Department of Parasitology

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WELCOME
Department of Parasitology Guangxi Medical
University
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HUMAN PARASITOLOGY
Huan huan Shi (???)
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HUMAN (MEDICAL) PARASITOLOGY
a branch of the medical sciences dealing
with the members of the animal kingdom living in
and on the body of humans and with aspects of
this host-parasite relationship having medical
significance. A science to study the
parasitism.
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HARMFULNESS OF PARASITES TO HUMAN BEINGS
Six important tropical diseases defined by
WHO 1 Malaria 2 Schistosomiasis 3 Filariasis
parasitosis 4 Leishmaniasis 5
Trypanosomiasis 6 Leprosy
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INTRODUCTION TO HUMAN PARASITOLOGY
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Hope you can answer following questions after my
lecture today.
1.What is the parasitism ? 2.Definition of
parasite, host, life cycle and infective
stage. 3. How do the parasites injure human
beings? 4. How do the parasites infect
host? 5.How to prevent and control parasitosis?
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PARASITISM, PARASITE AND HOST
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PARASITISM The relationship
between animals that live together (From
viewpoints of benefit and harm) Commensalism an
association which is benificial to one partner
and no harm to the other. Mutualism reciprocal
benefit between the two organisims. Parasitism
One partner derives benefit. Another is injured.
Parasitism involves two factors parasite and
host
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PARASITE and HOST Among the partners in the
parasitism,the one which benefits from the other
is a parasite,while the one which harmed by the
parasite is a host.
CLASSIFICATION OF PARASITES
1 Basing on the biologic taxonomy
(1) Medical protozoa (2) Medical helminths
(3) Medical arthropods
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2 Basing on the relationship between parasite
and host
(1). Obligative parasites Malaria
parasite (2). Facultative parasites
Strongyloides stercoralis (3). Endoparasite
Ascaris Lumbricoides (4). Ectoparasite Mosquito
,Fly, Flea. (5). Opportunistic parasite
Toxoplasma gondii
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Types of hosts
Definitive host those provide the living of
adult helminth or sexual stage of a protozoan.
Intermediate host those provide living of
larvae of helminth or asexual stages of a
protozoan. First and second intermediate host
Reservoir host those animal hosts of human
parasites in which parasites are kept alive for
long period of time with frequent excretion of
the eggs or pathogens(serve as a source of
infection for humans ).
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LIFE CYCLE AND INFECTIVE STAGE
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Life cycle The whole biological course of
growth, development and reproduction of a
parasite.
Infective stage The stage that is able to infect
men in life cycle.
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Sporocyst rediae
The life cycle of C.sinensis (A) definitive
host (B) Reservoir host (C) The first
intermediate host (D) The second intermediate
host (1) Adult (2) Egg (3) Cercaria which have
become free (4) metacercaria
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THE RELATIONSHIP BETWEEN PARASITE AND HOST
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1. Effects of Parasites on Host A. Uptaking
nutrition B. Physical trauma C. Chemical and
allergic effects a) Lytic necrosis Enzymes
b) Stimulation of host tissue reaction c)
causing hypersensitivity
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(No Transcript)
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2.Effects of Host on Parasite ---- immunity
(refer to immunology)

• Feature of parasitic immunity
• Complication of antigens
• Non-sterilizing immunity is commoner
  premunition (malaria),concomitant immunity
  (schistosoma)
• Re-infection occurs often

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• Results from reaction between parasite and host
• Parasite will be eliminated
• Keep balance ( suppressive infection ,carrier)
• Parasitosis

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EPIDEMIOLOGY OF PARASITOSIS
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1. Factors of transmission
Source of infection
parasite
Subjects of individuals
Pathways of transmission
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(1) Source of infection
A. patients B. carrier C. reservoir host
(2) Pathways of Transmission A. Oral route
Contaminated soil, food and water etc. mediate
it.
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Soil polluted with human excreta is
commonly responsible for exposure to infection
with Ascaris lumbricoides, Trichuris trichiura
Water may contain viable cysts of parasitic
ameba, intestinal flagellates, Taenia solium
eggs. Fresh-water fishes are sources for several
types of intestinal and liver flukes
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Crabs and crayfishes are sources for the oriental
lung fluke
Raw pork is the source for Trichinella
spiralis and Taenia solium beef is the source
for Taenia saginata buffalo nuts are the source
for the giant intestinal fluke (Fasciola buski),
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B. Skin and mucous membrane route
(a) Penetration of the intact skin
filariformlarvae of hookworm,Strongyloides
stercoralis on coming in contact with fecal
polluted soil.
(b) Piercing the skin cercariae of
Schitosoma japonicum,S.mansoni and S.haematobium
on coming in contact with infected water.
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C. Inoculation by an arthropode vector The
parasite is introduced percutaneously when the
arthropod punctures the skin to feed, i.e.
malaria parasites , the leishmanias, trypanosomes
and filariaes. D. Other route (a) Inhalation of
air-borne eggs of Enterobius vermicularis into
the posterior pharynx
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(b) Transplacental (congenital) infection
Toxoplasma gondi, and occasionally with malaria
parasites, blood flukes and others
(c) Blood transfusion malaria. (d)
Transmammary (milk) infection Strongyloides,
Ancylostoma, and certain trematodes. (e) By
sexual intercourse Trichomonas vaginalis.
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(3) Susceptible population or Subjects of
individuals Humans or animals who are weakly or
defectively resistant to certain parasites.
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2. Prevention and control

• Prevention of parasitic disease refers to
  its interception
• Control refers to check the possibilities of
  dissemination of infection and epidemics,reduce
  and maintain a low level of parasitic infections
  prevalent in human population

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• Three measures should be implemented
• Treatment of the source of infection
• (2) Blockade of the pathways of transmission
• (3) Protection of the susceptible population.

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Summary
Could you answer the 5 questions?
1.What is the parasitism ? 2.Definition of
parasite, host, life cycle and infective
stage. 3. How do the parasites injure human
beings? 4. How do the parasites infect
host? 5.How to prevent and control parasitosis?