes; Cattle dung pollution; Culex; Mosquito oviposition; Nutrient loading
  11. J Med Entomol. 2020 Feb 05. pii: tjaa014. [Epub ahead of print]
    Tak JH, Coquerel QRR, Tsikolia M, Bernier UR, Linthicum K, Bloomquist JR.
      Aedes aegypti L. (Diptera: Culicidae) is one of the most medically important mosquito species, due to its ability to spread viruses of yellow fever, dengue fever, and Zika in humans. In this study, the insecticidal activity of 17 plant essential oils was evaluated via topical application against two strains of Ae. aegypti mosquito, Orlando (insecticide-susceptible) and Puerto Rico (pyrethroid-resistant). Initial screens with the Orlando strain showed that cucumber seed oil (2017 sample) was the most toxic, followed by sandalwood and thyme oil. When the essential oils were mixed with permethrin, they failed to show any significant synergism of insecticidal activity. Sandalwood and thyme oils displayed consistently high mortality against the resistant Puerto Rico strain, with low resistance ratios of 2.1 and 1.4, respectively. In contrast, cucumber seed oil showed significantly less activity against Puerto Rico mosquitoes, with a resistance ratio of 45. Bioactivity-guided fractionation of the 2017 sample of cucumber seed oil sample via flash column chromatography produced 11 fractions, and gas-chromatography/mass spectrometry analysis revealed that the three active fractions were contaminated with 0.33, 0.36, and 0.33% of chlorpyrifos-methyl, an organophosphorus insecticide, whereas inactive fractions did not show any trace of it. These results suggested that the insecticidal activity of cucumber seed oil was probably due to the presence of the insecticide, later confirmed with a clean batch of cucumber seed oil obtained in 2018, which showed negligible insecticidal activity. These findings demonstrate clearly the need for essential oil analysis to confirm purity before any claims are made about pesticidal potency.
    Keywords:   chlorpyrifos-methyl; cucumber seed oil; insecticide synergism; plant essential oils
  12. Am J Health Behav. 2020 Mar 01. 44(2): 188-199
    Diptyanusa A, Kusumasari RA, Satoto TBT.
      Objectives: In this study, we aimed to assess health beliefs, barriers, and motivations of individuals that will be useful in formulating the appropriate social and behavior change communication (SBCC) campaigns regarding dengue vector control. Methods: We conducted this qualitative study among adult residents of Gergunung and Kajen villages in Klaten, Indonesia. We conducted in-depth interviews (IDIs) and focus group discussions (FGDs) using interview an interview guide. We had audio-recorded interviews transcribed and coded. The analysis focused on general perspectives and practices of behaviors in the attempt of vector control. Results: We recruited 188 participants from 2 villages for the study. Our study revealed knowledge deficits among the villagers. Barriers include incorrect perceptions on disease severity, perceived mosquito breeding places, improper practice on mosquito source reduction, and perceived toxicity of the insecticides. Households tend to weigh the benefits of performing vector control versus perceived benefits. Conclusions: By using the Health Belief Model, a future SBCC campaign should address changing beliefs that DHF is a serious disease, increasing knowledge about mos- quito source reduction and insecticide use, and promoting benefits of performing dengue vector control.
  13. Sci Rep. 2020 Feb 04. 10(1): 1752
    Carvalho MS, Freitas LP, Cruz OG, Brasil P, Bastos LS.
      Despite all the research done on the first Zika virus (ZIKV) epidemics, it was only after the Brazilian epidemic that the Congenital Zika Syndrome was described. This was made possible due to the large number of babies born with microcephaly in the Northeast region (NE) in a narrow time. We hypothesize that the fivefold difference in the rate of microcephalic neonates between the NE and other regions is partially an effect of the population prior immunity against Dengue viruses (DENV), that cross-react with ZIKV. In this ecological study, we analysed the interaction between dengue fever epidemics from 2001 to 2014 and the 2015/2016 microcephaly epidemic in 400 microregions in Brazil using random-effects models under a Bayesian approach. The estimated effect of the time lag between the most recent large dengue epidemic (>400/100,000 inhabitants) and the microcephaly epidemic ranged from protection (up to 6 years prior) to an increased risk (from 7 to 12 years). This sustained window of protection, larger than described in previous longitudinal studies, is possibly an effect of herd immunity and of multiple exposures to DENV that could boost immunity.
  14. Insects. 2020 Feb 01. pii: E95. [Epub ahead of print]11(2):
    Cabral S, de Paula A, Samuels R, da Fonseca R, Gomes S, Silva JR, Mury F.
