1. Arthropods
of
Medical
Importance

2. Objectives
1. To identify the common characteristics of
medical arthropods and its classification.
2. To discuss the mechanisms of transmission
and causation of diseases.
3. To describe the diseases caused or transmitted
by medical arthropods.
4. To implement appropriate
prevention, control, and treatment.

3. Introduction: Arthropods
1. Segmented body.
2. Paired segmented appendages.
3. Bilateral symmetry.
4. Chitinous exoskeleton.
5. Tubular alimentary canal with mouth and anus.
6. Open circulatory system, a tubular dorsal blood
vessel.
7. Body cavity or coelom.
8. Nervous system of anterior ganglia and paired nerve
cords.
9. Striated muscles in skeletal system.
10. Respiration by gills, tracheae, or spiracle.

4. Medical Arthropod
Arthropods related with human health.
Medical Arthropodology
Morphology, taxonomy, life cycle, ecology,
transmission of the diseases, control measures.
Examples: Flea - Plague,
Soft tick - Q fever,
Mosquito - Malaria

5. Morphology
 Bilateral symmetry
 segmented body and appendages
 Chitinous exoskeleton
 Circulatory system is open.
 Ecdysis and metamorphosis

6. Development
Embryonic development
Complete in eggs
Postembryonic development
Egg hatch larva molt next stage larva
Pupation pupa emergence adult stage.

7. Arthropods as Direct Causes of Injury
Injury Agents
Envenomization Venomous arthropods: bees,
wasps, kissing bugs, ants,
caterpillar hairs, centipede bite,
spider and scorpion
Ectoparasitism Non-venoomous arthropods:
mosquito, flea, lice, mite, and
ticks
Inhalant Dead/decomposing bodies of
allergens insects; cockroach feces, hairs
and spines; house dust mites
(HDM)

8. Arthropods as Direct Causes of Injury
Injury Agents
Ingestant Mites, cockcroach feces, larval stages
allergens of small beetles
Contact Urticating caterpillar hair, blister
allergens beetles, millipede
Food and Water Moth, beetle, mites, chironomids,
pests maggots
House pests Mosquitoes, flies, cockcroaches
Myiasis Fly maggots, feeding on human
wounds

9. Harm for human health
Direct harms
1. Harassment and sucking blood: mosquito, fly
2. Allergy and toxicosis: dust mite-asthma
3. Invading tissue: itch mite -scabies
maggot-myiasis

10. Indirect harms
(transmit pathogen，cause arbo-diseases)
1. Mechanical transmission
Arthropods which
Arthropods carry pathogens from one person to
transmit pathogens
Medical
the next withoutvector
development or multiplication of
arthropod
pathogens. Diseases transmitted
by medical arthropods
2. Biological transmission
pathogen Arbo-disease
sick
Pathogens develop or multiply within
arthropods, only transmitted to vertebrate hosts.

11. Types of biological transmission
 Development: pathogens develop to infective
stage in arthropod, no proliferation.
larva of filaria mosquito infective stage.
 Proliferation: pathogens proliferate in
arthropod, forms no change.
Yersinia pestis flea bacteria embolism

12. Types of biological transmission
 Development and proliferation: pathogens
develop and proliferate in arthropod.
Plasmodium: gametocyte mosquito great
number of sporozoite
 Transmit by eggs: pathogens invade ovary,
transferred to filial generation
Dengue virus.

13. Arthropod as a vector
1. Biological evidences：
 closely related with humans: biting or sucking
humans, lapping or contaminating foods.
 common species at local area, dense
population.
 life span is long enough to complete the
development or proliferation.
2. Epidemiological evidences：
 geographic and seasonal distribution

14. 3. Laboratory evidences:
arthropod can be infected with the pathogen by
experiment methods, pathogen can develop
into infective stage.
4. Natural infection evidences:
 in epidemic season, the pathogen can be
examined from arthropod at the field.
the most important evidence to judge the
vector.

