Medically important Arthropods

Presenter – Dr. Sukumar T K

Arthropods

• Invertebrate animals with jointed legs.• Exoskeleton – chitin.• Segmented bodies.• Bilaterally symmetrical• Tubular alimentary canal with mouth and anus.• Coelom

Medical anthropodology

• Majority of arthropods are not harmful to humans.

• Arthropod related with human health.– Harmful – nuisance, discomfort, bites.– Ectoparasites – live and feed on exterior of host

without transmitting germs.– Mechanical transporters.– Vectors .

• Class Arachnida– Ticks and mites (order Acarina)

• Class Insecta– True flies (order Diptera)– True bugs (order Heteroptera / Hemiptera)– Lice (order Anoplura)– Fleas (order Siphonaptera)

Class

• Insecta– 3 disntict regions– 3 pairs of legs– Wings present– 1 pair of antennae– Segmented abdomen.

• Arachnids– 2 regions– 4 pair of legs– No wings– No antennae– Abdomen usually not

segmented.

Metamorphosis

• The change in form during an insect’s development is called metamorphosis.

• Complete metamorphosis.• Incomplete metamorphosis

Phylum Arthropoda

• Class Crustaceae – cyclops, crabs.

• Medical importance – Cyclops are intermediate hosts of the fish

tapeworm and Dranculus medinensis.

• Spiders, scorpions, ticks and mites.• 4 pair of legs• Pedipalps – aid in chewing• Incomplete metamorphosis

Order Acarina

• Only group in Arachnida that sucks blood and serves as vector.

• Commonly called• Ticks

– Hard tick (family Ixodidae)– Soft tick (Argasidae)

• Mite– Trombiculid mite, itch mite, dust mite

• Medical importance– Tick paralysis– Bite injury– Ixodidae – Borrelia burgdoferi, Babesia microti

and Ehrlichia spp.– Soft tick – vectors of endemic relapsing fever and

Q Fever.

• Soft tick– Body is often wrinkled.– Mouth parts are ventral and not visible.– Female and male – same appearance.

• Hard tick– Body is usually smooth.– An inflexible, dorsal scutum covers the idisoma of

the male and the anterior part of the idisoma of female.

– Mouth parts are terminal and visible from above.

• Soft ticks lay eggs more than once.– feed in night.

• Hard ticks lay eggs only once.– Feed on host for few hrs,

in day.

• Control– Environmental management– Acaricides– Personal protection

• Trombiculid mite– Larvae – reddish or orange, 3 pairs of legs.– Adult – bright red, hairy or granular, 4 pairs of

legs.

• Life cycle

• Chiggers – parasitic with low specificity.• Chigger dermatitis – reaction of host.• Scab – raised, reddened wheal with a

depressed center.• Scrub typhus• Epidemic haemorrhagic fever??

• Diagnosis– Recent h/o being to grassy area– Fever, itching papules, scab

• Prevention– Eradication of wild weed– Control of rats and mice– DDT– Personal protection

• Sarcoptes scabiei– Commonly called itch mite.– Causes scabies– Disc shaped with distinctive sculptured lines– Stubby legs– Male – 4th pair has amlulacra– Female – 4th pair terminate in long setae

• Female burrows in the skin and lays eggs in sinuous tunnel.

• Selects places where skin is thin and wrinkled, between fingers, elbows, feet, etc.

• Children – whole body.

Presentations

Treatment

• Prevention– Aggressive treatment of infested patients and all

close contacts,– Disposal or hot wash-dry sterilization of clothes.– Provision of improved access for personal hygiene

and health care– Aggressive control of outbreaks of zoonotic

scabies with the potential for human transmission

– House dust mite - Dermatophagoides pteronyssinus, Dermatophagoides farinae, Euroglyphus maynei.

– Morphology• White – tan• Tiny oval shaped• Covered with striations

Class Insecta

• Lice– Head louse - Pediculous humanus var capitis

• Pediculosis– Body louse - Pediculoushumanus var carporis

• Epidemic fever, Trench fever, Relapsing fever– Pubic / Crab louse – Pthrius pubis

• Morphology – Pediculous humans– Greyish, wingless, 3pairs of legs.– Abdomen

• Male – V• Female - W

Pediculous humanus capitis

Louse – life cycle

• Therapy – Management of pediculosis capitis includes two

topical or systemic treatments with pediculocides, 7 to 10 days apart.

