Human ParasitologyHuman Parasitology

Shandong UniversityShandong UniversityDepartment of ParasitologyDepartment of Parasitology

He Shenyi He Shenyi （何深一 ）（何深一 ）MD, Ph.D. ProfessorMD, Ph.D. Professor

Introduction to Human Introduction to Human ParasitologyParasitology

Concept of Human ParasitologyConcept of Human ParasitologyThe Scope of Human ParasitologyThe Scope of Human ParasitologyTerms of ParasitologyTerms of ParasitologyParasites’Parasites’ Harms to Man Harms to Man Human Immunity against ParasitesHuman Immunity against ParasitesCharacteristicsCharacteristics of parasitic diseases of parasitic diseases

Human parasitologyHuman parasitology

Human parasitology is the study of those organHuman parasitology is the study of those organisms which parasitise humans.  According to thisms which parasitise humans.  According to the very broad definition of parasitology, parasitee very broad definition of parasitology, parasites should include the viruses, bacteria, fungi, prs should include the viruses, bacteria, fungi, protozoa and metazoa (multi-celled organisms) wotozoa and metazoa (multi-celled organisms) which infect their host species.  However, for histhich infect their host species.  However, for historical reasons the first three have been incorpoorical reasons the first three have been incorporated into the discipline of Microbiology. rated into the discipline of Microbiology. 

2. The Scope of Human Parasitology2. The Scope of Human Parasitology

Parasitology claims those protozoa (single celled animals), Parasitology claims those protozoa (single celled animals),

helminths (worms) and arthropods whose existence depends ohelminths (worms) and arthropods whose existence depends o

n the availability of host animals It is also possible to argue abn the availability of host animals It is also possible to argue ab

out whether certain insects and mites are "temporary parasitout whether certain insects and mites are "temporary parasit

es" or "micro-predators", insects as a group belong to the dises" or "micro-predators", insects as a group belong to the dis

cipline of Entomology, while ticks and mites are the concern ocipline of Entomology, while ticks and mites are the concern o

f Acarology.  The insects that are of most interest in human pf Acarology.  The insects that are of most interest in human p

arasitology are those that are vectors of several parasitic infecarasitology are those that are vectors of several parasitic infec

tionstions.

Human Parasitology

Medical

Helminthology

Medical

Protozoology

Medical

Arthropodology

• Class Nematoda• Class Trematoda• Class Cestoda• Class MetacanthocephalaClass Metacanthocephala

• Class Lobosea• Class Zoomastigophorea• Class Sporozoa• Class Ciliophora

• Class Insecta • Class Arachnida• Class Crustacea• Class Chilopoda

Class LoboseaClass Lobosea

Entamoeba histolyticaNon-pathogenic amoeba

Class ZoomastigophoreaClass Zoomastigophorea

Leishmania sp

Trichomonas vaginalisGiardiaGiardia

Class SporozoaClass Sporozoa

Plasmodium spp

Toxopasma gondii CryptosporidiumPneumocycstis carinii

Class CiliophoraClass Ciliophora

– Balantidium coli

Class NematodaClass Nematoda

Ascaris lumbricoides

Trichuris trichiuraHookworm

Enterobius vermicularisFilaria

Trichinella spiralis

NematodaNematoda

Class TrematodaClass Trematoda

Clonorchis sinensis

Fasciolopsis buskiParagonimus westermani Schistosoma japonicum

TrematodaTrematoda

Class CestodaClass Cestoda

Taenia solium

Taenia saginata Echinococcus granulosus

CestodaCestoda

ClassClass Metacanthocephala Metacanthocephala

Macracanthorhynchus hirudinaceus

Class InsectaClass Insecta

Anopheles sinensis Lucilia sericata

LiceSandflies , Fleas

Class ArachnidaClass Arachnida

Sarcopes scabiei

follicle mite

Ticks; Mites

Class CrustaceaClass Crustacea

Cambaroides Potamon  

Class ChilopodaClass Chilopoda

centipede

4. Terms of Parasitology 4. Terms of Parasitology

SymbiosisSymbiosis

(1)Symbiosis(1)Symbiosis （共同生活）（共同生活） Two differTwo different organisms live together and interent organisms live together and interact, in this association one partner liact, in this association one partner lives in or on another one’s body. inclves in or on another one’s body. including 3 types:Mutualism, Commensuding 3 types:Mutualism, Commensalism, Parasitism.alism, Parasitism.

