1. ENVIRONMENTAL CHANGE AND
VECTOR-BORNE DISEASE
By Dr Nik Nor Ronaidi bin Nik Mahdi

2. SCENARIOS OF GLOBAL CHANGE
 Global change refers to the complex of
environmental changes that is occurring around
the world as a result of human activities.
 Environmental change issues:
1. Atmospheric composition
2. Climate change
3. Urbanization
4. Land use and biodiversity loss
5. Industrial and agricultural pollution
6. Trade and travel

3. ASSESSMENT OF IMPACTS TO VBD
 Vulnerability:
 a measure of the potential impacts of a given change,
taking into account the adaptive capacity that is available
to the affected community to respond to that change.
 Exposure:
 A change in the geographical distribution of a VBD will
affect the exposure of naive hosts to that disease.
 Such a change can come about from the movement of
either a vector or pathogen to a new environment through
trade, human movement, or natural means.
 Sensitivity:
 the degree to which a system responds to an external
perturbation, (eg: change of temperature)
 The sensitivity of a human population to a change in
exposure depends on the immune status of the population.

5. ATMOSPHERIC COMPOSITION
 The Earth’s surface is kept warm by greenhouse gases, (water
vapor, CO2, methane, NO, and some industrial gases like
CFC).
 Concentrations of these gases is rising as a result of the
anthropogenic activities:
 burning of fossil fuels for power and transport →↑CO2
 Livestock and leakage from coal beds →↑methane.
 ↑CO2 →reduce the water loss through transpiration and act
as a fertilizer in plants.
 Indirect impact to VBD:
 ↑CO2 → plants produce more foliage (provide more favorable
microclimates for insect vectors) + plant growth seasons will be
extended (effectively increasing the duration of favorable
microclimates) + larger plants (provide more humid shelter for
insect vectors and pathogens)
 higher water table and soil moisture content →↑ in the frequency of
pools of open water that provide suitable habitat for mosquito
breeding.

6. CLIMATE CHANGE
 What is the different between weather and
climate?
 Weather is the continuously changing condition of
the atmosphere, usually considered on a time scale
that extends from minutes to weeks.
 Climate is the average state of the lower atmosphere,
and the associated characteristics of the underlying
land or water, in a particular region, usually
spanning at least several years.
 A statistical analysis to separate solar and
anthropogenic influences implied that 60% of the
warming in the last 140 years was due to human
activity (Beer et al, 2000)

7. CLIMATE CHANGE
 The increasing temperatures will intensify the
hydrological (rainfall and evaporation) cycle,
leading to an increased frequency and intensity
of extreme weather events such as storms, floods,
and droughts.
 It is estimated that average global temperatures
will have risen by 1.0–3.5 oC by 2100, increasing
the likelihood of many vector-borne diseases
(Watson RT et al, 1998).

8. CLIMATE CHANGE
 Mosquito species (e.g: Anopheles gambiae complex,
A. funestus, A. darlingi, Culex quinquefasciatus and
Aedes aegypti) are sensitive to temperature changes:
 larvae mature faster in higher temperature → greater
capacity to produce more offspring
 adult female mosquitoes digest blood faster and feed
more frequently in warmer climate → increasing
transmission intensity.
 malarial parasites complete extrinsic incubation faster
within the female mosquito as temperature rises →
increasing the proportion of infective vectors
 Increased precipitation may increase the number
and quality of breeding sites for vectors (e.g:
mosquitoes) and the density of vegetation,
increasing the availability of resting sites.

