ArthropodsArthropodsof of

Medical Medical ImportanceImportance

1. To identify the common characteristics of

medical arthropods and its classification.

2. To discuss the mechanisms of transmission

and causation of diseases.

3. To describe the diseases caused or transmitted

by medical arthropods.

4. To implement appropriate prevention,

control, and treatment.

Objectives

1. Segmented body.2. Paired segmented appendages.3. Bilateral symmetry.4. Chitinous exoskeleton.5. Tubular alimentary canal with mouth and anus.6. Open circulatory system, a tubular dorsal blood vessel.7. Body cavity or coelom.8. Nervous system of anterior ganglia and paired nerve

cords.9. Striated muscles in skeletal system.10. Respiration by gills, tracheae, or spiracle.

Introduction: ArthropodsIntroduction: Arthropods

Medical Arthropod Arthropods related with human health.

Medical Arthropodology Morphology, taxonomy, life cycle, ecology, transmission of the diseases, control measures.

Examples: Flea - Plague, Soft tick - Q fever,

Mosquito - Malaria

MorphologyMorphology Bilateral symmetry segmented body and appendages

CChitinous exoskeleton

Circulatory system is open.

Ecdysis and metamorphosis

DevelopmentDevelopment

Embryonic development

Postembryonic development

Complete in eggs

Egg hatch larva molt next stage larva

Pupation pupa emergence adult stage.

Arthropods as Direct Causes of Injury

Injury AgentsEnvenomization

Venomous arthropods: bees, wasps, kissing bugs, ants, caterpillar hairs, centipede bite, spider and scorpion

Ectoparasitism

Non-venoomous arthropods: mosquito, flea, lice, mite, and ticks

Inhalant allergens

Dead/decomposing bodies of insects; cockroach feces, hairs and spines; house dust mites (HDM)

Arthropods as Direct Causes of Injury

Injury AgentsIngestant allergens

Mites, cockcroach feces, larval stages of small beetles

Contact allergens

Urticating caterpillar hair, blister beetles, millipede

Food and Water pests

Moth, beetle, mites, chironomids, maggots

House pests Mosquitoes, flies, cockcroaches

Myiasis Fly maggots, feeding on human wounds

Direct harms

1. Harassment and sucking blood: mosquito, fly

2. Allergy and toxicosis: dust mite-asthma

3. Invading tissue: itch mite -scabies

maggot-myiasis

Harm for human Harm for human healthhealth

sickArbo-disease

Medical arthropod

Indirect harms (transmit pathogen ， cause arbo-diseases)

vector

pathogen

Diseases transmittedby medical arthropods

Arthropods whichtransmit pathogens

1. Mechanical transmission

Arthropods carry pathogens from one person to the next without development or multiplication of pathogens.

2. Biological transmission

Pathogens develop or multiply within arthropods, only transmitted to vertebrate hosts.

Proliferation: pathogens proliferate in arthropod,

forms no change.

Yersinia pestis flea bacteria embolism

Development: pathogens develop to infective

stage in arthropod, no proliferation.

larva of filaria mosquito infective stage.

Types of biological transmission

Transmit by eggs: pathogens invade ovary,

transferred to filial generation

Dengue virus.

Development and proliferation: pathogens

develop and proliferate in arthropod.

Plasmodium: gametocyte mosquito great

number of sporozoite

Types of biological transmission

Arthropod as a vectorArthropod as a vector

1.1. Biological evidences ： closely related with humans: biting or sucking

humans, lapping or contaminating foods.

common species at local area, dense population.

life span is long enough to complete the development or proliferation.

2. Epidemiological evidences ： geographic and seasonal distribution

3. Laboratory evidences:

4. Natural infection evidences:

the most important evidence to judge the

vector.

in epidemic season, the pathogen can be examined from arthropod at the field.

arthropod can be infected with the pathogen by experiment methods, pathogen can develop into infective stage.

Integrated control Integrated control is the is the bestbest measure. measure.

