1. Medical Entomology

2. Introduction
Arthropod borne diseases constitute a major health problem in India, accounting for about 50% of total deaths in the country.

3. Definition
A study of the arthropods of medical importance is known as medical entomology.

4. Classification Class: INSECTA Class: ARACHINIDA Class: CRUSTACEA
1. Mosquitoes: Anopheles Ticks: Hard ticks Cyclops
Culex Soft ticks
Aedes
Mansonoides Mites: Trombiculid mite
2. Flies: House flies Itch mite
Sandflies
Tse Tse flies
Black flies
3. Human Lice: Head & body lice
Crab lice
4. Fleas: Rat fleas
Sand fleas
5. Bugs: Bed bugs
Reduvid bugs

5. Distinctive characteristics
Insecta
Arachnida
Crustacea 1
Body division
Head, thorax & abdomen
Cephalo thorax & abdomen 2
Legs
3 pairs
4 pairs
5 pairs 3
Antennae
1 pair
None
2 pairs 4
Wings
1 or 2 pairs, 5
Adult Habitat
Terrestrial
Aquatic

6. Arthropod borne diseases
DISEASE TRANSMITTED
1.Mosquitoes: Anopheles:
Culex:
Aedes:
Mansonoides:
Malaria
Filaria
Bancroftian filariasis
Japanese encephalitis
West Nile Fever
Viral Arthritis (Epidemic/ polyarthritis)
Yellow fever (Not in India)
Dengue
Dengue Haemorrhagic fever
Chikungunya fever
Chikungunya haemorrhagic fever
Rift Valley fever
Filaria (Not in India)
Malayan(Brugian) Filariasis
2.House flies
Bacterial: Typhoid
Diarrhoea
Paratyphoid
Dysentries
Viral: Polio Myelitis
Viral conjunctivitis
Parasitic: Amoebiasis
Helminthic Infestations

7. Arthropod borne diseases (Cont.)
ARTHROPODS
DISEASES TRANSMITTED
Sand fly Kala azar,
Oriental sore
4 Tse Tse fly Sleeping sickness
5 Black fly Onchocerciasis
Louse Epidemic typhus
Relapsing fever
Trench Fever
Pediculosis
Rat flea Bubonic plague
Endemic typhus, etc.
8 Reduviid bug Chagas disease
Tick: Hard Ticks: Tick Typhus
Hemorrhagic fever
Relapsing fever etc.
Soft Ticks: KFD
Q Fever
Mite Scrub typhus
Scabies
Cyclops Guinea worm disease
Fish tape worm

8. Modes of transmission 1. Direct contact:
Arthropods are directly transmitted from man to man through close physical contact
Ex. Pediculosis, Scabies
2. Mechanical transmission:
The disease agent is just mechanically carried by the Arthropod
Ex. Typhoid, Cholera, Dysentery etc. by houseflies

9. Contd… 3. Biological transmission:
Propagative: The disease agent multiplies in number in the body of arthropod without under going developmental change
Ex. Plague bacilli in rat fleas
Cyclo propagative: The disease agent undergoes both developmental change and multiplies in number
Ex. Malaria parasite in Anopheles

10. Cyclo developmental: The disease agent undergoes only developmental change (no multiplication)
Ex. Filaria larva in culex and Guinea worm embryo in cyclops

11. Trans ovarian transmission:
The disease agent is passed onto the next generation through the eggs of the insect.
Ex. Scrub typhus in thrombuculid mite
Trans stadial transmission:
The disease agent is passed from one stage of life cycle to another and then transmit the disease to man.
Ex. Typhoid in housefly

12. General principles of arthropod control
Protective measures:
Physical barriers: Mosquito nets, screening of building against houseflies etc.
Chemical barriers: Application of repellent cream to body and clothing. Ex. Use of odomas against mosquitoes

13. Aggressive Measures
Source Reduction (Environmental manipulation): Ensuring efficient drainage of waste water collection (to prevent mosquito breeding) and quick and effective removal of garbage to prevent fly breeding.

14. 2. Mechanical control – Use of sticky paper bait for houseflies.
3. Chemical control – By use of insecticides which are classified as Larvicides: against Larvae.
Imagicides: against adults.

