3. Intro….
• Medical entomology: study of arthropods as;
– Vectors of disease causing microorganisms in humans and
animals
– Causes of diseases/discomfort/pain in humans and
animals
– Such arthropods: vectors/pests
• Public health entomology: arthropods with human health
• Veterinary entomology: arthropods with pets, livestock and
wildlife
• Arachinoloy: study of arachinids (ticks, mites, spiders and
scorpions)
• Acarology: study of ticks and mites
• Vectors: arthropods/insects capable of carrying/transmitting a
parasite/pathogen from an infected host to another
– A vector may be an intermediate host (e.g. culicines
transmitting filariasis) or not (e.g. house flies mechanically
transmitting bacteria) 3
4. Intro….
• Arthropods: characterized by an exoskeleton made up of
chitin and segmented body with jointed appendages,
largest of all animal kingdom
– 10 18 individual insects known to exist 200 million for
each person
– Not all are harmful – majority useful or neutral
– Those affecting man and animals –only are a small
proportion
– Only few species feed on blood
4
5. Entomological terminologies
• Arbovirus: arthropod-borne virus
– A virus that multiplies in a blood sucking arthropod and
is principally transmitted by the bite of arthropods to
vertebrate hosts, e.g. yellow fever virus.
– Viruses, such as myxoma virus in rabbits, transmitted
mechanically by arthropods (e.g. fleas and mosquitoes)
and involving no cyclical development in the vector are
not arboviruses
• Biological vector:
– that transmit disease pathogens after the multiplication
and/or development of the pathogen in the insect gut or
muscle. E.g. malarial mosquito (female anopheles
mosquito) 5
6. Entomological terminologies
• Mechanical vector:
– that transmit pathogenic microorganisms without
undertaking any developmental change. E.g. common
house fly
• New World:- Countries or regions in the Western
hemisphere
• Old World:- Eastern hemisphere; the world of Europe, Asia
and Africa
• Definitive host:
– Host in which parasites reach maturity
– Rarely occurs in arthropod vectors, but the noted
exception is the development of malarial parasites
(sexual reproduction in mosquitoes) 6
7. Entomological terminologies
• Intermediate host:
– Host in which a parasite does not reach sexual
maturity
– Applies to most parasites in arthropod vectors
• E.g. filarial parasites in mosquitoes and simuliids
• Extrinsic incubation period:
– Duration of the part of a parasite’s life cycle that is
completed in a vector, that is the time from a vector
becoming infected to it being infective (i.e. capable of
transmitting the vector)
• Intrinsic incubation period:
– Duration of the life cycle of a parasite in the
vertebrate host; interval between infection and 1st
7
8. Entomological terminologies
• Longevity:
– How long an organism lives, often expressed as the
mean expectancy of life
– Vector longevity- one of the most important factors in
disease transmission dynamics and vector control
• Two types of vectors
– Primary vector- play major responsibility for infecting
man or other domestic animals
– Secondary vector- normally unimportant because of
low density or because of alternative hosts for feeding,
but assume its significance during outbreaks, or
during certain seasons of the year; its density is high
• E.g. Anopheles arabiensis vs An. pharoensis
8
9. How arthropods affect man and animals
• As vectors/intermediate hosts of disease causing
organisms
– E.g. plasmodium spp.- cause of malaria- female
anopheles mosquitoes
• Direct agents of diseases or discomfort
– E.g. scabies- skin infestation (disease) by mites
(Sarcoptes scabiei); scabies/itch mite
– Tungiasis – flea infestation (Tunga penetrans) chilota
– Myiasis- infestation by maggots (dipteran larvae)
• By envenomization
– Stings from bees, wasps, ants, spiders, and
scorpions
• Biting nuisances (annoying pests): biting insects (e.g.
9
10. As vectors of diseases
• Two ways:
– Mechanical transmission
– Biological/cyclical transmission
• Mechanical: indirect & direct
– Indirect: non-biting insects:- passive carriers of
disease agents
• House flies:-GI diseases via contamination(e.g.
Cholera, Entamoeba, Trachoma, etc.)
