Oviposition ecology and species composition of Aedes spp. and Aedes aegypti dynamics in variously urbanized settings in arbovirus foci in southeastern Côte d'Ivoire

Background Aedes mosquito-transmitted outbreaks of dengue and yellow fever have been reported from rural and urban parts of Côte d’Ivoire. The present study aimed at assessing Aedes spp. oviposition ecology in variously urbanized settings within arbovirus foci in southeastern Côte d’Ivoire. Methods Aedes spp. eggs were sampled using a standard ovitrap method from January 2013 to April 2014 in different ecosystems of rural, suburban and urban areas. Emerged larvae were reared until the adult stage for species identification. Results Aedes spp. oviposition ecology significantly varied from rural-to-urban areas and according to the ecozones and the seasons. Species richness of Aedes spp. gradually decreased from rural (eight species) to suburban (three species) and urban (one species) areas. Conversely, emerged adult Aedes spp. mean numbers were higher in the urban (1.97 Aedes/ovitrap/week), followed by the suburban (1.44 Aedes/ovitrap/week) and rural (0.89 Aedes/ovitrap/week) areas. Aedes aegypti was the only species in the urban setting (100 %), and was also the predominant species in suburban (85.5 %) and rural (63.3 %) areas. The highest Ae. aegypti mean number was observed in the urban (1.97 Ae. aegypti/ovitrap/week), followed by the suburban (1.20 Ae. aegypti/ovitrap/week) and rural (0.57 Ae. aegypti/ovitrap/week) areas. Aedes africanus (9.4 %), Ae. dendrophilus (8.0 %), Ae. metallicus (1.3 %) in the rural, and Ae. vittatus (6.5 %) and Ae. metallicus (1.2 %) in the suburban areas each represented more than 1 % of the total Aedes fauna. In all areas, Aedes species richness and abundance were higher in the peridomestic zones and during the rainy season, with stronger variations in species richness in the rural and in abundance in the urban areas. Besides, the highest Culex quinquefasciatus abundance was found in the urban areas, while Eretmapodites chrysogaster was restricted to the rural areas. Conclusions Urbanization correlates with a substantially higher abundance in Aedes mosquitoes and a regression of the Aedes wild species towards a unique presence of Ae. aegypti in urban areas. Aedes wild species serve as bridge vectors of arboviruses in rural areas, while Ae. aegypti amplifies arbovirus transmission in urban areas. Our results have important ramifications for dengue and yellow fever vector control and surveillance strategies in arbovirus foci in southeastern Côte d’Ivoire

Assessing Anopheles vector species diversity and transmission of malaria in four health districts along the borders of Côte d’Ivoire

