1.general introduction to medical parasitology

Medical
（ Human ） Parasitology
Cheng Yanbin
chengyb@mail.xjtu.edu.cn
Department of Immunology &
Pathogenic Biology
2017

Pathogens
 pathogens ---- human infectious diseases.
 Include viruses, bacteria, and
fungi （ microbiology ）
 And parasites (parasitology) .
 Parasitic diseases.
 Parasitology is very important in medicine.

Nobel laureates who study on parasite or
parasitic disease
1880 1897 1917 1948

Tu Youyou (herbal
expert), Chinese
scientist, won the
Nobel Prize in 2015 for
discovering artemisinin
(also known
as qinghaosu ，青蒿
素 )
and dihydroartemisinin
, used to treat malaria,
which saved millions
of lives.

How to study human parasitology?
 listen to the teachers in class carefully
 Observe the specimens in laboratory carefully
 Review the knowledge points frequently
 Discuss with teachers or other students actively
 Read textbooks or related websites extensively

Teaching requirements
(knowledge points )
 GRASP (KNOW VERY WELL):
morphology and life cycle of parasites;
 FAMILIARIZE (KNOW WELL):
pathogenesis and diagnosis of parasitic
diseases.
 UNDERSTAND (KNOW):
prevalence, and the prevention and control
of parasitic diseases.

Teaching types & program
 Lecture: 24 hours (3 hours×8)
(teachers) Introduce main
parasites and related parasitic diseases
 Experiment: 12 hours (3 hours×4)
(you) Observe the morphologic
characteristics of parasites with the
microscope or by your eyes
(you) Draw the structures of
parasites according to your observation

Reference books
 Apurba Sankar Sastry, and Sandhya Bhat K. Essentials
of Medical Parasitology. London: JAYPEE BROTHERS
MEDICAL PUBLUSGERS LTD. 2014
 Wang Shiping and Ye Siying. Textbook of medical
microbiology and parasitology. Beijing: Science press.
2006
 Lynne Shore Garecia. Diagnostic medical parasitology.
Washington: ASM Press. 5th ed. 2006
 He Shenyi. Human parasitology. Shandong: Shandong
university press. 2011

Websites for parasitolgy &
parasitic disease (browse)
 http://www.dpd.cdc.gov/DPDx/HTML/iMAGE_Libr
 http://www.cdc.gov
 http://www.dpd.cdc.gov/DPDx/Default.htm
 http://apps.who.int/tdr/
 http://www.parasite.org.au/

General Introduction to
Medical Parasitology
 What is the Medical Parasitology?
 Taxonomy of parasites
 Conceptions related to medical parasitology
 Relationships between parasites and hosts
 Laboratory diagnosis of parasitic diseases
 Treatment of parasitic diseases
 The basic factors of transmission of parasitic diseases
 The preventive measures of parasitic diseases

What is the Medical
Parasitology?
 It deal with the study of parasites, which infect
and produce diseases in human beings.
 Include the morphology, the life cycle,
pathogenesis of parasites , and the diagnosis,
the transmission, prevalence, and the prevention
and control of the diseases.
 So, study parasites and parasitic diseases.

Medical Parasitology
Parasites Parasitic diseases
Morphology
LifeCycle
Pathogenesis
Diagnosis
Treatment
Transmission
Prevention

 All parasites are classified under the following
taxonomic units—the (sub) kingdom, (sub)
phylum, (super) class, (sub) order, (super)
family, genus and species.
 Each parasites has two names: a genus and a
species name.
 The generic name of the parasite always begins
with an initial capital letter and species name
with an small letter, e.g., Entamoba histolitica.
Taxonomy of parasites

Taxonomy of parasites
 Derived from: names of their discoverers, Greek
or Latin words of the geographical area where
they are found, habitat of the parasite, or hosts
in which parasites are found and its size and
shape. e.g., Entamoba coli. Toxoplasma gondii.
shape organ shape area
(change of form) (colon) (toxo-) (gondii)
Brugia malayi (are found in malaysia)
Wuchereria bancrofti (are found by bancroft)

Conceptions related to
medical parasitology
 Symbiosis
 Parasite and type of parasites
 Host and common type of host
 Life cycle and type of life cycle

Symbiosis
------This is about the biological phenomenon.
The relationship between two living things
(animals). Two living things live together and
involve protection or other advantages to one
or both partner.
 Commensalism
 Mutualism
 Parasitism*

Commensalis
m
---- commensalism is a
class of relationship
between two
organisms where one
organism benefits but
the other is neutral
(there is no harm or
benefit).
Fig. A female pea crab in the
mantle cavity of its mussel host.
The crab does not damage the
mussel and uses its shell purely
for protection

Remora sharks have an adhesive disk on the
dorsal surface of their heads. They use this
adhesive disk to “hitch a ride” on whales. When
food floats away from the whale’s mouth, the
remora can unhitch itself and collect the scraps
of food floating by.

