Malaria in migrant agricultural workers in western Ethiopia: entomological assessment of malaria transmission risk

Abstract Background Ethiopia has made great strides in malaria control over the last two decades. However, this progress has not been uniform and one concern has been reported high rates of malaria transmission in large agricultural development areas in western Ethiopia. Improved vector control is one way this transmission might be addressed, but little is known about malaria vectors in this part of the country. Methods To better understand the vector species involved in malaria transmission and their behaviour, human landing collections were conducted in Dangur woreda, Benishangul-Gumuz, between July and December 2017. This period encompasses the months with the highest rain and the peak mosquito population. Mosquitoes were identified to species and tested for the presence of Plasmodium sporozoites. Results The predominant species of the Anopheles collected was Anopheles arabiensis (1,733; i.e. 61.3 % of the entire Anopheles), which was also the only species identified with sporozoites (Plasmodium falciparum and Plasmodium vivax). Anopheles arabiensis was collected as early in the evening as 18:00 h-19:00 h, and host-seeking continued until 5:00 h-6:00 h. Nearly equal numbers were collected indoors and outdoors. The calculated entomological inoculation rate for An. arabiensis for the study period was 1.41 infectious bites per month. More An. arabiensis were collected inside and outside worker’s shelters than in fields where workers were working at night. Conclusions Anopheles arabiensis is likely to be the primary vector of malaria in the agricultural development areas studied. High rates of human biting took place inside and outdoor near workers’ residential housing. Improved and targeted vector control in this area might considerably reduce malaria transmission.

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Malaria in migrant agricultural workers in western Ethiopia: entomological assessment of malaria transmission risk

10.21203/rs.3.rs-136085/v2 ◽

2021 ◽

Author(s):

Sisay Dugassa Lemma ◽

Mathew Murphy ◽

Sheleme Chibsa ◽

Yehualashet Tadesse ◽

Gedeon Yohannes ◽

...

Keyword(s):

Vector Control ◽

Malaria Transmission ◽

Anopheles Arabiensis ◽

Agricultural Development ◽

Transmission Risk ◽

Malaria Vectors ◽

Residential Housing ◽

Host Seeking ◽

Human Landing ◽

Western Ethiopia

Abstract Background Ethiopia has made great strides in malaria control over the last two decades. However, this progress has not been uniform and one concern has been reported high rates of malaria transmission in large agricultural development areas in western Ethiopia. Improved vector control is one way this transmission might be addressed, but little is known about malaria vectors in this part of the country. Methods To better understand the vector species involved in malaria transmission and their behaviour, human landing collections were conducted in Dangur woreda, Benishangul-Gumuz, between July and December 2017. This period encompasses the months with the highest rain and the peak mosquito population. Mosquitoes were identified to species and tested for the presence of Plasmodium sporozoites. Results The predominant species of the Anopheles collected was Anopheles arabiensis (1,733; i.e. 61.3% of the entire Anopheles), which was also the only species identified with sporozoites (Plasmodium falciparum and Plasmodium vivax). Anopheles arabiensis was collected as early in the evening as 18:00h-19:00h, and host-seeking continued until 5:00h-6:00h. Nearly equal numbers were collected indoors and outdoors. The calculated entomological inoculation rate for An. arabiensis for the study period was 1.41 infectious bites per month. More An. arabiensis were collected inside and outside worker’s shelters than in fields where workers were working at night. Conclusions Anopheles arabiensis is likely to be the primary vector of malaria in the agricultural development areas studied. High rates of human biting took place inside and outdoor near workers’ residential housing. Improved and targeted vector control in this area might considerably reduce malaria transmission.

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Malaria in Migrant Agricultural Workers in Dangur District, Benishangul-gumuz, Ethiopia. Entomological Assessment of Malaria Transmission Risk

10.21203/rs.3.rs-136085/v1 ◽

2020 ◽

Author(s):

Sisay Dugassa Lemma ◽

Mathew Murphy ◽

Sheleme Chibsa ◽

Yehualashet Tadesse ◽

Gedeon Yohannes ◽

...

