Illnesses Caused by Intestinal Protozoa

Protozoa are a group of unicellular organisms, which can exist in most environments. These organisms are microscopic in nature and in most instances, they provide useful support for other living beings. However, some protozoa could cause diseases and among them, diseases caused by intestinal protozoa are a significant health concern.

What protozoa can cause human diseases?

When considering the types of protozoa important for human health, Entamoeba histolytica, Cryptosporidium sp, Giardia intestinalis (lamblia), Isospora belli, Cyclospora cayetanensis, and members of the phylum Microsporidia will top the list. Although these organisms do not always cause serious illnesses, such manifestations are frequent in certain parts of the world, especially in areas with poor sanitary hygiene and less education on healthy practices.

What are the illnesses caused by intestinal protozoa?

Among the main protozoa infections pertaining to intestine, Amoebiasis and Giardiasis can be highlighted.


The commonest organism causing Amoebiasis is Entamoeba histolytica and the disease could often go unnoticed, as the symptoms may be rather mild. However, it can lead to diarrhea  and sometimes to dysentery. Among the complications of Amoebiasis, Amoebic dysentery, amoebic colitis, and amoebic liver abscess may manifest in certain instances. The spread of amoeba usually happens through the feco-oral route and indirect spread through contaminated hands is another major route of infection.


The protozoa responsible for Giardiasis is known as Giardia lamblia and once infected, it can give rise to a diarrheal illness. Certain individuals suffering from Giardiasis may complain of abdominal cramps, vomiting, foul smelling flatus, and fever. At the same time, long-term manifestations such as malaise, loss of appetite and fatigue could also present in patients with Giardiasis. It can spread through person-to-person, water-borne, and venereal routes whereas the number of incidence could rise during heavy rains. Although Giardiasis is more prevalent in developing countries, CDC reports detecting more than 20,000 patients each year in the United States.

Apart from these two, there may be other protozoa, which can give rise to intestinal related symptoms either directly or as an associated manifestation.

What are the methods of preventing intestinal protozoa illnesses?

The main strategy to prevent intestinal protozoa infections would be the practice of good hygienic practices and hand washing is the easiest and the most effective prevention strategy of them all. At the same time, using bottled water or boiled water for drinking and taking precautions on eating foods from unfamiliar places during travel, should also be practiced.

What treatment strategies are used for intestinal protozoa?

In most instances, medical treatment with anti-parasitic agents and with fluid resuscitation would be enough. However, in severe illnesses such as amoebic colitis, surgical repair of the intestine may be necessary. Such patients should also be followed-up in order avoid further complications.


Oxford Handbook of Tropical Medicine