MEDICAL ENTOMOLOGY is an important topic of Community Medicine.

1. MEDICAL ENTOMOLOGY

2. MEDICAL ENTOMOLOGY
A study of the arthropods of
medical importance is known
as medical entomology which
is an important branch of
preventive medicine.

5. Arthropods of medical
importance
Class: Insecta Class:Arachnida Class:Crustacea
1.Mosquitoes:
Anophelines
Culicines
1.Ticks:
Hard ticks
Soft ticks
1.Cyclops
2.Flies :
Houseflies
Sandflies
Tsetse flies
Blackflies
2.Mites (Chiggers)
Leptotrombidium
and Trombiculid
mites; Itch mite
3. Human Lies :
Head and body
lice,Crab lice
4.Fleas :
Rat fleas
Sand fleas
5.Reduviid bugs

6. Distinctive characters of arthropods of
medical importance

8. Insecta

9. Arachnida

10. Crustacea

12. Transmission of arthropod-borne
diseases
Three types of transmission cycles
are involved in the spread of
arthropod-borne disease –
(1) DIRECT CONTACT
(2) MECHANICAL TRANSMISSION
(3) BIOLOGICAL TRANSMISSION

14. Contd.
 (1) DIRECT CONTACT : In this method of spread,
the arthropods are directly transferred from man to
man through close contact, e.g., scabies and
pediculosis.
 (2) MECHANICAL TRANSMISSION : The
disease agent is transmitted mechanically by
the arthropod. The transmission of diarrhoea,
dysentery, typhoid, food poisoning and
trachoma by the housefly are examples of
mechanical transmission of the disease agent
by the vector.

15. Contd.
 (3) BIOLOGICAL TRANSMISSION : When the
disease agent multiplies or undergoes some developmental change
with or without multiplication in the arthropod host, it is called
biological transmission. This may be of three types-
(a) Propagative :
When the disease agent undergoes no cyclical
change, but multiplies in the body of the vector, transmission is said to
be propagative, e.g., plague bacilli in rat fleas .
(b) Cyclopropagative :
The disease agent undergoes cyclical change,and
multiplies in the body of the arthropod, e.g., malaria parasite in
anopheline mosquito .
(c) Cyclo-developmental :
When the disease agent undergoes cyclical change
but does not multiply in the body of the arthropod, e.g., filarial parasite
in culex mosquito and guineaworm embryo in cyclops.

16. VECTOR
 In communicable disease terminology, the word vector
means an "arthropod or other invertebrate
which transmits infection by inoculation into
or through the skin or mucous membrane by
biting, or by deposit of infective materials
on the skin or on food or other objects". The
period of time necessary for the
development of the disease agent in the
arthropod host is called extrinsic incubation
period.
 For example, the extrinsic incubation periods in malaria
and filaria are from 10 to 14 days or longer depending
upon the environmental temperature.

17. The host in which the sexual cycle
of the agent occurs is called the
definitive host, e.g.,mosquito is
the definitive host in malaria.
CONTD.

18. The host in which the asexual cycle of the
agent . occurs is called the intermediate
host e.g., mosquito in filaria and cyclops in
guinea-worm disease.
By infestation is meant the lodgement,
development and reproduction of
arthropods on the surface of the body or in
the clothing e.g., louse infestation.
CONTD.

19. Principles of arthropod
control
The general principles of
arthropod control are :
1. Environmental control
2. Chemical control
3. Biological control
4. Genetic control.

20. (1) Environmental control
 This offers the best approach to the control of arthropods,
because the results are likely to be permanent.
 Examples of environmental manipulation are: elimination of
breeding places (source reduction); filling and drainage .
operation; carefully planned water management; provision
of piped water supply; proper disposal of refuse and other
wastes; cleanliness in and around houses, etc.
Intensive health education of the public as well as political
support are essential prerequisites.

21. (2) Chemical
control
A wide range of
insecticides belonging to
the organochlorine,
organo-phosphorus and
carbamate groups of
compounds are available
for vector control.

22. (3) Biological control
 The use of larvivorous fish especially
Gambusia is well known in mosquito control.
 Fungi of the genus Coelomomyces are also
known to be pathogenic to mosquitoes. A
variety of other biological agents (e.g.,
bacteria, fungi, nematodes, protozoa and
viruses) are under study for the control of
insects.
 But the fear exists that the introduction of
biological agents for the control of
arthropods may pose a direct hazard to the
health of man himself.

23. (4) Genetic control
 Techniques such as sterile male
technique, cytoplasmic incompatibility
and chromosomal translocations have
been found to be effective in small field
trials.
 New and innovative methods are being
sought for pest control. These are
 (a) insect growth regulators
 (b) chemosterilants, and
 (c) sex attractants or
 pheromones .

24. Integrated approach
 Since no single method of control is likely to
provide a solution in all situations, the
present trend is to adopt an "integrated
approach" for vector control 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.

25. MOSQUITO
 Mosquitoes are found all over the world. The four important
groups of mosquitoes.
 in India which are related to disease transmission are the
Anopheles, Culex, Aedes and
Mansonia.

