Arthropod Vector-borne Diseases Definition. The significance of vector-borne diseases. Dynamics of Arthropod-Borne Diseases. Mechanisms of Vector-Borne Transmission. Factors Influencing Vector-Borne Transmission. Vector competence and vector capacity Host-vector-pathogen interactions Environmental factors and climate change Vector Control Strategies.

1. Vector-
borne
Diseases
Prof. Dr. Ibrahim Aboulasaad
MD Arthropod

2. Learning objectives:
In the present lecture, we will explore the followings:
• Definition.
• The significance of vector-borne diseases.
• Dynamics of Arthropod-Borne Diseases.
• Mechanisms of Vector-Borne Transmission.
• Factors Influencing Vector-Borne Transmission.
o Vector competence and vector capacity
o Host-vector-pathogen interactions
o Environmental factors and climate change
• Vector Control Strategies.

3. Vector-Born Diseases Definition
o ARTHROPODS, such as:
• Insecta: Mosquitoes, flies, fleas, lice and bugs, or
• Arachnida: Ticks, Mites, Spider, and Scorpion
• Crustacea: Cyclops, Crabs and Crayfish.
o NON-ARTHROPODS, such as:
• Snails (Mollusca) as;
• Fish: as;
Vector-borne diseases are infectious diseases caused by microorganisms (such as
bacteria, viruses, and parasites) that are transmitted to humans and animals by
vectors, which are living organisms capable of carrying and transmitting pathogens.
Vectors can be:

4. The significance of vector-borne diseases
1. Transmission: Vector-borne diseases are characterized by the transmission of pathogens
from an infected host to a susceptible individual via the bite or contact with the vector. The
vector acts as an intermediary, facilitating the transfer of the pathogen.
2. Wide Range of Diseases: Vector-borne diseases encompass a diverse range of illnesses. They
include viral, bacterial, and parasitic diseases. These diseases can cause significant morbidity
and mortality worldwide.
3. Global Impact: Vector-borne diseases are found in various parts of the world, affecting both
developed and developing countries. They pose a major public health challenge, particularly
in regions with inadequate healthcare infrastructure.
4. Disease Burden: Vector-borne diseases collectively contribute to a substantial disease
burden, resulting in significant disability-adjusted life years (DALYs) lost globally. They can
cause acute illnesses, chronic conditions, and long-term complications, leading to increased
healthcare costs and decreased productivity.
The disability-adjusted life year (DALYs) is a measure of overall disease burden, expressed as
the number of years lost due to ill-health, disability or early death.
The significance of vector-borne diseases lies in their global impact on public health,
socioeconomic development, and overall well-being. Here are some characteristic points
regarding vector-borne diseases:

5. 5. Geographic Distribution: The distribution of vector-borne diseases is influenced by the
presence and abundance of specific vectors, as well as environmental factors, including
temperature, humidity, and vegetation. Climate change and human activities can impact
the geographic range of vectors and alter disease transmission patterns.
6. Prevention and Control: Controlling vector-borne diseases requires a multi-faceted
approach. Prevention strategies focus on vector control measures, such as insecticide-
treated bed nets, indoor residual spraying, personal protective measures, and
environmental management. Early diagnosis, treatment, and surveillance are crucial for
managing cases and preventing outbreaks.
7. Emerging and Re-emerging Diseases: Vector-borne diseases continue to emerge or re-
emerge in different regions, posing new challenges to public health. Factors such as
urbanization, population movement, changes in land use, globalization, and drug resistance
contribute to the emergence and spread of these diseases.
Understanding the definition and significance of vector-borne diseases is essential for
healthcare professionals, and researchers to develop effective prevention and control
strategies, improve surveillance systems, and enhance public health interventions to
mitigate the impact of these diseases on global health.
The significance of vector-borne diseases

6. Dynamics of
Arthropod-Borne
Diseases
• The Dynamics of Arthropod-Borne Diseases
refers to the study of the complex interactions
between arthropod vectors, pathogens, and
hosts that influence the transmission and spread
of vector-borne diseases.
• Understanding the dynamics of these
diseases involves investigating various factors,
including vector ecology, pathogen biology,
host-vector interactions, and environmental
influences.
• By unraveling the complex dynamics of
arthropod-borne diseases, scientists strive to
mitigate the burden of these diseases on human
and animal populations and improve public
health outcomes.

7. 1. Vector Ecology and Behavior: Understanding the ecology and behavior of
arthropod vectors is crucial for unraveling disease dynamics. Factors such as
vector distribution, abundance, feeding preferences, biting rates, and vector
lifespan influence the transmission potential of diseases. Researchers study the
ecology and behavior of vectors to identify their habitats, breeding sites, and
feeding patterns, allowing for targeted control interventions.
2. Vector-Pathogen Interactions: The interaction between vectors and the
pathogens they carry is a critical component of disease dynamics. Researchers
investigate vector competence, which refers to the ability of vectors to acquire,
maintain, and transmit pathogens. Factors such as pathogen replication within
the vector, the ability to overcome vector immune responses, and the efficiency
of pathogen transmission to hosts contribute to disease spread.
3. Host-Vector Interactions: The interaction between hosts and vectors plays a
significant role in disease transmission. Host susceptibility, immune responses,
and behavior influence the likelihood of infection and subsequent transmission
to other hosts. Understanding the factors that determine host attractiveness to
vectors, the duration of viremia, and the immune responses to infection aids in
elucidating disease dynamics.
Aspects of The dynamics of arthropod-borne diseases:

8. 4. Environmental Influences: Environmental factors, such as temperature, humidity,
rainfall patterns, and land use, have a profound impact on the dynamics of
arthropod-borne diseases. Changes in climate and land use can affect vector
distribution, vector breeding sites, and host availability, altering disease transmission
patterns. Environmental factors also influence vector behavior, development rates,
and the survival of pathogens within vectors.
5. Pathogen Evolution and Genetic Diversity: Pathogens transmitted by arthropods
can undergo genetic changes and adaptations that influence disease dynamics.
Evolutionary processes such as mutation, recombination, and selection can result in
the emergence of new strains or variants with altered virulence, transmission
efficiency, or host range. Understanding pathogen genetics and their interactions
with vectors and hosts helps predict disease emergence and design effective control
strategies.
6. Mathematical Modeling and Surveillance: Mathematical models play a vital role in
understanding the dynamics of arthropod-borne diseases. These models integrate
data on vector populations, host dynamics, environmental factors, and disease
transmission to predict disease spread, assess intervention strategies, and inform
public health decisions. Surveillance systems monitor vector populations, disease
prevalence, and environmental parameters to provide timely information for disease
control and prevention efforts.

