Entomology part 1 Introduction, Classification of Vectors of Medical Importance & Mosquitoes

1. Dr. Sookun Rajeev K
M.D
Dept. Of Community Medicine

2. Introduction
Medical Entomology is the science that deals with insects,
arachnids and other arthropods which directly or indirectly
affects the human beings
Also it is the study of the biology and control of offending
arthropods and contributes to both public and individual health
and well-being.
The most abundant form of animal life on earth
Out of some 1¼ 000000 known animal species, about 4⁄5
th
belongs to arthropods.
The insects comprises about 70% of known species of all kinds
of animals

3. Over 800 000 species of insects described so far.
Three quarters of a million species of insect have already been
described and estimated number of about 1 million to 30 million
are still pipelined.
Entomology (from Greek , entomos, "that which is cut in pieces
or engraved/ segmented", hence "insect“
The term “Medical Entomology” is generally a misnomer cause
not only insects but other members of phylum arthropoda are
also included in the study.

4. Annoyance
Blood loss
Injury to sense organs
Dermatosis
Myiasis
Allergy
Anaphylactic shock
Envenomization
Entomophobia
Arthropods in relation to human health

5. Why are these arthropods so successful ???
Small size -there are many more niches for small organisms than for large
organisms
Short life cycle - this allows many generations within a given time for
selection and evolution to take place.
Large reproductive ability - large numbers of offspring support a large
variation for selection and evolution to act upon.
Variation in the life style of different stages in an insect's life (e.g.
caterpillar versus butterfly) reduces competition for resources within the
species.

6. Wings-the ability to fly has allowed them to colonise
freely.
Sensory sophistication - the sensory capabilities
surpasses most other organisms.
Evolutionary interactions with other organisms – co-
evolution leads to greater specialisation and speciation.
Adaptation of appendages - mouthparts, wings and legs
have often become highly specialised.

7. Modes of Disease Transmission by arthropods
1.Direct Contact-
With the direct contact of hosts, the arthropod vectors gets
transferred from one host to the other.
e.g. pediculosis and scabies.
2. Mechanical transmission :
The agent is mechanically transmitted by the arthropods on
the outside or inside their bodies
e.g. diseases transmitted by houseflies - diarrhoea, dysentery,
cholera, hepatitis A & E etc.

8. 3. Biological Transmission :
(a) Cyclo-developmental :
The agent undergoes cyclical changes but doesn’t multiplies in the
body of arthopods, e.g. W. bancrofti (Filariasis) transmitted in Culex
female.
(b)Cyclo-propagative :
The agent undergoes cyclical changes and also multiplies in the body
of arthropods. Example is Plasmodium sp in Anopheles female.
(c)Propagative :
The agent undergoes no cyclical changes but simply grows and
multiplies in the body of the vector, e.g. Plague bacilli in rat flea

9. Arthropods of medical importance
Class: Insecta Class: Arachnida Class: Crustacea
Mosquitoes
Anophelines
Culicines
Ticks
Hard tick
Soft tick
Cyclops
Flies
Housefly
Sandfly
Tsese fly
Blackfly
Mites (Chiggers)
Leptotrombidium mite
Tromboculid mite
Itch mite
Human lice
Head & body lice
Crab lice
Fleas
Rat flea
Sand flea
Reduiid bug

10. Characteristics of Arthropods
The name arthropod actually comes from the Greek “arthro,” meaning
joint, and “pod” meaning foot.
Invertebrates, Multicellular and body being bilaterally symmetrical
Body covered with hard chitinous exoskeleton
True segmentation of the body, each segment bearing a pair of joint
appendages.
Have a wide range of chemical and mechanical sensors, mostly based
on modifications of the many seatae (Bristles) that project through their
cuticles

11.  Muscles are straited
 No ciliated epithelium.
 Growth by periodical shedding of skin.
 Jaws present.
 Have compound eye, may be absent in some members
 Sexes are separate.
 The nervous system is dorsal (belly), the circulatory system is open and
ventral (back) and alimentary canal in between.
 Body cavity called “Haemocele” have free communication with circulatory
system.

12. Characteristics of Insects
Body divided into Head, Thorax and Abdomen.
Head bears a single pair of Antenna
Have a pair of mandibles and two pairs of maxillae
Generally visual organs are compound eyes, maybe absent in some
viz. fleas, pupiparan diptera
Thorax possess 3 pairs of legs and usually one or two pairs of wing.
Abdominal appendages are modified to terminal genital organs near
cadual end of the body

13. Nervous and circulatory system of arthropods

14. Compound eye of arthopods Molding in arthropods

15. Insects of Medical Importance
Directly cause damage to human tissue
Act as Vectors for disease-causing organisms
----------------------------------------------------------
Provide useful medical services/drugs
Are useful model systems in genetic studies

16. Features of arthropods of medical importance
Insecta Arachnida Crustacea
Body division Head
Thorax
abdomen
Cephalothorax
Abdomen
(No division in some
cases)
Cephalothorax
Abdomen
Legs 3 pairs 4 pairs 5 pairs
Antennae 3 pairs None None
Wings One or two pairs
Some are wingless
None
Where found On land On land In water

17. Class: Insecta

18. SAND FLY

19. Identifications
• Like a mosquito, except its body is hairy and the wings are feathery.
• Tiny insects (1-3 mm)
• Smaller than mosquitoes
• Hairs on body and wings
• Wings rest over body like “angel’s” wings
• Minute, hairy ,with wing kept erect while resting.
• Large compound eyes
• Hairy legs
• Long slender legs
• Wings are vertical and pointed
• Whole body is covered with hairs
• All 10 segments are abdomen are visible

20. Identifications
Male
• Posterior end of abdomen
carries prominent claspers as
stylus consisting the genitalia
Female
• Claspers absent but cercis are
present which are small and
round shape. Inside abdomen
are a pair of spermatheca

21. Only females suck blood.
Live in warm climates.
Breed in crack of soil and wall, rubbish heaps.
 Move in hops rather than fly.
 Nocturnal ,during day time rest in cool damp places.
 Vector of leishmaniasis, sand fly fever.

