The authors have declared that no competing interests exist.
Conceived and designed the experiments: MD. Analyzed the data: MD. Contributed reagents/materials/analysis tools: MD UK BA. Wrote the paper: MD BA UK.
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.
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.
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.
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.
According to the latest report of the Intergovernmental Panel on Climate Change (IPCC), the average warming of the global mean surface temperature was 0.85°C [0.65–1.06°C] over the period of 1880 to 2012 [
Most of the VBDs are transmitted by insect vectors and caused by pathogens that circulate in the human or between human and other animal populations [
Although no single factor can fully explain the transmission of VBDs, climate change can alter the geographical distribution of disease vectors and VBDs [
Nepal is one of the most vulnerable countries with respect to climate change because it is positioned in the southern rim of the so-called “Third Pole” of our planet (the Himalaya-Hindu Kush mountain range and the Tibetan Plateau). It has a complex topography and a low level of development [
Diseases | Pathogen | Reservoir | Principal vector | Reported confirmed cases in 2012 |
References |
---|---|---|---|---|---|
Malaria | Humans | 2,092 | [ |
||
Lymphatic filariasis | Humans | 28,855 | [ |
||
Visceral leishmaniasis (Kala-azar) | Mammals | 575 | [ |
||
Dengue fever | Dengue virus (Flaviviridae) | Humans | 183 | [ |
|
Japanese encephalitis | Japanese encephalitis virus (Flaviviridae) | Birds, pigs | 129 | [ |
aReported cases to the Epidemiology and Disease Control Division [
The Nepal National Adaptation Programme of Action (NAPA) to climate change has identified VBDs as one of the highest priority adaptation projects forthe health sector in Nepal [
A systematic literature search was performed and summarized information on climate change and the spatiotemporal distribution of VBDs in Nepal following providing items for systematic review and meta-analysis(PRISMA) guidelines. We searched for peer-reviewed articles published in English language before December2014 in the PubMed and Web of Science databases. Besides, we searched for relevant journal articles in Google Scholar and retrieved government reports from their web sites. We used the following search terms in title, abstract and keywords:
Nepal and Climate, climate change, temperature, rainfall, precipitation, relative humidity, weather,
We first screened “titles”, “abstracts” and “keywords” for relevant articles and then read full text articles to evaluate them according to our inclusion criteria. Furthermore, the reference lists of each selected research article were then evaluated using the snowball sampling technique if they had been missed in the electronic databases. Inclusion criteria for selecting studies are listed below:
Studies must include climatic variables (Rainfall, temperature and humidity) that analyse the trend of climatic data and are relevant for the study of VBDs
Epidemiological studies dealing with the spatial and temporal distribution of disease vectors and disease transmission and/or epidemiological studies assessing the association of VBDs with climatic variables
Only studies published before December2014 and with a study area in Nepal
The selected papers were systematically reviewed and thematically analysed. Conference proceedings, viewpoint articles, review articles, project reports and theses were excluded. Given the low number of studies meeting the inclusion criteria and their mostly descriptive nature, a quantitative meta-analysis was not appropriate. Therefore, we alternatively summarized the state of the art on climate change and the spatiotemporal distribution of VBDs in Nepal. The spatio-temporal distributions of VBDs from the published literature was projected onto a map of Nepal using GIS software.
The preferred PRISM flow diagram of our literature search is given in
Topics | Full-texts retrieved | Included in qualitative synthesis |
---|---|---|
Climate change | 65 | 12 |
Malaria | 98 | 8 |
Lymphatic filariasis | 8 | 7 |
Visceral leishmaniasis (Kala-azar) | 110 | 8 |
Dengue fever | 27 | 9 |
Japanese encephalitis | 45 | 11 |
Climatic factors and VBDs | 8 | 8 |
aSome studies dealt with more than one diseases and their vector. Hence, the total number of final studies included in the qualiatitive synthesis was 50 (Tables
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 associate climatic factors with VBDs in Nepal. Among these eight studies, one dealt with malaria and VL, one with dengue and LF, three dealt with malaria and one each with JE, LF and VL.
