Have you ever heard of immunity? What of infection? Great, then you know what follows. The commonest basis of infection for human beings is the human being. Wow, what a contradiction you say. Yeah, we've all suffered one or two symptoms of diseases where we blame the organism causing that illness without blaming ourselves too. First of all, three things come into play before a disease can occur. Thus, a favorable environment, a susceptible host, and the microorganism- what we termed "the disease triangle". But, infection and immunity involve interaction between the host and the infecting organism to cause diseases. Now, based on the relationship between the host and the microorganism, microorganisms can be classified into saprophytes and parasites.


Saprophytes are free-living microbes that pivot on decaying and dead organic matter. " Papers" is a Greek word that means decayed and " phyton" means plant. They are found in soil and water and play an important role in the degradation of organic matters in nature.

PARASITES on the other hand  are microbes that can establish
themselves and multiply in hosts.


Symbiosis- is an association between two or more organisms or species living together Symbiosis comprises a range of relationships called mutualism, parasitism ad commensalism.

COMMENSALISM is an association between two species in which one benefits and the other unharmed. For example, many microorganisms live on our skin surfaces and utilize the metabolic products secreted from the pores of the skin which we are neither harmed nor benefited from.

MUTUALISM- Mutualism is a type of symbiosis that benefits both organisms. For example, the large intestine contains bacteria such as Escherichia coli that synthesize vitamin K and some B vitamins

At the other end of the spectrum is the parasitism in which one organism, the parasite benefits from the relationship, whereas the other organism is harmed by it.


contamination-  It means that the microorganisms are present on inanimate objects, the surface of the skin, and mucous
Infection: It is the lodgment and multiplication of the parasite in or on the host tissue.
Disease: It is the disturbance in the state of health, where the body cannot carry out its normal functions.


Infections can be classified according to the extent to which the host’s body is affected.
1. Acute disease: disease in which symptoms develop rapidly and that runs its course quickly.
2. Chronic disease: Disease in which symptoms develop slowly and it is slow to disappear.
3. Subacute disease: disease in which symptoms intermediate between acute and chronic.
4. Latent infection: Disease in which symptoms appear or reappear long after infection.
5. Primary infection: Initial infection with a parasite in a host
6. Secondary infection: New parasite sets up an infection in a host, whose resistance is lowered by a pre-existing infectious disease.
7. Local infection: Infection confined to the small region of the body, such as a boil or bladder infection.
8. Cross infection: When a patient already suffering from a disease, a new infection is set up from another host or another external source.
9. Inapparent infection: Infection that fails to produce e full set of signs and symptoms.
10.  Mixed infection: Infection caused by two or more pathogens.


Infections can be sourced from human-to-human associations, animal-to-human interactions, the food we eat, and so on.

You can dissociate yourself from a person suffering from chicken pox because it's an identifiable disease and highly contagious. But, what about a person who doesn't show a sign of his infection? You easily interact right? Yeah, that's how infections spread unknowingly because you either get it from a carrier or a patient.
Anyway, a carrier is a person who bears the parasite but does not suffer from the illness or even show symptoms of the illness. However, there have been six well-known carriers and they are:

  1. A convalescent carrier is an individual who is healed from a particular disease but continues to harbor the pathogen.
  2. Healthy carriers sometimes called asymptomatic carriers are people who harbor the pathogen but have never suffered from the disease yet are capable of transmitting it to others.
  3. A temporary carrier is a person, who harbors the parasite for less than some months.
  4. A paradoxical carrier is a person, who acquires the pathogen from a carrier.
  5. Contact carrier gets the pathogen from a patient.
  6. A chronic carrier is a person who harbors the parasite for several months, sometimes for the rest of one’s life after their initial infection.
One way we get infected is through animal interaction.


Animals may act as a source of infection without suffering. How funny will it be for a bat to be diagnosed with covid-19 but they are the intermediate host of the disease. So, animals maintain the parasites in nature and act as a pool of human infections. The transmission of disease from animals to man is called zoonoses. And, they are bacterial, fungal, and, viral diseases. Some examples are the Plague from rats, Rabies from dogs, and Tapeworm infection from cattle.


Some pathogens can survive in water that causes hepatitis A and E diseases and cholera in humans. Also, Contaminated food may cause infection as a result of food poisoning by E.coli or Staphylococcus aureus. There may also be pre-existing infections of milk, meat, and some of the food materials.

In a nutshell, methods of transmission of infections are through vectors and other activities like kissing, shaking of hands, sexual contact, and more which will be part two of this story.  So, like and share your views on how diseases are spread and how bacteria behave in the human system. Enjoy your reading.


1. "Host-microbe interactions : Insight: Nature" Retrieved from

2. Sunil. K Mohanty, Professor, and Head Department of Microbiology -Kalinga Institute of Medical Sciences. Bhubaneswar, Odisha, India.Textbook of Immunology, second edition.



I am an artless lady who seeks to improve the health care of children in deprived areas with little knowledge l have. I love to write, motivate, and inspire people with academic challenges.