Introduction to Parasitology
MDCN247
Virology and Parasitology
Prof Gülden Çelik, MD
Yeditepe University
Department of Medical Microbiology
MDCN247
Virology and Parasitology
The program: on the web
 Opencourses emu edu tr
 Lab: lab reports are required(if you do not give, you will
not have the chance for lab examination
 2 examinations:

– Midterm (30%) multiple choice(25 questions)
– Final(50%) multiple choice (50 questions)
– Lab examination*(20 %) multiple choice (10 questions)
◦ Incomplete of final (50%) multiple choice (25 questions)
*No incomplete exam for lab
Introduction to parasitology(3h)

At the end of this introduction the student should be
able to
Defines ‘’parasite’’, ’’host’’, ‘’vector’’, ‘’zoonozis’’
 Defines types of organism relatıonships
 Lists the classification of parasitic infections
 Defines cell structure of protozoon and helminths
 Defines the life cycles of parasites
 Modes of infection

Medical microbiology
the study of the interactions between animals (primarily
humans):
 With microorganisms

◦
◦
◦
◦
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Bacteria
Viruses
Fungi
Parasites
Prions
Medical microbiology
the study of the interactions between animals (primarily
humans):
 With microorganisms

◦
◦
◦
◦
◦
Bacteria
Viruses
Fungi
Parasites
Prions
Medical Microbiology

primary interest :
◦ diseases caused by these interactions
◦ Microorganisms play a critical role in human survival.
◦ The normal commensal population of microbes
 participates in the metabolism of food products
 provides essential growth factors
 protects against infections with highly virulent microorganisms
 stimulates the immune response
In the absence of these organisms, life as we know it would be
impossible
Commensal and Pathogenic Microbial
Flora in Humans
The microbial flora in and on the human body:
 continual state of flux determined by a variety of factors
!
◦
◦
◦
◦
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Age
Diet
Hormonal state
Health
personal hygiene
Commensal and Pathogenic Microbial
Flora in Humans
◦ Human fetus lives in a protected, sterile environment
◦ Newborn human is exposed to microbes from the mother and
the environment.
◦ The infant’s skin is colonized first,
 followed by
 the oropharynx
 gastrointestinal tract
 and other mucosal surfaces.
◦ Throughout the life of a human being, this microbial
population continues to change
Commensal and Pathogenic Microbial
Flora in Humans
◦ Changes in health can drastically disrupt the delicate balance
that is maintained among the heterogeneous organisms
coexisting within us:
 hospitalization can lead to the replacement of normally avirulent
organisms in the oropharynx with resistant gram-negative rods (e.g.,
Klebsiella, Pseudomonas) that can invade the lungs and cause pneumonia.
 the indigenous bacteria present in the intestines restrict the growth of
Clostridium difficile in the gastrointestinal tract. In the presence of
antibiotics, however, this indigenous flora is eliminated, and C. difficile is
able to proliferate and produce diarrheal disease and colitis.
Exposure of an individual to an organism
lead to one of three outcomes:
(1) transiently colonize the person
(2) permanently colonize the person, or
(3) produce disease.
It is important to understand the distinction between
colonization and disease. (Note: Many people use the
term infection inappropriately as a synonym for both
terms.)

Exposure of an individual to an organism
Organisms that colonize humans (whether for a short
period, such as hours or days [transient], or
permanently) do not interfere with normal body
functions.
 In contrast, disease occurs when the interaction between
microbe and human leads to a pathologic process
characterized by damage to the human host.

Exposure of an individual to an organism
Disease occurs when the interaction between microbe
and human leads to a pathologic process characterized
by damage to the human host.
 This process can result from

◦ microbial factors (e.g., damage to organs caused by the
proliferation of the microbe or the production of toxins or
cytotoxic enzymes) or
◦ the host’s immune response to the organism :
 the pathology of severe acute respiratory syndrome [SARS] coronavirus
infections
A few infections

are caused by strict pathogens:
◦ organisms always associated with human disease
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Mycobacterium tuberculosis (tuberculosis)
Neisseria gonorrhoeae (gonorrhea)
Francisella tularensis (tularemia)
Plasmodium spp. (malaria)
Rabies virus (rabies)
Opportunistic pathogens
Most human infections are caused by them
 Members of the patient’s normal microbial flora :

◦ Staphylococcus aureus, Escherichia coli, Candida albicans
Do not produce disease in their normal setting but
establish disease when they are introduced into
unprotected sites (e.g., blood, tissues).
 If a patient’s immune system is defective, that patient is
more susceptible to disease caused by opportunistic
pathogens!!!!!

