Risk of Aedes-Borne Diseases in and around the Tanzanian Seaport of Tanga Despite Community Members Being More Concerned About Malaria

doi:10.21203/rs.3.rs-4843484/v1

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Risk of Aedes-Borne Diseases in and around the Tanzanian Seaport of Tanga Despite Community Members Being More Concerned About Malaria

https://doi.org/10.21203/rs.3.rs-4843484/v1

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Background: Increased global trade, while beneficial economically, can also increase the spread of vector-borne diseases, particularly those transmitted by Aedes mosquitoes spreading via trade routes. Yet, in sub-Saharan Africa, key Aedes-transmitted diseases remain under-studied, as the majority of mosquito-related research focuses on malaria. Given the heightened trade-induced activity at ports of entry, it is particularly crucial to assess the risk of mosquito-borne diseases in these settings. This study compared the risks of disease-transmitting mosquitoes in and around the eastern Tanzanian seaport of Tanga.

Methods: A 200m x 200m grid-based system was used to sample mosquitoes within the port area, and in surrounding areas at 2km, 2.5km, and 5km away, between June and Dec 2023. We characterized mosquito breeding habitats, collected mosquito larvae using standard dippers and tested susceptibility of Aedes aegypti populations to different insecticides. Adult mosquitoes were collected using BG sentinel traps (daytime) and CDC light traps (night-time). Additionally, over 200 port users and neighboring residents were surveyed to assess experiences and perceptions of mosquito biting and disease risks.

Results: There were 2,931 breeding sites, with 60.8% positive for Aedes larvae. The percentage of water-holding containers infested with Aedes immatures, i.e. Container Index (CI), was highest in the port area (66.2%), and lowest 5 km away (44.6%). The port area also had higher proportion of temporary breeding sites (64.9%) compared to surroundings. The adult mosquito surveys found 20,449 mosquitoes including: Ae. aegypti (5.09%), Culex quinquefasciatus (56.17%), Anopheles gambiae (0.08%), Anopheles funestus (0.01%), and Mansonia uniformis (38.72%). Ae. aegypti were more abundant in the port area than in surrounding areas (P<0.001), while Culex and Mansonia species were more abundant outside (P<0.001). Adult Anopheles were found only in the port area, but Anopheles larvae were found both within and outside the port areas. Tests on Ae. aegypti showed susceptibility to bendiocarb and DDT, and resistance to permethrin. Awareness of mosquito-borne diseases among respondents was high for malaria (64.8%), but low for dengue (26.3%) and Chikungunya (1.7%). Most respondents reported being bothered by mosquitoes mostly at night (53.4%) or evening (40.7%). Besides insecticidal bednets, used primarily against malaria, preventive measures for Aedes-borne diseases were limited.

Conclusion: This study identified significant potential risk of Ae. aegypti and associated diseases, but low perception of risk and inadequate personal protection measures in the study area. This low perception of risk highlights the need to improve public knowledge on transmission and control of Aedes-borne diseases.

Aedes aegypti

Mosquito-borne

Habitat characterization

Malaria

Insecticide susceptibility

Tanga port

Tanzania

Mosquito-borne diseases, such as dengue fever, chikungunya, and yellow fever, constitute significant health threats, and are increasingly recognized as a growing challenge in Africa – more so in urban areas [1]. Other than malaria, which causes 250 million cases and over 600,000 deaths annually [2], the World Health Organization (WHO), has indicated that global dengue incidence rates have also been surging dramatically in recent years [3, 4]. Official WHO estimates suggest that 390 million infections occur annually, of which 96 million manifest clinically, even though only a very small proportion of these cases are officially recorded and reported [5]. It has also been estimated that about 3.9 billion people across 128 countries are at risk of dengue infection [6]. This extensive burden, the multiplicity of mosquito-borne diseases - with half of the world’s population at risk of two or more of the diseases [7] and the close correlation with human factors like urbanization and trade [8, 9], all underscore the urgent need for effective surveillance and control measures to mitigate the impact of dengue, especially in vulnerable regions.

In Tanzania, while the burden of malaria is closely tracked by research groups and the Ministry of Health, [10–12] the full burden of other mosquito-borne diseases, notably Aedes-borne diseases is largely unknown, except for isolated research activities and reviews. For example, while dengue fever is known to occur in Tanzania in all four serotypes alongside Chikungunya and potentially other Aedes-borne diseases [13, 14], the overall burden of dengue in the whole country remains uncertain. One previous review indicated that seroprevalence estimates range from 11–50.6% [15], and that rates can be particularly high among patients presenting themselves with fever to health facilities. Despite repeated outbreaks in recent years, comprehensive data on the epidemiology of dengue or the ecology of its vector species is very limited, though there is a growing interest in Aedes studies in the country [16–19]. This gap in knowledge is particularly concerning given the potential for dengue outbreaks to exacerbate public health challenges in a country already burdened by other mosquito-borne diseases like malaria. Moreover, ecological, environmental and climate change concerns such as excessive temperature and frequent flooding [20], as well as poor waste management and uncontrolled water storage practices in urban areas [21, 22], will likely increase the burden and potentially disrupt health services. Indeed, it is now estimated that with warming climate, the dengue vector mosquitoes are expected to survive these warmer temperatures better than malaria vectors [23], meaning that Africa might see significant increases in Aedes-borne diseases as a direct result of climate change.

The ecology of Aedes mosquitoes is indeed intricately linked to urban environments, where they thrive in a variety of habitats especially human-made containers [24]. Aedes aegypti, the primary vector for dengue, chikungunya, and Zika, prefers to breed in artificial containers such as discarded vehicle tires, plastic containers, flowerpots, and water storage tanks [25], commonly abundant in urban settings. Like other container-breeding mosquito species, Ae. aegypti can thrive almost independently of rainfall seasons, as they exploit water sources that are continuously available in human communities. This ability allows them to maintain their population densities year-round, and therefore presenting a persistent risk of disease transmission. Despite the clear importance of understanding Aedes ecology for public health, surveys and studies on these mosquitoes remain limited in Tanzania, even in large cities and small towns.

Global travel, trade, and urbanization drive the spread of vector-borne diseases, with ports and airports acting as key conduits [26]. The international movement through seaports significantly expands the range of mosquito vectors, posing substantial risks to nearby populations. Studies have highlighted the prevalence of Ae. aegypti and Aedes albopictus on intercontinental travel routes by air and oceanic vehicles like barges, river boats and cruises [27–29], which amplifies the threat of arboviral infections near seaports. This has also been observed for some Culex species [30]. These vectors can readily establish and proliferate in the ports of entry if insufficient precautions are taken and the breeding habitats numerous. Indeed, mosquito invasions and densities tend to be higher near ports compared to other outdoor areas, further escalating the risk [31–33]. Furthermore, ports connecting urban areas along the Indian Ocean are crucial for the spread of invasive vectors, and have been linked to the recent invasions of the Asian malaria vector, Anopheles stephensi into the horn of Africa [34], potentially the Asian tiger mosquito, Aedes albopictus [35–38] and even multiple re-invasions of Ae. aegypti, which spread widely across the globe from Africa. In port towns and other travel hubs, it is therefore particularly important to conduct comprehensive entomological surveys in these port cities and town as a step towards outbreak mitigation as it could aid in developing targeted vector control strategies and invasive vector species [39].

