Arthropod
Transmission Of
Disease
What is an
‘Arthropod-borne Disease’?
A disease transmitted by an arthropod
So… “Why is it important for public health
staff to understand arthropod-borne
diseases?”
‘Top 5’ reasons to address
arthropod-borne diseases
5. Arthropod-borne diseases occur world-wide,
including Afghanistan
4. They’re making a comeback throughout the
world
3. Afghans are highly susceptible to these
diseases (both physically and mentally)
2. Very few vaccines exist for these diseases
1. MOST IMPORTANT: Military history shows
complacency, and ignorance of these vitally
important diseases kills and sickens troops
OBJECTIVE
‫هدف‬
Explain disease cycles and control measures
of vector-borne diseases.
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Overview
‫مرور‬
Transmission
Cycles
Types
Let’s use life cycles to
study arthropod-borne
diseases
What’s a life cycle?
It’s just a map that shows you how a
“germ” infects people
Next slide is an example
Types of Life Cycles
Three-factor cycle - African sleeping sickness
(trypanosomiasis) - it involves a human, a fly, and
the trypanosomiasis germ.
1. Host
2. Pathogen
3. Vector
Fly bites an uninfected
human and transfers the
Trypanosomiasis-causing
germ to the human.
Tse tse fly
Trypanosomiasis germ (T.b.
gambiense protozoa) in the
blood of the infected human is
ingested by a fly.
Types of Life Cycles
Four-Factor (Complex Cycle) - a disease of
animals that can be transmitted to humans
Also known as a complex cycle
Flea regurgitates
bacteria into rodent
when it feeds
1. Host
2. Pathogen
3. Vector
4. Reservoir
Plague bacterium is
in the rodent’s blood
Flea ingests bacteria
when it feeds on blood
Some fleas may move to
humans, feed, and transmit
the plague bacteria.
Terms and Concepts
You need to know the vocabulary of
arthropod-borne diseases because:
They use these terms at your public
health office (it’s nice to understand the
conversation)
The literature you’ll read at work uses
these terms (it’s nice to understand your
readings)
Terms and Definitions
Host – person or living animal that
provides food and lodging to the infectious
agent
Parasite – an organism that lives on or in
another organism or gets its food from that
organism
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Terms and Definitions
Pathogen – a parasite that causes disease
Arbovirus – virus carried by arthropods
Vector – a living non-human carrier of a
pathogen
Reservoir – any person, animal, arthropod,
plant, soil or substance in which an infectious
agent normally lives and multiplies
**In some cases a reservoir can also be a host
(i.e. dengue fever)**
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Terms and Definitions
Transmission Mechanisms:
Mechanical Disease Transmission –
parasite is carried accidentally on or in a
vector’s body (but does not go through
sexual changes in the vector)
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Terms and Definitions
Transmission Mechanisms:
Biological Disease Transmission – occurs
when a pathogen multiplies and/or
undergoes sexual growth changes in a
vector’s body
Malaria Death
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Terms and Definitions
Inoculation Mechanisms:
Active Inoculation – pathogen is
introduced into a host by the bite of an
infected vector
Passive inoculation – pathogen is
introduced to the host by rubbing vector
feces or other infective material into a
feeding wound, skin abrasion, or
mucous membrane
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Terms and Definitions
Transovarial transmission – pathogens
are passed on from infected female to her
eggs
Female mosquito
Mosquito eggs
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Terms and Definitions
Passage of Disease between regions:
Imported Disease – disease acquired in one area
and diagnosed in another
A
B
Introduced Disease – disease acquired in one
area, then brought into another area, and acquired
by a second individual
A
B
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Questions?
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Prevent Disease, Disability and Premature Death
Arthropod
Transmission Of
Disease
Part 2
Introduction
We covered Definitions in Part 1 -- Any
questions on those?
Apply those concepts to specific vectorborne diseases of particular importance...
starting with...
Mosquito – Borne
Diseases
Malaria
An acute & chronic disease caused by parasitic
protozoans in the genus Plasmodium.
Transmitted by certain Anopheles species
mosquitoes.
A complex 3-factor vector-borne disease of the
blood.
>1 pathogen species, vector species, man,
complicated ecology
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Four Plasmodium species
cause human malaria:
P. falciparum -- malignant tertian malaria.
P. vivax -- benign tertian malaria.
P. malariae -- quartan malaria.
P. ovale -- tertian malaria.
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The Malaria Pathogen
Life Cycle Is Complex
The primary (or sexual)
cycle is in the mosquito.