32. (1) Anopheles
 Some species of anopheles mosquitoes are-
 (1) An. culicifacies
 (2) An. fluviatilis
 (3) An. minimus
 (4) An. philippinensis
 (5) An. stephensi
 (6) An. Sundaicus and
 (7) An. leucosphyrus

33. (2) Culex
 Mosquitoes of the genus Culex are the common"nuisance
mosquitoes" which are terrible pests of man.
 Rapid urbanization and industrialization without adequate drainage
facilities are responsible for its increased spread.
 It breeds profusely in dirty water collections, viz. stagnant drains,
cesspools, septic tanks,burrow pits, and in fact, in all types of water
collection.
 The peak biting time is about midnight. Legs, particularly below the
knee are the preferred biting sites.
 During day, it may be seen resting indoors on walls, underneath
furniture, inside empty pots and in dark corners.

34. (2) Culex

35. (3) Aedes (Stegomyia)
 Aedes mosquitoes are easily distinguished by white stripes on a
black body. Because of the striped or banded character of their
legs they are sometimes referred to as "tiger mosquitoes".
 Aedes aegypti occupies a very special position in preventive
medicine. It is the first proved vector of a virus disease yellow
fever.
 Important members of this group of mosquitoes are :
 Aedes aegypti, Aedes vittatus and Aedes albopictus.
 Aedes mosquitoes are most abundant during rainy season.

36. (3) Aedes (Stegomyia)
 It breeds in artificial accumulations of water in and around
human dwellings, such as water found in discarded tins, broken
bottles, fire buckets, flower pots, coconut shells,earthen pots,
tree holes and the like. It lays eggs singly, and the eggs are
cigar-shaped.
 Under the International Health Regulations, Aedes aegypti
index is defined as "the ratio, expressed as percentage,
between the number of houses in a limited well-defined area on
the premises of which actual breeding of Aedes aegypti are
found, and the total number of houses examined in that area" .
This index is kept at zero at all ports.

38. (3) Aedes (Stegomyia)

39. (4) Mansonia
 The mosquitoes of this genus are big, black or brown mosquitoes
with speckling on their wings and legs.
 The common Indian species are : M.annulifera, M.uniformis,
M. indiana and M. longipalpis.
The mansonoides mosquitoes are peculiar in their breeding habits.
They breed in ponds and lakes containing certain aquatic
plants,especially the floating types like Pistia stratiotes and
water hyacinth.

40. Habits of mosquitoes
 (1) FEEDING HABITS-The males never bite : they
subsist on plant juices.
 The females on the contrary are haematophagous. They
require a blood meal, once in 2-3 days for the
development of eggs. The females differ in their feeding
habits.
 Some species (anthrophilic) prefer human blood, some
(zoophillic) prefer animal blood, and some indifferent in
their choice and feed on both man and animals.

41. CONTD.
 (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 (exophilia). The indoor resting places are usually the dark
corners of houses, -upper part of walls, behind pictures and under
furniture. The outdoor resting places are usually the vegetation, shrubs,
tree holes, cattle sheds and wells.
 (4) BREEDING HABITS : In general, the anophelines prefer clean water
for breeding; the culicines prefer dirty and polluted water; the aedes
prefer artificial collections of water. The mansonia breed in water
containing certain types of aquatic vegetation.

42. CONTD.
 (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 breed unless swept by currents of wind. The range of flight
varies with the species, and may range upto 11 kms.
 (7) LIFE SPAN : The life of a mosquito is influenced by temperature and
humidity. Both high and low temperatures are fatal. The normal life span
of mosquitoes varies from 8 to 34 days. The males, as a rule, are short-
lived.

43. Mosquito-borne diseases
 Types of MOSQUITO- Disease
 1) Anopheles - Malaria
Filaria ( Not in India)
2) Culex - Bancroftian filariasis
Japanese encephalitis
West Nile fever
Viral arthritis
(epidemic/polyarthritis)
3) Aedes Yellow fever (not in India)
Dengue
Dengue Haemorrhagic fever
Chikungunya fever
Chikungunya haemorrhagic fever
Rift valley fever
Filaria (not in India)
4)Mansonoides Malayan (Brugian) filariasis
Chikungunya fever

44. MOSQUITO CONTROL
MEASURES
 1 ANTI-LARVAL MEASURES
(a) Environmental control
(b) Chemical control
(c) Biological control.
 2 ANTI-ADULT MEASURES
(a) Residual sprays
(b) Space sprays
(c) Genetic control.
 3 PROTECTION AGAINST MOSQUITO BITES
(a) Mosquito net
(b) Screening
(c) Repellents.

45. 1. ANTI-LARVAL MEASURES
 (a) Environmental control -The most important step in reducing the
numbers of mosquitoes is to eliminate their breeding places. This is
known as "source reduction“.
 “Source reduction“ -# comprises minor engineering methods such
as filling, levelling and drainage of breeding places; and
# water management (such as intermittent
irrigation)
#rendering the water unsuitable for mosquito
breeding, as for example, changing the salinity of water
#adequate collection,removal and disposal of
sewage and waste water for Culex mosquito.

