Epidemic risk of arboviral diseases: Determining the habitats, spatial-temporal distribution, and abundance of immature Aedes aegypti in the Urban and Rural areas of Zanzibar, Tanzania

Abstract

Background In Zanzibar, little is known about the arboviral disease vector Aedes aegypti in terms of abundance, spatio-temporal distribution of its larval habitats or factors associated with its proliferation. Effective control of the vector requires knowledge on ecology and habitat characteristics and is currently the only available option for reducing the risk of arboviral epidemics in the island nation of Zanzibar. Methodology We conducted entomological surveys in households and surrounding compounds from February to May 2018 in the urban (Mwembemakumbi and Chumbuni) and rural (Chuini and Kama) Shehias (lowest government administrative unit) situated in the Urban-West region of Unguja island, Zanzibar. Larvae and pupae were collected, transported to the insectary, reared to adult, and identified to species level. Characteristics and types of water containers were also recorded on site. Generalized linear mixed models with binomial and negative binomial distributions were applied to determine factors associated with presence of Ae. aegypti immatures (i.e. both larvae and pupae) or pupae, alone and significant predictors of the abundance of immature Ae. aegypti or pupae, respectively. Results The survey provided evidence of widespread presence and abundance of Ae. aegypti mosquitoes in both urban and rural settings of Unguja Island. Interestingly, rural setting had higher numbers of infested containers, all immatures, and pupae than urban setting. Likewise, higher House and Breteau indices were recorded in rural compared to the urban setting. There was no statistically significant difference in Stegomyia indices between seasons across settings. Plastics, metal containers and car tires were identified as the most productive habitats which collectively produced over 90% of all Ae. aegypti pupae. Water storage, sun exposure, vegetation, and organic matter were significant predictors of the abundance of immature Ae. aegypti. Conclusions Widespread presence and abundance of Ae. aegypti were found in rural and urban areas of Unguja, the main island of Zanzibar. Information on productive habitats and predictors of colonization of water containers are important for the development of a routine Aedes surveillance system and targeted control interventions in Zanzibar and similar settings.

Risk factors for occurrence and abundance of Aedes aegypti and Aedes bromeliae at hotel compounds in Zanzibar

“…A great number of studies have reported strong associations between the abundance of Aedes mosquitoes and their larval habitats and poorly managed disposables as well as decorative containers [ 49 – 51 ]. These materials can hold water and organic debris for long periods, providing relatively stable micro-environmental and microclimatic conditions for proliferation of diverse mosquito species [ 24 , 25 , 51 , 52 ]. We also found high productivity of Aedes mosquitoes, particularly Ae.…”

“…aegypti and Ae. bromeliae across urban and rural areas of Zanzibar Island (also known as Unguja) has also been recently confirmed [ 23 – 25 ]. Infestation of Zanzibar Archipelago by these vectors is a serious threat, as arboviral epidemics will have devastating impacts on the fragile public health system and the tourism-based economy.…”

Microbial composition in larval water enhances Aedes aegypti development but reduces transmissibility of Zika virus

“…Urban-adapted Ae. aegypti larvae are known to develop within open containers including cemetery headstones, plant pots, rain barrels, abandoned tires, and bromeliads, which tend to accumulate nutrients and organic matter (17,(52)(53)(54). Outdoor and laboratory water sources were used in this study (Supplemental Table 1).…”

Emerging epidemics: is the Zanzibar healthcare system ready to detect and respond to mosquito-borne viral diseases?

“…These findings suggest that circulation of DENVs on the Zanzibar islands is under-recognized, as most likely for other arboviruses. Notably, we recently identified widespread infestation of urban and rural communities on Unguja Island by Aedes aegypti , the main vector of dengue, chikungunya, yellow fever and Zika viruses [ 27 , 28 ].…”

“…While available findings [ 27 , 28 ] suggest an overt risk of epidemic spread of MBVDs throughout all communities of the archipelago, this risk is projected to remain high through 2050 in the coastal regions of Tanzania including Zanzibar due to expanding presence of infected Aedes aegypti [ 29 ]. As evidenced by the 2005–2006 chikungunya outbreak on La Reunion, large-scale MBVD epidemics can have devastating social and economic consequences to small-island communities such as Zanzibar that are heavily dependent on global tourism [ 30 ].…”