– Direct: biting insects/arthropods
• Stable flies(stomoxys), horseflies (tabanids):-
transmit certain trypanosomes to animals
*** there are always other routes in mechanical
10
11. As vectors of diseases
• Biological transmission:
– most common means of disease transmission
– Mainly blood feeding insects/arthropods
– pathogen/parasite must complete part of its life cycle
in the insect
• 3 ways
I. Propagative transmission
Multiplication, but no morphological/anatomical
changes of the pathogen, common with
viral/bacterial pathogens
E.g. yersinia pestis (plague)- Fleas (rats)
Yellow fever virus- Aedes mosquitoes 11
12. As vectors of diseases
– Trans-ovarial transmission:- kind of propagative
transmission, common in tick borne diseases (viral
diseases)
II. Cyclopropagative transmission:
- Multiplication and morphological changes to an
infective stage
- Several parasites:
- plasmodium, leishmania, trypanosomia, etc.
III. Cyclodevelopmental transmission:
Only developmental changes & no multiplication
e.g. filarial parasites, O. volvulus, W. bancrofti
*** All the above must involve an insect vector 12
14. Common identification characteristics of
arthropods
• Phylum Arthropoda (insects, crabs,
spiders, scorpions, ticks, mites…)
– the body is composed of
several parts or segments,
some of which may be jointed
– the body is covered with a
tough skin called exoskeleton,
made up of cuticle containing
chitin
– the body normally has paired,
jointed appendages (legs,
wings and antennae)
14
15. Classification of P. Arthropoda
1. Cl. Crustacea :- decapods (crabs, lobsters, shrimps, Cray fish),
copepods (cyclops/water fleas), etc, majority marine
– Serve as intermediate hosts of some parasites
(Paragonimus westermani(parasitic
flatworm)/Paragonimiasis & D.medinensis)
2. Cl. Diplopoda:- millipedes, terrestrial, cylindrical and wormlike
- About 40 fused segments except the first 3 pair of segments
- Stink glands (producing bad smells) on each segment,
secrete defensive secretions
- Contact with the chemicals may result in swelling and
blisters (local reaction)
3. Cl. Chilopoda:- centipedes, terrestrial, dorsoventrally flattened,
have powerful jaw (chilopod with a poison gland) can inflict a
painful bite
- Tropical and large centipede can cause serious problems
15
16. Classification of P. Arthropoda
4. Cl. Pentostamida:- tongue worms
*** The above have minor importance
5. Cl. Arachnida:- scorpions, spiders, ticks and mites
Scorpions:– lowlands and deserts, nocturnal, have a
powerful sting(telson(stinger)) at the posterior tip of
the body, stings are very painful and can even
endanger humans life
Spiders:- have mouthparts with a poison gland, most
harmless, but some are harmful
Ticks and mites:- important groups, as vectors and
ectoparasites
6. Cl. Insecta:- insects, largest group (about 3/4th of all
arthropods) 16
17. Classification…
– Includes the great majority of insects of medical and
veterinary importance
– Of about 29 orders, only 8 orders affect human/animal
health
– Of these, some are of minor importance; others are of
great importance
• Four winged insects
– O.lepidoptera- butterflies and moths- minor medical
importance
– (some caterpillar larvae when in contact bring local
allergic reaction
17
18. Classification…
– O. Hymenoptera:- wasps, bees - sting and bring allergic
reaction
– O. Coleoptera- Beetles :- some members (meloidae)
bring canthariasis (cantharidin) (allergy)
– O. Blattaria:- cockroaches- mechanical vectors of
foodborne diseases (enteric bacteria and other
parasites)- minor importance
• Wingless insects
– O. Hemiptera:- Cimcidae (bed bugs)- biting nuisances
Triatominae (assasin/kissing bugs)-
Chagas disease(American
tryps)
18
19. Classification…
– O. Phthiraptera:- lice transmit louse borne typhus and
relapsing fever
– O.Siphonaptera:- fleas- bubonic plague and murine
typhus
19
20. Classification…
• Two winged insects (True flies)
– O. Diptera:- several groups and families that transmit
a number of diseases (man and animals)
• Culicidae (Mosquitoes)- malaria, filariasis and
