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					Human Parasitology

  Shandong University
Department of Parasitology
 He Shenyi (何深一 )
  MD, Ph.D. Professor
          Introduction to Human

 Concept of Human Parasitology
 The Scope of Human Parasitology
 Terms of Parasitology
 Parasites’ Harms to Man
 Human Immunity against Parasites
 Characteristics of parasitic diseases
         Human parasitology
   Human parasitology is the study of those
    organisms which parasitise
    humans. According to the very broad
    definition of parasitology, parasites should
    include the viruses, bacteria, fungi, protozoa
    and metazoa (multi-celled organisms) which
    infect their host species. However, for
    historical reasons the first three have been
    incorporated into the discipline of
 2. The Scope of Human Parasitology

   Parasitology claims those protozoa (single celled animals),

helminths (worms) and arthropods whose existence depends

on the availability of host animals It is also possible to argue

about whether certain insects and mites are "temporary

parasites" or "micro-predators", insects as a group belong to

the discipline of Entomology, while ticks and mites are the

concern of Acarology. The insects that are of most interest in

human parasitology are those that are vectors of several

parasitic infections.
                                      • Class Lobosea
                     Medical          • Class Zoomastigophorea
Human Parasitology

                     Protozoology     • Class Sporozoa
                                      • Class Ciliophora

                                      • Class Nematoda
                     Medical          • Class Trematoda
                     Helminthology    • Class Cestoda
                                      • Class Metacanthocephala

                                      •   Class   Insecta
                     Medical          •   Class   Arachnida
                     Arthropodology   •   Class   Crustacea
                                      •   Class   Chilopoda
      Class Lobosea

Entamoeba histolytica
Non-pathogenic amoeba
    Class Zoomastigophorea

                      Leishmania sp

Giardia        Trichomonas vaginalis
Class Sporozoa

        Plasmodium   spp

     Toxopasma gondii
     Pneumocycstis carinii
Class Ciliophora

 – Balantidium coli
Class Nematoda
                 Ascaris

             Trichuris trichiura
        Enterobius vermicularis
             Trichinella spiralis
Class Trematoda

    Clonorchis sinensis

   Fasciolopsis buski
   Paragonimus westermani
   Schistosoma japonicum
Class Cestoda

                Taenia solium

     Taenia saginata
     Echinococcus granulosus
Class Metacanthocephala

            Class Insecta
Anopheles sinensis   Lucilia sericata

 Sandflies , Fleas
Class Arachnida

 Ticks; Mites

                Sarcopes scabiei

                 follicle mite
    Class Crustacea

 Cambaroides
 Potamon
Class Chilopoda

4. Terms of Parasitology
(1)Symbiosis ( 共 同 生 活 ) Two
  different organisms live together and
  interact, in this association one
  partner lives in or on another one’s
  body. including 3 types:Mutualism,
  Commensalism, Parasitism.
 *(2)Mutualism(互利共生)is          a
  permanent association between two
  different organisms that life apart is
  impossible, two partners benefit each
  other, such as termites and flagellates.
 The mutuals are metabolically
  dependent on one another; one cannot
  survive in the absence of the other.
(3) Commensalism(片利共生或共栖)is the
  association of two different organisms, in
  which one partner is benefited while the
  other neither benefited nor injured, such as
  E. coli and man.
(4) Parasitism(寄生关系)is the association
  of two different organisms, in which one
  partner is benefited while the other is
  injured, such as Ascaris lumbricoides and
(5) Parasite(寄生虫) In parasitism,
  it is the benefited partner. It is an
  animal organism which lives in or on
  the host in order to obtain
  nourishment and shelter from the
  host as well as does harms to the host.

temporary parasite
permanent parasite
obligatory parasite
facultative parasite
accidental parasite
opportunistic parasite

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

(7) Carrier ( 带 虫 者 ) A person who
  harbours parasite has no clinical
  symptoms, is an important source of
  infection in epidemiology.
(8) Definitive (final) host ( 终 宿 主 )
  harbours adult or sexually reproductive
  stage of a parasite.
(9) Intermediate host(中间宿主)
  harbours larval or asexually
  reprodctive stage of a parasite,
  according to priority they are classified
  into first intermediate host, second
  intermediate host, third intermediate
 (10)Reservoir hosts(保虫宿主)
 are the vertebrate hosts which
 harbour the same species of parasite
 at same stage as a human host. They
 are an important source of infection
 in epidemiology.
(11) Zoonosis(人兽共患病)refers to
  animal’s diseases which can be
  transmitted to man. (These animals
  infected with parasites are called
  reservoir hosts.)
 (12) Paratenic host or transport host
 (转续宿主)is an abnormal host in
 which some parasitic larvae can
 survive but can’t develop into adults.
 If the larvae have a chance to enter
 their appropriate hosts, they can
 continue to develop into adults there.
(13) Larva migrans(幼虫移行症)
  means that the larvae living in their
  abnormal hosts in which they can
  not grow into adults but can wander
  everywhere and cause the local and
  systemic pathological lesions of the
              Life cycle