Parasites ingested from
an infected host develop
into sexual forms which
mate & reproduce.
Infective forms migrate to
the mosquito’s salivary
glands where they are
introduced into the next
host while the mosquito is
feeding.
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The malaria pathogen
life cycle is complex
The secondary (asexual, generative) cycle
occurs in humans.
The pathogens initially enter cells in the liver
where they continue their development.
The parasites then emerge and invade red
blood cells. Once in the red blood cells they
multiply asexually and produce huge numbers
of parasites, which attack additional red blood
cells.
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Symptoms
Symptoms occur
when red blood cells
(RBCs) rupture to
release pathogens
that have multiplied
within them.
When enough RBCs
are affected, anemia
develops.
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Symptoms
In falciparum malaria, RBCs “stick
together” causing blocked capillaries,
which then rupture -- When this happens
in the brain, cerebral hemorrhage may
cause brain damage and/or death.
The liver and spleen may also become
grossly enlarged.
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Symptoms
Commence 10-28 days after an infective
mosquito bite.
Initially anorexia, headache, fever, flu-like
symptoms.
After a period, RBCs rupture to release
pathogens at the same time, each 2 or 3 days,
depending on the species.
Release causes chills, high fever & profuse sweating.
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Symptoms
Other symptoms may
include headaches,
nausea, vomiting,
muscle & joint pains
Over time -- anemia,
cerebral hemorrhage,
impaired liver function.
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Treatment
Chloriquine
Primaquine
Doxycycline
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Malaria Distribution
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Epidemiology
Malaria is widespread throughout the tropical countries
of the world.
Transmission can also occur by blood transfusions &
hypodermic needles.
Communicability lasts as long as malaria pathogens are
in the blood.
Susceptibility is universal, but a previous case gives
some protection.
Diagnosis is by finding malaria pathogens in blood by
examination of blood smears, or from symptoms.
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Vector
Malaria is biologically
transmitted only by certain
species of Anopheles
mosquitoes
Most Anopheles cannot transmit
malaria.
There are 6 main Anopheles
vectors in Afghanistan:
a. Anopheles superpictus
b. A. culicifacies
c. A. stephensi
d. A. hycranus
e. A. pulcherrimus
f. A. fluviatilis
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Prevention
Personal protection from Anopheles mosquito
bites -- including use of repellents &
chemoprophylaxis.
Reduction of host habitat (if feasible).
Pesticides for vector control (if feasible).
Education on how & when to use the above.
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Dengue
An acute, febrile illness caused by an arbovirus
& transmitted by mosquitoes.
A simple 3-factor vector-borne disease.
There are 4 serological types (serotypes) & two
clinical forms:
Benign (Classical) Dengue, or “breakbone fever.”
Dengue Hemorrhagic Fever (DHF) or Dengue Shock
Syndrome (DSS).
Symptoms
Benign dengue symptoms include:
Fever (101°F).
Severe headache, muscle & joint pain (“breakbone”)
& sometimes a flat rash.
Commence 5 - 6 days after the infective mosquito
bite & last 5 - 7 days. Recovery is usually uneventful.
Patients are infective to another mosquito 1 - 4 days
after their symptoms occur.
Symptoms
DHF & DSS symptoms include:
Bleeding of the gums, nosebleeds,
gastrointestinal bleeding, & dengue
shock syndrome.
Death is most often due to internal
bleeding or shock.
Hemorrhaging -- on arm of child
Treatment
Classical dengue
None
Supportive, TLC – aspirin is not
advised
DHF/DSS
Intravenous (IV) transfusions & fluids to
prevent shock, & with corticosteroids.
Epidemiology
Found throughout much of the tropical
world, particularly in Mexico, Caribbean,
central America, west Africa, & south Asia.
Dengue Hemorrhagic Fever kills
thousands of south Asian children
annually.
Epidemiology
Transmitted by the bite of infective Aedes
species mosquitoes, principally Aedes
aegypti.
Vector
Aedes aegypti, yellow fever
mosquito
Daytime biter, weak flyer,
never found more than about
400 meters from human
habitation
Not able to overwinter in cold
areas.
Larvae are found in water in
artificial containers: cans, rain
gutters, & particularly rubber
tires.
Epidemiology of Dengue
Vectors =
Aedes aegypti
Aedes albopictus
Prevention
Personal protection from mosquito bites
Isolating infective people from mosquito
vectors
Reduction of mosquito habitat (if possible
& feasible)
Pesticides (if feasible)
Education about the above. It’s #1!!!