arboviruses
• Psychodidae (sand flies)- leishmaniasis and
arboviruses
• Simulidae (Blackflies):- onchocerciasis/river
blindness
• Ceratopogonidae (Biting midges)- filariasis and
arboviruses
• Tabanidae (Horsefies)- transmit filariasis (loaiasis)
• Glossinidae (tsetse flies)- African trypanosomiasis
• Muscidae (Houseflies) and related flies (several
families) mechanical transmitters of (enteric
20
21. Phylum mollusca
• a phylum of soft-bodied animals (Latin mollus, “soft”),
usually with a hard external shell
• the second largest in the animal kingdom, after the
arthropods
• Snails are the medically important ones
21
23. • Class: Insecta (hexapoda): locusts,
cockroaches, flies, fleas, lice etc.,
• Body is divided into 3 regions (head,
thorax and abdomen)
• Possess paired wings(last two
segments)
• 3 pairs of legs(each pair in the 3
thorax segments)
• Body covered with hairs and/or
scales
• Order: Diptera (flies: crane flies,
biting flies, chironomids/non biting
midge…)
• the thorax has one pair of visible
wings
• the hind wings, which are vestigial,
are small movable filaments known
as halters which are mainly used for
balance
• Undergo complete metamorphosis
23
24. Mosquitoes
• Family: Culicidae (mosquitoes)
• Subfamily: Anophelinae
(anophelines), Culicinae(culicines)&
Toxorhynchitinae (Toxorhynchites)
• 41 genera of anophelines and
culicines
• More than 3300 species
• Vary in their developmental stages
• Wide distribution, tropical,
temperate extending into Arctic
Circle
• Absent from Antarctica and a few
islands
• Found at elevation of 5500 meters
and down mines at depth of 1250 m
below sea level
24
25. Cont…
• Anophelinae and culicinae have
medical and veterinary
importance since they feed on
man and cattle
• Toxorhynchites(one genus) do
not depend on blood
• Mouth parts are curved
backwards
25
26. Cont…
• Three genera of Anophelinae: Anopheles, Bironella and
Chagasia
• Spp. belonging to Anopheles transmit malaria, filarial
worms, and few arboviruses
– 490 species and subspecies of Anopheles
– 70 can transmit malaria parasites
– 40 are known vectors
– 12 are major vectors
26
27. Cont…
• Culicinae
– 34 genera and 2700 species
• Medical importance:
– Filarial worms (W. bancrofti, Brugia malayi and B.
timori) and arboviral diseases (yellow fever,
chikungunya, dengue and dengue heamorhagic
fever, West Nile virus, Rift Valley fever etc.,)
– Aedes, Culex, Mansonia, Haemagogus, Sabethes
and Psorophora
27
28. External morphology of adults
• Distinguishing features of mosquitoes from other
dipterans having somewhat similar shape and size
– Possession of a conspicuous forwardly projecting
proboscis
– Presence of numerous appressed scales on the body
(thorax, legs, abdomen & wing veins)
– A fringe of scales along the posterior margin of the
wings
28
30. Cont…
• Mosquitoes sex identification:
– Males: feathery or bushy antennae(plumose appearance),
having long hairs
– females: short hairs (pilose antennae)
• How to differentiate culicines from anophelines???
– 1st determination of sex of adults
• Female- non plumose antennae (not bushy) -pilose
• Male- plumose antennae (bushy antennae)
– 2nd Palp observation(long or short and dilated or pointed at their
tips, depending on the sex of the adults and whether they are
anophelines or culicines)
• Female anopheles- palps as long as the proboscis & lie
closely
• Male anopheles-palps as long as the proboscis and
distinctly swollen at the ends(clubbed)
• Female culicine: palps not as long as the mouth part
• Male culicine: as the long as the proboscis and pointed at
the ends
30
34. Head…
A pair of palpi (5 segmented)
• Anopheles covered with scales of different
colors)
• Short: female culicines
• As long as proboscis: anophelines
34
35. Cont…
• Proboscis (stylets): collective name of mouthparts(piercing)
– contains seven mouth parts:
• a pair of mandibles: found b/n labrum and labium; above
maxilla
• a pair of maxillae(toothed): but it is found below
mandibles
• Hypopharynx: un-toothed
• Labrum: upper most structure(upper roof)