15. They are also classified as:
Stomach poisons: Eg. Paris green for anopheles larva and Baigon bait for cockroaches.
Asphyxiants: Eg. Oiling against anopheles larva, Fumigants (gases) like HCN, Se2 in warehouses.

16. Contact insecticides Space sprays (knock down agents) e.g. Pyrethrum
Residual sprays
Chlorinated compounds e.g. DDT
Organophosphorous compounds e.g. Parathion, Malathion, etc.
Carbamates e.g. Carbaryl, etc.

17. 4. Biological Control – e. g
4. Biological Control – e.g. use of Gambusia and Guppy fishes to eat anopheles larvae
5. Genetic Control – Releasing sterilized male insects in such numbers that they compete with the wild male insects to fertilize the wild female insects and thus eventually reduce the insect population. E.g. use of (irradiated) sterile male Culex in control of filariasis.

18. Questions What is a Vector? What is infestation?
Enumerate the blood sucking insects.
Enumerate the winged and wingless insects.
What is a definitive host and an intermediate host?
What is extrinsic incubation period?
What is trans-ovarian and trans-stadial transmission?

19. Mosquitoes
In India, mosquitoes constitute the most important group of insects of public health importance. A study of them is done under the following heads:
1. Structure and life history in brief.
2. Differentiation of mosquitoes.
3. Outline of mosquito-borne diseases.
4. Mosquito control measures.
5. Methods of collection and identification.

20. Structure and Life History
Morphology: The body of a mosquito is divided into head, thorax and abdomen.
Head: semiglobular, bears a pair of compound eyes, a pair of antenna (bushy in males), a pair of palpi and a central piercile proboscis.
Thorax: round, has a pair of wings dorsally and 3 pairs of legs ventrally.
Abdomen: long and narrow, 10 segments, the last 2 fused to form genitals.

21. Life History:
-Has 4 stages – egg, larva, pupa and adult.
-The eggs are laid only in water and hence presence of water is essential for the existence of all mosquitoes.
- The metamorphosis is complete, the egg and pupal stages are the resting stages while the alternating larval and adult stages are highly active.

22. The Life Cycle:
- Normally of about 2 weeks duration (Egg: 1-3 days, Larva: 7-10 days, Pupa: 1-3 days. Adult life span about 2 weeks-1 month).
- Only the females are blood sucking and males live on plant juices.
- Normally the mosquitoes (except Aedes) have a flight range of ½ to 1 mile and this is an important factor which determines the extent of the area to be included under mosquito-borne disease control operation.

23. Differentiation of Mosquitoes
Tribe
Genus
Important Species
Area of Distribution
Anophelini
Anopheles
Culicifacies
Philippinensis
Fluviatilis minimus
Sundaicus
Stephensi
Plains
Foothills
Coastal areas
Culicini
Culex
Aedes
Mansonoides
Fatigans
Tritaniorrhynchus
Aegypti
Annulifera
Uniformis

24. Anopheles Vs. Culex Stage of Life Anopheles Culex Egg Boat shaped
Laid singly
Have lateral floats
In fresh water
Oval
Laid in rafts
Without lateral floats
Usually in still dirty water
Larva
Lies horizontally with surface of water
No siphon tube
Has palmate hairs on abdomen
Lies at an angle with the surface of water
Siphon tube +
No palmate hairs
Pupa
- Breathing trumpet (siphon tube)
- Short and broad (funnel shaped)
- Long and narrow (trumpet shaped)
Adult
Body: at an angle with surface on which it rests
Wings: usually spotted
Palpi of male: club shaped
Palpi of female: as long as proboscis
More or less parallel with the surface on which it rests
Non-spotted
Not club shaped
Shorter than proboscis

26. Outline of Mosquito-Borne Diseases
Disease transmitted
Extrinsic Incubation Period
Mode of Transmission
Causative Agent
Reservoir of the Agent
Anopheles
Malaria
Not less than days
Bite of infective female mosquito
Plasmodium: vivax, falciparum, malariae & ovale
Man suffering from Malaria
Culex
fatigans
Urban filariasis
10-14 days
Deposition of infective larva at the site of bite by female mosquito
Wuchereria bancrofti
Man harbouring microfilaria
tritaeniorrh- ynchus
Japanese encephalitis
Some short time after the bite of infected pig
Bite of infected female mosquito
J.E. virus
Infected pig
Aedes
aegypti
Yellow fever
4-8 days
Virus
Infected man
Dengue fever
14 days
- do -
Haemorrhagic fever
Mansonoides
Rural filariasis
Deposition of infective larva on the site of bite by female mosquito
Brugia malayi

27. Mosquito Control Measures
Protective (Defensive) Measures:
Use of mosquito nets: The number of holes/sq. inch is 150
Screening of buildings with wire mesh having 16 meshes/inch
Use of chemical repellents like deet (diethyl toluamide), dimethylphthalate, etc.