46. CONTD.
 If Aedes mosquitoes are a problem, the
environment should be cleaned up and got rid of
water holding containers such as discarded tins,
empty pots, broken bottles, coconut shells and
similar other artificial collections of water.
 If Mansonia mosquitoes are a problem, the aquatic
plants to which the larvae attach themselves should be
removed or destroyed by herbicides.

47. (b) Chemical control
 The commonly used larvicides are :
(i) Mineral oils
(ii) Paris green
(iii) Synthetic insecticides
 (i) Mineral oils : The oils most widely used are the diesel oil,
fuel oil, kerosene and various fractions of crude oils. Special oils
(e.g., Mosquito Larvicidal Oil) are also available. Oil kills larvae
and pupae within a short time after application. Oil kills larvae and
pupae within a short time after application. When applied on
water, oil spreads and forms a thin film, which cuts off the air
supply to the mosquito larvae and pupae. Oil probably has also a
specific toxic action on these insect stages.

48. CONTD.
(ii) Paris green-Paris green or copper
acetoarsenite is an emerald green, micro -
crystalline powder practically insoluble in water.
A good sample of paris green must contain 50
per cent arsenious oxide. Paris green is a
stomach poison and kills mainly the Anopheles
larvae because they are surface-feeders.
 (iii) Synthetic insecticides -Fenthion,
Chlorpyrifos, and Abate are the most effective
larvicides. These organophosphorous
compounds hydrolyze quickly in water.

49. Biological control
 A wide range of small fish feed readily on mosquito larvae. The
best known are the Gambusia a/finis and Lebister
reticulatus (sometimes known as Barbados Millions).
 These fish can be used in burrow pits, sewage oxidation
ponds, ornamental ponds, cisterns and farm ponds.

50. 2. ANTI-ADULT MEASURES
 (a) Residual sprays-DDT is the insecticide of
choice and dosages of 1-2 grams of pure DDT
per sq. metre are applied 1-3 times a year to
walls and other surfaces where mosquitoes
rest.
 (b) Space sprays-Space sprays are those
where the insecticidal formulation is sprayed
into the atmosphere in the form of a mist or
fog to kill insects. The common space sprays
are :
 (i) Pyrethrum extract
 (ii) Residual Insecticides-The most extensively
 used insecticides are malathion and
fenitrothion for ULV fogging .

51. (c) Genetic control
 In recent years, control of mosquitoes by genetic methods
such as sterile male technique, cytoplasmic
incompatibility,chromosomal translocations, sex distortion,
and gene replacement have been explored.

52. 3. PROTECTION AGAINST MOSQUITO
BITES-

53. HOUSEFLIES
 Houseflies are· the commonest and most familiar of all insects
which live close to man.
 The most important of these are :
Musca domestica,
M. vicinia,
M. nebulo and
M. sorbens
Houseflies should be regarded as a sign of insanitation.

54. CONTD.
General characters-
 The common housefly (M. domestica) is-
 #colour-mouse-grey
 #The body- Head, Thorax and Abdomen
 #1) HEAD-The head bears a pair of antennae, a pair of large
compound eyes and a retractile proboscis, which is adapted for
sucking liquid foods.
#(2) THORAX-a)The thorax is marked with 2 to 4 dark longitudinal
stripes, which is characteristic of the genus, musca.
b) The thorax bears a pair of wings and three pairs of legs. Each leg
is provided with a pair of pads which enables the fly to walk on
highly polished surfaces.
c) The legs and the body are covered with numerous short and stiff
hairs, called the tenent hairs which secrete a sticky substance.

55. CONTD.
(3) ABDOMEN : The abdomen is
segmented and shows light and dark
markings.

56. CONTD.

57. Life history of housefly
 The housefly undergoes a complete metamorphosis with four stages in its life
cycle : egg, larva (maggot), pupa and adult.
 (1) EGG :The female lays from about 120 to 150 eggs
at one sitting in moist decaying organic matter such
as human and animal excreta, manure heaps, garbage
and. Vegetable refuse.
 (2) LARVA : The larvae or maggots measure 1 to 2
mm in length at birth.They moult twice in the course
of development. The full grown larva may measure up
to 12 mm in length.
 (3) PUPA : The pupa are darkbrown and barrel
shaped and measure about quarter of an inch.
 4) ADULT : The complete life cycle from egg to adult
may take 5 to 6 days during summer in India, but at
other times it may take 8 to 20 days.

59. Habits
 (1) BREEDING HABITS :
 (a) fresh horse manure
 (b) human excreta
 (c) manure of other animals
 (d) garbage
 (e) decaying fruits and vegetables
 (f) rubbish dumps containing organic matter
and
 (g) ground where liquid wastes are spilled

60. CONTD.
(2) FEEDING HABITS-It cannot eat solid
foods; it vomits on solid food to make a
solution of it and sucks in a liquid state.
Adult flies delight in sputum, faeces,
discharges from wounds and open sores.
(3) RESTLESSNESS-The fly is a restless
insect and moves back and forth between
food and filth.
(4) VOMIT DROP-The fly vomits
frequently. The "vomit drop" is often a
culture of disease agents.

