MOSQUITOES
If you would see all of Nature gathered
up at one point, in all her loveliness,
and her skill, and her deadliness, and
her sex, where would you find a more
exquisite symbol than the mosquito?
-- Havelock Ellis, 1920
HISTORY
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Ancient Rome
Scotland
Middle ages and Henry II
Ancient India and
Mesopotamia
Ancient China
Egypt
Alexander the Great 323 B.C.
Genghis Khan and Western
Europe
Alexander The
Great
• General, King,
Ruler
• Babylon 323 B.C.
• Malaria?
• WNV?
• Typhoid?
European Exploration
• European exploration of new
lands.
• Defensive and Offensive
diseases.
• Offensive germs in the New
World.
• Indigenous destruction
• Slave trade
• 1890’s and beyond…
The Family Culicidae - Mosquitoes
• Worldwide distribution
• > 3450 species and subspecies (38 genera)
• Great habitat diversity
• Approximately 40 million years older than humans
(fossils from Eocene, 38-54 mya)
• Anophelinae (subfamily) - Anopheles (genus)
• Culicinae (subfamily) - Aedes, Culex, Haemagogus,
Mansonia, Ochlerotatus and all other genera
Mosquito Characteristics
• Conspicuous proboscis - forward projecting
• Scales on thorax, abdomen, legs & wing veins
• A fringe of scales along the posterior margin of
the wings
Mosquito Characteristics (note
conspicuous forward projecting
proboscis)
Non-biting Gnat (note proboscis
curved under head)
Gnat
Mosquito
Mosquito Characteristics
• Bloodfeeding - only females take blood
• Males and females feed on plant sugars
• Gonotrophic cycle - feed, egg development,
oviposition (half-gravid, gravid)
• Egg biology - oviposition location, type of egg,
desiccation resistance, diapause
• Larval biology - aquatic, spiracle for breathing,
filter-feeders, some cannibalistic, variable habitats
(1) Eggs – 3 strategies
• Singly on water surface
– Anopheles
• Singly in a pile, on moist substrates
– Aedes/Ochlerotatus
• Form of a raft, on water surface
– Culex
– Culiseta
Mosquito eggs:
Culex egg raft
Anopheles egg
with ‘floats’
Aedes egg
Patterns on the
external egg
surface are
species specific
Egg stage comparison
CULEX Egg Raft
(2) Embryonation – 2 options
• Eggs hatch immediately (not all)
• OR
• Diapause required
– Triggered by decreasing day length.
• **Egg stage over wintering stage**
– Aedes/Ochlerotatus
(3) Larval Stage – Growth Stage
• Larval instars (4)
• Aquatic, Filter feeders
• Respiration
Anopheles
(4) Pupa – Lighter than water
• Non-feeding
• Respiration
Pupal Stage Comparison
Anopheline
Culicine
Mosquito Pupa and Larvae
Anopheles Pupa and Larvae
Mosquito Emerging
from Pupal Exuvia
(5) Adults
• Emergence
• Mating
• Feeding
Adult Stage Comparison
Anopheline
Culicine
females
Culicine
Anopheline
males
Comparison of
male and
female
Anophelines
vs. Culicines
Behavior
• Activity
• Host Specificity
– Zoophilous
– Anthropophilous
– Ornithophilous
HABITAT
Medical Importance
• Biting Nuisance (annoyance)
• Arboviruses
– Numerous (Yellow Fever, Dengue Fever,
WNV, JE, SLE, EEE, WEE, VEE).
• Filariasis
– Bancroftian and Brugian filariasis.
• Malaria
– 4 plasmodium species
Malaria History
• Ronald Ross (1897)
• Malaria Eradication?
• Between 350 and 500 million clinical
episodes of malaria occur every year.
• 1-2 million deaths occur every year.
• About 60% of the cases of malaria
worldwide and more than 80% of the
malaria deaths worldwide occur in Africa
south of the Sahara.
HUMAN MALARIA
• Parasite – Plasmodium spp.
– P. falciparum, P. vivax, P. malaria, P. ovale
• Vector – Anopheles spp.
• Host
• Reservoir
• Distribution
Anopheles
gambiae
WHO/TDR/HOLT Studios,
1992
Global Distribution
Distribution
• Distribution Model
Distribution
• Endemic /
Epidemic Risk
Areas
Distribution
• Duration of Malaria
Transmission Season.
