Introduction Parasitology. Parasites in the human body.

Introduction to parasitology in biomedical sciences include definition of parasitology, course overview, examples and summarized explanations on topics in parasitology. The types of parasites and their effect on the human body and it's systems

1. Department of Biomedical Sciences
©2021 chinyanta stanley
Introduction
20/07/2021
Parasitology

2. Introduction to Medical Parasitology
•Definition of Medical Parasitology
•The Scope of Medical Parasitology
•Classification of parasites
•Terms used in Parasitology
•Parasites’ Harms to Man (= pathogenic effects of parasites
on Man)
•Human Immunity against Parasites
•Characteristics of parasitic diseases

3. MEDICAL PARASITOLOGY
WHAT IS PARASITOLOGY?
Study of the biology of parasites
Medical Parasitology is the study of organisms
(parasites) that parasitize/infect humans.

4. Why study Parasitology?
•Many of these parasites are causative agents of major public
health problems of the world.
•Recent estimates of prevalence of parasites in the world
are:
Ascaris 1.5 billion
Hookworms 1.3 billion
Whipworms 1 billion
Filarial worms 657 million
Plasmodium sp 500 million
Schistosomes 270 million
Entamoeba 50 million
Tapeworms 50 million
Clonorchis 20 million
Chagas’ Disease 15 million
•These parasites cause untold suffering and death in the
world today.

5. The Scope of Human Parasitology
Parasitology deals with:
1)Protozoa(single celled animals) >>>> Protozoology
2)Helminths(worms) >>>>> Helminthology
3)Arthropods(Insects) >>>>>> Entomology
4)Ticks and mites are the concern of Acarology.
The insects that are of most interest in Human Parasitology
are those that are vectorsof several parasitic infections.

6. 1. Intra-specific Association: association
organisms within the same species
2. Inter-specific Association: association
between organisms of different species
All inter-specific associations are grouped
under Symbiosis( = living together)
sym = together, bios = life
Types of Animal Associations

7. Examples of Inter-specific associations
Commensalism:
Co= together, mensa= table
One organism benefits from the association & the
other is neither harmed nor benefited
No physiological dependence involved
Both partners can survive independently
Commensal:
Organism living on or within another, but not
causing injury to the host

8. Examples of Commensalism
a)Cleaning commensalism
b)Comouflage/protection commensalism
c)Housing commensalism
d)Transport/phoretic commensalism

9. 1. Cleaning commensalism:e.g
•Pilot fish and Sharks
2.Protection and camouflage commensal:
e.g pea crab in the mantle cavity of the mussel
3. House–burrows of larger animals become homes for
smaller animals
4. Transport/Phoretic commensalism
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
Symbiont = Phoront

10. Mutualism
Symbiosis in the restricted sense
-more intimate and essential association
than commensalism
-Both partners benefit
-mutualists cannot survive independently
-association is physiologically dependent
E.g Legume nodules andnitrogen fixing
bacteria (Rhizobium)

11. Mutualism-contd
An association which is beneficial to
both
living things
Fig 2. A selection of ciliates from the rumen. The
rumen contains enormous numbers of ciliates that
break down cellulose into food.

12. Parasitism:
Para = besides, sitos(Gk) = food
-One organism (parasite)is dependent on
another organism (host)
-Parasite benefits from the association at the
expense of the host
Aparasiteis an organism that lives in or on
another organism, the host, for purposes of
deriving food and/or shelterwhile offering no
benefit to the association

13. Parasitism:
is inter-specific
Is Intra-uterine development of the foetus
a form of parasitism?
It is NOT; because the association is intra-
specific

14. Types of Parasites
1. Ectoparasite: [Greek “Ektos”= outside; situated on the outside]
Parasite that lives on the external surface of another living
organism” –e.g. lice, ticks
Externally attached to the skin or superficial tissues
Cause infestation
2. Endoparasite: (Greek “Endon”= within; an inward situation)
a parasite that lives within another living organism” –e.g.
Plasmodium falciparum, Giardia lamblia, etc.
Cause internal infection
3. Facultative parasites:
can exist in the free living state, alternating of generations e.g
Strogyloides stecoralis
4. Obligate parasites:
cannot exist in the free living state i.e cannot complete their lifecycle
outside the host –but ova and cysts cansurvive

15. Intermittent parasites:
Visit and leave the host at intervals;
e.g micro-predators, leeches, ticks, mosquitoes,
fleas.
Mosquito Tick Flea
Leeches

16. Some typical Characteristics of
Parasitism
1. High reproductive potential (i.e multiple fission
in Apicomplexa; hermaphroditism of
trematodes; parthenogenesis in Strongyloides
spp., strobilation of tapeworms for high ova
output; and overall high ova/larval output of
many worms
2. They have unique morphological or
physiological specializations, loss of structures,
etc

17. a)Loss of the digestive tract of tapeworms
b)Loss of wings of fleas and lice
c)Loss of many sensory structures of nematodes
d)Development of special holdfast organs, including
hooks, suckers teeth, clamps, cutting plates, spines
e)Production of anti-coagulants in leeches and
hookworms
3. They often exhibit site specificity
4. Generally, they are much smaller than the host
5. Generally more numerous than hosts
6. They are usually, but not always, non-lethal to
the host