15. Control
 Integrated control is the best measure.
 Environmental management：
Objective: reduce or control the
resting/growing field or breeding
sites; reduce the arthropod population
by environmental modification and
sanitation.

16. Classification
Five classes of Arthropod are medical important.
1. Insecta
(fly, mosquito, bugs, etc
crab&shrimp
)
2. Arachnida (order
Acari : ticks. Mites)
3. Chilopoda (centipede)
millipede
4. Diplopoda (millipede) centipede
5. Crustacea tick

17.  Physical measures：control or drive away
Mosquito net
Insect Killer
Blue light fly killer Mosquito swatter

18.  Chemical measures：DTT, insecticides
Resistance, pollution
C4H10O2S2 chem. Formula of DTT

19.  Biological measures：
Bacterium: Bacillus thuringiensis
infect the larva of mosquito and kill them.
Parasitoid parasitize
Natural
enemy: Dragonfly prey on

20.  Genetic measures：mutation or gene transfer
Objective: produce infertile males which mate
with wild female, the female will not
reproduce filial generation.

21. Arachnida
Scorpions Araneae Acari

22. Acari
the only group that sucks blood and serves
as vector.
 tick: hard ticks, soft ticks
 mite: Trombiculid mite, Itch mite,
Demodicidae mite, Dust mite

23. Morphological features
1. Body regions consist of cephalothorax and
abdomen or further fused to idiosoma
2. No antennae, simple eyes.
3. No wings, 3(N) /4(A) pairs of legs.

25. Tick: hard ticks, soft ticks
An inflexible, dorsal scutum covers the idiosoma of the male and
Mouthparts partterminal and visible from above
the anterior are of the idiosoma of the female
The body is usually sooth.
hard tick (Ixodes

26. The body is often wrinkled.
Soft tick are leathery and lack the scutum ;
Mouthparts are ventral and not visible from above
Female and male have the similar appearance.
Soft tick (Ornithodorus persicus)

27. Life cycle
Soft ticks have a number of nymphal instars(3 or
Hard ticks only lay eggs once.
more), The female lay eggs a few times.

29. Ecology
Hard ticks:
suck in day
feed on the host for a few days
resting sites: forest, woods, grassland, pasturage
Soft ticks:
suck at night
feed on the host from minutes to one hour
resting sites: locate at the host’s nests and hovel.

30. Harm to humans
Direct injures
1. Irritation: sting, secondary infection, allergy
2. Tick paralysis : paralysis of the motor nerves ---
cannot walk or stand, has difficulty in
speaking, swallowing and breathing.

31. Harm to humans
Transmission of diseases
1. Tick-borne encephalitis/forest encephalitis
Xinjiang hemorrhagic fever
2. Tick-borne relapsing fever Lyme disease
3. Q fever and tick-borne typhus

32. Control
1. Environmental management: clean the stalls of
livestock, house and deal with mouse holes, etc.
2. Chemical measure: acaricides
3. Personal protection: protect body away from
ticks.

33. Trombiculid mite

34. Morphology
 The keys to identify are based on the
larvae(chigger).
 Larvae: reddish or orange, 3 pairs of
legs.
 Adult: bright red, hairy or granular, 4
pairs of legs.

35. Egg
Life cycle
Deutovum
Larva
Nymphochrysalis
Nymph
Imagochrysalis
Adult

36. Ecology
 All chiggers are parasitic.
 Low host specificity.

37. Harm to humans
Leptotrombidium deliensis Leptotrombidium scutellare
main vector in the south areas main vector in North China.

38. Chigger dermatitis
Result from a reaction of the host to the
salivary secretion of mites.
Scab：
The inflammatory
response gives rise to the
raised, reddened wheal
with a depressed center
characteristic of chigger
bite.

39. Scrub typhus
 Caused by: Orientia tsutsugamushi
Rickettsia tsutsugamushi
 Symptoms: prostration, headache, fever, body
rash and central nervous system
abnormalities.
 Epidemic hemorrhagic fever
is suspected of being transmitted by chiggers.