Mutualism
------ An association which is beneficial to both
living things.
Fig. A selection of ciliates from the rumen of cattle or
sheep. The rumen contains enormous numbers of ciliates
that break down cellulose in the feed. nourishment

 Red-billed oxpeckers are on the back of
impala, and feed on small insects or eggs in
back of impala. The relationship benefits both
animals.

Parasitism
------ An association which is beneficial to one
partner and harmful to the other partner.
The former that is beneficial to is called
parasite, the latter that is harmful to is
called host.
Human / Hookworm

Parasite and the types of
parasites
 Parasite: It is an animal that is dependent
on another animal (host) for its
survival.
 Types of parasites
Protozoa
Nematodes
Parasites Helminthes Trematodes Endo-
Cestodes
Arthropods ---------------- Ecto-

PROTOZOA: unicellular animals. It is very
small and range in size from 2 to more than
100µm. They have cell membrane, cell
plasma, nucleus.

NEMATODES: vermiform, cylindrical, bilaterally
symmetrical in structure and taper towards their
anterior and posterior ends. Adults are diecious
(sexes are separate)

TREMATODES: typically flattened and leaf-
shaped. There are male and female system
in a fluke body. Adults are hermaphroditic
(sexes are not separate)

CESTODES: long, ribbon-like in shape. Many
ribbon-like chain of segments. Each segment
bear a complete male and female system. Adults
are hermaphroditic (sexes are not separate)

Other classification
Parasites may be classified according to
different ways.
 Obligate parasite: a parasite which cannot
survive in any other manner.
 Facultative parasite: an organism which may
exist in a free-living state and which if
opportunity presents itself may become
parasitic.

Endoparasite and ectoparasite
----A parasite which lives in or on the
body of the host is called endoparasite
(protozoa and heminthes) or ectoparasite
(arthropods).

Host and type of host
 Host : An organism that harbors the parasite and
provides nourishment and shelter. usually larger
than the parasite.
 Intermediate host : The host harboring the larvae
or asexual multiplication (stage) of parasite.
 Final (definitive) host : The host harboring adult or
sexual multiplication (stage) of parasite.
 Reservoir host : Animals harboring the same
species of parasites as man. Potential sources of
human infection.

Life cycle and type of life
cycle
 Life cycle : The whole process of parasite growing
and developing.
 The direct life-cycle : When a parasite requires only
one host to complete its development, it is referred
as direct/simple life cycle. Life cycle with one host.
 The indirect life cycle : When a parasite requires
two hosts (one final host and intermediate host) to
complete its development, it is indirect/ complex life
cycle. Life cycle with more than one host.

Relationships (Effects)
between parasite and host
injure to
Parasites harbour in Host (animal or human)
to response immune produce
 Effects of the parasites on the host
 Effects of the host on the parasites

Effects of parasites on the
host
 Depriving the host of essential substance
Hookworm Suck blood Anemia
 Mechanical effects of parasites on the host
Ascaris Perforate (peritonitis) /
Obstruction(ileus)
 Toxic and allergic effect
E.h Proteolytic enzyme Necrosis/ulcer
Parasite antigen Immune system
e.g Anaphylaxis
Immune response
Allergy/
Hypersensitivity

Depriving the host of
nutrition
 Pathogens utilize nutrition from host environment
for their development and reproduction.
 Helminthes (nematodes or flukes --- have a gut
and mouth) feed upon the surrounding tissues,
body fluids or even host cell debris.
 Tapeworms (no gut or mouth) reply on the host’s
daily intake by their body wall absorbing for their
own food. (osmosis)

 The hookworms, after
completing its migration to small
intestine, feeds by biting deeply
into the mucosa and sucking
blood and tissue fluids.
Hookworm infection cause
anemia due to simple blood loss.

Mechanical effects of
parasites
 Entering the cells: Some protozoa must live and
reproduce in certain cells. Finally result in the
rupture of the host cells.

 Migration or penetration: through tissue or
organ.
such as the larvae of hookworm or Ascaris in
blood can penetrate the wall of capillary of lung
to alveoli, and cause mechanical damage
(Pneumonitis).

 Blockage and pressure: The intestinal lumen
can be blocked by worms. Hydatid cyst in liver
may reach volumes of 1-2 litres, it can cause
severe damage to organ.

Toxic and hypersensitivity
 Toxin: Many parasites can produce toxin and
cause damage to host. In contrast to bacterial
toxin, parasitic toxins have minimal role in
pathogenesis.
 Hypersensitivity: The metabolites, secretion,
excretion or other products --- antigen --- the
immune system of host --- immune response or
hypersensitivity (is harmful to host, or even fatal
reaction).

 Rupture of hydatid cysts with sudden release of
large amounts of fluid --- severe allergic reaction
(anaphylaxis), sometime lead to shock or dead
of patients.