The WHO urges member states to conduct vector surveillance at ports to maintain mosquito densities below national thresholds, as stipulated by the International Health Regulations (IHR) [39]. Unfortunately, many sub-Saharan African countries face significant challenges, including inadequate investments in surveillance infrastructure. For example, in Tanzania, despite the IHR 2005 recommendations for strong vector surveillance at points of entry [40], there is a lack of comprehensive data on mosquito composition nor their insecticide susceptibility status. This data gap hinders accurate estimates of the risk of mosquito-borne diseases in these settings. A study conducted along Kenya’s coast revealed that a 2019 dengue outbreak caused by the DENV-3 serotype originated from Pakistan, highlighting the consequences of global travel [41]. Separately, an analysis of the molecular diversity of dengue outbreaks in Tanzania revealed a serotype shift from DENV-3 (2017/2018) to DENV-1 in 2019, indicating that contemporary circulating serotypes did not cause the major epidemic of 2019 and highlighting the increased risk of severe symptoms due to antibody-dependent enhancement for patients previously infected with a different serotype [42]. More recent surveys have found all four serotypes of dengue, and even chikungunya further interior in Ifakara, some 450km out of Dar es Salaam, suggesting widespread transmission [43]. These studies underscore the critical need for regular and thorough surveys in ports to monitor and control the spread of vector-borne diseases effectively.

It is also widely recognized that community awareness and preparedness play a crucial role in the control and prevention of mosquito-borne diseases. In Tanzania, it is often assumed that there is already a high degree of awareness of dengue and other mosquito-borne diseases among communities due to extensive public health campaigns and education efforts [44]. However, knowledge about Aedes-borne diseases, such as dengue, chikungunya, and yellow fever, has not been adequately investigated. Yet insufficient knowledge poses a significant challenge for effective disease control, as communities may not take the necessary precautions to protect themselves from Aedes mosquitoes. Enhancing public awareness about Aedes-borne diseases and improving community preparedness through targeted education and outreach programs are essential steps in mitigating the risks posed by these diseases. This is particularly important in port areas, where the influx of travelers and goods increases the potential for disease spread.

The objective of this current study was to assess and compare the risks of disease-transmitting mosquitoes within the eastern Tanzanian seaport of Tanga and its surrounding urban areas along the Indian Ocean focusing especially on Ae. aegypti mosquitoes. We sought to establish the mosquito species composition, abundance, insecticide resistance status and their aquatic breeding preferences; and to use this information to evaluate and address the risks of mosquito-borne infections at this critical point of entry. Additionally, we assessed the perceptions of port users and residents of the surrounding urban areas to understand how such perceptions might inform effective control strategies including social and behaviour change communication strategies

Study Area

The study was conducted in the north-eastern Tanzanian port city of Tanga (Fig. 1). The central location was the Tanga seaport, with additional sampling in eight surrounding wards within the Tanga City Council: Central (5°04'19.26''S, 39°06'06.59''E), Chumbageni (5°04'14.66''S, 39°05'21.30''E), Kiomoni (5°03'13.24''S, 38°56'57.24''E), Mzizima (5°02'51.26''S, 39°02'37.72''E), Nguvumali (5°04'40.80''S, 39°04'39.87''E), Mnyanjani (5°05'56.22''S, 39°07'13.79''E), Ngamiani Kusini (5°05'00.42''S, 39°06'06.14''E), and Magaoni (5°06'12.49''S, 39°06'07.06''E). Tanga District is a border district in the north-eastern part of Tanzania. It is bordered by Mkinga District Council to the north, the Indian Ocean to the east, Muheza District to the south and west, and the country of Kenya to the north. The district seat is the city of Tanga, which also serves as the administrative and economic center of the region, major economic activities in this area including business, industrial activities, tourism, fishing and agriculture. According to the 2022 census, Tanga District had a total population of just under 400,000 in some ~ 100,000 households.

The Tanga seaport is the second largest international point of entry in Tanzania. It was the focal point of the study, and is located in the Central ward, which has an area of ~ 3.8 square kilometers and an altitude of 10m above sea level. All sampling sites across all the 8 wards located within 5 km of the port area (Fig. 1).

Sampling design and site selection

A cross-sectional entomological survey was conducted between June and December 2023 (the dry season). The reference sampling was within the Tanga seaport in the Central ward (within 500m of the seaport) but additional surveys were conducted at purposively selected sites 2.5 km and 5 km away from the port along three main roads: Pangani, Segera, and Mombasa Road, to understand mosquito distribution across the study area and expansion away from the port. An extra comparison site was selected 2 km south of the port area in the Mnyanjani ward. All sites were located in Tanga City Council (Fig. 1).

Sampling was conducted using a 200 x 200m grid-based system created in ArcGIS 11.1 environment (ESRI, USA), following the methodology used in a previous Aedes survey by Kahamba et al [16]. Preference was given to grids with human habitation and a total of 23 grids used for the sampling. Each grid was assigned a unique identifier (grid ID) consisting of letters and numbers, with letters representing longitudes and numbers representing latitudes (e.g., A1, A2). Randomization and grid selection procedures were consistent across all locations. An initial survey of the study area was conducted with the assistance of volunteer community resource persons. During the survey, features conducive to mosquito breeding, such as water wells, drains, containers, pots, flowerpots, tins, waste collection points, discarded tires, and drums, were identified. The coordinates of these features were recorded using a handheld GPS (Magellan eXplorist GC, USA). In the central reference area around the Tanga seaport, all grids within a 500m buffer zone were selected but no collections were made inside shipping vessels.

Sampling of adult mosquitoes

Adult mosquitoes were collected using two types of traps: BG-Sentinel traps for Aedes species and other culicines, and CDC light traps for Anopheles mosquitoes and culicines. Five CDC light traps were deployed indoors in selected bedrooms within each grid at night. The traps were set from 6:00 PM to 6:00 AM for six consecutive days before being moved to the next grid in a random fashion. Mosquitoes were retrieved daily from 7:00 AM to 10:00 AM. Retrieved mosquitoes were sorted and identified using taxonomic keys, then preserved in Eppendorf® tubes with silica gel. Concurrently, the BG-Sentinel traps, which were used for outdoor and day-time collections, were positioned in shaded areas in strategic locations – either near waste collection points, houses, garages, night clubs, and other areas considered to have high mosquito activity zones, the traps were added with BG lure and molasses mixed with yeast to increase mosquito attraction. Each grid had four traps operating from 6:00 AM to 6:00 PM for six consecutive days. Mosquitoes were retrieved from the traps daily from 5:00 PM to 6:00 PM, sorted, and identified using a dissecting microscope and taxonomic keys as described above.

For each collection, either by CDC light traps or BG Sentinel Traps, the additional metadata recorded included grid ID, date, distance from port area, GPS location, and house number. After the samples were sorted, all Anopheles and Aedes species mosquitoes were sent to Ifakara Health Institute for further analysis.