Although malaria and Anopheles mosquito vectors are highly prevalent in Côte d’Ivoire, limited data are available to help understand the malaria vector density and transmission dynamics in areas bordering the country. To address this gap, the Anopheles mosquito species diversity, the members of the Anopheles gambiae complex and the transmission of malaria were assessed in four health districts along the borders of Côte d’Ivoire. Methods From July 2016 through December 2016 and July 2017 through December 2017, adult Anopheles mosquitoes were collected in four health districts of Côte d’Ivoire (Aboisso, Bloléquin, Odienné and Ouangolodougou) using standardized window exit trap (WET) and pyrethrum knockdown spray collection (PSC) methods. The collected mosquitoes were identified morphologically at species level and the members of the An. gambiae complex were separated using short interspersed nuclear element-based polymerase chain reaction (SINE-PCR). Anopheles gambiae sensu lato (s.l.), Anopheles funestus s.l. and Anopheles nili specimens were analysed for malaria Plasmodium parasite detection using the cytochrome oxidase I gene (COX-I), and malaria prevalence among human population through local Ministry of Health (MoH) statistical yearbooks. Results A total of 281 female Anopheles were collected in Aboisso, 754 in Bloléquin, 1319 in Odienné and 2443 in Ouangolodougou. Seven Anopheles species were recorded including An. gambiae s.l. (94.8–99.1%) as the main vector, followed by An. funestus s.l. (0.4–4.3%) and An. nili (0–0.7%). Among An. gambiae s.l., Anopheles coluzzii represented the predominant species in Aboisso (89.2%) and Bloléquin (92.2%), while An. gambiae sensu stricto (s.s.) was the major species in Odienné (96.0%) and Ouangolodougou (94.2%). The Plasmodium sporozoite infection rate in An. gambiae s.l. was highest in Odienné (11.0%; n = 100) followed by Bloléquin (7.8%, n = 115), Aboisso (3.1%; n = 65) and Ouangologoudou (2.5%; n = 120). In An. funestus s.l., Plasmodium falciparum sporozoite infection rate was estimated at 6.2% (n = 32) in Bloléquin, 8.7% (n = 23) in Odienné. No An. funestus s.l. specimens were found infected with P. falciparum sporozoite infection in Ouangolodougou and Aboisso. No P. falciparum sporozoite was detected in An. nili specimens in the four health districts. Among the local human populations, malaria incidence was higher in Odienné (39.7%; n = 45,376) and Bloléquin (37.6%; n = 150,205) compared to that in Ouangolodougou (18.3%; n = 131,629) and Aboisso (19.7%; n = 364,585). Conclusion Anopheles vector species diversity, abundance and Plasmodium sporozoite infection were high within the health districts along the borders of the country of Côte d’Ivoire, resulting in high malaria transmission among the local populations. Anopheles gambiae s.l. and An. funestus s.l. were found to be highly infected with Plasmodium in the health districts of Bloléquin and Odienné where higher malaria incidence was observed than the other districts. This study provides important information that can be used to guide Côte d’Ivoire National Malaria Control Programme for vector control decision-making, mainly in districts that are at the country borders

Small-scale field evaluation of PermaNet ® Dual (a long-lasting net coated with a mixture of chlorfenapyr and deltamethrin) against pyrethroid-resistant Anopheles gambiae mosquitoes from Tiassalé, Côte d’Ivoire

Background: Due to the rapid expansion of pyrethroid-resistance in malaria vectors in Africa, Global Plan for Insecticide Resistance Management (GPIRM) has recommended the development of long-lasting insecticidal nets (LLINs), containing insecticide mixtures of active ingredients with different modes of action to mitigate resistance and improve LLIN efficacy. This good laboratory practice (GLP) study evaluated the efficacy of the chlorfenapyr and deltamethrin-coated PermaNet® Dual, in comparison with the deltamethrin and synergist piperonyl butoxide (PBO)-treated PermaNet® 3.0 and the deltamethrin-coated PermaNet® 2.0, against wild free-flying pyrethroid-resistant Anopheles gambiae sensu lato (s.l.), in experimental huts in Tiassalé, Côte d’Ivoire (West Africa). Methods: PermaNet® Dual, PermaNet® 3.0 and PermaNet® 2.0, unwashed and washed (20 washes), were tested against free-flying pyrethroid-resistant An. gambiae s.l. in the experimental huts in Tiassalé, Côte d’Ivoire from March to August 2020. Complementary laboratory cone bioassays (daytime and 3-min exposure) and tunnel tests (nightly and 15-h exposure) were performed against pyrethroid-susceptible An. gambiae sensu stricto (s.s.) (Kisumu strain) and pyrethroid-resistant An. gambiae s.l. (Tiassalé strain). Results: PermaNet® Dual demonstrated significantly improved efficacy, compared to PermaNet® 3.0 and PermaNet® 2.0, against the pyrethroid-resistant An. gambiae s.l. Indeed, the experimental hut trial data showed that the mortality and blood-feeding inhibition in the wild pyrethroid-resistant An. gambiae s.l. were overall significantly higher with PermaNet® Dual compared with PermaNet® 3.0 and PermaNet® 2.0, for both unwashed and washed samples. The mortality with unwashed and washed samples were 93.6 ± 0.2% and 83.2 ± 0.9% for PermaNet® Dual, 37.5 ± 2.9% and 14.4 ± 3.9% for PermaNet® 3.0, and 7.4 ± 5.1% and 11.7 ± 3.4% for PermaNet® 2.0, respectively. Moreover, unwashed and washed samples produced the respective percentage blood-feeding inhibition of 41.4 ± 6.9% and 43.7 ± 4.8% with PermaNet® Dual, 51.0 ± 5.7% and 9.8 ± 3.6% with PermaNet® 3.0, and 12.8 ± 4.3% and − 13.0 ± 3.6% with PermaNet® 2.0. Overall, PermaNet® Dual also induced higher or similar deterrence, exophily and personal protection when compared with the standard PermaNet® 3.0 and PermaNet® 2.0 reference nets, with both unwashed and washed net samples. In contrast to cone bioassays, tunnel tests predicted the efficacy of PermaNet® Dual seen in the current experimental hut trial. Conclusion: The deltamethrin-chlorfenapyr-coated PermaNet® Dual induced a high efficacy and performed better than the deltamethrin-PBO PermaNet® 3.0 and the deltamethrin-only PermaNet® 2.0, testing both unwashed and 20 times washed samples against the pyrethroid-susceptible and resistant strains of An. gambiae s.l. The inclusion of chlorfenapyr with deltamethrin in PermaNet® Dual net greatly improved protection and control of pyrethroid-resistant An. gambiae populations. PermaNet® Dual thus represents a promising tool, with a high potential to reduce malaria transmission and provide community protection in areas compromised by mosquito vector resistance to pyrethroids