Keyword(s):

Vector Control ◽

Malaria Transmission ◽

Anopheles Arabiensis ◽

Agricultural Development ◽

Transmission Risk ◽

Malaria Vectors ◽

Residential Housing ◽

Host Seeking ◽

Human Landing ◽

Primary Vector

Abstract Background: Ethiopia has made great strides in malaria control. However, this progress has not been uniform and one concern has been reported high rates of malaria transmission in large agricultural development areas in western Ethiopia. Improved vector control is one way this transmission might be addressed, but little is known about malaria vectors in this part of the country. Methods: To better understand the vector species involved in malaria transmission and their behavior, human landing collections were conducted in Dangur woreda, Benishangul-Gumuz, between July and December 2017. Mosquitoes were identified to species and tested for presence of Plasmodium sporozoites. Results: The predominant species collected was Anopheles arabiensis (61.3% of all Anopheles), which was also the only species identified with sporozoites (P. falciparum and P. vivax). Anopheles arabiensis was collected as early in the evening as 18:00h-19:00h, and host-seeking continued until 5:00h-6:00h. Nearly equal numbers were collected indoors and outdoors. The calculated entomological inoculation rate for An. arabiensis for the study period was 1.41 infectious bites per month. More An. arabiensis were collected inside and outside worker’s shelters than in fields where workers were working at night. Conclusions: An. arabiensis is likely to be the primary vector of malaria in the agricultural development areas studied. High rates of human biting took place inside and outdoor near workers’ residential housing. Improved and targeted vector control in this area might considerably reduce malaria transmission.

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The effect of cattle-administered ivermectin and fipronil on the mortality and fecundity of Anopheles arabiensis Patton

Parasites & Vectors ◽

10.1186/s13071-021-04846-8 ◽

2021 ◽

Vol 14 (1) ◽

Author(s):

Takalani I. Makhanthisa ◽

Leo Braack ◽

Heike Lutermann

Keyword(s):

Vector Control ◽

Malaria Transmission ◽

Anopheles Arabiensis ◽

Egg Production ◽

Control Strategies ◽

Indoor Residual Spraying ◽

Malaria Vectors ◽

Saline Control ◽

Control Group ◽

Duration Of Action

Abstract Background Malaria control primarily depends on two vector control strategies: indoor residual spraying (IRS) and long-lasting insecticide-treated nets (LLINs). Both IRS and LLIN target indoor-biting mosquitoes. However, some of the most important malaria vectors have developed resistance against the chemical compounds used in IRS and LLINs. Insecticide-induced behavioural changes in vectors, such as increased outdoor feeding on cattle and other animals, also limit the effectiveness of these strategies. Novel vector control strategies must therefore be found to complement IRS and LLINs. A promising tool is the use of cattle-applied endectocides. Endectocides are broad-spectrum systemic drugs that are effective against a range of internal nematodes parasites and blood-feeding arthropods. The aim of this study was to investigate the effect of two endectocide drugs, injectable ivermectin and topical fipronil, on the survival and fecundity of zoophilic Anopheles arabiensis. Methods Laboratory-reared mosquitoes were allowed to feed on cattle treated with either injectable ivermectin (0.2 mg/kg), topical fipronil (1.0 mg/kg) or saline (control) on days 0, 1, 4, 7, 13, 21 and 25 post-treatment, and mortality and egg production were recorded daily. Results Compared to controls, the mortality of An. arabiensis increased by 3.52- and 2.43-fold with injectable ivermectin and topical fipronil, respectively. The overall fecundity of mosquitoes that fed on both ivermectin- and fipronil-treated cattle was significantly reduced by up to 90 and 60%, respectively, compared to the control group. The effects of both drugs attenuated over a period of 3 weeks. Injectable ivermectin was more effective than topical fipronil and increased mosquito mortality by a risk factor of 1.51 higher than fipronil. Similarly, both drugs significantly reduced the fecundity of An. arabiensis. Conclusions This study demonstrates that injectable ivermectin and topical fipronil are able to suppress An. arabiensis density and could help to reduce outdoor malaria transmission. Data from the present study as well as from other similar studies suggest that current-generation endectocides have a limited duration of action and are expensive. However, new-generation, sustained-release formulations of ivermectin have a multi-week, high mortality impact on vector populations, thus holding promise of an effective reduction of outdoor malaria transmission. Graphical abstract

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Malaria vector species composition and entomological indices following indoor residual spraying in regions bordering Lake Victoria, Tanzania

Malaria Journal ◽

10.1186/s12936-020-03452-w ◽

2020 ◽

Vol 19 (1) ◽

Author(s):

Charles Kakilla ◽

Alphaxard Manjurano ◽

Karen Nelwin ◽

Jackline Martin ◽

Fabian Mashauri ◽

...