Effects of the host on the
parasites
----The host can produce certain degree resistance to
parasites in human body or re-infection. The
resistance (Immunity) is not very strong. In
general, It don’t wipe out parasites completely, but
may limit the number of parasites and establish
balance with parasites.
 Innate immunity
 Acquired immunity

Innate immunity
 Barrier : Prevent parasites to invade in certain
degree. Skin/Mucosa / Placenta.
 Acid in skin/stomach cause damage of parasites.
 Phagocytosis of phagocyte.
 Complements: it leads to the formation of holes in
the parasite membrane.
 Natural killer cells
----Non-specific/effective against a wide range of
parasitic infection/controlled by genetic factors.
But not very strong!

Acquired immunity
Mechanism : cellular and humoral immunity.
 Sterilizing immunity : Wipe out the parasites
completely, meanwhile get a long-term specific
resistance to re-infection. Rare!
 Non-sterilizing immunity : Wipe out most of the
parasites, but not completely. On the premise of
parasites in the body ， limit the number of
parasites in body ， and get a part of resistance
to re-infection. Common! No parasite, no
immunity!

Laboratory diagnosis of
parasitic diseases
 Parasitic diagnosis --- either microcopically or
macroscopically (parasites) --- very common
 Cultrure methods (parasites)
 Immunodiagnostic methods (antigen and antibody
detection) --- common
 Intradermal skin tests (immune reaction)
 Animal inoculation (parasites)
 Imaging techniques (shape/structure of parasites)

Treatment of parasitic
diseases
Treatment of parasitic diseases is primarily based
on chemotherapy and in some cases by surgery.
 Antiparasitic drugs various chemotherapeitic
agents are used for the treatment and
prophylaxis of parasitic infection.
 Surgical management for management of
parasitic diseases like cystic echinococcosis
and neurocysticercosis surgery is indicated.

The basic factors of
transmission of parasitic
diseases
 The source of the infection
 The modes of transmission
 The susceptible host
----The combined effect of those factors determine
the dispersal and the prevalence of the parasites
at a given time and place and regulate the
incidence of the parasitic diseases in certain
local population.

The source of the infection
 Man : Patient (Persons who have parasites in their
body and show clinical symptoms) or Carrier
(Persons who have parasites in their body, not
show symptoms).
 Animal: Reservoir host (Animals that harbors the
same species of parasites as man. Sometimes,
the parasites in animals can transmit into human).
 Vectors: an arthropod that transmitts the infection
from one infected human being to another.

The modes of transmission I
 Vertical (Congenital) transmission : From mother
(pregnant women) to infant. Toxoplasma gondii
 Contact transmission : Direct contact (sexual
contact)---Trichomonas vaginalis; Indirect
contact---Ascaris lumbricodes
 oral or feco-oral route: the most common mode.
Infection is transmitted orally by ingestion of food,
water or vegetables contaminated with feces
containing the infective stages of parasites

The modes of transmission II
 Penetration of the skin and mucous membranes:
infection is transmitted by the penetration of the
larval forms of parasite through skin.
 Bite of vectors: many parasitic diseases are
transmitted by insect bite such as: malaria,
filariasis, leishmaniasis..
 Blood transmission : Certain parasites can be
transmitted through transfusion of blood or blood
products. Plasmodium; Leishmania; toxplasma.

 Autoinfection: Few intestinal parasites may be
transmitted to the same person by contaminated
hand (external autoinfection) or by reverse
peristalsis (internal autoinfection). Eenterobius
vermicularis

The susceptible host
----In general, most people is the susceptible
host. The parasite reaching a susceptible
host must gain entrance and set up a
favorable residence in order to complete its
life cycle and cause the transmission of
parasitic diseases.

The prevention measures of
the parasitic diseases
 Controlling the source of the infection
Treatment of patients, carriers and reservoir hosts.
 Intervention at the routes of transmission
Managing feces and water resource,controlling or
eliminating vectors and intermediate hosts.
 Protecting the susceptible hosts
Paying attention to personal hygiene, changing bad
eating habit, taking medicine.

Expected questions
 Write short notes on:
(a) Life cycle of parasite
(b) Reservoir host
(c) Parasite
(d) Carrier
 Differentiate between:
(a) Definitive host and intermediate host
(b) Direct and indirect life cycle

 Single choice questions
1. A host harboring adult or sexual stage of a parasite
is called:
(a) Definitive host (b) Intermediate host
(c) Reservoir host (d) None of above
2. Parasite which may be transmitted by sexual
contact is:
(a) Trypanosoma cruzi (b) Trichomonas vaginalis
(c) Trypanosoma bruci (d) Ascaris

3. Which of the following parasite is transmitted by
dog:
(a) Taenia saginata (b) Hymenolepis nana
(c) Echinococcous granulosus
(d) None of above
4. blood-sucking vector may transmit:
(a) Ascaris lumbricoides (b) Hookworm
(c) Taenia saginata (d) Plasmodium

1.general introduction to medical parasitology

1.general introduction to medical parasitology

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