A summary of the main findings from the analysis of climatic variables is provided in
Panels A, B, C and D show, respectively, the trend of confirmed malaria, dengue fever, visceral leishmaniasis and Japanese encephalitis cases reported to the Epidemiology and Disease Control Division, Department of Health Services, Ministry of Health and Population, Government of Nepal.
Study | Location (Study period) | Climatic variables | Method | Main findings | Comments |
---|---|---|---|---|---|
Shrestha |
Nepal (1971–1994) | Maximum temperature | Trend analysis based on observed station data | Higher warming rates in high-elevation areas (mountain and Himalayan regions) compared to lowlands (Terai and Siwalik hills). Warming rates were highest in the post-monsoon season followed by winter | The rate of warming in Nepal shows features similar to that of the northern hemisphere but its warming rate is much higher than the global average |
Shrestha |
Nepal (1948–1994) | Rainfall | Trend and spectral analysis based on observed station data | Monsoon precipitation series shows great interannual variability and decadal variability in the amount of precipitation without any distinct trend | Precipitation records from Nepal resemble those of northern India suggesting that all-India precipitation data cannot provide a valid representation of the entire Indian sub-continent. |
Kansakar |
Nepal (1965–1995) | Precipitation | Cluster analysis based on observed station data | Reports spatial and temporal variation in precipitation pattern and significant roles of mountainous relief in yielding localized precipitation patterns, and precipitation timing is more stable than its amount. | Precipitation in Nepal is broadly contributed by monsoon and western disturbances |
Baidya |
Nepal (1961–2006) | Temperature and rainfall | Trend analysis based on observed station data | Both temperature and precipitation extremes show increasing trends. Decreasing trends of cool days and increasing trends of warm days are very prominent at higher elevation. Similarly, precipitation extremes show increasing trends in total and heavy precipitation events at most stations | The temperature data of only 8 stations from 1971–2006 and precipitation data of 26 stations between 1961–2006 were included in analyses. |
Dobler |
South Asia (1961–2100) | Precipiation | Regional Climate Models projections | Over 70% decrease in monsoon rainfall in parts of northern India at the end of 21 century is predicted. | Because of higher evapotranspiration rates with higher temperature, a decreasing trend in water availability is possible. |
Shrestha |
Nepal (1977–2000) | Maximum temperature | Trend analysis based on observed station data | The extended analysis also shows an increasing trend of maximum temperature without decrease; warming in winter is more pronounced compared to other seasons | A similar analysis of precipitation data does not reveal any significant trend (precipitation depends on monsoon circulation in Nepal) |
Kattel |
Nepal (1985–2004) | Temperature | Regression analysis based on observed station data | A bi-modal pattern in the annual cycle of temperature lapse rate is observed (two maxima in the pre-and post-monsoon seasons and two minima in the winter and summer season) which are in contrast to results from other mountain regions. | Air temperature records from 56 meteorological stations in Nepal ranging from 72 to 3920 m asl were used for analysis. The temperature lapse rates in the southern slopes of the central Himalayas are in contrast to those from other mountains suggesting that different controlling factors are associated with them. |
Shrestha |
Central Himalayas (1998–2008) | Rainfall | Spatiotemporal variation analysis based on satellite data | A strong positive relationship between elevation and rainfall during the pre-monsoon season and two significant rainfall peaks during the summer monsoon season were found over the southern slope of the Himalayas; the primary peak along the Sub-Himalayas (~500–700 m asl) and the second peak along the Lesser Himalayas (~2,000–2,200 m asl) | Only data from the pre-monsoon and summer monsoon seasons were included in analyses; the highest altitude considered was 5,000 m asl. |
Kattel |