      The mosquito Aedes aegypti is the most notorious vector of illness-causing viruses. The use of entomopathogenic fungi as bioinsecticides is a promising alternative for the development of novel mosquito control strategies. We investigate whether differences in immune responses could be responsible for modifications in survival rates of insects following different feeding regimes. Sucrose and blood-fed adult A. aegypti females were sprayed with M. anisopliae 1 × 106 conidia mL-1, and after 48 h, the midgut and fat body were dissected. We used RT-qPCR to monitor the expression of Cactus and REL1 (Toll pathway), IMD, REL2, and Caspar (IMD pathway), STAT and PIAS (JAK-STAT pathway), as well as the expression of antimicrobial peptides (Defensin A, Attacin and Cecropin G). REL1 and REL2 expression in both the midgut and fat body were higher in blood-fed fungus-challenged A. aegypti than in sucrose-fed counterparts. Interestingly, infection of sucrose-fed insects induced Cactus expression in the fat body, a negative regulator of the Toll pathway. The IMD gene was upregulated in the fat body in response to fungal infection after a blood meal. Additionally, we observed the induction of antimicrobial peptides in the blood-fed fungus-challenged insects. This study suggests that blood-fed A. aegypti are less susceptible to fungal infection due to the rapid induction of Toll and IMD immune pathways.
    Keywords:  Zika; dengue; gene expression; immune response; vector
  15. J Oleo Sci. 2020 ;69(2): 153-160
    Huong LT, Huong TT, Huong NTT, Hung NH, Dat PTT, Luong NX, Ogunwande IA.
      The chemical composition and larvicidal activity of essential oils from the leaves and rhizomes of Zingiber collinsii Mood & Theilade (Zingiberaceae) were reported. The main compounds in the leaf oil were α-pinene (25.6%), β-caryophyllene (16.8%), β-pinene (16.1%) and bicyclogermacrene (6.9%) while the rhizome oil consist mainly of camphene (22.5%), β-pinene (16.3%), α-pinene (9.0%) and humulene oxide II (9.0%). The rhizome oil demonstrated larvicidal effects towards fourth instant larvae of mosquito vectors. The highest mortality (100%) was observed at 24 h exposure against Aedes albopictus (concentration 100 μg/mL) and 48 h (concentration of 50 and 100 μg/mL), while the highest mortality (100%) was observed for Culex quinquefasciatus at 24 h and 48 h at concentration of 100 μg/mL. The 24 h mosquito larvicidal activity of the rhizome oil against Ae. albopictus were LC50 = 25.51 μg/mL; LC90 = 40.22 μg/mL and towards Cx. quinquefasciatus with LC50 = 50.11 μg/mL and LC90 = 71.53 μg/mL). However, the 48 h larvicidal activity were LC50 = 20.03 μg/mL and LC90 = 24.51 μg/mL (Ae. albopictus), as well as LC50 = 36.18 μg/mL and LC90 = 55.11 μg/mL (Cx. quinquefasciatus). On the other hand, no appreciable mortality and larvicidal activity was observed for the leaf oil. The larvicidal activity of the essential oils of Z. collinsii was being reported for the first time.
    Keywords:  Zingiber collinsii; essential oil composition; larvicidal activity; monoterpenes; sesquiterpenes
  16. Lancet Infect Dis. 2020 Feb;pii: S1473-3099(19)30748-0. [Epub ahead of print]20(2): 170
    Qiu X, Liu N, Yang C, Zhou X.
  17. PLoS One. 2020 ;15(2): e0228190
    Phommasone K, van Leth F, Peto TJ, Landier J, Nguyen TN, Tripura R, Pongvongsa T, Lwin KM, Kajeechiwa L, Thwin MM, Parker DM, Wiladphaingern J, Nosten S, Proux S, Nguon C, Davoeung C, Rekol H, Adhikari B, Promnarate C, Chotivanich K, Hanboonkunupakarn B, Jittmala P, Cheah PY, Dhorda M, Imwong M, Mukaka M, Peerawaranun P, Pukrittayakamee S, Newton PN, Thwaites GE, Day NPJ, Mayxay M, Hien TT, Nosten FH, Cobelens F, Dondorp AM, White NJ, von Seidlein L.
