Objectives1. 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.
Introduction: Arthropods1. 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.
Medical ArthropodArthropods 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
Morphology Bilateral symmetry segmented body and appendages Chitinous exoskeleton Circulatory system is open. Ecdysis and metamorphosis
DevelopmentEmbryonic development Complete in eggsPostembryonic developmentEgg hatch larva molt next stage larvaPupation 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 scorpionEctoparasitism Non-venoomous arthropods: mosquito, flea, lice, mite, and ticksInhalant Dead/decomposing bodies ofallergens insects; cockroach feces, hairs and spines; house dust mites (HDM)
Arthropods as Direct Causes of Injury Injury AgentsIngestant Mites, cockcroach feces, larval stages allergens of small beetlesContact Urticating caterpillar hair, blister allergens beetles, millipedeFood and Water Moth, beetle, mites, chironomids, pests maggotsHouse pests Mosquitoes, flies, cockcroachesMyiasis Fly maggots, feeding on human wounds
Harm for human health Direct harms1. Harassment and sucking blood: mosquito, fly2. Allergy and toxicosis: dust mite-asthma3. Invading tissue: itch mite -scabies maggot-myiasis
Indirect harms (transmit pathogen，cause arbo-diseases)1. Mechanical transmission Arthropods which Arthropods carry pathogens from one person to transmit pathogens Medical the next withoutvector development or multiplication of arthropod pathogens. Diseases transmitted by medical arthropods2. Biological transmission pathogen Arbo-disease sick Pathogens develop or multiply within arthropods, only transmitted to vertebrate hosts.
Types of biological transmission Development: pathogens develop to infective stage in arthropod, no proliferation. larva of filaria mosquito infective stage. Proliferation: pathogens proliferate inarthropod, forms no change. Yersinia pestis flea bacteria embolism
Types of biological transmission Development and proliferation: pathogens develop and proliferate in arthropod. Plasmodium: gametocyte mosquito great number of sporozoite Transmit by eggs: pathogens invade ovary, transferred to filial generation Dengue virus.
Arthropod as a vector1. 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:arthropod can be infected with the pathogen by experiment methods, pathogen can develop into infective stage.4. Natural infection evidences: in epidemic season, the pathogen can be examined from arthropod at the field.the most important evidence to judge the vector.
Control Integrated control is the best measure. Environmental management： Objective: reduce or control the resting/growing field or breeding sites; reduce the arthropod population by environmental modification and sanitation.
Classification Five classes of Arthropod are medical important.1. Insecta (fly, mosquito, bugs, etc crab&shrimp )2. Arachnida (order Acari : ticks. Mites)3. Chilopoda (centipede) millipede4. Diplopoda (millipede) centipede5. Crustacea tick
Physical measures：control or drive away Mosquito net Insect Killer Blue light fly killer Mosquito swatter
Chemical measures：DTT, insecticides Resistance, pollution C4H10O2S2 chem. Formula of DTT
Biological measures： Bacterium: Bacillus thuringiensis infect the larva of mosquito and kill them. Parasitoid parasitize Natural enemy: Dragonfly prey on
Genetic measures：mutation or gene transferObjective: produce infertile males which mate with wild female, the female will not reproduce filial generation.
Acarithe only group that sucks blood and servesas vector. tick: hard ticks, soft ticks mite: Trombiculid mite, Itch mite, Demodicidae mite, Dust mite
Morphological features 1. Body regions consist of cephalothorax and abdomen or further fused to idiosoma2. No antennae, simple eyes.3. No wings, 3(N) /4(A) pairs of legs.
Tick: hard ticks, soft ticks An inflexible, dorsal scutum covers the idiosoma of the male andMouthparts partterminal and visible from abovethe anterior are of the idiosoma of the female The body is usually sooth. hard tick (Ixodes
The body is often wrinkled.Soft tick are leathery and lack the scutum ;Mouthparts are ventral and not visible from above Female and male have the similar appearance. Soft tick (Ornithodorus persicus)
Life cycleSoft ticks have a number of nymphal instars(3 or Hard ticks only lay eggs once.more), The female lay eggs a few times.