*(2)Mutualism(*(2)Mutualism( 互利共生）互利共生） is a permis a permanent association between two differeanent association between two different organisms that life apart is impossint organisms that life apart is impossible, two partners benefit each other, sble, two partners benefit each other, such as termites and flagellates. uch as termites and flagellates.

The mutuals are metabolically depenThe mutuals are metabolically dependent on one another; one cannot survident on one another; one cannot survive in the absence of the other.ve in the absence of the other.

SymbiosisSymbiosis

(3)(3)  CommensalismCommensalism （片利共生或共栖）（片利共生或共栖） is this the association of two different organisms, in e association of two different organisms, in which one partner is benefited while the othwhich one partner is benefited while the other neither benefited nor injured, such as E. er neither benefited nor injured, such as E. coli and man.coli and man.

(4) Parasitism(4) Parasitism （寄生关系）（寄生关系） is the associatiois the association of two different organisms, in which one n of two different organisms, in which one partner is benefited while the other is injurpartner is benefited while the other is injured, such as Ascaris lumbricoides and man.ed, such as Ascaris lumbricoides and man.

SymbiosisSymbiosis

ParasiteParasite

(5) Parasite(5) Parasite （寄生虫） （寄生虫） In parasitism,In parasitism, it is the benefited partner. It is an an it is the benefited partner. It is an animal organism which lives in or on thimal organism which lives in or on the host in order to obtain nourishmene host in order to obtain nourishment and shelter from the host as well as t and shelter from the host as well as does harms to the host.does harms to the host.

ParasiteParasite

endoparasite endoparasite

ectoparasiteectoparasite

temporary parasitetemporary parasite

permanent parasite permanent parasite

obligatory parasiteobligatory parasite

facultative parasitefacultative parasite

accidental parasiteaccidental parasite

opportunistic parasiteopportunistic parasite

EndoparasiteEndoparasite

EctoparasiteEctoparasite

HostHost

(6) Host(6) Host （宿主） （宿主） In parasitism, it supplieIn parasitism, it supplies the parasite with nourishment and shelts the parasite with nourishment and shelter, it is the injured partner.er, it is the injured partner.

(7) Carrier(7) Carrier （带虫者） （带虫者） A person who harbA person who harbours parasite has no clinical symptoms, is ours parasite has no clinical symptoms, is an important source of infection in epidean important source of infection in epidemiology.miology.

(8) Definitive (final) host(8) Definitive (final) host （终宿主）（终宿主） harharbours adult or sexually reproductive stabours adult or sexually reproductive stage of a parasite.ge of a parasite.

(9) Intermediate host(9) Intermediate host （中间宿主）（中间宿主） haharbours larval or asexually reprodctive strbours larval or asexually reprodctive stage of a parasite, according to priority tage of a parasite, according to priority they are classified into first intermediate hey are classified into first intermediate host, second intermediate host, third inthost, second intermediate host, third intermediate host.ermediate host.

(10) Reservoir hosts(10) Reservoir hosts （保虫宿主）（保虫宿主） aare the vertebrate hosts which harbore the vertebrate hosts which harbour the same species of parasite at saur the same species of parasite at same stage as a human host. They are me stage as a human host. They are an important source of infection in ean important source of infection in epidemiology.pidemiology.

ZoonosisZoonosis(11) Zoonosis(11) Zoonosis （人兽共患病）（人兽共患病） refers trefers t

o animal’s diseases which can be trao animal’s diseases which can be transmitted to man. (These animals infensmitted to man. (These animals infected with parasites are called reservocted with parasites are called reservoir hosts.)ir hosts.)

(12) Paratenic host or transport hos(12) Paratenic host or transport hostt （转续宿主）（转续宿主） is an abnormal host iis an abnormal host in which some parasitic larvae can sun which some parasitic larvae can survive but can’t develop into adults. If rvive but can’t develop into adults. If the larvae have a chance to enter theithe larvae have a chance to enter their appropriate hosts, they can continur appropriate hosts, they can continue to develop into adults there.e to develop into adults there.