      BACKGROUND: Mass administrations of antimalarial drugs (MDA) have reduced the incidence and prevalence of P. falciparum infections in a trial in the Greater Mekong Subregion. Here we assess the impact of the MDA on P. vivax infections.METHODS: Between May 2013 and July 2017, four villages in each Myanmar, Vietnam, Cambodia and Lao PDR were selected based on high prevalence of P. falciparum infections. Eight of the 16 villages were randomly assigned to receive MDA consisting of three-monthly rounds of three-day courses of dihydroartemisinin-piperaquine and, except in Cambodia, a single low-dose of primaquine. Cross-sectional surveys were conducted at quarterly intervals to detect Plasmodium infections using ultrasensitive qPCR. The difference in the cumulative incidence between the groups was assessed through a discrete time survival approach, the difference in prevalence through a difference-in-difference analysis, and the difference in the number of participants with a recurrence of P. vivax infection through a mixed-effect logistic regression.
    RESULTS: 3,790 (86%) residents in the intervention villages participated in at least one MDA round, of whom 2,520 (57%) participated in three rounds. The prevalence of P. vivax infections fell from 9.31% to 0.89% at month 3 but rebounded by six months to 5.81%. There was no evidence that the intervention reduced the cumulative incidence of P.vivax infections (95% confidence interval [CI] Odds ratio (OR): 0.29 to 1.36). Similarly, there was no evidence of MDA related reduction in the number of participants with at least one recurrent infection (OR: 0.34; 95% CI: 0.08 to 1.42).
    CONCLUSION: MDA with schizontocidal drugs had a lasting effect on P. falciparum infections but only a transient effect on the prevalence of P. vivax infections. Radical cure with an 8-aminoquinoline will be needed for the rapid elimination of vivax malaria.
  18. Insects. 2020 Feb 01. pii: E92. [Epub ahead of print]11(2):
    de Jesus CP, Dias FBS, Villela DMA, Maciel-de-Freitas R.
      Deployment of Aedes aegypti mosquitoes carrying the endosymbiont bacterium Wolbachia has been identified as a promising strategy to reduce dengue, chikungunya, and Zika transmission. We investigated whether sampling larvae from ovitraps can provide reliable estimates on Wolbachia frequency during releases, as compared to the expensive adult-based BG-Sentinel. We conducted pilot releases in a semi-field system (SFS) divided into six cages of 21 m2, each with five ovitraps. Five treatments were chosen to represent different points of a hypothetical invasion curve: 10%, 25%, 50%, 75%, and 90% of Wolbachia frequency. Collected eggs were counted and hatched, and the individuals from a net sample of 27% of larvae per treatment were screened for Wolbachia presence by RT-qPCR. Ovitrap positioning had no effect on egg hatching rate. Treatment strongly affected the number of eggs collected and also the hatching rate, especially when Wolbachia was at a 10% frequency. A second observation was done during the release of Wolbachia in Rio under a population replacement approach when bacterium frequency was estimated using 30 BG-Sentinel traps and 45 ovitraps simultaneously. By individually screening 35% (N = 3904) of larvae collected by RT-qPCR, we were able to produce a similar invasion curve to the one observed when all adults were individually screened. If sampling is reduced to 20%, monitoring Wolbachia frequency with 45 ovitraps would be roughly half the cost of screening all adult mosquitoes captured by 30 BG-Sentinels. Our findings support the scale-up of Wolbachia releases, especially in areas with limited resources to afford massive trapping with BG-Sentinel traps.
    Keywords:  Aedes aegypti; BG-Sentinel; Wolbachia; ovitrap; sampling; surveillance
  19. Proc Natl Acad Sci U S A. 2020 Feb 03. pii: 201909369. [Epub ahead of print]
    Edgerton EB, McCrea AR, Berry CT, Kwok JY, Thompson LK, Watson B, Fuller EM, Nolan TJ, Lok JB, Povelones M.
      Mosquito-borne helminth infections are responsible for a significant worldwide disease burden in both humans and animals. Accordingly, development of novel strategies to reduce disease transmission by targeting these pathogens in the vector are of paramount importance. We found that a strain of Aedes aegypti that is refractory to infection by Dirofilaria immitis, the agent of canine heartworm disease, mounts a stronger immune response during infection than does a susceptible strain. Moreover, activation of the Toll immune signaling pathway in the susceptible strain arrests larval development of the parasite, thereby decreasing the number of transmission-stage larvae. Notably, this strategy also blocks transmission-stage Brugia malayi, an agent of human lymphatic filariasis. Our data show that mosquito immunity can play a pivotal role in restricting filarial nematode development and suggest that genetically engineering mosquitoes with enhanced immunity will help reduce pathogen transmission.
    Keywords:  Brugia; Dirofilaria; Malpighian tubule; immunity; mosquito
  20. J Med Entomol. 2020 Feb 05. pii: tjaa019. [Epub ahead of print]
    Sathantriphop S, Paeporn P, Ya-Umphan P, Mukkhun P, Thanispong K, Chansang C, Bangs MJ, Chareonviriyaphap T, Tainchum K.