Environmental managementEnvironmental management ：：

ControlControl

Objective: reduce or control the Objective: reduce or control the

resting/growing field or breeding resting/growing field or breeding sites; sites;

reduce the arthropod population reduce the arthropod population by by

environmental modification and environmental modification and

sanitation.sanitation.

1. Insecta (fly, mosquito,

bugs, etc)

2. Arachnida (order

Acari : ticks. Mites)

3. Chilopoda (centipede)

4. Diplopoda (millipede)

5. Crustacea (crabs,

shrimp, etc.)

crab&shrimp

ClassificatiClassificationon Five classes of Arthropod are medical important.

millipedecentipede

tick

Physical measures ： control or drive away

Insect KillerInsect Killer

Mosquito swatterBlue light fly killer

Mosquito net

Chemical measuresChemical measures ：： DTT, insecticidesDTT, insecticides

Resistance, pollutionResistance, pollution

C4H10O2S2 chem. Formula of DTT

Biological measuresBiological measures ：：Bacterium: : Bacillus thuringiensisBacillus thuringiensis

infect the larva of mosquito and kill them. infect the larva of mosquito and kill them.

Parasitoid parasitize Parasitoid parasitize

Dragonfly prey on Dragonfly prey on Natural enemy:

Genetic measuresGenetic measures ：： mutation or gene transfermutation or gene transfer

Objective: produce Objective: produce infertileinfertile malesmales which mate which mate with wild female, the female will not with wild female, the female will not reproduce filial generation. reproduce filial generation.

Arachnida Arachnida

Scorpions Araneae Acari

the only group that sucks blood and

serves as vector.

tick: hard ticks, soft ticks

mite: Trombiculid mite, Itch mite,

Demodicidae mite, Dust

mite

Acari

1. Body regions consist of cephalothorax and abdomen or further fused to idiosoma

2. No antennae, simple eyes.

3. No wings, 3(N) /4(A) pairs of legs.

Morphological features

hard tick (Ixodes persulcatus)

Tick: hard ticks, soft ticks

An inflexible, dorsal scutum covers the idiosoma of the male and the anterior part of the idiosoma of the female Mouthparts are terminal and visible from above The body is usually sooth.

Soft tick (Ornithodorus persicus)

Soft tick are leathery and lack the scutum ; Mouthparts are ventral and not visible from above The body is often wrinkled.

Female and male have the similar appearance.

Life cycleSoft ticks have a number of nymphal instars(3 or more), The female lay eggs a few times. Hard ticks only lay eggs once.

Ecology

Hard ticks: suck in day feed on the host for a few days resting sites: forest, woods, grassland, pasturage

Soft ticks:

suck at night feed on the host from minutes to one hourresting sites: locate at the host’s nests and hovel.

Harm to humans

Direct injures

1. Irritation: sting, secondary infection, allergy

2. Tick paralysis : paralysis of the motor nerves ---

cannot walk or stand, has difficulty in speaking,

swallowing and breathing.

Harm to humans

Transmission of diseases

1. Tick-borne encephalitis/forest encephalitis Xinjiang hemorrhagic fever

2. Tick-borne relapsing fever Lyme disease

3. Q fever and tick-borne typhus

Control

1. Environmental management: clean the stalls of livestock, house and deal with mouse holes, etc.

2. Chemical measure: acaricides

3. Personal protection: protect body away from ticks.

Trombiculid mite

The keys to identify are based on

the larvae(chigger).

Larvae: reddish or orange, 3 pairs

of legs.

Adult: bright red, hairy or

granular, 4 pairs of legs.

Morphology

Egg

Deutovum

Larva

Nymphochrysalis Nymph

Imagochrysalis Adult

Life cycle

Ecology

All chiggers are parasitic.

Low host specificity.

Harm to humans

Leptotrombidium deliensis main vector in the south areas

Leptotrombidium scutellaremain vector in North China.

