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What is a Pathogen?

Pathogens are microorganisms that enter, develop and cause illness to the body of its host. It only needs a host body to survive. Pathogens are capable of bypassing the immune system. It also uses bodily substances to exist. These microbes can spread from one host to another in various ways, depending on its type. 

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Notably, pathogens can transmit through the air, bodily fluids, skin contact, etc. 

Let us start with more details about what is a pathogen for a better grasp on this topic.

Features of Pathogens

The primary aim of pathogens is to exist and multiply in its host. Their target is to

  • Search for a compatible body part to survive which is full of nutrients. 

  • Infect the host.

  • Avoid or subvert the host’s natural immune responses. 

  • Reproduce with the help of a host’s resources. 

  • Enter a new host. 

Pathogens can study a cell’s mechanism very well and evolve accordingly to exploit its host organisms. 

Different Kinds of Pathogens

Primarily there are four types of pathogens. These are

1. Viruses 

Viruses are the most common type of pathogens. It is an infectious agent that colonises inside a living organism. Taking advantage of weak immunity power, it attacks host cells. Then viruses use the substances of host cells. Also it produces more viruses. Once the replication cycle ends, they travel to new hosts. 

They mainly damage infected cells. This can even stay dormant for a while before replicating. All these traits define pathogenic viruses. It is the main cause behind viral infections that tend to recur in the host body. Only a few antiviral medicines can kill these viruses. 

2. Fungi 

Millions of fungal species live on the plant. Not all of them cause diseases. Only about 300 of them are responsible for causing illness. Fungi are everywhere, be it on the surface of skin or inside your food. They cause sickness only if they overgrow. 

Fungi have two protective layers, a membrane and a cell wall, and they cannot be destroyed easily. The intensity of fungal infection can be moderate to severe, depending on its type. 

3. Bacteria 

Another common type of illness-causing pathogen is bacteria. It is a microscopic, unicellular organism. Just like fungi, not all bacteria cause illness. There are some bacteria which are beneficial for human health. For example, lactobacillus remains in curd. 

The bacteria that cause infection are pathogenic. Usually, bacterial illness can be treated using antibiotics. 

4. Parasites 

This pathogenic organism survives in its host’s body and takes benefits of it. In return, it causes harm to its host. They are mainly of three types- protozoa, ectoparasites and helminths. It can transit through several modes, including insect bite. 

Pathogens Inflicted Diseases

Viruses: Common flu, measles, herpes, COVID-19, chickenpox, HIV, AIDS, Hepatitis A B C D, etc.  

Fungi: Ringworm, vaginal yeast infection, jock itch, etc.  

Bacteria: Tuberculosis, Gonorrhoea, Lyme disease, etc. 

Parasites: Malaria, Intestinal worms, Lice, etc. 

Now that you know about what is a pathogen, let us discuss how to prevent its invasion. 

Safety Measures

  • Getting vaccinated regularly.

  • Washing hands properly.

  • Careful storage of food items.

  • Staying away from sharing personal products.

  • If symptoms like fever, vomiting, etc. arise, stay at home.

  • Practice safe sex.

  • Beware of insect bites. Use a product like a mosquito repellent. 

Multiple Choice Questions

1. What Causes Athlete Foot Disease?

  1. Virus

  2. Bacteria

  3. Parasite

  4. Fungi

2. Which One is a Good Bacteria for Humans?

  1. Probiotics

  2. Salmonella

  3. Vibrio

  4. Helicobacter

Answers: 1-d), 2-a)

For further information on what is a pathogen and its allied topics, access our detailed study material. Now you can also download our Vedantu app for easier access to these study materials and online interactive sessions.

Relation between Pathogens and Hosts

Pathogens are classified as facultative or obligate pathogens, depending on how closely their life cycle is linked to that of their host.

Facultative pathogens are those organisms that can reproduce in various types of environments other than the host.  They are bacteria and fungi found in the environment that can cause infection. Many of the most troublesome hospital-acquired microorganisms involved in the antibiotic resistance pandemic can be found there. Occasionally, a distinction is drawn between facultative and accidental pathogens, with the latter referring to those that only infect weakened or immunocompromised hosts on a rare basis. Neisseria meningitidis and Escherichia coli are two common 'accidental' infections.

Obligate pathogens need to have a host in order to complete their life cycle. All viruses are obligate pathogens, meaning they rely on their host's cellular machinery for replication. They include bacteria, such as tuberculosis and syphilis agents, as well as protozoans (such as malaria parasites) and macroparasites.

To complete their life cycle, some obligatory pathogens require several hosts. The definite host, which supports the pathogen's adult form, is usually a vertebrate, whereas the intermediate host (also known as a vector) is usually an arthropod or mollusc. Viruses (such as the Zika virus), bacteria (such as Lyme disease), and protozoa all have this switch between vertebrate and invertebrate hosts (malaria).


Trematodes (parasitic flatworms) go much further, with some of their life cycles being among the most ornate. They are based on a three-host system, with some species having a four-host system. For example, Halipegus occipitalis must infect a freshwater snail, an ostracod, and a dragonfly nymph in order to complete its cycle, which terminates when the dragonfly is consumed by the dragonfly.

How do Pathogens Spread Diseases?

Pathogens cause illness in their hosts in a variety of ways. The most obvious way is to cause direct harm to tissues or cells during replication, usually, by producing toxins, which permits the pathogen to spread to new tissues or depart the cells it reproduced in. Bacterial toxins are among the most lethal poisons known, with well-known examples including tetanus, anthrax, and botulinum toxin, better known as Botox in its commercial application.

The damage to the host, on the other hand, is frequently self-inflicted by a strong or sometimes excessive immune response that kills infected and uninfected cells alike and damages host tissues. Cirrhosis, liver cancer in hepatitis B (10), or the 1918–1919 influenza epidemic, where the toll was highest among the young and healthy, possibly because they mounted the strongest immune response and as a result died from a 'cytokine storm' in the lungs, leaving patients literally drowning in their own body fluids.

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FAQs on Pathogen

1. What do you Mean by Pathogens?

Pathogens are the organisms that cause diseases in its host body. The pathogens that make humans ill are called human pathogens. A few examples of pathogens are Listeria, Salmonella, etc. 

2. What are Viruses?

Pathogens cause infectious diseases. It includes viruses, protozoa, fungi, worms, etc. Therefore, a virus is one of the pathogens. 

3. What are the Four Main Groups of Pathogens?

The four main groups of pathogens are viruses, parasites, fungi and bacteria. Apart from these, there are other types of pathogens as well.