EcologyHard ticks:suck in dayfeed on the host for a few daysresting sites: forest, woods, grassland, pasturageSoft ticks:suck at nightfeed on the host from minutes to one hourresting sites: locate at the host’s nests and hovel.
Harm to humansDirect injures1. Irritation: sting, secondary infection, allergy2. Tick paralysis : paralysis of the motor nerves --- cannot walk or stand, has difficulty in speaking, swallowing and breathing.
Harm to humansTransmission of diseases1. Tick-borne encephalitis/forest encephalitis Xinjiang hemorrhagic fever2. Tick-borne relapsing fever Lyme disease3. Q fever and tick-borne typhus
Control1. Environmental management: clean the stalls of livestock, house and deal with mouse holes, etc.2. Chemical measure: acaricides3. Personal protection: protect body away from ticks.
Morphology 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.
Egg Life cycleDeutovum LarvaNymphochrysalis NymphImagochrysalis Adult
Ecology All chiggers are parasitic. Low host specificity.
Harm to humans Leptotrombidium deliensis Leptotrombidium scutellaremain vector in the south areas main vector in North China.
Chigger dermatitisResult from a reaction of the host to thesalivary secretion of mites. Scab： 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 tsutsugamushi Symptoms: prostration, headache, fever, body rash and central nervous system abnormalities. Epidemic hemorrhagic fever is suspected of being transmitted by chiggers.
Diagnosis A history of having recently been in a grassy or forest edge area. Fever, itching papules, scab. Prevention and control Environmental management: eradication of wild weed and control of rats and mice. Chemical measure: DTT Personal protection: tick repellents, clothing tied tightly at the ankles and wrists.
Itch mite Sarcoptes scabiei parasitizes on humans, which can cause scabies.
Morphology 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 .
Life cycleEgg larva protonymph tritonymph adult The female burrows into the skin and lays eggs in Larva - 3 pairs of legs a sinuous tunnel ). of legs. Nymphs - 4 pairs
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 skinreactions, such as itching and allergic reactions.
The hypersensitivitymay result from themite excretions. Secondary bacterialinfections may alsooccur, probably as aresult of scratching.
Diagnosis1. Symptoms:sinuous tracks in the skin, inflammation, itching;2. Find the mites in the skin.Prevention and control 1. All clothing and bedding should belaundered. 2. 10% Brimstone ointment
Demodicidae mite 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
Life cycle: 3 to 5 weeks Egg larva protonymph nymph adult: female lives more than 4 months
Diagnosis Squeeze skin and examine the mites inexudates under a microscope.Prevention and control 10% Brimstone ointment
Dust MiteMorphology: white to a light tan tiny, oval shaped covered with fine striations
Dust mites are members of the PhylumArthropoda, Group Arachnida and Order Acari.
Dermatophagoides pteronyssinus Dermatophagoides farinae and Euroglyphus maynei are responsible for allergy. D. pteronyssinus (Der p)D. Farinae (Der f)
Development and metamorphosis Developmental stages egg — larva—（pupa）— adult Metamorphosis From hatch of larva to adult, there are wide differences in the morphology, physiological function and living habits etc.
Complete metamorphosis: mosquito, fly, flea Egg larvae Pupa Adult There is pupa stage in their life cycle. The larvae and adult have difference in morphology and life habit.
Incomplete metamorphosis: louse, bug, cockroach Larvae Egg Adult (nymph) 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.
MOSQUITO Mosquito belongs to Class Insecta, Order Diptera, Family Culicidae. There are more than 3300 species of mosquitoesbelong to 38 genera.
MorphologyHead Piercing and sucking mouthparts. Slender proboscisQuestions: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?
