BackgroundIn 2010, 2012, 2013 and 2014 dengue outbreaks have been reported in Dar es Salaam, Tanzania. However, there is no comprehensive data on the risk of transmission of dengue in the country. The objective of this study was to assess the risk of transmission of dengue in Dar es Salaam during the 2014 epidemic.Methodology/Principal FindingsThis cross-sectional study was conducted in Dar es Salaam, Tanzania during the dengue outbreak of 2014. The study involved Ilala, Kinondoni and Temeke districts. Adult mosquitoes were collected using carbon dioxide-propane powered Mosquito Magnet Liberty Plus traps. In each household compound, water-holding containers were examined for mosquito larvae and pupae. Dengue virus infection of mosquitoes was determined using real-time reverse transcription polymerase chain reaction (qRT-PCR). Partial amplification and sequencing of dengue virus genome in infected mosquitoes was performed. A total of 1,000 adult mosquitoes were collected. Over half (59.9%) of the adult mosquitoes were collected in Kinondoni. Aedes aegypti accounted for 17.2% of the mosquitoes of which 90.6% were from Kinondoni. Of a total of 796 houses inspected, 38.3% had water-holding containers in their premises. Kinondoni had the largest proportion of water-holding containers (57.7%), followed by Temeke (31.4%) and Ilala (23.4%). The most common breeding containers for the Aedes mosquitoes were discarded plastic containers and tires. High Aedes infestation indices were observed for all districts and sites, with a house index of 18.1% in Ilala, 25.5% in Temeke and 35.3% in Kinondoni. The respective container indices were 77.4%, 65.2% and 80.2%. Of the reared larvae and pupae, 5,250 adult mosquitoes emerged, of which 61.9% were Ae. aegypti. Overall, 27 (8.18) of the 330 pools of Ae. aegypti were positive for dengue virus. On average, the overall maximum likelihood estimate (MLE) indicates pooled infection rate of 8.49 per 1,000 mosquitoes (95%CI = 5.72–12.16). There was no significant difference in pooled infection rates between the districts. Dengue viruses in the tested mosquitoes clustered into serotype 2 cosmopolitan genotype.Conclusions/SignificanceAe. aegypti is the main vector of dengue in Dar es Salaam and breeds mainly in medium size plastic containers and tires. The Aedes house indices were high, indicating that the three districts were at high risk of dengue transmission. The 2014 dengue outbreak was caused by Dengue virus serotype 2. The high mosquito larval and pupal indices in the area require intensification of vector surveillance along with source reduction and health education.
BackgroundDengue is the second most important vector-borne disease of humans globally after malaria. Incidence of dengue infections has dramatically increased recently, potentially due to changing climate. Climate projections models predict increases in average annual temperature, precipitation and extreme events in the future. The objective of this study was to assess the effect of changing climate on distribution of dengue vectors in relation to epidemic risk areas in Tanzania.Methods/FindingsWe used ecological niche models that incorporated presence-only infected Aedes aegypti data co-occurrence with dengue virus to estimate potential distribution of epidemic risk areas. Model input data on infected Ae. aegypti was collected during the May to June 2014 epidemic in Dar es Salaam. Bioclimatic predictors for current and future projections were also used as model inputs. Model predictions indicated that habitat suitability for infected Ae. aegypti co-occurrence with dengue virus in current scenarios is highly localized in the coastal areas, including Dar es Salaam, Pwani, Morogoro, Tanga and Zanzibar. Models indicate that areas of Kigoma, Ruvuma, Lindi, and those around Lake Victoria are also at risk. Projecting to 2020, we show that risk emerges in Mara, Arusha, Kagera and Manyara regions, but disappears in parts of Morogoro, Ruvuma and near Lake Nyasa. In 2050 climate scenario, the predicted habitat suitability of infected Ae. aegypti co-occurrence with dengue shifted towards the central and north-eastern parts with intensification in areas around all major lakes. Generally, model findings indicated that the coastal regions would remain at high risk for dengue epidemic through 2050.Conclusion/SignificanceModels incorporating climate change scenarios to predict emerging risk areas for dengue epidemics in Tanzania show that the anticipated risk is immense and results help guiding public health policy decisions on surveillance and control of dengue epidemics. A collaborative approach is recommended to develop and adapt control and prevention strategies.
