Dengue Vector Distribution and their Infection Status in Selected Regions in Tanzania

Dengue fever is an important arboviral infection globally. Tanzania has experienced multiple dengue outbreaks since 2010 leading to mortalities and public distress. Dengue is caused by viruses which are transmitted to humans by vector mosquitoes. Nevertheless, the abundance, distribution and extent of viral infections of these vectors are poorly understood. The aim of this study was to characterize dengue vectors and determine their virus infection rates. Adult mosquitoes were collected from selected regions in Tanzania including Dar es Salaam, Tanga, Coast, and Arusha regions using CO2 baited mosquito magnet traps between December 2018 to February 2019, additional samples were collected during dengue epidemic in June 2019. Samples were fixed in RNA later and preserved at –20 °C for virus detection using Reverse Transcriptase – Polymerase Chain Reaction (RT-PCR). A total of 1530 mosquitoes were collected and morphologically identified as: Aedes (75%), Culex (13%), Anopheles (10%) genera and 2% other mosquitoes. All Aedes mosquitoes were identified as Aedes aegypti of which 46% were from Dar es Salaam, 31% Tanga, 21% Coast and 2% from Arusha. The abundance of Ae. aegypti significantly differed across sampling locations (p = 4.6425E–09), and the virus infection rate was 2%. The presence of these vectors and the detection of dengue viruses is an indication of ongoing arboviral activities necessitating intensification of vector control programmes. Keywords: Aedes aegypti; dengue vectors; arboviruses; Tanzani

Larvicidal potency of Dioscorea sansibarensis leaf extract against vector mosquitoes: Anopheles gambiae s.s. and Culex quinquefasciatus

Mosquitoes are responsible for transmission of illnesses of public health importance including malaria, lymphatic filariasis, dengue, chikungunya, and many other diseases caused by viruses. Vector control using synthetic insecticides has been the cornerstone for management of vector-borne diseases. However, the chemical based interventions have not been sustainable due to emergency of resistance against insecticides among disease vectors. Plant based mosquitocidal products can be potential alternative tools in vector control. Therefore, the present study aimed at exploring the larvicidal properties of Dioscorea sansibarensis leaf extract against malaria and lymphatic filariasis vectors; Anopheles gambiae s.s. and Culex quinquefasciatus. The larvicidal activities of Dioscorea sansibarensis were assessed following WHO test procedures. Ethanol leaf extract of Dioscorea sansibarensis was evaluated against all the four instar larvae stages of An. gambiae s.s and Cx. quinquefasciatus susceptible laboratory colonies. The highest larvicidal potency was shown against the 4th instar stages of both species with the LC50 values of 60.915 ppm and 80.700 ppm for Cx. quinquefasciatus and An. gambiae s.s., respectively. The respective LC95 values for Cx. quinquefasciatus and An. gambiae s.s. were 168.898 ppm and 249.295 ppm. This implies that the extract can be applied as mosquito larvicide should its impact on non-targeted species be established. Keywords: Dioscorea sansibarensis; vectors, mosquitoes, Zanzibar yams, Dar es Salaam, Tanzani

The Impact of Insecticide Pre-Exposure on Longevity, Feeding Succession, and Egg Batch Size of Wild Anopheles gambiae s.l.

Background. Insecticide resistance among the vector population is the main threat to existing control tools available. The current vector control management options rely on applications of recommended public health insecticides, mainly pyrethroids through long-lasting insecticidal nets (LLINs) and indoor residual spraying (IRS). Regular monitoring of insecticide resistance does not provide information on important factors that affect parasite transmission. Such factors include vector longevity, vector competence, feeding success, and fecundity. This study investigated the impacts of insecticide resistance on longevity, feeding behaviour, and egg batch size of Anopheles gambiae s.l. Method. The larval sampling was conducted in rice fields using a standard dipper (350 ml) and reared to adults in field insectary. A WHO susceptibility test was conducted using standard treated permethrin (0.75%) and deltamethrin (0.05%) papers. The susceptible Kisumu strain was used for reference. Feeding succession and egg batch size were monitored for all survivors and control. Results. The results revealed that mortality rates declined by 52.5 and 59.5% for permethrin and deltamethrin, respectively. The mortality rate for the Kisumu susceptible strain was 100%. The survival rates of wild An. gambiae s.l. was between 24 and 27 days. However, the Kisumu susceptible strain blood meal feeding was significantly higher than resistant colony (t = 2.789, df = 21, P=0.011). Additionally, the susceptible An. gambiae s.s. laid more eggs than the resistant An.gambiae s.l. colony (Χ2 = 1366, df = 1, P≤0.05). Conclusion. It can, therefore, be concluded that the wild An. gambiae s.l. had increased longevity, blood feeding, and small egg batch size compared to Kisumu susceptible colonies

New record of Pithophora roettleri (Roth) Wittrock, 1877 (Chlorophyta: Pithophoraceae) for the São Francisco River basin and its potential geographic distribution in Brazil

Aedes aegypti (Diptera: Culicidae) is the main vector of the dengue virus globally. Dengue vector control is mainly based on reducing the vector population through interventions, which target potential breeding sites. However, in Tanzania, little is known about this vector's habitat productivity and insecticide susceptibility status to support evidence-based implementation of control measures. The present study aimed at assessing the productivity and susceptibility status of A. aegypti mosquitoes to pyrethroid-based insecticides in Dar es Salaam, Tanzania. An entomological assessment was conducted between January and July 2015 in six randomly selected wards in Dar es Salaam, Tanzania. Habitat productivity was determined by the number of female adult A. aegypti mosquitoes emerged per square metre. The susceptibility status of adult A. aegypti females after exposure to 0.05% deltamethrin, 0.75% permethrin and 0.05% lambda-cyhalothrin was evaluated using the standard WHO protocols. Mortality rates were recorded after 24 h exposure and the knockdown effect was recorded at the time points of 10, 15, 20, 30, 40, 50 and 60 min to calculate the median knockdown times (KDT50 and KDT95).\ud The results suggest that disposed tyres had the highest productivity, while water storage tanks had the lowest productivity among the breeding habitats Of A. aegypti mosquitoes. All sites demonstrated reduced susceptibility to deltamethrin (0.05%) within 24 h post exposure, with mortalities ranging from 86.3 ± 1.9 (mean ± SD) to 96.8 ± 0.9 (mean ± SD). The lowest and highest susceptibilities were recorded in Mikocheni and Sinza wards, respectively. Similarly, all sites demonstrated reduced susceptibility permethrin (0.75%) ranging from 83.1 ± 2.1% (mean ± SD) to 96.2 ± 0.9% (mean ± SD), in Kipawa and Sinza, respectively. Relatively low mortality rates were observed in relation to lambda-cyhalothrin (0.05%) at all sites, ranging from 83.1 ± 0.7 (mean ± SD) to 86.3 ± 1.4 (mean ± SD). The median KDT50 for deltamethrin, permethrin and lambda-cyhalothrin were 24.9-30.3 min, 24.3-34.4 min and 26.7-32.8 min, respectively. The KDT95 were 55.2-90.9 min for deltamethrin, 54.3-94.6 min for permethrin and 64.5-69.2 min for lambda-cyhalothrin. The productive habitats for A. aegypti mosquitoes found in Dar es Salaam were water storage containers, discarded tins and tyres. There was a reduced susceptibility of A. aegypti to and emergence of resistance against pyrethroid-based insecticides. The documented differences in the resistance profiles of A. aegypti mosquitoes warrants regular monitoring the pattern concerning resistance against pyrethroid-based insecticides and define dengue vector control strategies