Dengue virus, Nepal

Entomological surveillance of container-breeding mosquitoes focusing on Aedes (Stegomyia) (Diptera: Culicidae) vectors along altitudinal range in Nepal

Mosquitoes are a significant public health concern due to their role in transmitting various diseases. This study aimed to investigate mosquitoes' diversity, abundance, and ecological aspects, mainly focusing on Aedes (Diptera: Culicidae) mosquitoes, in central Nepal. The research explored variations across regions, seasons, altitudes, and years. Fieldwork for mosquito collection was conducted between May 2022 and October 2023. Dipping and pipetting methods were employed to collect larvae and pupae, whereas Biogents-Mosquitaire trap captured adult mosquitoes. A total of 7,223 (3,640 larvae and 3,583 adults) mosquitoes, belonging to 8 genera and 18 species, were collected and analyzed. Additionally, a survey examined 5,941 wet containers of 20 different types to assess potential breeding sites. The study revealed Culex pipiens (Linnaeus, 1758) (34.13%) and Aedes albopictus (Skuse, 1895) (27.36%) as the most abundant species. Interestingly, larvae were predominantly Aedes spp. (66.13%), whereas only 13.76% of adults belonged to this genus. Mosquito abundance varied across locations and altitudes, with Siwalik region (331-700 m asl) exhibiting the highest numbers. The monsoon season showed the highest overall abundance (1,492). Used tires were identified as significant breeding sites for Aedes mosquitoes, and infestation rates were higher in shaded containers. Seasonal analysis showed the House Index (HI) reaching its peak (10.92%) and the Breteau Index (BI) reaching 23.08% during the monsoon. Conversely, the Container Index (CI) reached its highest point (37.67%) in the post-monsoon season. The results emphasize the need for comprehensive disease prevention strategies at local and national levels, including public awareness campaigns, to address mosquito-borne illnesses in this famous tourist region.

Investigating public understanding and actions regarding Aedes mosquitoes and dengue prevention across altitudinal range in central Nepal

BACKGROUNDS OBJECTIVES

Dengue fever, transmitted by Aedes mosquitoes, is a significant public health concern in Nepal. An extensive Knowledge, Attitude, and Practice (KAP) survey related to Aedes mosquitoes and prevention of dengue was conducted along the route from Matihani (62 m above sea level) to Kalinchok (3840 m asl) in central Nepal. This research examined residents' awareness of Aedes mosquitoes and the diseases they transmit, aiming to support the World Health Organization's national and global fight against mosquito-borne diseases.

METHODS

The survey included 550 participants aged 18-75 years (249 males and 201 females). Door-to-door campaigns were conducted to gather data on knowledge scores, practices, and attitudes about Aedes mosquitoes using a standard structured questionnaire.

RESULTS

Findings of this study revealed a moderate level of knowledge across the study area, with a mean knowledge score of 5.525±2.58 (correct answer rate of 46.05%). While 99.6% of respondents were aware of dengue transmission by mosquitoes, only 64.5% were able to report Aedes mosquitoes as the key transmitter. Less than one-third of the participants (27.8%) were familiar with black-and-white stripes in Aedes. Additionally, only 36.7% were knowledgeable about the day-biting behavior of Aedes mosquitoes.

INTERPRETATION CONCLUSION

This KAP survey provides valuable insights into community understanding of Aedes mosquitoes and dengue prevention practices associated with various Nepalese communities residing in low to high altitudes of central Nepal. These findings can be adopted to address the increasing health burden faced by countries with low-to-high altitude regions within the Hindu Kush Himalayas.

The knowledge, attitude and practice of community people on dengue fever in Central Nepal: a cross-sectional study

Background

Since 2006, Nepal has experienced frequent Dengue fever (DF) outbreaks. Up to now, there have been no knowledge, attitude and practice (KAP) studies carried out on DF in Nepal that have included qualitative in-depth and quantitative data. Thus, we aimed to explore and compare the KAP of people residing in the lowland (< 1500 m) and highland (> 1500 m) areas of Nepal.

Methods

A cross-sectional mixed-method study was conducted in six districts of central Nepal in September–October 2018 including both quantitative (660 household surveys) and qualitative data (12 focus group discussions and 27 in-depth interviews). The KAP assessment was executed using a scoring system and defined as high or low based on 80% cut-off point. Logistic regression was used to investigate the associated factors, in quantitative analysis. The deductive followed by inductive approach was adopted to identify the themes in the qualitative data.

Results

The study revealed that both the awareness about DF and prevention measures were low. Among the surveyed participants, 40.6% had previously heard about DF with a significantly higher number in the lowland areas. Similarly, IDI and FGD participants from the lowland areas were aware about DF, and it’s associated symptoms, hence they were adopting better preventive practices against DF. The findings of both the qualitative and quantitative data indicate that people residing in the lowland areas had better knowledge on DF compared to people in highland areas. All IDI participants perceived a higher chance of increasing future dengue outbreaks due to increasing temperature and the mobility of infected people from endemic to non-endemic areas. The most quoted sources of information were the television (71.8%) and radio (51.5%). Overall, only 2.3% of the HHS participants obtained high knowledge scores, 74.1% obtained high attitude scores and 21.2% obtained high preventive practice scores on DF. Among the socio-demographic variables, the area of residence, educational level, age, monthly income, SES and occupation were independent predictors of knowledge level, while the education level of the participants was an independent predictor of the attitude level.

Conclusions

Our study found a very low level of knowledge and insufficient preventive practices. This highlights an urgent need for extensive dengue prevention programs in both highland and lowland communities of Nepal.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12879-022-07404-4.

