Other Biting Flies
Blackflies, Biting Midges, Tabanid
Flies, and Sandflies
Associated Pathogens, Life Cycles,
Vector Biology and Control
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Blackflies and Onchocerciasis
• Pathogens
• Life Cycles
• Vector Biology
• Vector Control
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Onchocerciasis
•
•
•
•
Non-fatal dermal and ocular disease
Human definitive host; fly intermediate host
No animal reservoir of O. volvulus
95% of all cases worldwide occur in Africa in poor
rural areas, approx. 17 million affected
• Three main symptoms (occur 1-3 yrs after initial
infection):
• Skin lesions (microfilariae in dermis)
• Painless nodules (where tissues thin, bone)
• Eye lesions (blindness – assoc. with dead mf)
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Onchocerca life cycle - 1
• During a blood meal, an infected blackfly (genus Simulium)
introduces third-stage filarial larvae onto the skin of the
human host, where they penetrate into the bite wound.
• In subcutaneous tissues the larvae develop into adult filariae,
which commonly reside in nodules in subcutaneous
connective tissues.
• Adults can live in the nodules for approximately 15 years.
Some nodules may contain numerous male and female
worms.
• Females measure 33 to 50 cm in length and 270 to 400 µm in
diameter, while males measure 19 to 42 mm by 130 to 210
µm.
• In the subcutaneous nodules, the female worms are capable
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of producing microfilariae for approximately 9 years.
Onchocerca life cycle - 2
• The microfilariae, measuring 220 to 360 µm by 5 to 9 µm
and unsheathed, have a life span that may reach 2 years.
• They are occasionally found in peripheral blood, urine, and
sputum but are typically found in the skin and in the
lymphatics of connective tissues.
• A blackfly ingests the microfilariae during a blood meal.
• After ingestion, the microfilariae migrate from the blackfly's
midgut through the hemocoel to the thoracic muscles.
• There the microfilariae develop into first-stage larvae and
subsequently into third-stage infective larvae.
• The third-stage infective larvae migrate to the blackfly's
proboscis and can infect another human when the fly takes
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a blood meal.
Onchocerciasis is endemic in more than 25 nations located in a broad band
across the central part of Africa. Small endemic foci are also present in the
Arabian Peninsula (Yemen) and in the Americas (Brazil, Colombia, Ecuador,
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Guatemala, southern Mexico, and Venezuela).
© Copyright 1997 OCP/APOC/WHO.
Adults of Onchocerca volvulus from nodule.
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Microfilaria of Onchocerca volvulus, from skin snip from a
patient seen in Guatemala. Wet preparation. Some
important characteristics of the microfilariae of this
species are shown here: no sheath present; the tail is
tapered and is sharply angled at the end.
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© Copyright 1997 OCP/APOC/WHO.
Blindness caused by onchocerciasis
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© Copyright 1997 OCP/APOC/WHO.
Maddening itching, depigmentation (leopard
skin), and thickened skin
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Eggs of Simulium damnosum attached to vegetation in running water.
Adults typically emerge in 8-12 days, depending on local temperature.
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Larva
Simulium naevei larvae
attached to a crab.
Pupae
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West Africa, 1990, WHO/TDR
Guatemala, 1991, WHO/TDR/Haaland
Simulium damnosum larvae.
Blackfly larvae and pupae
found during a survey of a
stream near Los Golindras, 3
hours drive north of Huixla,
Guatemala.
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Collecting blackfly immatures
Single blackfly larva and larvae
clustered on a stick in moving
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water
Nigeria, Africa, 1998, WHO/TDR/Crump
Uganda, Africa, 1996
WHO/TDR/Crump
The Simulium blackfly vectors
breed in fast-flowing river water
such as this, and threaten those
farming fertile riverside land with
infection and blindness.
Fast-flowing waters in rivers
are ideal breeding sites for
the blackfly.
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Ghana, Africa, 1973
WHO/TDR/Baldry
A breeding site for Simulium damnosum the blackfly vector
of Onchocerca volvulus. Human activities can sometimes
create the conditions sought by blackflies for breeding.