Nepal (1980–2009) | Temperature | Trend analysis based on observed station data | A statistically significant average warming trend with a prominent rise of maximum temperatures is found while minimum temperature trends show greater variability among stations | Only 13 mountain stations ranging from 1304–2566 m asl were included for analysis |
Kulkarni |
Hindu-Kush Himalayan (HKH) Region (1961–2098) | Temperature and rainfall | Regional Climate Models projections | The model projections indicate significant warming throughout the HKH region towards the end of the 21st century. For 2011–2040, temperature is projected to increase by 0.5–1°C; for 2040–2070, by 1–3°C and for 2071–2098, by 4–5°C. In contrast, precipitation projections indicate a declining trend of monsoon precipitation especially in the Central Himalayas between 2011–2070 compared to the baseline period 1961–1990 | The high resolution regional simulations were generated using the regional climate model PRECIS and were validated using observedAPHRODITE precipitation data and NCEP/NCAR temperature data. |
Qi |
Mt. Qomalangma (Everest) Region in Nepal (1971–2009) | Temperature and precipitation | Trend analysis based on observed station data | A significant increase in annual mean temperature (0.025°C/year) highly influenced by maximum temperature was found. Similarly, annual precipitation shows an increasing trend (4.77 mm/year) with concentration of precipitation mainly in the monsoon period. | In contrast, the northern slope temperature rise is highly influenced by minimum temperature and precipitation is many times lower compared to the southern slope indicating a barrier effect of the Himalayas. |
Aryal |
Mustang, Nepal (1987–2009) | Temperature and precipitation | Regression analysis based on observed station data | Maximum and minimum temperature have increased over the years with a significant average increase of the mean annual temperature (0.13°C/year). Similarly, precipitation has increased significantly (0.541 mm/year). | The significant snow melt perceived by local people might be due to combined effects of higher temperature and increased rainfall. |
Study | Location (Study period) | Diseases /vector | Method | Main findings | Comments |
---|---|---|---|---|---|
Pandey |
Nepal (2004) | Dengue | Case report | The first reported case of dengue virus (DENV) infection in Nepal | The case was a Japanese volunteer in Nepal |
Malla |
Nepal (2006) | Dengue fever and vector | Descriptive | First reported outbreak of dengue fever with confirmation of local transmission by |
All four serotypes of DENV reported to circulate |
Shah |
Western Nepal (August 2008-November 2009) | Dengue fever | Descriptive | Report of geographical expansion of dengue virus to new areas (western Nepal) | Only sero-prevalence survey |
Dumre |
Nepal (2005–2010) | Dengue fever | Descriptive | Rapid expansion of dengue fever within a short period of time with confirmation of dengue fever from 18 districts including four hill districts. | There is no dengue fever surveillance network and cases (from referral laboratory) are grossly underreported |
Pandey et al. 2013 [ |
Nepal (2010) | Dengue fever | Descriptive | Dengue virus 1 was possibly responsible for the 2010 epidemic and imported from India to the Terai lowlands of Nepal from where it spread to the highlands. The primary vector |
DENV isolation from mosquitoes was not performed |
Henderson |
Eastern Nepal (1983) | Japanese encephalitis | Descriptive | Report of JEV introduction in southern Nepal in the late 1970s after a major epidemic in northern states of India | High susceptibility of adults is taken as an indicator of a recent introduction of JEV |
Zimmerman |
Kathmandu valley (1995) | Japanese encephalitis | Descriptive | Report on first epidemic of JE among local residents of Kathmandu valley in 1995 | Records of only one hospital were reviewed excluding children |
Bista and Shrestha, 2005 [ |
Nepal (1978–2003) | Japanese encephalitis | Descriptive | JE was endemic in 24 districts of lowlands (Terai and inner Terai) with the majority of cases occurring in the monsoon season | Possible expansion of JE virus in temperate regions is discussed |
Partridge |
Kathmandu valley (2006) | Japanese encephalitis | Descriptive | Local transmission of JE in Kathmandu confirmed with majority of cases reported during and after the monsoon season. | Laboratory confirmed JE cases were followed up to confirm area of residence and travel history to JE endemic areas |
