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Human Parasitology. Shandong University Department of Parasitology He Shenyi (何深一 ) MD, Ph.D. Professor. Introduction to Human Parasitology. Concept of Human Parasitology The Scope of Human Parasitology Terms of Parasitology Parasites’ Harms to Man Human Immunity against Parasites

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Human Parasitology

Shandong University

Department of Parasitology

He Shenyi (何深一 )

MD, Ph.D. Professor

introduction to human parasitology
Introduction to Human Parasitology
  • 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
  • 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 Microbiology. 
2 the scope of human parasitology
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

  • Class Zoomastigophorea
  • Class Sporozoa
  • Class Ciliophora



Human Parasitology

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



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



class lobosea
Class Lobosea

Entamoeba histolytica

Non-pathogenic amoeba

class zoomastigophorea
Class Zoomastigophorea

Leishmania sp


Trichomonas vaginalis

class sporozoa
Class Sporozoa
  • Plasmodium spp

Toxopasma gondii Cryptosporidium

Pneumocycstis carinii

class ciliophora
Class Ciliophora
  • Balantidium coli
class nematoda
Class Nematoda
  • Ascaris lumbricoides

Trichuris trichiura


Enterobius vermicularis


Trichinella spiralis

class trematoda
Class Trematoda
  • Clonorchis sinensis

Fasciolopsis buski

Paragonimus westermani

Schistosoma japonicum

class cestoda
Class Cestoda
  • Taenia solium

Taenia saginata Echinococcus granulosus

class metacanthocephala
Class Metacanthocephala



class insecta
Class Insecta

Lucilia sericata

Anopheles sinensis


Sandflies , Fleas

class arachnida
Class Arachnida

Ticks; Mites

Sarcopes scabiei

follicle mite

class crustacea
Class Crustacea
  • Cambaroides
  • Potamon  

(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 man.


(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 host.


(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 hosts.

life cycle
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 cycle1
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 cycle2
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
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
4. Parasites’ Harms to Man
  • Mechanical effects of parasites on host tissues and organs: e. g. , biliary ascariasis and larva migrans.
  • 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
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
(WHO) - Priority Diseases

1. Schistosomiasis

2. Malaria

3. Filariasis

4. Trypanosomiasis

5. Leishmaniasis

6. Leprosy (replaced by HIV/AIDS)

why were they selected
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
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
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
Presence of Diseases in a Population (Prevalence):

Factors required:

1. Source

infected persons



presence of diseases in a population prevalence1
Presence of Diseases in a Population (Prevalence):

2. Mode of transmission




3. Susceptible host



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 infections
Diagnosis of Parasitic Infections:

1. Clinical diagnosis

2. Laboratory diagnosis

treatment of parasitic infections
Treatment of Parasitic Infections:

1. Medical and surgical

2. Chemotherapy

3. Adequate nutrition

prevention and control
Prevention and Control:

1. Reduction in sources

2. Education

3. Destruction and/or control of reservoir hosts and vector