9. 7. Disease Outbreaks and Epidemics: Arthropod-borne diseases can exhibit sporadic
outbreaks or larger-scale epidemics. Researchers investigate the factors
contributing to the emergence and escalation of disease outbreaks, such as changes
in vector populations, introduction of novel pathogens, or shifts in environmental
conditions. Studying outbreak dynamics helps in implementing rapid response
measures, outbreak containment, and prevention of further spread.
8. One Health Approach: The dynamics of arthropod-borne diseases require a One
Health approach, which recognizes the interconnectedness of human, animal, and
environmental health. Many arthropod-borne diseases affect both humans and
animals, and zoonotic transmission can play a significant role. Investigating the
transmission dynamics among different host species, including wildlife and
domestic animals, is essential for understanding the overall disease ecology and
developing comprehensive control strategies.
By studying the dynamics of arthropod-borne diseases, researchers aim to develop
effective strategies for disease prevention, surveillance, and control. This involves
implementing vector control measures, improving diagnostic tools, developing
vaccines, and educating communities on preventive measures. The interdisciplinary
nature of this field allows for a comprehensive understanding of the complex factors
influencing disease transmission, aiding in the mitigation of the burden of arthropod-
borne diseases on global health.

10. Mechanical
Transmission
Mechanical transmission refers to the passive transport of pathogens by a vector from an infected
source to a susceptible host without any involvement of the pathogen's replication or development
within the vector. In mechanical transmission, the vector serves as a carrier, simply transporting the
pathogen on its body or appendages.
Mechanisms of Vector-Borne Transmission
Mechanical transmission can occur through:
• External Mechanical Transmission: For example, flies and cockroaches have numerous
hairs, spines, and setae on their bodies that collect contaminants as the insects feed on
dead animals or excrement. When they subsequently walk on food or food preparation
surfaces, mechanical transmission occurs.
• Internal Mechanical Transmission: Mechanical transmission may also occur if a blood-
feeding arthropod has its feeding event disrupted. For example, if a mosquito feeds briefly
on a viremic man and is interrupted, a subsequent immediate feeding on a second man
could result in virus transmission. This would be similar to an accidental needle stick.

11. Examples of
Mechanical
Transmission
Houseflies and Diarrheal Diseases: Houseflies are known to mechanically
transmit pathogens causing diarrheal diseases, such as Escherichia coli,
Shigella, and Salmonella. These flies can come into contact with contaminated
feces or decaying organic matter and then transfer the pathogens to food or
surfaces, leading to potential infection when ingested by humans.
Musca sorbens (eye-seeking fly) and Trachoma: Trachoma is an eye infection
caused by the bacterium Chlamydia trachomatis. Flies, such as Musca sorbens,
can mechanically transmit the bacteria by coming into contact with eye
discharge from infected individuals and then transferring it to the eyes of
healthy individuals.
Cockroaches and Pathogenic Bacteria: Cockroaches have been found to carry
and mechanically transmit various pathogenic bacteria, including those
responsible for food poisoning, such as Staphylococcus aureus and Clostridium
perfringens. Cockroaches can contaminate food and surfaces by picking up
bacteria from unsanitary environments and then depositing them elsewhere.
Beetles and Wound Infections: Certain beetles, such as the Dermestidae
family, can mechanically transmit bacteria, including those causing wound
infections. These beetles can carry bacteria on their bodies and transfer them
to open wounds or surgical sites, potentially leading to infection.

12. Biological Transmission
Mechanisms of Vector-Borne Transmission
Transmission Mechanisms:
Biological transmission can occur through different mechanisms, including:
• Salivary transmission: Anterior station infection: The vector injects saliva containing the
pathogen into a new host during feeding (Malaria, Filaria)
• Fecal-oral transmission: Posterior station infection: Transmission occurs when the feces
contaminate a new host's environment or are ingested by the host (Chagas disease)
• Crushing of infected arthropod, (Epidemic Typhus. …….)
• Ingestion of infected arthropod, (Hymenolepiasis)

13. Examples for Biological transmission

14. • Onchocerciasis (River Blindness): Onchocerciasis is caused by the filarial worm Onchocerca
volvulus, which is transmitted by black flies of the Simulium genus. The larvae of the worm
develop within the black fly and are transmitted to humans during blood-feeding.
• Filariasis: Filariasis encompasses several diseases caused by filarial worms transmitted by
different mosquito species. For example, lymphatic filariasis is caused by Wuchereria bancrofti,
Brugia malayi, or Brugia timori and transmitted by mosquitoes like Anopheles, Culex, or Aedes.
The filarial worms undergo development and maturation within the mosquito's body before
being transmitted to a new host during blood-feeding.
Examples for Biological transmission

15. Examples for Biological transmission
• Dengue Fever: Aedes mosquitoes transmit the dengue virus, which undergoes replication
within the mosquito's salivary glands, facilitating transmission to a new host during
subsequent feeding.
• Zika Virus: Zika virus is primarily transmitted by Aedes mosquitoes, particularly Aedes aegypti
and Aedes albopictus. The virus replicates within the mosquito's salivary glands and is
transmitted to humans during blood-feeding.
• Sandfly Fever: Sandfly fever is caused by viruses belonging to the Phlebovirus genus, which
are transmitted by phlebotomine sandflies. The viruses replicate within the sandfly and are
transmitted through their bites.
• Colorado Tick Fever: Colorado tick fever is caused by the Colorado tick fever virus, which is
primarily transmitted by Dermacentor ticks. The virus multiplies within the tick and is
transmitted during feeding.