      Contact irritant (locomotor excitation) and noncontact spatial repellent avoidance behavior to deltamethrin and cypermethrin at dosages 0.025, 0.05, and 0.1 g/m2 impregnated on papers were evaluated in the laboratory against deltamethrin- and cypermethrin-resistant field populations of female Aedes aegypti (L.) from Rayong and Chanthaburi Provinces, Thailand. Pyrethroid-resistant populations were compared with a susceptible laboratory strain (NIH-Thai) using an 'excito-repellency' (ER) test system. Both NIH-Thai and field mosquitoes had stronger contact irritancy responses compared to the relatively weak noncontact repellency effects. Contact assays with deltamethrin and cypermethrin at 0.1 g/m2 showed high escape rates for Rayong (80.1 and 83.4%, respectively) and Chanthaburi (84.6 and 73.1%, respectively) mosquitoes. Cypermethrin produced significantly different (P < 0.05) percent escape responses in contact tests between NIH-Thai and field mosquitoes. Only deltamethrin contact at 0.05 g/m2 produced a significant escape response (P < 0.001) between NIH-Thai and Rayong mosquitoes. These results suggest that there may not be an overall significant effect of background pyrethroid resistance on escape response, and the differences by comparisons may reflect inherent individual variation when using the ER bioassay system. The results show that pyrethroid resistance in Ae. aegypti does not appear to influence or reduce contact avoidance responses with the compounds tested. In particular, deltamethrin at 0.1 g/m2 was an effective contact irritant and toxic compound against pyrethroid-resistant populations of Ae. aegypti. Therefore, 0.1 g/m2 deltamethrin could be considered for residual applications of either fixed surfaces or materials (e.g., curtains) as a supplemental control measure against adult dengue vectors.
    Keywords:   Aedes aegypti ; behavioral avoidance; cypermethrin; deltamethrin; resistance
  21. Parasit Vectors. 2020 Feb 07. 13(1): 53
    Kahamba NF, Limwagu AJ, Mapua SA, Msugupakulya BJ, Msaky DS, Kaindoa EW, Ngowo HS, Okumu FO.
      BACKGROUND: Aedes-borne diseases such as dengue and chikungunya constitute constant threats globally. In Tanzania, these diseases are transmitted by Aedes aegypti, which is widely distributed in urban areas, but whose ecology remains poorly understood in small towns and rural settings.METHODS: A survey of Ae. aegypti aquatic habitats was conducted in and around Ifakara, a fast-growing town in south-eastern Tanzania. The study area was divided into 200 × 200 m search grids, and habitats containing immature Aedes were characterized. Field-collected Ae. aegypti were tested for susceptibility to common public health insecticides (deltamethrin, permethrin, bendiocarb and pirimiphos-methyl) in the dry and rainy seasons.
    RESULTS: Of 1515 and 1933 aquatic habitats examined in the dry and rainy seasons, 286 and 283 contained Aedes immatures, respectively (container index, CI: 18.9-14.6%). In the 2315 and 2832 houses visited in the dry and rainy seasons, 114 and 186 houses had at least one Aedes-positive habitat, respectively (house index, HI: 4.9-6.6%). The main habitat types included: (i) used vehicle tires and discarded containers; (ii) flowerpots and clay pots; and (iii) holes made by residents on trunks of coconut trees when harvesting the coconuts. Used tires had highest overall abundance of Ae. aegypti immatures, while coconut tree-holes had highest densities per habitat. Aedes aegypti adults were susceptible to all tested insecticides in both seasons, except bendiocarb, against which resistance was observed in the rainy season.
    CONCLUSIONS: To our knowledge, this is the first study on ecology and insecticide susceptibility of Ae. aegypti in Ifakara area, and will provide a basis for future studies on its pathogen transmission activities and control. The high infestation levels observed indicate significant risk of Aedes-borne diseases, requiring immediate action to prevent potential outbreaks in the area. While used tires, discarded containers and flowerpots are key habitats for Ae. aegypti, this study also identified coconut harvesting as an important risk factor, and the associated tree-holes as potential targets for Aedes control. Since Ae. aegypti mosquitoes in the area are still susceptible to most insecticides, effective control could be achieved by combining environmental management, preferably involving communities, habitat removal and insecticide spraying.
    Keywords:  Aedes aegypti; Chikungunya; Dengue; Habitat characteristics; Ifakara Health Institute; Insecticide susceptibility; Tanzania
  22. Cien Saude Colet. 2020 Feb;pii: S1413-81232020000200665. [Epub ahead of print]25(2): 665-672
    Barreto E, Resende MC, Eiras AE, Demarco Júnior PC.
