The Risk of Dengue Virus Transmission in Dar es Salaam, Tanzania during an Epidemic Period of 2014

Abstract

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.

Description and lessons learned from the 2014 Dengue outbreak in Dar es Salaam, Tanzania. Knowledge, attitudes and bite prevention practices among those with confirmed Dengue

“…aegypti to measure its efficiency for predicting suitable habitats and areas where targeted environmental management should be conducted. However, data agree well with work of Mboera and colleagues [27] in Dar es Salaam and Lutomiah et al [36] and Ngugi [37] in Mombasa, who identified large items of household waste such as buckets and tyres to be the most important sources of mosquitoes as was seen here in Kinondoni.…”

“…africanus, which maintains sylvatic yellow fever, or Ae. albopictus that is a dengue vector currently invading into a number of African countries [40] but has not yet been found in Tanzania [27,41]. Study findings show that higher quality breeding habitats in relatively more wealthy households are likely to be a potential source of Dengue vectors.…”

“…Salaam it is of great significance to prevent future outbreaks through targeted control of Dengue vectors and disseminating appropriate behaviour change communication messages to 1) improve household level environmental modification or destruction of breeding sites around homes, 2) to encourage adherence to personal protection and 3) identification of disease symptoms of the disease as is successfully used in many endemic countries [24]. Future outbreaks have a high probability of occurring more frequently since there have been outbreaks in 2007-8 [7], 2010 (Type III detected in Zanzibar ) [25], 2013 (Type II) [26] and 2014 (Type II) [27] as well as locally reported cases in 2017)…”

Distribution ofAedesmosquitoes in the Kilimanjaro Region of northern Tanzania

“…Although Ae. aegypti has been reported to be responsible for DENV epidemics in the low-altitude coastal region of Tanzania, 8 the presence of Aedes mosquitoes has not been described in the high altitudes of the Kilimanjaro Region.…”

Advances in Dengue Vaccine: A Review Study

“…Certain genotypes within particular serotypes are associated with epidemics of dengue hemorrhagic fever (DHF) vs. classic dengue [11,13]. Aedes aegypt mosquitoes are the primary vectors of DENV throughout the tropics [14]. DENV infection is categorized as asymptomatic infection, subclinical infection, undifferentiated fever, dengue fever, DHF with or without dengue shock syndrome (DSS) and other severe forms of dengue.…”