1. Parasitology Department
General Parasitology By
Hala Elwakil, MD

2. Intended Learning Outcomes
By the end of this lecture , the student will be able to:
Differentiate between types of hosts
Differentiate between types of parasites
Identified the different stages in the life cycle
Classify the parasites of medical importance.
Differentiate between the general characters of different helminthes’ classes

3. Which of the following figures represent parasitism?B C
Prof. Hala Elwakil

5. MEDICAL PARASITOLOGY
Is the science that deals with the parasites, which cause human infections and the diseases they produce.
It is broadly divided into 2 parts
€ Protozoology
€ Helminthology.

6. They multiply or undergo development in the host.
Parasites are living organisms, which depend on a living host for their nourishment and survival.
They multiply or undergo development in the host.

7. Parasites
Types
Hosts

8. ECTOPARASITES
ENDOPARASITES
Infestation
Infection

9. Permanent parasite
Temporary parasite

10. Facultative parasite
Obligate parasite

11. Accidental parasite
Aberrant parasite

12. Opportunistic parasites
Parasites capable of producing a disease or flaring up of infection in a person with a poorly functioning immune response or with immune deficiency conditions (immunocompromised)

13. High host specificity parasites Low host specificity parasites
Zoonosis
WHO defined zoonosis as “those diseases and infections, which are naturally transmitted between vertebrate animals and man”.

14. Host Intermediate host Definitive host
The host, in which the adult parasite lives and undergoes sexual reproduction
The host, in which the larval
stage of the parasite lives or asexual multiplication takes place
It is an organism, which harbors the parasite and provides nourishment and shelter to latter

15. Vector
It is usually an arthropod that transmits the parasites from one host to another
Mechanical
Biological
No role in parasite development
It is essential for parasite development
Parasites are on vector body parts and are passively brushed off
Parasites are within the vectors and transmission is through a bite

16. Reservoir host
reservoir source of infection to man
It is the animal host that harbors the same species and same stages of a parasite as man.
Accidental host
The host, in which the parasite is not usually found
It may or may not complete life cycle ( dead end host)
Paratenic host
It is a host, in which larval stage of the parasite remains viable without further development

17. Parasites’ life cycle Direct Indirect
Parasites have complex life cycles: Involving one, two, three or even four consecutive hosts
Alternation between vertebrate hosts and invertebrate hosts and between terrestrial and aquatic environments.
Helminths form three main life-cycle stages: eggs, larvae and adults
Direct
Indirect

18. Importance of knowing a parasite life cycle phases

19. Control DH IH RH Habitat Larval stages Infective stage
Mode of infection
Diagnostic stage
Control

20. Scientific Nomencluture
Animal Kingdom
Phylum
Class
Order
Family
Genus
species

21. Helminth parasite Platyhelminths flat worm Trematodes Cestodes
Nemathelminths round worms
Nematodes

22. What is trematodes?
suckers
Flattened( leaf like)
No body cavity

23. The alimentary canal is incomplete, and no anus is present.
- mouth
-oesophegus
-intestinal caeca
Nutrition is taken from the surrounding fluids

24. Most trematodes are hermaphrodites monecious
Female organs
18-Ovary
19-Seminal receptacle
Oviduct
20-Laurer’s canal
21-Ootype
22-Mehli’s gland
23-uterus
24-yolk gland
25-common yolk channel
Male organs
10-Testis
11-Vas efferens
12-Vas deferns
13-Seminal vesicles
14-Prostate glands
15-Cirrus
16-Cirrus sac

25. Schistosomes spp. are diecious

26. The flukes are oviparous. They lay operculated eggs.
Schistosomes eggs are not operculated.

27. Life cycles
Indirect

28. Cercaria
CERCARIAE leave the sporocyst or redia, migrate out of the snail,
1. Cercarial body
Oral sucker and acetabulum are present
Digestive tract is complete
Many types of gland cells are present
no reproductive structures

29. Cercaria 2. Tail -Used for swimming.
- May be unbranched with or without fins
Type of cercaria is based on characteristics of the body and tail.
Furcocercous type – forked tail
Leptocercus type – straight tail
Microcercous type – short tail
Lophocercus type – tail covered with membrane
Microcercous cercaria
Furcocercous cercaria

30. CESTODES

31. General features of Cestodes
Flat worms and tape like
Length from 1 cm to several meter
3. NO alimentary system.
4. monoecious
5. Body cavity is absent.
6. Oviparous.

32. Helminth parasite Platyhelminths flat worm Trematodes Cestodes
Nemathelminths round worms
Nematodes
Pseudophyllidea
Cyclophyllidea

33. Cestodes morphology
Cyclophyllidea
Pseudophyllidea

34. Cestodes larvae

35. Cestodes life cycles

36. What is the type of life cycle? What is the mode of infection?
What is the class of the parasite?

37. Learning resources Medical parasitology Part 1
( by: Staff of Parasitology department )
-Paniker’s Textbook of Medical Parasitology:
General introduction, Chapter 1: 1-8.
Helminths general features, Chapter 11:
Cestodes general characters, Chapter 12:
Trematodes general characters, Chapter 13:

38. Prof.Hala Elwakil