Download Human parasitology

Introduction to Parasitology

Medical parasitology deals with parasites
which cause human infections and diseases they
produce.
Taxonomic classification of protozoa
Sub
kingdom
Protozoa
Phylum
Sarcomastigophora
further divided into
Sub-phylum
Sarcodina-- -
Genusexamples
Speciesexamples
Entamoeba
E. histolytica
Giardia
G. lamblia
Plasmodium
P. falciparum,
P. vivax,
P. malariae,
P. ovale
Balantidium
B. coli
Enterocytozoa
E. bienusi
move by
pseudopodia
Mastigophora
move by flagella
Apicomplexa
no organelle of
locomotion
Ciliophora
move by cillia
Microspora
Spore-forming
• Class Lobosea
Medical
• Class Zoomastigophorea
Protozoology
• Class Sporozoa
Medical
Helminthology
• Class Ciliophora
• Class Nematoda
• Class Trematoda
• Class Cestoda
A parasite: “a living organism that acquires some of its
basic nutritional requirements through its intimate contact
with another living organism”.
 Parasites may be simple unicellular or complex
multicellular.
Protozoa: unicellular organisms, e.g. Plasmodium
Metazoa: multicellular organisms, e.g. helminths (worms)
and arthropods (ticks, lice)
An endoparasite: “a parasite that lives within
another living organism” – e.g. malaria, Giardia
An ectoparasite: “a parasite that lives on the
external surface of another living organism” – e.g.
lice, ticks
Vector: “a living carrier (e.g.an arthropod) that
transports a pathogenic organism from an infected to
a non-infected host”. Eg; female Anopheles mosquito
that transmits malaria
Endoparasite
Ectoparasite
“the organism in, or on, which the parasite
lives and causes harm”
 Host:
host: “the organism in which the adult or
sexually mature stage of the parasite lives”
 Definitive
host: “the organism in which the
parasite lives during a period of its development
only”
 Intermediate

Reservoir hosts: 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.
Life cycle

Life cycle 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.

Infective Stage is a stage when a parasite can
invade human body and live in it .

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.
Mechanical Transmission: Arthropods play a
role in the transportation of pathogens, which is
not indispensable for the disease transmission.
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.
Protozoans
Microscopic single celled organisms that are
categorized according to their method of
movements
– Ciliates – the only parasitic ciliate that causes
disease in humans in Balantidium coli
– Flagellates – three of the most common and
medically significant include
Giardia lamblia, Trypanosome sp. and
Trichomonas vaginalis
Amoeba –
Eg; Entamoeba - cause dysentery in humans
Examples of important intestinal protozoa
Transmitted by the faecal-oral route
 Giardia lamblia: live in small
intestine and results in
malabsorption
 Entamoeba histolytica: may invade
the colon and cause bloody
diarrhoea – amoebic dysentery.
Also causes ameobic liver abscess.
 Cryptosporidium parvum: prevalent
in immunocompromised
 Balantidium coli: a large motile
ciliated parasite that lives in the
colon of pigs, humans and rodents
and can lead to colonic ulceration
Electron micrograph of G.
lamblia trophozoites (feeding
stage)
Typical flask-shaped ulcer
due to E. histolytica in the
colonic mucosa
Taxonomic classification of helminths
Sub
kingdom
Metazoa
Phylum
Class
Genus –
examples
Ascaris (roundworm)
Trichuris (whipworm)
Ancylostoma (hookworm)
Necator (hookworm)
Enterobius (pinworm or
threadworm)
Strongyloides
Nematodes
Round worms; appear round
in cross section, they have
body cavities, a straight
alimentary canal and an
anus
Platyhelminthes
Cestodes
Flat worms; dorsoventrally
flattened, no body cavity
and, if present, the
alimentary canal is blind
ending
Adult tapeworms are found in
the intestine of their host
They have a head (scolex) with
sucking organs, a segmented
body but no alimentary canal
Each body segment is
hermaphrodite
Trematodes
Non-segmented, usually leafshaped, with two suckers but
no distinct head
They have an alimentary canal
and are usually hermaphrodite
and leaf shaped
Schistosomes are the
exception. They are threadlike, and have separate sexes
Taenia (tapeworm)
Fasciolopsis (liver fluke)
Schistosoma (not leaf
shaped!)
Cestodes
Intestinal - (“tapeworms”)
Taenia saginata
– acquired by ingestion of contaminated,
uncooked beef
– a common infection but causes minimal
symptoms
 Taenia solium
– acquired by ingestion of contaminated,
uncooked pork that contains cystercerci
– Less common, but causes cystercicosis – a
systemic disease where cysticerci encyst in
muscles and in the brain
1.

2. Systemic
 Echinococcus granulosus (dog tapeworm) and
Echinicoccus multilocularis (rodent tapeworm)
–
Hydatid disease occurs when the larval stages
of these organisms are ingested
Examples of important metazoa –trematodes
(flukes)
Intestinal
 Fasciola hepatica
(liver fluke)Fasciolopsis buski
Primarily, a parasite of
sheep, humans become
infected when they
ingest metacercariae
that have encysted on
watercress. The adult
trematode lives in the
intra-hepatic bile ducts
of the liver.
“Fascioliasis” can lead
to severe anaemia in
humans
Nematodes – intestinal nematodes




Trichuris (whipworm)
 Ascaris (roundworm)
– A soil transmitted helminth
– Found world-wide
Ancylostoma and Necator
in conditions of
(hookworms)
poor hygiene,
– A major cause of anaemia in the
transmitted by the
tropics
faecal- oral route
Strongyloides
– Adult worms lives
– inhabits the small bowel
in the small
– infection more severe in
immunospressed people (e.g.
intestine
HIV/AIDS, malnutrition,
intercurrent disease
Enterobius (pinworm or
threadworm)
Heavy intestinal infections may occur
– found mainly in children
with Ascaris. Adult worms can be
several cms long.
Examples for systemic nematodes
Filaria including:

Wuchereria bancrofti
– The major causative
agent of lymphatic
filariasis

Brugia malayi –
Another microfilarial
parasite that causes
lymphatic filariasis
Parasites’ Harms to Man




Mechanical effects
Depriving nourishment from hosts
Toxic effect
Immuno-pathological lesion
Pathogenesis:

1. Source of infection
– infected persons
– carriers
– animals

2. Mode of transmission
– ingestion
– Through skin contact
– Vectors
– direct

3. Susceptible host
– immunity
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