The microbial population
that colonizes the human body is numerous and diverse.
 Our knowledge of the composition of this population is
currently based on comprehensive culture methods
 However, it is estimated that only a small proportion of
the microbes can be cultivated.

Human Microbiome Project (HMP)

To better understand the microbial population, a large
scale project has been initiated to characterize
comprehensively the
◦ human microbiota
◦ analyze its role in human health and disease
Human Microbiome Project (HMP)
The skin and all mucosal surfaces of the human body are
currently being analyzed systematically by genomic
techniques.
 The initial phase of this study was completed in 2012,
and it is apparent that the human microbiome is
complex, composed of many organisms not previously
recognized, and undergoes dynamic changes in disease.
 http://nihroadmap.nih.gov/hmp/.

TYPES OF ORGANISM RELATIONSHIPS

Normal Flora. Normal flora consists of microorganisms that are normally
and consistently found in or on the body in the absence of disease.

Symbiosis. This is the close association or living together of two
organisms of different species; each party involved in this relationship is
called a symbiont.

Mutualism. This is a type of symbiosis in which both organisms (host and
parasite) benefit from the association.
TYPES OF ORGANISM RELATIONSHIPS

Commensalism. This is also a type of symbiosis, but in this
case, the parasite (commensal) is benefited and the host is
neither benefited nor harmed by the relationship

Parasitism. Parasitism is an obligatory relationship in which one
organism, the parasite, is metabolically dependent on another
organism, the host. The host may be harmed by such a
relationship.
Parasitology
Introduction
Parasitic Classification
 Structure
 Replication

Parasites
interrelationships among parasitic organisms
 their epidemiology
 transmission of disease
 the specific disease processes involved
 the possibilities for prevention and control of maladies

Worldwide disease burden

Malaria >500 million infected people,
annual death

Ascariasis 1.3 billion infected annual 60.000 death
2-3 million
Case History

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



An 18-year-old villager girl
reported to the emergency department
with a history of recurrent vomiting and abdominal pain of
one day duration. The patient gave history of loss of appetite
and nausea of the same duration
put on NPO, I.V.-fluids
On the next day, the nasogastric tube got blocked and was
subsequently removed.
On removal, the head end of a tapeworm which was
retrieved through the nose:
http://ispub.com/IJS/16/2/9449
http://ispub.com/IJS/16/2/9449
The patient got instant relief of her symptoms.
 Microbiological examination confirmed it to be a 6.3
meter long Taenia saginata strobila with immature,
mature and gravid proglottids.
 The patient was given a single dose of praziquantel: 15
mg/kg body weight.
 Parasitological controls (two series of three fecal samples
each), performed two months later, were negative for
Taenia eggs.

http://ispub.com/IJS/16/2/9449
Taenia saginata,
 the beef tape worm
 a parasite (cestode) of both cattle and humans,
 which can only reproduce in humans. T. saginata occurs
where cattle is raised, human feces is improperly disposed
off, meat inspection programs are poor, and where meat is
eaten without proper cooking.
 Approximately 50 million people worldwide are infected by
T saginata or T solium.

http://ispub.com/IJS/16/2/9449
Taenia genus

Two species from the genus are common parasites of man:
◦
◦
◦
◦
◦
Taenia solium (the pork tapeworm)
Taenia saginata (the beef tapeworm).
Improperly disposed human feces,
poor meat inspection programs, and
eating of improperly cooked meat are well known risk factors for the
transmission of the disease.
◦ Rarely, the worm may be present in the stomach leading to potentially
infective oro-gastric secretions of these patients. Contamination with
these secretions may lead to infection to the caregivers making it an
unusual but important route of transmission of taeniasis, particularly in
the highly endemic areas.
Some basic parasite terminology
Ectoparasites:
 Ectoparasites are true parasites in that they depend on the host for habitat
and nutrition but they live on and not in theirs hosts.
 While less invasive some ectoparasites can nonetheless cause serious
disease.
Endoparasites:
 These parasites live in the bodies and tissues of their hosts, some
even live within the cells that make up their hosts.
◦ Malaria :the red bloods cells of the circulatory system
◦ Tape worm: lives in the intestine.
Some basic parasite terminology
Infection:
 Infectious diseases are caused by
◦ transmissible organisms
◦ biological agents (in the case of viruses and prions).
In its narrower definition infection
implies that the biological agents multiplies within the host.
In the case of malaria :
-the mosquito injects 10-100 parasites
-within two weeks multiply into many millions. This multiplication
is essential to the development of disease.