28. Aggressive Measures: Anti-larval measures: Environmental Control:
It involves chiefly the water management. If Anopheles are a problem, their breeding places should be abolished by proper methods like filling and drainage.
If Culex are a problem, the waste water collected to be suitably drained.
In case of Aedes, the artificial collection of water in containers, etc. to be eliminated and prevented.
For Mansonia, the aquatic plants should be destroyed and further growth checked.

29. The commonly used larvicides are:
Chemical Control:
The commonly used larvicides are:
Mineral oil (Malariol) acting as asphyxiant applied at the rate of litres/hectare;
Paris green (copper acetoarsenite) acting as a stomach poison is applied as a 2% dust at 1 kg/hectacre;
Synthetic insecticides baytex (Fenthion) 1000 applies as emulsion at litres/hectare
Biological Control: By use of larvae eating (larvivorous) Gambusia and guppy fishes in control of Anopheles

30. Anti-adult measures:
Insecticides: As space sprays (knock-down agents) – use of Pyrethrum extract (1 oz/1000 cu.ft. space); ULV (ultra low volume) fogging of malathion or fenthion in outdoors in control of Aedes (a day biter). Residual sprays for indoors, lindane (0.5 g/m2), DDT (1 or 2 g/m2), malathion (1 g/m2), etc.
Genetic Control: Sterile males release technique (Culex fatigans control) and other approaches like use of insect growth regulators, chemosterilants, etc.

31. Methods of Mosquito Collection and Identification
For Larva:
- A laddle (long-handled spoon) of 3.5” diameter is taken and dips are made along the edges of breeding water source.
-At least 5 dips are taken in each breeding place. The number of larvae/dip are counted and identified (using dissecting microscope) and the average number of the five dips is taken as Larval Density, an indicator of magnitude of mosquito breeding in the area.

32. For Adult:
The most commonly occurring adult Culex and Anopheles mosquitoes rest in the day in darkness on damp walls and corners of the room.
They are collected by using a suction tube – a glass tube of 9” size is taken.
A gauze piece is tied on the one end and connected to a rubber tube. The other end is kept open to suck in the mosquitoes.
The adult mosquitoes are caught with the help of this sucking tube from the dark corners of the living rooms, cattle sheds, etc., by using torch light in the early hours of the morning.

33. The mosquitoes so collected are transferred to a test tube which is subsequently closed with a cotton plug.
The mosquitoes collected are killed by vigorous shaking of test tube. The total time of collection per person is noted.
The mosquitoes collected are counted and subsequently identified with a hand lens or dissecting microscopes.
The total number of mosquitoes collected per person per hour is calculated and expressed as Man Hour Density (MHD). The mosquito catching is done for 2-3 days and the average is taken for better reliability of the result. The MHD of mosquito indicates the magnitude of mosquito menace in the area.

34. Questions
Draw a neat diagram of Life History of Anopheles, Aedes and Mansonoides mosquitoes.
Draw a simple diagram of the mouth parts of Anopheles and Culex mosquitoes and label the parts.
Define the terms – Esophagus, Exophilic, Endophagus, Endophilic, Zoophilic and Anthrophilic.
Describe the Aedes aegypti indices.
5 persons collected 250 mosquitoes in a house in 5 hours. What is the MHD?
Mosquito larvae collection was done around KIMS hostel by using a ladle and the number of larvae collected per dip at 2 places was as follows:
1st place – 5, 6, 3, 3, 8
2nd place – 2, 4, 6, 3, 0
Calculate the larval density.

35. Flies
Non-Biting: Housefly
Biting:
Sandfly
Tsetse Fly
Blackfly

36. Housefly (Musca domestica)
The presence of housefly is an index of poor sanitation.
Structure:
-The body is divided into head, thorax and abdomen, and it has 3 pairs of legs and 1 pair of wings.
-The legs and body are covered with numerous short and stiff hairs, called the tenent hairs, which contain a sticky substance.
-Each leg has a pair of foot pads which help the fly to walk on smooth surfaces.

