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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  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 Microbiology.

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 Protozoology

• Class Zoomastigophorea • Class Sporozoa

Human Parasitology

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

Medical Helminthology

Medical

Arthropodology

• • • •

Class Class Class Class

Insecta Arachnida Crustacea Chilopoda

Class Lobosea

Entamoeba histolytica Non-pathogenic amoeba

Class Zoomastigophorea
Leishmania sp

Giardia

Trichomonas vaginalis

Class Sporozoa
 Plasmodium

spp

Toxopasma gondii Cryptosporidium Pneumocycstis carinii

Class Ciliophora

– Balantidium coli

Class Nematoda


Ascaris lumbricoides

Trichuris trichiura Hookworm Enterobius vermicularis Filaria Trichinella spiralis

Nematoda

Class Trematoda
 Clonorchis sinensis

Fasciolopsis buski Paragonimus westermani Schistosoma japonicum

Trematoda

Class Cestoda



Taenia solium

Taenia saginata Echinococcus granulosus

Cestoda

Class Metacanthocephala

Macracanthorhynchus hirudinaceus

Class Insecta Anopheles sinensis Lucilia sericata

Lice Sandflies , Fleas

Class Arachnida Ticks; Mites
Sarcopes scabiei

follicle mite

Class Crustacea



Cambaroides  Potamon

Class Chilopoda

centipede

4. Terms of Parasitology

Symbiosis
(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.

Symbiosis
 *(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.

Symbiosis
(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.

Parasite
(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.

Parasite
endoparasite ectoparasite temporary parasite permanent parasite obligatory parasite facultative parasite accidental parasite opportunistic parasite

Endoparasite

Ectoparasite

Host
(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.

Zoonosis
(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
(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 ectoparasite temporary parasite permanent parasite obligatory parasite facultative parasite accidental parasite opportunistic parasite

Free living
Commensalism(片利共生) Symbiosis Mutualism(互利共生) Parasitism carrier parasite Host Patient

Final host Intermediate host

Reservoir host Zoonosis

Paratenic host Larva migrans

4. Parasites’ Harms to Man


Mechanical effects of parasites on host tissues
and organs: migrans. 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 secretion blood focus of infection

food, water, finger direct or indirect contact

mouth skin or wound mucosa placenta

blood transfusion, injection, intermediate host, insects sucking blood, congenital , touch soil, water, grass

Diagnosis of Parasitic Infections:


1. Clinical diagnosis  2. Laboratory diagnosis

Treatment of Parasitic Infections:


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


				
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