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West Africa, 1990
WHO/TDR/W. Imber
Adult Simulium
damnosum taking a
bloodmeal – only
females take blood and
may live up to 4 weeks
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Onchocerciasis Control
Vector Control - The principal method for controlling
onchocerciasis has been to break the cycle of transmission by
eliminating the black fly. Simulium larvae are destroyed by
application of selected insecticides through aerial spraying of
breeding sites in fast-flowing rivers. Once the cycle of river
blindness has been interrupted for 14 years the reservoir of adult
worms dies out in the human population, thus eliminating the
source of the disease.
Ivermectin Treatment - To complement vector control
activities, the drug ivermectin is distributed where needed through
a community directed approach. Ivermectin kills the larval worms
that cause blindness and other onchocercal manifestations and
acts to decrease transmission as well. Ivermectin became
available in 1987 to complement blackfly control activities.
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Treatment (CDC Recs)
• Use of antibacterial cream on wounds stops bacterial
infections and keeps swelling from worsening.
• Diethylcarbamazine (under an investigational New Drug
Protocol from CDC's Drug Service) and ivermectin* are
effective for the treatment of filariasis.
• Albendazole* is also included among the choices for
treatment of filariasis.
* This drug is approved by the FDA, but considered
investigational for this purpose.
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DRUG MODE OF ACTION
• Ivermectin (Mectizan®)- binds to glutamate gated chloride
channels in the parasites’ nervous system, causing them to
open.
• Albendazole - works by keeping the worm from absorbing
sugar (glucose), so that the worm loses energy and dies.
• Diethylcarbamazine – causes hyperpolarization of nerve
membrane and flaccid paralysis of the nematode, worms are
removed by normal peristalsis
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Onchocerciasis
Control
Programme in
West Africa
(1974-2002)
The Onchocerciasis Control Programme in
West Africa (OCP) has brought onchocerciasis
under control in the savanna areas of 11 West
African countries where the disease used to be
a major public health problem and a serious
obstacle to socio-economic development. The
current challenge of OCP, which ended in the
year 2002, is to ensure that its achievements
can be maintained by the countries
themselves.
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Microfilarial
Prevalence 20
Years Later
Pre-Control
Microfilarial
Prevalence
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The African Programme for
Onchocerciasis Control
(APOC) covers 19 African
countries and more than
85% of all people affected
by onchocerciasis, or river
blindness, in the world.
With the goal of elimination
of river blindness as a
public health and socioeconomic problem
throughout Africa, APOC
intends to establish selfsustainable communitydirected treatment with
ivermectin throughout the
endemic areas and to
eradicate the vector in
selected foci.
African
Programme for
Onchocerciasis
Control
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Existing oncho foci
in the Americas
Onchocerciasis Elimination Program in the Americas (OEPA)
To coordinate onchocerciasis control efforts in the 6 endemic countries
of the Americas and to reach the goal of eliminating first the pathology
and then the disease, the Onchocerciasis Elimination Programme for
the Americas (OEPA) was created in 1992 with the support of PAHO,
the Inter-American Development Bank, a consortium of NGDOs, and
all of the affected countries.
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Mali, Africa, 1996, WHO/TDR/Crump
Mali, Africa, 1996, WHO/TDR/Crump
Flies collected during Man-bait capture and essential tools for Man-bait
capture. A volunteer sits by a fast-flowing part of a river where the
Simulium blackfly vectors breed. Flies which land on him are collected32in
tubes, labeled and then dissected to see if they are carrying parasites.
© Copyright 1997 OCP/APOC/WHO.
Vector collectors catch the Simulium fly as it
lands on the legs to take up a blood meal
through its bite.
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Mali, Africa, 1996,
WHO/TDR/Crump
Man-bait capture. Flies which land on the volunteer are
collected in tubes, labeled and then dissected to see if
they are carrying parasites.
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West Africa, 1990, WHO/TDR/OCP/Ward
As part of the Onchocerciasis Control Programme (OCP),
helicopters and fixed wing aircraft are used to spray
insecticides (chemical and biological) on rivers and fastflowing water where larvae of the blackfly, Simulium
damnosum, breed. Insecticide types used are
organophosphates, carbamates and pyrethroids.