AntennaeMale: circular hairs Female：circular hairsare long and dense are short and sparse
Labrum - 1 Mandibles - 2 Hypopharynx - 1 Proboscis Maxilla - 2 Labium - 1 The male lack ofmandibles and maxillas
Life cycle Complete metamorphosis Water Larvae Pup Eg Adult (4 instars) a gImportant vectors: limited in Anopheles, Culex and Aedes
Life cycle Egg Culex: :Olive-shaped, laid single onand float onAnopheles: Boat-shaped, laid They are laid stuckof Aedes Cylindrical, no float. single the bottomthe water in “egg’s rafts. together surface. waterAnopheles Culex Aedes
Ecology Breeding habit Five types of breeding site: Paddy fields Slowly flow water Jungle areas Dirty water Container water
Paddyfield type Anopheles sinensis Anopheles anthrophagusThe most important vectors of malaria and Brugia malayi Culex tritaeniorhynchusThe most important vectors ofepidemic B encephalitis.
Slow flow type Stream and irrigation, clean and flow slowly water. Anopheles minimusThe 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.
Mosquito and diseases Direct harmBiting by mosquitoes- irritation or allergicreaction.
As vectors, mosquitoes can transmit lots of arbo-diseases.Arbo-disease Mosquito Epidemic area1.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 Hainan2. Japanese B Culex tritaeniorhynchus Paddy fieldencephalitis3. Falariasis Culex pipiens pallens As a vector of Filariasis C.p. quinquefasciantus bancrofti in North areas of Yangtse river Anopheles sinensis As a vector of filariasis A. anthropophagus malayi4. Dengue fever Aedes aegypti Tropical areas A.albopicutus In China: Hainan, Guangdong etc
Fly Order Diptera. The medical important species: Muscidae, Calliphoridae, Sarcophagidae, Oestrodae
Morphology mouthparts Piercing and sucking mouthpart. Tsetse fly LabellumLapping mouthparts of housefly
ThoraxEach leg terminates in a pair of claws and a pair ofpulvilli claw pulvilli
Life cycle Complete metamorphosis Larvae (4 instars)
Morphology and habits whichrelated to disease transmissionShort legs and big abdomen, the whole body bear hairs;Lapping mouthparts.Interdigital pod is supplied with glandular hairs, it alsocan secrete mucusFlies have dirt habits of feeding indiscriminately on bothexcreta and foods.Flies excrete and regurgitate their partially digested mealsover food.
Fly and DiseasesMechanical transmission: Cholera, Typhoid fever, Bacillary dysentery, Amebic dysentery, HelminthiasisBiological transmission:African trypanosomiasisBloodsucking flies：tsetse fliesMyiasis :Caused by the parasitism offly larva.
Sandfly Order Diptera , Psychodidae Medical important: Phlebotomus chinensis Ph. c. longiductusVector of Leishmaniasis.
Morphology Tiny, dark, hairy body Head: large black eyes, short suckingmouthparts, long filiform antennae Thorax: humpback erect V shaped position of the wings at rest.
Life cycle Complete metamorphosis, 6-9w The eggs turn dark after being laid and have sculpted surface. Egg Larva(4 instars) Pupae are naked.Adult Pupa
Ecology 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 disease Vector of LeishmaniasisLeishmaniasis The adult sandfly is the only stage in transmission sandfly fever Bartonellosis Sucking blood
Flea Ecto-parasite. Morphology： Brown-yellow color, Body is covered with bristle
EggAdult Flea Life cycle Complete metamorphosisPupa Larva
Harm to humans 1. Irritation. 2. Parasitism (tungiasis) 3. Transmission of diseases a.) Plague: pathogen-Yersinia pestis b.) Hymenolepis diminuta c.) Dipylidium caninum
A flea (Xenopsy cheopis) taking a blood meal on ahuman subject. Note that the flea lifts itself almostvertically upward during the act of feeding.