Host-Parasite relationship is the extreme case of animal association, in which both partners influence each others life by affecting each others metabolism and behaviour using different adaptive mechanisms in order to ensure their survival.

1. Amjad Khan Afridi
Lecturer,
Department of Health & Biological Sciences
Abasyn University Peshawar
Host-parasite
interactions

2.  Whether or not you will catch a disease depends on:
(1) YOU: your health, nutrition, immune status.
(2) The pathogen's VIRULENCE
(A) How TOXIC the organism is?
(B) How INVASIVE the organism is

3.  SYMBIOSIS: The term host and parasite relationship is also know
as Symbiosis mean the coexistence of two organisms in which one
extracts the nutrition from other.
 PARASITIOLOGY: Is a branch of microbiology, refer to the
scientific study of parasitism.
 DISEASE: Any abnormal form or condition of the body is called
“Disease”.
 INFECTIOUS DISEASE: A disease condition caused by the
presence or growth or increased numbers of infectious
microorganisms or parasites.
 PATHOGEN: Is defined as any microorganism that has the
capacity to cause disease.
 VIRULENCE: The degree of pathogenicity in of microorganism:

4.  MUTUALISM: Is a symbiosis in which both members benefit from
the relationship
 COMMENSALISM: Is a relationship in which one member
benefits, and the other one neither benefits
nor is harmed.
 OPPORTUNISTS: These are organisms that normally don't cause
disease but will if given an opportunity.
 NORMAL FLORA: Harmless microbes. Do not cause disease but
give benefit to its host.

5.  A HOST is any organism that allows another organism/bacteria etc.
to live in or on it.
 The organism on which parasite lives is known as the host.
 Host is larger in size.
 Host is always harmed ( Infection/disease/death).
HOST

6.  The PARASITE is the organism loving on or in the host
 Smaller in size and get its food and shelter from its host
 May be Microscopic ( Bacteria, fungus, Viruses) or Macroscopic i.e.
(Helminths, protozoa, algae etc.)
 Some parasitic diseases are easily treated and some are not.
 In biology/ecology, parasitism is a non-mutual symbiotic relationship
between species.
 Where one species, the parasite, the benefits at the expense of the
other, the host.

7. Parasitism

8. There are there types of parasites that feast on humans:
1. Protozoa
2. Helminths
3. Ectoparasites
Types of Parasites in Human

9. PROTOZOA

10. HELMINTHS

11. ECTOPARASITES

12. Host Parasite Interactions

13. Cont….

14. Cont….

21. HOW TO DETERMINE IF AN ORGANISM IS THE ETIOLOGIC
AGENT OF DISEASE
 REVIEW KOCH'S POSTULATES:
1. The agent must be observed in every case of the disease.
2. The agent must be isolated from a diseased host and grown in pure
culture.
3. When purified agent is inoculated into a healthy but susceptible
host, it must cause the same disease.
4. The agent must be reisolated from the newly infected, diseased
host, and be identical to the previously identified causative agent.

23. 6th March, 2023