Admitted Cases of Dengue Fever among Dengue Positive Cases in a Tertiary Care Hospital: A Descriptive Cross-sectional Study

INTRODUCTION

Dengue fever, a mosquito-borne disease, is one of the emerging tropical diseases that appear primarily in rainy seasons. The number of dengue cases was increased in recent years in Nepal. Chitwan is one of the risky areas of dengue. This aim of the study is to find out the prevalence of hospital admission among the dengue positive cases.

METHODS

The descriptive cross-sectional study was carried out among 323 serologically confirmed dengue fever positive patient admitted in Medicine Inpatients Department of Chitwan Medical College Teaching Hospital. Ethical approval was taken from the Institutional Review Committee (Reference number. 076/077-121 dated August 30, 2019). Data were collected from 1st September 2019 to 31st December 2019 using a structured interview schedule and record review. Convenience sampling was done. Data was analysed using Statistical Package for Social Sciences version 11. Point estimate at 95% Confidence Interval was calculated, with frequency and percentage.

RESULTS

Among 1206 patient with dengue fever, 323 (26.78%) (24.29-29.27 at 95% confidence Interval) were admitted in the tertiary care hospital. Study findings revealed that out of 323 admitted patients with dengue fever, 182 (56.3%) patients were between 20-40 years of age and 179 (55.4%) were males. The highest number of patients were admitted in the months of September 192 (59.4%) and October 101 (31.2%).

CONCLUSIONS

Admission rate among dengue positive cases are comparable to other studies of the similar settings. Dengue fever is common among community people especially in young adult and males. Hence, screening of dengue fever in febrile illness is necessary for the early diagnosis and prompt treatment.

Epidemiology and challenges of dengue surveillance in the WHO South-East Asia Region

Dengue poses a significant health and economic burden in the WHO South-East Asia Region. Approaches for control need to be aligned with current knowledge on the epidemiology of dengue in the region. Such knowledge will ensure improved targeting of interventions to reduce dengue incidence and its socioeconomic impact. This review was undertaken to describe the contemporary epidemiology of dengue and critically analyse the existing surveillance strategies in the region. Over recent decades, dengue incidence has continued to increase with geographical expansion. The region has now become hyper-endemic for multiple dengue virus serotypes/genotypes. Every epidemic cycle was associated with a change of predominant serotype/genotype and this was often associated with severe disease with intense transmission. Classical larval indices are widely used in vector surveillance and adult mosquito samplings are not implemented as a part of routine surveillance. Further, there is a lack of integration of entomological and disease surveillance systems, often leading to inaction or delays in dengue prevention and control. Disease surveillance does not capture all cases, resulting in under-reporting, and has thus failed to adequately represent the true burden of disease in the region. Possible solutions include incorporating adult mosquito sampling into routine vector surveillance, the establishment of laboratory-based sentinel surveillance, integrated vector and dengue disease surveillance and climate-based early warning systems using available technologies like mobile apps.

Epidemiology of dengue virus infections in Nepal, 2006-2019

BACKGROUND

Dengue is one of the newest emerging diseases in Nepal with increasing burden and geographic spread over the years. The main objective of this study was to explore the epidemiological patterns of dengue since its first outbreak (2006) to 2019 in Nepal.

METHODS

This study is a retrospective analysis that covers the last 14 years (2006-2019) of reported dengue cases from Epidemiology Diseases Control Division (EDCD), Ministry of Health and Population, Government of Nepal. Reported cases were plotted over time and maps of reported case incidence were generated (from 2016 through 2019). An ecological analysis of environmental predictors of case incidence was conducted using negative binomial regression.

RESULTS

While endemic dengue has been reported in Nepal since 2006, the case load has increased over time and in 2019 a total of 17 992 dengue cases were reported from 68 districts (from all seven provinces). Compared to the case incidence in 2016, incidence was approximately five times higher in 2018 [incidence rate ratio (IRR): 4.8; 95% confidence interval (CI) 1.5-15.3] and over 140 times higher in 2019 (IRR: 141.6; 95% CI 45.8-438.4). A one standard deviation increase in elevation was associated with a 90% decrease in reported case incidence (IRR: 0.10; 95% CI 0.01-0.20). However, the association between elevation and reported cases varied across the years. In 2018 there was a cluster of cases reported from high elevation Kaski District of Gandaki Province. Our results suggest that dengue infections are increasing in magnitude and expanding out of the lowland areas to higher elevations over time.

CONCLUSIONS

There is a high risk of dengue outbreak in the lowland Terai region, with increasing spread towards the mid-mountains and beyond as seen over the last 14 years. Urgent measures are required to increase the availability of diagnostics and resources to mitigate future dengue epidemics.

Spatiotemporal Distribution of Dengue and Chikungunya in the Hindu Kush Himalayan Region: A Systematic Review

The risk of increasing dengue (DEN) and chikungunya (CHIK) epidemics impacts 240 million people, health systems, and the economy in the Hindu Kush Himalayan (HKH) region. The aim of this systematic review is to monitor trends in the distribution and spread of DEN/CHIK over time and geographically for future reliable vector and disease control in the HKH region. We conducted a systematic review of the literature on the spatiotemporal distribution of DEN/CHIK in HKH published up to 23 January 2020, following Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) guidelines. In total, we found 61 articles that focused on the spatial and temporal distribution of 72,715 DEN and 2334 CHIK cases in the HKH region from 1951 to 2020. DEN incidence occurs in seven HKH countries, i.e., India, Nepal, Bhutan, Pakistan, Bangladesh, Afghanistan, and Myanmar, and CHIK occurs in four HKH countries, i.e., India, Nepal, Bhutan, and Myanmar, out of eight HKH countries. DEN is highly seasonal and starts with the onset of the monsoon (July in India and June in Nepal) and with the onset of spring (May in Bhutan) and peaks in the postmonsoon season (September to November). This current trend of increasing numbers of both diseases in many countries of the HKH region requires coordination of response efforts to prevent and control the future expansion of those vector-borne diseases to nonendemic areas, across national borders.

