This document provides an introduction to medical parasitology. It outlines the learning outcomes which are to provide knowledge on principles of medical parasitology, the role of parasites in health and disease, clinical manifestations of infectious diseases, laboratory diagnosis of parasites and treatment. It then discusses various aspects of parasitology including types of parasites, hosts, sources of infection, portals of entry, life cycles, immunity, and laboratory diagnosis. Key points covered are microparasites vs macroparasites, types of hosts including definitive, intermediate, reservoir and vectors. Sources of infection include contaminated soil, water, undercooked meat. Portals of entry include skin, sexual contact, congenital. Life cycles vary from no intermediate host to one or two
2. Learning outcomes
• To give sufficient knowledge on Principles of medical
parasitology
• To elaborate on the role of parasites in health and
diseases
• To enhance the knowledge on the clinical
manifestations of infectious diseases
• To develop the skill on Laboratory diagnosis of
parasites and its treatment
• To enhance the knowledge on epidemiology of
common infectious diseases
3. Parasitology
Parasitology is the area of biology/science
that deals with organisms that seek
shelter and nourishment on or within
other living
organism
This means it forms a synthesis of
other discipline on techniques from
fields such as cell biology, molecular
biology, genetics, ecology, evolution,
biochemistry and immunology
4. Point to focus on:-
a. Types of parasites
b. Type of host
c. Sources of infection
d. Portal of Entry
e. Life Cycle of Parasite
f. Laboratory Diagnosis
5. a. Types of Parasites
Parasites
Microparasite Macroparasite
Small, unicellular & multiplies Large, multicellular and has
within its vertebrate host, example no direct reproduction within
like protozoa, fungi, bacteria its vertebrate host
Ectoparasites- organism which live on the surface of the body eg mites
Endoparasites- organism that live within the body of the host are known
endoparasites. Example of endoparasites are obligate parasites,
facultative parasites, accidental parasites, aberrant parasites &
free living
6. Endoparasites
• Obligate parasites- cannot exist without a
parasitic life
• Facultative parasites- organism that under favorable
circumstance may live either a parasitic or free living
existence
• Accidental parasites- organism that attack an unusual
host
• Aberrant parasites- organism that attack a host
where they cannot live or develop further
• Free living- non-parasitic stages of existence which are
lived independently of a host, eg hookworms
7. Host
An organism which harbours the parasite & provides the
nourishment and shelter to the parasites
i) Definitive host
ii) Intermediate host
iii) Paratenic host
iv) Reservoir host
v) Compromised host
vi) Zoonosis
vii) Vector
8. Type of
Host
Definitive host
Harbours the adult or sexually mature
stages of the parasite
(or in whom sexual reproduction occurs)
e.g. man is DH for Schistosoma
haematobium, while female Anopheles
mosquito is DH for Plasmodium species
(malaria parasites
Intermediate host
Intermediate host (IH) that harbours
larval or sexually immature stages of
the parasite (or in whom asexual
reproduction occurs)
Paratenic host
It is a host is which larval stage of a
parasite survives but does not
develop further
Reservoir host
Reservoir host harbors the same species and same stages
of the parasite as
man. It maintains the life cycle of the parasite in nature
and is therefore, a reservoir
source of infection for man. e.g. sheep are RH for Fasciola
hepatica
Compromised Host
A host in whom defense
mechanism are impaired
(e.g AIDS), absent (e.g.,
congemital deficiences)
Zoonosis
An animal infection that is
naturally transmissible to
humans either directly or
indirectly
Vector
An agent that transmits an infection from
one human host to another
9. Host-Parasite Relationship
Symbiosis
An association
whereby both partners
benefits from the
association.
Neither of the partners
suffers from any harm
from this association
Commensalism
An association in which only
parasite derives benefit without
causing injury to the host
Parasitism
An association in
which the a parasite
benefits & the host
provides the
benefits
10. S
o
u
r
c
e
o
f
I
n
f
e
c
t
i
o
n
Contaminated soil; Ascaris lumbricoides, Necator
americanus, Strongloides stercoralis, Trichuris
trichiura
Contaminated water; Entamoeba histolytica,
Giardia lamblia, Balantidium coli, Hymenolepsis
Contaminated freshwater fishes, constitute the
source of Clonorchis sinensis
Raw or undercooked beef/pork, can contribute
to T.solium, T.saginata and Trichinella spiralis
Dog and cats can cause Toxoplasma spp
11. Portal of Entry Into the Body
Skin- A.duodenale,
N.americanus,
S.stercoralis,
Plasmodium spp
Sexual contact-
Trichomonas vaginalis.
E.histolytica and
G.lamblia may also be
transmitted.
Kissing- E.gingivalis can
be transmitted from
peson-to-person by
kissing
Congenital- Infection
with T.gondii and
Plasmodium spp may be
transmitted from
mother to foetus
transplacentally
Latrogenic infection
Malaria parasites may
be transmitted by
transfusion of blood
from the donor whom
positive for malaria
12. Life Cycle of Parasites
No Intermediate Host
Protozoa
Entamoeba histolytica
Giardia lamblia
Balantidium coli
Trichomonas vaginalis
One Intermediate Host
Pig Taenia solium
T.saginata, Trichinella spiralis
Cow Taenia saginata
Mosquito Wuchereria bancrofti
Two Intermediate Hosts
Snail, plant Paragonimus westermani
Fasciola spp
13. Immunity in Parasitic Infections
• Due to their biochemical & structural complexity,
protozoa and helminths present a large number of
antigens to their host.
• But immunological protection against parasitic
infection is less efficient in human compared to
bacterial and viral infections.
• This is due to parasites a very large in group and
more structurally complex.
• Immune response for parasitic infections are
contributed by Cytotoxic T (Tc) cells, Natural killer
(NK) cells, Activated macrophages and antibody
(produced by B-cells).
14. Laboratory Diagnosis
• Clinical Specimens:-
• A) Blood
Blood film used in diagnosis for
Plasmodium spp, Babesia spp, W.bancrofti
• B) Stool
Used mainly to diagnosis intestinal
parasitic infections & helminthic infections
of the biliary tract . Example E.histolytica,
G.lamblia, B.coli, Ascaris lumbricoides,
trichuris trichiura