The Arboviral
Encephalitides
“Arthropod Borne
Viruses” = Arbovirus
The Arboviral
Encephalitides...
Acute infections of the brain and/or spinal
cord
Encephalitides is the plural of encephalitis
-- includes more than one encephalitic
disease.
Complex four-factor vector-borne
diseases.
May be mild to fatal
The Arboviral
Encephalitides
There are over 100 arboviruses that
produce disease in humans.
Transmission is by the bite of an infected
arthropod (including mosquitoes, sand
flies, ticks)
Mosquito-borne
Encephalitides
In the Afghanistan there are several types :
Japanese Encephalitis Infections may occur
nationwide.
Sindbis Fever Probably not endemic nationwide.
West Nile Virus Probably not endemic to
Afghanistan but may be more common in desert
environments.
Symptoms/Treatment
Range from asymptomatic, through general flu-like
illness, to severe central nervous system (CNS)
damage or death.
Usually fever, headaches & drowsiness.
Sometimes vomiting, stiff neck, tremors, confusion, &
convulsions.
Severity varies by species of virus.
Incubation period from infective bite to sickness ranges
from 2 - 20 days.
Treatment is supportive -- there is no medicine to kill
just the virus.
Epidemiology
The epidemiology of the
mosquito-borne
encephalitides is complex
Several vectors &
reservoirs, & much is
unknown.
All humans without previous
exposure to a given virus are
susceptible to infection
Certain viruses “prefer”
certain age groups.
Mosquitoes cannot pass
arboviral encephalitis from
one human to another.
Vector
In Afghanistan, arboviral encephalitides
are spread only by mosquitoes.
Several species of Aedes, Culex, & others
are involved.
Reservoir ???
Japanese Encephalitis-Birds.
West Nile Virus – Birds.
Sindbis Fever-Birds, rodents.
Many other reservoirs are possible:
rodents, bats, reptiles, amphibians, etc.
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Prevention
Personal protection from mosquito bites.
Reduction of mosquito habitat (if feasible).
Surveillance for vectors & pesticides for
control (if necessary).
Monitoring with sentinel chickens.
Education about the above.
Tick-Borne
Diseases
Crimean Congo
Hemorrhagic Fever
•
Tick-borne disease caused by a
Nairovirus in the family Bunyaviridae. It
is primarily transmitted by a bite or
exposure to hard ticks (Family Ixodidae)
in the genus Hyalomma.
Symptoms
Sudden, with initial signs including headache, high fever,
back pain, joint pain, stomach pain, and vomiting.
Other symptoms include red eyes, flushed face, a red
throat, and red spots on the palate.
Symptoms may also include jaundice, and in severe
cases changes in mood and sensory perception.
As the illness progresses, large areas of severe bruising,
severe nosebleeds, and uncontrolled bleeding at injection
sites can be seen, beginning about on the fourth day of
illness and lasting for about two weeks.
Fatality rates in hospitalized patients range from 9% to
50%.
Diagnosis is by laboratory tests and clinical findings.
Treatment
Treatment is primarily supportive, and
attention to fluid balance and correction of
electrolyte abnormalities, oxygenation,
and hemodynamic support, as well as
appropriate treatment of secondary
infections. The antiviral drug ribavirin has
also been used for treatment with some
benefit.
Epidemiology
In Afghanistan, there is nationwide evidence of CCHF
viral antibodies. Habitats that are conducive to tick
occurrence are dry areas, including animal stables,
trails, and former pastures.
CCHF is maintained in nature by Hyalomma ticks. Soft
ticks (Family Argasidae), such as Ornithodoros
lahorensis are also considered secondary vectors and
are often found in animal stables. Numerous wild and
domestic animals, such as cattle, goats, sheep, and
hares, serve as amplifying hosts for the virus.
Epidemiology
CCHF is transmitted to humans biologically by the bite of
an infected tick (active inoculation) or exposure to
infected blood (passive inoculation). It can be
transmitted from human to human by contact with
infectious blood or fluids, or improper sterilization of
medical equipment.
The transmission period is primarily from May-October.
Animal herders, livestock workers, and slaughter houses
in endemic areas area at risk of CCHF. Healthcare
workers in endemic areas are also at risk.
Vector
CCHF vectors in
Afghanistan are:
Hyalomma marginatum
(Primary vector)
H. anatolicum, H. detritum, H.
dromedarii, H. impeltatum, H.
schulzei, and H. asiaticum;
also the soft tick Ornithodoros
lahorensis (Secondary
vectors)
Prevention
Personal protection measures against
ticks, including self-inspection & “buddy”
inspection.