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West Africa, 1990, WHO/TDR/OCP/Ward
Seven insecticides are currently available to the Program: Bti,
Abate, pyraclofos, phoxim, permethrin, carbosulfan and
vectron. They are used on a rotational basis depending on the
river disharge, the level of toxicity with respect to non-target
organisms and the level of sensitivity of the local Simulium
species to each of the compounds.
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New villages in
areas formerly
uninhabitable
because of river
blindness
The result has been
increased activity and
productivity in many
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of these areas
Nine million children born
after 1974 have been saved
from river blindness
Formerly empty schools
have reopened their doors
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Mansonella ozzardi
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• M. ozzardi consists of
two biological forms.
Mansonella ozzardi
distribution
• One is transmitted by
black flies of the
Simulium family and is
mainly found in the
Amazon and parts of the
South American
mainland.
• The other form is
transmitted by midges of
the Culicoides family and
is endemic to beach
areas in the Caribbean
where these pests are
common.
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Mansonella ozzardi
• Once in the human host the larvae move into the
peritoneal cavities.
• The adults then mate and produce unsheathed
microfilariae about 207-232 x 3-4 micrometers in size.
• The microfilaria closely resemble those of M. perstans
except they have a sharp tail.
• They are non-periodic like their vectors and can be found
in the blood and skin at all times.
• Most infected people are completely symptomless.
• However, joint pains, headaches, coldness of the legs,
inguinal adenitis, and itchy red spots have been described
in conjunction with infection.
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Summary - Blackflies
• Pathogens
• Life Cycles
• Vector Biology
• Vector and Disease Control
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Other Bloodsucking Flies
Associated with Filarial
Transmission
Vector Biology and Pathogen Transmission
• Culicoides sp. (Biting Midges)
• Tabanidae (Horse flies and Deer flies)
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Biting Midges – Medical Importance
• PEST impact – tourism, economics
• Mansonella perstans and M. streptocerca (filarids)
transmitted by Culicoides sp. In Africa
• M. ozzardi transmitted by C. furens in S. & C.
America
• Filariae develop in thoracic flight muscles
• Oropoche virus (Brazil, Trinidad and Colombia)
• Blue tongue virus (cattle, sheep – vet. importance)
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• Mansonella perstans occurs in both Africa and South America
• Infections by Mansonella perstans, while often asymptomatic,
can be associated with angioedema, pruritus, fever,
headaches, arthralgias, and neurologic manifestations.
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• Mansonella streptocerca is found in Africa
• Mansonella streptocerca can cause skin manifestations
including pruritus, papular eruptions and pigmentation
changes.
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• May be transmitted by
midges of the Culicoides
family and is endemic to
beach areas in the
Caribbean where these
pests are common.
Mansonella ozzardi
distribution
• Most infected people are
completely asymptomatic.
However, joint pains,
headaches, coldness of the
legs, inguinal adenitis, and
itchy red spots have been
described in conjunction
with infection.
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Culicoides larva
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Biting Midges
Culicoides pupae and adult
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Culicoides habitat – many larval habitats similar
to that of mosquitoes
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Family Tabanidae – Medical Importance
• Large biting flies in two genera – Tabanus,
Chrysops
• Tabanus sp. – horseflies (tularemia)
• Chrysops sp. – deerflies (Loa loa, tularemia)
• Filariae develop in fat body of thorax and
abdomen
• Large biting mouthparts, pool feeders (females
only)
• Usually diurnal activity, powerful fliers
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• The vectors for Loa loa filariasis are flies from two species
of the genus Chrysops, C. silacea and C. dimidiata. Loiasis
only occurs in Africa and infection is often asymptomatic.
• During a blood meal, an infected fly (genus Chrysops, daybiting flies) introduces third-stage filarial larvae onto the skin
of the human host, where they penetrate into the bite
wound .
• The larvae develop into adults that commonly reside in
subcutaneous tissue .
• Adults produce microfilariae measuring 250 to 300 µm by 6
to 8 µm, which are sheathed and have diurnal periodicity.