40. Life History
The female lays eggs in moist decaying organic matter like human & animal excreta, manure heaps & garbage.
The eggs are white, 1 mm size and just visible to naked eye (resembling polished rice grain).
The eggs hatch larvae (maggots) which are creamy white, segmented & footless, active and eat voraciously & grow up to 1 cm. They resent light and bury themselves under manure heaps.
When about to pupate, they migrate to outer dry regions. The pupa measures ½ cm and is dark brown and barrel-shaped.
From the pupa, adult fly comes out and the life cycle is completed in 1-3 weeks.

41. Mode of Disease Transmission: They carry the pathogens (mechanically) on their feet and hairy legs. In addition, the flies frequently vomit (vomit drop) and defecate which also contain ingested pathogens in viable state.

42. Diseases Transmitted:
Bacterial: Typhoid & Paratyphoid, Cholera, Bacillary dysentery, Gastroenteritis, Yaws, Anthrax
Viral: Trachoma, Viral conjunctivitis, Poliomyelitis, Infective hepatitis
Parasitic – Amoebiasis, Giardiasis, Ascariasis

43. Fly Control Measures:
Environmental control: Safe and sanitary disposal of: human excreta (sanitary latrines) & animal excreta (manure pits with earth cover or by composting); Garbage & refuse (refuse bins with tight lids, composting, etc.). A clean house with a clean surrounding is the best solution.

44. Protective measures: Use of fly-proof meshes (14/inch) for windows and even doors (provided with springs to keep always closed)
Mechanical control: By use of sticky fly papers, fly traps, etc.
Chemical control:
Larvicides: Use of DDT, 0.5% Diazinon, etc. for fly breeding sources
Imagicides: Use of baits (Baigon-2% propuxur) and occasionally space sprays (Pyrethrum/Malathion)

45. Lastly a “Fly Consciousness” should be created among people through Health Education and only with the active cooperation of the people the fly menace can be controlled.

46. Sandfly (Phlebotomus)
These are slightly smaller than mosquitoes, light brown-colored, hairy, winged insects with slender long 3 pairs of legs.
The wings are held at 45° to body and these insects (though winged) only jump (hop) short distances.
They mostly breed in cattle sheds, stables and poultries and are within 50 yards from their breeding place.
They are nocturnal biters (only female bite) and during daytime hide in cracks & crevices of walls dark nook corners of cattle sheds, poultry, bathroom, etc.
The life cycle consists of egg, larva, pupa and adult and this is usually complete in 2-4 weeks, mostly in cattle sheds and poultries.

51. Diseases Transmitted Sandfly Species Disease Agent P. argentipes
Kala-azar
Leishmania donovani
P. sergenti
Oriental sore
Leishmania tropica
P. punjabensis
Sandfly fever
Virus
P. papatasi

52. Control Measures
By locating cattle sheds, poultries and stables 50 yards away from house
By tight cement plastering of cracks and crevices in the walls & floors
By use of insecticides like DDT spraying (1-2 g/sq. m.) of cattle sheds and other resting places
Use of insect repellants
Sandfly net: 45 mesh/inch may be used to protect against bite

53. Tsetse Flies (Glossinae)
These are blood sucking insects found in Africa and attack man and animals during daytime.
Tsetse flies are vectors of Trypanosomiasis or sleeping sickness, affecting man, domestic animals and wild game.
They breed in woodland vegetation and females give birth to larvae (no egg laying).
Control measures include aerial spraying of insecticides of large areas for woodland vegetation.

55. Blackflies (Simulidae)
These are vectors of Onchocerciasis in Africa and Central and South America.
They breed under submerged stones and weeds in running streams.
As they have a flight range of up to 100 miles, the control measure is aimed at aquatic breeding source through aerial spraying of insecticides.

56. Questions Draw a neat diagram of Life History of Housefly.
Draw a neat diagram of adult Sandfly and label the parts.

57. Lice The Lice which infest man (pediculosis) are:
Head Louse: Pediculus capitis
Body Louse: Pediculus corporis
Pubic Louse: Phthirus pubis
Pediculosis is seen in low socioeconomic people living in poor hygienic conditions, where people are crowded in tenements, prisons, refugee camps and barracks and the spread occurs rapidly through close physical contact and through fomites (combs, clothes, bedding, etc.).

