Medical Arthropod Associate Prof. Dr. Yulin Wang Email:[email protected] Tel: +86 411 86110306 Department of parasitology Dalian Medical University.

Medical Arthropod

Associate Prof. Dr. Yulin WangEmail:[email protected]

Tel: +86 411 86110306

Department of parasitologyDalian Medical University

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What is Medical Arthropod? (1)

• Phylum ArthropodaThe phylum is subdivided into a number of classes, many of which are

of medical importance. The classes main include the Class Arachnida and Class Insecta. The Arachnida, or spiderlike animals, possess a body divided into two parts, the cephalothorax and the abdomen. Adults have four pairs of legs. Included in this class are the scorpions, the spiders, and the ticks and mites. Certain ticks and mites many transmit diseases. Insects have three pairs of legs and a body divided into three distinct parts: Insects head, thorax, and abdomen. Included in this class are mosquitoes, flies, lice, and bugs etc.

http://jpkc.sysu.edu.cn/jscx/Textbook/senven-1.htmlhttp://jpkc.sysu.edu.cn/jscx/Courseware/Theroy.html

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What is Medical Arthropod? (2)

These arthropods related with human health are named as “Medical arthropod”, which threatens the human health by their bites, stings, bloodsucking, parasitism or pathogen transmission. Some species are both parasites and vectors of disease. Medical arthropodology is a science that study the morphology, taxonomy, life cycle, zoology, geographic distribution of medical arthropodology, and the relationship of medical arthropods with the transmission of the disease , as well as the measures for medical arthropods control.

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MORPHOLOGY• The organisms in the phylum Arthropoda belong to diverse group, but they

have some features in common.– 1) Bilateral symmetry.– 2) Chitinous exoskeleton with jointed legs.– 3) Growth by molting, which is controlled by hormones– 4) A complete digestive tract extending from an anterior mouth to a posterior anus.– 5) A nervous system consisting of an anterior set of ganglia and commissures, which

extend around the esophagus and pass posteriorly as two fused chains of ventral ganglia.

– 6) True segmentation or metamerism . Primitively, each segment had a pair of legs, neural ganglia, probably an excretory unit, an a set of muscles. In primitivearthropods there is little difference among the segments along the length of the animal(homonymous metamerism), but in more advanced forms, there is movement toward specialized changes in segments(heteronomous metamerism) or the merging of segments into distinct body parts(tagmatosis).

– 7) The body cavity is a hemocoel and the circulatory system is open. In an open circulatory system, blood moves into the heart through openings or ostia and is umped out to various parts of the body, where it leaves the vessels and bathes the tissues directly.

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CLASSIFICATION

• Medical arthropod belong to Class Crustacea （甲壳纲）， Diplopoda （倍足纲） , Chilopoda （唇足纲） , Arachnida （蛛形纲） , and Insecta （昆虫纲） . Among them, most medical arthropod is from Class insecta and archnida.– Insecta: mosquito （蚊） , fly （蝇） , sandfly （白蛉） ,

flea （蚤） , louse （虱） , cockroach （蟑螂） , etc.– Archnida: tick （蜱） , mite （螨） , spider （蜘蛛） ,

etc– Crustacea: crab （蟹） , shrimp （虾） , etc.– Chilopoda: centipede （蜈蚣） .– Diplopoda: millipede （马陆） .

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CLASS ARACHNID

• The morphological features of the arachnids are as follows:– 1) There is no head, as such, because the segments

are fused to form a cephalothorax （头胸部） and abdomen, which make up the body regions; in the mites, there is futher fusion of body regions.

– 2) Antennae( 触须 ) are lacking and they have only simple eyes.

– 3) They have four pairs of legs and are lacking wings.– 4) Developmental patterns are such that the larva

form have much the same body form as the adults.

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CLASS INSECTA

• 1) Head: a pair of compound eye, a pair of antennae, three types of mouthparts( chewing 咀 嚼 式 , sucking 刺 吸 式 and sponging type mouthparts/mopping type mouthparts 舐 吸 式口器 ).

• 2)Thorax( 胸 ): it consists of prothorax, mesothorax and metathorax; the thorax bears three pairs of legs and two pairs of wings.

• 3)Abdomen: 11 segments; the ecto-reproduction organ( 外生殖器 ) also locate in the part.

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DEVELOPMENT AND METAMORPHOSIS

• Complete metamorphosis– Some species of insects belong to complete metamorphosis

arthropod, including mosquito, fly, sandyfly and flea etc. The pattern of the development is as follows: Egg->larva->pupa/chrysalis->adult. The larva and adult have differences in morphology and life habits; There is the pupa stage in the life cycle.