• Labium (lower gutter): largest component; terminates in
a pair of labella
– Cross-sectionally, seen as by almost encircling all
other components of the mouthparts
– Serve as protective sheath
35
37. Cont..
• Maxilla and mandible: cut and tear skin
• Hypopharynx: pumps saliva
• Labrum: ingests blood
• Saliva is produced by salivary glands and contains
anticoagulants, anesthetic substances and
solubilizers for solid sugars
• Promote haematoma formation facilitating blood
vessel location and shorten the time of contact with
the host
• Culicines: Middle lobe of salivary glands is as long as
lateral lobes
• Anophelines: middle lobe is shorter 37
39. Thorax
• Divided into three sections:
prothorax, mesothorax and
metathorx
• Dorsal plates: tergites
• Ventral plates: sternites
• Pleural segments
•Dorsal thorax: scutum and
scutellum
•Rounded scutellum: anophelines
•3 lobed scutellum: culicines
•A pair of wings (fore wings)
Hind wings are modified to
halters for balancing
•3 pairs of legs 39
40. Wings
• Have several veins
covered with brown,
black, white or cream
scales
• Each vein is given a
number and/or name
• Veins 2, 4 and 5 are
forked
• Back edge has fine
scales
40
41. Legs:
• Coxa (base segment of
the leg), femur, tibia and
tarsus
• Tarsus has 5 segments=
tarsomeres
• Colored scales
41
42. •Tip of tarsus with a pair
of toothed or simple
claws
•Culex have a pair of
fleshy pulvilli
42
43. Abdomen
•8 visible segments
•Segment 9 and 10 are
telescoped
• can be covered with scales
and hairs
•Culicinae: brown, blackish or
whitish scales
•Anophelinae: devoid of
scales
•Last segment of abdomen
•Cerci (in females)
• Claspers in males
• Female Culex: tip blunt,
cerci retracted
•Female Anopheles: tip
pointed, cerci extended
43
46. Life cycle
• Four stages: egg, larva, pupa and adult
• Complete metamorphosis
• Metamorphosis: change in form
• Females of the majority of mosquitoes require first blood
meal for the development of eggs in the ovaries = An
autogenous development/normal procedure
• Some species oviposit without taking first blood meal=
autogenous development (from the sugar they feed)
• Initial batch of eggs often develops after 2 blood meals,
while the successive batches usually require only 1
blood meal 46
48. Cont…
• Females also feed on plant
nectar to obtain energy for
flight and dispersal
• Males exclusively survive on
plant sugar
• In most cases, blood feeding
is followed by mating
48
49. Cont…
Mating:
• Males engage in swarming (large
groups in flight)
• Hover a marker(float or flutter in the
air without moving very far from the
same spot)—tops of tall trees or host
• Virgin females can be encountered
by a male and insemination takes
place
• Spermatozoa are deposited in the
spermathecae (females body part)
• Male deposits mating plug in the
female
• Plug contains matron-substance that
stimulates oviposition and inhibits
mating (males inhibit mating to
preserve their genome= genogreedy)
• A female mosquito mates once in her
life time but sometimes it can mate
more than once 49
50. Cont…
Host location identification
Visual
Can detect a host from a few meters: less than
20 meters
Odor
Stimuli emanating from the host (breath or sweat);
CO2, lactic acid (product of muscular activity),
octenol, as well as body odors and warmth
Lactic acid in combination with carbon dioxide
*** Children and pregnant women are more attractive
sweaty socks 50
51. Cont…
• Host preference
– Anthropophagic, anthropophilic e.g Anopheles
gambiae s. s., Ae. aegypti
– Zoophagic, zoophilic e.g An. quadriannulatus
– Anthropozoophagic, anthropozoophilic e.g An.
arabiensis
– Ornithophagic, ornithophilic e.g. some Culex species
51
52. Cont…
Site of feeding
– Endophagic e.g An. gambiae s.s
– Exophagic e.g An. nili, Ae.aegypti
– Partially endophagic and exophagic e.g. An. arabiensis (what can you
say in this case??????)