      Dengue transmission has been known in East Timor since 2005, but the country is not equipped with an Aedes aegypti mosquito monitoring and control program. This study aimed to evaluate the baited ovitrap as a possible tool to monitor the arbovirus vector Dengue (DENV), Chikungunya (CHIKV) and Zika (ZIKV) and was conducted in the city of Dili, capital of East-Timor, between epidemiological weeks 32 (02/08) and 48 (02/12) of 2016. In total, 70 ovitraps were installed in residences scattered throughout fifteen streets of four Administrative Posts (districts) of the city. The following entomological indicators were used: Ovitrap Positivity Index (OPI), Vector Density Index (VDI), and Egg Density Index (EDI). A total of 158.904 eggs were collected during the experiment. The OPI showed that 98-100% of traps contained Aedes spp. in all areas of the study. The EDI and OPI indicators were positively and significantly correlated with the temperature. The two- and three-week lag for rainfall indicated a significant positive correlation for VDI and EDI. Therefore, the ovitrap is a tool that can integrate the actions of an Aedes spp. monitoring and control program in East-Timor.
  23. Proc Natl Acad Sci U S A. 2020 Feb 05. pii: 202000122. [Epub ahead of print]
    Cha SJ, Jacobs-Lorena M.
  24. Wellcome Open Res. 2019 ;4 60
    Shretta R, Silal SP, Celhay OJ, Gran Mercado CE, Kyaw SS, Avancena A, Fox K, Zelman B, Baral R, White LJ, Maude RJ.
      Background: The Asia-Pacific region has made significant progress against malaria, reducing cases and deaths by over 50% between 2010 and 2015. These gains have been facilitated in part, by strong political and financial commitment of governments and donors. However, funding gaps and persistent health system challenges threaten further progress. Achieving the regional goal of malaria elimination by 2030 will require an intensification of efforts and a plan for sustainable financing. This article presents an investment case for malaria elimination to facilitate these efforts. Methods: A transmission model was developed to project rates of decline of Plasmodium falciparum and Plasmodium vivax malaria and the output was used to determine the cost of the interventions that would be needed for elimination by 2030. In total, 80 scenarios were modelled under various assumptions of resistance and intervention coverage. The mortality and morbidity averted were estimated and health benefits were monetized by calculating the averted cost to the health system, individual households, and society. The full-income approach was used to estimate the economic impact of lost productivity due to premature death and illness, and a return on investment was computed. Results: The study estimated that malaria elimination in the region by 2030 could be achieved at a cost of USD 29.02 billion (range: USD 23.65-36.23 billion) between 2017 and 2030. Elimination would save over 400,000 lives and avert 123 million malaria cases, translating to almost USD 90 billion in economic benefits. Discontinuing vector control interventions and reducing treatment coverage rates to 50% will result in an additional 845 million cases, 3.5 million deaths, and excess costs of USD 7 billion. Malaria elimination provides a 6:1 return on investment. Conclusion: This investment case provides compelling evidence for the benefits of continued prioritization of funding for malaria and can be used to develop an advocacy strategy.
    Keywords:  costs; donor; elimination; financing; government; malaria; resource mobilization
  25. PLoS Negl Trop Dis. 2020 Feb 04. 14(2): e0008034
    Malafa S, Medits I, Aberle JH, Aberle SW, Haslwanter D, Tsouchnikas G, Wölfel S, Huber KL, Percivalle E, Cherpillod P, Thaler M, Roßbacher L, Kundi M, Heinz FX, Stiasny K.
      BACKGROUND: Zika virus has recently spread to South- and Central America, causing congenital birth defects and neurological complications. Many people at risk are flavivirus pre-immune due to prior infections with other flaviviruses (e.g. dengue virus) or flavivirus vaccinations. Since pre-existing cross-reactive immunity can potentially modulate antibody responses to Zika virus infection and may affect the outcome of disease, we analyzed fine-specificity as well as virus-neutralizing and infection-enhancing activities of antibodies induced by a primary Zika virus infection in flavivirus-naïve as well as yellow fever- and/or tick-borne encephalitis-vaccinated individuals.METHODOLOGY: Antibodies in sera from convalescent Zika patients with and without vaccine-induced immunity were assessed by ELISA with respect to Zika virus-specificity and flavivirus cross-reactivity. Functional analyses included virus neutralization and infection-enhancement. The contribution of IgM and cross-reactive antibodies to these properties was determined by depletion experiments.
