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Adaptation to Vector borne
Diseases Due to Climate
Change
Prof. Dr. Hidayatulfathi Othman, Faculty of Health Sciences,
Universiti Kebangsaan Malaysia.
What is Climate Change?
Climate change (a.k.a. global warming) is significant statistical, lasting change of weather over decades or longer spans of time. LocalGlobal
Not from seasonal or single events.
Climate Forcings
Factors that can shape climate: • Variations is solar radiation• Deviations in the earth’s orbit• Mountain building/continental
drift• Changes in greenhouse gas
concentrations
Climate vs. Weather Effects
Climate
Average trend of
weather patterns for a
given location (averages
over a long time period)
Constrains the range of
infectious disease
E.g., malaria in Kenyan
Highlands
Epstein, 2001; Patz, 2002
Weather
Day-to-day climate
conditions for a given
location (shorter time
periods, highly variable)
Affects the timing and
intensity of outbreaks
E.g., dengue outbreak
in Sumatra
Human Influences
Vector-borne Disease
What is VBD?
Types of VBD transmission:
Human-vector-human
(Anthroponotic Infections)
Vector
Humans
Humans
Vector
Malaria
Dengue
Yellow fever
Animal-vector-human
(Zoonotic Infections)
Vector Vector
Animals
Animals
Humans Lyme disease
Hantaviral disease
Most arboviral diseases (e.g., WNV)
Vector-borne Disease Dynamics
Susceptible
population
• Migration (forced)
•Vector environment
Vector
•Survival, lifespan
•Reproduction/breeding patterns
•Biting behavior
Pathogen
•Survival
•Transmission
•Replication in host
What Does Climate Change
Have to Do With Bugs and
Disease?
The World is a Smaller Place
Air Travel
Shipping Routes
Global Temperature
Temperature Increase
U.K.’s Hadley Centre for Climate Change “Business as Usual Prediction”
NOAA’s Prediction
Vector-borne Disease Mortality Distribution
WHO, 2005
Vector-borne Diseases of Concern
Disease Pathogen Vector Transmission
Protozoan
Malaria Plasmodium falciparum,
vivax, ovale, malariae
Anopheles spp. Mosquitoes Anthroponotic
Leishmaniasis * Leishmania spp. Lutzomyia & Phlebotomus
spp. Sandflies
Zoonotic
Trypanosomiasis * Trypanosoma brucei
gambiense, rhodesiense
Glossina spp.
(tsetse fly)
Zoonotic
Chagas disease * Trypanosoma cruzi Triatomine spp. Zoonotic
* WHO neglected tropical disease Hill et al., 2005
Vector-borne Diseases of Concern (cont.)
Disease Pathogen Vector Transmission
Viral
Dengue * DEN-1,2,3,4 flaviviruses Aedes aegypti mosquito Anthroponotic
Yellow fever Yellow fever flavivirus Aedes aegypti mosquito Anthroponotic
Encephalitis
(West Nile, Lyme, etc.)
Flavi-,alpha- and
bunyaviruses
Mosquitoes and ticks Zoonotic
Firlarial nematodes
Lymphatic filariasis * Brugia malayi, timori,
Wuchereria bancrofti
Anopheles, Culex, Aedes
mosquitoes
Anthroponotic
Onchocerciasis * Onchocerca volvulus Simulium spp. blackflies Anthroponotic
* WHO neglected tropical disease Hill et al., 2005
Main cause for VBD
outbreaks
Temperature
Rainfall change
Extreme event
Precipitation (?)
Precipitation Effects on Vectors
Vector Survival: increased rain may increase larval
habitat
Excess rain can eliminate habitat by flooding
Low rainfall can create habitat as rivers dry into
pools (dry season malaria)
Decreased rain can increase container-breeding
mosquitoes by forcing increased water storage
Heavy rainfall events can synchronize vector
host-seeking and virus transmission
Increased humidity increases vector survival and
vice-versaGubler et al., 2001
Precipitation Effects on Pathogens
PathogenFew direct effects : e.g. exhibited some data on
humidity effects on malarial parasite development.
Extrinsic incubation period affected
Gubler et al., 2001
Climate Change, Disease and
Vectors
Effects of Climate Change
Warmer Winters•Higher survival rates for vectors
Predicted to produce more extreme weather: Effects of Hurricane Katrina
•Heavy Rains•Flooding
Displaced people particularly vulnerable to disease.
Drivers of global change considered in relation to potential changes in the status of vector-borne diseases.
Sutherst R W Clin. Microbiol. Rev. 2004;17:136-173
https://www.npr.org/assets/graphics/2019/03/mosquito-habitat.gif
Source: Sadie J. Ryan, Colin J. Carlson, Erin A. Mordecai, and Leah R. JohnsonCredit: Koko Nakajima/NPR
Mosquito-Borne Diseases
http://www.google.com/imgres?q=dengue&um=1&hl=en&safe=active&sa=N&rls=com.microsoft:en-us&biw=1680&bih=866&tbm=isch&tbnid=3PDoJlm517-70M:&imgrefurl=http://www.dengue-fever-symptoms.com/&docid=lM31_6PNhUNGvM&imgurl=http://www.dengue-fever-
symptoms.com/images/dengue%252520fever%252520symptoms.gif&w=356&h=356&ei=p_wzT9iXJeWqiQKwkoW3Cg&zoom=1&iact=rc&dur=78&sig=113004992271279760932&page=1&tbnh=152&tbnw=163&start=0&ndsp=28&ved=1t:429,r:2,s:0&tx=123&ty=104
Increased relative humidity increases activity, heavy rainfall decreases activity
Increased activity increases transmission rates
Ogden et al., 2005;
Vail and Smith, 1998
National Geographic Ranger DJ
Vector Activity
Direct effects of temperature on mortality rates* Temperature effects on development: at low
temperatures, lifecycle lengthens and mortality outstrips
fecundity*
Tsetse mortality,
Rogers and Randolph, 2003
* Non-linear
(quadratic)
relationships
with temperature
Vector Survival
Vector and Host Seasonality
Vector-borne zoonoses mostly maintained
by wildlife
Humans are irrelevant to their ecology
Vectors and their hosts are subject to
seasonal variations that are climate
related (e.g., temperature) and climate
independent (e.g., day-length)
Seasonal variations affect abundance and
demographic processes of both vectors and
hosts
Vector seasonality due to temperature affects
development and activity → transmission
Host demographic processes (reproduction, birth and
mortality rates), affected directly by weather and indirectly by resource availability → VBD
epidemiology
Vector and Host Seasonality (cont.)
Evidence Reviewed by the IPCC
Emerging evidence shows:
• Altered the distribution of some infectious
disease vectors (medium confidence)
• Altered the seasonal distribution of some
allergenic pollen species (high confidence)
• Increased heatwave-related deaths (medium
confidence)IPCC AR4, 2007
Responding to Possible
Climate Change
Long-term ecological and epidemiological research on how environmental changes influence disease cycles.
Enhanced surveillance
- Appearance of human cases in previously disease-free areas
- Introduction of new vectors, hosts, or pathogens
- Changing transmission patterns in existing foci
Strengthen public health infrastructure to improve
recognition and response
Responding to Possible
Climate Change
Identify potentially vulnerable
populations.
Maintain awareness of other changes that could interact with climate changes to result in emerging disease risks.
Measures to reduce the spread of disease or disease vectors and hosts.
Review, evaluate and prepare countermeasures (vaccines, therapeutic agents, insecticides, etc.).
The question
Are we ready to face VBD explosion due to climate change?