Protozoal Infection

Protozoal infections are parasitic diseases caused by those organisms that were formerly classified within the protozoan kingdom in biological systematics. Important examples of causes of protozoal diseases are Entamoeba histolytica as the causative agent of amoebic dysentery, Plasmodium falciparum as the trigger of malaria tropica, Giardia lamblia, which around ten percent of the world’s population carry in their intestines, or Trypanosoma brucei, which triggers African sleeping sickness via the infected tsetse fly.

Protozoal Infection

What is a protozoal infection?

Protozoal infection is that pathological condition resulting from invasion of the body by pathogenic protozoa. Protozoonosis, as the protozoal infection is also called, is a disease caused by a series of unicellular organisms, the protozoa. This means that protozoal infections are also a subset of parasitoses; consequently all those diseases that can be caused by parasites. See gradinmath for What is Balkan Nephropathy.

The term infection is justified in this context because the typifying sequence of penetration, multiplication and reaction is present. Due to the constant progress in knowledge in biology, the systematic categorization in a taxon Protozoa is outdated. The phylogenetic relationships of the groups summarized as protozoa turned out to be far more complex than could originally be assumed from the morphological consideration of the “protozoa”.

A definition of protozoa based on biological systematics is therefore no longer possible. The retention of designations such as protozoology or even protozoal infection only serves practical considerations. Because the common systematic denominator of the organisms commonly referred to as protozoa goes back to the biological domain of the eukaryotes.


The causes of the protozoal infection in humans lie in disease-causing microorganisms which, as parasites, are dependent on humans as host organisms. The trigger of the protozoonoses is based on a variety of different organisms. The International Classification of Diseases ICD-10, published by the World Health Organization (WHO), lists diseases caused by protozoa in Sections A06 to A07 and B50 to B64.

It should be noted here that the ICD-10 with regard to protozoonoses in its systematics is based on the overview of the clinical picture caused. In general, an infection with protozoa occurs via the intake of contaminated food, water, contaminated drinking or bathing water or via the route of the intermediate host. The causative organisms are therefore included as examples in the following list, where “spec.” denotes several or unknown species of a genus:

  • A06 – Amoebiasis: infection by Entamoeba histolytica.
  • A07 – Other intestinal diseases caused by protozoa: infections by Balantidium coli, Giardia intestinalis, Cryptosporidium spec….
  • B50 – Malaria tropica: infection by Plasmodium falciparum.
  • B51 – Malaria tertiana: infection by Plasmodium vivax.
  • B52 – Malaria quartana: infection by Plasmodium malariae.
  • B53 – Other parasitologically confirmed malaria: Infections caused by Plasmodium ovale or simian Plasmodium.
  • B54 – Malaria, unspecified: Clinically diagnosed malaria without parasitological confirmation.
  • B55 – Leishmaniasis: Infections caused by Leishmania spec.
  • B56 – African trypanosomiasis: infections caused by trypanosomiasis gambiensis, trypanosomiasis rhodesiensis…
  • B57 – Chagas disease: Infection by Trypanosoma cruzi.
  • B58 – Toxoplasmosis: infection by Toxoplasma gondii.
  • B59 – Pneumocystosis: infections caused by Pneumocystis carinii, Pneumocystis jirovecii…
  • B60 – Other protozoal diseases not elsewhere classified: Infections caused by Babesi spec., Acantamoeba spec., Naegleria fowleri…
  • B64 – Unspecified protozoal disease.

Symptoms, Ailments & Signs

The symptoms can vary considerably depending on the triggering parasite. In general, a protozoal infection is manifested by fever, flu-like symptoms and general malaise. Sometimes the sufferers are more irritable and have an increased heart rate. Clearly recognizable signs of disease

are the occurrence of nausea, weight loss and vomiting. Symptoms in the stomach area, caused by abdominal pain, diarrhea and flatulence, often indicate an infection. Bleeding from the rectum can sometimes occur.

Diagnosis & course of disease

A whole range of infections caused by protozoa can be diagnosed using microscopic methods. After an incubation period of a few days, amoebic dysentery causes very frequent bowel movements, which can amount to several dozen times a day in the case of severe cramps. If left untreated, amebiasis can lead to death.

Malaria tropica becomes noticeable by a reduction in the hemoglobin concentration and often by a rhythmic course of fever. Impaired consciousness can occur as neurological complications. There is a risk that malaria tropica will lead to death. Lamblia infection can easily go unnoticed. This applies to the majority of the approximately ten percent of the world’s population who carry Giardia lamblia in their intestines.

Nevertheless, there are occasional complaints in the stomach area, which can manifest themselves in the form of pressure pain, diarrhea and weight loss. In the case of African sleeping sickness, the diagnosis is made via the microscopic identification of the triggering trypanosomes in a tissue sample. In most cases, this is based on a blood test.

In addition, there is the possibility of diagnostic detection using trypanosoma-specific antibodies, which, however, is subject to some uncertainty due to the variability of the parasite in this regard. The course of the disease is two-stage. The hemolymphatic phase is characterized by fever, headache, joint pain and itching. The phases of fever attacks occur at intervals.