Sampling of immature mosquitoes and characterization of their aquatic habitats

Surveys for immature mosquitoes and characterization of breeding habitats were conducted in all selected grids where adult mosquito trapping was being conducted. The search for mosquito larvae focused on various natural and human-made water-holding objects, including used tires, surface drains, wells, discarded containers, animal feeding containers, flowerpots, and buckets. Additional habitats such as tree holes (holes on tree stems), discarded boots, plant leaves, and other small objects that could hold water for more than three days were also examined. Breeding sites with mosquito larvae or pupae were geo-referenced using handheld GPS devices. The breeding sites were further characterized by assessing habitat type, location (whether it was indoors that means present inside the houses or building or outdoors), algae quantity, watercolor, presence of vegetation, water movement, water source, habitat mobility, and the surrounding environmental and social activities. All information was recorded on breeding site characterization forms.

To collect the mosquito immatures (larvae and pupae) we used a 350 ml dipper or a smaller 70 ml dipper for smaller habitats as adopted from Claudia [45]. Collected larvae and pupae were placed in white trays for morphological identification using pictorial keys [46–48]. Immature mosquitoes were sorted, counted, and data recorded by habitat type, location, and date.

Testing the susceptibility of mosquitoes to insecticides

Aedes larvae were reared to adulthood for susceptibility testing to establish resistance profiles. Collected immatures were maintained to the adult stage using water from their known breeding habitats mixed with tap water in plastic containers. For rearing, the immatures were placed in labeled basins and were fed Tetramine® baby fish food. Their water changed every three days to facilitate growth. The rearing was conducted at 26°C ± 2°C and 82% ± 10% relative humidity. Pupae were collected daily, counted, and transferred to 30 cm x 30 cm x 30 cm netting cages. Emerged adults were fed 10% glucose and identified morphologically under a microscope using identification keys [49].

The susceptibility tests were conducted using WHO guidelines for Anopheles mosquitoes [50] since we did not have access to appropriate insecticide-impregnated papers for use on Aedes aegypti. Adult female Aedes aegypti, were obtained from the rearing cages to be used for these tests when they were 3–5 days. The mosquitoes were tested against commonly used insecticides, including pyrethroids (deltamethrin at 0.05% & 0.5% doses and permethrin at 0.5% & 0.75%), an organophosphate (pirimiphos-methyl at 1.25% & 2.5% doses), an organochlorine (DDT 4%), and carbamates (bendiocarb 0.5% & 1%). The higher doses for pyrethroid insecticides were included so as to test the intensity of resistance.

In each bioassay experiment, 120–150 mosquitoes were distributed into six holding tubes, with 20–25 mosquitoes per tube. Eighty mosquitoes (20 per tube) were exposed to the test insecticide, while 40 mosquitoes (20 per tube) served as controls. Mosquitoes in control tubes were exposed to untreated filter papers, while those in the treatment tubes were exposed to filter papers impregnated with the respective doses of the candidate insecticides. The test and control mosquitoes were observed for 60 minutes, and the number mosquitoes of knocked down recorded at 10, 15, 20, 30, 40, 50, and 60 minutes. After this, the mosquitoes were transferred back to holding tubes and provided with 10% glucose solution, then maintained for a day at 28°C ± 1°C and 80% ± 10% relative humidity. Mortality was assessed 24 hours post-exposure in both the control and treatment arms. A mosquito was considered alive if it could fly, regardless of number of legs remaining; or dead if they were immobile, unable to stand or take off or obviously moribund.

Survey of opinions and perceptions of port users and residents of neighboring wards

To complement the entomological surveys, a comprehensive qualitative survey was conducted to gauge the opinions and perceptions of port users and residents of the neighboring wards regarding mosquito-related risks and disease transmission at entry point and in their areas of residence. We deployed the survey using the Kobo Collect toolkit programmed in PC tablets and used a structured questionnaire for the interviews. All participants were recruited voluntarily and were all aged 18 and above. They included locals, port workers, office staff, entrepreneurs, passengers, drivers, security guards, market vendors, and fishermen, representing the diverse groups across the study areas.

Recruitment was done by visiting workplaces and homes and participants were recruited and surveyed to understand their views on mosquito-related risks at points of entry. A total of 236 participants voluntarily consented and were recruited. The structured questionnaire assessed key issues such as knowledge of diseases transmitted by mosquitoes in the Tanga port area and surrounding wards, opinions on groups at greater risk of infection, mosquito biting experiences, and personal protection methods used against mosquito bites. Responses were analyzed to identify trends based on occupational status and education levels, providing valuable insights into community awareness and preparedness regarding mosquito-borne diseases.

Statistical analysis and presentation

Analysis of the quantitative data was conducted using open-source software, R version 3.6.2 [51], and ArcGIS [52]. Data were initially entered into MS Excel and then exported to R in a csv format for cleaning and coding. Initially, a descriptive analysis was done, where we calculated the abundance and distribution of mosquitoes (both adult and immature stages) across sampling locations. A Generalized Linear Model (GLM) with Poisson variate was then employed to determine the association of mosquito larvae in breeding habitats with habitat characteristics such as watercolor and movement, presence of vegetation, and whether the habitat was natural or artificial included as main predictors. Another GLM, with a negative binomial distribution was used to assess the relative comparison of mosquito abundance between sampling areas, trap types, and indoor-outdoor settings at the point of entry, with grid ID as a random variable to identify significant factors.

To estimate the Aedes insecticide resistance profile, mosquito populations were categorized as susceptible if the mortality rate was greater than 98%, suggesting or unconfirmed resistance that need further investigation if between 90% and 98%, and as resistant if below 90% [50]. All the visualization and spatial analyses was done in the GIS Environment using QGIS software to analyse mosquito species diversity, abundance, and distribution by interpolation techniques. The environmental data, such as the number of mosquitoes per species, location of collection, and grid ID, trap type, were extracted and compared with Cx. quinquefasciatus, Ma. uniformis, and Ae. aegypti abundance. Hotspot analysis using Inverse Distance Weighted (IDW) interpolation was used to identify grids with high mosquito abundance, which were statistically significant and crucial for targeting control measures. IDW was chosen as interpolation method since ‘it estimates cell values by averaging the values of sample data points in the neighborhood of each processing cell. The data was interpolated by means of IDW and transformed from vector into raster.

Lastly, the questionnaire data from the survey of port users and residents were analyzed using descriptive statistics to summarize the participants' knowledge, opinions, and practices regarding mosquito-related risks and disease transmission.

Ethical statement

The approval for conducting the survey was obtained from ethical committee and institutional review board of Ifakara Health Institute (Ref: IHI/IRB/No:39-2023), and from the Medical Research Coordinating Committee (MRCC) at the National Institute for Medical Research (NIMR) (Ref: NIMR/HQ/R.8a/Vol.IX/4178). Community meetings with local leaders were held to explain the study aims, benefits, and risks, and to obtain permission for the study. Informed consent was obtained from all household members for mosquito trapping and surveys, and an information sheet was read to each questionnaire participant to explain the study's objectives, benefits, risks, and their rights, seeking their consent to participate.

