introduction to medical parasitology

1. Medical parasitology
ABDIRAHMAN JIBRIL WARSAME

2. INTRODUCTION
 Human and other living things on earth live in closed
relationship with each other.
 They don’t exist in an isolated fashion.
 They are interdependent; each forms a strand in the
web of life.
 Parasitology is the study of parasites, their hosts, and
the relationship between them.

3. Cont’d
 Medical parasitology is the subject which deals with the
parasites that infect human being, the diseases caused by
them, clinical feature and the response generated by human
being against them.
 It's also concerned with the various methods of their
diagnosis, treatment and finally their prevention & control.

4. Definitions of keys terms
 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 protozoa or complex multicellular
metazoa
Eukaryote: a cell with a well-defined chromosome in a membrane-bound
nucleus.
All parasitic organisms are eukaryotes

5. Cont”d
 Protozoa: unicellular organisms.
 Metazoa: multicellular organisms, e.g. worms and
arthropods.
 An endoparasite: a parasite that lives within another
living organism
 An ectoparasite: a parasite that lives on the external
surface of another living organism e.g. lice, ticks

6. Cont’d
 Host: the organism in or/on which the parasite lives/
or An organism that harbors the parasite usually larger
than the parasite
 Definitive host: the organism in which the adult or
sexually mature stage of the parasite lives
 Intermediate host: the organism in which the parasite
lives during a period of its development only/ The host
harboring the larvae or asexual stage of parasite.

7. Cont’d
 Zoonosis: a parasitic disease in which an animal is
normally the host - but which also infects man
 Vector: a living carrier (e.g.an arthropod) that
transports a pathogenic organism from an infected to
a non-infected host.
 There two types of vectors: mechanical and biological

8. Epidemiology
 Although parasitic infections occur globally, the
majority occur in tropical regions, where there is
poverty, poor sanitation and personal hygiene.

9. DIFFERENT KINDS OF
PARASITES
• Ectoparasite e.g. lice, ticks, mites etc
• Endoparasites e.g. Entamoeba histolytica
• Obligate Parasite e.g. Plasmodium spp
Notes: Non-pathogenic parasites : live in/on the body of the host do
not cause disease
 Opportunistic parasites: cause illness in individuals with impaired
defense mechanism, is becoming of paramount importance because
of the increasing prevalence of HIV/AIDS.

10. DIFFERENT KINDS OF HOSTS
 Definitive host: harbors a parasite in the adult stage or
where the parasite undergoes a sexual method of
reproduction.
 Intermediate host :harbors the larval stages of the
parasite or an asexual cycle of development takes
place.
 Paratenic host:
An intermediate host whose presence may be
 required for the completion of a parasite's life
 cycle but in which no development of the
parasite occurs

11. Host cont...
 Reservoir host : makes the parasite available for the
transmission to another host and is usually not
affected by the infection. /animals harboring the same
species of parasites as man. Potential sources of
human infection.
 Accidental host a host that is under normal
circumstances not infected with the parasite.

12. Life cycle and type of life cycle
 Life cycle : The whole process of parasite growing and
developing.
 The direct life-cycle : Only one host (no intermediate host).
 The indirect life cycle : Life cycle with more than one host
(intermediat host and final host).

13. Symbiotic relationships
 Organism that spends a portion or all of its life cycle intimately
associated with another organism of a different species is
considered as Symbiont.
 This relationship is called symbiosis (symbiotic relationships).

14. Cont’d
 The three common symbiotic relationships are:
 Mutualism: both partners are metabolically
dependent upon each other and one cannot live
without the help of the other; however, none of the
partners suffers any harm from the association.
 Example is the relationship between certain species of
flagellated protozoa living in the gut of termites

15. Cont’d
 Commensalism: an association in which the
commensal takes the benefit without causing injury to
the host.
 E.g. Most of the normal floras of the human body.

16. Cont’d
 Parasitism : an association where one of the partners
is harmed and the other lives at the expense of the
other.
 E.g. Worms like Ascaris lumbricoides reside in the
gastrointestinal tract of man, and feed on important
items of intestinal food causing various illnesses.

17. The basic factor of transmission of
parasitic diseases
 The source of the infection
 The routes of transmission
 The susceptible host

18. The source of the infection
 Patient : Persons who have parasites in their body and show
clinical symptoms.
 Carrier : Persons who have parasites in their body, not show
symptoms.
 Reservoir host : Animals that harbors the same species of
parasites as man. Sometimes, the parasites in animals can
transmit into human.

