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

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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?