Diversity and abundance of adult mosquitoes in the Port area and surrounding wards

A total of 20,449 mosquitoes were collected between June and December 2023 (Table 1 and Figure 2). Among these, 5.09% (1,042) were identified as Aedes Aegypti, 56.17% (11,488) as Culex quinquefasciatus, 0.08% (16) as Anopheles gambiae s.l., 0.01% (3) as Anopheles funestus s.l, and 38.72% (7,919) as Mansonia uniformis. Indoor collections using CDC light traps accounted for 46.07% (9,421) of the total, while outdoor collections using BG sentinel traps comprised 53.79% (11,028).

Most Ae. aegypti mosquitoes were collected outdoors (97.79%; 1,019/1,042), while Cx. quinquefasciatus showed a distribution of 41.07% indoors and 58.92% outdoors. The mean catches and associated error estimates are summarized in Table 1. The highest abundances of Aedes mosquitoes were observed in the port area, with populations significantly declining in surrounding areas. Generalized linear mixed model analysis using a negative binomial distribution revealed that the likelihood of catching Ae. aegypti outdoors decreased with distance from the port area. The relative risk (RR) of catching Ae. aegypti was 0.22 [CI: 0.11, 0.42] at 2 km, 0.39 [CI: 0.24, 0.63] at 2.5 km, and further declined to 0.33 [CI: 0.20, 0.54] at 5 km, all with p-values <0.001, reaffirming the trend of diminishing presence with increased distance from the port (Table 1). The number of blood-fed Ae. aegypti were 37 in the port area, 0 at 2 km, 0 at 2.5 km, and 2 at 5 km, while unfed mosquitoes were 672 in the port area, 41 at 2 km, 166 at 2.5 km, and 137 at 5 km, with no gravid mosquitoes caught at any location.

For Cx. quinquefasciatus, the abundance varied significantly between locations. The indoor mean catches were 8.99 [95% CI: 7.10, 11.37] in the port area, increasing to 14.27 [9.17, 22.20] at 2 km, and then decreasing to 9.84 [7.27, 13.31] at 2.5 km, and 5.02 [3.69, 6.82] at 5 km. The RR for outdoor catches showed similar trends, with significant increases at 2 km and 2.5 km (RR = 1.91 [1.32, 2.79] and RR = 1.91 [1.43, 2.54], respectively, p < 0.001), before decreasing at 5 km (RR = 1.33 [1.00, 1.78], p < 0.05). Ma. uniformis showed the highest indoor abundance at 2.5 km (mean = 16.76 [95% CI: 9.81, 28.64], RR = 3.19 [1.62, 6.30], p < 0.001) and the lowest at 2 km (mean = 0.02 [0.002, 0.14], RR = 0.01 [0.00, 0.03], p < 0.001). The outdoor abundance of this species showed a peak at the port area and declined with increasing distance.

Table 1: Mean number of mosquitoes caught at different distances from the Port Area using the CDC light traps (placed indoors for nighttime collections) and the BG Sentinel taps (placed outdoors for daytime collections)

Species	Distance (km) from Port	CDC Light Traps (Indoors)				BG-Sentinel (Traps Outdoors)
Species	Distance (km) from Port	Total	Mean [95%CI]*	RR [95%CI]	P-Values	Total	Mean ± 2SE	RR [95%CI]	P-Values
Culex quinquefasciatus	0 (Port Area)	1,932	8.99 [7.10, 11.37]	1		1,938	5.63 [4.72, 6.73]	1
	2	856	14.27 [9.17, 22.20]	1.59 [0.96, 2.62]	0.070	1,035	10.78 [7.75, 15.00]	1.91 [1.32, 2.79]	<0.001
	2.5	1,279	9.84 [7.27, 13.31]	1.10 [0.75, 1.61]	0.643	2,234	10.74 [8.58, 13.44]	1.91 [1.43, 2.54]	<0.001
	5	652	5.02 [3.69, 6.82]	0.56 [0.38, 0.82]	<0.01	1,562	7.51 [5.99, 9.42]	1.33 [1.00, 1.78]	<0.05
Aedes aegypti	0 (Port Area)	14	0.065 [0.04, 0.12]	1		682	1.98 [1.49, 2.64]	1
	2	0	0	NA		41	0.43 [0.23, 0.78]	0.22 [0.11, 0.42]	<0.001
	2.5	6	0.046 [0.02, 0.11]	0.71 [0.24, 2.06]	0.526	160	0.77 [0.52, 1.14]	0.39 [0.24, 0.63]	<0.001
	5	3	0.023 [0.01, 0.08]	0.35 [0.09, 1.34]	0.127	136	0.65 [0.44, 0.97]	0.33 [0.20, 0.54]	<0.001
Mansonia uniformis	0 (Port Area)	1,129	5.25 [3.45, 7.99]	1		1,411	4.10 [2.98, 5.65]	1
	2	1	0.02 [0.002, 0.14]	0.01 [0.00, 0.03]	<0.001	14	0.45 [0.07, 0.32]	0.04 [0.02, 0.08]	<0.001
	2.5	2,179	16.76 [9.81, 28.64]	3.19 [1.62, 6.30]	<0.001	1,231	5.92 [3.93, 8.91]	1.44 [0.86, 2.43]	0.167
	5	1,370	10.54 [6.16, 18.02]	2.00 [1.02, 3.97]	<0.05	584	2.81 [1.87, 4.25]	0.66 [0.41, 1.16]	0.155

Spatial distribution of adult Aedes mosquitoes

The distribution of adult Aedes mosquitoes varied across the surveyed administrative wards. The results from interpolation techniques by Inverse Distance Weighted (IDW) interpolation of a point vector layer revealed a significantly higher density of Aedes mosquitoes in the port area, in the Central ward, indicating these as hotspots. Conversely, areas such as Magaoni (5 km from the port), Kiomoni (5 km from the port), and Mnyanjani (2 km from the port) were identified as having lower densities of Aedes mosquitoes as shown in figure 3.

Diversity and abundance of immatures and their aquatic habitats in the Port area and surrounding wards

The larval searches and habitat characterization activities identified immature stages of Anopheles, Culex, and Aedes mosquitoes in several habitats across the study area. Out of 2,934 sampled mosquitoes, 60.7% were Aedes, 39.1% were Culex, and 0.1% were Anopheles (Table 2). High densities of Aedes immatures were found in Central ward within the Port Area (68.3%), followed by Nguvumali ward (11.9%), with the lowest density in Kiomoni ward (1.1%). Notably, Anopheles larvae were only detected in Magaoni ward. Culex larvae were most prevalent in Central ward (60.4%), followed by Nguvumali (12.9%).

