EntomologyPart-IV

By

Dr Utpal Sharma

Assistant Professor

Department of Community Medicine

SMIMS, Gangtok, Sikkim

Louse (plural: lice) Common name for members of over 3,000 species of wingless

insects of the order Phthiraptera

Taxonomic classification Phylum:Arthropoda Class:Insecta Subclass:Pterygota Order:Phthiraptera

Three of which are classified as human disease agents. Head louse (Pediculus humanus capitis) Body louse(Pediculus humanus humanus/corporis) Pubic louse(Pthirus pubis)

They are obligate ectoparasites of every avian and mammalian order except for monotremes (the platypus and echidnas), bats, whales, dolphins, porpoises and pangolins.

Biology Color varies from pale beige to dark gray; however, if feeding on

blood, it may become considerably darker.

Female lice are usually more common than the males, and some species are even known to be parthenogenetic.

A louse’s egg is commonly called a nit.

Many lice attach their eggs to their host’s hair with specialized saliva; the saliva/hair bond is very difficult to sever without specialized products.

Lice inhabiting birds, however, may simply leave their eggs in parts of the body inaccessible to preening, such as the interior of feather shafts.

Living lice eggs tend to be pale white. Dead lice eggs are more yellow.

Cont….

Most lice are scavengers, feeding on skin and other debris found on the host’s body, but some species feed on sebaceous secretions and blood.

Most are found on only specific types of animals, and, in some cases, on only a particular part of the body;

Some animals are known to host up to fifteen different species, although one to three is typical for mammals, and two to six for birds.

Lice generally cannot survive for long if removed from their host

Vector BiologyThree types of lice:

Head lice: Pediculus humanus capitis (2-3 mm long)

Body lice: Pediculus humanus humanus (2.3-3.6 mm long)

Pubic lice (crabs): Phthirus pubis (1.1-1.8 mm long)

Morphology of louse Dorsoventrally flattened, elongated body is divuded into head,

thorax and abdomen

Head Smaller than thorax, rectangular-ovoidal and pointed

anteriorly Antennae 5 jointed pair situated anterior to eye Bears 6 pairs of prestomal teeth haustellum. Teeth used to anchor to the skin and everted during sucking. Cutting organ/stylet contains..

– A pair of fused maxillae– Hypophyrynx– Labium placed ventrally supporting hyphyrynx and maxillae

Morphology of louse

Cont…

Thorax Squarish in shape Externally 3 segments not distinct Possess 3 pair of very strong legs,each of the leg 5-

segmented Tarus is unjointed each ends in a hooked claw A thumb like projectio lower part of each tibia helps insect to

grasp hair /fibre with tarsal claw

Abdomen Divided into 9 segments Posterior part narrow and rounded in males In females terminal segment is bilobed Last segment bears a pair of internally curve gonopods

used to grasp hair or fibre

Life cycle Three stages in the life cycle of a louse

Eggs Called “nits”, laid singly or in groups, are firmly attached to the hair or

fibreby cementing substance Small white ovoid bodies, pointed at one end and truncated and pitted at

one end. Female lays upto 300 eggs at the rate of 4-9/day Hatches within 6-9 days under favourable conditions (>22° C)

Larva/ nymph Looks very much like the adult Feeds on host acquires maturity after 3 moulds Stage may take 10 -15 days

Adults Entire cycle takes around 15-17 days from egg to adult Adult lives around 30-50 days

Life cycle of louse

Public health importance

Lice are the vector of the following diseases:

Disease Causative agent

Epidemic typhus Rickettsia prowazeki

Relapsing fever Borrelia recurrentis

Trench fever Rickettsia quintana

Dermatitis Due to scratching and secondary infection

Control of lice Insecticides Head & crab lice Lotion containing 0.5% malathion Should be left for 12-24 hours and than washed Dust containing carbaryl is also effective

Body lice Powder containing 1% of malatthion is treatment of choice Applied to the inner surface of the clothing and socks About 50 gm of insecticidal powder id needed for single person

Personal hygine Daily bath with soap and water Good care of long hair Clothings tobe washed in hotwater and soap and ironed

Summary

Body lice are more serious than pubic or head lice because they can transmit disease.