Bhattachan |
Nepal (2007) | Japanese encephalitis | Descriptive | JE confirmed as endemic in 21 additional hill and 3 three mountain districts previously considered non-endemic | No detailed information on new JE endemic districts is provided |
Impoinvil |
Nepal (2004–2008) | Japanese encephalitis | Local Indicators of Spatial Association (LISA) analysis and Spatial lag regression model | The distribution of JE after 2005 has shifted to Kathmandu valley and mountain districts showing a significant negative relationship between JE incidence and April precipitation, and a significant positive association between JE incidence and the percentage of irrigated land, climatic, agriculture and land cover parameter. Before 2006, JE cases were clustered in the lowlands | Only data of 2005 was used to fit a spatial lag regression model with climate, agriculture and land cover as explanatory variables |
Thakur |
Four mountain districts of Nepal (July-August 2010) | Japanese encephalitis | Generalized linear mixed modelling | Report of JE virus infections among pig populations in high-altitude mountain districts with decreasing risk of seropositivity with increasing elevation | Impact of climate change on the circulation of JE virus in mountain districts is discussed |
Robertson |
Nepal (2007–2011) | Japanese encephalitis | Geographically weighted regression | Cases were positively associated with a high degree of landscape mixing and small-scale agriculture | A recent trend towards establishment of Japanese encephalitis in the Kathmandu valley and mountain districts was confirmed in this analysis |
Jung 1973 [ |
Kathmandu (1972) | Lymphatic filariasis and vector | Descriptive | Study area was limited to Central Nepal | |
Scherchand |
Nepal (2001) | Lymphatic filariasis | Descriptive | Epidemiological mapping of lymphatic filariasis showed that 33 out of 37 districts were endemic including densely populated districts of Kathmandu valley (~1,400 m asl) | The highest altitude sampled was 1,400 m asl |
Adhikari |
Four districts of Nepal (Feb-July 2007) | Lymphatic filariasis | Descriptive | The highest microfilaria infection rate and aysmptomatic cases were recorded in mountain districts compared to lowland and hill districts. | Entomological data were not collected |
Pradhan |
Mugu district (Gum Valley) (1969) | Malaria and vector | Descriptive | Local malaria transmission along with malaria vectors were recorded above 1,800 m in Nepal. The malaria vector |
Malaria transmission was seasonal |
Sakya 1981 [ |
Nepal (1978–1980) | Malaria | Descriptive | Malaria cases were reported from 38 districts out of a total of 75 districts, including the Terai lowlands and hill districts mostly below 1,200 m asl. | Cases were detected under active malaria surveillance and follow-up of all confirmed cases was performed |
Dahal 2008 [ |
Nepal (1978–2006) | Malaria and Visceral leishmaniasis | Descriptive | Malaria incidence has declined remarkably over the years but the number of districts where malaria is prevalent increased to 67. A positive relationship between rainfall and malaria cases with a certain time lag (1–2 months) is reported. Similarly, positive relationship between annual mean temperature and rainfall with Visceral leishmaniasis cases is reported | Only a few years monthly data were used to show an association of rainfall and malaria outbreaks. Only few years monthly data of Visceral leishmaniasis was used. |
Bhandari |
Jhapa district (1998–2009) | Malaria | ARIMA Time series analysis | Significant positive correlations between the climatic variables temperature (minimum and maximum), rainfall and malaria cases were found. However, in time series analysis, climatic variables were not significant predictors of malaria incidence | Non-climatic variables were not included in time series analysis and climatic variables were not significant predictors |
Dhimal |
Nepal (2004–2012) | Malaria | Generalized linear models | Despite normal seasonality of rainfall and temperature during the study period, the incidence of annual confirmed malaria cases declined significantly in historical lowland high and moderate-risk districts. This coincided with the free distribution of long-lasting insecticidal nets (LLINs) suggesting that effective vector control interventions can outweigh the role of climate. However, the risk of malaria epidemics in highlands is predicted to increase due to climate change. | Malaria, non-malaria (Total outpatients visits per year, childhood diarrheal diseases and acute respiratory infection) and climatic data were analysed. |
