Importance Of Host-Pathogen Interactions

HOST PATHOGEN INTERACTIONS

LEARNING OBJECTIVES

• Interaction between host and the pathogen

• Defense mechanisms of host as well as the pathogen

• Components of host-pathogen interactions

• Basis of host-pathogen interactions

• Types of interactions

• Significance of host-pathogen interactions

INTRODUCTION

Every organic being is related, in the most essential yet often hidden manner, to that of all other organic beings, with which it comes into competition for food or residence, or from which it has to escape, or on which it preys… Charles Darwin

ECOLOGY is the branch of science dealing with the classification and richness of organisms in the ecosystem and their kind of interactions with the

The commensal is usually provided by the food and shelter by the host. There is no direct dependency of the commensal on the host as the commensal can survive even without the host.

 When the waste product of one organism is a substrate for the other organism. Example: the process of Nitrification in which the ammonium ions are oxidised to the nitrites by microorganisms like Nitrosomonas, and the nitrites are then oxidised to nitrate by the Nitrobacter. Nitrobacter when associated with the Nitrosomonas provides it with the nitrite that helps it to obtain energy.

 Commensalism occurs when one organism alters the environment to make it suitable for the other. Example: Non-pathogenic E.Coli lives in the gut of human colon can grow well outside the colon also. When oxygen is present, the facultative anaerobic E.Coli can use it and even the obligatory anaerobic organisms such as Bacteroids can grow. Thus, anaerobes are benefitted but no such benefits to the

Eg: bacteria, viruses

OBLIGATORY PARASITES Cannot survive without host

FACULTATIVE PARASITES Can survive without host

MICROPARASITES Small size, small life cycle, reproduces inside the host

MACROPARASITES Large size, do not need reproduce inside the host

 Example: Lichens, which is the association between fungi and algae. Fungal partner is mycobiont and the algal is phycobiont. Being a phycobiont, algae provides the fungi with the food in exchange of the protection from the high light intensities, water and minerals from the fungi.

 Lamprey, a vertebrate parasite which obtains its food by attaching to other fishes. It has a circular toothfilled mouth, thus sucks blood and other bodily fluids. Thus, at last they kill their host.

SUMMARY OF HOST PATHOGEN INTERACTIONS

• The host provides the pathogen with the necessary requirements and it depends on the pathogen how to use the host mechanism for its benefits.

• As the pathogens are capable of causing a disease in the host, it doesn’t mean that they will cause disease in all the host cells.

• Due to the various activities of the pathogen within the host, the host’s immune response gets activated and can kill the pathogens in some