– Removal of all viable nits by carefully combing wet hair.

• Pthirus pubis– Smaller– Broad body– Large claws on middle

and hind legs.

• Therapy– Management includes initial bathing with soap and

water, followed by two topical or systemic treatments with pediculicides, 7 to 10 days apart

Prevention

• Prevention strategies– Combinations of sanitizing the environment.– Eliminating all human reservoirs of head lice in

households, apartments, housing complexes, classrooms, and schools.

• Common preventive interventions– avoiding contact with potentially contaminated

items – soaking all combs and brushes in isopropyl alcohol

or 2% Lysol solution– sanitizing the household environment by high heat

cycle washing and drying of all bedding, clothing and headgear

• Fleas – Oriental / Tropical rat flea – Xynopsilla cheopis

• Plague, Endemic Typhus, Host of Hymenolipis tapeworm.

– Northern rat flea – Nasopsylla fasciatus• Endemic typhus

– Human flea – Pulex irritans• Skin irritation, Intermediate host of Hymenolepis and

Dipylidium tapeworm larvae.

• Morphology– Brown yellow colour– Body covered with

bristles

Tungiasis

• Bugs– Bed bugs – Cimex lectularius, Cimex hemipterus

• Allergy, secondary bacterial infection.– Reduvid bug – Rhodnius, Triatoma, Pastrongylus

• American trypanosomiasis ( Chaga’s disease)

• Diverse in appearance– Piercing & sucking mouth

parts– When present, 2 pairs of

wings (hind pair reduced)– Incomplete life cycle

• Identification– Small, apricot-coloured & wingless– Circular body & flattened extensions of prothorax behind eyes

• Reduvid bug• Identification

– Large robust bugs = ambush predators of arthropods

– Strong recurved beak for biting• Inject paralytic toxin to subdue

prey• Bite very painful to humans• No species in SA usually bite

mammals• Medical importance

– South American subfamily Triatominae (kissing bugs)

• Feed on human & animal blood• Transmit Chagas’ disease

• Flies– Sandfly – Phlebotomus, Lutzomyia

• Leishmaniasis, Bartonellosis, sandflyfever– Black fly/Buffalo gnats - Simulium

• Onchocercariasis / river blindness– Tsetse fly – Glossina

• African trypanosomiasis– Deer fly/ Yellow fly – Chrysops

• Loiasis, Tularemia– Domestic fly – Musca domestica

Sandfly Tsetse fly

Flies

• Morphology – 1pair of membranous fore wings– Hind wings reduced to form halters– Mouth parts – proboscus / piercing like.

• Larval– No conspicuous head.– Legless– Slender bodies.

• Mosquitoes– Anopheline

• Anopheles culcifacies – Malaria• Clear, stagnant/ sluggishly moving water.• Rest at an angle to the resting surface.

– Culicine• Filarial - Culex fasciatus

– Stagnant, polluted water– Lymphatic filariasis

• J.E - Culex gelidus, Culex tritaeniorhyncus, Culex fuscocephela

– Japanese encephalitis

• Aedes– Aedes aegypti

• Urban vectors.• Man made small collection of clear water.• Dusk and dawn biters

– Aedes albopictus• Rural vectors• Natural collections of clear water

• Dengue, Yellow fever, Chickungunya

• Mansonia– Rural vector– Breeds on the undersurface of water plants– Brugian filariasis, transmits Dirofilaria repens.

• Mosquitoes identification– Long and narrow wings– Anopheles – adults rest with abdomen steep angle

to substrate. Larvae rest horizontally to water surface.

– Culex and Aedes – rest with abdomen at an angle to substrate. Larvae hang at an angle from water surface.

Antennae

Male Female

• Egg– Anopheles boat shaped, single and float on water.– Culex cylindrical, laid together – rafts, no float.– Aedes olive shaped, single and bottom of water.

• Larvae

Anopheles

Culex

Aedes

References

• Meical Parasitology – Ruth Leventhal, Russel F. Cheadle.

• Principles and Practices of Infectious Diseases 7th Edition – Mandell, Douglous, Bennet.

THANK YOU