40. Diagnosis
 A history of having recently been in a grassy or
forest edge area.
 Fever, itching papules, scab.
Prevention and control
 Environmental management: eradication of
wild weed and control of rats and mice.
Chemical measure: DTT
Personal protection: tick repellents, clothing
tied tightly at the ankles and wrists.

41. Itch mite
 Sarcoptes scabiei parasitizes on humans,
which can cause scabies.

42. Morphology
 Disc-shape, distinctive sculptured lines.
 Stubby legs.
 The anterior two pairs of legs have ambulacra
 Female－ the 4th pair of legs terminate in long setae .
Male－ the 4th pair of legs have ambulacra .

43. Life cycle
Egg larva protonymph tritonymph adult
The female burrows into the skin and lays eggs in
Larva - 3 pairs of legs
a sinuous tunnel ). of legs.
Nymphs - 4 pairs

44. Pathogenesis
 Selects places where the skin is thin and wrinkled.
between fingers, wrists, elbows, feet, etc.
 Children may be found burrowing on whole body.

45. The mite can cause more severe skin
reactions, such as itching and allergic reactions.

46.  The hypersensitivity
may result from the
mite excretions.
 Secondary bacterial
infections may also
occur, probably as a
result of scratching.

48. Diagnosis
1. Symptoms:sinuous tracks in the
skin, inflammation, itching;
2. Find the mites in the skin.
Prevention and control
1. All clothing and bedding should be
laundered.
2. 10% Brimstone ointment

49. Demodicidae mite
 Human have two species
D. folliculorum - in hair follicles
D. brevis - in sebaceous glands
(Demodex folliculorum) (Demodex brevis)

50. Morphology
 Elongate, 4 pairs of stubby legs.
 Mouthparts - not apparent;
hysterosoma - quite long

51. Life cycle: 3 to 5 weeks
Egg
larva
protonymph
nymph
adult: female lives more than 4 months

52. Diagnosis
Squeeze skin and examine the mites in
exudates under a microscope.
Prevention and control
10% Brimstone ointment

53. Dust Mite
Morphology:
 white to a light tan
 tiny, oval shaped
 covered with fine
striations

54. Dust mites are members of the Phylum
Arthropoda, Group Arachnida and Order Acari.

55. Dermatophagoides pteronyssinus
Dermatophagoides farinae and
Euroglyphus maynei are responsible for allergy.
D. pteronyssinus
(Der p)
D. Farinae (Der f)

56. Life cycle

57. Diagnosis
Serological tests: detect the serum antibody,
ELISA, skin test, etc.
Prevention and control
Immunotherapy.

58. Insecta
mosquito
fly
sandfly
flea
louse
cockroach

59. Ecto-morphology
Mouthparts :
chewing ,
sucking ,
lapping mouthparts

60. Development and metamorphosis
 Developmental stages
egg — larva—（pupa）— adult
 Metamorphosis
From hatch of larva to adult, there are
wide differences in the morphology,
physiological function and living habits etc.

61. Complete metamorphosis: mosquito, fly, flea
Egg larvae Pupa Adult
There is pupa stage in their life cycle.
The larvae and adult have difference in morphology
and life habit.

62. Incomplete metamorphosis: louse, bug, cockroach
Larvae
Egg Adult
(nymph)
 There is no pupa stage in life cycle.
 The larvae is similar in morphology and life
habit with the adult, but the sexual organ still
undeveloped.

63. MOSQUITO
 Mosquito belongs to Class Insecta,
Order Diptera, Family Culicidae.
 There are more than 3300 species of mosquitoes
belong to 38 genera.

64. Morphology
Head  Piercing and sucking mouthparts.
 Slender proboscis
Questions:
1. How to distinguish the female mosquitoes from
the male?
2. What are the main effect of antennae in finding
host?
3. Why don’t the male mosquitoes suck blood?

