Pathogens: Definition and Meaning of Pathogens, Pathogenicity

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Meaning of Pathogens

  • Pathogens can be defined as the infectious agents that can cause illness and infection.

  • The term pathogen came into use in the 1880s.

  • Infectious diseases are caused by various pathogenic microorganisms for e.g. virus, bacteria, protozoan, fungi, and other parasites.

  • The infectious diseases can be transmitted by animals, humans, insects, or other agents.

Pathogenicity

  • It is the potential disease-causing capacity of pathogens.

  • An organism can be pathogenic or non-pathogenic, but one cannot be more pathogenic than the other.

  • A pathogen may be described in terms of its ability:

    • To produce toxins.

    • Enter tissue

    • Hijack nutrients

    • To immunosuppress the host

    • Immunosuppress is the reduction of activation or efficacy of the immune system.

Context-Dependent Pathogenicity

  • Pathogenicity depends on the microbial ecosystem as per the modern view.

  • A bacterium may participate in opportunistic infections in immunocompromised hosts. Opportunistic infection means infections caused by pathogens taking advantage of an opportunity normally not available.

  • Immunodeficiency or immunocompromise can be defined as a state in which the immune system’s ability to fight infectious disease and cancer is compromised or entirely absent.

Classification of Pathogens

Class I

  • They should not be part of an identified group.

  • The non-pathogenicity of the species has been demonstrated authoritatively both in vivo and in vitro testing.

Class II

  • Species spreading diseases in humans or animals might not spread to the humans.

  • Having the essential prophylaxis or therapy.

Class III

  • Species that cause serious disease in humans, spread to the humans.

  • Having the essential prophylaxis or therapy.

Class IV

  • Species causing serious human disease likely to disseminate in the human population.

  • No prophylaxis or therapy exists.

Types of Pathogens

Algae

  • Algae are single-celled eukaryotes.

  • Eukaryotes are those organisms with cells having a nucleus enclosed within a nuclear envelope.

    • Non-pathogenic although pathogenic varieties do exist.

  • Protothecosis

    • A disease found in dogs, cats, cattle, and humans.

    • This disease is caused by a type of green alga known as prototheca that lacks chlorophyll.

Bacteria

  • Bacteria are microorganisms made of a single cell.

  • Pathogenic bacteria can cause infectious diseases.

  • They are diverse having a variety of shapes and features.

Commensals vs pathogens mechanism

Commensals vs Pathogens Mechanism

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Fungi

  • They can be found indoors, outdoors, and on human skin.

  • The typical fungal spore size is <4.7 μm in length.

  • Fungi cells contain a nucleus and other components protected by a membrane.

Parasites

  • These are the organisms that behave like tiny animals, living in or on a host.

  • Parasitic infections are more common in tropical and subtropical regions.

Three Main Types of Parasites

Helminths

Commonly known as worms are larger, multi-celled organisms that can live inside or outside the human body.

Protozoa
  • These are single –celled organisms that that can live and multiply in the body.

  • Ectoparasites are multi-celled organisms that live on or feed off the skin.

  • This also includes some insects like ticks and mosquitos.

Viroid’s

  • These are the smallest pathogens known.

  • These are composed solely of a short strand of circular, single-stranded RNA.

Prions

  • These are misfolded proteins that can transfer their misfolded state to other normally folded proteins of the same type.

  • They do not contain any DNA or RNA and cannot replicate.

Viruses

  • These are small particles typically between 20 and 300 nanometers in length.

  • They contain RNA or DNA.

  • They require a host cell to replicate.

Pathogen Hosts

Pathogen hosts

Pathogen Hosts

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FAQs

Q. What are pathogens?

Answer:

A pathogen can be referred to as an infectious agent or simply a germ that can produce diseases. Pathogenicity is the potential disease-causing capacity of pathogens.

Q. What are the four most common types of pathogens?

Answer:

The four most common types of pathogens are:

i) Viruses

ii) Bacteria

iii) Fungi

iv) Parasites

Q. In how many classes pathogens can be classified?

Answer:

Pathogens can be classified into four classes namely Class I, Class II, Class III and Class IV.