1. Dr. Nik Ahmad Irwan Izzauddin Nik Him
Room 4o3, nikirwan@usm.my
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2. Introduction and important aspects of vectors in
disease transmission – important concepts, terms and
definitions
Arthropod vectors – Mosquitoes as disease vectors-its
role as important human disease vector for dengue,
microfilaria and malaria
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3. Introduction and important aspects of vectors
in disease transmission – important
concepts, terms and definitions
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4. The most successful animal
group
Arthropods have huge impact on
health of humans & domestic
animals
Irritation & diseases
Relatively few species involved
but serious social & economic
consequences Leishmaniasis
Transmit diseases (vectors)
Inject venoms & transmit allergens
Cause wounds Myiasis
Create nuisance & phobias
Other arthropod groups also
very important
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6. Nuisance mostly related to high
densities & not real hazards
Justified in case of biting, venomous &
filth-frequenting species
Major causes of nuisance &
irritation
Blood-feeding species
Lachrymal-feeders
Immunological reactions
Phobic responses (delusory parasitosis)
Large industries are focused on pest
control
Mosquito feeding frenzy
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7. Vector
- Definition: Organism that are capable of transmitting other
organisms that cause disease in vertebrate host
Carrier, bearer
In parasitology An organism or vehicle that
transmits the causative agent or disease-causing
organism from reservoir to the host
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8. Vectors generally don’t become “ill” from carrying their
various viral, protozoan and nematode infections.
They might accrue some damage to their tissues, but in
some cases this “damage” actually makes them more likely
to transmit and infect.
A mosquito with problems in its feeding apparatus will
need to take additional bites to complete a blood meal.
A flea with a gut clogged with plague bacteria will
regurgitate more.
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11. Primary vector
- If they are proved to be transmitting a pathogen to man or other
animal
Secondary vector
- If they play a supplementary role in transmission, but would be
unable to maintain a disease in the absence of primary vector
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12. Case sample:
In the transmission of dengue fever in Malaysia
Aedes egypti is the main
vector…
and Aedes albopictus is
the secondary vector
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13. In instances where a disease of unknown cause is
occurring, certain general characteristics help to
identify its vector
Establishment of the relationship of arthropod
populations to transmission of a particular disease
agent is called vector incrimination
The process of knowing which species of arthropod is
serving as a vector of a particular disease
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14. • There are 4 major criteria for incriminating
arthropods as vectors of human disease
Barnett, H. C. 1956. The transmission of western equine encephalitis virus
by the mosquito Culex tarsalis Coq. Am. J. Trop. Med. Hyg. 5: 86-98. 14
15. Identifying contact between arthropod and host
- suck blood for meal YES
Having a biological association in time
- the rate of cases higher in correlation to the higher number of Aedes
YES
Repeated demonstration of disease between arthropod and host
- The infective stage have been found consistently in Aedes and they
transferred it during feeding YES
Replicable under experimental conditions
- Can be rearing in the lab and the and can be replicated YES
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16. The time that elapses between the invasion of a susceptible host
by an infectious agent and the onset of symptoms of the disease
caused by that agent is called the incubation period
The length of the incubation period varies greatly
Extrinsic Incubation period
– a period in a vector during which the disease-producing
organism/parasite increases or transforms to a point where it can
be transmitted.
Intrinsic incubation period
– a period in the vertebrate host before disease is expressed
clinically
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18. Vectorial capacity describes the potential of a
group of arthropods to transmit a given pathogen
Vector effectiveness
There are 6 main determinants:
– Abundance
– Host preference and host-feeding patterns
– Reproductive capacity
– Longevity
– Dispersal
– Vector competence
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19. The more vectors there are, the higher the probability
of disease transmission
because it has a direct bearing on the probability of
vector-host contact
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20. Knowing what the vectors feed upon allows for
identification of disease transmission
Patterns of host feeding that are determined by
identification of blood meals in vectors are usually the
end result of many factors, including host preference
and host availability.
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21. A measure of the rate at which a population of vectors
increases
Fecundity is a related term which relates to the
number of generations, broods, or litters produced per
unit of time.
The net reproductive rate of a population of vectors is
a combination of fecundity and survival.
Survival is influenced by various mortality factors,
including predation and diseases, as well as accidents
and natural aging
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22. Longevity is knowing how long the stages of the
vector’s life cycle last
A vector must feed more than once to transmit
pathogens
It is essential that a vector live a sufficient period of
time
Maximal longevity will permits vectors to serve as
essential parts of the reservoir of infection.
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23. Dispersal is knowing how far a vector can fly or move about freely
– The greater the movement, the greater chance for spread of disease
Vectors that can move freely and for long distances will have greater
chances for contact with humans, and will be more likely to move
between infected and noninfected hosts.
Superior mobility aids in the dissemination of pathogens over a
wide area, so that their associated diseases are not limited or focal
in nature.
Flying vectors (e.g. mosquitoes, flies) generally make a good vector;
however crawling vectors (e.g. fleas, lice, mites and ticks) are
distributed by the relative mobility of their hosts.