• Incomplete metamorphosis– Some species of insects belong to incomplete metamorphosis

arthropod, such as louce, bug( 臭虫 ), and cockroach etc. The pattern of the development is as follows: Egg->nymph->adult. The larva/nymph stage is similar to the adult in morphology and life habits, but the sexual organ still undeveloped; there is no pupa stage in their life cycle.

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IMPORTANT MEDICAL INSECTS

• Order Diptera( 双翅目 )– Mosquito （蚊） , fly （蝇） , sandyfly （白蛉）

etc• Order• Siphonaptera( 蚤目 )– Flea( 蚤 )

• Order Blattaria( 蜚蠊目 )– Cockroach( 蟑螂 )

• Order Hemiptera( 半翅目 )– bug( 臭虫 )

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HARM FOR HUMAN HEALTH

• Direct harms• 1) Harassment and sucking blood

– ( 骚扰 and 吸血 ) Bloodsucking arthropods such as mosquito, louse, tick, mite, etc bite human by penetrating the skin with their mouthpart and cause harassment to humans.

• 2) Allergy and toxicosis– When bloodsucking, arthropod bites human, various secretions

including salivary fluid are injected into the body, and may be cause hypersensitivity(allergy) or toxicosis. After contacting with the proteins of arthropods such as the secretions of cockroachcan, some individual occur serious allergical reaction e.g., asthma of child.

• 3) Invading tissue – Some larva of flies can parasitize in the skin or the cavity , and cause

myiasis( 蝇蛆病 ). Itch mite can invade the subcutaneous and cause scabies( 疥螨 ).

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• Indirect harmsAethropods are of great importance as vectors of disease-producing agents to humans and other animals. Disease transmission can be accomplished in two general ways. It may be mechanical, which means that the arthropod carries an infectious organism from one person or object to the next without serving as a host for the development or multiplication of this organism. Transmission many also be biolog ical, in which case the infectious organism develops or multiplies within the arthropod host and is only then transmitted to the vertebrate host.

1) Mechanical transmission ( 机械性传播 ) Among those diseases that may be transmitted in a mechanical manner are the bacterial enteritis （肠炎） . Enteric organisms may be carried by files that feed on fecal material to foods destined for human consumption. Pathogenic bacteria may be found on the mouth parts, legs, or intestinal contents of flies feeding on excreta; some protozoan cysts may be carried in a like manner. Flies have long been thought to play a role in the mechanical transmission of those viral diseases in which the organisms are passed in the feces.

2) Biological transmission ( 生物性传播 ) Some infectious organisms require an arthropod host for completion of their life cycle and also utilize this host as a vector. Most arthropod-borne diseases are carried in this fashion, reaching the vertebrate host through the agency of the bite of the vector. Examples of such diseases are malaria and filariasis. An arthropod may serve as intermediate host for an organism that is acquired by the vertebrate host when that host ingests the infected arthropod. There are four types of biolog ical transmission.

a) for development: the pathogen develop to infective stage in the arthropod, but don’t proliferation, e.g., larva of filarial develop in mosquito;b) for proliferation: the pathogen proliferate in the arthropod, but it’s form don’t change, e.g., yersinia pestis( 鼠疫杆菌 ) proliferate in flea ;c) for development and proliferation: the pathogen either develop or proliferate in the arthropod, e.g., plasmodium in mosquito;d) transmission by egg: the pathogen not only can develop or/and proliferate in the arthropod, but also invade the ovum of female arthropod. The pathogen can be transferred to filial generation( 子代 ) of the arthropod by egg. The filial generation also become infective vector. For example, Rickettsia tsutsugamushi( 恙虫病立克 次体 ) in Leptotrombidium deliensis( 地里纤恙螨 ) 。

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ARTHROPOD AS A VECTOR

ARTHROPOD AS A VECTOR ： Arbo-disease is the disease transmitted by arthropods. When an arbo-disease occurs, how do we judge the vector of the disease? The evidences for the judgment are as follows.

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ARTHROPOD AS A VECTOR

Biological evidences As a vector of arbo-diseases, the arthropod should

have the below biological features: 1.It is closely related with humans, e.g., having the

habit of biting or sucking humans; its activity is correlated with humans’ foods, e.g.lapping foods ( 舐 吸 ) or contaminated foods.

2. The arthropod is a common species of arthropods at local area, or the population of the arthropod is dense.

3. The life span of the arthropod is long enough and can provide the time for the pathogen to complete the development or proliferation.

