1. 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

2. HISTORY 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

3. Alexander The Great General, King, Ruler Babylon 323 B.C. Malaria?
WNV?
Typhoid?

4. 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…

5. 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, mya)
Anophelinae (subfamily) - Anopheles (genus)
Culicinae (subfamily) - Aedes, Culex, Haemagogus, Mansonia, Ochlerotatus and all other genera

6. Mosquito Characteristics
Conspicuous proboscis - forward projecting
Scales on thorax, abdomen, legs & wing veins
A fringe of scales along the posterior margin of the wings

7. Mosquito Characteristics (note conspicuous forward projecting proboscis)
Non-biting Gnat (note proboscis curved under head)
Mosquito
Gnat

9. 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

11. (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

12. Mosquito eggs:
Culex egg raft
Anopheles egg with ‘floats’
Aedes egg
Patterns on the external egg surface are species specific

13. Egg stage comparison

14. CULEX Egg Raft

15. (2) Embryonation – 2 options
Eggs hatch immediately (not all) OR
Diapause required
Triggered by decreasing day length.
**Egg stage over wintering stage**
Aedes/Ochlerotatus

16. (3) Larval Stage – Growth Stage
Larval instars (4)
Aquatic, Filter feeders
Respiration
Anopheles

17. (4) Pupa – Lighter than water
Non-feeding
Respiration
Pupal Stage Comparison
Anopheline
Culicine

18. Mosquito Pupa and Larvae

19. Anopheles Pupa and Larvae

20. Mosquito Emerging from Pupal Exuvia

21. Adult Stage Comparison
Emergence
Mating
Feeding
Adult Stage Comparison
Anopheline
Culicine

22. Comparison of male and female Anophelines vs. Culicines
females
Comparison of male and female Anophelines vs. Culicines
Culicine
Anopheline
males

23. Behavior Activity Host Specificity Zoophilous Anthropophilous
Ornithophilous

24. HABITAT

28. Medical Importance Biting Nuisance (annoyance) Arboviruses Filariasis
Numerous (Yellow Fever, Dengue Fever, WNV, JE, SLE, EEE, WEE, VEE).
Filariasis
Bancroftian and Brugian filariasis.
Malaria
4 plasmodium species

29. 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.

30. HUMAN MALARIA Parasite – Plasmodium spp. Vector – Anopheles spp. Host
P. falciparum, P. vivax, P. malaria, P. ovale
Vector – Anopheles spp.
Host
Reservoir
Distribution

31. Anopheles gambiae
WHO/TDR/HOLT Studios, 1992

32. Global Distribution

33. Distribution
Distribution Model

34. Distribution
Endemic / Epidemic Risk Areas

35. Distribution
Duration of Malaria Transmission Season.

36. Start / End of Transmission Season
Distribution
Start / End of Transmission Season

37. Distribution
Population Distribution

38. Filariasis History Patrick Manson (1877) Worked in Taiwan
Autopsies in China
Threadlike worms
“Nothing walks with aimless feet.:”

39. 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

40. Urban and Rural Disease
Urban Disease (Bancroftian filariasis)
Parasite –
An anthroponosis
Bancroftia
Rural Disease (Brugian filariasis)
An anthroponosis or zoonosis
Brugian

41. Transmission (1) Microfilariae in blood. (2)
(3) Microfil. Penetrate midgut  thoracic muscles.
(4)
(5) Enter new host.

42. Periodicity
(1) Periodic Infection
(2) Subperiodic Infection

43. VECTORS (1) Bancroftian Filariasis (2) Brugian Filariasis
Cx. pipiens quinquefasciatis
Cx. pipiens pipiens
Anopheles spp.
Aedes spp.
(2) Brugian Filariasis
Mansonia (genus)

44. DISTRIBUTION Tropics and subtropics
Wuchereria bancrofti is encountered in _________________.
Brugia malayi is limited to _____.
Dog Heartworm (Dirofilaria immitis, D. repens)

45. 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.

46. Yellow Fever History

47. Yellow Fever 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)

48. YELLOW FEVER Is a _______ Prevented the building of the Panama Canal.
Pathogen:
Vector: Aedes aegypti, Aedes spp., Haemagogus
Host:

49. Reservoir Human-mosquito in urban cycle,
Monkey-mosquito in forest cycle;
Deforestation may force infected monkeys into areas where human-mosquito transmission can occur.

50. African Yellow Fever Transmission Cycle
Vectors:
Ae. Africanus (sylvatic)
Ae. Bromeliae (rural)
Ae. Aegypti (urban)
Transovarial Transmission

51. Central and South America Yellow Fever Transmission Cycle
Vectors:
Haemagogus spp. (jungle)
Haemagogus spp. (rural)
Ae. Aegypti (urban)
Transovarial Transmission

52. Distribution

53. 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.