Gravitrap deployment for adult Aedes aegypti surveillance and its impact on dengue cases

House Index, Container Index, and Breteau Index are the most commonly used indices for dengue vector surveillance. However, these larval indices are a poor proxy for measuring the adult population—which is responsible for disease transmission. Information on the adult distribution and density are important for assessing transmission risk as well as for developing effective control strategies. This study introduces a new entomological index, Gravitrap aegypti index (GAI), which estimates the adult female Aedes aegypti population in the community and presents its association with dengue cases. Gravitraps were deployed across 34 treatment sites in Singapore from September 2013 to September 2016. The GAI, derived from the Gravitrap surveillance data, was analysed to investigate the spatio-temporal patterns of the Ae. aegypti population in Singapore. The index was further categorised into low, moderate, and high-risk groups and its association with dengue cases were examined. A Before-After Control Impact analysis was performed to evaluate the epidemiology impact of Gravitrap system on dengue transmission. The Ae. aegypti population exhibits a seasonal pattern, and spatial heterogeneity in Ae. aegypti abundance was observed among treatment sites. The Ae. aegypti population was also found to be unevenly distributed among floors of an apartment block, with low floors (floors 1–4) having a higher abundance of mosquitoes trapped than mid (floors 5–8) and high (floors ≥9) floors. Areas with high GAI were shown to have higher dengue case count. Gravitrap has also demonstrated to be a good dengue control tool. The contribution of cases by treatment sites to the national numbers was lower after Gravitraps deployment. The GAI, which is of better relevance to dengue transmission risk, could be recommended as an indicator for decision making in vector control efforts, and to monitor the spatio-temporal variability of the adult Aedes population in the country. In addition, findings from this study indicate that Gravitraps can be used as a dengue control tool to reduce dengue transmission.

In the absence of an effective vaccine: vector surveillance and control remain the key strategy for dengue prevention and control. The collection of the adult female Aedes mosquito is thus important to understand disease transmission dynamics. Information on its distribution and density are also essential for assessing transmission risk as well as for devising an effective control strategy. Here, we described a new approach to dengue vector surveillance based on adult female Aedes trapping using Gravitraps. Using the Gravitrap surveillance data, we derived a new entomological index, Gravitrap aegypti index (GAI), which estimates the adult female Ae. aegypti population in the community and presents its association with dengue cases. When analysed, the index can provide useful information on the spatio-temporal distribution of the Ae. aegypti population in the country and hence, assist planning of vector control. The GAI, which is of better relevance to dengue transmission risk, could be used as an indicator for decision making in vector control efforts, and to monitor the spatio-temporal variability of the adult Aedes population. In addition, findings from this study indicate that Gravitraps can be used as a dengue control tool to reduce dengue transmission.

Distribution and pyrethroid resistance status of Aedes aegypti and Aedes albopictus populations and possible phylogenetic reasons for the recent invasion of Aedes aegypti in Nepal

Background

When the first systematic list of mosquitoes in Nepal was reported in 1990, there was no description of Aedes aegypti (L.), while Aedes albopictus (Skuse) has been included in the Stegomyia subgroup since the 1950s. The first record of Ae. aegypti in Nepal was reported in 2009, suggesting some coincidence between the invasion of this species and the first record of dengue fever in Nepal in 2006.

Results

We performed a field survey of the distribution and insecticide susceptibility of Ae. aegypti and Ae. albopictus in Nepal in 2017 and 2018. Mosquito larvae were collected from used tires located along the streets of Kathmandu, Bharatpur and Pokhara, and a simplified bioassay was used to assess the susceptibility of the larvae to pyrethroid insecticides using d-allethrin. The presence or absence of point mutations in the voltage-gated sodium channel was also detected by direct sequencing. V1016G was detected at a high frequency and a strong correlation was observed between the frequencies of V1016G and susceptibility indices in Ae. aegypti populations. F1534C was also detected at a relatively low frequency. In Ae. albopictus populations, susceptibilities to d-allethrin were high and no point mutations were detected. Analysis of the cytochrome c oxidase subunit 1 (cox1) gene was performed for assessing genetic diversity and the existence of two strains were identified in Ae. aegypti populations. One consisted of 9 globally-distributed haplotypes while the other was derived from an African haplotype.

Conclusions

The high pyrethroid resistance, high V1016G frequency, and relatively low quantity of insecticides used to control dengue vectors in Nepal may have resulted in only weak selection pressure favoring insecticide resistance and could support the hypothesis that this species has recently been introduced from neighboring Asian countries where pyrethroid resistance is relatively widespread.

Climatic factors influencing dengue incidence in an epidemic area of Nepal

Objective

Geographic expansion of dengue incidence has drawn a global interest to identify the influential factors that instigate the spread of this disease. The objective of this study was to find the environmental factors linked to dengue incidence in a dengue epidemic area of Nepal by negative binomial models using climatic factors from 2010 to 2017.

Results

Minimum temperature at lag 2 months, maximum temperature and relative humidity without lag period significantly affected dengue incidence. Rainfall was not associated with dengue incidence in Chitwan district of Nepal. The incident rate ratio (IRR) of dengue case rise by more than 1% for every unit increase in minimum temperature at lag 2 months, maximum temperature and relative humidity, but decrease by .759% for maximum temperature at lag 3 months. Considering the effect of minimum temperature of previous months on dengue incidence, the vector control and dengue management program should be implemented at least 2 months ahead of dengue outbreak season.