Infestation:


Some parasites do not multiply within the host:
This situation is referred to as infestation:
◦ This is true for most worms. A person who swallows three
tape worm larvae will not develop more than three tape
worms.
◦ The severity of disease in infestations therefore is often highly
dependent of the infectious (or infestious) dose.
Infection is often used more generally to describe both
phenomena.
Obligate/facultative parasitism

Obligate Parasitism:
◦ complete dependence of the parasite on the host
The vast majority of parasites that cause human disease are
obligate parasites

Facultative parasites:
◦ Can switch between a parasitic and a free-living lifestyle. This is
often triggered by ecological factors (e.g. the availability of hosts or
nutrition)
Parasite

eukaryotic organisms:
◦
◦
◦
◦
◦
mainly protozoa
helminths
some arthropods
annelids
molluscs.
Medical parasitology


200 or so species of helminth worms
about 80 species of protozoa that infect humans.
Ancient History
The Ebers papyrus, written about 1600 BC, contains
references to the presence of parasitic worms in man.
 The laws of the Mosaic code prohibiting the consumption
of meat from unclean animals indicate that the early
Israelites had knowledge about parasitic infections.
 There is also evidence of parasitic recognition among the
Roman, Greek, Persian, and Phoenician scientists.
 Chinese doctors were aware of parasites as early as 300
BC.

Modern History
 The
liver fluke Fasciola hepatica was
discovered by Jehan de Brie in 1379 from
sheep.
 Anton Van Leewenhoek (1632-1723)
described the morphology of the protozoan
Giardia lamblia from his own stool.
 In 1880, Laveran demonstrated the
intracellular parasites of malaria.
Misconceptions

Many people believed that lice protected children from disease and
leeches were used extensively for blood letting as a cure.

For a time, intestinal parasites were thought to help incleaning the tract of
excess food and waste

Until recently, the Chinese believed that powdered Ascaris was helpful for
medicinal treatment of impotency. In France, the heads of
tapeworms(scolices) were once used as weight control measures.
Present Ideology
Modern medicine:
 recognized the pathogenic effects of parasites
◦ searching for drugs useful in the treatment of parasitic
infections
 Prevention
is the best method to attack the
problem of parasites.
Life cycles
Definitive host:
 This is the host in which the parasite reproduces sexually.
Intermediate host:
 One or several successive hosts in which the parasite might
increase its number by asexual multiplication.
Vector:
 Hosts that actively transmit the parasite to the next host as
opposed to just being by that next host.
◦ Mosquito which injects malaria parasites with it salvia into humans
during a blood meal.
Life cycles
Transport (or paratenic) hosts:
 No parasite development or multiplication occurs
 The parasite just hitches a ride on the food chain:
◦ The larva of the fish tape worm can move in this way from smaller fish to
bigger fish and yet bigger fish awaiting the definitive
mammal host to eat a fish.
Life cycles
Reservoir host:
 Some parasites can infect a variety of mammals in addition to humans.
 Biologically these hosts are equal to humans meaning that they occupy
the same position in the life cycle and are not up or downstream.
 These hosts (often wild or domestic animals living İn proximity to
humans) present a reservoir out of which humans can be re-infected
even if the disease has been cleared from all humans in the area.
 The presence or absence of a reservoir is obviously a very important
consideration for programs aimed at controlling or eradicating a
disease. while a dead end for the parasite this can still cause disease. We
will highlight some examples of such disease when we discuss human infection with cat and dog
parasites.
Disease Terminology
Prepatency:
 The phase of the disease between infection and the appearance
of diagnosable parasite stages
◦ the appearance of tape worm eggs in the feces
◦ malaria parasites in a routine blood smear

This time frame can change with improvements in the sensitivity
of diagnostic assays

A patent infection is thus at an established diagnosable stage.
Disease Terminology
Incubation period:
 The incubation period is the time between infection and the
development of symptoms (signs of disease like fever, pain or
discomfort)
Acute disease:
 With the onset of symptoms the infection enters its acute (lat. sharp)
phase.
 Acute diseases have a relatively quick onset and short duration.
 The symptoms worsen into a crisis and then the disease resolves
spontaneously into healing, results in the death of the patient, or
transforms into chronic disease.
Chronic disease:

Chronic diseases (gr. chronos, time)
◦ develop slowly (often over years)
◦ Persistent
◦ might show no symptoms once chronic or worsen
over time.
In chronic infections the parasite survives or
persists over time (this time can be the rest of the life of
the patient).
Convalescence:
period after healing
Describes a phase in which balance is regained and damage
repaired.
 This phase is characterized by the absence of infectious agents
and symptoms, and in certain cases goes along with the
development of long-term immunity to reinfection.


