A study of the arthropods of medical importance is
known as medical entomology.
Arthropods are invertebrates with jointed legs.
Class: Insecta Class: Arachnida Class: Crustacea
3. Human Lice:
Head and body lice,
4. Fleas:Rat fleas
5. Reduvid bugs
Distinctive characters of arthropods of
Insecta Arachnida Crustacea
1. Body divisions
5. Where found
One or two pairs;
Transmission of Arthropod-borne
There are three types of transmission
cycles which are involved in the spread
of arthropod-borne diseases:
(1) Direct Contact- directly
transferred from man to man through
close contact. e.g. scabies and
(2) Mechanical Transmission-
diarrhoea, dysentery, typhoid, food
poisoning by housefly through their
(3) Biological Transmission- when
the disease agent multiplies or
undergoes some developmental
change with or without
multiplication in the arthropod host.
Biological transmission may be of three
no cyclical changes of
only multiplies in the body
of the vector
Example- Plague bacilli rat fleas.
undergoes cyclical changes
Example- malaria parasite
in anopheline mosquito.
undergoes cyclical changes
does not occur
Example- filarial parasite in culex
mosquito and guineaworm
embryo in cyclops.
Principles of arthropod control
The general principles of arthropod
elimination of breeding places
filling and drainage operation
carefully planned water
provision of piped water supply
proper disposal of refuse and other
cleanliness in and around houses
A wide range of insecticides belonging to
the organochlorine, organophosphorus and
carbamate groups of compounds are
available for vector control
The use of larvivorous fish (Gambusia) is
well known in mosquito control.
Different techniques can help in genetic control of
mosquito. Such as sterile male
technique, cytoplasmic incompatibility and
No single method of control is likely to provide a
solution in all situations. “Integrated approach” for
combining two or more methods with a view to
obtain maximum results with the minimum effort
and to avoid the excessive use of any one method.
The body of a mosquito consists of
a) Head: semi-globular in outline
and bears the following
i. A pair of large compound eyes
ii. A long needle-like
structure, called proboscis
iii. A pair of palpi, situated on
either side of proboscis
iv. A pair of antennae.
b) Thorax: the thorax is large and rounded and bears-
i. A pair of wings dorsally. The buzzing noise which
the mosquitoes produce is due to the beating of their
wings, and not to “singing”.
ii. Three pairs of leg ventrally
c) Abdomen: The abdomen is long and narrow and
composed of 10 segments, the last two of which are
modified to form the external genitalia.
There are four stages in the life history
1) Egg: Eggs are laid on the surface of
water, 100-250 at a time. Under
favourable conditions, the egg stage
of mosquitoes lasts for 1-2 days.
2) Larva: The larva is a free swimming creature with
an elongated body divisible into head, thorax and
abdomen.It feeds on algae, bacteria and vegetable
matter. The larva stage occupies 5-7 days.
3) Pupa: The pupa is coma shaped in appearance,
with a large rounded cephalothorax and a narrow
abdomen. The pupa represents the resting stage
in the life history of the mosquito which lasts for
4) Adult: When the development is complete; the pupal skin
splits along back and the adult mosquito or imago emerges.
Under favourable conditions of temperature and food
supply the life cycle from egg to adult is complete in 7-10
days. Normally the adult mosquito lives for about 2 weeks.
Differentiation between anophelini and culicini
Anophelini Anopheles Culicini Culex, Aedes,
Eggs 1) Laid singly
2) Eggs are boat-shaped, and
provided with lateral floats
1) Laid in clusters or rafts, each
raft containing 100-250 eggs
2) Eggs are oval-shaped, and not
provided with lateral floats
Larva 1)Rest parallel to water surface
2) No siphon tube
3) Palmate hairs present on
1) Suspended with head
downwards at an angle to
2) Siphon tube present
3) No palmate hairs
Pupae Siphon tube is broad and short Siphon tube is long and narrow
Adults 1) When at rest, inclined at an
angle to surface
2) Wings spotted
3) Palpi long in both sexes
1) When at rest, the body
exhibits a hunch back
2) Wings unspotted
3) Palpi short in female
Anopheles mosquitoes are characterized by dark and
pale scale blocks arranged on their wings. Wings are
spotted. For breeding they prefer clean, stagnant
Anopheles phillipinensis- Plain area
Anopheles minimus- mountainous area (Mymensingh)
Anopheles sundicus- coastal region (Cox’s bazaar)
Anopheles ballabacensis- Hilly and forest (Ctg.
Anopheles annularis- Narayanganj
Anopheles vagus- Kishoregonj.
They are known as “nuisance mosquitoes”. An
important member of this group is Culex fatigans, the
vector of Bancroftian filariasis. It breeds profusely in
dirty water collections. Eg- stagnant drains, septic
tanks, burrow pits.
They are easily distinguished by
white stripes on a black body. For
this sometimes they are reffered as
“tiger mosquitoes”. Important
members of this group are :
Aedes aegypti, Aedes albopictus.
They breeds in artificial
accumulations of water in and
around human dwellings, such as
water found in discarded tins,
broken bottles, flower pots,
coconut shells, earthen pots, tree
Habits of mosquitoes:
1) Feeding habits: The males never bite. They
subsist on plant juices. The females are
haematophagous. They require a blood meal for
the development of eggs.
2) Time of biting: In general mosquitoes bite in the
evening or in the early part of the night.
3) Resting habits: Mosquitoes obscure themselves
during the day in dark and cool corners. Some
rest indoors (endophilia), and some outdoors
4) Breeding habits: The anophelines prefer clean
water; the cuilicines prefer dirty and polluted
water; the aedes prefer artificial collections of
5) Hibernation: Mosquitoes are known to hibernate
in the adult stage when the environmental
conditions are not favourable.