61. CONTD.
(5) DEFECATION -The housefly has the
habit of defecating constantly all the day.
Thus it deposits countless bacteria on
exposed food.
(6) RESTING HABITS-Flies have a
tendency to rest on vertical surfaces and
hanging objects.
(7) DISPERSAL : Normally houseflies
remain close to their breeding places, but
they disperse frequently up to 4 miles.

62. Transmission of disease
 Flies are potential vectors of many diseases :
 typhoid and paratyphoid fevers,
 diarrhoeas and dysenteries,
 cholera, and gastroenteritis,
 amoebiasis, helminthic infestations,
 poliomyelitis, conjunctivitis, trachoma, anthrax, yaws.
Flies transmit disease in the following
ways-
(1) MECHANICAL TRANSMISSION
Houseflies are therefore called "porters
of infection."

63. CONTD.
(2) VOMIT DROP
(3) DEFECATION

64. FLY CONTROL MEASURES
1. Environmental control-
 (1) storing garbage,kitchen wastes and other refuse in
bins with tight lids,pending disposal.
 (2) efficient collection, removal and disposal of refuse
by incineration, composting or sanitary landfill.
 (3) provision of sanitary latrines, e.g., pit privies,
 septic tanks, water-seal latrines and sanitary system.
 (4) stopping open air defecation.
 (5) sanitary disposal of animal excreta, and
 (6) stepping up general sanitation. A clean house with
clean surroundings is the best answer to the fly
problem.

65. CONTD.
2. Insecticidal control-
 # RESIDUAL SPRAYS :DDT (5%), methoxychlor
(5%),lindane (0.5%), or chlordane (2.5%) sprayed at about 5
litres per 100 square metres of surface.
 #SPACE SPRAYS :pyrethrin and DDT or HCH.
#LARVICIDES:0.5% diazinon,
2%dimethoate

66. Contd.
3. Fly papers -Sticky fly papers are useful
adjuncts to other methods of control. These papers can
be easily made by mixing 2 lbs of resin and one pint of
castor oil which should be heated together until the
mixture resembles molasses. This should, while hot, be
smeared on paper by using an ordinary paint brush.
4. Protection against flies-Screening
of houses, hospitals, food markets,
restaurants and all other similar
establishments will give considerable
relief from houseflies.

67. Contd.
5. Health education-A "fly
consciousness" should becreated
among the people, through health
education.
Fly control campaigns require
organized individual and community
effort which is the basis of a
successful public health programme.

68. SAND FLIES
 Sandflies are small insects, light or dark-
brown in colour.
 They are smaller than mosquitoes, measuring
1.5 to 2.5 mm in length with their bodies and
wings densely clothed with hair.

69. SAND FLIES
 The important ones are :
 Phlebotomus argentipes,
P. papatasii,
P. sergenti, and
Sergentomyia punjabensis

70. General characters
 The body of a sandfly is divided into -head,
thorax and abdomen.
 (1) HEAD-The head bears a pair of long, slender
and hairy antennae; palpi and a proboscis. Only
the females bite, the males live on vegetable
juices.
(2) THORAX-The thorax bears a pair of wings and
three pairs of legs. The wings are upright,
lanceolate in shape and densely hairy.
(3) ABDOMEN-The abdomen has 10 segments
and is covered with hair.

74. Habits
 Sandflies are troublesome noctural pests. Their bite is irritating and
painful, while their presence is scarcely observed.
 They infest dwellings during night, and take shelter during day in
holes and crevices in walls, holes in trees, dark rooms, stables and
store rooms. The females alone bite, as they require a blood meal
every third or fourth day for oviposition. Sandflies are incapable of
flying over long distances; they merely hop about from one place to
another. Sandflies are generally confined to within 50 yards of their
breeding places.

75. CONTD.
Diseases transmitted-
 SPECIES DISEASES
Kala-azar
Phlebotomus argentipes
Phlebotomus papatasii Sandfly fever
Oriental sore
Phlebotomus sergenti Oriental sore
S. Punjabensis Sandfly fever

77. Control of sandflies
 Sandflies are easily controlled because they do
not move long distances from the place of their
breeding-
(1) INSECTICIDES-
-Resistance to DDT has not been demonstrated. A single application
of 1 to 2 g/m2 of DDT or 0.25 g/m2 of lindane has been found
effective in reducing sandflies.
DDT residue may remain effective for a period of 1 to 2 years, and
lindane only for a period of 3 months .
Spraying should be done in the human dwellings, cattle
sheds and other places.

78. CONTD.
 (2) SANITATION : Sanitation measures such as
removal of shrubs 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 human
habitations should receive attention.