Tick control -- may be of limited
effectiveness & use.
Education.
Miscellaneous
Arthropod-Borne
Diseases
Plague
Plague
A zoonotic vector-borne disease caused
by the bacterium Yersinia pestis
Transmitted by fleas.
Historically known as “black death”
because of the symptomatic appearance
of dark hemorrhagic areas in the skin of
infected persons.
Septicemic
Plague -- Note
darkening of skin,
hence the term
“black death.”
Plague
A complex two-, three-, or four-factor
disease.
Can take three forms -- bubonic,
septicemic, & pneumonic -- depending on
the system & organs affected.
Symptoms...
Bubonic form (most
common)
Swollen lymph nodes
draining the flea bite,
“buboes” in groin, armpit
or neck
Buboes may be inflamed,
painful, & may ooze.
Untreated, mortality rate
is 50%, but responds well
if treated early.
Plague buboes in
axillum
Feline Plague: Sub-maxillary
buboes on the neck of a cat
Symptoms
Septicemic form -- “blood” plague.
Dissemination in the blood to various
parts of the body.
Can progress rapidly.
Untreated mortality rate is over 90%.
Septicemic plague symptoms -gangrene of fingers and toes
Symptoms
Pneumonic form -- “plague pneumonia”
Secondary involvement of the lungs.
Person-to-person transmission by
sneezing & coughing is a threat,
particularly in a hospital environment.
Untreated mortality rate is over 90%.
Treatment
Must be started immediately.
A number of antibiotics work well, but
penicillin is not particularly useful.
Diagnosis is by microscope examination
of blood or bubo fluid or by other
laboratory tests -- Early diagnosis is
essential.
Epidemiology
Distribution is throughout much of the
world, although large areas are plaguefree.
Found in many species of wild & domestic
animals.
Some are asymptomatic carriers, others become
symptomatic & die quickly -- All are reservoirs.
Epidemiology
Plague can be spread by
Bite of infected flea (vector transmission),
Respiratory aerosols (non-vector
transmission)
Blood to blood contact, a form of indirect
inoculation (non-vector transmission).
Epidemiology
Plague can thus be -A 4-factor disease (prairie dog to humans by a
flea),
or
A 3-factor disease (human to human by flea),
or
A 2-factor disease (human to human by
respiratory aerosol or indirect blood to blood
inoculation).
Epidemiology
Incubation period
2 - 6 days from flea bite or blood-blood contact.
1 - 6 days from aerosol inoculation.
Susceptibility is general.
Recovery confers some immunity.
Excellent vaccine available.
Separate cycles in nature for
Urban (murine) spread by domestic rodents .
Rural (sylvatic) spread by wild rodents.
Vector
Many species of vector fleas, some much more
efficient than others.
Can be transmitted from reservoir to reservoir,
reservoir to human, & human to human.
Transmission most dangerous when flea’s gut is
“blocked” by plug of plague bacteria.
Flea continues to try to feed, regurgitating
contaminated blood through the feeding wound into a
new host.
Blocked Flea
Prevention
Educate everyone at risk on plague
avoidance.
Use personal protection measures.
Implement rodent exclusion & harborage
elimination.
Prevention
Control fleas in wild rodent burrows
Animal control is not always practical, but
if attempted, it’s mandatory that fleas are
killed first, so they are not actively seeking
a new host when their previous one has
been killed.
Vaccination of at-risk personnel.
Contact protection in hospitals, elsewhere
as necessary.
Break
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Epidemic Typhus
“The great scourge of
humanity”
Epidemic Typhus
Caused by the rickettsia Rickettsia
prowazekii.
Transmitted by the body louse Pediculus
humanus humanus.
Also known as louse-borne typhus,
classical typhus fever, & historically as the
“red death.”
Complex 3-factor disease
Symptoms...
Sudden onset with chills, fever, headache,
pains, prostration.
Body rash appears on the 5th or 6th day.
Incubation period 7 - 14 days after
infection.
Lasts 2 - 3 months unless death occurs
first.
Symptoms
Toxemia (blood poisoning) pronounced &
severe.
Mortality in untreated epidemic typhus
can reach 40%.
Diagnosis is by laboratory tests -- clinical
diagnosis can be difficult except in
epidemic situations.
Treatment
Various antibiotics until one day after fever
breaks.
Epidemiology
Potential occurrence throughout most of the
world.
