Lecture 8 - Vector-borne Diseases & Vector Control.pdf

Vector-borne Diseases & Vector Control PPT

1. Vector-borne diseases
&
vector control
Assoc. Prof. DrRozitaHod
Public Health Physician (MMC:30633) NSR:127702
MD(UKM),
MCommMedicine(Environmental Health),
PhD (Environmental & Development)(UKM)
Environmental Health Unit
Department of Community Health,
Faculty of Medicine, UKM
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Source: Nature

2. Definition
Vector-Borne Disease:
Disease that results from an infection transmitted to humans and
other animals by blood-feeding anthropods, such as mosquitoes, ticks,
and fleas.
Examples of vector-borne diseases includeDengue fever, West Nile
Virus, Lyme disease, and Malaria.
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Source: The Conversation

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Travel, global trade, animal movement, climate change
and modern agricultural practices are among the factors
that contribute to the spread of vectors and the diseases
they carry from tropical areas to more temperate zones,
such as Europe.

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Source: UCAR 2021 & Hugo AhleniusUNEP/GRID-Arendel
Red zone: projected in 2050

6. Vector borne diseases
Disease Agent Vector
Dengue/DHF,
Chikungunya
Den 1,2,3,4
Chikungunya virus
Aedes aegypti,
Aedes Albopictus
Yellow Fever Flavivirus Aedesaegypti
Malaria Plasmodium sp Anopheles
Filariasis Wucheriabancrofti,
Brugiamalayi
Culexsp
Mansoniasp
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7. Vectors for Dengue fever/DHF
Aedes
albopictus
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Aedesaegypti
Aedesaegypti
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9. Common breeding sites
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Breeding site in Madurai, India
Potential breeding site
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11. Environmental sanitation
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These conditions include:
(1) clean and safe water
supply,
(2) clean and safe ambient air,
(3) efficient and safe animal,
human, and industrial waste
disposal,
(4) protection of food from
biological and chemical
contaminants, and
(5) adequate housing in clean
and safe surroundings.
Also called
environmentalhygiene.
Slovenia
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12. Vector borne diseases
Disease Agent Vector
Cholera Vibrio cholera fly
Amoebic dysentryEntamoebahistolytica fly
Bacillus dysentryShigellasp fly
Endemic typhus Rickettsiaprowazekii flea
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13. Vector borne diseases
Disease Agent Vector
Leishmaniasis L.tropica,
L.braziliensis
sandfly
Japanese
encephalitis
JE virus Culex
Murine typhus Rickettsiatyphi
(R.mooseri)
fleas
Scrub typhus Rickettsia
tsutsugamushi
(R.orientalis)
mites
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14. Mechanical transmission
•Vectors act as passive carrier, carrying the patogens into food and drink,
after the vector landed in contaminated area such as rubbish dumps,
fecal matter and others.
•typhoid,
•paratyphoid.
•trichuris,
•cholera.
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15. Biological transmission
Pathogens replicate in
vectors without life
cycle changes, and gets
transmitted to human.
E.g; agents for
plague,typhus,dengue,y
ellow fever.
•Cycloreproductive-
pathogens replicate &
undergo life cycle
changes before getting
transmitted to humans.
E.g: malaria,
kala azar
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16. Pathogens replicate in vectors without life cycle changes&
gets transmitted to human.
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Malaria : Cycloreproductive-pathogens replicate & undergo life cycle changes
before getting transmitted to humans.
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18. Biological transmission..cont
•Cyclo-development:pathogenundergo growth without life cycle
changes and no reproduction.
E.gfilaria
•Transovarial: Pathogen is transmitted via vector egg.
E.gscrub typhus
•Others: tissue e.gscabies.
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Filaria: Cyclo-development:pathogenundergo growth without life cycle
changes and no reproduction
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20. Disease surveillance
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21. The environment & the
vectors
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22. Human activities ,the environment & vector
population
•land development, human activities that interfere
with the natural environment, have direct & indirect
impact on vector population
•Urbanization such as land clearing, deforestation,
filling up of water holes and lakes, will affect the
vector population, due to effects on breeding area,
and closer contacts with humans.
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23. E.g: Dengue
•Factors that favour the rural transmission of aedes
•Population growth
•Rural urban migration
•Inadequate basic infra structure(construction sites, rumah kongsi)
•Human behaviour-littering, empty cans, polysterenes, tyres.
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24. VECTOR CONTROL
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25. Vector Control
There are various approaches for vector control:
•(A): The environment
•(B): Chemical
•(C): Biological
•(D) Health promotion & education
•(E) Legislation & enforcement
•(F) Integrated approach
•(G) Community-orientated Approach
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26. A) The environment
Environment-vector control can be achieved by
destroying the breeding areas
E.g can reduce anopheles population by draining
out the swamp,abandoned pools,developing the
swamp area, increase sun light to the breeding
area
Water canals/water ways should be cleansed to
ensure smooth water flow.This is to avoid
contamination by fecal matter that will attract flies
to breed.
Destroy empty tins/tyres/polysterene food
containers that can breed aedes.
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27. B) Chemical
•Pesticide-insecticide
•E.g Abate to kill the larva of Aedes and Anopheles.
•Malathion to kill adult mosquitoes
•Disadvantage:
•i)resistance to insecticide
•ii)toxic to other organism including humans
•Iii) environmental pollution,residuals, persistent in
the environment
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28. C) Biological
•Using natural organisms existing in the environment
•Using bacteria that is pathogenic to the mosquito
•Genetic manipulation:radiation to create a
population of insects that cannot reproduce
•Using natural enemies e.g fish to eat the larva, frogs
and lizards to eat adult mosquitoes
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29. Wolbachia
•IMR project : to replace wild dengue-transmitting mosquito
populations with populations that are unable to transmit dengue,
Zikaor chikungunya viruses to people.
•This will be done using bacteria calledWolbachia, which are naturally
found inside many insects including mosquitoes and are passed from
female insects to their offspring.
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Source: IMR