• Microfilariae have been recovered from spinal fluids, urine,
and sputum. During the day they are found in peripheral
blood, but during the noncirculation phase, they are found in
the lungs .
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Tabanid Teeth
Serrated edges usually associated with
bloodfeeding species.
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Deer flies feeding
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Summary - Bloodsucking Flies
Associated with Filarial
Transmission
• Culicoides sp. (Biting Midges)
• Tabanidae (Horse flies and Deer flies)
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Other Bloodsucking Flies:
Sandflies and Leishmania
Vector Biology and Pathogen Transmission
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Sandflies – Medical Importance
• Small biting flies in two genera – Phlebotomus
(Old World), Lutzomyia (New World)
• Transmit leishmaniasis (worldwide)
• Transmit sandfly fever virus (Mediterranean)
• Transmit Carrion’s disease (bartonellosis) Peru, Ecuador and Columbia
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LEISHMANIASIS
• Caused by obligate intracellular protozoa of the genus
Leishmania.
• Human infection is caused by about 21 of 30 species that
infect mammals.
• These include the L. donovani complex with 3 species (L.
donovani, L. infantum, and L. chagasi); the L. mexicana
complex with 3 main species (L. mexicana, L. amazonensis,
and L. venezuelensis); L. tropica; L. major; L. aethiopica; and
the subgenus Viannia with 4 main species (L. (V.) braziliensis,
L. (V.) guyanensis, L. (V.) panamensis, and L. (V.) peruviana).
• The different species are morphologically indistinguishable,
but they can be differentiated by isoenzyme analysis,
molecular methods, or monoclonal antibodies.
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During bloodfeeding, female sandflies inject the infective promastigote stage.
Promastigotes that reach the puncture wound are phagocytized by
macrophages and transform into amastigotes. Amastigotes multiply in
infected cells and affect different tissues, depending in part on the
Leishmania species. This originates the clinical manifestations of
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leishmaniasis.
Sandflies become infected during blood meals on an infected host when they
ingest macrophages infected with amastigotes. In the sandfly's midgut, the
parasites differentiate into promastigotes, which multiply and migrate to the
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proboscis.
Leishmania donovani promastigotes
(form present in sandfly host)
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Leishmania donovani extracellular amastigote
(form present in vertebrate host)
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LEISHMANIASIS - manifestations
• Human leishmanial infections can result in 2 main
forms of disease, cutaneous leishmaniasis (CL) and
visceral leishmaniasis (VL) (also known as kala-azar).
• Two less common forms also occur: mucocutaneous
leishmaniasis (MCL), due to L. braziliensis infection,
and diffuse cutaneous leishmaniasis (DCL), which
produces disseminated and chronic skin lesions.
• The factors determining the form of disease include
leishmanial species, geographic location, and immune
response of the host.
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LEISHMANIASIS - pathology
Cutaneous forms of the disease normally produce skin ulcers
on the exposed parts of the body such as the face, arms and
legs. The disease can produce a large number of lesions sometimes up to 200 - causing serious disability and leaving the
patient permanently scarred.
In mucocutaneous forms of leishmaniasis , lesions can lead to
partial or total destruction of the mucose membranes of the
nose, mouth and throat cavities and surrounding tissues.
Visceral leishmaniasis - also known as kala azar - is
characterized by irregular bouts of fever, substantial weight loss,
swelling of the spleen and liver, and anemia (occasionally
serious). If left untreated, the fatality rate can be as high as
100%.
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Leishmaniasis – Cause and Effect
• Leishmaniasis is related to environmental changes such
as deforestation, building of dams, new irrigation
schemes, urbanization and migration of non-immune
people to endemic areas.
• It seriously hampers productivity and socioeconomic
progress and epidemics have significantly delayed the
implementation of numerous development programs.
• This is particularly true in Saudi Arabia, Morocco, the
Amazon basin and the tropical regions of the Andean
countries.
