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:
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.
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:
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:
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.
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)
* 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).
* 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.
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).
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.
A stereomicroscope is used to view a water flea
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:
* Avoid pressing to see live daphnia
Petri Dish with Agar - Preparation, Requirements and Procedure
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.