1. The Weird, Wild
World of Parasites

2. DISCLAIMER
Parasitologists do not usually include bacteria, fungi, or viruses in what they study, but of course many bacteria and fungi, and all viruses, fit into the definition of parasites – “organisms” that benefit at the expense of other organisms.
The most typical definition of parasite includes such organisms as protists, flatworms, nematodes, and arthropods that live in or on other organisms.
Humans are hosts to over a hundred different kinds of parasites (not all at the same time!). Just about any wild (or domestic) animal you encounter will have parasites.
Even most people that live in quite sanitary environments have at least some parasites on or in them. We will emphasize the most common and/or harmful examples. Note that leeches are omitted as parasites; they are more-or-less temporary visitors that feed on blood but are not permanent residents. I guess the same could be said for ticks and fleas.

3. Katherine Hepburn checks out Humphrey Bogart’s leech collection
Katherine Hepburn checks out Humphrey Bogart’s leech collection. (Some say leeches are not parasites, but they look like it to me.)

4. Blood-sucking ticks carry several rickettsial diseases such as Lyme disease and Rocky Mountain Spotted Fever. Rickettsias are very small prokaryotic organisms. Of course, one really killer bacterial disease, bubonic plague, is transmitted by fleas from rats.
Lyme disease vector
Rocky Mountain Spotted Fever vector
A gang of fleas having dinner together.

5. HARMFULNESS OF PARASITES TO HUMAN BEINGS
Six important tropical diseases defined by WHO:
1 Malaria
2 Schistosomiasis
3 Filariasis parasitosis
4 Leishmaniasis
5 Trypanosomiasis
6 Leprosy

6. GENERAL PARASITOLOGY
Main Stuff to Know

7. The association between the parasite and the host may be:
Medical parasitology is the science that deals with parasites that affect human.
The parasite is an organism that lives at the expense of the host.
The host is the animal species which harbours the parasite.
The association between the parasite and the host may be:
Symbiosis
Mutualism
Commensalism
Parasitism

8. Mutualism Symbiosis (Living together)
Both partners benefit from the relationship.
Permanent relationship, organisms can’t exist separately.
Mutualism
Symbiosis
(Living together)

9. Commensalism Parasitism
One partner benefits (commensal) while the other (host) is unaffected.
The parasite lives at the expense of the host, shelter from it and causes harm to it
Commensalism
Parasitism

10. Types of parasites Endoparasite: Lives within the body (infection).
Protozoa
Helminthes

11. Ectoparasite: Lives on the outside of the body (infestation).
Arthropods
Medical parasitology
Helminthology
(helminthes)
Protozoology
(protozoa)
Entomology
(arthropods)

12. Obligate parasites: Completely dependent upon its host and can not lead a free life.
Facultative parasites: Capable of leading both a free living and parasitic existence.
Accidental parasite: Can establish itself in a host in which it does not ordinarily live.
Temporary parasite: Free living but seeks the host from time to time for food.

13. Permanent parasite: Remains all or most of its life in or on the host.
Coprozoic or spurious parasite: Free living parasite passing through alimentary tract without infecting the host.
Opportunistic parasite: Produces disease in immunocompromised hosts and does not affect immunocompetent individuals.

14. Types of hosts
Final or definitive host: harbours the mature stage of the parasite.
Intermediate host: harbours the immature stage of the parasite.
Reservoir host: animal (other than man) that harbours the same species of parasite as man and constitutes a source of infection to him.
Diseases of animals that are transmitted to man are called zoonotic diseases.
Vector is arthropod that transmit a parasite to its host.
Remarks

15. Source of parasitic infection
- Raw vegetables Meat.
- Fish Water.
- When it is contaminated with animal or human excreta.
Food and water
Soil
Animal reservoir host
Arthropods
Air-borne

16. Accidental laboratory infection
Mode of infection
Oral route
Skin penetration
Contact
Sexual
Congenital
Inhalation
Accidental laboratory infection

