Department of Parasitology
Guangxi Medical University
HUMAN
PARASITOLOGY
Huan huan Shi (石焕焕)
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.
HARMFULNESS OF PARASITES
TO HUMAN BEINGS
Six important tropical diseases defined by
WHO:
1 Malaria
2 Schistosomiasis
3 Filariasis
4 Leishmaniasis
5 Trypanosomiasis
6 Leprosy
parasitosis
INTRODUCTION
TO HUMAN
PARASITOLOGY
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?
1
PARASITISM, PARASITE
AND HOST
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
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
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
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 ).
2
LIFE CYCLE AND
INFECTIVE STAGE
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.
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
3
THE RELATIONSHIP
BETWEEN
PARASITE AND
HOST
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
2.Effects of Host on Parasite ---- immunity
(refer to immunology)
Feature of parasitic immunity
1. Complication of antigens
2. Non-sterilizing immunity is commoner:
premunition (malaria),concomitant
immunity (schistosoma)
3. Re-infection occurs often
Results from reaction between
parasite and host
1. Parasite will be eliminated
2. Keep balance ( suppressive
infection ,carrier)
3. Parasitosis
4
EPIDEMIOLOGY OF
PARASITOSIS
1. Factors of transmission
Source of infection
parasite
Subjects of
individuals
Pathways of
transmission
(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.
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;
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),
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.
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;
(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.
(3) Susceptible population or Subjects of
individuals
Humans or animals who are weakly or
defectively resistant to certain parasites.
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
Three measures should be implemented:
(1) Treatment of the source of infection;
(2) Blockade of the pathways of transmission;
(3) Protection of the susceptible population.
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?