This document outlines host-parasite interactions. It defines parasites and hosts, and describes different types of parasites including protozoa, helminths, and ectoparasites. It discusses parasitism and how parasites live in or on hosts, harming the host for their own benefit. The document also examines various parasite life cycles involving definitive, intermediate, and paratenic hosts. It explores modes of transmission between hosts and how infections establish within hosts.

1. Host Parasite Interactions
Bilal Nasir

2. Outlines of Session
• Parasite
• Host
• Different Examples of Parasite
• Parasitism
• Types of Parasites
• Host Parasite Interactions

3. Parasite
• A parasite is an organism that lives on or in a host
• Parasite gets its food from its host.
• Parasites can cause disease in humans.
• Traditionally parasite (in biological usage) referred
primarily to organisms visible to the naked eye, or
macroparasites (such as helminths).

4. Contd. . . .
• Some parasitic diseases are easily treated and some are not.
• The burden of these diseases often rests on communities in
the tropics and subtropics
• parasitic infections also affect people in developed countries.

5. Parasite and parasitism
• Parasite is a living organism (bacteria, viruses, fungi, protozoa,
helminthes) that lives in another organism, and receives
shelter and nourishment.
• In biology/ecology, parasitism is a non-mutual symbiotic
relationship between species,
• where one species, the parasite, benefits at the expense of the
other, the host.

6. Examples of Parasites

7. Examples of Parasites

8. Examples of Skin parasites

9. Host
• The organism on which a parasite lives is known as the host.
• The association between a host and parasite is called
parasitism.
• Parasite is Always Smaller in Size
• While Host Is Larger in Size
• Parasite Gets Benefits (Food and Shelter)
• Host Is Always Harmed (Infection / Disease/ Death )

10. Parasitism
• Parasitism is a relationship between two
organisms
• Host and parasites are involved in relationship
• where one is usually harmed and the other gets
benefits from the relationship.
• Parasites are smaller than their host organism
• Parasites reproduce quicker,

11. Contd. . . .
• Thus causing more damage to the host.
• Host get Disease And eventually Death
• Malaria is the most prevalent parasitic disease worldwide.
• killing more than 1 million people each year.

12. Diagrammatic Illustration of parasitism

13. Types of Parasite in Human
• There are three types of parasites that feast on humans:
• Protozoa
• Helminths
• Ectoparasites

14. Protozoa
• One-celled organisms that live and multiply in the blood or
tissue of humans.
• They infect the body via mosquitoes and flies and are found in
soil and water.
• They may be found and transmitted from different animals.
• Examples Giardia Lamblia

15. Example of protozoan's

16. Helminths
• They live in the gastrointestinal tract, blood, lymphatic system, and
other tissues.
• Examples are :
• Parasitic flatworms,
• flukes,
• tapeworms,
• thorny-headed worms,
• roundworms, and
• pinworms.

17. Helminthes

18. Tape Worm

19. Fluke (Liver Fluke)

20. Round Worms (Nematodes)

21. Ectoparasites
• Ectoparasites live on the surface of a human host and attach or
burrow into the skin .
• Examples are
• ticks,
• fleas,
• lice,
• and mites.

22. Host Parasite interactions
• Strict or obligate parasite is an organism that cannot live
without a host. That is they have no free-living existence.
Examples: Treponema pallidum, viruses, malarial parasite.
• Facultative parasite is an organism that has both a free-living
and a parasitic existence, e.g. Clostridium species,
Pseudomonas species.

23. Host Parasites Interactions
• Nonpathogenic: An organism that does not cause disease. It
may be a member of normal flora.
• Opportunistic pathogen is an organism (nonpathogen,
commensal or saprophyte) that can cause disease only in
immuno-compromised individuals that is having impaired
resistance. Example : Cytomegalovirus, Pneumocystis carinii,
Atypical mycobacteria, opportunist fungi.
• Saprophyte is an organism that lives on dead organic matter.

24. Host Parasite Interactions
• NORMAL FLORA are Microorganisms that is present on the
skin and mucous membrane of normal (healthy) persons.
• Non-pathogen, or opportunistic pathogen.
• Normal flora is of two types:
• (1) Resident flora
• (2) Transient flora

25. Resident flora.
• These are microorganisms regularly present in the region at a
given age, e.g.
• Viridans streptococci in mouth and throat,
• Escherichia coli in intestine.