(13)(13)    Larva migransLarva migrans （幼虫移行症）（幼虫移行症）means that the larvae living in their means that the larvae living in their abnormal hosts in which they can noabnormal hosts in which they can not grow into adults but can wander evt grow into adults but can wander everywhere and cause the local and syserywhere and cause the local and systemic pathological lesions of the hosttemic pathological lesions of the hosts.s.

Life cycleLife cycle

(14)(14) Life cycleLife cycle （生活史） （生活史） is the process of is the process of a parasite’s growth, development and repra parasite’s growth, development and reproduction, which proceeds in one or more oduction, which proceeds in one or more different hosts depending on the species of different hosts depending on the species of parasites. parasites.

(15)Infective Stage(15)Infective Stage （感染期）（感染期） is a stage wis a stage when a parasite can invade human body anhen a parasite can invade human body and live in it .d live in it .

Life cycleLife cycle

(16)(16) Infective RouteInfective Route （感染途径）（感染途径） is the speis the specific entrance through which the parasite icific entrance through which the parasite invades the human body.nvades the human body.

(17)(17) Infective ModeInfective Mode （感染方式） （感染方式） means means how the parasite invades human body, suchow the parasite invades human body, such as the cercariae of the blood fluke activeh as the cercariae of the blood fluke actively penetrate the skin of a swimming man aly penetrate the skin of a swimming man and the infective ascaris eggs are swallowed nd the infective ascaris eggs are swallowed by man. by man.

Life cycleLife cycle

(18) Alternation of Generation: (18) Alternation of Generation: In life cycles of some parasites, there In life cycles of some parasites, there

are the regular alternations of sexual are the regular alternations of sexual and asexual reproductions , this pheand asexual reproductions , this phenomenon is called alternation of gennomenon is called alternation of generation, such as the life cycle of eration, such as the life cycle of PlasPlasmodium vivaxmodium vivax..

(19) (19) Mechanical Transmission: ArthrMechanical Transmission: Arthropods play a role of the transportatioopods play a role of the transportation of pathogens, which is not indispenn of pathogens, which is not indispensable for the disease transmission, susable for the disease transmission, such as flies carry typhoid bacilli, ascarch as flies carry typhoid bacilli, ascarid eggs and amoebic cysts.id eggs and amoebic cysts.

(20) Biological Transmission: Pathogens have to s(20) Biological Transmission: Pathogens have to s

pend a part of their life cycle in the vector arthrpend a part of their life cycle in the vector arthr

opods in which they multiply or develop into thopods in which they multiply or develop into th

e infective stage and then invade the human boe infective stage and then invade the human bo

dy under the help of the arthropod, such as Andy under the help of the arthropod, such as An

opheles mosquitoes transmit malariaopheles mosquitoes transmit malaria ..

Evolution of ParasitismEvolution of Parasitism

endoparasite Free living ectoparasite Commensalism （片利共生） temporary parasite Symbiosis Mutualism （互利共生） permanent parasite Parasitism obligatory parasite carrier facultative parasite parasite Host accidental parasite Patient opportunistic parasite Final host Intermediate host Reservoir host Paratenic host Zoonosis Larva migrans

4. Parasites’ Harms to Man4. Parasites’ Harms to Man Mechanical effectsMechanical effects of parasites on host tissues a of parasites on host tissues a

nd organs: e. g. , biliary ascariasis and larva migrans.nd organs: e. g. , biliary ascariasis and larva migrans. Depriving nourishmentDepriving nourishment from hosts: e.g. hookw from hosts: e.g. hookw

orms suck blood.orms suck blood. Toxic effect:Toxic effect: e. g., mosquitoes, spiders and ticks i e. g., mosquitoes, spiders and ticks i

ntroduce venom when they insert their mouth parts inntroduce venom when they insert their mouth parts into the skin.to the skin.

Immuno-pathological lesionImmuno-pathological lesion e.g. schistosoma li e.g. schistosoma liver cirrhosis; when hydatid fluid is released from the ver cirrhosis; when hydatid fluid is released from the rupture of a hydatid cyst anaphylaxis often results. rupture of a hydatid cyst anaphylaxis often results.