59. Head & Body Lice
They differ very little in structure except in their habitat.
Morphology:
-The body is flattened dorso-ventrally and the head has a pair of 5 jointed antennae.
-The thorax has 3 pairs of legs with strong terminal claws which help to cling to the clothing.
-The last abdominal segment is pointed in males and bilobed in females.

60. Life History
The eggs (Nits) are glued to individual hairs near the root (head lice)/glued to the cloth especially along seams and in folds (body lice). The next is a two-stage Nymph which resembles adult except in size. The life cycle is completed in 15 days-1 month.

62. Pubic (Crab) Lice Are normally found in the hair of pubic region.
Pubic louse has a small square body, head impacted on thorax and first pair of les being smaller than the other two.
Pubic louse infestation is considered under sexually transmitted diseases (STD).

65. Louse-Borne Diseases
Both nymph and adult are blood sucking ectoparasites of man.
Disease
Agent
Epidemic typhus
Rickettsia prowazeki
Relapsing fever
Borrelia recurrentis (Spirochete)
Trench fever
Rickettsia quintana
Dermatitis (Vagabond’s disease)
Directly caused due to irritation, scratching and secondary infection resulting in rough, thickened and deeply pigmented skin

66. Lice Control Head Lice:
-1% Gammabenzene hexachloride (Pediscab lotion, Emscab lotion) or 0.25% malathion (Licel) to be applied thoroughly over whole scalp, particularly to be rubbed along the roots of hairs.
-After 24 hours, hairs to be washed by shampooing and another application repeated.
-Simultaneously, combs are cleaned in hot water and bed linen washed in soap and hot water.
-To avoid reinfestation, the other members of the family should be examined for the presence of head lice and simultaneously treated if found infested.

67. Body Lice:
-1% Gammabenzene hexachloride lotion is applied all over the body below neck.
- After 24 hours, a bath is taken and another application repeated after 7 days.
-All used clothes, towels and bed linen of the infected individual to be boiled separately.
To avoid reinfestation, the other members of the family should be examined for the presence of head lice and simultaneously treated if found infested.

68. Mass Delousing: By use of hand operated dusters, 50 g of insecticides (DDT 10%) per person and a second application after a week (to kill late hatching lice) will usually eradicate lice. Concurrent boiling or autoclaving and hot ironing of clothes is essential.
A daily bath with soap and water and washing of clothes with soap will prevent lice infestation.

69. Fleas
The fleas of public health importance are Rat fleas (tropical and temperate), Human fleas, cat and dog fleas and sand fleas.
The fleas found on one particular animal host usually do not seek another type of animal host unless compelled by necessity.

71. Rat Fleas (Tropical or Oriental)
These include Xenopsylla cheopis, X. astia and X. braziliensis.
All 3 are found on domestic rats.
Fleas are small, bilaterally compressed, wingless insects with a hard chitinous exoskeleton and covered with backwardly directed strong bristles.
Both sexes are blood sucking and usually jump vertically 6” height.

73. Morphology and Life History
-The head is conical.
-The thorax has 3 pairs of strong legs
and no wings.
- The abdomen in the female flea has a
short stumpy structure called
spermatheca.

74. Life History The eggs are oval, laid in dark palces of rat holes.
The larva is a caterpillar-like maggot and feeds on the bloody excreta of adult fleas.
The larva spins a cocoon and pupates.
The adult comes out of cocoon. The life cycle is completed in 1 month-1 year.
Adult fleas may live for many months in burrows of wild rodents and thus serve as a means of survival for plague bacilli during inter-epizootic periods.