Dhimal |
Kailali and Jhapa districts of Nepal (2004–2012) | Malaria | Generalized additive mixed models | Strong relationship between monthly temperature and malaria incidence is reported. A 1°C increase in minimum and mean temperatures increased malaria incidence by 27% and 25%, respectively. Malaria hotspots persisted mostly in the same villages of Kailali district, whereas in Morang district malaria hotspots shifted to new villages after the introduction of LLINs. | A combined model with both climatic and non-climatic predictors was not developed and net effect of vector-control interventions and climatic factors is not known. |
Kakchapati and Ardkaew, 2011[ |
Nepal (1998–2009) | Malaria | Negative binomial regression modelling | A decreasing trend in the incidence of malaria (1998–2004), followed by a more moderate upward trend until 2008 is found. Zero malaria incidences occurred in six districts for over twelve years and higher incidences were reported among districts bordering India except Kavre district. | Only yearly malaria incidence was used without categorizing indigenous and imported cases, or malaria infections by parasite species |
Peters and Dewar 1956 [ |
Central Nepal (1954–1955) | Vector | Descriptive | Secondary vector of dengue ( |
Highest altitude district studied was Kathmandu |
Joshi |
Nepal (1956–1965) | Vector | Descriptive | Principal vector of JE, |
The highest altitude surveyed was 1400 m asl; survey confined to eastern and central Nepal only |
Darsie and Pradhan 1990 [ |
Nepal (1950–1989) | Vector | Descriptive | The principal vectors of lymphatic filariasis ( |
The principal vector of dengue virus ( |
Darsie |
Mustang district (1993) | Descriptive | Breeding of |
These |
|
Gautam |
Kathmandu (April-June 2009) | Vector | Entomological survey | First report of the dengue virus vector |
Only larvae were recorded (in June) |
Byanju |
Bhakatapur, Nepal (April-September 2011) | Vector | Descriptive | Lymphatic filariasis vectors ( |
No significant effects of month and climatic variables reported (but sampling only in warm months and method of data analysis is not explained in detail) |
Dhimal |
Nepal (September 2011-February 2012) | Vectors | Generalized linear models | Significant effects of climatic factors (temperature, relative humidity, precipitation) on the abundance of |
|
Dhimal |
Eastern Nepal (2012–2013) | Vectors | Longitudinal Entomological survey | The known malaria vectors in Nepal, |
The maximum altitude covered in the survey was 2,500 m asl and relationship with climatic factors was not determined in this study. |
Joshi |
Khotang district 2006 | Visceral leishmaniasis | Case study | Autochthonous Visceral leishmaniasis case (10 yearl-old girl) from a Visceral leishmaniasis non-endemic district of eastern Nepal. | Referral case for diagnosis; the patient had no travel history to India or Visceral leishmaniasis endemic areas within Nepal. |
Joshi |
Nepal (1980–2003) | Visceral leishmaniasis | Descriptive | Increasing trend of Visceral leishmaniasis reported with majority of cases occurring during the rainy season and fewest during the winter. | Cased were confined to districts bordering the Indian state of Bihar |
Pandey |
Doti district 2011 | Visceral leishmaniasis | Case study | The first autochthonous case of Visceral leishmaniasis(13-year-old male) from a VL non-endemic hilly district of western Nepal. | Referral case for diagnosis; the patient had no travel history to India or Visceral leishmaniasis endemic areas within Nepal. |
Pun |
Nepal (April 1999-March 2009) | Visceral leishmaniasis | Descriptive | Increasing trend and geographic distribution of visceral leishmaniasis at a referral hospital from a non-endemic district | No classification of cases into autochthonous and imported ones |
Scharz |
Achham district, Nepal (2011) | Visceral leishmaniasis | Case study | An autochthonous Visceral leishmaniasis case (17year-old woman) is reported from a Visceral leishmaniasis non-endemic hilly district of western Nepal. | Referral case for diagnosis; the patient had no travel history to India or Visceral leishmaniasis endemic areas within Nepal. |