Electronic supplementary material

The online version of this article (10.1186/s13104-019-4185-4) contains supplementary material, which is available to authorized users.

Effect of meteorological factors on the seasonal prevalence of dengue vectors in upland hilly and lowland Terai regions of Nepal

Background

The expansion of dengue vectors from lowland plains to the upland hilly regions of Nepal suggests the likelihood of increased risk of dengue. Our objective was to assess the effects of meteorological variables on vector indices and populations of dengue vectors in two different ecological regions of Nepal. An entomological survey was conducted in Kathmandu and Lalitpur (upland) and Chitwan (lowland) of Nepal in three different seasons from July 2015 to May 2016. The effect of meteorological variables on vector indices (house index, container index and Breteau index) and Aedes spp. population abundance was analyzed. A gamma regression was used to fit the models for vector indices and a negative binomial regression was used to model Aedes spp. population abundance.

Results

Monsoon season showed higher values for vector indices and vector populations compared to post-monsoon and pre-monsoon. Overall, the factor temperature-rainfall effect had a more significant influence on vector indices compared to relative humidity. The regression models showed that relative humidity has a greater impact in Chitwan than in Kathmandu. Variation was observed in the effect of predictor variables on Aedes aegypti and Ae. albopictus abundance.

Conclusions

Temperature and rainfall contribute to the vector indices in the upland hilly region while relative humidity contributes in the lowland plains. Since vector prevalence is not only linked to meteorological factors, other factors such as water storage practices, waste disposal, sanitary conditions and vector control strategy should also be considered. We recommend strengthening and scaling up dengue vector surveillance and control programmes for monsoon season in both upland and lowland regions in Nepal.

Electronic supplementary material

The online version of this article (10.1186/s13071-019-3304-3) contains supplementary material, which is available to authorized users.

Profile of the 2016 dengue outbreak in Nepal

OBJECTIVE

The objective of this study was to obtain clinical, virological and demographic data detailing the 2016 dengue outbreak in Nepal.

RESULTS

Dengue disease was first reported in Nepal in 2004 and several major outbreaks have occurred since then, with a significant impact on public health. An outbreak of dengue fever occurred in Nepal during June to November 2016, with a peak number of cases reported in September. 1473 patients with laboratory confirmed DENV infections visited or were admitted to hospitals during this period. The most common clinical symptoms included fever, headache, joint pain and thrombocytopenia. Serotyping of 75 serum samples from patients having fever for less than 4 days was carried out with a dengue virus (DENV) serotype-specific RT-PCR strategy. Our results indicate that the dengue outbreak in Nepal during 2016 was caused predominantly, if not exclusively, by DENV-1, representing a shift in the prevailing serotype from DENV-2, the dominant serotype characterizing the 2013 dengue epidemic in Nepal. Hopefully, this report will assist Nepalese public health agencies in developing improved dengue-related programs including mosquito-vector control, DENV surveillance, and diagnosis and treatment of dengue fever patients, in order to reduce the impact of future dengue epidemics.

Dengue periodic outbreaks and epidemiological trends in Nepal

Dengue is a global health problem and expansion of its endemics towards new territories in the hilly regions in Nepal is a serious concern. It appeared as a new disease in Nepal in 2004 from Japanese traveler with sporadic cases every year and massive outbreaks in 2010, 2013 and 2016. The serotype was responsible for outbreak in particular year was dengue virus serotype-1 (DENV-1) in 2010, 2016; and DENV-2 in 2013. Nepal lacks basic health related infrastructure in rural areas and does not have a stringent health care policy. With severances of epidemic like dengue, a new surveillance or an upgrading of existing one are direly needed to better challenge the possible outbreaks. This review paper aims to explain the dengue trend in last one decade in Nepal and warrants concerted and timely public health interventions to minimize the deleterious effects of the disease.

Emergence of dengue in Nepal

Dengue virus is a major health problem in Nepal. The endogenous dengue appeared in 2006 in the country with reported outbreaks in 2010, 2013 and 2016. Eleven years vertical data show there were sporadic cases in all the years and mostly adults between 25 and 40 years of age were infected with dengue virus. Compared with primary infections, secondary infections were observed in relatively larger numbers during the period of 2008-2016. Most of the cases had symptoms of dengue fever; while 7 and 19 cases demonstrated dengue hemorrhagic fever/dengue shock syndrome in 2010 and 2013 respectively. The proportion of dengue hemorrhagic fever amongst all cases of dengue fever was 2.5:4.7% in 2010 and 2013. We found there is shift of serotype from dengue virus serotype-1 (DENV-1) in 2010, DENV-2 in 2013 and DENV-1 in 2016. We feel there is urgent need for better community, hospital and laboratory based surveillance system capable of monitoring the circulating dengue virus (DENV) serotypes in different districts of Nepal. With improvement in surveillance system and efficient management of cases, the case fatality rate due to severe dengue can be reduced.