A typical parasite life cycle diagram
The fish tape worm
Parasite stages are shown in the outer
circle and hosts in the center
 The worm reproduces sexually in
mammals (definitive host).
 A motile larva hatches and infects the
first intermediate host a waterflea and
transforms and grows.
 The waterflea is eaten by a fish again
the parasite transforms and now lives
in the musculature of the fish.
Note that there is no further development of
the parasite from trout to pike. The pike is a transport
host.

PARASITIC ATTRIBUTES THAT INFLUENCE
DISEASE
Virulence. Virulence refers to the ability of a parasite to establish itself in a
host, maintain that infection, and damage the body of the host. For one reason or
another, one strain of a parasite may cause a more serious disease process than other
strains of the same species.
Parasitosis. The more parasites infecting a host, the more severe will be the
effect on that host.
Life Span of the Parasite. The longer the parasite lives in or on the host, the
greater the damage that will be caused.
Repeated Contact.
 The more times that a host is parasitized by an organism, all other factors
being equal, the worse the prognosis of the disease.
Competition for Food.
 Intestinal parasites deprive the host of the necessary nutrients required for
survival.
Mechanical Interference.
 Some parasites accumulate (like in the intestines) in such great numbers that
the normal flow of nutrients, waste, or fluid is obstructed.
 For example, the microfilariae of some nematodes obstruct the lymphatic
system in elephantiasis. Their presence prevents lymphatic fluid from being
circulated out of lymphatic tissue and the swelling associated with
elephantiasis results.
Toxic Effects.
 By-products of metabolism and anatomic parts of the parasite
can be very toxic to the host.
In cases of massive infections with Trichinella spiralis, it is this toxicity that is lethal to
the host.
Tumor.
 Tumor formation in the host is a common occurrence with parasites
that invade or irritate the tissue of the host.
 Pathologists have suggested that repeated infections with Trichomonas vaginalis
could lead to cervical cancer ?
 recently, some cases of malignant neoplasms have been reported from Egypt and
attributed to Schistosoma infections.
 Some benign tumors are caused by the larval stage of the tapeworm Taenia solium
in muscle tissue.
Loss of Blood and Body Fluids.
 The loss of blood and body fluids caused by parasites is significant.
 For example, it has been calculated that about 0.5 ml of blood per worm
per day is lost by the host during a hookworm infection.
These fluids contain nutrients and electrolytes needed by the host.
Destruction of Host Tissue.
 Parasites destroy the host's tissue structures by the presence and
activity of the adults, by the migration of larval forms, and by ovipository
migrations.
Psychological Disorders.
 The knowledge of parasites crawling inside the body can affect anxiety
level of the host. But, the more detrimental psychological effects are
those caused by the accumulation of chemicals in the system of the
host.
HOST ATTRIBUTES THAT INFLUENCE RESISTANCE TO PATHOGENIC
EFFECTS OF PARASITISM
Fitness of the Host.
 The nutritional and emotional state of the
host can effect the degree of pathogenicity caused by the
parasite.
Host Age.
 Both the very young and the very old are affected to a
Greater degree by a parasitic infection than are young adults.
HOST ATTRIBUTES THAT INFLUENCE RESISTANCE TO PATHOGENIC
EFFECTS OF PARASITISM
Specific Factors That Influence Resistance.
Immunity.
Host resistance to parasitic infection is very similar to the
resistance shown against bacteria.
 The immune system works by the formation of antibodies against
a limitless amount of
substances recognized as foreign antigens by the B lymphocytes.