Diseases associated with body lice are severe!Epidemic typhus (R. prowazekii)

Refugees and those affected by humanitarian crises are particularly at risk.

Insecticide spraying is an important control measure

Bed bugs The name “bed bug” derives from the preferred habitat of the

insect: warm houses and nearby or inside of beds and beddings.

Parasitic insects that feed exclusively on blood.

Feeds on their hosts without being noticed.

Taxonomic classification Phylum:Arthropoda Class:Insecta Order:Hemiptera Suborder:Heteroptera Family:Cimicidae

Family Cimidae consists of 4 subfamilies and 35 species, of these only C. Lectularis and C hemipterus are medically important.

Cimex lectularius, the common bed bug, is the best known, as it prefers to feed on human blood.

Biology Adult bed bugs are light brown to reddish-brown, flattened, oval-

shaped and have no hind wings.

Newly hatched nymphs are translucent, lighter in color and become browner as they moult and reach maturity.

Adults grow to 4–5 millimetres long and 1.5–3 millimetres width.

Nymph of any age, has just consumed a blood meal have bright red translucent abdomen.

In next several hours fading to brown and to opaque black within two days as the insect digests its meal.

Bed bugs, when warm and active their movements are more ant-like.

Like most other true bugs, they emit a characteristic disagreeable odor when crushed due to their stink gland in the metasternum

Morphology Dorso-ventrally flattened,measures 4-6 mm in length and 3

mm in breadth

Body consists of head, thorax and abdomen

Head Short and broad with two small compound eyes 4 jointed antennae, long and slender 3 jointed proscis , it is kept withdrawn on the ventral surface of

the head and thorax when not sucking blood

Thorax Consists of 3 segments,prothorax is the largest one. Has 2 wing like expansions anteriorly The front wings are vestigial and reduced to pad-like

structures, covers the 2nd & 3rd segments The tarus is 3 segmented , ends in 2 small claws

Morphology cont… Abdomen

Has 9 segments Tip of the abdomen is broad in females and narrow in males. Males has reproductive organs on the 8th segment whereas a slit

acts the same on th 4th segments in case of females

Bed bugs have segmented abdomens with microscopic hairs that give them a banded appearance.

Life cycleBed bugs are hemimetabolous, consisting of egg, 5

immature nymphyl stages and a final sexually mature adult stage.

Each nymphal stage requires about 5-7 days

Whole life cycle completed in as little as one to two months

Both male and females sucks blood, the nymphs and adult takes blood intermittantly.

In a single blood meal it may take 7.6 gm of blood

A female with enough food can lay lay three to four eggs each day continually 200-500 eggs in a lifetime

Life cycle cont….

Eggs are white, flask shaped about 1mm long and sticky,seen in cluster.

Laid in the cracks and crevices along with the black tarry stool

Adult can live for 1-1.5 years, with frequent feeding and lives only 3 months without food

They attack man once or twice a week usually during night

Bed bugs can detect prey only upto a distance of 10 cm.

in dark sorroundings and starved conditions they also bite in the daytime.

Life cycle of bed bug

Public health importanceBed bugs can cause a number of health effects,

including skin rashes, psychological effects, and allergic symptoms.

Can be infected by at least 28 human pathogens, but no estabilished evidence of transmission of the pathogen to a human being with possible exception of Hepatitis B.

Experimentally transmitter of kala-azar, oriental sore, leprosy Chaga’s Disease, typhus etc.

Bed bug bites or cimicosis may lead to a range of skin manifestations from no visible effects to prominent blisters.

Cont…

Diagnosis involves both finding bed bugs and the occurrence of compatible symptoms

Treatment involves the elimination of the insect and measures to help with the symptoms until they resolve.