Outbreak investigation of fever mimicking dengue in Havelock Island, an important tourist destination in the Andaman & Nicobar Archipelago, 2014

An upsurge of fever cases of unknown origin, but resembling dengue and leptospirosis was reported in Havelock, Andaman & Nicobar Islands, an important tourism spot, during May 2014. Investigations were carried out to determine the aetiology, and to describe the epidemiology of the outbreak. The data on fever cases attending Primary Health Centre (PHC), Havelock showed that the average number of cases reporting per week over the last 2 years was 46·1 (95% confidence interval 19·4-72·9). A total of 27 (43·5%) patients out of the 62 suspected cases were diagnosed as having DENV infection based on a positive enzyme immunoassay or reverse transcriptase-polymerase chain reaction. The overall attack rate was 9·4 cases/1000 population and it ranged between 2·8 and 18·8/1000 in different villages. The nucleotide sequencing showed that the virus responsible was DENV-3. DENV-3 was first detected in the Andaman & Nicobar Islands in 2013 among wharf workers in Port Blair and within a year it has spread to Havelock Island which is separated from South Andaman by 36 nautical miles.

Dengue Virus Serotypes Circulating in Khyber Pakhtunkhwa Province, Pakistan, 2013-2015

From 2013 to 2015, the National Institute of Health, Pakistan, received 1,270 blood samples of suspected dengue cases reported from inpatient and outpatient departments of various hospitals in Khyber Pakhtunkhwa (KPK) province. In this study, we determined the circulating dengue virus (DENV) serotypes using real-time reverse transcriptase (RT)-PCR to understand the serotype-based epidemiology of DENV. All four serotypes (DENV-1 [6%], DENV-2 [33%], DENV-3 [47%], and DENV-4 [0.1%]) were found circulating during the study period. Our findings suggest the need for an active surveillance system coupled with the laboratory diagnosis, especially in the chronic endemic areas of the country. Public awareness programs are needed for effective control and prevention of outbreaks in the future.

Re-emergence of dengue virus serotype 2 strains in the 2013 outbreak in Nepal

Background & objectives:

Epidemiological interventions and mosquito control are the available measures for dengue control. The former approach uses serotype and genetic information on the circulating virus strains. Dengue has been frequently reported from Nepal, but this information is mostly lacking. The present study was done to generate a comprehensive clinical and virological picture of a dengue outbreak in Nepal during 2013.

Methods:

A hospital-based study involving patients from five districts of Nepal was carried out. Demographic information, clinical details and dengue serological status were obtained. Viral RNA was characterized at the molecular level by reverse-transcription polymerase chain reaction (RT-PCR), nucleotide sequencing and phylogenetic analysis.

Results:

From among the 2340 laboratory-confirmed dengue cases during the study period, 198 patients consented for the study. Clinically they had fever (100%), headache (59.1%), rashes (18.2%), retro-orbital pain (30.3%), vomiting (15.1%), joint pain (28.8%) and thrombocytopenia (74.3%). Fifteen (7.5%) of them had mucosal bleeding manifestations, and the rest were uncomplicated dengue fever. The patients were mostly adults with a mean age of 45.75 ± 38.61 yr. Of the 52 acute serum samples tested, 15 were positive in RT-PCR. The causative virus was identified as DENV serotype 2 belonging to the Cosmopolitan genotype.

Interpretations & conclusions:

We report here the involvement of DENV serotype 2 in an outbreak in Nepal in 2013. Earlier outbreaks in the region in 2010 were attributed to serotype 1 virus. As serotype shifts are frequently associated with secondary infections and severe disease, there is a need for enhancing surveillance especially in the monsoon and post-monsoon periods to prevent large-scale, severe dengue outbreaks in the region.

Tourniquet Test for Dengue Diagnosis: Systematic Review and Meta-analysis of Diagnostic Test Accuracy

BACKGROUND

Dengue fever is a ubiquitous arboviral infection in tropical and sub-tropical regions, whose incidence has increased over recent decades. In the absence of a rapid point of care test, the clinical diagnosis of dengue is complex. The World Health Organisation has outlined diagnostic criteria for making the diagnosis of dengue infection, which includes the use of the tourniquet test (TT).

PURPOSE

To assess the quality of the evidence supporting the use of the TT and perform a diagnostic accuracy meta-analysis comparing the TT to antibody response measured by ELISA.

DATA SOURCES

A comprehensive literature search was conducted in the following databases to April, 2016: MEDLINE (PubMed), EMBASE, Cochrane Central Register of Controlled Trials, BIOSIS, Web of Science, SCOPUS.

STUDY SELECTION

Studies comparing the diagnostic accuracy of the tourniquet test with ELISA for the diagnosis of dengue were included.

DATA EXTRACTION

Two independent authors extracted data using a standardized form.

DATA SYNTHESIS

A total of 16 studies with 28,739 participants were included in the meta-analysis. Pooled sensitivity for dengue diagnosis by TT was 58% (95% Confidence Interval (CI), 43%-71%) and the specificity was 71% (95% CI, 60%-80%). In the subgroup analysis sensitivity for non-severe dengue diagnosis was 55% (95% CI, 52%-59%) and the specificity was 63% (95% CI, 60%-66%), whilst sensitivity for dengue hemorrhagic fever diagnosis was 62% (95% CI, 53%-71%) and the specificity was 60% (95% CI, 48%-70%). Receiver-operator characteristics demonstrated a test accuracy (AUC) of 0.70 (95% CI, 0.66-0.74).

CONCLUSION

The tourniquet test is widely used in resource poor settings despite currently available evidence demonstrating only a marginal benefit in making a diagnosis of dengue infection alone.

REGISTRATION

The protocol for this systematic review was registered at

PROSPERO

CRD42015020323.