22. Sand Fly

23. Genitalia
Male Female

24. Diseases Transmitted
•The sandflies are responsible for the transmission of:
1. kala- azar (P. argentipes),
2. oriental sore (P. papatasii and P. sergenti)
3. sandfly fever (P. papatasii and P. punjabensis).

25. Control Measures
•Breeding is prevented by filling cracks and cervices on
the walls and removing any stone or rock piles.
•The adults are killed by indoor residual spray
insecticides like DDT and lindane in concentrations of
1-2 and 0.25 g per square metre respectively.
•Repellents used on clothes or applied to skin such as
deet, DMP, etc. are effective against

26. ANOPHELES

27. The Anopheles Mosquito
• About 380 species of Anopheles occur around the world
• Some 60 species are sufficiently attracted to humans to act as
vectors of malaria
• A number of Anopheles species are also vectors of filariasis
and viral diseases.
• Female Anopheles mosquito spread the disease. 27

28. 28
• The anophelines that enter houses to feed often rest indoors for a few
hours after feeding.
• They may then leave for outdoor sheltered resting sites, among them
vegetation, rodent burrows, cracks and crevices in trees or in the
ground, caves and the undersides of bridges.
• Many Anopheles species feed on both humans and animals.
• They differ, however, in the degree to which they prefer one over the
other.
• Some species feed mostly on animals while others feed almost entirely
on humans.

29. 29
• The most preferred breeding sites are pools, seepages, quiet
places in slow-running streams, rice fields, leaf axils of
certain epiphytic plants and puddles of rainwater.
• Artificial containers, such as pots, tubs, cisterns and
overhead tanks are not usually suitable.
• Anopheles mosquitos are active between sunset and
sunrise.
• Each species has specific peak biting hours, and there are
also variations in their preference for biting indoors or
outdoors.

30. Identifications
Male Anophelene
• Maxillary palpi is equal in length to
proboscis.
• Palpi are club shape at the tip
• Antenna are hairy
• Clasper or style is the terminalia
Female Anophelene
• Maxillary palpi is equal in length to
proboscis
• Palpi are not club shaped but
straight
• Antenna are sparsely hairy or even
absent
• Palps are as long as their proboscis
• Cerci is the terminalia

32. Diseases Transmitted
1. Malaria – P.Vivax, P.Falciparum,
P.Malariae
2. Black water fever – P.Vivax,
P.Falciparum, P. Malariae
3. Cerebral Malaria –
P.Falciparum

33. Control Measures
1. Anti-Larval measures
a)Environmental control:
Eliminating breeding places and reducing source of transmission (e.g. by
filling, leveling, drainage of breeding places and water management.
b)Chemical control :
Use of mineral oils (diesel, fuel oil, kerosene), paris green, synthetic
insecticides (Fenthion, chlorpyrifos).
c)Biological control:
Use of Gambusia Affinis (mosquitofish) and Lebistes Reticulatus in pits,
sewage ponds, farm ponds etc…

34. 2. Anti-Adult measures:
a) Residual Sprays : Malathion, DDT, Propoxur
b) Space Sprays : Pyrethrum , fenitrothion.
c) Genetic control : Sterile male technique, sex distortion, gene replacement,
cytoplasmic Incompatibility etc..
3. Protection against mosquito bites:
a) Mosquito nets
b) Screening with copper or bronze gauze
c) Repellant : Diethyltoluamide, Indalone, dimethyl carbate

35. CULEX MOSQUITO

36. The Culex Mosquito
•Culex sp is a markedly domestic species
• The adult females bite people and animals
throughout the night, indoors and outdoors
• During the day they are inactive and are often found
resting in dark corners of rooms, shelters and culverts
• They also rest outdoors on vegetation and in holes in
trees in forested areas

37. Identifications
Male
• Maxillary palps is larger than
proboscis. They are bent
outward with pointed tips.
• The antenna are hairy
• Claspers or style is the
terminalia.
Female
• Maxillary palps are 1/3 of
proboscis.
• The antenna are small and little
hairy
• Cerci is the terminalia.

38. Male Female

39. Culex Mosquito Heads

40. Diseases Transmitted
• Arbovirus infections
• West Nile Virus
• Filariasis
• Japanese Encephalitis
• St. Louis Encephalitis
• Avian Malaria

41. Control Measures
1. Anti-Larval measures
a)Environmental control:
Eliminating breeding places and reducing source of transmission (e.g. by filling,
leveling, drainage of breeding places and water management.
b)Chemical control :
Use of mineral oils (diesel, fuel oil, kerosene), paris green, synthetic insecticides
(Fenthion, chlorpyrifos).
c)Biological control:
Use of Gambusia Affinis (mosquitofish) and Lebistes Reticulatus in pits, sewage
ponds, farm ponds etc…

42. 2. Anti-Adult measures:
a) Residual Sprays : Malathion, DDT, Propoxur
b) Space Sprays : Pyrethrum , fenitrothion.
c) Genetic control : Sterile male technique, sex distortion, gene replacement,
cytoplasmic
Incompatibility etc..
3. Protection against mosquito bites:
a) Mosquito nets
b) Screening with copper or bronze gauze
c) Repellant : Diethyltoluamide, Indalone, dimethyl carbate