Human Parasites – Everything You’ll Need To Know Including Different Classifications And How To Observe Them Under A Microscope

Parasites can be defined as an organism that lives inside, or on a living host.

Parasites have been a common thing in nature for a very long time, but the first evidence of human parasites is from 5000BC, and they tend to do damage to whatever human host they attach themselves to.

Human Parasites - Everything You’ll Need To Know Including Different Classifications And How To Observe Them Under A Microscope

There are three main types of human parasites, generally composed of Helminths, Protozoa, and Ectomorphs.

Human parasites are a pretty scary idea, and if this is the first time you’ve heard about them you probably have some questions.

If this sounds like you – then you’ve come to the right article! We’re going to be exploring everything there is to know about human parasites.

We’ll outline their types, and standard classifications, as well as the common ways that they are observed under the microscope.

There are lots of different ways to do this, so it’s important to understand the safety procedures and standard practices.

We’ve also made sure to include a short FAQ that will help answer any other questions you may have.

What Is A Human Parasite?

A human parasite is a term we use to describe parasites that choose humans as a host. They require a living human in order to live, and this usually means that they are unable to survive without them.

There are many different types of parasites (some of which we are going to outline below), but generally, they all require a series of conditions for them to be able to survive including, perfect temperature ranges, environments with moisture, and the right nutrients.

The first evidence that has been found by researchers is the eggs of the Lung Fluke, which was found in preserved human feces.

This was then dated and is believed to have been from 5900BC. Of course, this isn’t all that early in the history of humanity, but it does prove that parasites have been present throughout much of studied world history and that they are likely to be much, much older.

There are also early medical writings from different parts of the world that support evidence of their early existence.

Parasites cause upwards of 1 million annual deaths in humans, with the most deadly killer being Malaria.

There is a long list of different parasites in humans, all of which exist in different ways and cause lots of different physical problems.


Parasites are generally organized into three different categories, we’re going to give you a quick rundown of each of these here.


Ectoparasites are probably the most commonly known parasites, and usually the least dangerous of the different categories.

Ectoparasites are parasites that embed themselves into the coat or skin of their chosen host. The most common ectoparasites you’ve probably heard of already are fleas and lice.

Ectoparasites are usually much easier to deal with in humans, as they are usually immediately visible providing you a look.

Head lice are the most common form here that are very easy to see, and something that a lot of people (usually in childhood) go through.


Protozoa are single-celled parasites that come in a variety of different shapes and sizes.

Because of their size, protozoa live in a variety of different settings, and can often do a lot of damage to their chosen host.

There are more than 50,000 species of protozoa and they are very common within the natural world. In fact, it’s predicted that almost all habitats have at least some form of protozoa living within them.

More than this, it’s estimated that all humans have protozoa living in or attached to their body at some point, though real infestations that cause harm are much rarer.

Protozoa-based diseases can range in terms of their symptoms. Sometimes infestations cause no symptoms, or symptoms that appear after a long time, whilst others are immediately life-threatening.

One of the most common and deadly protozoa-based diseases is malaria – which we will cover in more detail below.


You’ll probably know these as worms. These are larger parasites that are multicellular and often live in the intestines of their host.

Some of the most common forms of Helminths in humans are tapeworms, pinworms, and flukes.

You’re most likely to find people inflicted with helminth infections in either subtropical or tropical areas, but that’s not to say that they don’t thrive in other environments.

The main way that helminths come into contact with humans is through poor hygiene, specific types of food, and climate.

They can sometimes also be spread through vectors (an animal that acts as a host and carries them to humans).


This is the process by which Endoparasites (protozoa, helminths), enter and exist inside the body of a host.

These parasites will find a way into the body through openings in the nose, skin, anus, or mouth, and search for an environment with the right conditions for them to live and thrive.

Human Parasites Under The Microscope

In this section, we’re going to be taking a look at what some common ectoparasites and endoparasites look like under the microscope.

Human Parasites - Everything You’ll Need To Know Including Different Classifications

We’ll break down how they are commonly observed. It’s worth noting that there are a lot of different species, so these are just a small sample size.


Flea (order Siphonaptera)

The first thing to know about the flea is that it is actually a name that encompasses a long list of different species.

They are all flightless and exist as ectoparasites to both mammals and birds. If you’ve ever had a pet you’ll know how common they are, increasing in the summer when a dog or cat is more likely to be outside.

Fleas can cause a wide range of different problems including dermatitis, bacterial or fungal infections, many diseases, allergic reactions, and health problems as a result of hematophagy (feeding on blood).

Fleas have also acted as vectors throughout human history, and are thought to be the main culprit responsible for the black plague.

Observing Fleas

Fleas are commonly observed by the use of a stereomicroscope, a sample, and some additional items such as cover slips, paper towels, a dropper, a petri dish, and glass slides.