Effects of Larval Nutrition on Wolbachia-Based Dengue Virus Interference in Aedes aegypti (Diptera: Culicidae)

In order to assess the broad-scale applicability of field releases of Wolbachia for the biological control of insect-transmitted diseases, we determined the relationship between the larval diet of Aedes aegypti L. mosquitoes infected with Wolbachia strains and their susceptibility to dengue virus (DENV) infection via intrathoracic injection and oral inoculation. Larvae were reared on diets that varied in the quantity of food which had the effect of modifying development time and adult body size. Wolbachia wMel infection was associated with highly significant reductions in dengue serotype 2 (DENV-2) infection rates of between 80 and 97.5% following intrathoracic injection of adults emerging from three diet levels. Reductions were 100% in two diet level treatments following oral inoculation. Similarly, wMelPop infection was associated with highly significant reductions in DENV-2 infection rates of between 95 and 100% for intrathoracic injection and 97.5 and 100% for oral inoculation across diet level treatments. Larval diet level had no significant effect on DENV-2 infection rates in the presence of Wolbachia infection in mosquitoes that were intrathoracically injected with the virus. This indicates that the effectiveness of Wolbachia on vector competence disruption within Ae. aegypti is unlikely to be compromised by variable larval nutrition in field settings.

Dengue outbreak in Swat and Mansehra, Pakistan 2013: An epidemiological and diagnostic perspective

OBJECTIVE

To high light some epidemiological, clinical and diagnostic features of dengue fever during an outbreak and the role of different diagnostic techniques to achieve the highest level of accuracy in results.

METHODS

Blood samples (n = 323) were collected along with epidemiological and clinical data from suspected dengue patients who visited different hospitals in Swat and Mansehra district of Pakistan between May-November 2013 during a dengue outbreak. Samples were tested for the detection of viral nucleic acid by real-time PCR, non structural protein-1 (NS1) antigen and IgM antibodies by ELISA.

RESULTS

Out of 323 cases with clinical dengue infection, 304 were positive by one or more diagnostic parameter; 201 samples were positive by real-time PCR, 209 were positive by NS1 ELISA and 190 were positive by IgM antibodies. Sensitivities of real-time PCR and NS1 ELISA were comparable for early diagnosis of dengue virus infection, IgM antibody detection assay was found useful for the diagnosis in the samples collected later than day 5 of onset.

CONCLUSIONS

The use of real-time PCR or detection of non structural protein NS1 by ELISA followed by IgM antibodies detection can be recommended for early diagnosis of dengue virus infection with a high level of accuracy.

Serological and Entomological Study of Dengue in Dang and Chitwan Districts of Nepal

A descriptive cross-sectional study was carried out among 264 suspected dengue patients in two districts (Dang and Chitwan) of Nepal from June 2013 to November 2013. The anti-dengue IgM positivity was found to be (51/264)19.31% by capture ELISA, of which 21 (41.2%) were male and 30 (58.8%) were female. Symptoms of seropositive cases were fever, anorexia, nausea, headache, retro-orbital pain, skin rashes, and myalgia. Hematological features like thrombocytopenia and leucopenia were found to be significantly associated with the dengue fever (DF). Discarded tires were found as the commonest breeding habitats for the dengue vectors. Higher sero-positivity was recorded from the area having higher Breteau index (BI). The pH, chloride ion concentration and the salinity of the water from breeding habitats were found to be ranging from 6.9±0.82 to 8, 103.33±17.52 mg/L to 140.65 mg/L, and 0.19±0.032 ppt to 0.25 ppt respectively. This study may be helpful for the health authorities and public health workers for early diagnosis of DF and for the improved preventive measures to be adopted in the epidemic and possible epidemic areas.

Persistent dengue emergence: the 7 years surrounding the 2010 epidemic in Nepal

BACKGROUND

Dengue fever (DF) is an emerging public health problem in Nepal, and yet neither the magnitude of the DF burden or its epidemiological trends are well understood.

METHODS

We conducted a sero-epidemiological, seasonal trend and demographic analysis of the trends in DF in the Terai region of Nepal, from 2007 to 2013. In that period, 2002 serum samples were collected from febrile patients suspected of dengue virus infection. Samples were screened by IgM antibody ELISA analysis for the presence of anti-dengue IgM antibodies.

RESULTS

The overall prevalence of DF cases was found to range from 26.1 to 55.4%. Infection was found to be more common among adults and males. Seasonal trends revealed that cases peaked in October and November.

CONCLUSIONS

The study offers perspective on the dengue fever burden before, during and after a major epidemic and can now be used as a basis for formulating strategies by policy makers that will enhance and develop relevant control and preventive measures against dengue fever. The findings of this study reinforce the perceived need for urgent dengue virus surveillance to enhance dengue control strategies that need to be developed for future preparedness. In the light of the recent earthquakes, future major outbreaks of vector borne disease are likely to recur.

Climate Change and Spatiotemporal Distributions of Vector-Borne Diseases in Nepal--A Systematic Synthesis of Literature

Background

Despite its largely mountainous terrain for which this Himalayan country is a popular tourist destination, Nepal is now endemic for five major vector-borne diseases (VBDs), namely malaria, lymphatic filariasis, Japanese encephalitis, visceral leishmaniasis and dengue fever. There is increasing evidence about the impacts of climate change on VBDs especially in tropical highlands and temperate regions. Our aim is to explore whether the observed spatiotemporal distributions of VBDs in Nepal can be related to climate change.

Methodology

A systematic literature search was performed and summarized information on climate change and the spatiotemporal distribution of VBDs in Nepal from the published literature until December2014 following providing items for systematic review and meta-analysis (PRISMA) guidelines.