65. Antennae
Male: circular hairs Female：circular hairs
are long and dense are short and sparse

66. Labrum - 1
Mandibles - 2
Hypopharynx - 1
Proboscis
Maxilla - 2
Labium - 1
The male lack of
mandibles and maxillas

67. Life cycle
Complete metamorphosis
Water
Larvae Pup
Eg Adult
(4 instars) a
g
Important vectors: limited in Anopheles, Culex and Aedes

68. Life cycle
Egg
Culex: :Olive-shaped, laid single onand float on
Anopheles: Boat-shaped, laid They are laid stuckof
Aedes Cylindrical, no float. single the bottom
the water in “egg’s rafts.
together surface.
water
Anopheles Culex Aedes

69. Larvae
Siphon (respiratory tube)
Aedes
Anopheles
Culex

70. Pupa
 Comma-shaped.
 A pair of respiratory trumpets dorsally.
The nonfeeding pupal stage lasts from 4 to 5
days.

71. Adult
Anopheles Culex Aedes

72. Ecology
Breeding habit
 Five types of breeding site:
Paddy fields
Slowly flow water
Jungle areas
Dirty water
Container water

73. Paddyfield type
 Anopheles sinensis
 Anopheles anthrophagus
The most important vectors of
malaria and Brugia malayi
 Culex tritaeniorhynchus
The most important vectors of
epidemic B encephalitis.

74. Slow flow type
 Stream and irrigation, clean
and flow slowly water.
 Anopheles minimus
The most important vectors of
malaria in south mountain
areas.

75. Jungle type
 Mountain stream, stone cave
and spring, pond .
 Anopheles dirus
The important vector of
malaria in Hainan mountain
area.

76. Dirty water type
 Dirty water
pit, sewer, fecal pit. The
water is dirty and contains a
large amount of humus.
 Culex pipiens pallens
C. p. quinquefasciatus
The main vectors of W. bancrofiti

77. Container type
 Water vats, jars, bamboo
container, tree hole.
 Aedes albopictus
 Aedes aegypti
The most important
vectors of Dengue virus
and Chikungunya virus

78. Bloodsucking habit
 Both male and female mosquitoes take nectar
as source of energy.
 Only females take blood after mating for
production of eggs.

79. Resting habit
After having a blood meal, the female
mosquito find a place for resting.
 Endophilic type: rest inside house for blood
digestion and maturation of the ovaries.
 Half Endophilic type : rest inside house for a
while, then fly to outdoor.
 Exophilic type : feed and rest outside.

80.  Gontrophic cycle: The period from feeding
blood to laying eggs.
 Physiological age: the times of spending
gontrophic cycle.

81. Activity
 Anopheles ：act in the evenings, at night or in
the early morning.
 Culex：feed at night.
 Aedes：feed during the day or early evening.

82. Overwinter (Hibernation)
 No activity and no eating until next spring.
 The most common stage of hibernation is adult.
Aedes ：eggs.
Anopheles minimus ：larvae.
 In sub-tropic and tropic areas, the average month
temperature is over 10℃. So no hibernation.

83. Mosquito and diseases
Direct harm
Biting by mosquitoes
- irritation or allergic
reaction.

84. As vectors, mosquitoes can transmit lots of arbo-diseases.
Arbo-disease Mosquito Epidemic area
1.malaria Anopheles sinensis Plain areas
A. anthropophagus Mountain or hilly areas
in South China
A. minimus Mountain or hilly areas
in South China
A. dirus Jungle areas of Hainan
2. Japanese B Culex tritaeniorhynchus Paddy field
encephalitis
3. Falariasis Culex pipiens pallens As a vector of Filariasis
C.p. quinquefasciantus bancrofti in North areas
of Yangtse river
Anopheles sinensis As a vector of filariasis
A. anthropophagus malayi
4. Dengue fever Aedes aegypti Tropical areas
A.albopicutus In China: Hainan,
Guangdong etc