76. Diseases Transmitted Disease Agent Mode of Transmission Bubonic plague
Y. pestis
Bite of infected rat flea
Murine typhus
R. mooseri
H. diminuta (Helminth)
H. diminuta
Accidental ingestion of the infected flea

77. Flea Control
10% DDT (or 5% Malathion) as dust is applied along rat runs
Use of 10% DDT as dust should also be blown into rodent burrows with the help of dust-blowers (30 g/burrow)
Use of repellants by man
Flea control should be followed by rodent control

79. Bugs
Bed Bugs (Cimex):
Small, brown, wingless insects which harbor in cracks and crevices of wooden furnitures, cots, etc., used by man
They are not known to transmit any human diseases. But their bites are irritating and cause sleeplessness.
The control includes spraying 1% Fenitrothion or 2% Fenthion of all sources of breeding and concurrent boiling (steam disinfection) of all clothes.
Reduvid (cone nose) Bugs: are vectors of Chagas disease (Trypanosoma cruzii) in Central and South America.

80. Questions
Draw a neat diagram of an (a) adult head/body louse and (b) male and female adult rat flea.
Describe the flea indices and mention their significance.
What are blocked fleas?

81. Ticks, mites and cyclops
1.Hard ticks (Ixodidae )
2.Soft ticks (Argasidae)
The ticks essentially transmit the viruses, spirochaetes, rickettsiae and bacteriae from wild animal reservoirs (rabbits fouls monkeys, cattles,etc. ) to man.
The domestic animals ( cattles and dogs )may link the wild animal reservoirs to man, if they visit the forests regularly ( eg.cattle for grazing ) by bringing on them the infected ticks to mans residence.

82. The ticks are blood sucking ectoparasites.
The hard ticks feed both day and nightand are invariably found always attached by their mouth parts to a host and they can not withstand starvation.
However, the soft ticks can withstand starvation for several months and are found in the tracks and crevices during day time and emerge in the nights (i.e. nocturnal ) to feed on the host.

83. Morphology
The body is oval and one fused mass, with 4 pairs of legs and no wings and no antennae.
Hard tick
Soft tick 1
Scutum
(hard chitinous shield on dorsum )
In males, covers the entire back
In females, covers only a small portion in the front.
Absent 2
Head
Situated at anterior end
Lies ventrally not seen from above.

87. Life history
Includes eggs which are laid in the cracks and crevices of ground, trees etc.
The larvae are 6 legged and attack a suitable host for blood meal and drop off to moult to Nymph- 8 legged, smaller than adults and moults to grow to an adult.
Normally the life cycle is completed in a few months and the ticks live for about 1-2 years.

90. Tick borne diseases Hard tick Soft tick (ornithodorus moubata)
Haemophysalis spiniegera
Turturis
Kyasanur forest disease
Tick paralysis
Arbovirus
Neurotoxin
Dermacentor andersoni
Tick Typhus (Rocky mountain Spotted Fever)
R.Rickettsi
Soft tick (ornithodorus moubata)
Relapsing fever
Borrelia recurrentis

91. Tick control
Persons frequenting tick infested areas should wear protective clothes impregnated with repellants ( dimethyl phthalate)
After return from work the whole body should be examined for ticks and if found, to be removed gently with a pointed forceps.
insecticide (5% malathion 1% lindane ) as dust or spray of infested areas and simultaneous treatment of domestic animals with the same.

92. Mites
Itch mite
Thrombiculid mite

93. Itch mite Morphology : - It is 0.5mm in size and is just visible to
naked eye.
- The body is tortoise shaped with two pairs of
legs-anteriorly and 2 pairs posteriorly.

97. Life history
The pregnant itch mite burrows into the horny layer of the skin and unless scratched out remains in her burrow for the rest of her life.
The eggs are laid in the burrow.
The larvae leave the burrow and enter the hair follicles
They moult to form nymph which grow to become adult.

98. Mode of spread: Site of lesions:
Is mostly through close physical contact, though fomites ( bedding also play a role ).
Site of lesions:
The disease most frequently affects the hands and wrists elbows, scrotum,buttocks,auxilla and in women nipples.
In very young children the whole body is affected.

99. Diagnosis : Itching worse at night
Presence of follicular lesions at the affected site
Secondary infection leading to boils and pustules
Usually the other members of the family are also affected
Presence of the parasites in the skin scrapings under microscope.

102. Contral of scabies:
It is essential to treat all members of the affected household simultaneously to prevenrt reinfestation.

103. Treatment
A. 25% benzyl benzoate emulsion –Ascabiol 50ml (for children ) and 125ml (for adults ) (infants –dilute wth 3 parts of water, young children – dilute with 2 parts of water ) or 1% gamma BHC lotion (Emscab -55ml,110ml).
First a bath is taken with hot water and soap with fine scrubbing (to open up the burrows ) then the emulsion is applied on the whole body below the neck and more on the body folds (groin, armpits, fingerwebs etc. ) . In case of infants head also must be treated.