79. TSETSE FLIES
 Tsetse flies attack man, animals, wild game of all kinds, birds, lizards
and snakes. Both the sexes bite, mainly during day.
 Tsetse flies or the Glossinae are bloodsucking flies, which present a
general resemblance to the common housefly.
 They are yellow or dark-brown in colour, and measure about half.an
inch long.
 The riverine species (e.g., G. palpalis and G. tachinoides) have a
distinct attraction to man.
 Tsetse flies are vectors of trypanosomiasis or "sleeping
sickness"

80. Contd.
Life history-
 1)LARVA-The female does not lay eggs, but gives birth
to a living larva,one at a time, at 10-day intervals. The
female produces only a few offspring in its life time.
 2) Pupa
 3) Adult

81. CONTD.

82. CONTD.
Control of tsetse flies –
(1) INSECTICIDES-DDT (25%) and
 dieldrin (18-20%) are the most commonly used
pesticides
(2) CLEARING OF VEGETATION
(3) GAME DESTRUCTION
(4) GENETIC CONTROL-Currently,
research is centred round genetic control of
tsetse flies using the "sterile male release"
technique .

83. BLACKFLIES
 Blackflies or simuliidae are small robust flies with short stout legs,
large broad wings and a short proboscis.
 Simulum indicum is the Indian species.
 Blackflies attack domestic animals ci.nd man and suck blood.
 They are vectors of onchocerciasis in Africa, Mexico, and
Central and South America.
Life Cycle-
1)Egg
2)Larva
3) Pupa
4) Adult

84. Contd.
Control of Blackflies-
1)Abate is used which kills the
blackfly larvae without causing harmful
effects to mammals or other aquatic
fauna. It is added to river water in
weekly doses of 0.05 to 0.1 mg/litre
over a period of 10 minutes.
2)Control of the adult fly is difficult,
because the range of the fly is about
100 miles.

85. BLACKFLIES

86. LICE
 The lice that infest man are of three
kinds :
 Head louse (Pediculus capitis),
 Body louse (Pediculus corporis), and
 Pubic or crab louse (Phthirus pubis).

87. Head and body lice
 The head lice inhabit the hairs of the scalp, and the body lice occur
mainly in the seams of clothing and on the bodies of the hosts.
 The body of a louse is flattened dorso-ventrally, and is divided into -
Head,
Thorax
and Abdomen.
#Life history-There are three stages in the life
history of lice : egg, larva and adult.
Metamorphosis is gradual.

88. CONTD.(HEAD ,BODY AND
PUBIC LICE )
 H

90. CONTD.
Dissemination-
(1) DIRECT CONTACT-
 a)Overcrowding
b) Children get easily infested at school.
(2) INDIRECT CONTACT-
Lice may also be acquired from clothing,
bedding, combs or brushes used by lousy
persons. Lice have been seen to be blown
by puffs ofwind from heavily infested
persons.

91. CONTD.(Lice and disease)
DISEASE CAUSATIVE AGENT
1. Epidemic typhus Rickettssia prowazeki
2. Relapsing fever Borrelia recurrentis
3. Trench fever Rickettssia quintana
4. Dermatitis Due to scratching and
secondary infection

92. Crab louse
 The crab louse or pubic louse (Phthirus pubis) is generally found in
the pubic and perinea! region, but at
times it may occur in the other parts of the body as well.
# The crab louse has a characteristic body form, and
is readily recognized by (1) its small size and square body,
(2) head impacted on the thorax,
(3) the relatively enormous
and powerful legs and claws,
(4) the first pair of legs
slenderer than others and,
(5) its extreme inertness

93. Control of lice
 (1) INSECTICIDAL CONTROL:A lotion containing 0.5
percent malathion.
 Dust containing carbaryl may also be used.
 (2) PERSONAL HYGIENE-
 A daily bath with soap and
 water is essential in a country like India to prevent
lice infestation. Women with long hair should wash
and clean their hair frequently.
 Clothing, towels and sheets should be washed in hot
water and soap and pressed with hot iron.
 Autoclaving of clothes and bedding in steam
sterilizers may be required for body louse control

94. FLEAS
 They are blood sucking ecto-parasites of mammals and birds.
 Fleas are small, bilaterally compressed, wingless insects with
a hard chitinous exoskeleton and covered with backwardly
directed strong bristles.
Types of fleas-
1. Rat fleas
(Oriental)
-Xenopsylla cheopis
-Xenopsylla astia
-Xenopsylla braziliensis
2. Rat fleas
(Temperate zone)
Nosopsyllafasciatus
3. Human fleas Pulex irritans
4. Dog and cat fleas Ctenocephalus canis
Ctenocephalus felis
5. Sand fleas Tunga penetrans

95. The
sexes are easily distinguished
 The body of a flea is divided into –
1)Head-a)The head is conical in shape
 b) The head bears short,piercing mouth parts which are
conspicuous and project downwards from the head.
 c)The mouth parts are adapted for piercing and sucking blood.
2) Thorax -The thorax is composed of three segments - the
prothorax, mesothorax · and metathorax. There are three pairs of strong
legs
attached to the thorax. The flea has no wings.
3)Abdomen-The abdomen consists of 10 segments. The sexes
are easily distinguished.