16. Vector-borne
Vertical
Transmission
• Vector-borne vertical
transmission refers to the
transmission of pathogens from an
infected female vector to her
offspring during the process of
reproduction or development. In
this case, the vector serves as
both the host and the transmitter
of the pathogen to the next
generation.

17. Vertical
Transmission
Mechanisms
Vector-borne vertical transmission can occur through various
mechanisms, including:
• Transovarial Transmission: The pathogen is transmitted from
the infected female vector to her eggs, allowing the offspring to
be infected from the moment of hatching or birth.
• Transovum Transmission: The pathogen is present on the outer
surface of the eggs, allowing the newly hatched larvae or
nymphs to acquire the infection.
• Transstadial Transmission: The pathogen persists and is
transmitted between different life stages of the vector, such as
from larvae to pupae or from nymphs to adult stages.

18. Mosquito-borne Vertical Transmission

19. Examples of Vector-Borne Vertical Transmission

20. • Sustained Pathogen Presence: Vertical transmission allows pathogens to
persist within vector populations over time. Infected female vectors can
pass the pathogen to their offspring, ensuring a continuous reservoir of
infected vectors, even in the absence of external sources of infection.
This can contribute to the long-term persistence of diseases within
endemic areas.
• Increased Disease Transmission Potential: Vector-borne vertical
transmission can lead to an increased transmission potential of the
pathogen. As infected vectors give birth to infected offspring, the
number of infected vectors in the population can rapidly multiply. This
can lead to higher rates of disease transmission to susceptible hosts,
including humans and animals, resulting in increased disease prevalence
and potential outbreaks.
Implications of Vector- borne Vertical
Transmission for Disease persistence
Vector-borne vertical transmission has important implications for the persistence
and spread of diseases. Here are some key implications:

21. • Maintenance of Disease Transmission Cycles: Vertical transmission plays a crucial role
in maintaining the transmission cycles of vector-borne diseases. By perpetuating the
infection within vector populations, it ensures a constant source of infected vectors
capable of transmitting the pathogen to new hosts. This continuous cycle of
transmission contributes to the endemicity of vector-borne diseases in certain regions.
• Geographic Expansion: Vector-borne vertical transmission can facilitate the
geographic expansion of diseases. Infected vectors that have vertically transmitted the
pathogen to their offspring can disperse to new areas, carrying the disease with them.
This can lead to the establishment of disease in previously unaffected regions,
expanding the geographical range of the disease.
• Challenges for Control Measures: Vector-borne vertical transmission poses challenges
for disease control efforts. The presence of infected offspring among vector
populations can make it difficult to control the transmission of diseases solely through
traditional vector control methods. Targeting both adult vectors and their offspring
becomes necessary to effectively interrupt the transmission cycles and reduce disease
burden.
Implications of Vector-Borne Vertical Transmission

22. Factors Influencing
Vector- borne
Transmission:
• Vector competence and vector capacity
• Factors affecting vector's ability to
acquire and transmit pathogens
• Impact of vector genetics and
environmental factors
• Host-vector-pathogen interactions
• Immune responses and evasion
strategies
• Pathogen adaptation to vector
biology
• Environmental factors and climate
change
• Effects on vector distribution and
behavior
• Altered transmission patterns and
emergence of new diseases

23. Vector
competence
and vector
capacity
Vector competence and vector capacity are important
concepts in the field of medical entomology, specifically
in the study of vector-borne diseases. These terms help
us understand the ability of a particular arthropod
species (known as a vector) to transmit a pathogen (such
as a virus, bacterium, or parasite) to a susceptible host,
typically humans.
Vector Competence:
Vector competence refers to the inherent ability of a
vector species to acquire, maintain, and transmit a
pathogen.
Vector Capacity:
Vector capacity refers to the potential of a vector
population to transmit a pathogen under specific
environmental conditions.

24. Components of Vector Competence
A. Acquisition: Vector competence begins with the
acquisition of the pathogen by the vector. This can
occur through various mechanisms, such as feeding
on an infected host or acquiring the pathogen
transovarially (from infected parents to offspring).
B. Maintenance: Once acquired, the vector must be
able to support the replication, survival, and
maintenance of the pathogen within its body. Some
vectors may have physiological barriers or immune
responses that can limit the pathogen's survival.
C. Transmission: Vector competence also
encompasses the vector's ability to effectively
transmit the pathogen to a susceptible host. This
can involve specific behaviors, such as probing,
feeding, or biting, which allow the pathogen to be
transferred from the vector's salivary glands into
the host's bloodstream.

25. Factors affecting vector competence
Understanding vector competence and vector capacity is crucial in studying and controlling
vector-borne diseases. By identifying competent vectors and assessing their capacity to transmit
pathogens, researchers can develop targeted strategies for disease prevention and control, such
as vector surveillance, vector control measures, and the development of vaccines or vector-
targeted interventions.
I. Intrinsic factors: These are inherent characteristics of the vector species, that determine the
vector's ability to transmit the pathogen. such as:
their lifespan, reproductive capacity, feeding pattern, and host preference.
II. Extrinsic factors: include:
a) The host: Number of host animals, their activity patterns,
b) The pathogen: Genetic variation in the infectivity of the pathogen, and competition
between microorganisms inside a vector may also affect vector competence. This has
often been referred to as the “interference phenomenon”
c) The ecosystem: Factors related to the environment in which the vector and pathogen
interact. They include temperature, humidity, availability of suitable breeding sites, and
the density of hosts. Environmental conditions can influence vector abundance, survival,
and activity, thereby affecting vector capacity.
Vector Competence and Capacity are influenced by both intrinsic and extrinsic factors:

