Human Parasites Under the Microscope

Types and Classification

What is a Parasite?

Essentially, a parasite is a living organism that lives in (or on) another living organism (host) for survival. In most cases, the parasite is unable to live independently and thus requires a host that provides favorable conditions for growth and multiplication.

Some of the favorable conditions that parasites may need from the host include:


  • Ideal temperature range
  • Nutrients (carbohydrates, amino-acids etc)
  • Moist environment

Parasites often cause harm to the host and have been associated with such health implications as malnutrition, body rashes, weight loss and general malaise among others. If left untreated, parasites can and have caused the death of the host as is the case with malaria parasites in various parts of Africa. In such cases, the parasite also dies or finds a new host for survival. 

Parasites may be grouped into three main categories.  These include:

Protozoa - Protozoa are single-celled organisms that live and thrive within the host. A good example of protozoa is plasmodium malariae, which can be found within the red blood cells of the host (the destruction of red cells by the parasites causes anemia).


Helminths -  Unlike protozoa, Helminths are multicellular parasites that are commonly referred to as parasitic worms. They can also be found within the host living in such organs as the intestines.

Some of the most common helminths include:


  • Pinworm
  • Tapeworm
  • Fluke
  • Parasitic flatworms such as schistosomes

Ectoparasites - Ectoparasites are also multicellular organisms. Unlike helminths, ectoparasites live on the host and can be found on the skin or scalp.

Some of the most common ectoparasites include:

  • Fleas
  • Lice

Human Parasites

Human parasites affect human beings and may cause diseases. However, some cause no disease or have minimal effects on the host, which makes them the most successful parasites. This is due to the fact that they continue to live within or on the skin of the human host for a long time while benefiting from the favorable conditions.

These parasites are divided into two main categories depending on where they live.

These include:


Ectoparasites - Ectoparasites or external parasites are the type of parasite that can be found on the skin or the head. They can be stationary or temporary where the stationary ectoparasites (such as the female pregnant lice) always live on the scalp while the temporary ectoparasites such as the female mosquito suck on human blood at intervals.


Endoparasites - Endoparasitism is the activity in which parasites enter and live in the body of the host. Endoparasitism is common with both unicellular and multicellular microorganism. In endoparasitism, the parasites may enter the body through such routes as the mouth, nose, skin and even through the anus. Different endoparasites will move and live in different parts of the body.

For example, whereas most parasitic worms can be found living in the intestines, various unicellular endoparasites will be found in blood cells and other types of cells (intracellular) and body/body fluid tissues (extracellular). 


Human Parasites Under the Microscope


Endoparasites  (Unicellular parasites)


Malaria parasite (Plasmodium falciparum)


The malaria parasite is spread by female anopheles mosquitoes. It causes malaria, which has been shown to present significant health risks to pregnant women and infants. Once in the body, the malaria parasite infects the red cells where it thrives.

When a positive slide is viewed under the microscope, it's possible to see the parasite inside the red cells (intracellular) as well as outside the cells (extracellular).


Microscopy of malaria parasites (Protozoa)





Smear Preparation


*  If a Giemsa-stained blood film is not readily available, then it can be prepared using the following procedure (make sure to use a clean pair of gloves, a clean needle and glass slide).


  • Using a clean, spirit swab, wipe the tip of the third finger and allow it to dry (of the patient with malaria)
  • Using the needle/lancet, prick the cleaned finger tip and allow a drop or two to ooze out
  • Take a glass slide and collect two drops from the finger tip at the center of the glass slide
  • Using another slide with a smooth edge, spread the blood drops on the slide to create a thin smear
  • (You can collect another blood drop using another clean slide for a thick smear)
  • Allow the slides to dry (air dry thick smear for about 30 minutes and thin smear for about10 minutes)
  • Fix the thin smear with methanol by dipping the slide in methanol for 5 seconds (do not fix the thick smear)