Principal Findings

We found 12 studies that analysed the trend of climatic data and are relevant for the study of VBDs, 38 studies that dealt with the spatial and temporal distribution of disease vectors and disease transmission. Among 38 studies, only eight studies assessed the association of VBDs with climatic variables. Our review highlights a pronounced warming in the mountains and an expansion of autochthonous cases of VBDs to non-endemic areas including mountain regions (i.e., at least 2,000 m above sea level). Furthermore, significant relationships between climatic variables and VBDs and their vectors are found in short-term studies.

Conclusion

Taking into account the weak health care systems and difficult geographic terrain of Nepal, increasing trade and movements of people, a lack of vector control interventions, observed relationships between climatic variables and VBDs and their vectors and the establishment of relevant disease vectors already at least 2,000 m above sea level, we conclude that climate change can intensify the risk of VBD epidemics in the mountain regions of Nepal if other non-climatic drivers of VBDs remain constant.

Risk factors for the presence of chikungunya and dengue vectors (Aedes aegypti and Aedes albopictus), their altitudinal distribution and climatic determinants of their abundance in central Nepal

Background

The presence of the recently introduced primary dengue virus vector mosquito Aedes aegypti in Nepal, in association with the likely indigenous secondary vector Aedes albopictus, raises public health concerns. Chikungunya fever cases have also been reported in Nepal, and the virus causing this disease is also transmitted by these mosquito species. Here we report the results of a study on the risk factors for the presence of chikungunya and dengue virus vectors, their elevational ceiling of distribution, and climatic determinants of their abundance in central Nepal.

Methodology/Principal Findings

We collected immature stages of mosquitoes during six monthly cross-sectional surveys covering six administrative districts along an altitudinal transect in central Nepal that extended from Birgunj (80 m above sea level [asl]) to Dhunche (highest altitude sampled: 2,100 m asl). The dengue vectors Ae. aegypti and Ae. albopictus were commonly found up to 1,350 m asl in Kathmandu valley and were present but rarely found from 1,750 to 2,100 m asl in Dhunche. The lymphatic filariasis vector Culex quinquefasciatus was commonly found throughout the study transect. Physiographic region, month of collection, collection station and container type were significant predictors of the occurrence and co-occurrence of Ae. aegypti and Ae. albopictus. The climatic variables rainfall, temperature, and relative humidity were significant predictors of chikungunya and dengue virus vectors abundance.

Conclusions/Significance

We conclude that chikungunya and dengue virus vectors have already established their populations up to the High Mountain region of Nepal and that this may be attributed to the environmental and climate change that has been observed over the decades in Nepal. The rapid expansion of the distribution of these important disease vectors in the High Mountain region, previously considered to be non-endemic for dengue and chikungunya fever, calls for urgent actions to protect the health of local people and tourists travelling in the central Himalayas.

The local transmission of dengue fever was confirmed in five lowland urban areas in 2006, along with the first report of the primary vectors of dengue virus, Aedes aegypti mosquitoes. Subsequent studies revealed a wide distribution of Ae. aegypti in 2009, and the first locally acquired dengue fever case in Kathmandu, the capital city of Nepal, during an epidemic in 2010. These records of a rapid expansion of dengue viruses and their primary vector, Ae. aegypti, in the Middle Mountain region and the more pronounced warming of mountains prompted us to investigate the altitudinal distribution and determinants of the abundance of dengue virus vectors in central Nepal. The first local transmission of chikungunya virus was recently reported from central Nepal in 2013. In this study, we document the distribution of Ae. aegypti and the secondary vector of dengue viruses, Aedes albopictus, from the lowlands (80 m) up to 2,100 m altitude in Dhunche, Rasuwa district. The climatic variables rainfall, temperature and relative humidity were significant predictors of their abundances. The distribution extension of these important disease vectors in the High Mountain region calls for urgent actions to protect the health of local people and tourists travelling in the central Himalayas.

Knowledge, attitude and practice regarding dengue fever among the healthy population of highland and lowland communities in central Nepal

Background

Dengue fever (DF) is the most rapidly spreading mosquito-borne viral disease in the world. In this decade it has expanded to new countries and from urban to rural areas. Nepal was regarded DF free until 2004. Since then dengue virus (DENV) has rapidly expanded its range even in mountain regions of Nepal, and major outbreaks occurred in 2006 and 2010. However, no data on the local knowledge, attitude and practice (KAP) of DF in Nepal exist although such information is required for prevention and control measures.

Methods

We conducted a community based cross-sectional survey in five districts of central Nepal between September 2011 and February 2012. We collected information on the socio-demographic characteristics of the participants and their knowledge, attitude and practice regarding DF using a structured questionnaire. We then statistically compared highland and lowland communities to identify possible causes of observed differences.

Principal Findings

Out of 589 individuals interviewed, 77% had heard of DF. Only 12% of the sample had good knowledge of DF. Those living in the lowlands were five times more likely to possess good knowledge than highlanders (P<0.001). Despite low knowledge levels, 83% of the people had good attitude and 37% reported good practice. We found a significantly positive correlation among knowledge, attitude and practice (P<0.001). Among the socio-demographic variables, the education level of the participants was an independent predictor of practice level (P<0.05), and education level and interaction between the sex and age group of the participants were independent predictors of attitude level (P<0.05).

Conclusion

Despite the rapid expansion of DENV in Nepal, the knowledge of people about DF was very low. Therefore, massive awareness programmes are urgently required to protect the health of people from DF and to limit its further spread in this country.