85. Fly
 Order Diptera.
 The medical important species:
Muscidae, Calliphoridae,
Sarcophagidae, Oestrodae

86. Morphology
mouthparts
Piercing and sucking
mouthpart.
Tsetse fly
Labellum
Lapping mouthparts of housefly

87. Thorax
Each leg terminates in a pair of claws and a pair of
pulvilli
claw
pulvilli

88. Life cycle Complete metamorphosis
Larvae
(4 instars)

89. Morphology and habits which
related to disease transmission
Short legs and big abdomen, the whole body bear hairs;
Lapping mouthparts.
Interdigital pod is supplied with glandular hairs, it also
can secrete mucus
Flies have dirt habits of feeding indiscriminately on both
excreta and foods.
Flies excrete and regurgitate their partially digested meals
over food.

90. Fly and Diseases
Mechanical transmission:
Cholera, Typhoid fever, Bacillary dysentery,
Amebic dysentery, Helminthiasis
Biological transmission:
African trypanosomiasis
Bloodsucking flies：tsetse flies
Myiasis :
Caused by the parasitism of
fly larva.

91. Sandfly
 Order Diptera , Psychodidae
 Medical important:
Phlebotomus chinensis
Ph. c. longiductus
Vector of Leishmaniasis.

92. Morphology
 Tiny, dark, hairy body
 Head: large black eyes, short sucking
mouthparts,
long filiform antennae
 Thorax: humpback erect V shaped
position of the wings at rest.

93. Life cycle Complete metamorphosis, 6-9w
The eggs turn dark
after being laid and
have sculpted surface.
Egg
Larva(4
instars)
Pupae are naked.
Adult Pupa

94. Ecology
 Distribute in North areas of Yangtse River.
 Both sexes feed on plant juice and sugary
secretions. Only the females suck blood.
 One generation a year. The population density
peak occurs in summer.
 The stage of hibernation: larva.

95. Sandflies and disease Vector of Leishmaniasis
Leishmaniasis The adult sandfly is the
only stage in transmission
sandfly fever
Bartonellosis
Sucking blood

96. Flea
 Ecto-parasite.
 Morphology：
Brown-yellow color,
Body is covered with bristle

97. Egg
Adult
Flea
Life cycle
Complete metamorphosis
Pupa
Larva

98. Harm to humans
1. Irritation.
2. Parasitism (tungiasis)
3. Transmission of diseases
a.) Plague: pathogen-Yersinia pestis
b.) Hymenolepis diminuta
c.) Dipylidium caninum

99. A flea (Xenopsy cheopis) taking a blood meal on a
human subject. Note that the flea lifts itself almost
vertically upward during the act of feeding.

100. Tungiasis

101. Louse
 Permanent ectoparasite.
 The parasitic lice of humans :
Pediculus humanus : P. humanus capitis
(2 subspecies) P. h. humanus
Pthirus pubis

102. Morphology
Pediculus humanus
 Color: grayish,
 Wingless, 3 pairs of legs.
 Abdomen: male“V”，
female“W”.

103. Pthirus pubis
 Smaller than Pediculus,
2 mm in length.
 Body is broad with very
large claws on the middle
and hind legs.

104. Life cycle Incomplete metamorphosis
Egg Nymph adult
Oval, white and Resemble a
firmly attached small adult; Louse
to the hairs or 3 instars
to the clothes

105. Harms to humans
Pediculosis
Symptoms: cutaneous irritation, loss of sleep
and psychological depression.

106. Transmission of diseases
Epidemic typhus
Louse-borne
relapsing fever
Trench fever

107. Cockroach
Periplaneta americana Blattella germanica

108. life cycle
Incomplete
metamorphosis
Resting and activity moist and warm places
sites

109. Medical importance
 Mechanical vectors carry various pathogens
 Intermediate host of hookworm larvae
 Cockroach allergens - children asthma