17. Why Parasites are Particularly Unpleasant
1. Effects of Parasites on Host
A. Stealing nutrition (eats your food)
B. Physical trauma (chews holes in you)
C. Toxins (fill you with irritating/harmful chemicals)
a) Lytic necrosis: Dissolving you w/enzymes
b) Tissue reaction: rashes, itchiness, swelling
END NOTES HERE - the rest are examples and images

18. Protists

19. The most deadly parasite for humans has been a protist (Plasmodium) that causes malaria. More people have died of malaria than any other cause. Even now malaria kills 1-2 million people each year. A fairly close relative, Toxoplasma, is much less dangerous. In fact, almost everyone has it living in them without any noticeable effects. It is only a problem to those with weak immune systems – fetuses and AIDS sufferers. Other protists shown here include Giardia, Cryptosporidium (which killed over 200 people in Milwaukee), and Trypanosoma (African sleeping sickness, Chagas disease). There are many others that could have been included. Many parasites, not just protists, have different parts of their life cycle in different kinds of hosts. As you go through the examples, note the different hosts involved.

21. Anopheles mosquito and Plasmodium (causative agent of malaria) in and among red blood cells.

22. Life cycle of Toxoplasma gondii (Toxoplasmosis)

23. Toxoplasma is found in many people without any symptoms – exceptions are fetuses and AIDS sufferers.

24. Giardia – commonly found in swimming pools; lacks mitochondria and has an amusing appearance.
Causes intense diarrhea and is readily transmitted within households.

26. Cryptosporidium in human intestinal lining
Cryptosporidium in human intestinal lining. This protist sickened thousands and killed 200 in Milwaukee in 1993.
Cryptosporidium merozoites breaking out

28. Blood-sucking conenose (Triatoma) - vector for Chaga’s disease (Trypanosoma cruzi) It is now thought that Charles Darwin contracted this, causing him to be a near invalid most of his life.

29. Life cycle of Trypanosoma spp
Life cycle of Trypanosoma spp. – cause of African Trypanosomiasis (sleeping sickness)

30. Tsetse fly (Glossina)
Causative agent of African sleeping sickness (Trypanosoma, sp.)

31. Flatworms

32. Some flatworms are free-living animals such as the planaria.
However, most flatworms are parasites such as flukes and the tapeworms.
Most flukes and tapeworms have quite complex life histories with multiple hosts. In many tapeworms there is an alternation between herbivore and carnivore hosts. The herbivore gets the parasite by consuming plants on which fecal wastes bearing eggs or other stages have been deposited. Once in the herbivore host the parasite often forms cysts within muscles or other tissues; it is passed on when the host is eaten by a carnivore. In the carnivore the parasite forms the adult tapeworm that lives in the intestine. If a human ingests eggs, etc., the result can be devastating, inasmuch as the parasite can form cysts just about anywhere – heart, lung, brain, bones, etc. You can see the result on a subsequent slide showing hydatid cysts of Echinococcus, the dog tapeworm.

33. Life cycle of Fasciola hepatica (Sheep Liver Fluke)

34. Fasciola – 2 species of sheep liver fluke

35. Immature stages of Fasciola
Fasciola miracidium (from eggs in water; penetrate snail host)
Immature stages of Fasciola
Fasciola cercaria (penetrate vertebrate host in water)
Fasciola redia (emerge from sporocysts in snail)

37. Once a male finds a female he never lets her go – even if she drops dead. (live in large veins in abdomen)
Cercaria (larva) of Schistosoma

39. Taenia solium – scolex (how it holds on in the gut)
Tapeworm cyst in human brain
Taenia solium – cysts in human eye (cysts can be just about anywhere in body)

40. Echinococcus – dog tapeworm. Actual size is only 3 to 6 mm in length.

41. Hydatid cysts (Echinococcus) in a monkey
Each cyst is filled with thousands of small parasite units.

42. Hydatid cyst in human brain (left)
Human kidney with hydatid cysts (arrows)