18. 7. They have evolved methods of evading the
host’s immune system e.g
a)Antigenic variation of trypanosomes
b)Tough tegument of acanthacephalans
c)Intracellular habitat of coccidia and Trichinella larvae
d)Antigen acquisition of schistosomes
e)Suppression of eosinophil or neutrophil migration to the site
of the parasite
f)Encystment
g)Ability to cleave antibodies or consume the complement
system
h)Ability to trigger certain arms of the immune response,
which may in turn damage host tissue enough to facilitate
parasite invasion

19. Harmful Effects of Parasites on their Hosts
a)Compete with hosts for food including vitamins e.g Ascarid
round worms, tapeworms like Diphyllobothrium latum)
b)Decrease utilization and absorption of nutrients (e.g
Haemonchus contortus in sheep)
c)Reduction in feed intake by animals
d)Increase in the passage of food without proper digestion
through the digestive tract of animals
e)Changes or reduces the absorptive surface of the intestine e.g
Giardia lamblia
f)Alteration in the efflux and influx of water and ions into the
bowel
g)Removal of host’s body fluid including blood, e.g hookworms,
blood sucking insects, ticks
h)Cause mechanical obstruction of the gut lumen, air passages,
ducts, blood vessels e.g Ascarids, liver fluke, blood fluke

20. Types of Hosts
Host: is a non parasitic member of the
association
1. Definitive /Final Host: host in which a
parasite reaches sexual maturity and
reproduces. Example: Cattle, buffaloes,
sheep and goats are definitive hosts for
Fasciola hepatica

21. 2. Intermediate Host:
One in which early development of the parasite
occurs to produce usually infective stages of it
without reaching sexual maturity e.g snails in the
life cycle of S. haematobium
3. Vector
Usually a blood-sucking arthropod which
transmits the parasite from the infected
vertebrate animal to another susceptible
vertebrate animal

22. BiologicalVector
Mechanical Vector
Transmits the parasite after some biological
development of the parasite to make it infective for a
susceptible host
Example: Mosquitoes involved in the transmission of
various filarial round worms and malarial parasites
Transmits the parasite in a short time as such without
undergoing any developmental or biological change
Example: Tabanid flies transmit Trypanosoma evansi

23. 4. Paratenic/Transport host:
It is one that picks up the infective stage of a
parasite either from the intermediate host or
directly from the atmosphere without any
development of the parasite; but the parasite
continues to live and is ineffective to the next host
Example: A mouse is the paratenic host for
Toxocara canis

24. 5. Reservoir Host: reservoir of infection
It is a vertebrate animal which may or may
not be the natural host of a parasite and
possess parasitic infection without any
clinical manifestation that serves as sources
of infection to other susceptible hosts
6. Carrier Host:
it is a vertebrate animal which had suffered
from an infection and in later stage carries
the infective organisms in its body without
showing any clinical signs

25. Types of Parasitic infections
1.Auto-infection: self infection with a
pathogen
The host animal is the own direct source
of exposure
Autoinfection can be either externalor
internal e.ginfection with Strongyloides
stercoralis
2. Super-infection: re-infection with the same
parasite species, while harboring the same
species of the parasite
3. Hyper infection –high infection

26. Prepatent versus Clinical Incubation Period
1.Biological incubation period = Prepatent
period
Interval between exposure to a pathogen and
time when parasites or their products can be
demonstrated in body products, biopsy, or
other diagnostic procedures
2.Clinical incubation
Interval between exposure to a pathogen and
the earliest evidence of signs and symptoms
produced as a result of the infection

27. Types of Life Cycle
1. Direct Life Cycle
2. Indirect Life Cycle
Does not involve any intermediate host
between the parasite and its host
Example: infection with Strongyloides
stercoralis
Involves necessarily one or more intermediate
hosts or vector(s) to complete its life cycle

28. 3. Simple Life Cycle
4. Complex Life Cycle
One in which a parasite simply multiplies by
binary fission both in its vertebrate host and its
insect vector for its propagation
Example: Trypanosomaspp
One in which there is an alteration of both
asexual and sexual processes of reproduction in
the life cycle of a parasite
Example: All helminth parasites

29. Examples of Important Intestinal
Protozoa
Transmitted by the faecal-oral route and cause
diarrhoea
•Giardia lamblia: world-wide distribution,
lives in the 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: more prevalent in
the immunocompromised (HIV patients).
•Balantidium coli: alarge motile ciliated
parasite that lives in the colon of pigs,
humans and rodents and can lead to colonic
ulceration
•Enterocytozoon bienusi: a microsporidian
that parasitises the small intestine. Also
more common in the immunocompromised.
Giardia lamblia

30. Examples of important systemic protozoa
Detected in the blood
•Plasmodium: the cause of malaria.
There are 4 species that infect man:
P.falciparum, P. vivax, P. ovale and
P. malariae
•Toxoplasma gondi: transmitted by
the ingestion of oocysts from cat
faeces. Infection can lead to ocular
problems and is also a cause of
neonatal toxoplasmosis
•Leishmania: transmitted by sand
flies, can lead to visceral, cutaneous
and mucocutaneous leishmaniasis
•Trypanosoma: haemoflagellates
which cause
In Africa -sleeping sickness (transmitted
by the Tsetse fly
In South America -Chagas disease
(transmitted by the Reduviid bug)
Typical lesion of cutaneous leishmaniasis
Tsetse fly –the vector of African
trypanosomiasis It has a painful bite!

