Background The lack of information on behavioural patterns of Aedes aegypti and Aedes albopictus has become a significant limitation in vector control and disease management programmes. Therefore, the current study was focused on determining some bionomics aspects: breeding, resting, host-seeking and feeding preferences of Ae. aegypti and Ae. albopictus in Sri Lanka. Methods Larval and adult surveys were conducted from April 2017 to April 2019 monthly in six selected Medical Officer of Health (MOH) areas in Gampaha Distinct, Western province, Sri Lanka, representing urban, suburban and rural settings. Resting preferences of adult mosquitoes were observed from indoor and outdoor places using a Prockopack aspirator. The information on resting height, surface, material and locality was recorded. Human-baited double-net traps were used to determine the host-seeking time of Aedes mosquitoes. Statistical differences in the spatial distribution of mosquitoes in selected MOH areas and prevalence of vectors were analysed using general linear model (GLM). A chi-square test was used to analyse the resting behaviour. Results Total of 19,835 potential breeding sites were examined at 13,563 premises, and 18.5% (n = 1856) were positive for Aedes larvae. Distribution of Ae. aegypti and Ae. albopictus was statistically significant at species level (df = 1; F = 137.134; P < 0.05 GLM) and study setting (df = 2; F = 8.125; P < 0.05). Aedes aegypti breeding was found mainly in temporary removals (18.8%; n = 34), discarded non-degradables (12.15%; n = 22) and tyres (9.95%; n = 18). Natural (14.7%; n = 246) and temporary removals (13.6%; n = 227) and discarded non-reusable items were the key ovipositing sites for Ae. albopictus. In the adult mosquito survey, the majority was comprised of Ae. albopictus (54.5%; n = 999), which denoted exophilic nature (90.8%; n = 758), and 45.5% (n = 835) represented by Ae. aegypti mosquitoes who were mainly endophilic (84.3%; n = 842). Aedes aegypti rested on cloth hangings and curtains, followed by the furniture, while Aedes albopictus was predominant in outdoor vegetation. In both vectors, biting patterns denoted a typical diurnal pattern with two peaks of host-seeking and biting activity in the morning and afternoon. Conclusions The majority (80%) of the larval habitats were artificial containers. The use of larvicides for vector control as the prominent measure is questionable since applying these chemicals may target only 20% of the total breeding grounds, which are permanent. The resting places of adult mosquitoes are mainly indoors. Therefore, using thermal space spraying of insecticide may not be appropriate, and indoor residual spraying is recommended as a suitable intervention to target adult mosquitoes. This study warrants a holistic vector control approach for all medically important mosquitoes and insects, ensuring the rational use of finance and resources. Graphical Abstract
Background. To date, dengue is considered an important public health problem in Sri Lanka. Irrational use of insecticides without evidence-based applications has primed the development of resistance in mosquito vectors. Method. The present study investigated the resistance status of Aedes aegypti and Aedes albopictus to commonly used insecticides in three selected Medical Officer of Health (MOH) areas (i.e., Attanagalla, Dompe, and Negombo) in Gampaha District, Western Province of Sri Lanka. Entomological surveys were performed using ovitraps and larval collections. Larval bioassays were carried out to determine the LC50, LC90, and LC95 and susceptibility status for organophosphate temephos, whereas adult bioassays were performed to test the 0.03% deltamethrin and 0.8% malathion susceptibility. Results. The study revealed that the temephos concentrations required to control Ae. aegypti (13.7-17.7 times) and Ae. albopictus (4.6-7.6 times) are higher than the diagnostic concentration (0.012 mg/L) proposed by the World Health Organization. The highest resistance levels were observed for both Ae. aegypti ( 14 ± 1.87 ) and Ae. albopictus ( 36 ± 1.87 ) collected from the Negombo MOH area. Therefore, the WHO recommended diagnostic concentration is no longer effective in controlling Ae. aegypti and Ae. albopictus larvae in these areas. Both the dengue vectors have evolved a high level of insecticide resistance to malathion and deltamethrin in the Gampaha District except Ae. albopictus mosquitoes in rural areas. Further, vectors in rural areas are indicated susceptible (>98%) to pyrethroids and emergence of resistance (<97%) for organophosphate insecticides. Conclusion. The results of this study warrant the vector management authorities on the proper application of insecticides and rational use in vector control. The susceptibility status of vector mosquitoes should be continuously monitored especially in dengue-endemic areas parallel to the routine surveillance programme. Further molecular studies are strongly recommended to determine the Knockdown Resistance (kdr) mutations among Aedes populations.