Complement system.
 This is a complex system of enzymes found in normal serum that aids the
lysis (destruction) of the parasite during an antigen-antibody reaction.
 Complement is composed of nine components labeled C-1 through C-9.
Interferon.
 Interferon is composed of a group of soluble small proteins produced by
infected cells that inhibit multiplication of virus.
 The proteins are not virus specific, but they are cell specific in production
and effects.
Nonspecific Factors That Influence Resistance.
 There are some Barriers that affect parasitism.
 These barriers may be chemical, physical,or biological (the
antagonistic effect of organisms already present at the
site in question).
Barriers
Chemical barriers.
The host combats the invasion of micro-organisms by the secretion of
chemicals that are antimicrobial in nature:
 The acid pH of the stomachskin, and vagina;
 the bile salts of the intestines; and
 the lysozymes of the eyes and saliva serve as deterents to the invasion of
microorganisms.
(1)
Barriers
(2) Physical barriers.
 The intact skin,
 mucus (sticky lining of the mucous membranes)
 nasal hairs,
 cilia of the respiratory epithelium,
 Peristaltic movement, and
 normal microbial flora (occupying attachment sites)
prevent the entrance of microorganisms.
Barriers
(3) Microbial antagonism.
 Antiparasitic factors present in the serum
 competition for nutrients from the normal flora
also serve as obstacles for the possible pathogenic parasites.
TAXONOMY OF PARASITES INFECTING HUMANS
All living organisms have been divided into groups with similar
characteristics.
 These groups have been subdivided further until organisms that
have identical traits are classified under the same genus and
species.
 It is important that you be familiar with the principles of
taxonomy pertaining to parasites.

TAXONOMY OF PARASITES INFECTING HUMANS
DIVISIONS OF LIVING ORGANISMS
a. Kingdom. This is a large group of organisms with similar features. In the
literature, various authors list from two to five kingdoms.
(1) Kingdom PLANTA. This kingdom contains all of the plants. There are
no plants parasitic to man.
(2) Kingdom PROTISTA. Members of this kingdom are unicellular (onecelled) organisms. The kingdom is further divided into two subkingdoms.
(a) Subkingdom EUCARYOTA. Eucaryotes are characterized by a
nuclear membrane separating the nucleus from the cytoplasm, DNA that is
grouped into units called chromosomes, multiplication accomplished by
mitosis, and energy produced in structures called mitochondria. Some
examples are protozoans and fungi.
(b) Subkingdom PROCARYOTA. The procaryotes are characterized
by no nuclear membrane (therefore, there is no organized
nucleus); no chromosomes (the DNA is not separated but is a
continuous strand); no mitosis (multiplication is accomplished by
simple cell division); and no mitochondria (energy is produced at
The mesosomes). Some examples are bacteria and bluegreen
algae.
(3) Kingdom ANIMALIA. The higher animals, including man, are
placed in this kingdom. There are many parasites that infect man
in this kingdom.
Phylum. A phylum is a major division of a kingdom. There are
four phyla (plural of phylum) that contain human parasites:
PROTOZOA from the subkingdom EUCARYOTA, and phyla
PLATYHELMINTHES, ASCHELMINTHES, and
ACANTHOCEPHAHELMINTHES from the kingdom ANIMALIA.
c. Class. A phylum is divided into classes. The name of the class
should end in "a." Some examples are Cestoda and Nematoda.
d. Order. Several orders may be contained within a class. This
name ends in "ea." Some examples are Filaroidea,
Pseudophyllidea.
e. Family. An order may be subdivided into families. The family's
ending is "ae." Some examples are Heterophyidae and
Endamoebidae.
f. Genus.
Each family is made up of various genera (plural of Genus). The
genus name may have various endings. The first letter of the genus is
capitalized and the name is underlined. The first letter may be used as an
abbreviation:
Macracanthorhynchus and Entamoeba.
g. Species.
 Each genus is composed of species. The species' name may also
have various endings. All letters are small case and the name is underlined.
However,the species' name should never be abbreviated:
E. histolytica and M. hirudinaceus.
h. Identification. Parasitic organisms identified by laboratory procedures are
reported by using the genus and species names. Some examples are Giardia
Lamblia and Enterobius vermicularis.

Taxonomy
The major divisions involved in medical parasitology:
 Protozoa
◦ intestinal and urogenital protozoa
◦ blood and tissue protozoa
nematodes, trematodes, cestodes
 arthropods.