96. Rat fleas

97. Life cycle of flea

98. CONTD.
 Habits- 1)Fleas are found on their normal hosts and in the
nests,burrows and lairs of their hosts. They are also found
in the dwellings, on the ground, in cracks and crevices, and
under carpets. Both the sexes bite and suck blood.
 2)They feed at frequent intervals, usually once a day and
sometimes more often.
 3)Fleas cannot fly, but they are capable of making vertical
jumps of about 4 inches when starved, and about 3 inches
when gorged. The distance they can cover by horizontal
jumps is less than 6 inches.
Fleas are passively transported by-
 (a) their hosts (b) transport vehicles (c) humans - on the
 person or in the luggage, and (d) the movement of goods
like grain, raw cotton, gunny bags, rags and hides.

99. Flea indices
 The following indices are used in flea surveys :
 (1) GENERAL FLEA INDEX : It is. the average number of
 fleas of all species per rodent.
 (2) SPECIFIC FLEA INDEX : (X.cheopis index; X.astia index, etc.) It is
the average number of fleas of each species, found per rodent.
 (3) PERCENTAGE INCIDENCE OF FLEA SPECIES : It is the percentage
of fleas of each species, found per rodent.
 (4) RODENT INFESTATION RATE : It is the percentage of rodents
infested with the various flea species.

100. Fleas and human disease
Fleas are known to transmit the following
diseases :
(1) Plague (bubonic),
 (2) Endemic or murine typhus,
(3) Chiggerosis, and
 (4) Hymenolepis diminuta.
MODE OF TRANSMISSION-
(1) Biting
(2) Mechanical transmission
(3) Faeces

101. 'blocked' fleas
 Some fleas which ingest plague bacilli become blocked due to
the multiplication of plague bacilli in their proventriculus or
stomach. Fleas affected in this way are called 'blocked' fleas.
The blockage of the food passage renders the flea unable to
obtain further blood feeds. Because of hunger, the flea begins
to bite more ferociously and makes frantic efforts to suck
blood. Each time it bites, instead of sucking blood, it injects
plague bacilli into the wound. Such 'blocked' fleas play a great
role in the spread of plague.

102. Control of fleas
 (1) INSECTICIDAL CONTROL-
 1)10 per cent DDT dust.
 2) In a number of plague areas, the rat fleas have developed
resistance to DDT and/or to gamma HCH and dieldrin. In such areas,
carbaryl or diazinon (2%) or malathion (5%) should prove effective .
The sprays should be applied to floors and walls up to a height of
about1 ft.
 (2) REPELLENTS- Diethyltoluamide
 Benzyl benzoate
 (3) RODENT CONTROL

103. SAND FLEA
 Sand fleas occur in the tropical regions of Africa and
America.
 They are also known as Jigger or Chigoe fleas. Of particular
importance is the sand flea, Tunga penetrans.
 The fertilized female burrows into the skin of the feet, often
beneath the nail and causes ulcers. Tetanus and gas
gangrene frequently occur because of secondary infection.
 T. penetrans has been recorded in the western parts of
India;
 It flourishes best in sandy soil.
 Its hosts are usually domestic animals.

104. REDUVIID BUGS
 Reduviid bugs, also known as cone-nose bugs, are vectors of
Chagas' disease in Mexico and Central and South America.
 All are of large size, about an inch or more in length.
 Adults have wings. These bugs live exclusively on the blood of
animals including man and transmit Trypanosoma cruzi, the
causative agent of Chagas' disease.
 These bugs occur in India , but are not incriminated in the
transmission of any disease.
 These bugs frequently attack man and their bites may cause intense
itching, nausea, flushed face, palpitation of the heart, etc.
 Reduviid bugs live in cracks, fissures and other hiding places in walls
and ceilings of human dwellings and in animal habitations and nests.
 Residual spraying with HCH (0.5 g/m2 or dieldrin (1 g/m2) is
commonly used for control of these bugs.

105. Reduviid bugs

106. Ticks
 Ticks are of two kinds:
 hard ticks (ixodidae) and
 soft ticks( argasidae)
Identification Features of Hard Ticks –
 -Body of is oval in shape
 -Body is not distinctly separated into head, thorax and abdomen.
 -Four pairs of legs, and no antennae.
 -The hard ticks are covered on their dorsal surface by a chitinous
shield, called scutum

107. Ticks

108. CONTD.

109. LIFE CYCLE

110. TROMBICULID MITES
 These are spider-like arthropods.
 The important species are Leptotrombidium deliense and L.
akamushi which are vectors of scrub typhus in Asia and
South Pacific.
 # Life Cycle –
 (1) EGG
 (2) LARVA
 (3) NYMPH
 (4) ADULT

111. ITCH MITE
 The itch mite (Sarcoptes scabiei or Acarus scabiei) is an extremely
small,
globular arthropod just visible to the naked eye.
The female parasite burrows into the epidermis where it breeds and
causes the condition known as scabies or itch.
#General description-
-The itch mite ismeasuring 0.4 mm in size and has a body shaped like a tortoise.
- The body shows no demarcation into cephalothorax or abdomen.
-The parasite has two pairs of legs in front, and two pairs
behind.
-The front legs end in long tubular processes known
as suckers.
-The male has suckers on all the legs excepting the third pair, which
distinguishes it from female .

