medical entomology & vector bionomics

1. Medical Entomology and
Vector Bionomics
By
Dr Utpal Sharma
Assistant Professor
Dept Of Community Medicine
Sikkim Manipal Institute of Medical Sciences

2. Introduction
Medical Entomology is the science that deals with insects,
arachnids and other arthropods which directly or indirectly
effects 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 one and a quarter million known animal
species, about 4/5th belongs to arthropods.
The insects comprises about 70% of known species of all
kinds of animals

3. Cont….
 Over 8 lacs 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
artropoda are also included in the study.

4. Characteristics of Artropods
 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

5. Characteristics of arthropods

6. Characteristics….cont..
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.

7. Nervous and circulatory system of
arthropods

8. Characteristics…..cont….
Compound eye of arthopods Molding in arthropods

9. Arthropods of medical
importance
Class: Insecta Class: Arachnida Class: Crustacea
Mosquitoes
Ticks
Cyclops
Anophelines
Hard tick
Culicines
Soft tick
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. 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

11. 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

12. Class: Insecta

13. Class: Arachnida and Crustacea

14. Arthopods in relation to
human health
Annoyance
Blood loss
Injury to sense organs
Dermatosis
Myiasis
Allergy
Anaphylactic shock
Envenomization
Entomophobia

15. Why are these arthopods 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.

16. Cont…
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.

17. Modes of Disease Transmission by
arthropods
Direct Contact-
With the direct contact of hosts, the arthropod vectors
gets transferred from one host to the other.
e.g. pediculosis and scabies.
Mechanical transmission :
The agent is transmitted 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.

18. Cont…
Biological Transmission :
 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.
 Cyclo-propagative :
 The agent undergoes cyclical changes and also multiplies in the
body of arthopods r. Example is Plasmodium sp in Anopheles
female.
 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

19. Vector Bionomics

20. Introduction
Bionomics (Greek: bio = life; nomos = law) is the
comprehensive study of an organism and its relation
to its environment.
Why is it important ???..
Establishing the relationship between the
epidemiology of a disease and the ecological status
of its vector.
To devise effective measures to control the vector
with understanding this relationship.

21. Cont…
Bionomics of vectors include the development of
immature stages to adults under the influences of….
Environmental conditions.
Genetic factors,
Ecological factors, which may produce different type of
reaction in a population having the same genetic
characteristics.
Each vector occupies a separate ecological habitat,
and has specific requirements to be able to…..
… Breed, Develop, Feed, Mate and Lay Eggs

22. Factors influencing vector
bionomics
 Temperature: Between species, variations exist in
temperature tolerance eg Plasmodium survives in the vector
at 20º to 30º C
 Humidity: Direct effect on the longitivity of the vector eg. A
relative humidity of 60 is necessary for the mosquito and
flea to survive through its normal life span.
 Rainfall: This increases the relative humidity and hence
chances of survival.
 Topology: Found at the height 14000 ft above to 3760 ft
below sea level, however Anophilines doesn’t survies above
2000 to 2500 mt

23. Factors effecting….
Water movement:
Species differ in their tolerance of current and wave
action eg. An fluviatilis.
Salinity:
Some species are fresh-water species; others prefer
brackish water eg. An sundaicus.
Pollution:
Some species react differently to oxygen tension and
the presence of organic matter eg Culex

24. Cont…
Turbidity: The depth to which sunlight penetrates can
be a factor
Microflora: Different species prefer different
compositions of microscopic plant life as the source of
larval food, which must be present in abundance.
Macroflora: Emerging adults have specific
requirements of shade, protection, and resting places.
Fauna: The presence of predators and parasitizing
organisms reduce the number of immature forms.

25. Cont…
Gonotrophic cycle: This is the cycle in the life from
taking a blood-meal to oviposition.
 After feeding, gorged with blood, rest for 24-48 hrs need for
meal to get digested and mature eggs have formed in the
ovary.
Dispersal: Under normal atmospheric circumstances,
flights range from 1 to 11km.
 Dispersal is mostly downwind, and strong winds may carry
mosquitoes much further.
 Passive dispersion through boats, buses, trains, and aircraft is
common nowadays.

26. Cont…
Biting behaviour:
 Flight, host-seeking, and feeding generally take place in a
warm and humid environment.
 Many principal malaria vectors, bite in the latter half of the
night when relative humidity is high.
 Species may bite during daytime or at dusk eg Aedes
 Some mosquitoes prefer biting inside houses (Endophagic)
others bite outdoors (Exophagic).
Host preference:
 Anthropophilic: The preferred vertebrate host may be man
eg Culex
 Zoophilic: The preferred vertebrate host maybe animals.

27. Cont…
Resting habits:
 Endophilic: The vector prefer resting inside the houses
 Exophilic: The vector prefer resting outside the houses.
 The design and construction of houses can greatly influence
the extent to which they are entered by mosquitoes.
Seasonal prevalence:
 Some arthropods Hibernate to survive winter temperatures,
either in the egg or the larval stage e.g. moth, grasshoppers.
 Hibernation doesn’t occurs in pupal stage in mosquitos.
 Aestivation: Some vectors, including An. Gumbiue and fleas,
are able to survive hot, dry, and apparently waterless periods.

28. Cont…
Longevity:
 Climatic factors greatly influence the vector longevity and
mortality.
 Also heavy parasitic infections shorten their life expectancy eg
blocked flea, mosquitoes.
 The vectorial status of arthropods depends on the margin by
which longevity exceeds the Extrinsic incubation period.
Susceptibility to insecticides:
 Insecticide resistance is induced through the selection of
vectors surviving dosages of insecticides which kill susceptible
individuals.
 Once induced, resistance is inherited by the next generation.

29. Thank you