19. The routes of transmission
 Congenital transmission : From mother to infant. Eg:
Toxoplasmosis
 Contact transmission : Direct contact (E.g:Trichomonas
vaginalis);Indirect contact (E.g:Ascaris lumbricodes)
 Food transmission : The infectious stage of parasites
contaminated food / The meat of the intermediate hosts
containing infectious stage of parasites.

20. Cont’d
 Water transmission : Drink or contact the water contaminated
the infectious stage of parasites.
 Soil transmission : Contamination of the soil by feces
containing the certain stage of parasites.
 Arthropod transmission : Vectors of certain parasitic diseases.

21. 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.

22. The site of invasion
 Digestive tract : Most common avenue of entrance. (Food/
Water transmission)
 Skin : Infective larvae perforate skin and reach to body and
establish infection. (soil/ water transmission)
 Blood : Bloodsucking insects containing infective parasites bite
the skin and inject parasites into human blood. (Arthropod
transmission---malaria).

23. The prevention measures of the parasitic
diseases
 Controlling the source of the infection.
Treatment of the 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.

24. EFFECT OF PARASITES ON
THE HOST
 Mechanical injury: may be inflicted by a parasite by
means of pressure as it grows larger, e.g. Hydatid cyst
causes blockage of ducts such as blood vessels
producing infraction,
 e. g. , biliary ascariasis and larva migrans, Ascaris
Perforate/Obstruction

25. Effects cont...
 Deleterious effect of toxic substances: in P.
falciparum production of toxic substances may cause
rigors and other symptoms.
 e. g., mosquitoes, spiders and ticks introduce venom
when they insert their mouth parts into the skin.

26. Effect Cont’d
 Deprivation of nutrients, fluids and metabolites -
parasite may produce disease by
competing with the host for nutrients. e.g. hookworms
suck blood.

27. Effect cont..
 Immunological reaction: Tissue damage may be
caused by immunological response of the host,
 e.g. schistosoma liver cirrhosis; when hydatid fluid is
released from the rupture of a hydatid cyst anaphylaxis
often results.
 nephritic syndrome following Plasmodium infections.

28. Classification
 The classification of parasites is controversial - there is
no universally accepted system.
 Parasites form part of the animal kingdom which
comprises some 800,000 identified species categorised
into 33 phyla.
 The parasitic organisms that are of importance for
human health are eukaryotes

29. Cont’d
 Parasites are classified into 2 sub-kingdoms:
Protozoa (unicellular)
helminths, and Metazoa (multicellular)

30. Cont’d
 Metazoa (multicellular) include:
The worms (helminths) and
The arthropoda

31. Nomenclature of parasites
 Each parasite possesses two names, a generic and a
specific
 the former begins with an initial capital and the latter
with an initial small letter, after which comes the
designator’s name, followed by punctuation and finally
the year.
 The generic and specific names are in italics but not
the designator’s name.

32. Nomenc cont..
 for example, the common intestinal roundworm of
man is named Ascaris lumbricoides Linnaeus, 1758.
This means that it belongs to the Genus Ascaris and
the name of the species lumbricoides was given by
Linnaeus in the year 1758.

33. Classification of parasites
 The parasites which medical human have to deal are divided into three
main groups:
 Phylum Protozoa- single-celled organism, multiply in human host, Medical
Protozoology
 Phylum Platyhelminthes and Phylum Nemathelminthes- multicellular
worms, do not normally multiply in human host, medical Helminthology.
 Phylum Arthropoda – Medical Entomology

34. Taxonomic classification of
protozoa

35. Mastigophora:
 All are flagellates. They have one or more whip like
flagella for locomotion at some stage of their life cycle.
In some cases, there is the presence of undulating
membrane (Eg. Trypanosoma).
 The mastigophore includes the intestinal and
genitourinary flagellates and the blood and tissue
flagellates.

36. Mastig..
 The intestinal and genitourinary flagellates are Giardia,
Trichomonas, Dientamoeba, Chilomastik, etc.
 The blood and tissue flagellates are Trypanosoma,
Leishmania, etc.

37. Sarcodina:
.They are all typically amoeboid and include Entamoeba,
Endolimax, Iodamoeba, Naegleria, Acanthamoeba, etc.
amoebae consist of a shapeless mass of moving
cytoplasm which is divided in to granular endoplasm
and clear ectoplasm.
 They move by pushing out the ectoplasm to form
pseudopodia (false feet) into which the endoplasm
then low.
 Amoebae reproduce asexually by simply dividing into
two (binary fission

38. Sporozoa:
 The members of this super-class undergoes complex
life cycle with alternating sexual and asexual
reproductive phases involving two different hosts.
 Coccidia are intacellular parasites that reproduce
asexually by a process called schizogony (merogony)
and sexually by sporogony.
 Class Coccidia includes Isospora and Toxoplasma and
class Haematozoa includes the malarial parasites-
Plasmodium species.