Pun |
Nepal (September 2010-October 2011) | Visceral leishmaniasis | Descriptive | Report of a series of locally transmitted autochthonous Visceral leishmaniasis cases from areas previously considered non-endemic, mostly in hill and mountain regions | Only referral cases in a tertiary care hospital in Kathmandu were included; the actual incidence of Visceral leishmaniasis in non-endemic areas can be expected to be many times higher |
Uranw |
Dharan, Sunsari district (2000–2008) | Visceral leishmaniasis | Outbreak investigation including case-control study | Report of urban transmission of Visceral leishmaniasis in Dharan city with a strongly clustered distribution | High chances of recall bias especially among control group; climatic variables not considered in analysis. |
Although analyses of observed temperature and precipitation data are still limited in Nepal, climate change effects are already occuring. Temperature data show a warming trend in Nepal. This warming trend is influenced by maximum temperatures with higher warming rates in the mountain regions compared to the lowlands of Nepal [
However, changes in the extreme events, consistent with climate change effects, are more significnat in Nepal. A declining trend of cool days and inclining trend of warm days are observed in the higher altitudes of Nepal [
The Hadley Centre's high-resolution regional climate model PRECIS (Providing Regional Climates for Impact Studies) projects significant warming towards the end of the 21st century and a decrease in monsoon precipitation over the Central Himalayan region (which includes Nepal) during the period 2011–2040 and an increase in seasonal rainfall during the period 2071–2098 compared to the baseline period (1961–1990) [
In Nepal, a heterogeneous spatial distribution and fluctuating trend of malaria incidence has been reported with a higher incidence in southern districts bordering India [
The active case detection of malaria in Nepal between 1978 and 1980 recorded autochthonous malaria cases from 38 districts of the Terai and hill regions (< 1,200 m above sea level). Autochthonous malaria cases were recorded from 26 additional districts of Nepal between 1981 and 2012; these numbers also include malaria cases from mountain regions. The symbol (*) indicates that the classification of reported malaria cases, i.e., as autochthonous or imported, is not known.
The first reported case of dengue virus (DENV) infection in Nepal was a Japanese volunteer in 2004 [
Autochthonous dengue fever cases were recorded from ten districts of Nepal during the first outbreak in 2006. The travel history of dengue fever cases reported from Kathmandu in 2006 was not known. However local transmission of dengue virus and the presence of the primary dengue virus vector
In Nepal, VL cases were first recorded in 1980. At that time confirmed cases were confined to lowland Terai districts of eastern and central Nepal that border India’s state of Bihar, followed by records from 13 endemic districts and an increasing trend of incidence until 2003 [
Before 2006, visceral leishmaniasis (VL) was endemic only in 13 lowland districts of the Terai region bordering Bihar state, India. Between 2006 and 2011, autochthonous VL cases were reported from 11 additional districts mostly in the hills but including one in the mountains. Moreover, VL cases were reported from 25 additional districts but their origin (i.e., autochthonous or imported) is not known.
Infections with Japanese encephalitis virus (JEV) moved northward in India and began to be seen in Nepal in the late 1970s [
Japanese encephalitis (JE) cases were recorded only from 24 districts of the lowland Terai between 1978 and 2003 in Nepal. After the start of surveillance for acute encephalitis syndrome with the support of the World Health Organization (WHO) in May 2004, JE cases were reported from 40 additional districts including mountain regions between 2004 and 2012. Among these 40 additional districts, JE endemicity was confirmed for 27 districts including three mountain districts.
The mosquito species
In 2001, lymphatic filariasis mapping using immunochromatographic card tests in 37 districts of Nepal showed that LF was endemic in only 33 districts. Between 2002 and 2012, LF was confirmed as endemic in 60 districts of Nepal including mountain region districts.