Can originate in & be limited to a defined area -For example, in 1979, there were:
18,364 reported cases worldwide,
18,278 cases were in Africa,
17,499 cases were in Ethiopian refugee camps (over
95% of the cases for that year).
Epidemiology
Non-human reservoir doubtful
No direct person-to-person
transmission.
Infection occurs when louse feces or
fluids from crushed lice are rubbed into
feeding wounds or other breaks in the skin
-- Passive inoculation
Transmitted biologically
Epidemiology
Epidemic typhus is a risk whenever
poverty creates conditions favoring poor
hygiene & crowding.
Risk increases with wars, famines, &
natural disasters creating refugees.
Susceptibility is universal, but attack
confers long-term immunity.
A vaccine is available.
Vector
Transmitted by the body louse
The head louse is a capable secondary
vector of endemic typhus, but the pubic
louse is not a vector.
These species of lice live only on humans.
The human body louse,
Pediculus humanus
humanus
Prevention
Improve sanitation & personal hygiene
Change clothes, wash clothes & bedding
in hot water or bake in oven.
Disinsection of clothes on body with
insecticidal dusts, or, issuance of
permethrin-treated clothing
Vaccinate personnel at risk.
Leishmaniasis
Leishmaniasis
Caused by protozoans of the genus Leishmania.
Transmitted by sand flies of several species.
A complex 4-factor vector-borne disease.
3 species of pathogen
Several vector species
Complex ecology
Leishmaniasis
There are 3 clinically separate types caused by
separate species of Leishmania:
Cutaneous
Uta, chiclero ulcer
Mucocutaneous (not know to occur in Afghanistan)
Papalomoyo, espundia
Visceral
Kala azar, dumdum fever, tropical splenomegaly
Symptoms
Vary with type of infection...
Cutaneous
Leishmaniasis
Dry or moist ulcerating lesion (usually single) or
nodular lesions (usually multiple)
May last for months, usually leave large scars.
Usually affect ear, face or extremities, unusual
on trunk
Not fatal but is debilitating & disfiguring.
Usually resolve spontaneously in 6 - 12 months.
Cutaneous
Leishmaniasis
Mucocutaneous
Leishmaniasis
Affects
face only -- skin,
mucous membranes, muscle
& bone.
Severely
disfiguring if not
diagnosed & treated soon
after exposure.
Fatalities
result from
secondary infections,
asphyxiation from dislodged
tissue.
Mucocutaneous Leishmaniasis
Early stage
Untreated case
Visceral Leishmaniasis
Chronic disease of lymphatic system,
liver, & spleen, with fever, anemia, &
progressive, physical wasting away until
the patient dies.
Mortality is up to 95% in untreated cases - early detection is vital.
Diagnosis
Through biopsy cultures from sores, &
microscopic & other laboratory tests.
Treatment
Several medicines are available but early
diagnosis is important to prevent
disfigurement, or death in the visceral form.
Epidemiology of cutaneous &
mucocutaneous forms
Transmission is biological through active
inoculation -- through the bite of an infected
sand fly.
Non-human reservoirs include dogs, cats,
rodents, perhaps other small mammals.
No human-to-human infection except for
human-to-human contact of abraded skin.
Epidemiology of cutaneous &
mucocutaneous forms
Occurs in pockets throughout Central &
South America, Africa, Europe & Asia
usually in rural areas.
Incubation period is a few days to many
months.
Susceptibility is universal
Immunity to the cutaneous form
develops after lesions heal.
Leishmaniasis
Distribution
Vector
Transmitted biologically by several species of
Phlebotomus sand flies.
Prevention
Early case detection & treatment.
Chemical & cultural sand fly control.
Personal protection.
Education.
Lessons
Learned
Unpredictable
Occurrence of vector-borne diseases can be
extremely unpredictable.
Outbreaks of disease caused by arboviruses cannot
be predicted based upon history.
A small area may have a major outbreak, although
there was not a single case in the area prior to the
outbreak & may not be another case in the area for
decades afterwards.
The Importance Of
Vector Surveillance
Disease surveillance is “looking for” a
disease.
If we know the disease is in the area we
can take precautions to prevent it.
With vector-borne diseases we can also
survey for the vectors through vector
surveillance, & control them before they
can spread a significant amount of
disease.
Vector-Borne Disease Threat
Military Significance
Many areas of the world harbor vectorborne diseases that are only found in
those areas & nowhere else.
If these areas are of military interest, we
must know what vector-borne diseases
occur there so we can prevent them in
our personnel.
Summary
Transmission
Cycles
Types
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