54. 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.

55. Dengue Fever History

56. Dengue (Breakbone) Fever
Dengue has four serological types
(DEN-1,DEN-2,DEN-3 and DEN-4).
Pathogen:
Host:
Reservoir:

57. VECTORS Aedes aegypti (Yellow fever Mosquito)
Aedes albopictus (Asian Tiger Mosquito)
Aedes scutellaris
Aedes polynesiensis

59. Transmission Cycle Blood meal from viremic human. Midgut replication
Salivary glands, pass on during feeding.
Transovarial transmission
SE Asia – monkey cycle

60. Replication and Transmission of Dengue Virus (Part 1)
1. Virus transmitted to human
in mosquito saliva 1
2. Virus replicates
in target organs 2 4
3. Virus infects white
blood cells and
lymphatic tissues 3
4. Virus released and circulates in blood 6

61. Replication and Transmission of Dengue Virus (Part 2)6
5. Second mosquito
ingests virus with blood
6. Virus replicates
in mosquito midgut
and other organs,
infects salivary
glands 7 5
7. Virus replicates
in salivary glands 7

62. Distribution

63. 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

64. 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

65. Trouble Ahead? 2.5 billion people at risk world-wide
In the Americas, 50-fold increase in reported cases of DHF ( compared to )*
Widespread abundance of Aedes aegypti in at-risk areas
* Organization of American States, Human Health in the Americas, 1996

66. 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)

67. 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.

68. Eastern Equine Encephalitis (EEE)
Distribution: Along the Gulf and Atlantic Coasts, from Canada to Florida.
Disease: fatal disease that predominantly affects horses.
Reservoir:
Pathogen:

69. Transmission Mainly bird/mosquito cycle.
Man and Horses are dead-end hosts.

70. Maintenance VECTOR
Culiseta melanura
The bird cycle
Habitat:

71. Bridge VECTORS East and Gulf Coast Ae. taeniorhynchus, Ae. sollicitans
Florida
Culex nigripalpis
Inland
Ae. vexans,
Coquillattidia perturbans

72. 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.

73. 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:

74. Distribution

75. Transmission Bird/mosquito cycle
Humans and mammals are dead end hosts.
Transovarial transmission in lab, but probably not in nature.

76. VECTORS Culex pipiens pipiens (Northern House)
Culex pipiens quinquefasciatus (Southern House)
Culex nigripalpus
Culex tarsalis

77. 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.

78. 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:

79. Transmission See handout Humans and horses are dead end hosts.
The rabbit cycle is thought to go in two directions making them a reservoir.

80. VECTORS Culex Tarsalis Culiseta melanura Culiseta inornata
WEE-leporidae transmission system
Ochlerotatus dorsalis
Ochlerotatus melanimon

81. Signs and Symptoms Mild to severe neurologic deficits in survivors.
Symptoms range from mild flu-like illness to frank encephalitis, coma and death.
Mild to severe neurologic deficits in survivors.
Inapparent infections in up to 11% of humans in endemic zones.
639 confirmed cases in the U.S. since 1964.
Treatment is supportive.

82. 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:

83. 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.

84. VECTORS Ochlerotatus triseriatus Ochlerotatus hendersoni
Aedes dorsalis (Utah).

85. Signs and Symptoms Approximately 70 cases reported per year.
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.

86. 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.

87. Transmission Humans and mammals are dead end hosts.
Bird/mosquito cycle.
Virus cycles in the birds blood for a few days.

88. VECTORS Culex pipiens (East) Culex tarsalis (West)
Aedes vexans (Amplifyer?)
Several other species that have
shown promise as possible vectors.

90. 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.

91. 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:

92. 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:

93. Mosquito Protection

94. Mosquito Surveillance

95. Control Directed at the Immature Stages
Biological Control
Predators
Pathogens and Parasites
Genetic Control
Mechanical (Environmental) Control
Source Reduction
Environmental Manipulation
Chemical Control
Oils
Paris Green
Insecticides
Insect Growth Regulators (IGRs)

96. Control Directed at the Adult Stages
Aerosols, Mists and Fogs
Ultra-low-volume applications
Residual house-spraying

97. Malaria Control Larval Control Adult Control Habitat elimination
Bio, Env, and Chemical
Adult Control
Residual house-spraying
Insecticide-impregnated
bed-nets
Eradication

98. Malaria Control

99. RESEARCH $40 million into research! DNA, other molecular techniques
Release Programs
Drugs, vaccines
Control
Ecology, Biology, Behavior
Education