Dengue vector habitats in Ouagadougou, Burkina Faso, 2020: an unintended consequence of the installation of public handwashing stations for COVID-19 prevention

Correspondenc

SARS-CoV-2 Viral Shedding and Transmission Dynamics: Implications of WHO COVID-19 Discharge Guidelines

The evolving nature of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has necessitated periodic revisions of COVID-19 patient treatment and discharge guidelines. Since the identification of the first COVID-19 cases in November 2019, the World Health Organization (WHO) has played a crucial role in tackling the country-level pandemic preparedness and patient management protocols. Among others, the WHO provided a guideline on the clinical management of COVID-19 patients according to which patients can be released from isolation centers on the 10th day following clinical symptom manifestation, with a minimum of 72 additional hours following the resolution of symptoms. However, emerging direct evidence indicating the possibility of viral shedding 14 days after the onset of symptoms called for evaluation of the current WHO discharge recommendations. In this review article, we carried out comprehensive literature analysis of viral shedding with specific focus on the duration of viral shedding and infectivity in asymptomatic and symptomatic (mild, moderate, and severe forms) COVID-19 patients. Our literature search indicates that even though, there are specific instances where the current protocols may not be applicable ( such as in immune-compromised patients there is no strong evidence to contradict the current WHO discharge criteria

Urbanization is a main driver for the larval ecology of Aedes mosquitoes in arbovirus-endemic settings in south-eastern Côte d'Ivoire.