Chigger dermatitis

Scab ：

Result from a reaction of the host to the salivary secretion of mites.

The inflammatory response gives rise to the raised, reddened wheal with a depressed center characteristic of chigger bite.

Scrub typhus

Caused by: Orientia tsutsugamushi

Rickettsia tsutsugamushiSymptoms: prostration, headache, fever, body rash and central nervous system abnormalities.

Epidemic hemorrhagic fever is suspected of being transmitted by chiggers.

Diagnosis

Prevention and control

A history of having recently been in a grassy or

forest edge area.

Fever, itching papules, scab.

Environmental management: eradication

of wild weed and control of rats and mice. Chemical measure: DTTPersonal protection: tick repellents,

clothing tied tightly at the ankles and wrists.

Itch Itch mite mite

Sarcoptes scabiei parasitizes on

humans, which can cause

scabies.

MorphologyMorphology

Disc-shape, distinctive sculptured lines. Stubby legs.

The anterior two pairs of legs have ambulacra

Female － the 4th pair of legs terminate in long setae .

Male － the 4th pair of legs have ambulacra .

Egg larva protonymph tritonymph adult

Life cycle

Larva - 3 pairs of legs Nymphs - 4 pairs of legs.

The female burrows into the skin and lays eggs in a sinuous tunnel ).

Pathogenesis Selects places where the skin is thin and wrinkled. between fingers, wrists, elbows, feet, etc. Children may be found burrowing on whole body.

The mite can cause more severe skin reactions,

such as itching and allergic reactions.

The hypersensitivity

may result from the

mite excretions.

Secondary bacterial

infections may also

occur, probably as a

result of scratching.

Diagnosis

Prevention and control

1. Symptoms:sinuous tracks in the skin,

inflammation, itching;

2. Find the mites in the skin.

1. All clothing and bedding should be

laundered.

2. 10% Brimstone ointment

Demodicidae Demodicidae mitemite

Human have two species

D. folliculorum - in hair follicles D. brevis - in sebaceous glands

(Demodex folliculorum) (Demodex brevis)

Morphology

Elongate, 4 pairs of stubby legs.

Mouthparts - not apparent; hysterosoma - quite long

Egg

larva

protonymph

nymph

adult: female lives more than 4 months

Life cycle: 3 to 5 weeks

Diagnosis

Prevention and control

Squeeze skin and examine the mites in

exudates under a microscope.

10% Brimstone ointment

Dust MiteDust Mite

Morphology:

white to a light tan

tiny, oval shaped

covered with fine

striations

Dust mites are members of the Phylum Arthropoda, Group Arachnida and Order Acari.

Dermatophagoides pteronyssinus

Dermatophagoides farinae and

Euroglyphus maynei are responsible for

D. pteronyssinus

(Der p)

D. Farinae (Der f)

allergy.

Life cycle

Serological tests: detect the serum antibody,

ELISA, skin test, etc.

Diagnosis

Prevention and control

Immunotherapy.

mosquito

fly

sandfly

flea

louse

cockroach

Insecta

Mouthparts : chewing , sucking , lapping mouthparts

Ecto-morphologyEcto-morphology

Developmental stagesDevelopmental stages

egg — larva— （ pupa ）— adult

MetamorphosisMetamorphosis

From hatch of larva to adult, there are wide differences in the morphology, physiological function and living habits etc.

Development and metamorphosisDevelopment and metamorphosis

Complete metamorphosis: mosquito, fly, flea

Egg larvae Pupa Adult

There is pupa stagepupa stage in their life cycle.

The larvae and adult have difference in morphology and life habit.

Incomplete metamorphosis: louse, bug, cockroach

Egg

There is no pupa stage in life cycle.

The larvae is similar in morphology and life habit with the adult, but the sexual organ still undeveloped.

Larvae(nymph)

Adult

MOSQUITOMOSQUITO

Mosquito belongs to Class Insecta,

Order Diptera, Family Culicidae.