Table 2: Sampled populations of Aedes, Anopheles, and Culex larvae

Wards	*Aedes*	*Culex*	*Anopheles*
Wards	N %	N %	N %
Central (port found)	1217 68.3	694 60.4	0 0
Chumbageni	132 7.4	77 6.7	0 0
Kiomoni	20 1.1	84 7.3	0 0
Magaoni	52 2.9	28 2.4	4 100
Mnyanjani	69 3.9	36 3.1	0 0
Mzizima	32 1.8	56 4.9	0 0
Ng/Kusini	47 2.6	26 2.3	0 0
Nguvumali	212 11.9	148 12.9	0 0

Key: N=number of larvae collected and %=percentage of larvae by ward surveyed

Larval indices – for Aedes mosquitoes

A total of 2,931 breeding sites were visited in 416 households. Of these, 60.8% (1,781/2,931) were positive for Aedes immatures. Various indices were calculated, including the Container Index (CI), House Index (HI), and Breteaux Index (BI). The highest CI values were observed in the port area (66.2%), 2.5 km away (51.5%), and 5 km away (44.6%). For the HI, the highest values were at 5 km (61.5%) and 2 km (60%) from the port, while the port area had the lowest HI (44%). Lastly, the highest BI values were found at 2 km (45.7%) and 5 km (30.3%) from the port, with the port area having the lowest BI (7.7%), as shown in Table 3 and Figure 4

Table 3: Summary of Ae. aegypti larval survey indices

Name of area	No. of premises	No. of positive premises	House Index (HI)	No. of Containers surveyed	No. of Positive containers	Container Index (CI)	Breteaux Index (BI)
Port area	150	66	44	1748	1158	66.2	7.7
2 km away	35	21	60	195	16	8.2	45.7
2.5 km away	122	66	54.1	68	35	51.5	28.9
5km away	109	67	61.5	74	33	44.6	30.3

Container Index (CI): ratio of larval infested to total inspected containers,

House Index (HI): ratio of larval infested houses to all inspected houses and

Breteaux Index (BI): ratio of positive containers per 100 houses inspected

Habitat characterization

During the habitat search for Aedes mosquitoes, the breeding sites were characterized based on physical parameters such as algal quantity, water source, watercolor, water movement, water type, and vegetation quantity (Table 4). A total of 2,931 breeding sites were identified, of which 22.65% (664/2,931) were used tires, 71.1% (2,085/2,931) were containers (both plastic and metal), 1.3% (38/2,931) were surface drains, 4.5% (132/2,931) were flowerpots, and 0.4% (12/2,931) were coconut shells. The majority of positive breeding habitats for Aedes mosquitoes had clear water (62.9%; 1,242/1,973), moderate vegetation (66.9%; 696/1,041), water resulting from rainfall (60.9%; 1,529/2,525), scarce algal quantity (60.8%; 1,033/1,698), and stagnant water (61%). The different habitat types of Aedes mosquitoes observed in the study area are shown in figures 5a and 5b.

Table 4: Physical characteristics of breeding habitats of Aedes mosquitoes identified in study area.

Parameter	Category	Positive n (%)	Negative n (%)	Total
Habitat type	Disposed containers*	1158(55.5)	927(44.5)	2085
	Coconut shell	12(100)	0	12
	Surface drains	15(39.5)	23(60.5)	38
	Flowerpots	100(75.8)	32(24.2)	132
	Tires	496(74.8)	167(25.2)	664
Alga quantity	None	360(57.4)	267(42.6)	627
	Moderate	372(65.1)	199(34.9)	571
	Scarce	1033(60.8)	665(39.2)	1698
	Abundant	16(47.1)	18(52.9)	34
Water source	Domestic	252(62.2)	153(37.8)	405
Water source	Rainwater	1529(60.6)	996(39.4)	2525
Water colour	Clear	1242(62.9)	731(37.1)	1973
Water colour	Polluted	539(56.3)	418(43.7)	957
Water movement	Stagnant	1777(61.1)	1134(38.9)	2911
Water movement	Slow	4(21.1)	15(78.9)	19
Water type	Permanent	530(52.8)	473(47.2)	1003
Water type	Temporary	1251(64.9)	676(35.1)	1927
Vegetation quantity	None	452(51.9)	419(48.1)	871
	Moderate	696(66.9)	345(33.1)	1041
	Scarce	454(61.1)	289(38.9)	743
	Abundant	179(65.1)	96(34.9)	275

Note (*): The disposed containers included plastic drums, buckets, tins, plastic barrels, basins, metal drums, jerrycans, and tanks.

Figure 5a: Common habitat types observed in the study area (clockwise from top left: Stream pool, plastic buckets for animal drinking, discarded car tires, discarded bowl holding water, used tires kept for protecting trees from pests, surface drain, and shallow well)

Figure 5b: Common habitat types observed in the study area (clockwise from top left: Flowerpots, inspection chamber, plastic container holding water placed under charcoal burner, fire hydrant, root hole of banana tree, container for feeding hens)

Association between habitat characteristics and mosquito densities

The GLM analysis revealed significant associations between certain habitat characteristics and mosquito densities. Disposed containers were the primary habitat for both Aedes aegypti and Culex quinquefasciatus mosquitoes, with a significant number of mosquitoes caught. Overall, the likelihood of capturing Aedes mosquitoes in disposed tires was about three times higher compared to disposed containers (RR = 2.75 [95% CI: 2.10, 3.59], p<0.001), as shown in Table 5. Other habitat types, such as coconut shells, drainage, flowerpots, and tires, were also preferred by mosquitoes but to varying degrees. Tires were notably more attractive to Aedes mosquitoes, with a mean density of 7.09 ± 2.12 and a highly significant p-value (<0.001). Statistical analysis indicated a strong preference for tires as habitats for Aedes mosquitoes (p<0.001).

Aedes species also preferred habitats with none or moderate algae over those with scarce or abundant algae, with statistically significant differences in preference for moderate algae levels (p<0.05). Rainwater, polluted water, stagnant water, and semi-permanent water bodies were generally associated with higher mosquito counts, especially for Aedes mosquitoes. The significance of these associations varied, with some being statistically significant and others not (Table 5). The presence of vegetation also influenced mosquito counts, with habitats with no vegetation generally showing higher counts, particularly for Aedes mosquitoes. The effect of vegetation quantity on mosquito abundance was less clear-cut.

Table 5: Mean number of mosquitoes collected in different habitat types (and 95% CI)

	Habitat Characteristics		Total	Mean± 2SE	RR [95%CI]	P-Values
Aedes aegypti	Habitat Type	Disposed containers	1158	4.3 ± 1.0	1
		Coconut shell	12	2.4 ± 1.2	0.9 [0.6, 2.4]	=0.846
		Surface drains	15	1.2 ± 0.8	0.8 [0.4, 1.6]	=0.528
		Flowerpots	100	3.0 ± 1.2	1.3 [0.9, 2.0]	=0.187
		Tires	496	7.1 ± 2.1	2.8 [2.1, 3.6]	<0.001
	Algae Quantity	None	360	13.0 ± 5.9	1
		Moderate	372	3.0 ± 0.9	0.6 [0.4, 0.9]	<0.05
		Scarce	1033	4.5 ± 1.0	0.7 [0.4, 1.0]	<0.05
		Abundant	16	3.2 ± 2.6	0.6 [0.2, 1.7]	=0.348
	Water Source	Domestic	252	3.1 ± 0.8	1
	Water Source	Rainwater	1529	5.0 ± 1.0	0.8 [0.6, 1.1]	=0.156
	Water Color	Clear	1242	5.1 ± 1.0	1
	Water Color	Turbid	539	3.7 ± 1.3	0.7 [0.6, 0.9]	<0.01
	Water Type	Permanent or Semi-Permanent	530	23.0 ± 8.0	1
	Water Type	Temporary	1251	3.4 ± 0.5	0.1 [0.1, 0.2]	<0.001
	Vegetation Quantity	None	452	14.6 ± 5.8	1
		Moderate	696	3.6 ± 0.6	1.1 [0.8, 1.6]	=0.638
		Scarce	454	3.7 ± 1.5	1.1 [0.6, 2.0]	=0.746
		Abundant	179	4.2 ± 2.2	0.9 [0.6, 1.3]	=0.414