Failure in detecting naturally occurring breeding sites of Aedes mosquitoes can bias the conclusions drawn from field studies, and hence, negatively affect intervention outcomes. We characterized the habitats of immature Aedes mosquitoes and explored species dynamics along a rural-to-urban gradient in a West Africa setting where yellow fever and dengue co-exist. Between January 2013 and October 2014, we collected immature Aedes mosquitoes in water containers in rural, suburban, and urban areas of south-eastern Côte d'Ivoire, using standardized sampling procedures. Immature mosquitoes were reared in the laboratory and adult specimens identified at species level. We collected 6,159, 14,347, and 22,974 Aedes mosquitoes belonging to 17, 8, and 3 different species in rural, suburban, and urban environments, respectively. Ae. aegypti was the predominant species throughout, with a particularly high abundance in urban areas (99.37%). Eleven Aedes larval species not previously sampled in similar settings of Côte d'Ivoire were identified: Ae. albopictus, Ae. angustus, Ae. apicoargenteus, Ae. argenteopunctatus, Ae. haworthi, Ae. lilii, Ae. longipalpis, Ae. opok, Ae. palpalis, Ae. stokesi, and Ae. unilineatus. Aedes breeding site positivity was associated with study area, container type, shade, detritus, water turbidity, geographic location, season, and the presence of predators. We found proportionally more positive breeding sites in urban (2,136/3,374, 63.3%), compared to suburban (1,428/3,069, 46.5%) and rural areas (738/2,423, 30.5%). In the urban setting, the predominant breeding sites were industrial containers (e.g., tires and discarded containers). In suburban areas, containers made of traditional materials (e.g., clay pots) were most frequently encountered. In rural areas, natural containers (e.g., tree holes and bamboos) were common and represented 22.1% (163/738) of all Aedes-positive containers, hosting 18.7% of Aedes fauna. The predatory mosquito species Culex tigripes was commonly sampled, while Toxorhynchites and Eretmapodites were mostly collected in rural areas. In Côte d'Ivoire, urbanization is associated with high abundance of Aedes larvae and a predominance of artificial containers as breeding sites, mostly colonized by Ae. aegypti in urban areas. Natural containers are still common in rural areas harboring several Aedes species and, therefore, limiting the impact of systematic removal of discarded containers on the control of arbovirus diseases

Effect of land-use changes on the abundance, distribution, and host-seeking behavior of Aedes arbovirus vectors in oil palm-dominated landscapes, southeastern Côte d’Ivoire

Background Identifying priority areas for vector control is of considerable public health relevance. Arthropod-borne viruses (arboviruses) spread by Aedes mosquitoes are (re)emerging in many parts of the tropics, partially explained by changes in agricultural land-use. We explored the effects of land-use changes on the abundance, distribution, and host-seeking behavior of Aedes mosquitoes along a gradient of anthropogenic disturbance in oil palm-dominated landscapes in southeastern Côte d’Ivoire. Methodology Between January and December 2014, eggs, larvae, pupae, and adults of Aedes mosquitoes were sampled in four types of macrohabitats (rainforest, polyculture, oil palm monoculture, and rural housing areas), using standard procedures (bamboo-ovitraps, metallic-ovitraps, larval surveys, and human-baited double-net traps). Immature stages were reared and adult mosquitoes identified at species level. Principal findings A total of 28,276 Aedes specimens belonging to 11 species were collected. No Aedes-positive microhabitat and only four specimens of Ae. aegypti were found in oil palm monoculture. The highest abundance of Aedes mosquitoes (60.9%) was found in polyculture, while the highest species richness (11 species) was observed in rainforest. Ae. aegypti was the predominant Aedes species, and exhibited high anthropophilic behavior inflicting 93.0% of total biting to humans. The biting rate of Aedes mosquitoes was 34.6 and 7.2-fold higher in polyculture and rural housing areas, respectively, compared to rainforest. Three species (Ae. aegypti, Ae. dendrophilus, and Ae. vittatus) bit humans in polyculture and rural housing areas, with respective biting rates of 21.48 and 4.48 females/person/day. Unexpectedly, all three species were also feeding during darkness. Aedes females showed bimodal daily feeding cycles with peaks at around 08:00 a.m. and 05:00 p.m. Host-seeking activities were interrupted between 11:00 a.m. and 02:00 p.m. in rural housing areas, while no such interruption was observed in polyculture. Some rainforest-dwelling Aedes species displayed little preference to feed on humans. Conclusions In southeastern Côte d’Ivoire, the agricultural land-use/land-cover changes due to the conversion of rainforest into oil palm monocultures influence the abundance, distribution, and host-seeking behaviors of anthropophagic and non-anthropophagic Aedes vectors. As a result, there is higher risk of humans to arbovirus transmission in polyculture and rural housing areas. There is a need for integrated vector management, including landscape epidemiology and ecotope-based vector control