6) Dispersal: Mosquitoes do not generally fly far
from the place where they bread unless swept by
currents of wind.
7) Life span: The life of a mosquito is influenced by
temperature and humidity. The normal life span
varies from 8 to 34 days.
Type of mosquito Disease
1. Anopheles Malaria, Filaria
2. Culex Bancroftian filariasis, japanese encephalitis, West Nile
fever, Viral arthritis
3. Aedes Yellow fever, Dengue, Dengue haemorrhagic fever,
4. Mansonoides Malayan filariasis, Chikungunya fever
Mosquito born diseases:
Mosquito control measures:
1. Anti-larval measures
a) Environmental control-
b) Chemical control-
mineral oils, paris green
c) Biological control
2. Anti-adult measures
a) Residual sprays- DDT
b) Space sprays
c) Genetic control
3. Protection against
a) Mosquito net
Musca domestica, M. Vicinia,
M. Nebula, M. Sorbens.
1) Head: A pair of antennae, a
pair of large compound
eyes and a retractile
proboscis, which is
adapted for sucking
2) Thorax: A pair of wings,
three pairs of legs.
3) Abdomen: Abdomen is
1) Breeding habits: fresh horse manure, human excreta,
manure of other animals, garbage, decaying fruits and
vegetables, rubbish dumps containing organic matter.
2) Feeding habits: The housefly does not bite. It is
attracted to food by its sense of smell. It vomits on solid
food to make a solution of it and sucks in a liquid state.
3) Restlessness: The fly is a restless insect. It moves back
and forth between food and filth and thus spread
4) Vomit drop: The fly vomit frequently and spread
5) Defecation: The housefly has the habit of defecating
constantly all the day. Thus it deposits countless
bacteria on exposed food.
6) Resting habits:
Rest on vertical
remain close to
frequently up to 4
Transmission of disease:
Diseases: Typhoid and
dysenteries, cholera and
Ways of transmission:
1) Mechanical transmission: Through their feet
and hairy legs.
2) Vomit drop
Fly control measures-
1) Environmental control- Elimination of their breeding
a) storing garbage, kitchen wastes and other refuse in
bins with tight lids.
collection, removal and
disposal of refuse by
or sanitary landfill.
c) provision of sanitary
d) stopping open air
e) sanitary disposal of
2) Insecticidal control-
a) Residual sprays: DDT
(5%), lindane or chlordane
c) Cords and ribbons
d) Space spray
3) Fly papers
4) Protection against flies
5) Health education
Sandflies are small insects, light or dark-brown in colour. They
are smaller than mosquitoes. Their bodies and wings are
densely clothed with hair.
a) Head-The head bears a pair of long, slender and hairy
antennae, palpi and proboscis. Only the female bite.
b) Thorax-The thorax bear a pair of wings and three pairs of
c) Abdomen- The abdomen has 10 segments and is covered
Special characteristics- Sandflies hop about, and do
Sandflies are troublesome nocturnal pests. Their
bite is irritating and painful. They take shelter
during day in holes and crevices in walls, holes in
trees, dark rooms, stables and store rooms.
Sandflies are incapable of flying over long
distances, they merely hop about from one place to
another. They are generally confined to within 50
yards of their breeding places.
Control of sandflies:
1. Insecticides: A single application of 1 to 2 g/m2 of DDT or
0.25 g/m2 of lindane has been found effective in reducing
2. Sanitation: Removal of refuse and vegetation within 50
yards of human dwellings, filling up cracks and crevices in
walls and floors, and location of cattle sheds and poultry
houses at a fair distance from habitations.
The itch mite (Sarcoptes
scabiei) is an extremely
small, globular arthropod.
The female parasite burrows
into the epidermis where it
breeds and causes the
condition known as scabies.
Mode of spread:
a) Close contact: Scabies is
usually transmitted by close
contact with an infested
person. This is often due to
sleeping in the same bed or
children playing with each
other or nursing an infested
b) Contaminated clothes: The disease may be acquired
sometimes from contaminated cloths and bed linen.
Site of lesion:
The disease classically affects the hands and wrist, the
extensor aspect of elbow. The axilla, buttocks, lower
abdomen, feet and ankles, palms in infants.
a) The patient complains of itching which is worse at night
b) Examination reveals follicular lesions at the affected
c) Other members of the household are affected
d) Confirmation of the diagnosis may be made by
searching for the parasite in the skin debris under
Control of scabies:
1. Benzyl benzoate: Before commencing the treamtent
the patient is given a good scrub with soap and hot
water. Benzyl benzoate should be applied to every inch
of the body below the chin including the soles of the
feet and allowed to dry. In case of babies, the head must
also be treated. The application should be repeated
after 12 hrs and after a further 12 hrs a bath given and all
cloths and sheets changed and washed.
4. Sulphur ointment
Insecticides are substances which are
used to kill insects.
The word pesticides is a general term
insecticides, fungicides, rodenticides, he
rbicides, disinfectants, repellents etc.
Insecticides are classified into three
a) Contact poisons-are those which
kills insects primarily by contact, e.g-
pyrethrum, DDT,HCH, dieldrin.
b) Stomach poisons-are those which
when ingested cause the death of the
insects.e.g. Paris green, sodium
c) Fumigants-are those which give off
vapours which have a lethal effect on
the insects, e.g. Sulphur dioxide.
Another classification may be:
Group i – Organochlorine
compounds: DDT, HCH, dieldrin,
chlordane, methoxychlor etc.
Group ii – Organophosphorous
compounds: malathion, fenthion,
Group iii – Carbamates: Propoxur,