Culex quinquefasciatus	Habitat Type	Disposed containers	927	3.5 ± 0.8	1
		Coconut shell	0	0	0.0 [0.0, 0.0]	0.999
		Surface drains	23	1.8 ± 0.6	0.8 [0.4, 1.7]	0.591
		Flowerpots	32	1.0 ± 0.6	0.5 [0.3, 0.8]	<0.01
		Tires	167	2.4 ± 1.0	1.1 [0.8, 1.4]	0.629
	Algae Quantity	None	267	9.5 ± 5.0	1
		Moderate	199	1.6 ± 0.3	0.5 [0.3, 0.9]	<0.05
		Scarce	665	2.9 ± 0.7	0.7 [0.4, 1.0]	=0.067
		Abundant	18	3.6 ± 2.0	1.6 [0.6, 4.5]	=0.401
	Water Source	Domestic	153	1.9 ± 0.7	1
	Water Source	Rainwater	996	3.2 ± 0.7	1.3 [1.0, 1.8]	=0.064
	Water Color	Clear	731	3.0 ± 0.8	1
	Water Color	Turbid	418	2.9 ± 1.0	1.3 [1.1, 1.7]	<0.05
	Water Type	Permanent or Semi-Permanent	473	20.6 ± 5.5	1
	Water Type	Temporary	676	1.9 ± 0.3	0.2 [0.1, 0.2]	<0.001
	Vegetation Quantity	None	419	13.5 ± 5.0	1
		Moderate	345	1.8 ± 0.3	0.6 [0.4, 1.1]	=0.057
		Scarce	289	2.4 ± 0.9	0.6 [0.4, 1.0]	<0.05
		Abundant	96	2.2 ± 0.5	0.6 [0.4, 1.1]	=0.095

Susceptibility of Aedes aegypti mosquitoes to public health insecticides

Susceptibility tests for female Aedes aegypti mosquitoes aged 3 to 5 days were conducted against five insecticides at various concentrations - including permethrin (0.5%, 0.75%), deltamethrin (0.05%, 0.5%), pirimiphos-methyl (1.25%, 2.5%), DDT (4%), and bendiocarb (0.5%, 1%). After 24hrs post-exposure, the average mortality rates for Aedes aegypti against bendiocarb (1%) and DDT (4%) were 98.75% and 100%, respectively, indicating full susceptibility. The average mortalities against pirimiphos-methyl (1.25%) and deltamethrin (0.05%) were 94.37%, 93.75%, respectively, suggesting possible or unconfirmed resistance. Increasing the dose of deltamethrin to 0.5% increased the 24-hr mortality to 96.25%, suggesting that even at this dose the mosquitoes were still slightly resistant. Tests against permethrin showed average mortality rates of 73.75% and 88.75%, indicating clear confirmed resistance even at the five times higher dose of 0.75%. In contrast the Aedes aegypti mosquitoes were fully susceptible to DDT and bendiocarb (Figure 6).

Figure 6: Results of the susceptibility tests for female Aedes aegypti mosquitoes showing mean mortality after 24hrs of monitoring post-exposure to the candidate insecticides. The dotted green lines (≥98% mortality) indicate full susceptibility, while the dotted blue lines (90-98% mortality) indicate possible resistance or unconfirmed resistance requiring confirmation

Awareness and perceptions of the risk of mosquito mosquito-borne diseases

Demographic characteristics of survey respondents

A total of 236 respondents participated in the survey within the port area and the nearby community (Table 6). Of the participants, 58.1% (n = 137) were male and 41.9% (n = 99) were female. Majority had a secondary level of education (47.0%, n = 111), with age interval between 36-45 years (36.4%, n = 86). Primary economic activities among respondents were entrepreneurship including self-employment (73.3%, n = 173), formal employment (16.5%, n = 39), fishing (3.0%, n = 7) and other port workers (4.7%, n = 11).

Table 6: Characteristics of study respondents at Tanga point of entry (N=236)

Category

Variable

No. Participants n (%)

Sex

Female

Male

99 (41.9%)

137 (58.1%)

Occupation

Entrepreneur

Fisherman

Health worker

Peasant

Port worker

Other

173 (73.3%)

7 (3.0%)

39 (16.5%)

2 (0.8%)

11 (4.7%)

4 (1.7%)

Age

18- 25

26 - 35

36 - 45

46 - 50

50-Above

45 (19.1%)

84 (35.6%)

86 (36.4%)

20 (8.5%)

1 (0.4%)

Education level

None

Primary

Secondary

College (certificate/diploma)

University

3 (1.3%)

47 (19.9%)

111 (47.0%)

60 (25.4%)

15 (6.4%)

Marital status

Married

Unmarried

Widow

131 (55.5%)

104 (44.1%)

1 (0.4%)

Awareness, perception and experience of mosquito-borne diseases among residents of Tanga seaport

The results from survey questionnaire revealed that about two thirds of the respondent reported that only female mosquitoes bite humans and transmit diseases 69.8% (n=134) while about one third reported that both sexes of mosquito bite human and transmit diseases 27.6% (n=53). Overall, about two thirds (64.8%, n = 153) of all respondents were aware of mosquitoes transmitting only malaria, and less than a third (26.3%, n = 62) were aware that mosquitoes also transmit dengue fever viruses. Chikungunya was far less recognized and was identified as a mosquito-borne disease by only 4 respondents (1.7%).

About 97.9% (n = 231) of the respondents perceived that there is a risk of contracting mosquito-borne diseases or infections at the seaport where only 5 respondents (2.1%) reported no perceived risk. Additionally, about two thirds of all respondents reported that workers at the port are perceived to be at greatest risk of mosquito-borne infections 61.4% (n=145) followed by community living nearby port area 28% (n=67) showing that people who resided around the seaport area, had the highest perception of risk compared to those away from the seaport. Lastly, the majority of the survey respondents reported being bothered by mosquito bites at night (53.4%; n = 126) and in the evening (40.7%; n = 96). Other than insecticide treated nets (ITNs), which were widely used for malaria prevention, only a smalls percentage of respondents reported using any other interventions against mosquito-borne diseases, these other interventions being use of long clothing (19.1%, n = 45), topical repellents (12.3%, n=29), and swatting with bare hands (11.9%, n = 28) as shown in table 7.

Table 7: Awareness, perception and experience of mosquito-borne diseases among residents of Tanga seaport.

Question asked

Variables

Percentages (n)

Do you know the sex of mosquito that bite human?

Yes

192 (81.4%)

44 (18.6%)

Which sex of mosquito biting human?