31. Taxonomic Classification of Helminths
Sub
kingdom
Phylum Class Genus –
examples
Metazoa Nematodes
Round worms; appear round
in cross section, they have
body cavities, a straight
alimentary canal and an
anus
Ascaris (roundworm)
Trichuris (whipworm)
Ancylostoma (hookworm)
Necator (hookworm)
Enterobius (pinworm or
threadworm)
Strongyloides
Platyhelminthes
Flat worms; dorsoventrally
flattened, no body cavity
and, if present, the
alimentary canal is blind
ending
Cestodes
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
Taenia(tapeworm)
Trematodes
Non-segmented, usually leaf-
shaped, 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 thread-
like, and have separate sexes
Fasciolopsis(liver fluke)
Schistosoma(not leaf
shaped!)

32. Examples of important metazoa –intestinal
nematodes
•Trichuris(whipworm)
–A soil transmitted helminth
–prevalent in warm, humid conditions
–Can cause diarrhoea, rectal prolapse
and anaemia in heavily-infected
people
•Ancylostomaand Necator(hookworms)
–A major cause of anaemia in the
tropics
•Strongyloides
–inhabits the small bowel
–infection more severe in
immunosupressed people (e.g.
HIV/AIDS, malnutrition, intercurrent
disease)
•Enterobius(pinworm or threadworm)
–prevalent in cold and temperate
climates but rare in the tropics
–found mainly in children
•Ascaris(roundworm)
–Found world-wide in conditions of
poor hygiene, transmitted by the
faecal-oral route
–Adult worms lives in the small
intestine
–Causes eosinophilia
Heavy intestinal infections may occur with Ascaris. Adult
worms can be several cms long.

33. Examples of important metazoa
nematodes and cestodes
•Onchocerca volvulus–
Transmitted by a black fly, this
microfilarial parasite can cause
visual impairment, blindness
and severe itching of the skin
in those infected
•Wuchereria bancrofti–The
major causative agent of
lymphatic filariasis
•Brugia malayi–Another
microfilarial parasite that
causes lymphatic filariasis
Intestinal-(“tapeworms”)
•Taeniasaginata
–acquired by ingestion of
contaminated, uncooked beef
–a common infection but
causes minimal symptoms
•Taeniasolium
–acquired by ingestion of
contaminated, uncooked pork
that contains cystercerci
–Less common, but causes
cystercicosis–a systemic
disease where cysticerci
encystin muscles and in the
brain –may lead to epilepsy

34. 34
Examples of important metazoa –trematodes
(flukes)
•Clonorchis sinensis(liver fluke)-
Widespread in China, Japan, Korea
and Taiwan, this parasite is acquired
by ingestion of infective
metacercariae in raw or pickled fish
•Schistosoma haematobium, S.
mansoni and S. Japonicum.
•Fasciola hepatica(liver fluke)-
Primarily, a parasite of sheep, humans
become infected.

35. Human Parasitology
Medical
Helminthology
Medical
Protozoology
Medical
Arthropology
•Class Nematoda
•Class Trematoda
•Class Cestoda
•Class Lobosea (sarcodina)
•Class Zoomastigophorea
•Class Sporozoa (Apicoplexa)
•Class Ciliophora
•Class Insecta
•Class Arachnida
•Class Crustacea
•Class Chilopoda

36. The Routes of Parasitic
Transmission
•Congenital transmission : From mother to
infant. Toxoplasmosis
•Contact transmission : Direct contact---
Trichomonas vaginalis; Indirect contact---
Ascaris lumbricodes
•Food transmission : The infectious stage of
parasites -->contaminated food / The meat
of the intermediate hosts containing
infectious stage of parasites.

37. 2. The Routes of Transmission II
•Water transmission : Drink or contact the
water contaminated with the infectious
stage of parasites.
•Soil transmission : Contamination of the soil
by feces containing the certain stage of
parasites and this stage can develop into an
infective stage.
•Arthropod transmission : Vectors of certain
parasitic diseases.

38. 3. The Susceptible Host
•In general, most people are susceptible
hosts.
•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.

39. The Avenues 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).

40. PARASITOLOGY IN RELATION
TO OTHER SPECIALIZATIONS
Virology–viruses, purely parasitic
Bacteriology–Medical Bacteriology deals
with parasitic bacteria.
Plant Pathology–Study of parasites of
plants
Mycology – study ofparasitic fungi

41. Time for Questions?