Background The aim was to investigate an emerging focus of cutaneous leishmaniasis (CL) in Gampaha district, Western Sri Lanka. Methods Sociodemographics of CL patients in Mirigama, Gampaha district, were compared with controls using a structured questionnaire. Clinical data and geographic positioning system coordinates of patients were recorded. Sandflies collections were performed in four selected sites using indoor hand collection (162 units) and cattle-baited net traps (n=3). Results Of 73 patients (mean age 43.6 y; SD 20), 58.9% were males. Lesions consisted of nodules (52.1%) and ulcers (47.9%). Single lesions were seen in 69.9% of patients, while 30.1% had multiple lesions. Except for one mucosal lesion, all the others were cutaneous. Treatment consisted of sodium stibogluconate and cryotherapy (46.6%), sodium stibogluconate (45.2%) or cryotherapy (8.2%). Multiple lesions were more likely to receive combination therapy (p=0.013). The majority of those employed (81.1%; 27/33) were engaged in outdoor work. Male gender, low education attainment and poor disease awareness were significant risk factors for CL (p<0.05). Four households reported multiple cases. Phlebotomus argentipes was detected in all cattle-baited net traps and 35.3% of indoor hand collection units. Conclusions CL is emerging in Gamapha district with Mirigama as the epicentre. Case distribution indicates local transmission, with P. argentipes as the probable vector.
Background: Cutaneous leishmaniasis (CL) appears to be spreading to previously non-endemic regions of Sri Lanka. The aim of this study was to describe a newly emerging focus of CL in the district of Gampaha, in Western Sri Lanka. Methods: A case based descriptive study was carried out from January 2018 to April 2019 in the Mirigama Medical Officer of Health (MOH) area, which reported the highest number of CL cases in Gampaha District. Laboratory confirmed cases were traced and socio-demographic and clinical data were collected via a validated questionnaire and clinic records respectively. The quality of life (QOL) of study participants was measured using the Dermatology Life Quality Index (DLQI). Global Positioning System (GPS) coordinates of patient residences were recorded using handheld GPS receivers. Sand-flies were collected from four selected sites, using Indoor Hand Collection (IHC) (162 units) and Cattle Baited Net Traps (CBNT) (n = 3) and a battery-operated aspirator. Results: Of 73 patients identified in this study, 58.9% were males, with a mean age of 43.6 years (SD 20.1). The lesions included nodules (52.05%) and ulcers (47.9%). Single lesions were seen in 69.86%, while 30.1% had multiple. Except for one mucosal lesion, all others were on skin. Treatment varied from sodium stibogluconate (SSG) + cryotherapy (46.57%), SSG (45.2%) and cryotherapy (8.2%). Patients with multiple lesions were more likely to be treated with combined SSG + cryotherapy (p < 0.05). The mean DLQI score was 8.14 (SD = 7). Most patients engaged in outdoor activities that exposed them to the risk of sand-fly bites Workplaces of 81.1% (27/33) were located within the district. Housing conditions of study participants were of moderate (59%), good (35.6%) and poor (5%) quality. Four households reported multiple cases. Spatial distribution of cases indicated notable clustering in seven adjacently located Public Health Inspector (PHI) areas. Phlebotomus argentipes was detected in all CBNTs and 35.28% of IHC units surveyed. Conclusions: CL is emerging in Gamapha district with Mirigama MOH area being the epicentre of infection. The disease had a moderately negative impact on QOL of patients. Minimal migration of cases, clustering of cases within households and in the locality indicates local transmission with P. argentipes as the probable vector.
Background Cutaneous leishmaniasis (CL) appears to be spreading to previously non-endemic regions of Sri Lanka. The aim of this study was to describe a newly emerging focus of CL in the district of Gampaha, in Western Sri Lanka. Methods A case based descriptive study was carried out from January 2018 to April 2019 in the Mirigama Medical Officer of Health (MOH) area, which reported the highest number of CL cases in Gampaha District. Laboratory confirmed cases were traced and socio-demographic and clinical data were collected via a validated questionnaire and clinic records respectively. The quality of life (QOL) of study participants was measured using the Dermatology Life Quality Index (DLQI). Global Positioning System (GPS) coordinates of patient residences were recorded using handheld GPS receivers. Sand-flies were collected from four selected sites, using Indoor Hand Collection (IHC) (162 units) and Cattle Baited Net Traps (CBNT) (n=3) and a battery-operated aspirator. Results Of 73 patients identified in this study, 58.9% were males, with a mean age of 43.6 years (SD 20.1). The lesions included nodules (52.05%) and ulcers (47.9%). Single lesions were seen in 69.86%, while 30.1% had multiple. Except for one mucosal lesion, all others were on skin. Treatment varied from sodium stibogluconate (SSG) + cryotherapy (46.57%), SSG (45.2%) and cryotherapy (8.2%). Patients with multiple lesions were more likely to be treated with combined SSG + cryotherapy (p< 0.05). The mean DLQI score was 8.14 (SD=7). Most patients engaged in outdoor activities that exposed them to the risk of sand-fly bites Workplaces of 81.1% (27/33) were located within the district. Housing conditions of study participants were of moderate (59%), good (35.6%) and poor (5%) quality. Four households reported multiple cases. Spatial distribution of cases indicated notable clustering in seven adjacently located Public Health Inspector (PHI) areas. Phlebotomus argentipes was detected in all CBNTs and 35.28% of IHC units surveyed. Conclusions CL is emerging in Gamapha district with Mirigama MOH area being the epicentre of infection. The disease had a moderately negative impact on QOL of patients. Minimal migration of cases, clustering of cases within households and in the locality indicates local transmission with P. argentipes as the probable vector.
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