    PRINCIPAL FINDINGS: Pre-existing flavivirus immunity had a strong influence on the antibody response in primary Zika virus infections, resulting in higher titers of broadly flavivirus cross-reactive antibodies and slightly lower levels of Zika virus-specific IgM. Antibody-dependent enhancement (ADE) of Zika virus was mediated by sub-neutralizing concentrations of specific IgG but not by cross-reactive antibodies. This effect was potently counteracted by the presence of neutralizing IgM. Broadly cross-reactive antibodies were able to both neutralize and enhance infection of dengue virus but not Zika virus, indicating a different exposure of conserved sequence elements in the two viruses.
    CONCLUSIONS: Our data point to an important role of flavivirus-specific IgM during the transient early stages of infection, by contributing substantially to neutralization and by counteracting ADE. In addition, our results highlight structural differences between strains of Zika and dengue viruses that are used for analyzing infection-enhancement by cross-reactive antibodies. These findings underscore the possible impact of specific antibody patterns on flavivirus disease and vaccination efficacy.
  26. Science. 2020 Feb 07. 367(6478): 681-684
    Greppi C, Laursen WJ, Budelli G, Chang EC, Daniels AM, van Giesen L, Smidler AL, Catteruccia F, Garrity PA.
      Mosquitoes transmit pathogens that kill >700,000 people annually. These insects use body heat to locate and feed on warm-blooded hosts, but the molecular basis of such behavior is unknown. Here, we identify ionotropic receptor IR21a, a receptor conserved throughout insects, as a key mediator of heat seeking in the malaria vector Anopheles gambiae Although Ir21a mediates heat avoidance in Drosophila, we find it drives heat seeking and heat-stimulated blood feeding in Anopheles At a cellular level, Ir21a is essential for the detection of cooling, suggesting that during evolution mosquito heat seeking relied on cooling-mediated repulsion. Our data indicate that the evolution of blood feeding in Anopheles involves repurposing an ancestral thermoreceptor from non-blood-feeding Diptera.
  27. J Exp Biol. 2020 Feb 07. pii: jeb208181. [Epub ahead of print]223(Pt Suppl 1):
    Raban RR, Marshall JM, Akbari OS.
      Vector-borne diseases, such as dengue, Zika and malaria, are a major cause of morbidity and mortality worldwide. These diseases have proven difficult to control and currently available management tools are insufficient to eliminate them in many regions. Gene drives have the potential to revolutionize vector-borne disease control. This suite of technologies has advanced rapidly in recent years as a result of the availability of new, more efficient gene editing technologies. Gene drives can favorably bias the inheritance of a linked disease-refractory gene, which could possibly be exploited (i) to generate a vector population incapable of transmitting disease or (ii) to disrupt an essential gene for viability or fertility, which could eventually eliminate a population. Importantly, gene drives vary in characteristics such as their transmission efficiency, confinability and reversibility, and their potential to develop resistance to the drive mechanism. Here, we discuss recent advancements in the gene drive field, and contrast the benefits and limitations of a variety of technologies, as well as approaches to overcome these limitations. We also discuss the current state of each gene drive technology and the technical considerations that need to be addressed on the pathway to field implementation. While there are still many obstacles to overcome, recent progress has brought us closer than ever before to genetic-based vector modification as a tool to support vector-borne disease elimination efforts worldwide.
    Keywords:  CRISPR; Cas9; ClvR; Homing drives; Medea; Split drive
  28. Genes (Basel). 2020 Jan 29. pii: E143. [Epub ahead of print]11(2):
    Menze BD, Kouamo MF, Wondji MJ, Tchapga W, Tchoupo M, Kusimo MO, Mouhamadou CS, Riveron JM, Wondji CS.
      Growing insecticide resistance in malaria vectors is threatening the effectiveness of insecticide-based interventions, including Long Lasting Insecticidal Nets (LLINs). However, the impact of metabolic resistance on the effectiveness of these tools remains poorly characterized. Using experimental hut trials and genotyping of a glutathione S-transferase resistance marker (L119F-GSTe2), we established that GST-mediated resistance is reducing the efficacy of LLINs against Anopheles funestus. Hut trials performed in Cameroon revealed that Piperonyl butoxide (PBO)-based nets induced a significantly higher mortality against pyrethroid resistant An. funestus than pyrethroid-only nets. Blood feeding rate and deterrence were significantly higher in all LLINs than control. Genotyping the L119F-GSTe2 mutation revealed that, for permethrin-based nets, 119F-GSTe2 resistant mosquitoes have a greater ability to blood feed than susceptible while the opposite effect is observed for deltamethrin-based nets. For Olyset Plus, a significant association with exophily was observed in resistant mosquitoes (OR = 11.7; p < 0.01). Furthermore, GSTe2-resistant mosquitoes (cone assays) significantly survived with PermaNet 2.0 (OR = 2.1; p < 0.01) and PermaNet 3.0 (side) (OR = 30.1; p < 0.001) but not for Olyset Plus. This study shows that the efficacy of PBO-based nets (e.g., blood feeding inhibition) against pyrethroid resistant malaria vectors could be impacted by other mechanisms including GST-mediated metabolic resistance not affected by the synergistic action of PBO. Mosaic LLINs incorporating a GST inhibitor (diethyl maleate) could help improve their efficacy in areas of GST-mediated resistance.