Semi-field evaluation of the space spray efficacy of Fludora Co-Max EW against wild insecticide-resistant Aedes aegypti and Culex quinquefasciatus mosquito populations from Abidjan, Côte d’Ivoire

Abstract Background Space spraying of insecticides is still an important means of controlling Aedes and Culex mosquitoes and arboviral diseases. This study evaluated the space spray efficacy of Fludora Co-Max EW, (water-based insecticide space spray combining flupyradifurone and transfluthrin with film forming aqueous spray technology (FFAST)), against wild insecticide-resistant Aedes aegypti and Culex quinquefasciatus mosquitoes from Abidjan, Côte d’Ivoire, compared with K-Othrine EC (deltamethrin-only product), in small-scale field trials. Methods Wild Ae. aegypti and Cx. quinquefasciatus mosquito larvae were collected in Abidjan, Côte d’Ivoire from August to December 2020. Mosquito larvae were reared in the laboratory until the adult stage. Fludora Co-Max EW and K-Othrine EC were tested against emerged adult females (F0 generation) using ultra-low volume cold fogging (ULV) and thermal fogging (TF) delivery technology, both outdoors and indoors in Agboville, Côte d’Ivoire. Specifically, cages containing 20 mosquitoes each were placed at distances of 10, 25, 50, 75 and 100 m from the spraying line for outdoor spraying, and at ceiling, mid-height and floor levels for indoor house spraying. Knockdown and mortality were recorded at each checkpoint and compared by treatments. Results Overall, Fludora Co-Max EW induced significantly higher knockdown and mortality effects in the wild insecticide-resistant Ae. aegypti and Cx. quinquefasciatus compared with K-Othrine EC. In both species, mortality rates with Fludora Co-Max EW were > 80% (up to 100%) with the ULV spray outdoors at each distance checkpoint (i.e. 10–100 m), and 100% with the ULV and TF sprays indoors at all checkpoints (i.e. ceiling, mid-height and floor). K-Othrine EC induced high mortality indoors (97.9–100%), whereas mortality outdoors rapidly declined in Ae. aegypti from 96.7% (10 m) to 36.7% (100 m) with the ULV spray, and from 85.0% (10 m) to 38.3% (100 m) with the TF spray. Fludora Co-Max EW spray applied as ULV spray outdoors had higher knockdown and higher killing effects on Ae. aegypti and Cx. quinquefasciatus than when applied as TF spray. Fludora Co-Max EW performed better against Cx. quinquefasciatus than against Ae. aegypti. Conclusions Fludora Co-Max EW induced high mortality and knockdown effects against wild insecticide-resistant Ae. aegypti and Cx. quinquefasciatus Abidjan strains and performed better than K-Othrine EC. The presence of flupyradifurone and transfluthrin (with new and independent modes of action) and FFAST technology in the current Fludora Co-Max EW formulation appears to have broadened its killing capacity. Fludora Co-Max EW is thus an effective adulticide and may be a useful tool for Aedes and Culex mosquito and arbovirus control in endemic areas. Graphical Abstrac

<i>Aedes</i> mosquito species dynamics, as revealed by larval collections in breeding sites in rural, suburban, and urban areas in south-eastern Côte d’Ivoire from January 2013 to October 2014.

<p><i>Aedes</i> mosquito species dynamics, as revealed by larval collections in breeding sites in rural, suburban, and urban areas in south-eastern Côte d’Ivoire from January 2013 to October 2014.</p

<i>Aedes</i> mosquito species occurrence among the macrohabitats in oil in oil palm-dominated landscapes in southeastern Côte d’Ivoire from January to December 2014.

<p>Error bars represent the standard error (SE). Letters indicate the results of the GLMM. Groups that do not share the same letter for the same sampling method are significantly different.</p