26. Impact of vector genetics on the dynamics of
vector-borne diseases
• Vector genetics play significant roles in shaping the dynamics of vector-
borne diseases. Here's an overview of their impact:
a. Genetic Resistance: Vector populations can exhibit genetic variation in their
susceptibility to pathogens. Some individuals may possess genetic traits that make
them more resistant to pathogen infection or reduce their ability to transmit the
pathogen. This natural genetic resistance can influence the overall transmission
dynamics of the disease.
b. Vector Competence: Vector genetics can also determine the level of vector
competence, i.e., the ability of vectors to acquire, maintain, and transmit
pathogens. Genetic factors may affect the vector's immune response, ability to
support pathogen replication, or interactions between the vector and the
pathogen. Variations in these genetic traits can influence the vector's vector
competence, ultimately impacting disease transmission potential.
c. Vector evolution and adaptation: Vector genetics can drive evolutionary
changes in vector populations. Environmental pressures, including exposure to
insecticides or changes in climate, can select for genetic variations that provide a
survival advantage to vectors. For example, certain genetic mutations may confer
resistance to insecticides, making vector control strategies less effective.

27. Impact of environmental factors on the dynamics of vector-borne
diseases.
• The environmental factors play significant roles in shaping the dynamics of vector-borne
diseases. Here's an overview of their impact:
Environmental Factors:
a) Climate and Habitat: such as: temperature, humidity, and rainfall patterns, strongly influence
vector populations. Climate change can alter the distribution and abundance of vectors, as
well as the geographic range of vector-borne diseases. Changes in temperature and rainfall
patterns can affect vector breeding habitats and their ability to survive and transmit
pathogens.
b) Land Use and Urbanization: Human-induced modifications of landscapes can impact vector
populations and disease transmission. Deforestation, urbanization, and agricultural practices
can create new vector breeding sites, increase human-vector interactions, and disrupt
natural ecological balances. These changes can lead to an upsurge in disease transmission.
c) Human Behavior and Socioeconomic Factors: Environmental factors related to human
behavior and socioeconomic conditions can affect vector-borne disease transmission. Factors
such as poor sanitation, inadequate housing, and limited access to healthcare can increase
the risk of vector exposure and disease transmission. Human mobility and travel patterns can
also influence the spread of vector-borne diseases to new regions.

28. Host- Vector-
Pathogen
Interactions
• Host-vector-pathogen interactions refer to the complex relationships and interactions between a
host organism, a vector (usually an arthropod), and a pathogen (such as a virus, bacterium, or
parasite). These interactions are critical in the transmission and progression of vector-borne diseases.
The merit of interaction between H/V/P defend the amplitude or nidus of pathogen transmission. The
nidus of pathogen transmission is dependent on environmental factors or ecological factors.
• Understanding the intricacies of host-vector-pathogen interactions is crucial for developing effective
strategies to control and prevent vector-borne diseases. Researchers study these interactions to identify
vulnerabilities in the transmission cycle, target specific stages of the pathogen's life cycle, develop
vaccines or therapeutics, and implement vector control measures. By unraveling the complexities of
these interactions, scientists can make significant strides in mitigating the impact of vector-borne
diseases on human and animal populations.

29. Impacts of host Immune responses and pathogen
evasion strategies on Host-vector-pathogen interactions
• Immune responses and evasion strategies play a crucial role in shaping host-vector-pathogen
interactions. These mechanisms have significant impacts on the outcome of infection, transmission
dynamics, and the ability of pathogens to establish and persist within host and vector populations.
Here are some key impacts of immune responses and evasion strategies on host-vector-pathogen
interactions:
1. Disease Outcome: Host immune responses are critical for controlling and eliminating
pathogens. Strong and effective immune responses can limit pathogen replication, clear
infections, and promote recovery from disease. Conversely, inadequate or compromised
immune responses can result in persistent infections, chronic diseases, or severe clinical
manifestations. The interplay between the host immune response, vector, and pathogen
determines the severity and duration of disease.
2. Transmission Efficiency: The ability of a vector to transmit a pathogen depends on various
factors, including the presence of specific molecules or receptors on the vector's salivary
glands, which facilitate pathogen transmission during feeding. The host's immune response
can impact the transmission efficiency by neutralizing the pathogen in the vector's saliva or by
impeding the vector's feeding behavior. Some pathogens have evolved evasion strategies to
overcome host immune responses, allowing them to persist and enhance their transmission
potential.

30. • Immune-Mediated Resistance: Host immune responses can confer resistance or
tolerance to subsequent infections by the same or related pathogens. Upon
primary infection, the host's immune system can generate immune memory,
enabling a faster and more robust response upon re-infection. This immune-
mediated resistance can impact the transmission dynamics of vector-borne
diseases by reducing the number of susceptible hosts.
• Evasion Strategies: Pathogens have evolved diverse mechanisms to evade or
subvert host immune responses. These evasion strategies allow the pathogen to
establish and maintain infection within the host or vector. Examples of evasion
strategies include antigenic variation (changing surface proteins to evade
recognition), immune modulation (interfering with host immune signaling),
production of immunosuppressive molecules, or hiding within host cells or vector
tissues to evade immune surveillance.
• Co-evolutionary Dynamics: Host-vector-pathogen interactions often involve
dynamic co-evolutionary processes. Host immune responses exert selective
pressure on pathogens, favoring the emergence of variants with increased evasion
capabilities. This ongoing arms race between hosts and pathogens can lead to the
generation of diverse pathogen strains or variants with different virulence,
transmission potential, or immune recognition patterns..

