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

Dhimal M, Ahrens B, Kuch U - PLoS ONE (2015)

Bottom Line: 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.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.

View Article: PubMed Central - PubMed

Affiliation: Nepal Health Research Council (NHRC), Ministry of Health and Population Complex, Kathmandu, Nepal; Biodiversity and Climate Research Centre (BiK-F), Senckenberg Gesellschaft für Naturforschung, Frankfurt am Main, Germany; Institute for Atmospheric and Environmental Sciences (IAU), Goethe University, Frankfurt am Main, Germany; Institute of Occupational Medicine, Social Medicine and Environmental Medicine, Goethe University, Frankfurt am Main, Germany.

ABSTRACT

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 December 2014 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.

No MeSH data available.


Related in: MedlinePlus

Spatiotemporal distribution of malaria in Nepal (1978–2012).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.
© Copyright Policy
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC4472520&req=5

pone.0129869.g003: Spatiotemporal distribution of malaria in Nepal (1978–2012).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.

Mentions: In Nepal, a heterogeneous spatial distribution and fluctuating trend of malaria incidence has been reported with a higher incidence in southern districts bordering India [90]. The distribution of the disease, which was previously confined to the forest and forest fringe regions of the Terai lowlands and so-called Inner Terai valleys and hills (<1,200 m asl) in 38 districts [86], is now observed to extend to the hills and mountains (> 2,000 m) [87] and malaria is now endemic in 65 out of the 75 administrative districts [89,102]. Fourty four species of Anopheles mosquitoes have been recorded in Nepal and out of these, seven have been incriminated in malaria transmission (Anopheles minimus, An. fluviatilis, An. maculatus, An. dravidicus, An. pseudowillmori, An. willmori and An. annularis). They were observed at least 2,000 m asl [95] and cause seasonal malaria epidemics in Nepal, including in areas above 2,000 m [51,52]. During the last decade, the incidence of confirmed malaria cases has declined significantly in Nepal following the introduction of the free distribution of long-lasting insecticide impregnated bed-nets (LLINs) and artemisinin combination therapy (ACT) for the treatment of Plasmodium falciparum malaria [89]. However, the proportions of P. falciparum and imported malaria cases have increased considerably in comparison to the total number of confirmed malaria cases [89]. This implies the possibility of a gradual shift in the Plasmodium parasite population possibly due to the rising temperature trends. Moreover, indigenous cases of P. vivax malaria and P. falciparum infections have been reported from the hill and mountain regions of Nepal in later years. A positive relationship between rainfall and malaria cases with a certain time lag has been observed in Nepal [87]. A significantly positive correlation of malaria incidence with minimum as well as maximum temperatures and rainfall was found in a study conducted in the high-endemic malaria district of Jhapa [88]. However, non-climatic variables were not included in the analysis in that study, and the climatic variables assessed were not significant predictors of malaria incidence in time series analysis. Another recent study shows that a1°C increase in minimum and mean temperatures increased malaria incidence by 27% and 25%, respectively. The reduction in malaria incidence was 25% per one unit increase of LLINs [23]. The spatiotemporal distribution of malaria in Nepal (1978–2012) is presented in Fig 3 [50,86,90,103].


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

Dhimal M, Ahrens B, Kuch U - PLoS ONE (2015)

Spatiotemporal distribution of malaria in Nepal (1978–2012).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.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4472520&req=5

pone.0129869.g003: Spatiotemporal distribution of malaria in Nepal (1978–2012).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.
Mentions: In Nepal, a heterogeneous spatial distribution and fluctuating trend of malaria incidence has been reported with a higher incidence in southern districts bordering India [90]. The distribution of the disease, which was previously confined to the forest and forest fringe regions of the Terai lowlands and so-called Inner Terai valleys and hills (<1,200 m asl) in 38 districts [86], is now observed to extend to the hills and mountains (> 2,000 m) [87] and malaria is now endemic in 65 out of the 75 administrative districts [89,102]. Fourty four species of Anopheles mosquitoes have been recorded in Nepal and out of these, seven have been incriminated in malaria transmission (Anopheles minimus, An. fluviatilis, An. maculatus, An. dravidicus, An. pseudowillmori, An. willmori and An. annularis). They were observed at least 2,000 m asl [95] and cause seasonal malaria epidemics in Nepal, including in areas above 2,000 m [51,52]. During the last decade, the incidence of confirmed malaria cases has declined significantly in Nepal following the introduction of the free distribution of long-lasting insecticide impregnated bed-nets (LLINs) and artemisinin combination therapy (ACT) for the treatment of Plasmodium falciparum malaria [89]. However, the proportions of P. falciparum and imported malaria cases have increased considerably in comparison to the total number of confirmed malaria cases [89]. This implies the possibility of a gradual shift in the Plasmodium parasite population possibly due to the rising temperature trends. Moreover, indigenous cases of P. vivax malaria and P. falciparum infections have been reported from the hill and mountain regions of Nepal in later years. A positive relationship between rainfall and malaria cases with a certain time lag has been observed in Nepal [87]. A significantly positive correlation of malaria incidence with minimum as well as maximum temperatures and rainfall was found in a study conducted in the high-endemic malaria district of Jhapa [88]. However, non-climatic variables were not included in the analysis in that study, and the climatic variables assessed were not significant predictors of malaria incidence in time series analysis. Another recent study shows that a1°C increase in minimum and mean temperatures increased malaria incidence by 27% and 25%, respectively. The reduction in malaria incidence was 25% per one unit increase of LLINs [23]. The spatiotemporal distribution of malaria in Nepal (1978–2012) is presented in Fig 3 [50,86,90,103].

Bottom Line: 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.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.

View Article: PubMed Central - PubMed

Affiliation: Nepal Health Research Council (NHRC), Ministry of Health and Population Complex, Kathmandu, Nepal; Biodiversity and Climate Research Centre (BiK-F), Senckenberg Gesellschaft für Naturforschung, Frankfurt am Main, Germany; Institute for Atmospheric and Environmental Sciences (IAU), Goethe University, Frankfurt am Main, Germany; Institute of Occupational Medicine, Social Medicine and Environmental Medicine, Goethe University, Frankfurt am Main, Germany.

ABSTRACT

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 December 2014 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.

No MeSH data available.


Related in: MedlinePlus