•
Distribution
Start / End of Transmission Season
Distribution
• Population
Distribution
Filariasis History
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Patrick Manson (1877)
Worked in Taiwan
Autopsies in China
Threadlike worms
• “Nothing walks with
aimless feet.:”
Mosquito-Borne Human
Filariasis
• 250 million infections each year
• 2-3 million cases of obstructive filariasis
• 20% of pop in Calcutta infected
• 2 diseases that affect humans
– Urban Disease
– Rural Disease
Urban and Rural Disease
• Urban Disease (Bancroftian filariasis)
– Parasite –
– An anthroponosis
– Bancroftia
• Rural Disease (Brugian filariasis)
– Parasite –
– An anthroponosis or zoonosis
– Brugian
Transmission
• (1) Microfilariae in
blood.
• (2)
• (3) Microfil. Penetrate
midgut  thoracic
muscles.
• (4)
• (5) Enter new host.
Periodicity
• (1) Periodic
Infection
• (2) Subperiodic
Infection
VECTORS
• (1) Bancroftian Filariasis
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Cx. pipiens quinquefasciatis
Cx. pipiens pipiens
Anopheles spp.
Aedes spp.
• (2) Brugian Filariasis
– Anopheles spp.
– Aedes spp.
– Mansonia (genus)
DISTRIBUTION
• Tropics and subtropics
• Wuchereria bancrofti is encountered in
_________________.
• Brugia malayi is limited to _____.
• Dog Heartworm (Dirofilaria immitis, D.
repens)
Mosquito Arboviruses
• Intrinsic incubation
period of a virus in
humans is a few days.
• Host becomes viraemic.
• Viraemia lasts typically 3
days then disappears
from the peripheral
blood.
• An arthropod must bite a
viraemic host if it is to
become infected.
Yellow Fever History
Yellow Fever
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Brought to U.S. via slave trade.
Aedes aegypti
Originally in New World Monkey populations
Jungle Yellow fever (3-factor disease in monkeys)
New World people bring to town
Old World mooting monkeys bring to town.
Does occasionally occur in U.S.
1964 Eradication program (U.S. Public Health)
YELLOW FEVER
• Is a _______
• Prevented the building of
the Panama Canal.
• Pathogen:
• Vector: Aedes aegypti,
Aedes spp., Haemagogus
• Host:
Reservoir
• Human-mosquito in urban cycle,
• Monkey-mosquito in forest cycle;
• Deforestation may force infected monkeys
into areas where human-mosquito
transmission can occur.
African Yellow Fever
Transmission Cycle
Vectors:
• Ae. Africanus (sylvatic)
• Ae. Bromeliae (rural)
• Ae. Aegypti (urban)
• Transovarial
Transmission
Central and South America
Yellow Fever Transmission
Cycle
Vectors:
• Haemagogus spp. (jungle)
• Haemagogus spp. (rural)
• Ae. Aegypti (urban)
• Transovarial
Transmission
Distribution
Diagnosis and Symptoms
• Most infections are mild, but the disease can cause
severe, life-threatening illness.
• Symptoms of severe infection are high fever, chills,
headache, muscle aches, vomiting, and backache.
After a brief recovery period, the infection can lead to
shock, bleeding, and kidney and liver failure. Liver
failure causes jaundice (yellowing of the skin and the
whites of the eyes).
• Diagnosed by blood test.
Prevention and Treatment
• General precautions to avoid mosquito bites; the use
of insect repellent, protective clothing, and mosquito
netting.
• Yellow fever vaccine has been used for several
decades. A single dose has a lasting immunity of 10
years or more. (Live virus vaccine)
• Booster dose is given every 10 years as needed.
• Treatment: No real treatment, drink plenty of fluids,
keep away from mosquitoes to protect others, most
people get better over a long recovery period.
Dengue Fever History
Dengue (Breakbone) Fever
• Dengue has four
serological types
(DEN-1,DEN-2,DEN-3
and DEN-4).
• Pathogen:
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• Host:
• Reservoir:
VECTORS
• Aedes aegypti (Yellow fever Mosquito)
• Aedes albopictus (Asian Tiger Mosquito)
• Aedes scutellaris
• Aedes polynesiensis
Transmission Cycle
• Blood meal from
viremic human.
• Midgut replication
• Salivary glands, pass
on during feeding.