5. Human Immunity against Parasites5. Human Immunity against Parasites

Its intensity and specificity are usually at a lower leveIts intensity and specificity are usually at a lower level than those produced by bacteria and viruses. It referl than those produced by bacteria and viruses. It refers to Non-sterilizing immunity (Premunitions to Non-sterilizing immunity (Premunition 带虫免疫；带虫免疫；Concomitant immunityConcomitant immunity 伴随免疫伴随免疫 ). The host may be ). The host may be protected from superinfectionprotected from superinfection 重复感染重复感染 as long as the as long as the parasites remain in the body. This situation is known parasites remain in the body. This situation is known as premunition(as premunition( 带虫免疫带虫免疫 ). This may be of great imp). This may be of great importance in endemic areas in limiting the severity of infortance in endemic areas in limiting the severity of infection with Plasmodium, Schistosome , hookworms aection with Plasmodium, Schistosome , hookworms and other parasites.nd other parasites.

(WHO) - Priority Diseases(WHO) - Priority Diseases

1. Schistosomiasis1. Schistosomiasis2. Malaria2. Malaria3. Filariasis3. Filariasis4. Trypanosomiasis4. Trypanosomiasis5. Leishmaniasis5. Leishmaniasis6. Leprosy (replaced by HIV/AIDS)6. Leprosy (replaced by HIV/AIDS)

Why were they selected?Why were they selected?

Schistosomiasis - 200,000,000 infectedSchistosomiasis - 200,000,000 infected

500,000-1,000,000 deaths/year500,000-1,000,000 deaths/year Malaria - 500,000,000 infectedMalaria - 500,000,000 infected

2,500,000 deaths/year2,500,000 deaths/year Filariasis - 250,000,000 infectedFilariasis - 250,000,000 infected Trypanosomiasis - 25,000,000 infectedTrypanosomiasis - 25,000,000 infected

65,000 deaths/year65,000 deaths/year Leishmaniasis - 1,200,000 infectedLeishmaniasis - 1,200,000 infected Leprosy - 1,300,000 infectedLeprosy - 1,300,000 infected Approximately 25% of world's population infected by oApproximately 25% of world's population infected by o

ne of these.ne of these.

General Characteristics:General Characteristics:

1. Chronic diseases1. Chronic diseases2. No effective vaccine2. No effective vaccine3. No practical chemotherapy3. No practical chemotherapy4. Affect young4. Affect young5. Affect underprivileged5. Affect underprivileged6. Vector-borne6. Vector-borne

Geographic Distribution FactorGeographic Distribution Factors (Endemicity):s (Endemicity):

1. Presence of a suitable host1. Presence of a suitable host2. Habits of the host2. Habits of the host3. Escape from the host3. Escape from the host4. Favorable conditions outside of host4. Favorable conditions outside of host5. Economic and social conditions5. Economic and social conditions

Presence of Diseases in a Presence of Diseases in a Population (Prevalence):Population (Prevalence):

Factors required:Factors required:1. Source1. Source infected personsinfected personscarrierscarriersanimalsanimals

Presence of Diseases in a Presence of Diseases in a Population (Prevalence):Population (Prevalence):

2. Mode of transmission2. Mode of transmissiondirectdirect indirectindirectvectorsvectors3. Susceptible host3. Susceptible host immunityimmunity

Three key links of disease transmissionThree key links of disease transmission

1.Source of infection 2. Route of transmission 3. Susceptible people1.Source of infection 2. Route of transmission 3. Susceptible people

excrement mouthexcrement mouth

secretion food, water, finger skin or woundsecretion food, water, finger skin or wound

blood direct or indirect contact mucosablood direct or indirect contact mucosa

focus of placentafocus of placenta

infection blood transfusion, injection, infection blood transfusion, injection,

intermediate host, intermediate host,

insects sucking blood,insects sucking blood,

congenital ,congenital ,

touch soil, water, grass touch soil, water, grass

Diagnosis of Parasitic Diagnosis of Parasitic Infections:Infections:

1. Clinical diagnosis1. Clinical diagnosis2. Laboratory diagnosis2. Laboratory diagnosis

Treatment of Parasitic Treatment of Parasitic Infections:Infections:

1. Medical and surgical1. Medical and surgical2. Chemotherapy2. Chemotherapy3. Adequate nutrition3. Adequate nutrition

Prevention and Control:Prevention and Control:

1. Reduction in sources1. Reduction in sources2. Education2. Education3. Destruction and/or control of reservoir 3. Destruction and/or control of reservoir

hosts and vectorhosts and vector