Keyword(s):

Species Composition ◽

Vector Control ◽

Malaria Vector ◽

Lake Victoria ◽

Indoor Residual Spraying ◽

Transmission Risk ◽

Malaria Vectors ◽

Vector Species ◽

Sporozoite Rate ◽

Pirimiphos Methyl

Abstract Background Vector control through long-lasting insecticidal nets (LLINs) and focal indoor residual spraying (IRS) is a major component of the Tanzania national malaria control strategy. In mainland Tanzania, IRS has been conducted annually around Lake Victoria basin since 2007. Due to pyrethroid resistance in malaria vectors, use of pyrethroids for IRS was phased out and from 2014 to 2017 pirimiphos-methyl (Actellic® 300CS) was sprayed in regions of Kagera, Geita, Mwanza, and Mara. Entomological surveillance was conducted in 10 sprayed and 4 unsprayed sites to determine the impact of IRS on entomological indices related to malaria transmission risk. Methods WHO cone bioassays were conducted monthly on interior house walls to determine residual efficacy of pirimiphos-methyl CS. Indoor CDC light traps with or without bottle rotator were hung next to protected sleepers indoors and also set outdoors (unbaited) as a proxy measure for indoor and outdoor biting rate and time of biting. Prokopack aspirators were used indoors to capture resting malaria vectors. A sub-sample of Anopheles was tested by PCR to determine species identity and ELISA for sporozoite rate. Results Annual IRS with Actellic® 300CS from 2015 to 2017 was effective on sprayed walls for a mean of 7 months in cone bioassay. PCR of 2016 and 2017 samples showed vector populations were predominantly Anopheles arabiensis (58.1%, n = 4,403 IRS sites, 58%, n = 2,441 unsprayed sites). There was a greater proportion of Anopheles funestus sensu stricto in unsprayed sites (20.4%, n = 858) than in sprayed sites (7.9%, n = 595) and fewer Anopheles parensis (2%, n = 85 unsprayed, 7.8%, n = 591 sprayed). Biting peaks of Anopheles gambiae sensu lato (s.l.) followed periods of rainfall occurring between October and April, but were generally lower in sprayed sites than unsprayed. In most sprayed sites, An. gambiae s.l. indoor densities increased between January and February, i.e., 10–12 months after IRS. The predominant species An. arabiensis had a sporozoite rate in 2017 of 2.0% (95% CI 1.4–2.9) in unsprayed sites compared to 0.8% (95% CI 0.5–1.3) in sprayed sites (p = 0.003). Sporozoite rates were also lower for An. funestus collected in sprayed sites. Conclusion This study contributes to the understanding of malaria vector species composition, behaviour and transmission risk following IRS around Lake Victoria and can be used to guide malaria vector control strategies in Tanzania.

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Insecticide resistance status of Anopheles arabiensis in irrigated and non-irrigated areas in western Kenya

Parasites & Vectors ◽

10.1186/s13071-021-04833-z ◽

2021 ◽

Vol 14 (1) ◽

Author(s):

Pauline Winnie Orondo ◽

Steven G. Nyanjom ◽

Harrysone Atieli ◽

John Githure ◽

Benyl M. Ondeto ◽

...

Keyword(s):