Classification
The parasites of humans:
 the four eukaryotic kingdoms:
 Protozoa,
 Animalia (Metazoa)
 Fungi(Microspora )
 Stramenopila (formerly Chromista).
Classification

Morphology
◦ intracytoplasmic structures:the nucleus
◦ the type of locomotive organelles
◦ Mode of reproduction


Biochemistry
Molecular biology of lower organisms (e.g., Protozoa, Fungi,
and Stramenopila)
◦ Comparisons of
 small subunit ribosomal ribonucleic acid (SSU rRNA)
 protein sequences have made it possible to arrange organisms within groups
based on evolutionary distances.
Classification

The Protozoa:
◦ animals whose life functions occur in a single cell
Classification

The microsporidians
◦ single-celled organisms
◦ previously classified among the protozoans
◦ now thought to be more closely related to fungi
Classification

Kingdom Animalia:metazoans
◦ multicellular animals
◦ life functions occur in cellular structures organized as tissue
and organ systems.
Protozoa
simple microorganisms
 size ranges from 2 to 100 µm
 their protoplasm is enclosed by a cell membrane

◦ contains numerous organelles:




a membrane-bound nucleus
endoplasmic reticulum
food-storage granules
Contractile digestive vacuoles
Protozoa
The nucleus contains clumped or dispersed chromatin
and a central karyosome.
 Organs of motility vary from simple cytoplasmic
extrusions or pseudopods to more complex structures,
such as flagella or cilia.
 The kingdom Protozoa:

◦ 13 major subgroups, or phyla
◦ 7 of which are the concern of medical parasitology.
Kingdom: Protozoa
Phylum:
 The Flagellates
 Amoebozoa
 Sporozoa
 Ciliophora
Protozoa

The Flagellates:
-Move by the lashing of their whiplike flagella
-The number and position of the flagella vary a great deal
in different species.
-Flagella may produce a characteristic morphologic
appearance that may be useful in species identification.
Protozoa
Amoebozoa
 Locomotion of amebae is accomplished by the extrusion
of pseudopodia (“false feet”).
 Amebae are phagocytic and contain mitochondria with
tubular cristae.

Protozoa
Sporozoa
-large group
-sexually reproducing
- spore-forming protozoans
- similar morphology at the electron microscopic level
- These organisms have a system of organelles at their
apical end that produces substances to help the organism
penetrate host cells and thus become an intracellular
parasite

Protozoa
Ciliophora
 free-living and symbiotic species.
 locomotion involves the coordinated movement of rows
of hairlike structures, or cilia.
 Cilia are structurally similar to flagella but are usually
shorter and more numerous.
 Some ciliates are multinucleate. The only ciliate parasite
of humans, Balantidium coli, contains two nuclei: a large
macronucleus and a small micronucleus.
Classification

Protozoa

Sarcomastigophora (flagellates and amebas)

Apicomplexa (sporozoans)

Ciliophora (ciliates)

Microspora

Helminths

Plathyhelminthes (flatworms)
◦ Cestoda (flukes)
◦ Trematoda (flukes)

Nemathelminthes (worm like, seperate-sexed, unsegmented roundworms)
Flagellates
Intestinal flagellates
 Giardia intestinalis
 Trichomonas spp
 Dientamoeba fragilis

Trichomonas vaginalis
Hemoflagellates
 Leishmania donovani
 Trypanosoma cruzi
Amebas
Intestinal amebas
 Entamoeba histolytica
 Entamoeba coli
 Balantidium coli



Free-living amebas
Naegleria fowleri
Acanthamoeba castellani
Sporozoans

Blood sporozoans

Plasmodium vivax

Plasmodium malariae

Plasmodium ovale

Plasmodium falciparum

Babesia microti

Other

Isospora belli

Sarcocystis bovihumanis

Cryptosporidium parvum

Toxoplasma gondii
Animalia (Metazoa)
eukaryotic organisms :
 Helminths (“worms”)
◦ Nemathelminthes
◦ Platyhelminthes
 Trematodes, or flukes
 Cestodes, or tapeworms

Arthropods (crabs, insects, ticks, and others)
Helminths
complex multicellular organisms
 Elongated
 bilaterally symmetric
 They are considerably larger than the protozoan
parasites
 generally are macroscopic, ranging in size from less than
1 mm to 1 m or larger.

Helminths
The external surface of some worms is covered with a
protective cuticle, which is acellular and may be smooth or
possess ridges, spines, or tubercles.
 The protective covering of flatworms is known as a
tegument.
 Often helminths possess elaborate attachment structures,
such as hooks, suckers, teeth, or plates. These structures are
usually located anteriorly and may be useful in classifying and
identifying the organisms
 Helminths typically have primitive nervous and excretory
systems. Some have alimentary tracts; however, none have a
circulatory system.