• Transovarial
transmission
• SE Asia – monkey
cycle
Replication and Transmission
of Dengue Virus (Part 1)
1. Virus transmitted to human
in mosquito saliva
2. Virus replicates
in target organs
3. Virus infects white
blood cells and
lymphatic tissues
4. Virus released and
circulates in blood
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Replication and Transmission
of Dengue Virus (Part 2)
5. Second mosquito
6
ingests virus with blood
6. Virus replicates
in mosquito midgut
and other organs,
infects salivary
glands
7. Virus replicates
in salivary
glands
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5
Distribution
Recent Dengue in the U.S.A.
(Texas)
• Dengue epidemics occurred in the USA in the
1800s and the first half of the 1900s.
• Recent indigenous transmission
– 1980: 23 cases, first locally acquired since 1945
– 1986: 9 cases
– 1995: 7 cases
– 1997: 3 cases
– 1998: 1 case
– 1999: 18 cases
• Lack of recent transmission likely due to changes in
life-style
Reasons for Dengue
Expansion in the Americas
• Extensive vector infestation, with declining vector
control
• Unreliable water supply systems
• Increasing non-biodegradable containers and poor
solid waste disposal
• Increased air travel
• Increasing population density in urban areas
Trouble Ahead?
• 2.5 billion people at risk world-wide
• In the Americas, 50-fold increase in reported
cases of DHF (1989-1993 compared to 19841988)*
• Widespread abundance of Aedes aegypti in atrisk areas
* Organization of American States, Human Health in the Americas, 1996
Signs and Symptoms
• Sudden onset of fever usually high fever,
severe headache, backache, joint pains,
nausea and vomiting, eye pain, and
rash.
• Dengue hemorrhagic fever (more severe
form)
Treatment and Prevention
• There is no specific medication for treatment of a
dengue infection.
• Persons who think they have dengue should use
analgesics (pain relievers) with acetaminophen and
avoid those containing aspirin. They should also rest
and drink plenty of fluids.
• General precautions to avoid mosquito bites; the use
of insect repellent, protective clothing, and mosquito
netting.
Eastern Equine Encephalitis
(EEE)
• Distribution: Along the Gulf and Atlantic Coasts, from
Canada to Florida.
• Disease: fatal disease that predominantly affects
horses.
• Reservoir:
• Pathogen:
Transmission
• Mainly bird/mosquito
cycle.
• Man and Horses are
dead-end hosts.
Maintenance VECTOR
• Culiseta melanura
• The bird cycle
• Habitat:
Bridge VECTORS
East and Gulf Coast
• Ae. taeniorhynchus,
Ae. sollicitans
Florida
• Culex nigripalpis
Inland
• Ae. vexans,
Coquillattidia perturbans
Signs and Symptoms
• Most people infected with EEE do not become ill
and others may have only a mild influenza-like illness
with fever, headache and sore throat. In rare cases,
infection of the central nervous system can occur,
causing sudden fever, muscle pains and a headache
of increasing severity often followed by seizures and
coma.
• About 50% of these human cases are fatal, with young
children and the elderly most at risk.
• Symptoms in humans usually occur from 4 to 10 days
after the bite of an infected mosquito.
St. Louis Encephalitis (SLE)
• Distribution: West of Mississippi River, Florids, Ohio
River Valley, NJ and NY. Everywhere in the U.S.
except New England area.
• Disease: mammals are accidental hosts. It is a more
serious problem for the elderly. We see epidemics of
up to 2000 cases in 10 year cycles.
• Reservoir:
• Pathogen:
Distribution
Transmission
• Bird/mosquito cycle
• Humans and
mammals are dead
end hosts.
• Transovarial
transmission in lab,
but probably not in
nature.
VECTORS
• Culex pipiens pipiens (Northern House)
• Culex pipiens quinquefasciatus (Southern House)
• Culex nigripalpus
• Culex tarsalis
Signs and Symptoms
• Mild infections occur without apparent symptoms other
than fever with headache. More severe infection is
marked by headache, high fever, neck stiffness,
stupor, disorientation, coma, tremors, occasional
convulsions (especially in infants) and spastic (but
rarely flaccid) paralysis.
• There is no specific treatment. Intensive supportive
therapy depending on the individual.
Western Equine
Encephalomyelitis (WEE)
• Distribution: Wisconsin, Illinois, all states west of the
Mississippi River valley, not found east of it.