A flea is typically picked up with a standard pair of tweezers and placed onto a microscope slide. You can then lay the cover slip over the top and observe using specifications of 4x and 10x.


Hookworms (Ancylostoma or Necator)

Hookworms are parasitic roundworms that tend to live in the intestines. The most common species that affect humans are Necator and Ancylostoma.

These worms infect humans usually as a result of bad hygiene or sanitation.

Their lifecycle usually consists of eggs being laid in feces, larva hatching from those feces, then that larva finding a way into a human through the skin or other means.

There are different sizes and species of hookworms, but these parasites can cause a lot of problems for humans.

Some of the first symptoms of a hookworm include itching, diarrhea, weight loss, anemia, fatigue, and severe abdominal pain.

They are typically treated through the use of modern anthelminthic medicine, but with severe infections more strict measures such as blood transfusions are sometimes required.

Observing Hookworms

In order to observe hookworms, you’re going to want to have a good, bright lighting system, with either an LED or halogen light source.

Whilst a monocular microscope may be cheaper, a binocular microscope is going to get you a better image. Hookworm samples will need to be wet mounted (in a hygienic setting without contact with your skin).

As for magnification, for a more general look, you’re going to want to use around 40x magnification, but you may need to go all the way up to 200x magnification if you want to observe eggs in detail.

Malaria Parasite

The malaria parasite is one of the deadliest to humans in the world. It is spread by female anopheles mosquitos as they feed off of human blood.

The malaria parasite causes cases of malaria, which is a very serious and sometimes deadly disease that can cause humans to become very sick.

Typical symptoms include chills and flu-like symptoms with extremely high fevers.

As with all Endoparasites, malaria parasites are unicellular and begin to multiply in the liver.

From there, they will travel into red blood cells, where additional broods of parasites will grow and begin to destroy them.

The daughter parasites are known as merozoites and will then continue this process by invading other red cells, so on and so forth.

Malaria is typically carried from one person to another through mosquitos, who are more numerous in hot climates.

When a female mosquito feeds on human blood, the parasites mate in its stomach and then begin to multiply and grow within it.

They then embed themselves into the saliva of the mosquito which will pass it on to other humans. Interestingly, the mosquitos do not suffer problems from the parasite as a human will.

Observing Malaria Parasites

Malaria Parasites are observed with compound microscopes. The specimen (typically Giemsa Stained Blood) is usually mixed with immersion oil and then placed onto a clean microscope slide.

This slide is then covered and clipped onto the compound microscope. It’s worth noting that a lot of care needs to be taken when preparing the slide.

Contact with human blood infected with malaria can be dangerous, even in small doses.

The general specifications to observe a malaria parasite are typically 40x and 100x power objectives, which will allow you to see them in greater detail.

If you still have some questions, check below for our extensive FAQ section below.

Frequently Asked Questions

What Is The Most Common Human Parasite?

The most common human parasites are Helminths, but thankfully they are also some of the least dangerous and easy to treat, especially if the symptoms are caught early.

Protozoa are much more difficult to treat because of their single-celled nature, and often cause much more damage at a cellular level.

What Is The Most Dangerous Human Parasite?

The most dangerous human parasite is most likely Naegleria, otherwise known as the brain-eating amoeba.

They are single-celled organisms that are commonly found in bodies of fresh water.

They typically infect people through water entering the nose and then go to the human brain where they begin to do damage.

Typical symptoms in a human after infection include severe headaches, nausea, vomiting, and fever, which then develop into more serious symptoms like confusion and hallucinations.

If this sounds concerning, one thing to know is that infections from this parasite are fairly rare, and there are a few treatments that have allowed people to recover.

How Can I Prevent Internal Parasites?

As we outlined above, there are a lot of different types of human parasites, all of which manifest and find their way into humans in different ways.

In the western world, a lot of measures have been taken in order to lessen the spread of parasites, but they can still manifest.

Modern public hygiene procedures have been put in place to make sure that food and public spaces are kept clean, but common practices to avoid parasites include hand washing, food washing, drinking clean water, and staying away from animal or human feces.

What Happens If A Human Gets Worms?

Generally, hookworm, roundworm, or tapeworm infections are not deadly, but they can cause a lot of problems if left untreated.

However, the treatment is often simplistic and can be cleared up with medicine.

Mebendazole is a common medicine that you can get via a pharmacy or with a doctor, and will typically fix the problem within a few days.

There are a few common side effects such as stomach pain or diarrhea that can come as a result of taking it.

Final Thoughts

So there you have it! There are a lot of different human parasites, all of which can cause a lot of problems for humans.

Thankfully, because of modern technology and advancements in medicine, we now have ways of properly identifying and treating them.

The study of human parasites is a fascinating field that can not only deepen your understanding of microbiology but also help others.

We hope that this guide has told you everything you wanted to know about the basics of human parasites and that you now feel a lot more confident about the two main classifications, and how some of these species work.

Jennifer Dawkins

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