9. URBANIZATION
 Critical factors:
 Drainage and water supplies
 Poverty → no necessary infrastructure for the safe
storage and distribution of water and drainage of
wastewater (provide safe place for vector breeding)

10. LAND USE AND BIODIVERSITY
 Agricultural activities↑ due to population growth:
 ↑ needs for deforestation and water storage, supply, and
distribution for human consumption and irrigation
 These developments affects the opportunities available
for breeding by vectors of diseases.
 With changes in land use comes fragmentation of
habitats, loss of biodiversity and alteration of existing
vector-host-parasite relationships
 Deforestation:
 May increase the breeding of sun-loving Anopheles vectors
of malaria in Africa
 May reduce the incidence of lymphatic filariasis by exposed
the mosquito breeding sites to sunlight in Indonesia

11. INDUSTRIAL AND AGRICULTURAL
POLLUTION
 Endocrine-disrupting chemicals (EDCs):
 mimic or disrupt the activity of hormones, especially
estrogen and thyroid hormones, in humans and
animals
 include alkyl phenols, dioxins, organochlorine
pesticides, phthalates, polychlorinated biphenyls,
polybrominated diphenyl ethers, and synthetic
pyrethroids
 found in plastics, herbicides, and pesticides that are
distributed widely around the world.
 The side effects of these chemicals could reduce
options for human adaptation to vector-borne diseases
either by degrading immune responses or by
withdrawal of vector control products from the market.

12. TRADE AND TRAVEL
 One million people are reported to travel
internationally each day, and one million people
travel from developed to developing countries (and
vice versa) each week (Garret L, 1996).
 International trade in merchandise has increased
three- to fourfold over the period from 1980 to 2000,
with most of the increase occurring in Asia, where
there was a fivefold increase in the value of exports
(World Trade Organization)
 These movements has the potential to spread
disease pathogens and their vectors over long
distances.

14. MALAYSIA’S EXPERIENCE
 Filariasis:
 Wuchereria bancrofti and Brugia malayi
 main species of parasites in Malaysia are the periodic and
subperiodic strains of Brugia malayi
 Periodicity refers to the habit of the microfilaria, migrating
to peripheral blood at certain distinct times of the day.
 Periodic → night; Subperiodic → partially nocturnal and are
also found in peripheral circulation throughout the 24 h
cycle
 This synchronization of the parasite cycle to the circadian
rhythm is an evolutionary adaptation to the biting behavior
of the predominant vector
 Periodic B. malayi vectors (Anopheles campestris
mosquitoes, Mansonia uniformis and M. Annulifera) adapt
well to the rice fields and their associated irrigation canals,
ditches and drains in the coastal plains of northern
Peninsular Malaysia.

15.  Thus, the expansion of rice cultivation in the broad alluvial plains
of the states of Kedah, Perlis, Penang and Perak, resulted in
increased prevalence of periodic brugian filariasis in the 1960s and
70s (Cheong, 1983).
 However, Malaysia’s successful malaria control program, which
curtailed breeding of Anopheline mosquitoes, have resolved the
periodic B. Malayi endemic by the early 1990s.
 Subperiodic B. malayi adapts to a different ecosystem. Its vectors
(Mansonia bonneae, M. dives, M. uniformis and M. Indiana) breed
in riverine swampforest ecotypes → These habitats are often
inaccessible to mosquito larviciding, making these vectors
particularly difficult to control.
 In addition, subperiodic B. malayi is a zoonosis, with several
species of leaf monkeys (Presbytis spp.) and domestoc cats acting
as natural hosts.→rubber cultivation intrudes into the foraging
range of reservoir hosts (monkeys) which harbor subperiodic B.
malayi.
 However, as Malaysia industrializes, the changes in land use
patterns resulted in a gradual decrease in disease rates.

16.  Dengue:
 The ecology of dengue in Malaysia was dramatically altered
by the rapid pace of urbanization that occurred from the mid–
1970s onwards.
 Vectors: Aedes aegypti and A. Albopictus
 A. aegypti is well adapted as an urban, domestic,
anthropophilic mosquito, breeding in artificial containers
where relatively clean clear water is retained.
 A. albopictus was originally a sylvatic/rural mosquito,
breeding in outdoor natural water-retaining habitats such as
tree holes and leaf axils of some plant species including
banana plants and various types of palm.
 A variety of other human activities contribute to breeding of
Aedes
 Agricultural refuse of plantation cash crops such as cocoa and
coconuts produces water-filled pods and shells which provide
Aedes breeding niches → outbreak in cocoa pods in Serian,
Sarawak.