39. Ciliophora:
 These are the complex protozoa bearing cilia (short
hairs) distributed in rows or patches by which they
move.
 They have two kinds of nuclei (macronucleus and
micronucleus) and a large contractile vacoule.
 Balantidium coli, a giant intestinal ciliate of humans
and pigs, is the only human parasite representative of
this group.

40. The parasitic worms, or helminths, of human
beings belong to two phyla- Platyhelminthes
(flatworms) and Nemathehelminthes (Round
worms).
Helminths
Nemathehelminthes Platyhelminthes
Nematoda (Round
worms) Cestoda Trematoda
(Tapeworms) (Flukes)
Helminths:

41. helminthes

42. Cestodes:
 These are tape-like, segmented and hermaphrodite
organism. They have suckers in their head and in some
species also hooks that attach the tapewor to its host..
 It consists of a head (scolex) and many proglottids.
Alimentary canal and body cavity are absent. Examples
are Diphyllobothrium, Taenia, Echinococcus,
Hymenolepsis, etc.

43. Trematodes:
 They are leaf-like unsegmented organism. Sexes are
not separate except Schistosomes which are diecious.
They don’t have hooks and suckers in their head.
Alimentary canal is present but is not complete (anus
absent). The body cavity is absent.
 Examples are Schistosoma, Gastrodiscoides,
Fasciolopsis, Fasciola, Clonorchis, Heterophyes, etc.

44. Nematodes:
• Their body is elongated, cylindrical and
unsegmented. Sexes are separate (diecious). They
also lack hooks and suckers.
• They possess the complete alimentary canal and
body cavity. Examples are:
Intestinal
i. Small intestine only: Ascaris
lumbricoides (Common round
worm), Ancyclostoma
duodenale (The old world
hook worm), Necator
americanus (American
hookworm)

45. Nematode cont..
ii. Caecum and vermiform
appendix: Enterobius
vermicularis (Threadworm or pin
worm), Trichuris trichuria
(Whipworm).
2. Somatic (inside the tissues and organs)
i. Lymphatic system: Wuchereria bancrofti, Brugia
malayi
ii. Subcutaneous tissue: Onchocerca volvulus,
Dracunculus medinensis
iii. Lungs: Strongyloides stercoralis
iv. Conjunctiva: Loa loa

46. The burden of some major
parasitic infections
Parasite Diseases No. people
infected
Deaths/yr
Plasmodium malaria 273 million 1.12 million
Soil transmitted
helminths:
• Roundworm
(Ascaris)
• Whipworm
(Trichuris)
•
• Hookworm
(Ancylostom
a and
Necator)
Pnemonitis,
intestinal
obstruction
Bloody diarrhoea,
rectal prolapse
Coughing,
wheezing,
abdominal pain
and anaemia
2 billion 200,000
Schistosoma Renal tract and
intestinal disease
200 million 15,000
Filariae Lymphatic
filariasis and
elephantiasis
120 million Not fatal but 40
million
disfigured or
incapacitate
d

47. Geographic Distribution
Factors (Endemicity):
 1. Presence of a suitable host
 2. Habits of the host
 3. Escape from the host
 4. Favorable conditions outside of host
 5. Economic and social conditions

48. Diagnosis of Parasitic
Infections:
 1. Clinical diagnosis
 2. Laboratory diagnosis

49. Treatment of Parasitic
Infections:
 1. Medical and surgical
 2. Chemotherapy
 3. Adequate nutrition

50. Prevention and Control:
 1. Reduction in sources
 2. Education
 3. Destruction and/or control of reservoir hosts and
vector

51. Difference bet cestode, trematode and nematode
Cestode Trematode Nematode
Shape
Sexes
Head space
Alimentary canal
Body cavity
Tape-like;
segmented
Not separate,
i.e.,Hermaphrdit
(monoecious)
Suckers, often with hooks
Absent
Absent
Leaf-like;
unsegmented
Not separate
(monoecious),
Except Schistosomes
which are diecious
Suckers, no hooks
Present but
incomplete; no anus
Absent
Elongated, cylindrical;
unsegmented
Separate (diecious)
No suckers, no hooks. Well
developed buccal capsule in
some species
Present and complete; anus
present
present