    Keywords:  Anopheles funestus; Long Lasting Insecticidal Nets; glutathione S-transferase; insecticide resistance; malaria; metabolic resistance; piperonyl butoxide
  29. Transbound Emerg Dis. 2020 Feb 03.
    de Oliveira Filho EF, Carneiro IO, Ribas JRL, Fischer C, Marklewitz M, Junglen S, Netto EM, Franke R, Drexler JF.
      An orthobunyavirus termed Fort Sherman virus (FSV) was isolated in 1985 from a febrile US soldier in Panama, yet potential animal reservoirs remained unknown. We investigated sera from 192 clinically healthy peri-domestic animals sampled in northeastern Brazil during 2014-2018 by broadly reactive RT-PCR for orthobunyavirus RNA, including 50 cattle, 57 sheep, 35 goats, and 50 horses. One horse sampled in 2018 was positive (0.5%; 95% CI, 0.01-3.2) at 6.2x103 viral RNA copies/mL. Genomic comparisons following virus isolation in Vero cells and deep sequencing revealed high identity of translated amino acid sequences between the new orthobunyavirus and the Panamanian FSV prototype (genes: L, 98.8%; M, 83.5%; S, 100%), suggesting these viruses are conspecific. Database comparisons revealed even higher genomic identity between the Brazilian FSV and Argentinian mosquito- and horse-derived viruses sampled in 1965, 1982 and 2013 with only 1.1% maximum translated amino acid distances. The Panamanian FSV strain was an M gene reassortant relative to all Southern American FSV strains, clustering phylogenetically with Cache Valley virus (CVV). Mean dN/dS ratios among FSV genes ranged from 0.03-0.07, compatible with strong purifying selection. FSV-specific neutralizing antibodies occurred at relatively high end-point titers in the range of 1:300 in 22.0% of horses (11 out of 50 animals), 8.0% of cattle (4/50 animals), 7.0% of sheep (4/57 animals) and 2.9% of goats (1/35 animals). High specificity of serologic testing was suggested by significantly higher overall FSV-specific compared to CVV- and Bunyamwera virus-specific end-point titers (p=0.009), corroborating a broad vertebrate host range within peri-domestic animals. Growth kinetics using mosquito-, midge- and sandfly-derived cell lines suggested Aedes mosquitos as potential vectors. Our findings highlight the occurrence of FSV across a geographic range exceeding 7000 kilometers, surprising genomic conservation across a timespan exceeding 50 years, M gene-based reassortment events, and the existence of multiple animal hosts of FSV.
    Keywords:  Arbovirus; Orthobunyavirus; PCR; livestock; reservoirs; serology; zoonosis
  30. Can J Public Health. 2020 Feb 04.
    Rocheleau JP, Kotchi SO, Arsenault J.
      OBJECTIVES: This study aimed at (1) describing the local risk of West Nile virus (WNV) infection in humans based on previous case reports and (2) investigating the spatial clustering of cases in the five most affected administrative regions of Quebec, Canada, for the 2011-2016 period.METHODS: Human WNV cases declared to the Ministry of Health and Social Services of Quebec (Ministère de la santé et des services sociaux, MSSS) were retrieved. Incidence risk by age and sex was calculated for the study period. The yearly and monthly occurrence of cases in geographical units (GUs) was described and the probability of observing cases in a GU with cases reported in the previous year or month was assessed. Moran's I was used to assess global clustering across the study area. Spatial clusters were identified by the Kulldorff scan statistic.
    RESULTS: A total of 261 WNV cases were declared to the MSSS between 2011 and 2016 in the study area. Overall, a low percentage of GU with cases reported had additional cases reported over the next month or year. Global spatial clustering was weak but statistically significant (p < 0.05) for 2012 and 2015. For these two years, spatial clusters of high-risk GUs were identified.
    CONCLUSION: Results underline the challenge of predicting the distribution of WNV incidence risk in Quebec based on previous occurrence of human cases. Ongoing research with high spatial resolution entomological data is still necessary to understand the spatial distribution of risk at a local scale.