Insecticide Resistance ◽

Vector Control ◽

Anopheles Arabiensis ◽

Crop Protection ◽

Indoor Residual Spraying ◽

Malaria Vectors ◽

Western Kenya ◽

Animal Protection ◽

Selection Of ◽

Selection Of Resistance

Abstract Background Malaria control in Kenya is based on case management and vector control using long-lasting insecticidal nets (LLINs) and indoor residual spraying (IRS). However, the development of insecticide resistance compromises the effectiveness of insecticide-based vector control programs. The use of pesticides for agricultural purposes has been implicated as one of the sources driving the selection of resistance. The current study was undertaken to assess the status and mechanism of insecticide resistance in malaria vectors in irrigated and non-irrigated areas with varying agrochemical use in western Kenya. Methods The study was carried out in 2018–2019 in Homa Bay County, western Kenya. The bioassay was performed on adults reared from larvae collected from irrigated and non-irrigated fields in order to assess the susceptibility of malaria vectors to different classes of insecticides following the standard WHO guidelines. Characterization of knockdown resistance (kdr) and acetylcholinesterase-inhibiting enzyme/angiotensin-converting enzyme (Ace-1) mutations within Anopheles gambiae s.l. species was performed using the polymerase chain reaction (PCR) method. To determine the agricultural and public health insecticide usage pattern, a questionnaire was administered to farmers, households, and veterinary officers in the study area. Results Anopheles arabiensis was the predominant species in the irrigated (100%, n = 154) area and the dominant species in the non-irrigated areas (97.5%, n = 162), the rest being An. gambiae sensu stricto. In 2018, Anopheles arabiensis in the irrigated region were susceptible to all insecticides tested, while in the non-irrigated region reduced mortality was observed (84%) against deltamethrin. In 2019, phenotypic mortality was decreased (97.8–84% to 83.3–78.2%). In contrast, high mortality from malathion (100%), DDT (98.98%), and piperonyl butoxide (PBO)-deltamethrin (100%) was observed. Molecular analysis of the vectors from the irrigated and non-irrigated areas revealed low levels of leucine-serine/phenylalanine substitution at position 1014 (L1014S/L1014F), with mutation frequencies of 1–16%, and low-frequency mutation in the Ace-1R gene (0.7%). In addition to very high coverage of LLINs impregnated with pyrethroids and IRS with organophosphate insecticides, pyrethroids were the predominant chemical class of pesticides used for crop and animal protection. Conclusion Anopheles arabiensis from irrigated areas showed increased phenotypic resistance, and the intensive use of pesticides for crop protection in this region may have contributed to the selection of resistance genes observed. The susceptibility of these malaria vectors to organophosphates and PBO synergists in pyrethroids offers a promising future for IRS and insecticide-treated net-based vector control interventions. These findings emphasize the need for integrated vector control strategies, with particular attention to agricultural practices to mitigate mosquito resistance to insecticides. Graphic abstract

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Spatial heterogeneity of malaria vectors and malaria transmission risk estimated using odour-baited mosquito traps

Malaria Journal ◽

10.1186/1475-2875-13-s1-p41 ◽

2014 ◽

Vol 13 (S1) ◽

Cited By ~ 1

Author(s):

Alexandra Hiscox ◽

Tobias Homan ◽

Corné Vreugdenhil ◽

Bruno Otieno ◽

Anthony Kibet ◽

...

Keyword(s):

Spatial Heterogeneity ◽

Malaria Transmission ◽

Transmission Risk ◽

Malaria Vectors

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New Records of Anopheles benarrochi B (Diptera: Culicidae) in Malaria Hotspots in the Amazon Regions of Ecuador and Peru

Journal of Medical Entomology ◽

10.1093/jme/tjaa293 ◽

2021 ◽

Author(s):

Diego Morales Viteri ◽

Manuela Herrera-Varela ◽

Maribel Albuja ◽

Cristina Quiroga ◽

Gloria Diaz ◽

...

Keyword(s):