They have been found with methicillin-resistant Staphylococcus aureus (MRSA) and with vancomycin-resistant Enterococcus

Control of bed bugs Control is very difficult, resistant to DDT, BHC, and Deldrien

However following measures to be adopted:

Search to know the extent and location of the infestation Use of soap and warm water to clean the infested articles Insecticides- Pyrethrum sprays (0.2%),addition of pyrithrin (0.1-

0.2%) in insecticidal formulation increases efficacy Other insecticides- Malathion (-2%), Prorpoxur (1%) and

Dichlorovs(0.5%) Dose-Approx. 1 lit/25-5-m2

Precautions Complete air dryiny of beddings before reuse Infant bedding including cradels not to be treated with

insecticides

Sandflies Sandfly is name for any species or genus of flying, biting, blood

sucking Dipteran encountered in sandy areas. Taxonomic classification Phylum:Arthropoda Class:Insecta Order:Diptera Family:Psychodidae Subfamily:Phlebotominae

Phlebotominae subfamily contains more than 600 species.

Important of these are P. argetipes, P. papatasii, P. sergenti and S. punjabensis

Biology

Small insects, light-brown in colour.

Measures 1.5-2.5 mm in length with their wings and bodies densely clothed with hair.

About 30 species recorded in India

Only females, sucks blood (0.1-0.25 ml) for oviposition.

In feeding on blood, they use their mouthparts to bleed the host, then suck up the exposed blood.

Inject biochemicals inhibiting blood clotting and…..……… stimulates mast cells to produce histamine

distending capillary vessels, promoting blood flow

Cannot fly more than 1Km from its breeding place.

Morphology Body divided into head, thorax and abdomen

Head Bears a pairs of long, slender and hairy antennae,palpi and

proboscis.

Thorax Bears a pair of wings and 3 pairs of legs. Wings upright,lanceolate and densly hairy and devoid of scales. Legs, longer than the body and slender

Abdomen Has 10 segments and covered with hair. Males has 3 claspers attached to the posterior end of the

abdomen.

MorphologyPair of wings (Hairy)

Head

Thorax

Abdomen

Antennae

Proboscis Legs (longer than the body)

Life cycle (stages) Female lays eggs in batches of 40-50.

Eggs are laid in dark humid animal burrows, cracks or crevices, or under dead leaves

Eggs torpedo shaped, hatch within 3-7 days

Larva is apodous maggot, with distinct head, 3 thoracic and 10 abdominal segments, eyes absent

There are 4 larval instars, the larval stage lasting a total of 4-6 weeks

The pupa requires 10-15 days for development

Usually lives for 15 days, total life span is about 40 days

Life cycle of sandfly

Adult

Egg

Larva Instar I

Larva Instar IV

Larva Instar III

Larva Instar II

Pupa

Sand fly vs. mosquitoes

Size- smaller than the mosquitoes

Wings- upright,lanceolate in shape and devoid of scales.

Legs- longer than the body

Hairs- Sandfly is a hairy insect

Hopping- Generally hops and do not fly by choice

If they flies, usually don’t fly above 3 feet.

HabitsMostly found in cowsheds and mudhuts

Distributed throughout the seasons, peak density in July to November.

They are troublesome nocturnal pests

Bite is irritating and painful, while their presence is hardly observed.

Infests dwellings during the night and takes shelter in holes, crevices, stables and dark corners.

Females requires bloodmeal every 3rd or 4th day for oviposition.

Public health importance

Sandflies are the vectors of many diseases of public health importance

Diseases transmittedSpecies Diseases carried

Phlebotomus argetipes Kala-azar

Phlebotomus papatasii Sandfly fever

Oriental sore

Phlebotomus sergenti Oriental sore

Sergentomyia punjabensis Sandfly fever

Control of sandflies Control is easy owing to lesser ambulation of the insect

Insecticides Still sensitive to DDT, a dose of 1-2 gm/m2 or 0.25gm/m2 of

Lindane

DDT effective for 1-2 years while for lindane it is 3 months

Spraying should be done in human dwellings, cattle sheds and other places

Sanitation Removal of shrubs and vegetation within 50 yards of dwellings

Filling up of the craks and crevices

Locating cattleshed at a fair distance from human habitation