104. The application to be repeated after 12hours and after 12hours a hot water bath taken.All the underclothes , clothes and sheets boiled and washed with soap.
Another application may be repeated after 1 week.

105. B. If the patient is found to have secondary infection, a course of antibiotics is given (if severe injection Strepto-penicillin for 5-7 days ) scabozon 4% sulphur and 15% benzyl benzoate as cream to be applied on the affected areas.
Once the secondary infection is cured application of Ascabiol is advised.
C. Simultaneously for some days Tetmosol soap may be used for bath.

106. Thrombuculid mite
These are spider like arthropods which transmit scrub typhus (transovarian transmission ).
The life cycle includes egg, larvae, nymph and adult.
The larval stage is infective and attacks men.

107. Cyclops
Measures about 1mm. The body is pear shaped, semi transparent and has a small pigmented eye anteriorly.
It has 2 pairs of antennae, 5 pairs of legs and a forked tail.
It swims in water with jerky movements.
Cyclops is the intermediate host of guinea worm disease and fish tape worm (rare in India).

108. Control measures
Straining of water through a piece of fine clean cloth
Boiling of water
Chlorination upto 5ppm followed by dechlorination kills larvae and adult
Use of gambusia and barbal fish which eat Cyclops
Abolition/conversion of step wells into draw wells.

109. Questions
Draw a neat diagram of adult- hard tick (male and female ) and soft tick.
Draw a neat diagram of adult –Sarcoptes and Cyclops.

110. Insecticides Definition :
-An insecticide is a chemical used for killing arthropods.
- A larvicide is an insecticide againist immature stages of arthropods.
- Imagicide (adulticide ) is againist the adult stages of arthropod.

111. Classification Chemical classification:
Group I : Organochlorine compounds – DDT, Gammaxane.
Group II :Organophosphorous compounds - Malathion, Fenthion, Fenitrothion, Parathion.
Group III : Carbamates - Propoxur, Carbaryl

112. According to their mode of action:
Stomach poisons: These must be ingested to kill ( effective againist insects with mouth parts for chewing) the arthropod. These may be
Spread over the natural food as a spray ofr dust ( paris green againist anopheles larvae ) or it may be incorporated in an attractive bait ( 2% carbamate in baigon bait againist houseflies and cockroaches ).

113. Asphyxiants:
1. Fumigants : These are gases which asphyxiate the arthropods. These are used in grain storage bins, warehouses and other enclosed areas where the insects cannot be reached by ordinary sprays or dusts, or where such insecticides may harm the material being infected.
Ex: Use of Hydrocyanic acid ( highly poisonous, to be operated by experienced persons with gas mask ). SO2 and Carbon di sulphide ( highly flammable and explosive ).

114. Oiling:
Ex. Malariol is applied on the water surface which forms a thin layer and kills larvae and pupae of mosquitoes.

115. Control insecticides:
which kill insects primarily by contact.
Knock down agents : these have a rapid paralysing effect . Ex: Pyrethrum.
Residual agents : are placed directly on or some surface upon which the arthropod will walk or rest and where it may retain its toxicity for 3-4 months. Ex: DDT, Malathion, etc. in anopheles control.
Space sprays: insecticidal solutuons which are dispersed as finely atomized droplets by means of a spraying device. Ex. Pyrethrum againist mosquitoes.

116. Contd..
4. Aerosols : a modified space spray where the liquefied gas aerosol consists of a solution of insecticide in dichloro difluoro methane of similar material which forms a gas at ordinary room temperature. Ex.Pyrethrum and DDT against mosquitoes

117. Ultra low volume ( ULV ) fog :
Application of highly concentrated of undiluted insecticides in the fornm of a fog – ( using helicopters or aeroplane ) Ex. Malathion in Aedes Aegypti control.

118. Selective insecticides
1. DDT ( Dichloro-Diphenyl-trifluoroethane )
It is a white e amorphous powder. The technical DDT contains 70-80% Para para isomer which is a active ingredient.
It is a contact nerve poison.
It permeates through the cuticle and causes paralysis of the nervous system.
The commercially available water dispersible DDT powder contains 50% or 75% DDT.