31. Wolbachia-based control strategies
1)Suppression-
Releasing very large number of male mosquitoes carryingWolbachia. When these
males mate with the wild females, eggs laid by female mosquitoes cannot hatch. This
sterilising effect is known as Cytoplasmic Incompatibility (CI). Sustained release
ofWolbachiainfected male mosquitoes over a period of time will eventually reduce
the naturalAedespopulation and hence stop disease transmission. China and
Singapore used this strategy to control theAedespopulation.
2)Replacement
Both male and female mosquitoes carryingWolbachiaare released.When these
mosquitoes mate with the wild male and female mosquitoes, eggs will be laid and
hatched. All the adult mosquitoes that subsequently emerge will carryWolbachia.
Dengue, Zikaand chikungunya virus cannot develop inWolbachia-infected adult
mosquitoes and so these viral diseases cannot be transmitted to human. To deploy
this strategy, relatively small number ofWolbachiacarrying male and female
mosquitoes will be released over a period of time, until about 60% of the natural
population carriesWolbachia. TheWolbachiainfection will eventually spread
through the wild population and disease transmission will cease since viruses cannot
develop in theseWolbachiainfected mosquitoes. Several countries such as Australia,
Indonesia etc.hadused the replacement strategy. Malaysia is currently embarking on
thisreplacement strategy.
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33. D) Health promotion & education
•Awareness and educate the public
•Information on the importance of good environmental
sanitation,insectrepellant,mosquitonets,personalprophylaxis etc.
•Via mass media or social media.
•Current, simple message, continuous and consistent.
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Published in Bernama, STAR, Borneo Post, The Straits Times on 21
st
April
2020.
Excerpt:
The highest number of cases recorded in the past decade was in 2015, with
120,835 cases and 336 deaths. In an interview with Bernama, Universiti
KebangsaanMalaysia public health specialist Associate Prof Dr Rozita
Hodexpressed her concern that the threat posed by dengue may have been
forgotten amid the Covid-19 crisis.
Dengue fever is caused by four different types of viruses transmitted to
humans by a bite from the female Aedesmosquito of the aegyptiand
albopictusspecies.
“As we all know, dengue is dangerous as it can cause death and there is no
specific cure for it.

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“Right now while we are busy fighting Covid-19, people are starting to forget how
dangerous dengue is,” Dr Rozitatold Bernama, adding that like Covid-19 cases,
dengue infections were also rising.
She said though there were more Covid-19 deaths in Malaysia than dengue
fatalities this year, dengue should not be taken lightly as it had directly affected
more people than Covid-19.
“The number of Covid-19 cases in Malaysia stood at 5,389 as of Sunday, but in
the case of dengue, over 30,000 cases were reported between Dec 29 and April
7,” Dr Rozitapointed out.
Not all dengue cases are treated in hospitals as only those suspected to have
dengue hemorrhagicfever are warded; the rest are given fever medicine but are
required to go for follow-up checks at the nearest clinic, she explained.
Considering that government hospitals and clinics are now busy handling Covid-
19 cases, the last thing they would want is an upsurge in dengue cases.
The Star 21 April 2020.

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Dissemination to public
Available online bookshop:
PenerbitUKM,
ilhambooks.com

37. E) Legislation & enforcement
•Very important.
•Local Government Act Seksyen 82
•The Destruction of Disease Bearing Insect Act 1975 (DDBIA
1975),enables enforcement officers to take actions against those
found guilty of breeding areas.
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38. F) Integrated approach
•Use of technology, management technique to control vectors
effectively at reasonable cost
•E.g of integrated approach, dengue control.
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39. G) Community-orientated Approach
•Involve preventing/lessening man-mosquito contact (personal or
household level)
•Household insecticides (aerosols,mosquito coil,electric vaporizing
mats,electric liquid vaporizers) ,repellents,insecticide impregnated
nets,curtains,
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40. Thank you
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