17.  The construction industry has also become an important
source of Aedes vectors, since many breeding habitats
are present in flooded basement parking lots, lift shafts,
foundation pits and balconies during the active phase of
construction.
 During the economic downturn in 1997/1998, numerous
abandoned construction sites in Penang became such a
serious source of breeding sites for aedes (Lim, Foong,
Abu-Hassan, & Kwa, 2000).

18. FRAMEWORK FOR DESIGNING
ADAPTATION OPTIONS
 Adaptation is the process by which the potential impacts
are reduced by applying a range of management options
 Management of VBD:
1) Vector control
 chemical, biological, trapping, and environmental management
techniques
2) Targeting the pathogens
 Chemotherapy
 Vaccines
 Successful control of VBD depends on three capacities:
1. effective surveillance to provide feedback on progress
2. community ownership of the new measures
3. a viable public health infrastructure to deliver the services

19. ADAPTIVE RESPONSE OPTIONS
1. Legislative:
 Many policy changes could be implemented to adapt the impacts
of VBD under global change
 They involve legislation or administrative actions to respond to
changes in distributions of vectors, diseases, and human hosts.
 The measures include changes of:
 monitoring, case detection, diagnosis and reporting,
 public information and education,
 knowledge capture and management using information technologies
such as remote sensing and mapping with geographical information
systems
 climate forecasting
 computer modeling
 quarantine surveillance
 early-warning systems
 mass vaccination programs.

20.  Efforts to eradicate malaria with insecticides failed in many
regions due to the withdrawal of DDT, the development of
resistance to the pesticides, or the reintroduction of the
mosquitoes from other areas.
1. Behavioral:
 personal behavioral responses include avoidance of exposure to
vectors by staying indoors at dawn and dusk and wearing
protective clothing.
2. Engineering:
 Habitat modification, insect screens, bednets, biological control,
pesticides, and repellents
 Targeting of pathogens with drugs or vaccines also provides
options to reduce transmission and to reduce symptoms.
 A range of chemical, biological, trapping, and environmental
management techniques are available for the control of disease
vectors
 Biological control of mosquito populations by using natural
enemies is a well-established practice and is based mostly on
predatory fish

21.  The incidence of JE in East Asia has been greatly
reduced by a combination of mass vaccination of
children, improved living conditions, reduced use of
water with new rice cultivars, and rehousing and
relocation of piggeries to prevent mosquito feeding and
reduce contact with human populations.

22. THREATS TO SUSTAINABILITY OF
ADAPTATION OPTIONS
 Resistance
 Drugs and pesticides
 E.g:
Resistance to permethrin and deltramethrin in Anophales
gambiae in West Africa.
The international spread of multiple drug-resistant malaria
organisms in Southeast Asia
 Human safety and nontarget effects of vector control
 For example, efforts to control Aedes aegypti with
organophosphorus insecticide led to three poisonings and
reduced cholinesterase levels in 53 out of 2,391 people
sampled from the local population in southern Brazil

23.  Community health and public health infrastructure
 The capability of a society to adapt to global change depends
also on the human resources and operational public health
system.
 So that developing countries have far fewer options available
to them than do developed countries
 Adaptive capacity of different social groups.

24.  THANK YOU

25. REFERENCES
Robert W. Sutherst (2004), Global Change and Human
Vulnerability to Vector-Borne diseases, Clinical
Microbiology Review 17(1):136-173
i B. H. Kwa (2006), Environmental change, development
and vectorborne disease: Malaysia’s experience with
filariasis, scrub typhus and dengue. Environ Dev
Sustain 10:209–217
b W. J. Tabachnick (2009), Challenges in predicting
climate and environmental effects on vector-borne
disease episystems in a changing world. The Journal
of Experimental Biology 213, 946-954
m WHO (2010), Global Environmental Change.
http://www.who.int/globalchange/environment/en /
accessed on 25th July 2010.