The review of observed and future projections of climatic data show a conducive environment for the transmission of VBDs in Nepal, especially in the highlands (mountains) which had been assumed to be free from these diseases. Despite a decade-long armed conflict and political instability in Nepal, there has been a substantial decline in the incidence of all major VBDs except DF which has only emerged in Nepal since 2004. The presence of disease vectors and reports of series of autochthonous cases of VBDs in hill and mountain regions of Nepal that had previously been considered to be non-endemic suggests that the local transmission of VBDs might be favoured by rising temperatures. However, the transmission of VBDs among humans is more complex than mere temperature changes, and this fact has been extensively reviewed [
A warming trend of annual mean temperatures is observed throughout the country indicating that climate change is already occuringin Nepal. However, large spatial and temporal variation in the trends of minimum and maximum temperatures is observed across different meteorological stations. The warming signal is clearer for maximum temperature with a more pronounced warming in the mountains compared to the lowlands ofNepal. This is in sharp contrast to the warming trend of the Tibetan Plateau where the minimum temperature is increasing at a faster rate than the maximum temeprature [
Precipitation is one of the major climatic factors affecting transmission of VBDs. The absence of a distinct long-term trend in precipitation changes in Nepal despite increasing GHG and strongly increasing aerosol concentrations in the region (especially through the neighbouring countries India and China) might be explained by a moister but less intense monsoon circulation [
The observed declining trend of cool days and increasing trend of warm days in the higer altitudes of Nepal [
A review of elevation-dependent warming and its possible causes in four high mountain regions–the Swiss Alps, the Colorado Rocky Mountains, the Tibetan Plateau/Himalayas, and the Tropical Andes–showed variation in the trends of extreme temperatures suggesting the need for a comprehensive study analysing the minimum and maximum temperatures separately for all mountain regions together to better understand elevation-based warming in mountains [
Several studies predict an increasing trend of the epidemic potential and the transmission season of malaria in temperate regions due to climate change [
Although the first autochthonous case of DENV in Nepal was confirmed at the beginning ofthe first outbreak in 2006, the case of a DENV infection in a Japanese volunteer to Nepal in 2004 [
Resistance development to first-line drugs against VL and the inadequate implementation of vector control interventions have been reported as the major causes for this increasing trend of VL in Nepal [
As the reported major environmental factors influencing JEV transmission in Asia including Nepal are temperature and precipitation [
The establishment of
Although socio-economic development, medical care and vector-control measures can outweigh the influence of climate change on VBDs in some areas [ Entomological, virological and parasitological research in different transects along an altitudinal gradient across the country to determine the presence of vectors and their role in disease transmission Development of VBD risk maps for Nepal based on entomological, virological and parasitological evidence and climatic as well as land use to better guide the allocation of limited resources to the most vulnerable groups Social-ecological and socio-economic research to identify the adaptation needs in different ecological regions and settings and plan public health preparedness, taking into account ethnic, religious, cultural and gender differences
The studies reviewed here suggest that both the observed and projected climate are conducive for the transmission of VBDs in the mountain regions of Nepal which had previously been considered non-endemic for these diseases. The short-term data shows a clear association between climatic factors and VBDs, but it is complex and difficult to project long-term effects of climate change in the face of rapid environmental and socio-economic changes and attribution to climate change is not determined in the existing studies. Despite continuous efforts of the government to control them and their declining incidence over the last decade (except for DF), VBDs have over the years been expanding their geographical ranges especially in mountain regions of the country. This might be attributed to environmental changes, in particular climate change, along with socio-economic factors. However, the observed spatial expansion of VBDs in new areas, especially in cool margins of mountain regions, that is correlated with the observed warming climate does not necessarily show a causal relationship. As VBDs show a heterogeneous distribution and spatiotemporal variation in the trends of climatic variables across the country, well-designed long-term local studies are needed to determine attribution of climate change to the observed transmission and distribution of VBDs in new areas. Therefore, VBD monitoring, surveillance and research should be strengthened in areas where risk of VBD is not yet determinedand VBD control programmes are not yet focused. Moreover, tourists and returning migrant workers coming to Nepal from disease endemic regions (including the country’s own lowlands) should be made aware about VBDs, their responsibility and potential role in spreading infections especially when travelling in mountain regions, and should be encouraged to engage in reasonable preventive and prophylactic measures including vaccination.