Resting places
– Endophilic; An. gambiae s.s what type of vector control you
recommend at the adult stage?
– Exophilic; Ae. aegypti
***few mosquitoes are entirely anthropophagic/zoophagic,
endophagic/exophagic, endophilic/exophilic. Otherwise the terms are
relative
### there is also change of resting site, feeding host and site of
mosquitoes
what are characteristics of the most efficient vector ?
Biting cycle
– Crepuscular: after sun set
– Nocturnal: Most mosquito species
– Diurnal: Mansonia and Aedes
– Indiscriminate 52
53. • Anopheline: most are crepuscular or nocturnal in their biting
period
– An.gambiae complex: bite at night
53
54. Cont…
Blood feeding
– Unfed, fresh fed/blood-fed, half gravid and gravid
– Gonotrophic cycle: period from blood meal to
oviposition
– Can take blood meal every two days, the first two
blood meals may not serve for oviposition
– Unfed: stomach empty, could be nulliparous or
parous
54
55. • Blood digestion can take a few minutes and the
abdomen will be distended with blood: abdomen
reddish, fresh fed
55
57. Cont…
After hours blood meal
darkens eggs develop in
ovaries;
Half of the abdomen with
dark blood with
developing ovules: half
gravid
57
58. Cont…
Blood meal completely
digested, abdomen with
developed eggs: gravid
• After blood ingestion
mosquitoes rest at a
preferred site
– Endophilic: An.
funestus
– Exophilic: An.
pharoensis
58
59. Cont…
Oviposition and biology of eggs
– Average life span of a female mosquito is 3-4
weeks
– female mosquitoes- 30-300 eggs (spp. dependent)
per a single oviposition
– Anopheline female oviposites from 50-150 eggs at a
time
– Culicines up to 300 eggs
– Most lay up to 3 batches, rarely up to 7 batches
– Many spp. of mosquitoes, such as anopheles and
culex; lay directly on the water surface
• Anopheles eggs laid singly
59
60. Cont…
• Mansonia eggs:
– laid in a sticky mass glued to the underside of floating
plants
• Anopheles, culex and mansonia eggs:
– unable to withstand desiccation why???
• Aedes, sabethes, heamagogus and psorophora eggs:
– not laid eggs on the water surface but just above the
water line on damp substrates;
• Mud and leaf litter
• Inside walls of tree holes and clay water-storage pots
– Withstand desiccation???
• Aedes & psorophora eggs may enter either : resting stages
– Quiescence, only hatching when suitable conditions occur
or
– Diapause, not hatching until some specific stimuli
60
61. 61
Laid vertically in several
rows held together by
surface tension to form
raft w/c floats on the
water
62. • Anopheles eggs: are boat
shaped and have a pair of air
filled sacs called floats
• Aedes eggs: are black, oval
shaped
• Culex eggs: are brown, long
and cylindrical
62
63. Larva (larvae): legless
– All mosquito larvae require water
in which to develop (unable to
withstand desiccation except in
wet mud)
– A larva hatches after 24 or 48
hours and feed on organic matter
from water
– Larvae are filter feeders: create
waves by mouth brushes
– Anopheline larvae feed on the
surface of water by resting
parallel to the surface and
rotating the head at 180
degrees(during feeding)
– Culicines: bottom feeders
• Hang from the surface by
siphon
63
64. • Mosquito larvae(except mansonia & a few other spp.):
– Must come to the water surface to breathe
– Atm. air is taken in through a pair of spiracles (dorsally on
10th abdominal segment): anophelines
– In culicinae, found in siphon
– Mansonia larvae possess specialized siphon(pointed at tip
& serrated cutting structures: used to insert to the roots or
stems of aquatic plants; obtaining oxygen for its
respiration)
– Anophelinae larvae have no siphon
– Culicine larvae have no abdominal palmate hairs and
tergal plates
64
65. • Larval habitats
– Small pools, fresh water bodies, rice puddles, drains,
ditches, running water with shade, brackish water, salt
water, stream, ponds, lakes, marshes, wells, water