31. • Pathogen adaptation to vector biology refers to the evolutionary changes that occur in
pathogens to enhance their ability to interact with and exploit the biology of their vector
hosts. These adaptations enable pathogens to overcome barriers within the vector, enhance
transmission efficiency, and establish successful infections. Here are some key aspects of
pathogen adaptation to vector biology:
Pathogen Adaptation to Vector Biology
“Pathogen-Vector Co-evolution”
1. Vector Recognition and Attachment: Pathogens may undergo adaptations to recognize and
attach to specific tissues or cells within the vector host. This recognition can involve interactions
between pathogen surface molecules and vector receptors. Pathogens may evolve specific
adhesion proteins or receptors that facilitate attachment to the vector's midgut, salivary glands,
or other relevant tissues.
2. Vector Immune Evasion: Pathogens have evolved strategies to evade or suppress the vector's
immune response, allowing them to establish infection and persist within the vector host. These
evasion mechanisms may involve the production of molecules that inhibit the vector's immune
system or the modulation of immune signaling pathways. By evading vector immune responses,
pathogens can establish longer-term infections and enhance their transmission potential.

32. 3. Manipulation of Vector Feeding Behavior: Some pathogens have evolved mechanisms to
manipulate the feeding behavior of their vector hosts to enhance transmission. For
example, certain pathogens may alter the vector's feeding preferences, increasing the
likelihood of feeding on susceptible hosts. Additionally, pathogens may modify the
vector's feeding physiology, such as enhancing blood-feeding efficiency or altering
salivary gland secretions, to facilitate pathogen transmission.
4. Enhanced Replication and Persistence: Pathogens may undergo adaptations that allow
them to replicate and persist within specific tissues or organs of the vector. This can
involve alterations in the pathogen's replication machinery, enabling efficient replication
in vector cells. Some pathogens have evolved to establish chronic or persistent infections
in vectors, ensuring their long-term survival and transmission potential.
5. Transmission-Enhancing Factors: Pathogens may produce molecules or factors that
enhance their own transmission by manipulating the vector host. These transmission-
enhancing factors can influence the vector's physiology, such as promoting survival,
reproduction, or dispersal, which ultimately benefits the pathogen. They may also
modulate vector behavior, increasing the likelihood of pathogen transmission to new
hosts.
6. Co-evolutionary Dynamics: The adaptation of pathogens to vector biology often involves
reciprocal evolutionary changes between the pathogen and the vector. Co-evolutionary
dynamics occur when selective pressures imposed by pathogens shape the genetic
diversity and traits of vector populations, and vice versa. This ongoing interaction drives
the evolution of both pathogens and vectors, influencing their biology, behavior, and the
epidemiology of vector-borne diseases.

33. Influencing of environmental factors and climate change on
Vector-Borne disease Transmission
• Environmental factors and climate
change have profound effects on the
transmission dynamics of vector-borne
diseases. Changes in temperature,
precipitation, humidity, and other
environmental variables can directly or
indirectly impact the abundance,
distribution, and behavior of vectors, as
well as the pathogens they transmit.
• The effects of environmental factors
and climate change on vector-borne
disease transmission encompass:
o Effects on vector distribution and
behavior
o Altered transmission patterns and
emergence of new diseases

34. Effects on vector distribution and behavior
1. Geographic Range Expansion: Warmer temperatures may allow vectors to survive and
reproduce in regions where they previously could not, extending their distribution into higher
latitudes or altitudes. This expansion can result in the emergence of vector-borne diseases in
new areas, affecting populations with little or no previous exposure to the diseases.
2. Altered Seasonal Activity: Warmer temperatures may result in extended periods of vector
activity, prolonging the transmission season and increasing the potential for disease
transmission. Conversely, alterations in rainfall patterns can create periods of water scarcity,
reducing breeding sites and leading to changes in vector abundance and behavior.
3. Shifts in Host-Vector Dynamics: Environmental changes can influence the interactions
between vectors, hosts, and pathogens. Changes in vegetation, land use, or water availability
can affect host availability, leading to shifts in host-seeking behavior or changes in feeding
preferences of vectors.
Environmental factors and climate change have significant impacts on vector distribution, behavior,
and the transmission dynamics of vector-borne diseases. Changes in temperature, precipitation
patterns, humidity, and other environmental factors can directly or indirectly influence vectors and
their interactions with hosts and pathogens. Here are some effects of environmental factors and
climate change on vector distribution and behavior:

35. Effects of Environmental factors and climate change on vector distribution and behavior
4. Vector Life Cycle and Reproduction: Temperature and humidity influence the
development rates, survival, and reproduction of vectors. For example, warmer
temperatures can shorten the development time of vector larvae, leading to faster
population growth and increased transmission potential.
5. Vector Behavior and Feeding Patterns: Changes in temperature and humidity may affect
the activity patterns and biting behaviors of vectors, such as shifts in peak biting times or
changes in host preference. These behavioral changes can impact the likelihood of vector-
human contact and disease transmission.
6. Vector-Pathogen Interactions: Changes in temperature, humidity, or other environmental
conditions can affect pathogen development, replication rates, and the ability of the
vector to transmit the pathogen to hosts. Altered environmental conditions may enhance
or hinder pathogen replication within vectors, thereby influencing disease transmission
dynamics.
7. Vector Adaptation and Evolution: Vectors with genetic traits that confer enhanced
survival or increased vector competence under changing environmental conditions may
have a selective advantage. This can lead to the emergence of new vector species or
genetic variants with altered behaviors, increased vector competence, or altered vector-
pathogen interactions.

