Prevalence of dengue and diversity of cultivable bacteria in vector Aedes aegypti (L.) from two dengue endemic districts, Kanchanpur and Parsa of Nepal

Abstract

BackgroundDengue fever, an endemic arboviral disease, represents one of the major public health concerns in Nepal. It is transmitted by bites of infected Aedes aegypti and Aedes albopictus, the former being primary vector. The bacterial community plays a significant role in biology of mosquitoes; however, the bacterial communities of primary vector A. aegypti remain unstudied in Nepal. The study was designed to determine the rate of dengue seropositivity and to explore the bacterial diversity of A. aegypti from dengue endemic districts, Kanchanpur and Parsa of Nepal.MethodsA cross-sectional study was conducted between June 2013 and November 2013 at two hospitals of Kanchanpur and Parsa. A total of 221 serum samples were collected from patients (inpatients and outpatients) suspected of suffering from dengue fever and attending Mahakali Zonal Hospital, Mahendranagar, Kanchanpur, and Narayani Zonal Hospital, Birgunj, Parsa. Detection of anti-dengue IgM was performed by using human dengue IgM capture ELISA. The larvae and pupae of mosquitoes (A. aegypti) were collected, reared, and emerged. Then, the bacteria were isolated and identified from the gut of identified mosquitoes by using standard methods.ResultsOut of total 221 serum samples collected from patients suspected of suffering from dengue fever, 34 (15.38%) were positive for anti-dengue IgM. Gram-negative bacteria were isolated in largest proportion (63%) followed by gram-positive cocci (23.27%) and gram-positive rods (13.73%). The most common cultivable bacteria isolated were Staphylococcus spp., Pseudomonas spp., and Acinetobacter spp. The average bacterial load in the vectors was 3.91 × 104 cfu/ml.ConclusionsHigh rate of anti-dengue IgM seropositivity was reported in our study. The environmental bacteria were predominantly isolated and identified in A. aegypti. The paratransgenic approach to control vector might be possible by spreading the genetically modified bacteria in larval habitat or shelter of adult mosquitoes.

Dengue periodic outbreaks and epidemiological trends in Nepal

“…The dengue-wave spread from Terai region and was detected every year in that particular Terai region. The Chitwan and Rupandehi districts in the Terai region of Nepal were focal epidemics during the outbreak in 2010, 2013 and 2016 [ 10 , 12 , 13 ]. Not only in the lowland inner Terai region (Parsa district), which is 300 m below sea level, DENV have been reported in the valleys of upland Hill regions at an altitude of 2500 m above sea level [ 14 ] (Fig.…”

Leishmania, microbiota and sand fly immunity

“…These are known to have an impact on L. longipalpis or other insects immunity (Boulanger et al , 2004 ; Telleria et al , 2013 ; Booth et al , 2015 ; Heerman et al , 2015 ; Husseneder et al , 2017 ; Keita et al , 2017 ). Other identified genera including Acinetobacter , Burkolderia , Citrobacter , Enterobacter , Pseudomonas and Ralstonia are commonly associated with Phlebotomus , mosquitoes, other insects or plants (Warburg, 1991 ; Dillon et al , 1996 ; Eilmus and Heil, 2009 ; Akhoundi et al , 2012 ; Maleki-Ravasan et al , 2015 ; Lalithambika and Vani, 2016 ; Sun et al , 2016 ; Husseneder et al , 2017 ; Takeshita and Kikuchi, 2017 ; Thapa et al , 2017 ; Osimani et al , 2018 ; Song et al , 2018 ; Ventura et al , 2018 ). Interestingly, Caulobacter genus that comprises environmental associated microbes was found in L. longipalpis as well as in glassy-winged sharpshooter Homalodisca vitripennis (Rogers and Backus, 2014 ) but very little is known about this bacterium.…”

“…Identified bacteria across larvae, pupae and adults collected from the same locality included Enterobacter, Pseudomonas, Bacillus and Lysobacter genera (Vivero et al, 2016). Interestingly, these bacterial genera are abundant in soil (Manfredi et al, 2015;Thapa et al, 2018). The presence of microbial strains in both larvae and adult sand flies will likely increase its utility in developing biological tools to control diseases transmitted by New World sand fly species.…”

Profile of the 2016 dengue outbreak in Nepal

“…The geographical footprint of both the Ae. aegypti vector and dengue disease has expanded from the Terai lowland of southern Nepal and now includes the most populous urban area, Kathmandu, located in a highland region of central Nepal [ 19 ]. As observed in previous outbreaks as well, there was a sharp increase in both the number of mosquitos and number of dengue disease cases during and soon after the monsoon season of June–September in 2016.…”