  • If using Giemsa stain, cover the slide (thin smear) with 10 percent Giemsa stain and allow to stand for about 30 minutes
  • Wash the slide with distilled water
  • Drain excess water using a blot paper (touching the blot paper on the edges of the slide)
  • Allow the slide to dry
  • Examine under the microscope
  • If using the Leishman's stain, add about 7 drops of the stain on the thin smear and allow to stand for 2 minutes. Add 12 drops of distilled water to mix and allow to stand for 6 minutes. Then was the slide with water (tap water or distilled water) and allow to dry
  • For the thick smear, add a drop of immersion oil and observe under 40x and 100x objectives

*  Care should always be taken when dealing with blood. Always use a pair of clean gloves, clean disposable needles and dispose any material used or any material contaminated with blood to avoid any injury.

Giemsa stain is a type of Romanowsky stain, which is composed of basic and acidic parts. When staining the smear, the nucleic parts of the parasite which is acidic will appear purple while the background will appear to be blue in color given that it is acidophilic.

Helminth Microscopy Using the Kato-Katz Technique

Kato-Katz Technique - The Kato-Katz technique is used for the purposes of detecting and determining the quantity of helminth eggs in a sample (feces).




  • The standard Kato-Katz plastic template
  • An aluminum foil
  • A wire mesh
  • A spatula
  • A cellophane that had been socked in methylene blue for about 24 hours
  • Clean glass slides




  • Place the Kato-katz template onto the microscope slide
  • Using a pair of gloves and a scraper/spatula, scoop about 2 grams of the feces and place it onto an aluminum foil
  • Press the wire mesh on top of the sample to sieve
  • Using another spatula, scrape the sieved material off so as to fill the hole in the template
  • Gently remove the template to have the sample remain on the slide
  • Place a piece of the cellophane over the sample
  • Using another clean slide, spread the smear to obtain a thick smear that is evenly distributed
  • Leave for about 40 minutes
  • View and examine the number of eggs present

From left to right


Ascaris fertile (roundworm), Trichuris (whipworm), Hymenolepis diminuta (rat tapeworm), Hymenolepis nana (Dwarf tapeworm), Tenia (tapeworm), Toxocara (roundworm), Necator Americanus (hookworm), Enterobius vermicularis (pinworm), Ascaris Lumbricoides.

Ectoparasites (Flea)

A stereomicroscope is used to view a water flea daphnia pulex




  • Glass slides with a pre-prepared electrical tape chamber
  • Cover slips
  • Paper towel
  • A dropper
  • Daphnia pulex
  • A Petri dish




A body flea can simply be picked up using a pair of tweezers and placed on a stereomicroscope for observation.

Otherwise, the following procedure can also be used with the Daphnia sample:


  • Using a dropper, suck some water from a container with pond water (containing daphnia)
  • Place a drop of the sample on to a microscope slide with the tape chamber
  • Gently lay a cover slip on the sample and avoid pressing
  • Place under the microscope and observe using 4x and 10x 


Avoid pressing to see live daphnia

More Experiments

Yeast Cells


Pond Water Microorganisms and a closer look at Diatoms

Petri Dish with Agar - Preparation, Requirements and Procedure

Learn about Cell StainingGram Staining and more about Blood Smears.

Take a look at how the iPhone is being used to diagnose Malaria

Return to Plasmodium species page

See more on Parasitology here

Return to Protozoa like Cyclospora, Cryptosporidium, Leishmania, Trypanosoma, Kinetoplastids

Return to Helminths

Return to Microscope Experiments Main Page and Microscopy Applications

Look at Protozoology as field of study

Return from Parasites under the Microscope to Microscopy Research Home



Heinz Mehlhorn (2016) Human Parasites: Diagnosis, Treatment, Prevention.


Moody AH, Chiodini PL. Methods for the detection of blood parasites. Clin Lab Haematol 2000;22:189-201.


 WHO, 1994. Bench aids for the diagnosis of intestinal parasites. Geneva: World Health Organization


WHO. Basic malaria microscopy: Part I Learner’s guide; Part II Tutor’s guide. Geneva, World Health Organization, 1991.

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