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24. The susceptibility of a group of arthropods to a given
strain of pathogen and the ability of those arthropods
to transmit the pathogen
These traits are under genetic control, and although
infection and transmission in vectors will vary with
temperature, vector competence is considered to be an
innate characteristic for a particular vector for a given
microorganism
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26. This is when the pathogen adheres to body hairs,
spines, sticky pads, or other structures of insects
– In the case of certain insects, transmission may be by regurgitation or
defecation
- Biting flies may transmit pathogens by biting with contaminated
mouthparts
Nearly all mechanically transmitted diseases can also
be transmitted in other ways (e.g., contaminated food
and water)
e.g. houseflies, cockroaches
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27. The parasites undergo several molts in the body of the
vector
No multiplication takes place within the body of the
vector
The only pathogens that are transmitted this way are
filarial nematodes
- Start out as a microfilariae and develops into an infectious larvae
Also known as Cyclical transmission
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29. In this type of transmission, the pathogen multiplies
within the body of the vector, but does not undergo
any changes in form
Most viral diseases fall into this category
Plague (a bacterial disease) is also an example
Any stage of these pathogens can infect a vertebrate
host
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30. Both multiplication and changes in the life form of the
pathogen occur within the vector
Examples are malaria, leishmaniasis, both caused by
protozoan parasites
Also known as Propagative and Cyclical transmission
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32. Horizontal and vertical transmission describe the
pathway a pathogen takes among vectors and hosts.
Horizontal transmission
- Horizontal transmission involves the pathogen being transmitted by
a vector to a host in a cyclical pathway
Ventricle transmission
- Vertical transmission is more direct and does not involve a host, but
occurs directly from infected mother/female to offspring
– This is also called transovarial transmission
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34. Dead end host
– a vertebrate that harbors the pathogen and is severely
affected by it, yet the level of pathogen in its body is too
low for blood sucking vector to become infective after
feeding on the host.
Amplifying host
– a vertebrate that has high level of pathogen that a feeding
vector will likely become infectious.
Silent host
– one that harbors the pathogen, but shows no obvious
signs of disease.
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35. Resistant host
– one that is not naturally affected by a pathogen.
Partially resistant host
– one that harbors the pathogens for a long period
before being overcome by it.
Susceptible host
– a victim of the pathogen
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36. Reservoir refer to any vector or host, capable of
maintaining a pathogen for considerable
periods of time.
Usually, they show no evidence of serious disease,
or a reservoir of infection may be maintained by
continuous transmission among a group of
severely affected animals.
Most vectors are short-lived and would not serve
as important components of reservoirs, except
possibly through aestivation or hibernation.
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37. At the end of the nineteenth century, it was discovered that certain
species of insects, other arthropods and freshwater snails were
responsible for the transmission of some important diseases.
The discovery of the insecticide dichlorodiphenyltrichloroethane
(DDT) in the 1940s was a major breakthrough in the control of vector-
borne diseases.
In 1950s and early 1960s -->
-To eradicate the diseases or to reduce transmission to such low level that control
could be maintained through the general health care facilities without the need of
control measures.
Problem resistance
expensive
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38. Vector control methods suitable for community
involvement should:
— be effective;
— be affordable;
— use equipment and materials that can be obtained
locally;
— be simple to understand and apply;
— be acceptable and compatible with local customs,
attitudes and beliefs;
— be safe to the user and the environment.
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39. Before starting any vector control activity, it is
important to ask two questions:
What result do you want to achieve: merely to protect
yourself or your family from biting pests and the
diseases they carry, or to reduce disease in the
community?
Are the health authorities already carrying out control
measures and do you want to provide the community
or your family with additional protection from disease?
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40. Important factors to take into consideration
- Biological factors
- Availability of technical tools
- Socio-economic considerations
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41. Species affected
Density of susceptible species
Wildlife reservoir
Vector transmission
Transmissibility
Current extent of disease
Survival in the environment
Carrier state
Ease of clinical recognition
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43. Cost and benefits of intervention
Ease of implementation
Stake holder engagement
Political will
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44. 2 control methods
1. Self-protection
2. Community control
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45. Self-protection measures are used to protect yourself, your
family or a small group of people living or working together
from insect pests or vectors of disease.
These measures include personal protection,
1. the prevention of contact between the human body and
the disease vector,
2. and environmental measures to prevent pests and vectors
from entering, finding shelter in, or breeding in or
around your house.
These measures are usually simple and inexpensive, and
can often be adopted without help from specialized health
workers.
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46. Example:
Repellents
Protective clothing
Insecticide vaporizers
Mosquito nets
Insecticides
- Insecticide spraying of walls
- Space-spraying with insecticides
- Treating fabrics with an insecticide
Anti-mosquito screening
Prevention of breeding
- Source reduction
- Biological control
- Larvicides
- Insect growth regulator
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47. The type of control may be the same as for the
protection of an individual or a family, but is, of
course, larger.
Before investing resources in community-wide control
efforts, advice should be obtained from health workers
on the type of measures most likely to be successful
under local conditions.
Before investing resources in community-wide control
efforts, advice should be obtained from health workers
on the type of measures most likely to be successful
under local conditions.
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48. Many factors need to be taken into account:
1. the vector species and its behaviour,
2. the compatibility of control methods with the local
culture,
3. affordability in the long term, the need for expert
advice
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