112. ITCH MITE

113. Contd.
Life history-
 (1) EGG
 (2) LARVA
 (3) NYMPH
 (4) ADULT
 #Mode of spread-
 (1) CLOSE CONTACT-Scabies is usually
transmitted by close contact with an infested
person. Scabies is therefore called a familial or
household infection.
 (2) CONTAMINATED CLOTHES

114. Site of lesions
 The disease classically affects the hands and wrist
(63%),
 The extensor aspect of elbows being next (10.9%).
 The axillae, buttocks, lower abdomen, feet and
ankles, palms in
infants are all common sites of infestation.
The disease also affects the breasts in women and the
genitals in men.

115. Diagnosis of scabies
 (1) the patient complains of itching which is worse
at night,
 (2) examination reveals follicular lesions at the
affected site,
 (3) secondary infection leads to crusted papules
and pustules,
 (4) the diagnosis is probable if the other members
of the household are affected,
 (5) confirmation of the diagnosis may be made by
searching for the parasite in the skin debris under
microscope

117. Control of scabies
 (1) BENZYL BENZOATE-Benzyl benzoate(25 per
cent) is an effective sarcopticide. It should be
applied with a paint brush or shaving brush to
every inch of the body below the chin including the
soles of the feet and allowed to dry. In the case of
babies, the head must also be treated, The
application should be repeated after 12 hours,and
after a further 12 hours a bath given and all
underclothes, clothes and sheets changed and
washed. Not more than two applications of benzyl
benzoate should be
given per week as excessive use can cause an
irritant dermatitis.
(2) HCH-0.5 to 1.0 per cent strength of gamma-HCH
(lindane) in coconut oil or any vegetable oil or
vanishing cream is an efficient sarcopticide

118. Contd.
 (3) TETMOSOL : A 5 per cent solution of tetmosol Is also an
efficient sarcopticide.
 (4) SULPHUR OINTMENT : 2.5 to 10 per cent daily for 4 days is
a cheap remedy.

119. Public health importance
 Hard ticks transmit the following diseases :
 (a) Tick typhus (Rocky mountain spotted fever)
 (b) Viral encephalitis (e.g., Russian spring-summer
 encephalitis)
 (c) Viral fevers (e.g., Colorado tick fever)
 (d) Viral haemorrhagic fevers (e.g. KFD in India)
 (e) Tularaemia
 (f) Tick paralysis, and
 (g) Human babesiosis.
 Soft ticks transmit:
 (a) Q fever
 (b) Relapsing fever, and
 (c) KFD.

120. Control of ticks and mites
(1) INSECTICIDAL CONTROL-DDT,chlordane,
dieldrin, lindane, malathion and toxaphane at rates of 1 to
2 lbs per acre give effective
Control.
(2) ENVIRONMENTAL CONTROL-Cracks and
crevices should be filled up.
 # Animal hosts such as wild rodents and dogs should be
reduced.
(3) PROTECTION OF WORKERS-
 # protective clothing
 #The best repellents against ticks and mites are
indalone, diethyltoluamide and benzyl benzoate

121. CYCLOPS
 Cyclops or water flea is a crustacean present
in most collections of fresh water.
 It is a tiny arthropod, not more than 1 mm in
length and just visible to the trained eye.
 It has a pear-shaped semi-transparent body,
a forked tail, 2 pairs
Of antennae, 5 pairs of legs and a small
pigmented eye.
It swims in water with characteristic jerky
movements

122. CONTD.
 (1) Cyclops is the intermediate host of
Dracunculiasis or guinea-worm disease. Man
acquires infestation by drinking water containing
infected cyclops.
2)Cyclops mediates also as one of the intermediate
hosts of fish tape worm, Diphytlobothrium latum
infestation.

123. Control of cyclops
 (1) PHYSICAL-
 (a) Straining
 (b) Boiling
 (2) CHEMICAL-
 (a) Chlorine
 (b) Lime
 (3) BIOLOGICAL

124. INSECTICIDES
 Insecticides are substances which are used to
kill insects.
 The word pesticide is a general term that
includes insecticides, fungicides rodenticides,
herbicides, disinfectants, repellents, and other
chemicals used for the control of pests.

125. CONTD.
 Insecticides are classified into three groups : contact poisons,
stomach poisons and fumigants.
 1)CONTACT POISONS are those which kill insects primarily by
contact e.g., pyrethrum, DDT, HCH, dieldrin.
 2) STOMACH POISONS are those which when ingested cause the
death of the insects, e.g., paris green, sodium fluoride.
 3)FUMIGANTS are those which give off vapours which have a lethal
effect on the insects, e.g., sulphur dioxide.

127. DDT
 DDT (Dichloro-diphenyl-trichloroethane) was first synthesized in
1874,'by a German chemist, Ziedler. It was in 1939, its
insecticidal properties were discovered by the Swiss scientist,
Paul Muller
 #PROPERTIES-DDT is a white amorphous powder with· a mild,
but not unpleasant smell. It is insoluble in water but dissolves in
most organic solvents.
 (b) ACTION : DDT is primarily a contact poison. It acts on the
nervous system of insects.
 (c) APPLICATION : As a residual spray, DDT is applied at a
dosage of 100-200 mg. per square foot area.