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

(15)Infective Stage ( 感 染 期 ) is a stage
  when a parasite can invade human body
  and live in it .
                Life cycle

(16) Infective Route ( 感 染 途 径 ) is the
   specific entrance through which the
   parasite invades the human body.
 (17) Infective Mode(感染方式) means
   how the parasite invades human body,
   such as the cercariae of the blood fluke
   actively penetrate the skin of a swimming
   man and the infective ascaris eggs are
   swallowed by man.
              Life cycle

 (18)  Alternation of Generation:
 In life cycles of some parasites, there
  are the regular alternations of sexual
  and asexual reproductions , this
  phenomenon is called alternation of
  generation, such as the life cycle of
  Plasmodium vivax.
(19) Mechanical Transmission:
  Arthropods play a role of the
  transportation of pathogens, which
  is not indispensable for the disease
  transmission, such as flies carry
  typhoid bacilli, ascarid eggs and
  amoebic cysts.
(20) Biological Transmission: Pathogens have to
  spend a part of their life cycle in the vector
  arthropods in which they multiply or develop
  into the infective stage and then invade the
  human body under the help of the arthropod,
  such as Anopheles mosquitoes transmit malaria.
               Evolution 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 Man
      Mechanical effects of parasites on host tissues
    and organs:     e. g. , biliary ascariasis and larva
      Depriving      nourishment from hosts: e.g.
    hookworms suck blood.
      Toxic effect: e. g., mosquitoes, spiders and ticks
    introduce venom when they insert their mouth parts
    into the skin.
      Immuno-pathological lesion e.g. schistosoma
    liver cirrhosis; when hydatid fluid is released from the
    rupture of a hydatid cyst anaphylaxis often results.
       5. Human Immunity against Parasites

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

 1. Schistosomiasis
 2. Malaria
 3. Filariasis
 4. Trypanosomiasis
 5. Leishmaniasis
 6. Leprosy (replaced by HIV/AIDS)
      Why were they selected?
 Schistosomiasis - 200,000,000 infected
  500,000-1,000,000 deaths/year
 Malaria - 500,000,000 infected
  2,500,000 deaths/year
 Filariasis - 250,000,000 infected
 Trypanosomiasis - 25,000,000 infected
  65,000 deaths/year
 Leishmaniasis - 1,200,000 infected
 Leprosy - 1,300,000 infected
 Approximately 25% of world's population infected by
  one of these.
    General Characteristics:

 1. Chronic diseases
 2. No effective vaccine
 3. No practical chemotherapy
 4. Affect young
 5. Affect underprivileged
 6. Vector-borne
    Geographic Distribution
     Factors (Endemicity):

 1. Presence of a suitable host
 2. Habits of the host
 3. Escape from the host
 4. Favorable conditions outside of host
 5. Economic and social conditions
    Presence of Diseases in a
    Population (Prevalence):
 Factors required:
 1. Source
 infected persons
 carriers
 animals
    Presence of Diseases in a
    Population (Prevalence):
 2. Mode of transmission
 direct
 indirect
 vectors
 3. Susceptible host
 immunity
        Three key links of disease transmission
1.Source of infection 2. Route of transmission   3. Susceptible people

excrement                                           mouth
secretion     food, water, finger                  skin or wound
blood         direct or indirect contact           mucosa
focus of                                           placenta
infection    blood transfusion, injection,
             intermediate host,
             insects sucking blood,
             congenital ,
             touch soil, water, grass
    Diagnosis of Parasitic

 1. Clinical diagnosis
 2. Laboratory diagnosis
    Treatment of Parasitic

 1. Medical and surgical
 2. Chemotherapy
 3. Adequate nutrition
    Prevention and Control:

 1. Reduction in sources
 2. Education
 3. Destruction and/or control of reservoir
  hosts and vector