26. Transient flora.
• The microorganism is present only for hours to weeks, e.g.
Streptococcus pyogenes in throat.
• Microorganisms of transient flora play no role when the
normal resident flora remains intact.
• But if the resident flora is disturbed than the microorganisms
of transient flora may colonize and produce disease.

27. Types of Host
There are Three types of Hosts
1. Definitive host.
2. Intermediate host.
3. Paratenic host.

28. Definitive host.
•In this host the adult stage of animal parasites lives and sexual
reproduction takes place.
•Man is the definitive host for all animal parasites except malarial
parasites and hydatid tapeworm.

29. Intermediate host.
•In this host the asexual reproduction takes place, or the larval
stages of animal parasites develops.
•When development of larval stage takes place in two different
hosts they are called 'first' and 'second' intermediate hosts.
•Man is the intermediate host for malarial parasites and hydatid
tapeworm.
•Man is both definitive and intermediate host for Taenia solium
and Trichinella spiralis.

30. Paratenic host.
A carrier or transport host.
That Carry the Parasite and don not have any disease or infection
There is no sign and symptoms of disease in Paratenic Host.

31. Host Parasite Interactions
• Infection is the multiplication of an infectious agent within the body.
• Multiplication of pathogenic bacteria (e.g. Salmonella typhi) even if the
person is asymptomatic is taken as an infection.
• Multiplication of bacteria of normal flora at its normal site is not an
infection.
• However, if they multiply and cause disease it is an infection, e.g.
Escherichia coli when causes diarrhoea.

33. NATURAL MICROBIAL HABITATS
Soil
Water/food
Air
Animals and Animal Products

34. Host Parasite Interactions
An infection involves the following :
• (1) Source or reservoir of infectious agent,
• (2) Transmission of the infectious agent from the source to the
host
• (3) Susceptible host- Portal or route of entry of the agent in
the host, its localization, multiplication and finally host-parasite
interactions which result in either
– (a) Destruction of the agent or,
– (b) Infectious disease.

35. Source (Reservoir)
• 1. Human Source.
• (a) Exogenous source : Patient or carrier,
• (b) Endogenous source : The individual himself.
• Carrier. A person with asymptomatic infection which can be
transmitted to another susceptible person.

36. Sources of infections
2. Foods and Drinks
• (a) Food :Any contaminated food,
• (b) Water contaminated with bacteria of typhoid fever, cholera, diarrhoea and dysentery,
• (c) Milk contaminated with salmonella, M. bovis.
3. Animals :
• Zoonoses are diseases which are transmitted from infected animals to humans.
– (a) Cow : Bovine tuberculosis, brucellosis by Brucella abortus, Salmonella food poisoning, anthrax,
Taenia saginata,
– (c) Dog. Rabies, hydatid disease, Weil's disease,
– (d) Horse. Tetanus and glanders,
– (e) Goat. Anthrax and brucellosis (by B. melitensis ),
– (f) Sheep. Anthrax and tetanus,
– (g) Cat. Cat scratch disease, (h) Rat. Plaque, Weil's disease, (i) Parrot and pigeons. Psittacosis.
4. Soil.
– Tetanus, gas gangrene

37. Modes of Transmission
• 1. Water-borne,
– e.g. cholera and other diarrhoea) diseases, enteric fever from contaminated water.
• 2. Food-borne
– (contaminated food) e.g. enteric fever, salmonella food poisoning (e.g. eggs of duck, foul). Milk
and milk products- enteric fever, bovine tuberculosis.
• 3. Air-borne
– e.g. Droplets. During coughing, sneezing and talking: Diphtheria, tuberculosis, measles,
chickenpox, mumps, influenza,
• 4. Dust-borne.
– e.g. tuberculosis,
• 5. Soil-
– Tetanus, gas gangrene.

38. Mode of transmissions
• 6. Contaminated fomites
– like beddings, clothings, utensils: Diphtheria, enteric fever, food poisoning.
• 7. Direct contact-
– STD like gonorrhoea, syphilis, AIDS.
• 8. Transplacental:
– Rubella, toxoplasma, congenital syphilis.
• 9. Insect borne.
– (a) Actively, e.g. malaria, filaria, kala azar, dengue, plague, yellow fever,
• 10. Blood or organ Transplant
– Tattoing or percing
– Blood transfusions
– Organs tranplant

39. Routes of Transmissions
• Portal or Route of Entry
• (1) Alimentary system by ingestion,
• (2) Respiratory system by inhalation,
• (3) Genitourinary system by food or water,
• (4) Skin due to trauma, bite of insects,
• (5) Placenta.
• (6) blood /plasma by transfusion