There are more than 3300 species of mosquitoes belong to 38 genera.

Questions:

1. How to distinguish the female mosquitoes from the male?

2. What are the main effect of antennae in finding host?

3. Why don’t the male mosquitoes suck blood?

Head Piercing and sucking mouthparts. Slender proboscis

MorphologyMorphology

Antennae

Female ： circular hairs are short and sparse

Male: circular hairs are long and dense

Labrum - 1

Mandibles - 2

Hypopharynx - 1

Maxilla - 2

Labium - 1

The male lack of mandibles and maxillas

Proboscis

Life cycleLife cycle

Complete metamorphosis

Egg

Larvae (4 instars)

Pupa Adult

Water

Important vectors: limited in Anopheles, Culex and Aedes

Culex: Cylindrical, no float. They are laid stuck together in “egg’s rafts.

Egg

Anopheles Culex Aedes

Life cycleLife cycle

Anopheles: Boat-shaped, laid single and float on the water surface.

Aedes :Olive-shaped, laid single on the bottom of water

Larvae

Siphon (respiratory tube)

Aedes

Culex

Anopheles

Pupa

Comma-shaped.

A pair of respiratory trumpets dorsally.

The nonfeeding pupal stage lasts from 4 to 5

days.

Adult

Anopheles Culex Aedes

EcologyEcology

Breeding habit

Five types of breeding site:

Paddy fields

Slowly flow water

Jungle areas

Dirty water

Container water

Paddyfield type

Anopheles sinensis Anopheles anthrophagus

The most important vectors of malaria and Brugia malayi

Culex tritaeniorhynchus

The most important vectors of epidemic B encephalitis.

Slow flow type

Stream and irrigation, clean and flow slowly water.

Anopheles minimus

The most important vectors of malaria in south mountain areas.

Jungle type

Mountain stream, stone cave

and spring, pond .

Anopheles dirus

The important vector of

malaria in Hainan mountain

area.

Dirty water type

Dirty water pit, sewer, fecal pit. The water is dirty and contains a large amount of humus.

Culex pipiens pallens

C. p. quinquefasciatus

The main vectors of W. bancrofiti

Container type

Water vats, jars, bamboo container, tree hole.

Aedes albopictus

Aedes aegypti The most important vectors of Dengue virus

and Chikungunya virus

Bloodsucking habit

Both male and female mosquitoes take nectar

as source of energy.

Only females take blood after mating for

production of eggs.

Resting habit

After having a blood meal, the female

mosquito find a place for resting.

Endophilic type: rest inside house for blood

digestion and maturation of the ovaries.

Half Endophilic type : rest inside house for a

while, then fly to outdoor.

Exophilic type : feed and rest outside.

Gontrophic cycle: The period from feeding blood to laying eggs.

Physiological age: the times of spending gontrophic cycle.

Activity

Anopheles ： act in the evenings, at night or in

the early morning.

Culex ： feed at night.

Aedes ： feed during the day or early evening.

Overwinter (Hibernation)

No activity and no eating until next spring.

The most common stage of hibernation is adult.

Aedes ： eggs.

Anopheles minimus ： larvae.

In sub-tropic and tropic areas, the average month

temperature is over 10 . So no hibernation.℃

Direct harm

Mosquito and diseasesMosquito and diseases

Biting by mosquitoes - irritation or allergic reaction.

As vectors, mosquitoes can transmit lots of arbo-diseases.

Arbo-disease Mosquito Epidemic area

1.malaria Anopheles sinensis Plain areas

  A. anthropophagus Mountain or hilly areas in South China

  A. minimus Mountain or hilly areas in South China

  A. dirus Jungle areas of Hainan

2. Japanese B encephalitis

Culex tritaeniorhynchus Paddy field

3. Falariasis Culex pipiens pallens C.p. quinquefasciantus

As a vector of Filariasis bancrofti in North areas of Yangtse river

  Anopheles sinensis A. anthropophagus

As a vector of filariasis malayi

4. Dengue fever Aedes aegyptiA.albopicutus

Tropical areasIn China: Hainan, Guangdong etc

FlyFly Order Diptera.