36. Altered transmission patterns and emergence of new diseases
1. Vector Distribution and Range Expansion: Rising temperatures and altered climatic conditions may
allow vectors to expand their range into new areas or higher altitudes. As vectors move into previously
unaffected regions, they can introduce and establish the transmission of new pathogens, leading to the
emergence of vector-borne diseases in these areas.
2. Altered Vector Abundance and Seasonality: Warmer temperatures and altered rainfall patterns can
lead to increased vector breeding, survival rates, and extended transmission seasons. These changes
can result in higher vector densities, increased contact rates with hosts, and prolonged periods of
disease transmission.
3. Changes in Host Distribution and Behavior: Altered environmental conditions can affect the
abundance, migration patterns, and habitat suitability of host populations. Changes in host
distributions can impact vector feeding opportunities, the availability of reservoir hosts, and the
potential for spillover events, facilitating the emergence of new vector-borne diseases or changing the
transmission dynamics of existing ones.
Environmental factors and climate change play a significant role in shaping the
transmission patterns and emergence of new vector-borne diseases. Changes in
temperature, precipitation, humidity, land use, and other environmental variables can
create favorable conditions for the transmission of existing diseases and contribute to
the emergence of novel diseases. Here are some key effects of environmental factors
and climate change on transmission patterns and the emergence of new vector-borne
diseases:

37. 4. Pathogen Evolution and Adaptation: Changes in Environmental factors factors may promote
the genetic diversification and selection of pathogens, leading to the emergence of novel
strains or variants with enhanced transmission capabilities, altered virulence, or expanded
host ranges.
5. Altered Ecological Interactions: Changes in temperature, precipitation, and vegetation
patterns can impact the availability of breeding sites, alter the distribution of suitable habitats
for vectors or hosts, and affect the abundance of natural predators or competitors.
6. Changes in Vector Behavior and Feeding Preferences: Environmental factors can influence
vector behavior, including host-seeking behavior and feeding preferences. These alterations
can affect the likelihood of contact between vectors and susceptible hosts, potentially
resulting in changes in the transmission dynamics of vector-borne diseases or the emergence
of novel disease reservoirs.
7. Land Use and Human Activities: Deforestation, agricultural practices, water management, and
urban expansion can modify vector habitats, create new breeding sites, or alter vector-human
contact rates. Such changes can contribute to the emergence or re-emergence of vector-borne
diseases, particularly in areas where human populations encroach upon natural environments
or where vector control measures are inadequate.

38. Vector Control
Strategies
• Vector control strategies
aim to reduce or eliminate the
population of disease-carrying
vectors to prevent the
transmission of vector-borne
diseases. studying vector
control strategies is crucial for
understanding and developing
effective measures to mitigate
the impact of these diseases.
Here are some approaches to
vector control strategies:
Chemical
Environment
al
Personal
Semiochemic
als
Biological
Genomics
Approaches
to Vector
Control

39. Chemical Control Approaches
Chemical control approaches in vector control involve the use of various insecticides
and chemicals to target and control vector populations. Here are some commonly used
chemical control approaches:
1. Residual Spraying: Residual spraying involves applying insecticides to surfaces such as walls,
ceilings, and floors, where vectors rest or come in contact with the insecticide. This approach is
effective against indoor-resting vectors such as mosquitoes and triatomine bugs.
2. Space Spraying: Space spraying, also known as fogging or aerosol spraying, involves the
application of insecticides in the form of fine droplets or aerosols to target vectors in the air.
This method is used to control flying vectors like mosquitoes and flies. Space spraying is often
conducted outdoors, in public spaces, or during outbreaks to rapidly reduce vector populations.
3. Insecticide-Treated Bed Nets (ITNs): ITNs are bed nets that are treated with insecticides,
typically long-lasting insecticidal nets (LLINs), which provide protection against nighttime biting
vectors. ITNs act as a physical barrier, preventing vectors from coming in contact with humans
while they sleep. The insecticide on the netting kills or repels the vectors. ITNs are particularly
effective in preventing malaria transmission.

40. 4. Indoor Residual Spraying (IRS): IRS involves applying insecticides to the interior surfaces of
houses or buildings where vectors rest or enter. IRS is effective against indoor-resting
vectors like mosquitoes and certain triatomine bugs. It is commonly used for malaria control
and can also be employed for other vector-borne diseases.
5. Larviciding: insecticides specifically targeting the immature stages (larvae and pupae) of
vectors, to breeding sites. This approach is effective in controlling mosquito populations and
reducing the risk of disease transmission.
6. Space Treatment: Space treatment involves the application of insecticides in enclosed
spaces, such as houses, to control vectors that rest or hide in those areas. This approach
targets vectors like fleas, lice, or bed bugs that infest human dwellings.
7. Ultra-Low Volume (ULV) Treatment: ULV treatment involves the application of insecticides
in extremely low volumes, typically in the form of aerosols or sprays, to control adult
vectors. ULV treatments are used in outdoor spaces, such as neighborhoods or agricultural
areas, to reduce vector populations rapidly.
8. Attract-and-Kill: Attract-and-kill approaches use attractive baits combined with insecticides
to lure vectors and kill them. This method is particularly effective against specific vector
species, such as tsetse flies, sandflies, or fruit flies.
Chemical control approaches

41. Limitations of Chemical control
• While chemical control is an essential tool in vector control programs, it also has certain
limitations and challenges. Here are some key limitations of chemical control:
1. Insecticide Resistance: Repeated and extensive use of insecticides can lead to the development
of insecticide resistance in vector populations.. This can reduce the effectiveness of chemical
control strategies over time, requiring the use of alternative insecticides or the implementation
of resistance management strategies.
2. Environmental Impact: Chemical control approaches can have negative impacts on the
environment and non-target organisms. Insecticides, especially those that persist in the
environment, may have unintended effects on beneficial insects, aquatic organisms, and other
wildlife. It is crucial to carefully select insecticides with low environmental toxicity and to follow
proper application protocols to minimize ecological harm.
3. Health and Safety Concerns: The use of insecticides raises concerns about potential health risks
for humans and animals. Direct exposure to insecticides can cause adverse health effects,
particularly if used improperly or without appropriate protective measures. Therefore,
adherence to safety guidelines, proper training, and the use of appropriate protective equipment
are crucial to mitigate health risks.