Female

Male

Both sex

134 (69.8%)

5 (0.6%)

53 ( 27.6% )

Which diseases you know are transmitted by mosquitoes?

Malaria

Chikungunya

Dengue

Malaria, Dengue, Chikungunya & Others

153 (64.8%)

4 (1.7%)

62 (26.3%)

17 (7.2%)

Is there any risk of contracting mosquito-borne diseases or infections while at seaport?

Yes

231 (97.9%)

5 (2.1%)

Which group is at greater risk of mosquito-borne infection in seaport?

All people

Nearby community

Fishers

Passengers/travelers at port

Undecided

Workers at port

4 (1.7%)

67 (28.4%)

2 (0.8%)

13 (5.5%)

5 (2.1%)

145 (61.4%)

Time at which mosquito bite more while at seaport

Evening

Morning

All the time

Night

Noon

96 (40.7%)

5 (2.1%)

7 (3%)

126 (53.4%)

2 (0.8%)

Personal protection methods used against mosquito biting at seaport

Swatting

Nothing

Use of long clothing

Use of repellents

28 (11.9%)

134 (56.8%)

45 (19.1%)

29 (12.3%)

Most studies on arbovirus vectors in Africa have been reactive to outbreaks or focused on large urban populations, neglecting high-risk areas like international points of entry, which can be hotspots for mosquito-borne viruses [53–57] Despite being of significant economic value, the international shipping activities at the ports can facilitate the migration of the vectors, and can pose significant threats in the absence of effective surveillance systems[26]. For this reason, strengthening the basic entomological surveillance systems at all major international points of entry has been recommended both by the International Health Regulations [58] and the Tanzania’s National Strategy for Vector Control (2019-2024) [40]. The aim of this study was therefore to compare the risks of disease-transmitting mosquitoes focus on Aedes within and in the surrounding urban areas of the eastern Tanzanian seaport of Tanga along the Indian ocean. To complement these entomological surveys, we also assessed the knowledge and perceptions of port users and residents of surrounding wards regarding the risk and control of mosquito-borne infections in the area.

The entomological study identified five mosquito species: An. gambiae s.l., An. funestus, Aedes aegypti, Culex quinquefasciatus, and Mansonia uniformis. The high abundance of Ae. aegypti in the port area suggests it is a hotspot for this species, consistent with findings from other studies [31,59]. The presence of discarded tires and containers likely contributes to this high density. While most Aedes mosquitoes were caught in outdoor BG Sentinel traps during the day, indicating significant outdoor biting activity, the Culex species were commonly found both indoors and outdoors. We note that the low numbers of Anopheles mosquitoes in the port area aligned with their ecological preference for rural areas and limited breeding opportunities in urban settings, resulting in low levels of malaria transmission. Overall, the findings of this study highlight the significant presence and distribution of key disease-transmitting mosquitoes, particularly Ae. aegypti, within the Tanga port area and its surrounding wards. The vector species preferred breeding in discarded tires and containers, such as water buckets and drums, consistent with findings from earlier studies [60,61]. These elevated densities underscore the importance of ports as critical points for mosquito surveillance and control – to address the risk of diseases such as dengue, chikungunya, and Zika. Field data from both the port and its surrounding wards clearly showed that, indeed, Aedes aegypti populations decreased with increasing distance from the port, confirming that the port area is a likely hotspot - potentially due to factors like stagnant water in containers and increased human activity.

Interestingly, while malaria remains the most recognized mosquito-borne disease among the respondents, awareness of dengue and other Aedes-transmitted diseases is considerably lower. Malaria is indeed also a significant public health problem in Tanzania though the risk in these urban settings is lower. The latest survey showed that malaria prevalence in Tanga was 4%, and in this survey, we found only a negligible number of Anopheles mosquitoes in the survey. According to the latest Demographic Health and Malaria Indicator Survey (TDHS&MIS 2022), household bed net use in Tanga was 84.2%, the percentage of children who had fevers in the preceding 2 weeks was 8.5% and overall malaria prevalence in children was 4% [11]. It is understandable why the communities continue with the emphasis on malaria but the neglect of Aedes-borne diseases is particularly concerning given the rising global incidence of dengue and the presence of Ae. aegypti in the region [35,38,54,62,63]. The limited use of personal protective measures, as indicated by our survey, further exacerbates the risk of mosquito-borne diseases. Other than bed nets, which protect people mostly at night-time, the majority of respondents did not use any form of protection against day-biting mosquito bites such as Ae. aegypti, with only a small fraction using methods such as long clothing or repellents. This highlights the urgent need for public health education campaigns to improve awareness and encourage the adoption of protective measures among port users and surrounding communities.

The susceptibility tests showed that Ae. aegypti were susceptible to Bendiocarb, but full susceptibility to DDT was observed, consistent with previous research in Ifakara, Tanzania [16]. However, reduced susceptibility to deltamethrin was detected consistent with previous study in Dar Es salaam [64], indicating possible resistance. The potential resistance to deltamethrin in our study may result from repeated chemical use in the area. Additionally, Ae. aegypti showed reduced susceptibility to pirimiphos-methyl, contradicting recent studies in Ifakara [16] and Nigeria [65]which reported full susceptibility. These differences might be due to either ecological differences or seasonal variations. Furthermore, the present study confirmed insecticide resistance of Aedes aegypti against permethrin similar to previous study in Dar Es salaam [64], one of the most common pyrethroids used in both agriculture and public health in the area. Overall, these investigations show that the available chemical options are increasingly limited and that greater vigilance is required. These tests should therefore be periodically repeated, preferably using more standardized tests with protocols designed specifically for Aedes aegypti mosquitoes as recommended by WHO [66]to best determine the range of options for control.

This study also revealed significant gaps in knowledge among port users and neighbouring residents regarding mosquito-borne diseases. While most participants were aware of malaria as a major public health problem, a very small proportion, consisting predominantly of people with tertiary education were aware of other mosquito borne diseases such as dengue and chikungunya viruses. This is a common phenomenon in malaria-endemic areas, where awareness of mosquito bites and their role in malaria transmission is commonly found to be higher, while knowledge about arboviral diseases transmitted by Aedes mosquitoes is notably low [67]. For instance, in one study in the Central African Republic, most respondents identified malaria as the sole mosquito-borne disease despite evidence of dengue and other mosquito-borne diseases in circulation [68]. It shows however that as these arboviruses become more significant public health challenge, greater efforts, including social and behaviour change communication strategies should be adopted to improve community knowledge on the diseases but also their prevention ad management.

In the assessment of community perceptions regarding groups at risk, a significant proportion of respondents acknowledged that port users and nearby communities are at risk of mosquito bites and infections – even though they did not distinguish between the different diseases. Moreover, people working at the port were considered to be at greater risk than the rest of the communities. Respondents also reported frequent mosquito bites, especially in the evening and at night, highlighting their exposure. This study aligns with previous research indicating that behavioral responses to infection risk are shaped by perceived exposure and bite frequency [69]. Despite recognizing their vulnerability, respondents showed poor adoption of personal protection measures. This mismatch of risk perception and self-protection was a surprise as previous studies have shown a direct correlation of these variables-people with high awareness being correlated with higher engagement in protective behaviors [70].