Vector Control ◽

Malaria Transmission ◽

New Records ◽

Final Analysis ◽

Human Landing Catch ◽

Light Traps ◽

Control Units ◽

Pcr Rflp ◽

Human Landing ◽

First Time

Abstract The increase in malaria transmission in the Amazon region motivated vector control units of the Ministry of Health of Ecuador and Peru to investigate Anopheles (Diptera: Culicidae) species present in transmission hotspots. Mosquitoes were collected using prokopack aspirators and CDC light traps (Ecuador) and human landing catch in Peru. In Ecuador, 84 Anopheles were captured from Pastaza, Morona Santiago, and Orellana provinces and identified morphologically [An. (An.) apicimacula Dyar and Knab, An. (Nys.) near benarrochi, An. (Nys.) near oswaldoi, An. (Nys.) near strodei, An. (An.) nimbus (Theobald, 1902), and An. (Nyssorhynchus) sp.]. In Peru, 1,150 Anopheles were collected in Andoas District. A subsample of 166 specimens was stored under silica and identified as An. near oswaldoi, An. darlingi, and An. (An.) mattogrossensis Lutz and Neiva. COI barcode region sequences were obtained for 137 adults (107 from Peru, 30 from Ecuador) identified by ITS2 PCR-RFLP as An. benarrochi Gabaldon, Cova Garcia, and Lopez and retained in the final analysis. Haplotypes from the present study plus An. benarrochi B GenBank sequences grouped separately from Brazilian An. benarrochi GenBank sequences by 44 mutation steps, indicating that the present study specimens were An. benarrochi B. Our findings confirm the presence of An. benarrochi B in Ecuador and reported here for the first time from the Amazonian provinces of Orellana and Morona Santiago. Furthermore, we confirm that the species collected in Andoas District in the Datem del Maranon Province, Peru, is An. benarrochi B, and we observed that it is highly anthropophilic. Overall, the known distribution of An. benarrochi B has been extended and includes southern Colombia, much of Peru and eastern Ecuador.

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Optimising systemic insecticide use to improve malaria control

BMJ Global Health ◽

10.1136/bmjgh-2019-001776 ◽

2019 ◽

Vol 4 (6) ◽

pp. e001776 ◽

Cited By ~ 1

Author(s):

Hannah R Meredith ◽

Luis Furuya-Kanamori ◽

Laith Yakob

Keyword(s):

Vector Control ◽

Malaria Transmission ◽

Drug Administration ◽

Mass Drug Administration ◽

Companion Animals ◽

Malaria Vectors ◽

Systemic Insecticide ◽

Blood Concentrations ◽

Systemic Insecticides ◽

The Impact

BackgroundLong-lasting insecticidal nets and indoor residual sprays have significantly reduced the burden of malaria. However, several hurdles remain before elimination can be achieved: mosquito vectors have developed resistance to public health insecticides, including pyrethroids, and have altered their biting behaviour to avoid these indoor control tools. Systemic insecticides, drugs applied directly to blood hosts to kill mosquitoes that take a blood meal, offer a promising vector control option. To date, most studies focus on repurposing ivermectin, a drug used extensively to treat river blindness. There is concern that overdependence on a single drug will inevitably repeat past experiences with the rapid spread of pyrethroid resistance in malaria vectors. Diversifying the arsenal of systemic insecticides used for mass drug administration would improve this strategy’s sustainability.MethodsHere, a review was conducted to identify systemic insecticide candidates and consolidate their pharmacokinetic/pharmacodynamic properties. The impact of alternative integrated vector control options and different dosing regimens on malaria transmission reduction are illustrated through mathematical model simulation.ResultsThe review identified drugs from four classes commonly used in livestock and companion animals: avermectins, milbemycins, isoxazolines and spinosyns. Simulations predicted that isoxazolines and spinosyns are promising candidates for mass drug administration, as they were predicted to need less frequent application than avermectins and milbemycins to maintain mosquitocidal blood concentrations.ConclusionsThese findings will provide a guide for investigating and applying different systemic insecticides to achieve more effective and sustainable control of malaria transmission.

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Reduced human-biting preferences of the African malaria vectors Anopheles arabiensis and Anopheles gambiae in an urban context: controlled, competitive host-preference experiments in Tanzania

10.21203/rs.3.rs-64353/v3 ◽

2020 ◽

Author(s):

Yeromin P Mlacha ◽

Prosper P. Chaki ◽

Athuman Muhili ◽

Dennis J. Massue ◽

Marcel Tanner ◽

...

Keyword(s):