128. HCH (BHC)
 HCH is a white or chocolate coloured powder with
a musty smell. It is irritating to the eyes, nose and
skin. In its crude form, it is composed of a number
of isomers of which the gamma isomer is the most
active constituent.
 HCH kills insects by direct contact, but its residual
action is of a shorter duration, up to 3 months or
so as compared with the longer residual action of
DDT. HCH kills insects by its vapour effect also.
 HCH is used like DDT. A dose of 25 to 50 mg of
gamma HCH per sq. ft. is recommended for
residual treatment.

129. Malathion
 Malathion is used in doses of 100-200 mg. per sq. ft.,
every 3 months.
 Because of its low toxicity, malathion has been
recommended as an alternative insecticide to DDT.
 As a low volume (ULV) spray, malathion has been widely
used for killing adult mosquitoes to prevent or interrupt
dengue-haemorrhagic fever, and mosquito-borne
encephalitis epidemics

130. Abate
 Abate (Temephos) is an organophosphorus compound.
 It is a brown viscous liquid, soluble in petroleum
solvents.
 Because of its low toxicity, it has been extensively used

131. Diazinon
 Diazinon is a liquid product. Being
volatile, it kills insects
not only by direct contact, but also by
fumigant action. It has proved effective
in the control of DDT - resistant insects.
At a dosage of 60 to 100 mg per sq.
foot, it has given satisfactory control of
flies and mosquitoes. Diazinon is more
toxic to man than malathion or
fenthion.

132. OTHERS
 Fenthion
 Dichlorovos
 Propoxur
 Pyrethrum
 Pyrethrum and DDT
 Synthetic pyrethroids
 Rotenone
 Mineral oils
 Paris green

133. RODENTS
 Rodents may be classified into two distinct
groups-(1) DOMESTIC RODENTS: The rodents of
chief public health concern are those that live in
close association with man, namely the black rat
(Rattus rattus) and the Norway rat (R. norvegicus)
and the house mouse (Mus musculus).
 (2) WILD RODENTS :The common wild rodents in
Indiaare Tatera indica. In India, Tatera indica has
been found to be the natural reservoir of plague.

134. Rodents and disease
 (1) Bacterial: plague, tularaemia, salmonellosis;
 (2) Viral : Lassa fever, haemorrhagic fever,
encephalitis
 (3) Rickettsial : scrub typhus, murine typhus,
rickettsial pox;
 (4) Parasitic : hymenolepis diminuata,
leishmaniasis,
 amoebiasis, trichinosis, Chagas disease; and
 (5) Others: rat bite fever, leptospirosis,
histoplasmosis, ring worm etc.

135. MODE OF TRANSMISSION
 The mode of transmission may be directly through
rat bite (e.g., rat bite fever); some through
contamination of food or water (e.g.,salmonellosis,
leptospirosis) and some through rat fleas (e.g.,
plague and typhus).

136. Antirodent measures
 1. Sanitation measures
 2. Trapping
 3. Rodenticides-Rodenticides are of
two main types
 single-dose (acute) and multiple-dose
(cumulative).

137. Rodenticides
 An Expert Committee of the WHO grouped the"acute" rodenticides as below:
 1. Those requiring ordinary care
 Red squill
 Norbromide
 Zinc phosphide
 2. Those requiring maximal precaution
 Sodium fluorocetate
 Fluoroacetamide
 Strychnine
 3. Too dangerous for use
 Arsenic trioxide
 Phosphorus
 Thallium sulphate
 ANTU
 Gophacide

138. CONTD.
 The commonly used poisons in this
country are :
 (i) Barium carbonate
 (ii) Zinc phosphide
 The multiple-dose (cumulative) poisons
are : warfarin,
 diphacinone, coumafuryl and pindone. As
anticoagulants, they cause internal
haemorrhage and slow death in 4 to 10
days.

139. ZOO NOSES

140. ZOO NOSES
 The Joint FAO/WHO Expert Committee (1967)
 defined zoonoses as "those diseases and
infections which are naturally
transmitted between vertebrate
animals and man".

141. CONTD.
“.
 Anthrax ----Herbivores, pigs
 Brucellosis----Cattle, sheep, goats,
camels, pigs,dogs, horses, buffaloes
 Ornithosis-----Wild and domestic birds
 Q fever---------Cattle, sheep, goats, wild
animals
 Leptospirosis-----Rodents, mammals
 Tuberculosis-------Cattle, sheep, goats,
pigs, cats, dogs
 Plague---------------Rodents.

142. CONTD.
 B. Viral infections-
 Yellow fever-------------------------Monkeys
 Cowpox--------------------Cattle
 Japanese encephalitis-------------------Wild birds
 Lassa fever ----------------------Multi-mammal rat
 Rabies--------------------------Dog,Fox etc.
 Leishmaniasis-----------------Dogs, cats, swine
 Trypanosomiasis---------------Game animals, cattle
 Schistosomiasis-----------------Rodents
 Taeniasis---------------------------Cattle

143. Control of zoonoses
 (a) Control in animals .
 (b) Control of vehicles of transmission.
 (c) Prevention and treatment in man