    Keywords:  Human; Public health; Risk distribution; Spatiotemporal; West Nile virus
  31. PLoS Pathog. 2020 Feb 06. 16(2): e1008102
    Bergren NA, Haller S, Rossi SL, Seymour RL, Huang J, Miller AL, Bowen RA, Hartman DA, Brault AC, Weaver SC.
      Understanding the circumstances under which arboviruses emerge is critical for the development of targeted control and prevention strategies. This is highlighted by the emergence of chikungunya and Zika viruses in the New World. However, to comprehensively understand the ways in which viruses emerge and persist, factors influencing reductions in virus activity must also be understood. Western equine encephalitis virus (WEEV), which declined during the late 20th century in apparent enzootic circulation as well as equine and human disease incidence, provides a unique case study on how reductions in virus activity can be understood by studying evolutionary trends and mechanisms. Previously, we showed using phylogenetics that during this period of decline, six amino acid residues appeared to be positively selected. To assess more directly the effect of these mutations, we utilized reverse genetics and competition fitness assays in the enzootic host and vector (house sparrows and Culex tarsalis mosquitoes). We observed that the mutations contemporary with reductions in WEEV circulation and disease that were non-conserved with respect to amino acid properties had a positive effect on enzootic fitness. We also assessed the effects of these mutations on virulence in the Syrian-Golden hamster model in relation to a general trend of increased virulence in older isolates. However, no change effect on virulence was observed based on these mutations. Thus, while WEEV apparently underwent positive selection for infection of enzootic hosts, residues associated with mammalian virulence were likely eliminated from the population by genetic drift or negative selection. These findings suggest that ecologic factors rather than fitness for natural transmission likely caused decreased levels of enzootic WEEV circulation during the late 20th century.
  32. Genes (Basel). 2020 Feb 05. pii: E165. [Epub ahead of print]11(2):
    Naumenko AN, Karagodin DA, Yurchenko AA, Moskaev AV, Martin OI, Baricheva EM, Sharakhov IV, Gordeev MI, Sharakhova MV.
      Chromosomal inversions are important drivers of genome evolution. The Eurasian malaria vector Anopheles messeae has five polymorphic inversions. A cryptic species, An. daciae, has been discriminated from An. messeae based on five fixed nucleotide substitutions in the internal transcribed spacer 2 (ITS2) of ribosomal DNA. However, the inversion polymorphism in An. daciae and the genome divergence between these species remain unexplored. In this study, we sequenced the ITS2 region and analyzed the inversion frequencies of 289 Anopheles larvae specimens collected from three locations in the Moscow region. Five individual genomes for each of the two species were sequenced. We determined that An. messeae and An. daciae differ from each other by the frequency of polymorphic inversions. Inversion X1 was fixed in An. messeae but polymorphic in An. daciae populations. The genome sequence comparison demonstrated genome-wide divergence between the species, especially pronounced on the inversion-rich X chromosome (mean Fst = 0.331). The frequency of polymorphic autosomal inversions was higher in An. messeae than in An. daciae. We conclude that the X chromosome inversions play an important role in the genomic differentiation between the species. Our study determined that An. messeae and An. daciae are closely related species with incomplete reproductive isolation.
    Keywords:  genome; internal transcribed spacer 2; malaria mosquitoes; polymorphic inversions
  33. Biol Pharm Bull. 2020 ;43(2): 284-288
    Badawi A, El Halawany M, Latif R.
      Thiamine hydrochloride has been suggested as a natural, safe yet effective alternative for chemical insect repellents. However, there is a demand for a reassessment of the minimum required dose that is sufficient to perform a topical repellency on the human skin. Therefore, the purpose of the current work is to establish a dose-response curve from which the effective dose (ED) is calculated. A series of increasing concentrations of thiamine hydrochloride were applied to the forearm of adult volunteers, the number of bites was counted and the percent repellency calculated accordingly. Data of percent repellency were converted to probit values which were plotted against log doses. A linear relation was obtained from the dose-response curve with an r2 = 0.958. Statistical validation of the equation was tested through linear regression analysis, where the slope and intercept were found significant from zero. No significant difference was shown between observed and expected responses (p > 0.05). ED 50 and 99.9% were computed from the linear equation and found to be 4.57 and 344 mg, respectively. This finding can be supported by future works in which a proper formulation of thiamine hydrochloride in the respective doses would be presented. One can get prolonged safe protection against insect bites.
    Keywords:  mosquitoes repellent; preformulation; probit plane analysis; skin protection; thiamine hydrochloride