42. 4. Sustainability and Cost: Chemical control strategies can be costly to implement, particularly
when considering the procurement, distribution, and application of insecticides. The need for
repeated applications to maintain efficacy further adds to the costs. Sustainability of chemical
control programs can be challenging, especially in resource-limited settings, where long-term
funding and capacity for continued implementation may be limited.
5. Limited Vector Range: Chemical control approaches are often specific to certain vector species
or groups. Some vectors may have behavioral characteristics that make them less susceptible
to chemical control, such as resting or breeding in areas that are difficult to treat or in hard-to-
reach locations.
6. Community Acceptance and Compliance: Successful implementation of chemical control
strategies relies on community acceptance and compliance. However, community perceptions,
cultural beliefs, and concerns about insecticides may affect acceptance and compliance rates.
Education and community engagement are crucial to address misconceptions, build trust, and
ensure community participation.
To overcome these limitations, it is important to adopt an integrated vector management (IVM)
approach that combines multiple strategies, including chemical control, with other approaches such as
environmental management, biological control, and community-based interventions. Additionally,
continued research and development of new insecticides, alternative control methods, and innovative
approaches are necessary to overcome the challenges associated with chemical control.

43. Environmental Control Approaches
• Environmental control in the context of vector control refers to the modification or
management of the physical environment to reduce or eliminate vector populations and interrupt
the transmission of vector-borne diseases. It focuses on altering the habitat and conditions that
support vector proliferation. Here are some key environmental control approaches:
1. Habitat Modification: Modifying the environment to eliminate or alter vector breeding sites is an
effective environmental control measure. It involves identifying and eliminating or reducing
sources of standing water. By eliminating breeding sites, the population size and distribution of
vectors can be significantly reduced.
2. Vegetation Management: Managing vegetation can help control vectors that rest or seek shelter
in dense vegetation. Trimming or clearing bushes, shrubs, and tall grasses in residential areas,
parks, or agricultural fields can reduce the availability of resting sites for vectors.
3. Water Management: Applying water management techniques can help reduce vector breeding
sites that are dependent on water availability. This involves implementing water control
measures, such as draining or filling channels to prevent the formation of stagnant water bodies
that support vector breeding.

44. 4. Reservoir Control: Targeting reservoirs or host species that maintain and amplify the
pathogen can be an effective environmental control measure. For example,
vaccination or treatment of reservoir animals can help reduce the pathogen's
presence in the environment, thereby lowering the risk of transmission.
5. Bioengineering and Natural Barriers: Using bioengineering techniques to modify the
environment can create natural barriers or obstacles that deter vector movement or
reduce breeding sites. For example, constructing physical barriers like fences or walls,
using biological control agents like mosquito-eating fish, or employing natural
predators can help control vector populations.
6. Urban Sanitation and Waste Management: Improving sanitation practices and waste
management systems in urban areas can help reduce vector breeding sites and
control populations. Proper waste disposal, regular garbage collection, and the use of
covered bins or containers can minimize the availability of food and breeding sites for
vectors.
Environmental control is most effective when integrated with other vector control strategies, such
as chemical control, biological control, or personal protection measures. Relying solely on
environmental control may not be sufficient to control vector populations or interrupt disease
transmission. Integrated approaches that combine multiple strategies tailored to the local context
are often necessary for optimal vector control outcomes.

45. Personal Protection Measures
• Personal protection measures are an important approach to vector control that focuses
on minimizing individual exposure to vectors and preventing vector-borne diseases. These
measures aim to protect individuals from vector bites and reduce the risk of infection.
Here are some key personal protection measures:
1. Use of Insect Repellents: Repellents containing active ingredients such as DEET (N,N-diethyl-
meta-toluamide), picaridin, or IR3535 are effective against a wide range of vectors.
2. Wearing Protective Clothing: Wearing long-sleeved shirts, long pants, socks, and closed-toe
shoes can provide physical barriers to prevent vectors from accessing the skin.
3. Use of Bed Nets: Sleeping under insecticide-treated bed nets (ITNs) can protect against
nocturnal biting vectors, such as mosquitoes. ITNs are typically treated with long-lasting
insecticides that repel or kill mosquitoes on contact.
4. Avoiding Peak Vector Activity Times: For example, mosquitoes that transmit dengue and
chikungunya viruses are most active during early morning and late afternoon hours, so
minimizing outdoor activities during these times can help reduce exposure.

46. 5. Screening and Sealing of Living Spaces: Proper sealing of gaps and cracks in walls
or roofs can further minimize vector entry points. This approach is particularly
relevant for indoor-resting vectors like mosquitoes and triatomine bugs.
6. Travel Precautions: When traveling to areas with known vector-borne disease
transmission, it is important to research and understand the specific risks and
preventive measures. This may include using bed nets, applying repellents,
wearing appropriate clothing, and seeking medical advice or vaccinations if
available.
7. Education and Awareness: Educating people about the risks, preventive
measures, and proper usage of personal protection methods can empower them
to take appropriate actions to protect themselves.
It is important to note that personal protection measures should be used in conjunction with other
vector control strategies, such as environmental control and chemical control, for comprehensive
and integrated vector management. The combination of multiple approaches tailored to the local
context and disease epidemiology can provide optimal protection against vectors and reduce the
burden of vector-borne diseases.