• Disease: Human mortality is 1-5%. Woman and
children more severely affected and more likely to
develop neurological disorders. Equine mortality is
high.
• Reservoir:
• Pathogen:
Transmission
• See handout
• Humans and horses are dead end hosts.
• The rabbit cycle is thought to go in two directions
making them a reservoir.
VECTORS
• Culex Tarsalis
• Culiseta melanura
• Culiseta inornata
WEE-leporidae transmission system
• Ochlerotatus dorsalis
• Ochlerotatus melanimon
Signs and Symptoms
• Symptoms range from mild flu-like illness to frank
encephalitis, coma and death.
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Mild to severe neurologic deficits in survivors.
• Inapparent infections in up to 11% of humans in
endemic zones.
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639 confirmed cases in the U.S. since 1964.
• Treatment is supportive.
LaCrosse Encephalitis (LE)
• Distribution: Ohio, Indiana, Illinois, Wisconsin,
Tennessee. Some in Western U.S, but not common.
• Disease: Subclinical or very mild, but like the others
sometimes develops into something more serious.
Mostly children under 16 years of age.
• Reservoir:
• Pathogen:
Transmission
• See handout!
• Virus cycles in woodland habitats between the
treehole mosquito (Aedes triseriatus) and vertebrate
hosts (chipmunks, squirrels)
• Vector uses artificial containers (tires, buckets, etc.) in
addition to treeholes.
VECTORS
• Ochlerotatus triseriatus
• Ochlerotatus hendersoni
• Aedes dorsalis (Utah).
Signs and Symptoms
• Frank encephalitis progressing to seizures, coma;
majority of infections are subclinical or result in mild
illness.
•
Approximately 70 cases reported per year.
• Treatment is supportive.
West Nile Virus (WNV)
• Distribution: throughout the United States
• Disease: 1999 first case in the U.S., NY.
• Reservoir:
• Pathogen:
• Originated in Africa, is a disease of children there.
Spread from Africa to other parts of the world.
Transmission
• Humans and
mammals are
dead end hosts.
• Bird/mosquito
cycle.
• Virus cycles in
the birds blood
for a few days.
VECTORS
• Culex pipiens (East)
• Culex tarsalis (West)
• Aedes vexans (Amplifyer?)
• Several other species that have
shown promise as possible vectors.
Signs and Symptoms
• Mostly flu like, but can develop into encephalitis.
• About one in 150 people will develop severe illness.
Which include high fever, headache, neck stiffness,
stupor, disorientation, coma, tremors, convulsions,
muscle weakness, vision loss, numbness and
paralysis.
• Children and elderly are most at risk.
• Can get via blood transfusions and organ transplants.
• Breastmilk – CDC had one case reported
• There is no specific treatment for WNV infection.
Japanese Encephalitis (JE)
• Distribution: Japan, China, Malaysia, Korea and
other areas of South-east Asia, India, and few in
Australia.
• Disease: Similar to other encephalitic diseases we
discussed.
• Reservoir:
• Vector: Culex tritaeniorhynchus, Cx. gelidus, Cx.
vishnui
• Pathogen:
Venezuelan Equine Encephalitis
(VEE)
• Distribution: Southern U.S. through Central America
to northern parts of South America.
• Disease: infection is fatal in horses, but very mild in
humans.
• Reservoir:
• Vector: Culex spp., Ochlerotatus taeniorhynchus,
Psorophora confinnis.
• Pathogen:
Mosquito Protection
Mosquito Surveillance
Control
Directed at the Immature Stages
• Biological Control
– Predators
– Pathogens and Parasites
– Genetic Control
• Mechanical (Environmental) Control
– Source Reduction
– Environmental Manipulation
• Chemical Control
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Oils
Paris Green
Insecticides
Insect Growth Regulators (IGRs)
Control
Directed at the Adult Stages
• Aerosols, Mists and Fogs
• Ultra-low-volume applications
• Residual house-spraying
Malaria Control
• Larval Control
– Habitat elimination
– Bio, Env, and Chemical
• Adult Control
– Residual house-spraying
– Insecticide-impregnated
bed-nets
– Eradication
Malaria Control
RESEARCH
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$40 million into research!
DNA, other molecular techniques
Release Programs
Drugs, vaccines
Control
Ecology, Biology, Behavior
Education