What are Human Parasites?

In today’s world, we are inherently becoming more health-conscious and aware of our external surroundings. We take charge of our bodies and take utmost precautions to keep our proximities as clean as possible. Even after such conscious effort, there remains a threat of alien bodies entering into our systems and harm them in unimaginable ways.

A small organism that is almost invisible from the naked eye can do more harm to our body than any other externalities. This may sound a bit alarming but this is the growing reality of today. Studies have shown that almost 300,000 people living in the USA get infected by parasites that cause Chagas disease. Over 14% of the population in the USA has been exposed to parasites in one way or another.

But what are these parasites that are harming the physical health of so many people around the world? Let’s dive deep into this subject and gather more information about what these parasites are.


A parasite, in general, is an organism that lives off its host. In this case human. They feed off the human body and cause harm to it by spreading diseases.

Some key features about parasites are:

  • Around 70% of them are not visible to the naked eye
  • They can be as small as a sesame seed and as big as 30m
  • Some parasites may live outside humans (Ectoparasites) and some inside it.


Parasites were first discovered in the 18th century. According to the study done by F.E. G. Cox, these parasites had 2 sources of origination; our ancestors and animals.

The paper continues to say that the first recorded evidence of such species dates back to 3000 to 300 BC in the Egyptian medicinal records.

We can list the milestones in the historical journey of the earliest known parasites in humans:

  • Eggs of lung fluke were found in feces that is said to be of 5900 BC were found fossilized in Northern Chile.
  • Hookworms were said to be discovered in 5000 BC near Brazil
  • Roundworms date back to 2330 BC. They were first found in Peru.
  • Ebers papyrus from 1500 BC describes the presence of Nematode worms in humans.
  • Schistosomiasis made its name in history during the epidemic that was spread in 1798 amongst Napoleon Army in Egypt.

The parasites have co-existed with our species for a long time now. They have evolved with the surroundings and have become more aggressive and intrusive to our system.

The family of parasites is ever-increasing and it was important to know its roots before we divide it into distinct categories.


Parasites that feed off humans can be categorized into two broad categories. The figure below can explain clearly what these categories are.

  • Ectoparasite- The parasites that live outside the humans. (See figure A for reference) They are mostly present on the skin or scalp. Some prominent examples are lice, mites, and ticks.
  • Endoparasites- Parasites that live inside the human body and harms the internal systems are known as endoparasites (See figure B for reference). Tapeworms, flukes, and other disease-generating parasites belong to this category.

These parasites further differ in nature. Some of them can be erratic, some accidental and some deemed to feed off its host.


Human parasites are intrusive to the functions of the body. It corrupts our systems and causes fatalities that in the worst of cases can lead to death.

We need to identify such parasites and the infections they cause and take appropriate measures accordingly.

Some of the most important categories are listed below with the infections they cause:

1. Protozoan

Protozoans are tiny organisms that have the potential to infect every tissue of our body.

  • Medium of infection- Contaminated water and insects
  • Diseases caused- Malaria fever
  • Human parts infected- Every tissue can be infected and it can remain active for a lifetime in its host.

2. Flukes/Trematodes/ Flatworms

Flatforms are the most common form of parasite known to exist. They are tiny, flat, and oval in structure. The length ranges from 1mm to 70mm. They are predominantly found in Europe and North America. They are highly infectious and multiply quickly to get into all organs of your body.

  • Medium of infection- Freshwater with snails
  • Disease caused– Fascioliasis
  • Human parts infected- Liver, heart, and kidneys

3. Roundworms/Nematodes

Roundworms ushers a species of varied organisms like hooks worms, threadworms, pinworms, and whipworms. Generally, its length is about 1mm. The symptoms of this disease are erratic, and they are highly infectious. They can be visible in human feces as well.

  • Medium of infection- Contaminated food or drinks
  • Disease caused– Enterobiasis, Ancylostomiasis, and Trichuriasis
  • Human parts infected- Mostly intestines

4. Tapeworms/Cestodes

Tapeworms are the fastest spreading parasite to be found in the human body. They travel across organs and multiply exponentially. They can lay a million eggs within one day. They have a good lifespan which nears about 25-30 years. The most alarming fact about tapeworms is that they can grow up to the size of 33 feet in our intestinal tract.

  • Medium of infection- Consuming raw fish and food infected by animal feces. Undercooked non-vegetarian foods are also a major contributor.
  • Disease caused– Taeniasis
  • Human parts infected- Any part of the body can be infected, and the infection can spread across organs.

5. Tapeworm Larvae

Tapeworm larvae are the eggs of tapeworms that can be accidentally ingested by humans. Once they get into the system, they start to form cysts in the organs. They can live for many years in your body and can grow up to the length of 40 inches. They are very invasive.

  • Medium of infection- Consuming raw fish and food infected by animal feces. Undercooked non-vegetarian foods are also a major contributor.
  • Disease caused– Cysticercosis
  • Human parts infected- Any part of the body can be infected, and the infection can spread across organs.


The lifecycle of a human parasite can be explained step by step as follows:

  1. The lifecycle of a human parasite primarily starts when you ingest something that has been infected by those parasites.
  2. Once the parasite enters your body orally, it enters your bloodstream.
  3. Through the bloodstream, the parasite looks for a suitable target organ where it can grow.
  4. Once they set their home, they start to eat up your cells. They also take up the nutrients present in your body.
  5. The intestinal tract is the primary target for such parasites, but the parasites can also travel to all organs are cause fatalities.
  6. They can harm your bones by eating up the calcium.
  7. They can also eat up the protein-coated outside nerves and disrupt brain activities.

Keeping our surroundings clean and having good hygiene does not guarantee the prevention of parasitic infection. Every one of us has equal chances of being exposed to parasites.


Parasitic infections are no longer a localized concept. They have made their presence felt across the globe. Developed countries are also not alien to it.

It is necessary to keep all the factors that affect our health in check, but it is crucial to understand that even these efforts can go in vain when it comes to being infected by parasites. So, is there no way out for us to prevent ourselves from such parasitic infection? Well, there is!