47. Semiochemicals
• Semiochemicals, also known as "chemical signals," are natural chemicals that serve
as communication signals between organisms. These chemical signals play a significant
role in the interactions between vectors, hosts, and pathogens in the context of vector-
borne diseases. Semiochemicals can be classified into two main types:

48. 1) Attract-and-Kill Strategies (A&K): The technique as the name implies simply use an
attractant or semiochemical to lure an insect to a point source that contains a killing agent
(insecticide, pathogen, or sterilant). This approach targets vector populations while minimizing
the use of broad-spectrum insecticides.
2) Mating disruption: The most commonly used technique. It manipulates insect behavior in
such a way that leads to population reduction. pheromones does not completely shut off
mating, but the delay in females mating may reduce their fecundity and their abilities to select
the suitable sites for oviposition.
3) Competitive attraction This happens when males respond to synthetic pheromone rather
than the natural pheromone emitted by the calling female.
4) Mass trapping: It is a pheromone technique commonly used for direct insect population
suppression. Mass trapping is effective in the case of male-emitted pheromone that attracts
females. In this system, females are trapped, thus mass trapping directly reduces egg laying.
5) Repellents: Semiochemicals can be used in the development of repellents that deter
vectors from approaching or biting humans or animals.
Applications of Semiochemicals for vector control and disease prevention:
Semiochemical-based approaches have the potential to complement existing vector control
strategies and enhance their effectiveness. However, the application of semiochemicals for
vector control requires a detailed understanding of the specific semiochemicals involved in vector
behavior, the ecological context, and the interactions between vectors, hosts, and pathogens.

49. Biological
Control
• Biological control is a vector control
strategy that utilizes natural enemies or
biological agents to reduce vector
populations and control the transmission of
vector-borne diseases. It involves the
introduction, augmentation, or conservation
of specific organisms that prey on, parasitize,
or compete with vectors.
• Here are key aspects of biological control:

50. 1. Predators and Parasites: Biological control can involve the introduction or augmentation of
predators or parasites that feed on vectors. For example, certain mosquito species can be
controlled by introducing or conserving predatory fish, such as Gambusia affinis or larvivorous
fish, in water bodies where mosquitoes breed. Similarly, parasitic wasps, mites, or fungi may
be used to control other vector species.
2. Competitors and Pathogens: Competitive interactions or the introduction of pathogens that
specifically target vectors can be employed in biological control. For instance, introducing
competitive mosquito species that outcompete disease-transmitting mosquitoes for
resources can help reduce the overall vector population. Pathogens, such as bacteria or
viruses, may also be used to infect and suppress vector populations selectively.
3. Sterile Insect Technique (SIT): The sterile insect technique is a biological control method
commonly used against certain insect pests, including vectors. It involves the mass rearing
and sterilization of male vectors using radiation or other techniques. These sterile males are
then released into the wild, where they compete with wild males for mates. The reproductive
potential of the vector population decreases over time.
4. Conservation and Enhancement of Natural Enemies: Biological control can also involve the
conservation or enhancement of naturally occurring organisms that are natural enemies of
vectors. This may include conserving natural habitats, promoting biodiversity, and
implementing practices that support the presence and abundance of natural predators,
parasites, or pathogens.
Aspects of biological control

51. Advantages of Biological control approaches:
1) Environmental Safety: Biological control methods are generally considered environmentally safe, as
they rely on naturally occurring organisms or specific biological agents that target vectors without
causing harm to non-target species or ecosystems.
2) Targeted Approach: Biological control methods can specifically target vector populations,
minimizing the impact on non-target organisms and reducing the need for broad-spectrum chemical
insecticides.
3) Long-Term Effectiveness: Biological control methods can provide long-term control by establishing
self-sustaining populations of natural enemies.
a) Specificity: The effectiveness of biological control agents can be limited to specific vector species or
environments.
b) Regulatory Considerations: The release of biological control agents may be subject to regulatory
approvals and considerations to ensure safety and prevent unintended consequences.
c) Research and Development: Further research is needed to improve the efficacy and cost-
effectiveness of biological control methods.
d) Integration with Other Strategies: Biological control is often most effective when integrated with
other vector control approaches, such as environmental management, chemical control, or personal
protection measures, as part of an integrated vector management (IVM) approach.
Limitations and challenges associated with biological control:

52. Vector
Genomics
• Vector genomics refers to the study
of the complete set of genes (the
genome) of vector species, such as
mosquitoes, ticks, or sandflies, that
play a role in transmitting diseases to
humans and animals.
• It involves the sequencing, analysis,
and interpretation of the genetic
information of vectors to gain insights
into their biology, evolution, and
interactions with pathogens.

53. 1) Understanding Vector Biology and Physiology: For example,
identifying genes involved in vector reproduction or host-seeking
behaviors can inform the development of novel control
approaches that disrupt these processes.
2) Identifying Vector Competence Factors: researchers can identify
genes associated with vector competence. This knowledge can
inform the development of interventions that target specific
genes or pathways to reduce vector competence and interrupt
disease transmission.
3) Studying Vector-Pathogen Interactions: By comparing the
genomes of vectors and their associated pathogens, researchers
can identify genetic factors that contribute to vector susceptibility
or resistance to specific pathogens. his information can guide the
development of targeted control strategies, such as disrupting
vector-paTthogen interactions or enhancing vector resistance to
pathogens.
Vector genomics has several applications that can contribute to vector and vector-borne
disease control efforts. Here are some of the key applications and benefits of vector
genomics in this context:

54. 4. Monitoring Insecticide Resistance:. This knowledge enables the
development of molecular diagnostic tools to monitor the
spread and intensity of resistance. It also helps in designing
insecticides that target specific resistance mechanisms or
developing alternative control strategies that bypass or
overcome resistance.
5. Genetic Modification and Control Strategies: For example, gene
editing techniques like CRISPR-Cas9 can be used to modify
vector genomes and confer traits that reduce vector
competence, disrupt reproductive processes, or enhance
susceptibility to control measures. These genetically modified
vectors can potentially be used in suppression or replacement
strategies to reduce vector populations or disease transmission.
6. Vaccine Development: Understanding vector genomics can aid
in the development of vaccines against vector-borne diseases.
By identifying vector-specific antigens or proteins involved in
host-pathogen interactions, researchers can develop vaccines
that target the vector rather than the pathogen.

55. Dr. Ibrahim