The medical important species:

Muscidae, Calliphoridae,

Sarcophagidae, Oestrodae

MorphologyMorphology

Lapping mouthparts of housefly

Labellum

Piercing and sucking mouthpart. Tsetse fly

mouthparts

Thorax

Each leg terminates in a pair of claws and a pair of pulvilli

claw

pulvilli

Larvae (4 instars)

Life cycle Complete metamorphosis

Morphology and habits which related to disease transmission

Short legs and big abdomen, the whole body bear hairs; Lapping mouthparts.

Interdigital pod is supplied with glandular hairs, it also can secrete mucus

Flies excrete and regurgitate their partially digested meals over food.

Flies have dirt habits of feeding indiscriminately on both excreta and foods.

Fly and Diseases

Mechanical transmission:Cholera, Typhoid fever, Bacillary dysentery,

Amebic dysentery, Helminthiasis

Biological transmission:African trypanosomiasis

Bloodsucking flies ： tsetse flies

Myiasis :Caused by the parasitism of fly larva.

Order Diptera , Psychodidae

Medical important:

Phlebotomus chinensis

Ph. c. longiductus

Vector of Leishmaniasis.

Sandfly

MorphologyMorphology

Tiny, dark, hairy body Head: large black eyes, short sucking

mouthparts,

long filiform antennae Thorax: humpback erect V shaped

position of the wings at rest.

Life cycleLife cycle Complete metamorphosis, 6-9w

Egg

Larva(4 instars)

PupaAdult

The eggs turn dark after being laid and have sculpted surface.

Pupae are naked.

EcologyEcology

Distribute in North areas of Yangtse River.

Both sexes feed on plant juice and sugary

secretions. Only the females suck blood.

One generation a year. The population density

peak occurs in summer.

The stage of hibernation: larva.

Sandflies and diseaseSandflies and disease

Leishmaniasis The adult sandfly is the only stage in transmission

Bartonellosis

sandfly fever

Vector of Leishmaniasis

Sucking bloodSucking blood

FleFlea a

Ecto-parasite.

Morphology ：

Brown-yellow color,

Body is covered with

bristle

FleaLife cycleLife cycle

Complete metamorphosis

Adult Egg

LarvaPupa

1. Irritation.

2. Parasitism (tungiasis)

3. Transmission of diseases

a.) Plague: pathogen-Yersinia pestis

b.) Hymenolepis diminuta

c.) Dipylidium caninum

Harm to humansHarm to humans

A flea (Xenopsy cheopis) taking a blood meal on a human subject. Note that the flea lifts itself almost vertically upward during the act of feeding.

Tungiasis

Permanent ectoparasite. The parasitic lice of humans :

Pediculus humanus : P. humanus capitis (2 subspecies) P. h. humanus

Pthirus pubis

LouseLouse

Pediculus humanus

Color: grayish,

Wingless, 3 pairs of

legs.

Abdomen: male“V” ， female“W”.

Morphology Morphology

Smaller than Pediculus,

2 mm in length.

Body is broad with very

large claws on the middle

and hind legs.

Pthirus pubis

Life cycleLife cycle

Egg Nymph adult

Incomplete metamorphosis

Oval, white and firmly attached to the hairs or to the clothes

Resemble a small adult; 3 instars

Louse

Harms to humans Harms to humans

Pediculosis

Symptoms: cutaneous irritation, loss of sleep

and psychological depression.

Transmission of diseases

Epidemic typhus

Louse-borne relapsing fever

Trench fever

Cockroach

Periplaneta americana Blattella germanica

Resting and activity sites

moist and warm places

Incomplete metamorphosis

life cycle

Medical importance

carry various pathogens Mechanical vectors

Intermediate host of hookworm larvae

Cockroach allergens - children asthma