First isolation of dengue virus from the 2010 epidemic in Nepal

Dengue is an emerging disease in Nepal and was first observed as an outbreak in nine lowland districts in 2006. In 2010, however, a large epidemic of dengue occurred with 4,529 suspected and 917 serologically-confirmed cases and five deaths reported in government hospitals in Nepal. The collection of demographic information was performed along with an entomological survey and clinical evaluation of the patients. A total of 280 serum samples were collected from suspected dengue patients. These samples were subjected to routine laboratory investigations and IgM-capture ELISA for dengue serological identification, and 160 acute serum samples were used for virus isolation, RT-PCR, sequencing and phylogenetic analysis. The results showed that affected patients were predominately adults, and that 10% of the cases were classified as dengue haemorrhagic fever/ dengue shock syndrome. The genetic characterization of dengue viruses isolated from patients in four major outbreak areas of Nepal suggests that the DENV-1 strain was responsible for the 2010 epidemic. Entomological studies identified Aedes aegypti in all epidemic areas. All viruses belonged to a monophyletic single clade which is phylogenetically close to Indian viruses. The dengue epidemic started in the lowlands and expanded to the highland areas. To our knowledge, this is the first dengue isolation and genetic characterization reported from Nepal.

Public health responses to a dengue outbreak in a fragile state: a case study of Nepal

Objectives. The number of countries reporting dengue cases is increasing worldwide. Nepal saw its first dengue outbreak in 2010, with 96% of cases reported in three districts. There are numerous policy challenges to providing an effective public health response system in a fragile state. This paper evaluates the dengue case notification, surveillance, laboratory facilities, intersectoral collaboration, and how government and community services responded to the outbreak. Methods. Qualitative data were collected through 20 in-depth interviews, with key stakeholders, and two focus-group discussions, with seven participants. Results. Limitations of case recognition included weak diagnostic facilities and private hospitals not incorporated into the case reporting system. Research on vectors was weak, with no virological surveillance. Limitations of outbreak response included poor coordination and an inadequate budget. There was good community mobilization and emergency response but no routine vector control. Conclusions. A weak state has limited response capabilities. Disease surveillance and response plans need to be country-specific and consider state response capacity and the level of endemicity. Two feasible solutions for Nepal are (1) go upwards to regional collaboration for disease and vector surveillance, laboratory assistance, and staff training; (2) go downwards to expand upon community mobilisation, ensuring that vector control is anticipatory to outbreaks.

Dengue virus and Japanese encephalitis virus epidemiological shifts in Nepal: a case of opposing trends

We report on the changing epidemiology of two important flaviviruses in Nepal: Japanese encephalitis (JE) and dengue viruses. Morbidity and mortality in Nepal is in the thousands since JE was introduced in 1978. Nepal launched an extensive laboratory-based JE surveillance in 2004. Nepal experienced a remarkable reduction in disease burden after mass immunizations from 2005 to 2010, when 2,040 JE infections and 205 JE-related deaths were confirmed. With its emergence in 2006, dengue has become a significant challenge in the country, highlighted by a sudden outbreak in 2010 that resulted in 359 confirmed dengue infections. Currently, both viruses cocirculate in Nepal. Here, we document the remarkable expansion of dengue in Nepal, which urgently requires national surveillance to refine the burden and make recommendations regarding control and prevention programs. We believe that the use of existing JE surveillance network for integrated dengue surveillance may represent the most appropriate alternative.

Dengue: a newly emerging viral infection in Andaman and Nicobar Islands, India

Prior to 2009 dengue fever had not been reported in the Andaman and Nicobar archipelago. In 2009, a few patients with dengue fever-like illness were reported, some of whom tested positive for dengue antibodies. In 2010, 516 suspected cases were reported, including some with dengue haemorrhagic fever (DHF) and dengue shock syndrome (DSS); 80 (15·5%) were positive for dengue antibodies. DENV RNA was detected in five patients and PCR-based typing showed that three of these belonged to serotype 1 and two to serotype 2. This was confirmed by sequence typing. Two clones of dengue virus, one belonging to serotype 1 and the other to serotype 2 appeared to be circulating in Andaman. Emergence of severe diseases such as DHF and DSS might be due to recent introduction of a more virulent strain or because of the enhancing effect of sub-neutralizing levels of antibodies developed due to prior infections. There is a need to revise the vector-borne disease surveillance system in the islands.

Imported dengue fever/dengue hemorrhagic fever cases in Japan

Several dengue outbreaks occurred in Japan from 1942 to 1945. Dengue fever emerged in Nagasaki in August 1942 and soon spread to other cities such as Sasebo, Hiroshima, Kobe and Osaka, recurring every summer until 1945 and constituting the greatest outbreak in the temperate zone. Domestic outbreaks have not been reported in Japan since then. However, the number of imported dengue cases has increased year by year: 868 imported cases were reported in Japan between 1999 and 2010 according to the Infectious Diseases Control Law. Moreover, 406 imported cases were confirmed to be dengue virus infection among 768 dengue suspected cases received at NIID from 2003 to 2010. A total of 142 cases (35.6%), 103 cases (25.8%) and 62 cases (15.5%) were noted in the 20–29, 30–39 and 40–49 age groups, respectively. Infecting dengue virus serotypes were determined for 280 of the 406 cases. The number of cases infected with each of the 4 serotypes was 98 (35%) with type 1, 78 (28%) with type 3, 72 (26%) with type 2, and 32 (11%) with type 4. Sixty percent of dengue cases were imported from July to October, the summer vacation season in Japan.

Diversity and origin of dengue virus serotypes 1, 2, and 3, Bhutan

To determine the serotype and genotype of dengue virus (DENV) in Bhutan, we conducted phylogenetic analyses of complete envelope gene sequences. DENV-2 (Cosmopolitan genotype) predominated in 2004, and DENV-3 (genotype III) predominated in 2005-2006; these viruses were imported from India. Primary dengue infections outnumbered secondary infections, suggesting recent emergence.