Helminths
two phyla, the Nemathelminthes and the
Platyhelminthes.
 Nemathelminthes:
 Roundworms
 cylindric bodies
 The sexes of roundworms are separate
 these organisms have a complete digestive system.
 intestinal parasites
 blood and tissue parasites

Helminths
two phyla, the Nemathelminthes and the
Platyhelminthes.
Platyhelminthes
 Flatworms
 flattened bodies
 leaflike or resemble ribbon segments
 Platyhelminthes :

◦ Trematodes
◦ Cestodes
Trematodes
Flukes
 leaf-shaped bodies
 Most are hermaphroditic, with male and female sex
organs in a single body.
 Their digestive systems are incomplete and only have
saclike tubes.
 Their life cycle is complex;
 snails serve as first intermediate hosts, and other aquatic
animals or plants serve as second intermediate hosts.

Cestodes
Tapeworms
 have bodies composed of ribbons of proglottids, or
segments.
 All are hermaphroditic,
 all lack digestive systems, with nutrition being absorbed
through the body walls.
 The life cycles of some cestodes are simple and direct,
whereas those of others are complex and require one or
more intermediate hosts.

Classification

Protozoa

Sarcomastigophora (flagellates and amebas)

Apicomplexa (sporozoans)

Ciliophora (ciliates)

Microspora

Helminths

Plathyhelminthes (flatworms)
◦ Cestoda (flukes)
◦ Trematoda (flukes)

Nemathelminthes (worm like, seperate-sexed, unsegmented roundworms)
Cestodes
Taenia solium
 Taenia saginata
 Echinococcus granulosus
 Echinococcus multilocularis
 Diphyllobothrium latum
 Hymenolepsis nana

Trematodes






Taenia solium
Taenia saginata
Echinococcus granulosus
Echinococcus multilocularis
Diphyllobothrium latum
Hymenolepsis nana
Nematodes










Ascaris lumbricoides
Dracunculus medinensis
Enterobius vermicularis
Wuchereria bacrofti
Ancylostoma duodenale
Toxocara spp.
Loa loa
Strongyloides stercoralis
Trichinella spiralis
Trichuris trichiura
Arthropods
largest group of animals in the kingdom Animalia.
 complex multicellular organisms:

◦ that may be involved
 directly in causing invasive or superficial (infestation) disease processes
 indirectly as intermediate hosts and vectors of many infectious agents,
including protozoan and helminthic parasites
 In addition, envenomization by biting and stinging arthropods can result
in adverse reactions in humans that range from local allergic and
hypersensitivity reactions to severe anaphylactic shock and death.
There are five major categories of arthropods





Myriapoda
painful bite
Pentastomida
Humans may serve as intermediate hosts for these parasites.
Crustacea
The crustaceans include familiar aquatic forms, such as crabs, crayfish, shrimp, and copepods. Several
are involved as intermediate hosts in life cycles of various intestinal or blood and tissue helminths.
Chelicerata
vectors for microbial diseases (mites and ticks)
venomous animals that bite (spiders) or sting (scorpions).
Insecta
aquatic and terrestrial forms: such as mosquitoes, flies, midges, fleas, lice bugs, wasps, and ants.
vectors for microbial diseases (mosquitoes, fleas, lice, and bugs)
s venomous animals that sting (bees, wasps, and ants).
Physiology and Replication of
Protozoa
The nutritional requirements are generally simple
 require the assimilation of organic nutrients.

◦ The amebae, ameboflagellates, and certain other protozoa accomplish this assimilation by
the rather primitive process of pinocytosis or phagocytosis of soluble or particulate
matter .The engulfed material is enclosed in digestive vacuoles.
◦ The flagellates and ciliates generally ingest food at a definitive site or structure, the
peristome or cytostome.
◦ Other unicellular parasites, such as the intracellular microsporidia, assimilate nutrients by
simple diffusion.
◦ The ingested food material may be retained in intracytoplasmic granules or in vacuoles.
◦ The undigested particles and waste may be eliminated from the cell by extrusion of the
material at the cell surface.
◦ Respiration in most parasitic protozoa is accomplished by facultatively anaerobic
processes.
Physiology and Replication of Protozoa
Under harsh or unfavorable environmental conditions
 Many develop
◦ cyst form:
 less metabolically active
 surrounded by a thick external cell wall capable of protecting the organism
from otherwise lethal physical and chemical insults
 an integral part of the life cycle of many protozoan parasites and facilitates the
transmission of the organism from host to host in the external environment

Parasites that cannot form cysts:
 must rely on direct transmission from host to host or
 require an arthropod vector to complete their life cycles.
Physiology and Replication of Protozoa
 Many
protozoan parasites have developed
◦ elaborate immunoevasive mechanisms that allow
them to respond to attack by the host immune
system
 by continuously changing their surface antigens,
 thus ensuring continued survival within the
host.
Physiology and Replication of Protozoa
Reproduction:
 generally by simple binary fission (merogony)
 although the life cycle of some protozoa, such as the
sporozoans, includes cycles of multiple fission
(schizogony) alternating with a period of sexual
reproduction (sporogony or gametogony).

