This is a simplified presentation of the paper published in nature microbiology. I had presented this paper in Emerging Infectious Diseases meeting.

1. Jeevan Kumar Shrestha
Email: jeevan@smail.nchu.edu.tw
National Chung Hsing University
Taichung city, Taiwan.
1

2. Outline
• Introduction
• Methods
• Results
• Discussion
• Conclusion
2
Fig. 1. Searching breeding sites of Aedes

3. Introduction
Dengue
• Mosquito-borne viral infection by dengue virus
(DENV).
• Four known serotypes - DENV1, DENV2, DENV3
and DENV4.
• Cross-immunity is temporary.
• Subsequent infections by other serotypes increase
the risk of developing severe dengue.
• Severe dengue is a leading cause of serious illness
and death
3
Fig. 2. Cartoon of mosquito attack
Source: news18.com

4. Transmission
• Tropical and sub-tropical climates,
mostly in urban and semi-urban
areas.
• Same vector for chikungunya, yellow
fever and Zika viruses.
• Eggs can remain dry for months and
hatch when in contact with water.
• Disease control depends on vector
control.
4
(Chen et al., 2011)
Fig. 3. Transmission route of dengue virus to
human population

5. Epidemiology
10,000 deaths each year
390 million sub-clinical infections
100 million have clinical symptoms
3.9 billion people are at risk in 125 countries
Half of the world population
5

6. 6
Ecological niche modelling
Boosted regression tree
Multivariate empirical relationship between
probability of dengue presence and the
environmental conditions
1. Locations of disease reports in humans
2. Environmental conditions
3. Socioeconomic covariates
5 × 5 km spatial resolution global map
Fig. 4. Flow-chart of methods
Machine learning technique
Regression to produce
prediction model
Predict distribution of
species based on
environmental data
13,604 dengue occurrence locations
Between 1960 and 2015
Relative Concentration Pathways (RCP)
Shared Socioeconomic Pathways (SSPs)
2015, 2020,
2050 and 2080

7. • Relative Concentration Pathways (RCP)
• Greenhouse gas concentration (not emissions)
• Predict the global warming
• RCP4.5, RCP6, and RCP8.5 means a possible range of radiative
forcing values in the year 2100 (4.5, 6.0 and 8.5 W/m2)
• Shared Socioeconomic Pathways (SSPs)
• SSP1-The world shifts gradually toward a more sustainable path
• SSP2- Social and economic trends do not change markedly.
• SSP3- Competitiveness and security threats, regional conflicts and issues.
7
Terminology from Intergovernmental Panel on Climate Change
(IPCC)

8. Socioeconomic and environmental covariates
• Temperature
• Cumulative annual precipitation
• Minimum relative humidity
• Gross domestic product (GDP) per capita
• Human population density
• Environmental suitability for Aedes aegypti
• Environmental suitability for Aedes albopictus
8

9. Fig. 5. Environmental suitability for dengue occurrence
according to RCP6.0 and SSP2. 9
Unsuitable
environment
Suitable
environment
0
1
Results
Global probability data for 2015
North America
South America
Europe
Eastern China
Africa
Australia

10. 10
Unsuitable
environment
Suitable
environment
0
1
Results
Global probability data for 2020
Fig. 6. Environmental suitability for dengue occurrence
according to RCP6.0 and SSP2.
North America
South America
Europe
Eastern China
Africa
Australia

11. 11
Unsuitable
environment
Suitable
environment
0
1
Results
Global probability data for 2050
Fig. 7. Environmental suitability for dengue occurrence
according to RCP6.0 and SSP2.
North America
South America
Europe
Eastern China
Africa
Australia

12. 12
Unsuitable
environment
Suitable
environment
0
1
Results
Global probability data for 2080
Fig. 8. Environmental suitability for dengue occurrence
according to RCP6.0 and SSP2.
North America
South America
Europe
Eastern China
Africa
Australia

13. Results
• Increase suitability
• Southeastern USA
• Higher altitudes in central Mexico
• Northern areas of Argentina
• Inland areas of Australia
• Coastal eastern China and Japan
• Southern Africa and West Africa
13
Decline suitability (Slight)
Some areas in central East Africa
India
Reason
Higher temperature and lower rainfall

14. 2015 to 2020
Contraction
Stability
Expansion
Contraction
Stability
Expansion 14
Results
Risk analysis
Fig. 9. Change in population at risk
North America
South America
Europe
Eastern China
Africa
Australia

15. 15
2020 to 2050
Contraction
Stability
Expansion
Contraction
Stability
Expansion
Results
Risk analysis
Fig. 10. Change in population at risk
North America
South America
Europe
Eastern China
Africa
Australia

16. 16
2050 to 2080
Contraction
Stability
Expansion
Contraction
Stability
Expansion
Results
Risk analysis
Fig. 11. Change in population at risk
North America
South America
Europe
Eastern China
Africa
Australia

17. 17
Fig. 12. Predicted changes in the land area
Results
• The global land area suitable for
dengue increase.
• Africa have largest suitable land
area
• Europe is almost unaffected

18. 18
Fig. 13. Predicted increase in population at risk of dengue
• Increase in global population at
risk
• Low in Americas and Asia
• High in Africa and Europe
Results

19. Billions
of
people
at
risk
2015 2020 2050 2080
19
Fig. 14. Predicted change in the people at risk
Results
• The decline in the population at
risk at RCP4.5/SSP1
• Sustainable approach may
control disease in the future.

20. 20
• Europe
• No disease over the coming decades. Coastal areas around Turkey and southern
Spain become suitable.
• Risk increase from 0.22% in 2015 to just 0.62% in 2080
• World
• 2.25 billion more people will be at risk in 2080 i.e. 6.1 billion or 60% of the world’s
population
• Driven by population growth in already endemic areas
• RCP4.5/SSP1 suggest decrease between 2050 and 2080.
Results

21. Discussion
21
• It is average trend, not specific for certain years.
• Assume the stationarity of the effects and interactions of drivers of
dengue transmission.
• Absence of innovations and improvements in dengue control.

22. Conclusion
• Prioritizing resources and long-term planning
• vaccine dissemination
• insecticide
• Predict the time and location of disease transmission
• Actions today will have a significant impact on the future distribution
of dengue.
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