Vector Control ◽

Anopheles Gambiae ◽

Anopheles Arabiensis ◽

Host Preference ◽

Urban Setting ◽

Sub Saharan Africa ◽

Rural Setting ◽

Malaria Vectors ◽

Baited Traps ◽

The Impact

Abstract BackgroundHost preference is a critical determinant of human exposure to vector-borne infections and the impact of vector control interventions. Widespread use of long-lasting insecticide-treated nets (LLINs) and indoor residual spraying (IRS) across sub-Saharan Africa, which protect humans against mosquitoes, may select for altered host preference traits of malaria vectors over the long term. Here, the host preferences of Anopheles arabiensis and Anopheles gambiae sensu stricto (s.s.) were experimentally assessed in the field, using direct host-preference assays in two distinct ecological settings in Tanzania.MethodsEight Ifakara Tent Trap (ITT), four baited with humans and four with bovine calves, were simultaneously used to catch malaria vectors in open field sites in urban and rural Tanzania. The numbers of mosquitoes collected in human-baited traps versus calf-baited traps were used to estimate human feeding preference for each site's vector species. ResultsThe estimated proportion [95% confidence interval (CI)] of mosquitoes attacking humans rather than cattle was 0.60 [0.40, 0.77] for An. arabiensis in the rural setting and 0.61 [0.32, 0.85] for An. gambiae s.s. in the urban setting, indicating no preference for either host in both cases (P=0.32 and 0.46, respectively) and no difference in preference between the two (Odds Ratio (OR) [95%] = 0.95 [0.30, 3.01], P=0.924). However, only a quarter of An. arabiensis in the urban setting attacked humans (0.25 [0.09, 0.53]), indicating a preference for cattle that approached significance (P=0.08). Indeed, urban An. arabiensis were less likely to attack humans rather than cattle when compared to the same species in the rural setting (OR [95%] = 0.21 [0.05, 0.91], P =0.037). ConclusionUrban An. arabiensis had a stronger preference for cattle than the rural population and urban An. gambiae s.s. showed no clear preference for either humans or cattle. In the urban setting, both species exhibited stronger tendencies to attack cattle than previous studies of the same species in rural contexts. Cattle keeping may, therefore, particularly limit the impact of human-targeted vector control interventions in Dar es Salaam and perhaps in other African towns and cities.

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Effect of bendiocarb based (Ficam® 80% WP) Indoor Residual Spraying on feeding patterns from malaria vectors in Burkina Faso, West Africa.

10.21203/rs.3.rs-20419/v1 ◽

2020 ◽

Author(s):

Sawdetuo Aristide HIEN ◽

Dieudonné Diloma Soma ◽

Simon Pengwende Sawadogo ◽

Serge Bèwadéyir Poda ◽

Moussa Namountougou ◽

...

Keyword(s):

Burkina Faso ◽

Anopheles Gambiae ◽

Malaria Transmission ◽

Malaria Vector ◽

Indoor Residual Spraying ◽

Transmission Risk ◽

Malaria Vectors ◽

Anopheles Coluzzii ◽

Transmission Season ◽

Density Methods

Abstract Background The fight against vector is essential in malaria prevention strategies in several endemic countries in Africa. In Burkina Faso, malaria transmission is seasonal in most parts of country, so a single round of spraying should provide effective protection against malaria, provided the insecticide remains effective over the entire malaria transmission season. The outcomes of indoor residual spraying towards curtailing malaria transmission are firstly to decrease the life span of vector mosquitoes and also to reduce the malaria vectors density. Methods CDC light trap and early morning collections by pyrethrum spray catches were performed monthly to determine the change in malaria vector indices in sprayed (Diebougou) and unsprayed sites (Dano). The female’s malaria vectors collected by both methods were used to determine their blood feeding, biting and sporozoites rate and malaria transmission risk estimated by entomological inoculation rate. Results Anopheles gambiae complex composed to Anopheles gambiae, Anopheles coluzzii and Anopheles arabiensis were present throughout the transmission season, but An. gambiae was the predominant species collected (P =0.0005), comprising 88% of the total collected and the most infected species. Malaria vectors densities were significantly lower in sprayed villages (n=4,303) compared with unsprayed villages (n=12,569) during post-spraying period (P = 0.0012). In addition, mean human biting rate of An. gambiae sl and An . funestus ss were significantly lower in sprayed areas compared to unsprayed areas (P<0.05). Overall, malaria vector transmission risk was significant lower in villages which received IRS (P=0.0001) whatever the malaria vectors species ( An. gambiae sl and An. funestus ss). Conclusions The results showed that in the sprayed area (Diebougou), vector densities, human biting rates and malaria transmission risks were very lower than unsprayed areas (Dano). The findings also showed a change in vector behavior especially within An. funestus which became more zoophagic following IRS. The indoor residual spraying could be recommanded as control tool in areas where malaria transmission occured a given period of year.

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