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Epidemiological evidences The geographic distribution and seasonal distribution of the arthropod are the same as the arbo-disease. Laboratory evidences The arthropod can bebe infected with the pathogen by experimental

methods and the pathogen can develop into infective stage in the arthropod in the laboratory.

Natural infection evidences In the epidemic season, the pathogen can be examined from the

arthropod at the field. This is the most important evidence to judge the vector.

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SOME IMPORTANT DISEASES TRANSMITTED BY ARTHROPODS

Following table lists some important diseases transmitted by arthropods in our country.

Arthropod DiseaseHard tick/Ixodidae (硬蜱 )

Forest encephalitis ( 森林脑炎 )Xingjing haemorrhagic fever ( 新疆出血热 ), Lyme disease ( 莱姆病 ) ， Q fever (Q热 )

Soft tick/Argasidae (软蜱 )

Tick-borne recurrent fever ( 蜱媒回归热 ) ， Q fever (Q 热 )

Chigger/Trombiculid mites (恙螨 ) Scrub typhus ( 恙虫病 )Itch mite/Sarcoptidae mite (疥螨 ) Scabies ( 疥疮 )Demodicidae mite (蠕形螨 ) folliculitis ( 毛囊炎 ) etcDust mite/Pyroglyphidae (尘螨 )

Asthma ( 哮喘 ) ， Allergic hinitis ( 过敏性鼻炎 ) ， Allergic dermatitis ( 过敏性皮炎 )

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Arthropod Disease

Mosquito ( 蚊 )

Malaria ( 疟 疾 ) ， Filariasis ( 丝 虫病 ) ， Japanese B encephalitis ( 流行性乙型脑炎 ) ， Dengue fever ( 登 革 热 ),Yellow fever ( 黄热病 )

Fly/Musca (蝇

)Dysentery ( 痢 疾 ) ， Typhoid fever ( 伤寒 ) ， Cholera ( 霍乱 ) ， Poliomyelitis ( 脊髓灰质 炎 ) ， Amebic dysentery ( 阿 米 巴 痢疾 ) ， Myiasis ( 蝇蛆病 )

Sandfly (白蛉 )

Kala-azar disease/ visceral leishmaniasis ( 黑 热病 )

Flea ( 蚤 )

Plague ( 鼠疫 ) ， Murine typhus ( 鼠型斑疹伤寒 ) ， Hymenolepiasis diminuta ( 微小膜壳绦虫病 )

Lice ( 虱 )

Epidemic typhus ( 流 行 性 斑 疹 伤 寒 ) ， Lice-borne relapsing fever ( 虱媒回归热 )

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CONTROL

The integrated measure ( 综合性措施 ) is considered as best measure for arthropods control. These measures are as follows:Environmental management

Its objective is to reduce or control the resting/growing field or breeding sites ( 滋生地 ), and reduce the arthropod population by environmental modification and sanitation.

Physical measures Its objective is to control or drive away medical arthropod. For example, bed-net is usually a useful tool to avoid the bite of mosquito.Chemical measures Since 1940s, four types of insecticides have been used widely. The use of DDT achieved eradication in controlled malaria transmission at some subtropical region. Gradually, however, DDT resistance developed and alternative insecticides were required. Organophosphates, Carbamates and Pyrethroids have been introduced as the spectrum of resistance that has widened. In recent year the development of the insecticide growth regulator , a new insecticide, has been used in the experimental areas. 1. Organochlorines ( 有机氯杀虫剂 ) e.g, DDT (dichlorodiphenyltrichlorethane). 2. Organophosphates ( 有机磷杀虫剂 ) e.g., malathion ( 马拉硫磷 ), fenitrothion ( 杀 螟松 ) etc. 3. Carbamates ( 氨基甲酸酯杀虫剂 ) e.g., bendiocarb ( 虫威 ), and propoxur ( 残杀威 ) etc. 4. Pyrethroids ( 拟除虫菊酯杀虫剂 ) e.g., permethrin ( 朴杀司林 ) etc.Biological measures

The bacterium Bacillus thuringiensis ( 苏云金杆菌 ), and B.sphaericus ( 球形芽胞杆菌 ), as well as Romanomermis culicavorax ( 罗索线虫 ) can infect the larva of mosquito and kill them. In the rice field,breeding fish is also a useful method to control the larva of mosquito.

Genetic measures Apply molecular biological methods such as mutation or gene transfer, produce infertility males of medical arthropod, and let them mate with wild female of medical arthropod. The female will not reproduce filial generation.

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