119. Strength of DDT powder
Quantity required in pounds
Gallon of water
%age of suspension
75% 2 3
5.0
50% 1

120. The DDT ifs taken in bucket, the measured quantity of water is slowly added to it and stirred to prepare a solution.
A 5% suspension when sprayed at a rate of 1 gallon/1000 sq.feet gives a dosage of 200mg/1000sq.feet.
As a residual spray it is sprayed indoors on the walls, ceiling etc. and it remains effective for 3 months.
As a 10% dust, DDT is used against lice, fleas and ticks.

121. 2. BHC (Benzene Hexa Chloride )
it is a white or chocolate powder with a musty smell. The technical BHC contains 13-16% of gamma isomer.
Pure BHC containing 99% of gamma isomer is called Lindane.
The commercially available powder contains 50% of the BHC.
It is a residual nerve poison.

122. 3. Malathion
It is the least toxic of all organophosphorous componds and is used as an alternative to DDT in some areas.
Commercially water dispersible powder is available and the same is used in doses of mg per sq.foot
It is also widely used as ULV spray.

123. 4. Pyrethrum It is extracted from the flowers of crysanthemum.
Its active ingredients are pyrethrins/
It is used as a knock down agent and it has no residual action.

124. Malariol
Applied at gallons per acre of water cuts off supply of air to larvae and pupa of mosquitoes by forming a thin film over the surface of water.
However it makes water unsuitable for domestic purpose and fishes may be killed.

125. 6. Paris Green (Copper aceto arsenite )
it is a green crystlline powder.
When sprayed as a 2% dust, at the rate of 1kg of actual paris green per hectare of water , it kills the anopheles larva by acting as a stomach poison.
In this dosage it does not harm fish, man or domestic animals.

126. Application of insecticides
Spraying
Knock down agents : Pyrethrum
Residual sprays : DDT, BHC, malathion
Space sprays : Pyrethrum
Aerosols : Pyrethrum and DDT
ULV fogging : Malathion

127. Dusting
Individuals : 10% DDT in body louse infestation
Rodent burrows, holes : 10% DDT in rodent and rat flea control.
Fumigation
Hydrocyanic acid against rat fleas, bugs,etc.

128. Repellants
A repellent is a chemical applied to the skin or clothing or other places to discourage arthropods from sitting on and attacking an individual.
Creams : Dimethylphthalate against mosquitoes, sand flies, ticks and mites.
Fumes (vapours) : mosquito coils

129. Insecticide resistance
The development of an ability in strain of insects to tolerate doses of toxicants which would prove lethal to the majority of individuals in normal population of the same species.
it may be due to
Genetic factors mutation
Biochemical factors - toxicant is converted to a nontoxicant by body enzymes.

130. Types
Single resistance : against only one insecticide
Double resistance : against two insecticides of one group Ex. DDT and Gammaxane
Cross resistance : against insecticides of two different groups – carbamates and OP compounds.

131. Rodents and their control
In India it is estimated that there are about milion rats, that is about 5-10 rats per person.
Six rats eat grain requirement of one person and spoil it equivalent to consumption of 10 persons.

132. Rodents and disease Disease Agent Vector/ transmission Bacterial
Bubonic plague
Y.Pestis
Rat flea
Food poisoning
Sal. Typhimurium enteritidis
Contamination of food or water by rat dropping
Rat bite fever
Spirillum minus
Bite
Ricketttsial
Murine typhus
r. Mooseri
Scrub typhus
R.Orientalis
Larva of mite
Parasitic
H.Diminita
Ingestion of infected rat flea
Amoebiasis
E.Histolytica
Food contamination by rat dropping

133. Anti rodent measures Sanitary measures
Rat proofing is done by plastering rat burrows and closing drains, screening windows lower part of doors protected with metal plate and doors provided with springs to keep them always closed.
Trapping
Rodenticides: single dose ( acute ) Ex.barium carbonate, zinc phosphide.
Fumigation of burrows : cyonogas

134. Questions Classify and enumerate the insecticides.
Briefly write the disadvantages of wide scale use of insecticides.
Draw a neat diagram of R.rattus and R.norvegicus and tabulate the differences in their characteristics.
What is the role of rodents in the transmission of plague