Host pathogen Interaction and Its Importance.

Host Pathogen Interaction

Before we proceed about Host pathogen interaction, first we need to know What is Host? and What Is pathogen?

The term pathogen refers to those agents, which has the capability to cause disease. For example, viruses, bacteria, fungi, parasites, has the capability to cause disease, so they will call pathogens.


The term host is refers to those organisms or animals that harbors a pathogen, it means that the host will provide nutrients and shelter to the pathogen. For example, animals playing host to parasitic worms.

Host pathogen interaction means, how a pathogen will survive within a host body, weather it causes disease or not.


What is Host Pathogen Interaction?

Host pathogen interaction means, how a pathogen or a disease-causing agent sustains within a host body based on a molecular, cellular, organismal, or population level.

Molecular, cellular, and population-level means, after infection to a host cell, the pathogen started rapid cell division and increase their population. After that, they started causing diseases by altering the body’s homeostatic or started to release toxins which produce symptoms in the host body.


There are several terms related to host-pathogen interaction such as infection, pathogenicity, invasion, toxigenicity, virulence, opportunistic infections, etc. Each of these terms we will discuss in this article with an appropriate definition and example.

Host-Pathogen Interaction


What is Infection?

Infection is a biological term in which involves the invasion of an organism’s body (Host) tissue or primary barrier by a pathogen or diseases causing agent and then it started to increase it’s number within the host body and produces toxins, which results some abnormal activity on host body.

The microorganisms which are responsible for the infection, they are known as infectious agents. There are present several types of Infectious agents such as viruses, bacteria, fungi, parasites, etc.


Infection is accomplished in this following steps.


It involves the Attachment of pathogen to the body surface of a host cell or an organism.


In this step the pathogen is started to enter the cell cytoplasm by penetrating the cell wall. For this purpose, the pathogen started to release several digestive enzymes or chemicals to its attachment site. Which will digest the cell wall component and as a result it will form a pore. Then the pathogen can easily enter to the cell cytoplasm through this pore.


In this step, after entering to the cell cytoplasm. The pathogen stated to increase their number by multiplication. After increasing the number, they started to infect other cells of host body. That’s how a pathogen cause an infection.

What is Disease?

Disease is an impairment of the normal state of an organism or any of its components that hinders the performance of vital functions.

A disease can be caused by both internal and external factors. External factors mean pathogens such as bacteria, viruses, fungi, etc.

Internal factor means Dysfunction of the immune system which can cause different types of disease such as immunodeficiency, hypersensitivity, allergies, and autoimmune disorders.

What is Sporadic?

The term sporadic refers to those diseases which occur in individual in different geographical area.

Example: Japanese encephalitis

Normal Flora of Hman Body

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What is Pathogen?

When a microorganism is capable of producing disease is called pathogen. The term “Pathogen” is used to denote any infectious agent such as viruses, Bacteria, Protozoa, Fungi, etc.

Example: Virus, Bacteria, etc.

What is Pathogenicity?

Pathogenicity means the disease-causing capacity of a pathogen. The term pathogenicity is used to describe the ability of a pathogen to produce toxins, enter tissue, colonize, hijack nutrients, and its ability to immunosuppress the host.

An organism’s pathogenicity depends on its ability to invade a host, multiply in the host, and avoid being damaged by the host’s defenses.

Example: Mycobacterium tuberculosis, frequently cause disease upon entering a susceptible host. Other agents, such as Staphylococcus epidermidis, cause disease only in a rare instances and usually only in hosts with poor defenses. Most infectious agents exhibit a degree of pathogenicity.

What is Virulence?

Virulence refers to the intensity of the disease produced by pathogens, and it varies among different microbial species.

The term Virulence also refers to the degree of damage caused by the pathogen to the host body.

The term virulence came from a Latin word “virulentus”, which means “a poisoned wound” or “full of poison.”

Example: Bacillus cereus causes mild gastroenteritis, whereas the rabies virus causes neurological damage that is nearly always fatal. Virulence also varies among members of the same species of pathogen.

What is Opportunistic Pathogen?

Opportunistic infection occurs when our body immune system becomes weak. There are present several pathogens in the host body such as viruses, bacteria, fungi, which can cause infection if the host body’s immune system becomes weak and this type of infection is called opportunistic infection.

You might be thinking why they are called Opportunistic Pathogen? so, let me explain this to you. They are called opportunistic pathogens because they can only cause disease by taking advantage of our weak immune system. In normal conditions, if the host immune system remains stronger than this pathogen then they can not cause any infection in the host body. So, this type of organisms are waiting for an opportunity to cause infection in the host body, that is why they are called Opportunistic Pathogen.

The pathogen which is waiting for an opportunity to cause an infection is called opportunistic pathogen and the infection which is caused by the opportunistic pathogen is called opportunistic infection.

Example: Aspergillus sp., Candida albicans, Clostridium difficile, Coccidioides immitis, Cryptococcus neoformans, etc.

What is Commensal?

Commensal is a type of biological interaction in which one species lives on or within another species and among them one species gets benefits but other species neither benefit nor are harmed. A Commensal should be smaller than the host.

So, in one sentence commensal define as when an organism that lives in or on another organism, deriving some benefit from the association but not harming the other party.

Example: One of the easiest examples of commensal is Clownfish and anemones.

What is Syndrome?

Syndrome is defined as a combination of both sign and symptom that occurs together and characterize a particular disease or abnormality.

Sign: Signs are objective changes in the body that can be directly observed.

Example: rash etc.

Symptoms: Symptoms are objective changes that are personally experienced by the patient.

Example: Pain and loss of appetite can only experience by the patients.

What is Incubation Period or Incubation?

Incubation is the period after pathogen entry and before signs and symptom appears. The infective agent after reaching the selective tissue undergoes multiplication during this period.


All the terms that I have described in the above article, all of these are related to the host and pathogen interaction. Those terms are used to describe a particular property of host and pathogen interaction.

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