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Currently the leishmaniases, prevalent in four
continents, are considered to be endemic in 88
countries, 72 of which are developing countries:
• 90% of all visceral leishmaniasis cases occur in
Bangladesh, Brazil, India, Nepal and the Sudan
• 90% of mucocutaneous leishmaniasis occurs in
Bolivia, Brazil and Peru
• 90% of cutaneous leishmaniasis cases occur in
Afghanistan, Brazil, Iran, Peru, Saudi Arabia and
Syria
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Leishmania/HIV co-infection
• Leishmaniasis is spreading in several areas of the world
as a result of epidemiological changes which sharply
increase the overlapping of AIDS and visceral
leishmaniasis.
• So far, 33 countries worldwide have reported coinfections.
• Intravenous drug users have been identified as the main
population at risk.
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TREATMENT
Andy Crump
WHO/TDR/Crump
A tube of paromomycin cream, used for
topical application on lesions in the
treatment of cutaneous leishmaniasis
A doctor filling a syringe from a phial of glucantime, a pentavalent
antimonial which is used for the treatment of cutaneous leishmaniasis
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Cutaneous Leishmaniasis
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Diffuse Cutaneous Leishmaniasis
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TREATMENT
Andy Crump
WHO/TDR/Crump
A bottle of capsules of
miltefosine, the first oral
drug for treating visceral
leishmaniasis.
A number of clinical studies to
test the effectiveness of
injectable paromomycin against
visceral leishmaniasis have
been carried out in India, where
the standard antimonial
treatment, sodium
stibogluconate, is not very
effective and failure rates are
high. Results show it to be safe
and effective.
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SANDFLIES
• Worldwide distribution
• 700 species in 5 genera (Family Psychodidae,
subfamily Phlebotominae)
• Three genera contain bloodsucking species
• Most important genera are Phlebotomus (Old
World) and Lutzomyia (New World)
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Important Vectors of Leishmaniasis
Visceral
Lutzomyia longipalpis
Central and South America
Phlebotomus argentipes
Middle East
Phlebotomus chinensis
China
Cutaneous
Phlebotomus sergenti
India
Phlebotomus papatasi
Mediterranean
Lutzomyia verrucarum s.l. Central and South America
Mucocutaneous
Lutzomyia intermedia
http://cipa.snv.jussieu.fr/index.html
Central and South America
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Sandfly Pupa
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Sandfly Larvae
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SANDFLIES: Adults
• Differentiate between Phlebotomus and Lutzomyia
by where (geographically) they are collected
• Very small (1.3-3.5 mm), very hairy, with long thin
legs
• Body tends to be brown/light brown in color
• Short mouthparts adapted for sucking – only
females take blood, usually nocturnal
• Wings held over the body when at rest – generally
poor fliers
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WHO/TDR/Stammers
Lutzomyia longipalpis feeding
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WHO/TDR/Stammers
Phlebotomus duboscqi feeding
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Dogs can act as
reservoirs of
Leishmania
parasites.
They also exhibit
symptoms of
infection.
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WHO/TDR/Mark Edwards
Rodent
reservoir
hosts
WHO/TDR/Crump
Rodent burrows
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WHO/TDR/Lainson
Rubber trees in part of a natural, uncut forest which is a locality for
the transmission of leishmaniasis (Espundia) in Brazil. People who
collect rubber in these situations, or who clear such areas for
agricultural use, are prone to infection.
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WHO/TDR/Mark Edwards
Rio de Janeiro. Homes built in newly-cleared forest areas
around the city perimeter, in transmission sites such as the
Fragrasia Mountains, expose the settlers to the sandflies
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which transmit leishmaniasis.
WHO/TDR/Mark Edwards
Sandfly habitat in Jacarepagua district on the outskirts of Rio de
Janeiro. Homes built in newly-cleared forest areas expose the
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settlers to the sandflies which transmit leishmaniasis.
Vector Control
Bednet protection from sand flies
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Spraying to control sand flies
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Summary - Biting Flies (Other
than Mosquitoes)
• Blackflies – Onchocera, Mansonella
• Biting Midges – Mansonella
• Tabanid Flies:
• Deer flies – Loa loa, tularemia
• Horse flies - tularemia
• Sandflies – Leishmania, sandfly fever
virus, bartonellosis
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