Physiology and Replication of Animalia
Helmintes:
 Nutritional requirements met by
◦ Active ingestion of host tissue, fluid: tisse distruction
◦ Passive absorbsion

Energy is used:
◦ Muscular motility
◦ Reproduction:
many worms quite profilic and produce as many as 20000 off springs
Physiology and Replication of Animalia
Helmintes:
-Generally lay eggs: oviparous
Few: bear live young(viviparous): produce larvae distinct
from adult
Primarily anaerobic
Larval forms may require oxygen
Physiology and Replication of Animalia
Most Helmintes:
Protection barrier:
-tough external layer-cuticle:tegument
Worms :
-secrete enzymes :destroy host cell and neutralize
immunologic and cellular defense mechanisms
Physiology and Replication of Animalia
Alter antigenic properties of external surfaces
Evade host immune system
Incorporate host antigen in their external cuticular layer
Avoid immunologic recognition:
Schistosomiasis
Physiology and Replication of Arthropods
Segmented bodies
Joined appendages
Well dveloped digestive and nervous systems
Seperate sex
Hard chitin outside:exoskeleton
Respiration via gills or tubular body structures
EPIDEMIOLOGY
Epidemiology is the science that studies
-propagation and prevalence of human disease
- It determines the frequency and distribution of a
disease in a community.
EPIDEMIOLOGY
.
a.
Endemic
A disease is endemic when it is present in a community at all times but is clinically
found in a few individuals and with low morbidity.
b. Hyperendemic
A hyperendemic disease is one that is present in a high frequency in a community.
c. Sporadic
A low frequency of disease that is not widely diffused is referred to as sporadic.
d. Epidemic
An epidemic occurs when a disease spreads rapidly through a community and affects a
large number of individuals.
Pandemic:Whole world is affected: Influenza, AIDS
Mode of Infection
 Some
parasites can infect the host by direct
contact while others require a complex
mechanism to enter the host:
(1)
Direct contact.
Some parasites can complete their life cycle by
being transmitted from an infected site to
another site where there is no disease. Then they
can parasitize either the new or the same host.
Mode of Infection
(2)
Congenital.
Some parasites can be transmitted to the younger
generation by the older generation.
◦ malaria,
◦ toxoplasmosis
◦ several other parasitic diseases may be
accomplished by parasitic forms crossing the placental barrier
from the mother's blood to the unborn fetus.

Mode of Infection
(3)
Ingestion.

Food and water are very important in the spread of parasitic
diseases because most parasites inhabit the gastrointestinal tract.
The infective form of the parasite (ova or larvae) may be present in the flesh
of the intermediate
host (plant or animal) or may be swimming free
in contaminated water.
The organism may gain access to food through contamination with
-soil
-water
-the hands of foodhandlers, by mechanical agents
-by biological carriers such as
insects.

In some instances, the intermediate hosts, like small arthropods, are
consumed with the food or water.


Mode of Infection
(4)
Arthropod-borne
Members of the phylum Arthropoda serve as vectors
(carriers) :
- parasitic diseases
- bacterial
- viral infections
 The vector is an integral part of the life cycle of the
parasite. In some instances the arthropods are
intermediate hosts while in others they are the definitive
host.

Mode of Infection
(5)
Active penetration
 larval
stage may have the capability of penetrating
the host tissues.
(6) Transfusion.
 Certain blood and tissue parasites
PREVENTIVE MEASURES
 The
individual, as well as the community, must get
involved in the prevention of parasitic infections.
 Life cycles of parasites may be interrupted by
eradication of the vectors.
 Education about hygiene, eating habits, and disposal of
human and animal wastes can also be used in
combating parasites.
 Treatment of diseased individuals not only relieves the
suffering, but also prevents the spread of the disease.
Medical Microbiology
Patrick R Murray
 Ken S Rosenthal
 Michael A Pfaller
 2002-2005-…2009- 2013 !