Although the main objectives were successfully achieved, this study had some limitations. First, the limited number of Aedes traps used for collecting adult mosquitoes may not have captured the full distribution effectively. Second, larvae and pupae collections were restricted to selected grids with human occupations or buildings, potentially leading to an underestimation of overall densities and distribution. Additionally, in the tests for insecticide susceptibility, WHO standard doses for Anopheles mosquitoes were used due to the lack of appropriate papers for testing Aedes mosquitoes. Some insecticides have different diagnostic concentrations specific for Aedes mosquitoes, which if used, might have yielded different results.

This study highlights the significant risk of Ae. aegypti and associated diseases within the Tanga port area, emphasizing the critical role of ports in the surveillance and control of mosquito-borne diseases, particularly those transmitted by Aedes mosquitoes. Despite the community being more concerned with malaria, awareness of other mosquito-borne diseases remains limited and should be enhanced given the observed risk. The high abundance of Ae. aegypti in the port area, especially in discarded tires and containers, underscores the need for targeted interventions and more broadly, environmental sanitation to reduce the risk. Insecticide susceptibility tests revealed full susceptibility to bendiocarb and DDT but emerging resistance to pirimiphos-methyl and deltamethrin, suggesting that the options for effective control may be limited and therefore there is need to for diversified control strategies. The study also revealed that the central port area, compared to the rest of the sites, is likely a hotspot for mosquito breeding, with Aedes populations decreasing with distance from the port. Since this study was the first dedicated mosquito survey to target this international point of entry, the results will form a basis for future research on pathogen transmission and also future control programs. The identification of key breeding habitats offers potential targets for Aedes control, emphasizing the need for integrated vector management involving community engagement, environmental management, and periodic insecticide rotation. Key recommendations are as follows: a) authorities should integrate environmental management, insecticide use, and community engagement to address discarded habitats; b) port health authorities should implement robust Aedes mosquito control measures to prevent potential outbreaks; c) future insecticide susceptibility studies should incorporate specific guidelines and appropriate concentrations for Aedes mosquitoes; d) educate port workers and nearby communities on mosquito control and prevention; and e) conduct year-round studies to understand seasonal variations in mosquito densities and resistance profiles. In conclusion, this study identified a relatively high potential risk of Ae. aegypti and associated diseases, but low perception of risk and inadequate personal protection measures in the study area. This low perception of risk highlights the need to improve public knowledge on transmission and control of Aedes-borne diseases

Acknowledgments

We would like to thank the team of the Mosquito Mobility Project of Ifakara Health Institute, Outdoor Mosquito Control (OMC) team, as well as our colleagues from the international project “Mobile Mosquitoes – understanding the entangled mobilities of Aedes mosquitoes and humans in India, Mexico, Tanzania and Germany” for their invaluable feedback and support throughout this survey. Special thanks is due to Richard Lumuli, Hussein Mwaiswelo, Julius Kihonda, Agnes Falle, Rukia Ahmed, Ridhia Mkabala, Chiku S. Mulula, Mwanamvua Jalala, Mwanamkasi Ally, Jumaa Jumaa, Hadija Kombo, Salma Kalovya, Shabani Dossa, Mwindadi Mohamed, Mwanamwaya Nyoro, Juma Mohamed, Thabiti Mitwango, Amina Kassim, Magesa B. Kusaga, Hussein J. Hussein, Maryam Kaguta, and Iddi H. Amani for their invaluable contributions to conducting the surveys, administering questionnaires, grids searching, habitat searches and laboratory procedures. We extend special thanks to colleagues MSc. Students undertaking Public Health Research from Nelson Mandela African Institution of Science and Technology including but not limited to Hassan Matimbwa, Salumu Chiamba, Aidi Lugenge, Fahad Mwakalebela, Muwonge Mukisa, Ampuriire Patience, and Sperancia Coelestine. Additionally, we extend our thanks to Maiko E. Kiberiti, the in-charge of Muheza Vector laboratory, students and staff at Muheza College of Health and Allied Sciences who contributed to this study.

Funding

Masters scholarship in Public Health Research awarded to the lead author funded by Ifakara Health Institute (IHI). Material, equipment and field activities were supported by Volkswagen Foundation (Grant Number 9B366) awarded to Ifakara Health Institute (IHI).

Availability of data and materials

All data generated from this study will be available from the corresponding authors upon request, the Ifakara Health Institute ethical review board in Tanzania with reference to ethical clearance certificate of (Protocol ID: IHI/IRB/No:39-2023) and the Medical Research Coordinating Committee (MRCC) at the National Institute for Medical Research, in Tanzania (Protocol ID: NIMR/HQ/R.8a/Vol.IX/4178).

Author contributions

Conceptualization: A.S.A., E.G.K., H.S.N., and F.O.O. Data curation: A.S.A, H.S.N, I.H.N., and D.S.M. Formal analysis: A.S.A, H.S.N., I.H.N., D.S.M., A.R.K., and F.O.O. Funding acquisition: F.O.O., N.F.K., and H.S.N. Investigation: A.S.A., HSN., N.F.K., E.G.K., and F.O.O. Methodology: A.S.A., A. J.S., Y.PM., N.F.K., M.L.F., M.B.K., A.S., H.S.N., E.E.K., and F.O.O. Project administration: A.S.A., H.S.N., R.M.N. Resources: A.S.A, R.A., H.J.H., F.O.O., H.S.N., and E.G.K. Supervision: F.O.O., and H.S.N. Validation: H.S.N., F.O.O., and E.G.K. Visualization: A.S.A, H.S.N., E.G.K., and F.O.O. Writing original draft: A.S.A., H.S.N., F.O.O., and E.G.K. Writing review & editing: All authors.

Ethics approval and consent to participate

Ethical approvals for this project were obtained from Ifakara Health Institute’s Institutional Review Board (Protocol ID: IHI/IRB/No:39-2023) and the Medical Research Coordinating Committee (MRCC) at the National Institute for Medical Research, in Tanzania (Protocol ID: NIMR/HQ/R.8a/Vol.IX/4178). Written consents were sought from all participants of this study, after they had understood the purpose and procedure of the study.

Consent for publication

Permission to publish this study was obtained from National Institute for Medical Research, in Tanzania Ref No. BD.242/437/01C/26.

Competing interests

The authors declare that they have no competing interests.

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Risk of Aedes-Borne Diseases in and around the Tanzanian Seaport of Tanga Despite Community Members Being More Concerned About Malaria

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Version 1

Abstract

Figures

Background

Methods

Study Area

Sampling design and site selection

Sampling of adult mosquitoes

Sampling of immature mosquitoes and characterization of their aquatic habitats

Testing the susceptibility of mosquitoes to insecticides

Survey of opinions and perceptions of port users and residents of neighboring wards

Statistical analysis and presentation

Results

Larval indices – for Aedes mosquitoes

Habitat characterization

Awareness, perception and experience of mosquito-borne diseases among residents of Tanga seaport

Discussion

Conclusion

Declarations

References

Additional Declarations

Status:

Version 1