BackgroundMalaria prevalence and transmission intensity in Tanzania is heterogeneous with spatial and temporal variations between geographical areas and ecological systems. The objective of this study was to determine the prevalence of malaria, anaemia and nutritional status in relation to livelihoods, ecosystem and health systems in Kilosa District in central Tanzania.MethodsThis study was conducted in four villages, two characterised by rice irrigation ecosystem and the other two by dry savannah ecosystem and pastoral livelihoods. In each ecosystem, one of the villages had a healthcare facility. Schoolchildren were screened for malaria infection using malaria rapid diagnostic test (mRDT) and microscopy and they were assessed for their anaemia and nutritional statuses.ResultsA total of 1,019 school children (age = 4–16 years) were screened for malaria infection. The overall prevalence of Plasmodium falciparum infection was 10.6 % and 4.5 % by mRDT and microscopy, respectively. Children from pastoral villages had lower (2.9 %) prevalence of malaria than their counterparts (18.2 %) in the rice irrigation villages. A significantly high risk of malaria was observed among children in rice irrigation than in the pastoral ecosystem (OR: 0.13; 95%CI 0.07, 0.23). Children living in areas with health care facilities had a low odd of malaria infection by 45 % (OR: 0.55; 95 % CI = 0.35, 0.86). Overall, the prevalence of anaemia in the district was 43.4 % (n = 775); and 58.3 % of those with severe anaemia were among children from the pastoral villages. Anaemia was significantly higher among children not using mosquito nets (p = 0.049); and among those with malaria infection (p <0.001). The majority (96 %) of the children had Body Mass Index less than 18.5 kg/m2 which indicate high proportion of underweight.ConclusionThere are significant variations in the risk of acquiring malaria infection between different ecosystems and livelihoods. These findings suggest that malaria control programmes must take into account ecosystems and livelihoods of the targeted population through an integrated management of malaria and nutrition approach.
This study was carried out to determine the spatial variations in malaria mosquito abundance and human biting rate in five villages representing rice-irrigation and savannah ecosystems in Kilosa District, central Tanzania. The study involved five villages namely Tindiga and Malui (wetland/rice irrigation), Twatwatwa and Mbwade (dry savannah) and Kimamba (wet savannah). Indoor mosquitoes were sampled using Centers for Disease Control and Prevention light traps in three houses in each village. Anopheles gambiae s.l. molecular identification was carried out using polymerase chain reaction (PCR). A total of 936 female mosquitoes were collected. About half (46.9%) were malaria mosquitoes (Anopheles gambiae s.l.=28.6%; An. funestus= 18.3%). A total of 161 (60.1%) of the morphologically identified An. gambiae s.l. (268) and subjected to PCR analysis for speciation were genotyped as An. arabiensis. The An. funestus complex mosquitoes were composed of An. funestus funestus and An. rivulorum at the 5:1 ratio. On average, 17.9 Anopheles mosquitoes were collected per village per day. Two-thirds (62.8%) of the malaria mosquitoes were collected in Malui (rice agro-ecosystem) and the lowest number (2.3%) in Twatwatwa (dry savannah ecosystem). The biting rate per person per night for An. arabiensis+An. funestus s.s. was highest in Malui (46.0) and lowest in Twatwatwa (1.67). The parity rate of the An. funestus mosquitoes was lower compared to that of An. arabiensis and none of the mosquitoes was infected with malaria sporozoites. In conclusion, An. arabiensis is the most abundant malaria vector in Kilosa district and its variation is related to the ecological system. The heterogeneity in malaria mosquito abundance and human biting rate could be used to guide selection of locally appropriated control interventions.
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