containers, discarded tin cans, discarded tyres, snail
shells and hoof-prints
– Almost any collection of permanent or temporary water
can constitute a mosquito larval habitat
– Some need sunny habitat while others prefer shaded
ones
65
66. 66
Mosquito larvae feed on yeasts, bacteria,
protozoans and numerous other Mos as
well as decaying plant and animal matter
in water
67. • Four larval stages: instars
• The small larva emerging
from the egg is called the
first instar
• After one or two days it
sheds its skin (=ecdysis)
and becomes the second
instar
• Skin= exuviae
• Third and fourth instars
emerge at further intervals
of about two days each
67
68. • The larva remains in the
fourth instar stage for
three or four more days
before changing to a
pupa
• The total time spent in
the larval stage is
generally eight to ten
days depending on the
water temperature and
larval food
• At lower temperatures,
the aquatic stages take
longer to develop 68
69. 69
• External
morphological
feature of an
anopheline larva
• Head, thorax and
abdomen
Anopheles(Cellia) Abdomen
AnteriorTergalPlate
PosteriorTergalPlate
AccessoryTergalPlate
PalmateHair
74. • Siphon
• Culex: often long and
narrow
• Aedes: short and
barrel-shaped
• Mansonia:
specialized for
piercing aquatic
plants , apical part
dark and
sclerotized,
serrated 74
75. • Pupa (pupae), comma shaped:
non feeder but mostly at the
surface to take air
• Is the resting stage where the
transformation to adult takes
place
• Unlike other pupa of insects,
mosquito pupa is active and react
to movement
• Pupal stage takes 2-3 days
• The body of the pupa is divided
into the cephalothorax and
abdomen
• Have a pair of breathing trumpets
• Short and broad: anophelines
• Long and narrow: culicines
• Peg like structures on the 75
Anopheles pupa
Used for floating
76. • Adult emergence
• Male and female
• Scales on wing veins(anopheles)- dark and pale
– Culicine- uniformly black or brown
• Anopheline adults form an angle with the surface
during resting whereas
• Culicines rest parallel to the surface
76
Anopheline
adults
Culicine
adults
77. 77
Developmental stage Anophelines Culicines
Eggs •Oviposited singly
•Boat shaped
•Have floats
•Oviposited singly (Aedes) or
together in a “raft” (Culex and
Mansonia)
•Oval or cylindrical
•Lack floats
Larvae •Rest parallel to the surface of water
•Lack siphon
•Subtend or hang
•Possess siphon
Pupae •Breathing trumpet is short and has wide
opening
•Peg-like structure on abdomen
•Breathing trumpet is long /short
and slender with a narrow
opening
•Lack such structure
Adults •At rest, they form an angle with the surface
•Palpi are as long as proboscis (females)
•Palpi are as long as proboscis and club-
shaped at tip (males)
•Rest parallel to resting surface
•Palpi are short (in females)
•Palpi are longer than proboscis
with tapered tips (males)
80. 80
Anophelines Culicines
Adults Scutellum rounded Scutellum trilobed
Salivary glands
Median lobe is shorter
Salivary glands
Median lobe is as long as the
lateral lobes
Scales on wing veins are arranged in
blocks(dark and pale)/spotted wings
No
Scales on wing veins are not
distinctively arranged(uniform)
appressed scales on the
abdomen(ventrally and dorsally)
A single spermatheca 2 Or 3 spermathecae
81. Culex
Adults
•Thorax, legs and wing veins could be
covered mostly with brown scales
•Abdomen covered with brown or
blackish scales, some whitish scales
on segments
•Tip of abdomen is blunt
•Lack ornamentation
•Tarsi have a pair of fleshy pulvilli
81
82. Aedes
Adults
•Thorax with black, white or
silvery scales
In some yellow scales
•Legs speckled with black
and white scales
•Scales on wing are black
(uniform)
•Abdomen covered with black
and white scales forming a
pattern
82
83. Mansonia
Adults
•mixture of dark and pale
scales cover the body
•Dusty appearance
•Broad scales on wing veins
have a speckled/contrasting
colors/ appearance
83