In addition, severe swelling of the lymph nodes can occur. The second phase of the disease – the neurological phase – occurs when the parasite begins to invade the central nervous system. The trypanosomes succeed in penetrating the blood-brain barrier.

As a result, infected individuals experience a disrupted sleep-wake cycle. These typical symptoms gave the sleeping sickness its name . Without treatment, sleeping sickness is fatal.


As a rule, the protozoal infection leads to symptoms that are very similar to influenza. For this reason, early diagnosis or detection of this disease is not possible in many cases. The patients suffer from a high fever and also from severe exhaustion. It also leads to discomfort and a general feeling of illness. The heart rate of the affected person is also increased by the protozoal infection.

Patients lose weight over the course of the disease and suffer from vomiting and nausea. Diarrhea or abdominal pain can also occur and thus significantly reduce the quality of life of those affected. In many cases, the protozoal infection also leads to very painful cramps, so that those affected also suffer from restricted movement.

If there is no treatment, this disease usually leads to the death of the person affected. Pain in the head or in the joints can also occur as a result of this disease. Treatment of this disease is carried out with the help of antibiotics and in most cases leads to a positive course of the disease. Special complications usually do not arise if the treatment starts early.

When should you go to the doctor?

A protozoal infection must always be examined and treated by a doctor. This disease usually does not heal itself and, in the worst case, leads to significant limitations in life. Early diagnosis and treatment always have a very positive effect on the course of the disease and can prevent further complications.

A doctor should be consulted for protozoal infection if flu-like symptoms occur. The sufferer is irritable and generally uncomfortable. The discomfort occurs for no particular reason and is accompanied by weight loss and nausea. Furthermore, the protozoal infection often leads to vomiting. In some cases, severe abdominal pain associated with bloating and diarrhea can also indicate protozoal infection and must be examined by a doctor.

The condition can be diagnosed by a general practitioner or in a hospital. During treatment, the patient is dependent on taking medication. In some cases, life expectancy may also be reduced.

Treatment & Therapy

Drug treatment is generally with antibiotics. In the case of amoebic dysentery, these are metronidazole and tetracyclines; chloroquine, an enantiomeric quinine derivative, is also used for this purpose. Quinine is the classic treatment option for malaria, especially malaria tropica. Not all cases of giardiasis require treatment.

As a rule, the body’s own defenses are sufficient to overcome the infection. In the case of an acute course of the disease or the existence of debilitating symptoms, drug treatment is required. Nitroimidazoles such as metronidazole, tinidazole, secnidazole or ornidazole are used for this purpose. Treatment of African sleeping sickness usually requires inpatient treatment.

The drugs used for this purpose cause considerable side effects to be triggered, especially in the second stage of the disease. While suramin can be given medicinally for the treatment in the first stage, the subsequent stage requires the use of arsenic-containing compounds.


Prevention is advised to avoid protozoal infection. First and foremost, this means avoiding areas that are epidemiologically relevant for this purpose. In addition, the known precautionary measures must be observed: cooking the food through, boiling the drinking water, using mosquito nets and insect repellents.

Occasionally there are instructions from authorities in the form of bathing bans at thermal springs. Possibilities for medicinal prophylaxis exist in the case of malaria. It should be noted here that chemoprophylaxis with drugs such as chloroquine or proguanil can only offer incomplete protection.


Since protozoa can potentially infect all organs and it is possible that some protozoa remain in the body even after successful treatment of a protozoal infection, regular follow-up examinations are necessary after a protozoal infection. If the mucous membranes were infected, swabs should be taken from the mucous membranes at regular intervals. In addition, regular blood tests must be carried out by the family doctor.

Not only should the protozoa be examined, but the organ values ​​should also be measured in order to detect any organ infestation as a long-term consequence of the protozoa infection at an early stage. If poor organ values ​​are measured or if an organ was affected by the protozoal infection, tissue samples (biopsies) should also be taken from the organ in question. Imaging procedures (MRI, ultrasound) can also be indicated here in order to detect any organ involvement.

In addition, a high standard of hygiene should be maintained to avoid renewed protozoal infection. This consists in particular of regular hand disinfection and avoiding visiting public toilets. If you cannot avoid going to a public toilet, you should then intensively disinfect all body regions that have come into contact with objects in the public toilet. Clothing should be washed with sanitizer after protozoal infection to prevent protozoa from remaining in clothing. In addition, contact with animals that can transmit protozoa should be avoided.

You can do that yourself

Treatment of a protozoal infection depends on which organism was found in the patient’s body. Since some protozoa can cause life-threatening diseases, conscientious diagnosis with appropriate microscopic examinations is important. The patient should then strictly follow the doctor’s prescriptions, especially with regard to taking antibiotics.

By the time the diagnosis is made, the patients have usually had a long ordeal behind them, were exhausted, suffered from nausea, diarrhea and/or vomiting and have often lost a lot of weight. Therefore, you should pay particular attention to a healthy lifestyle during the convalescence period. This includes that those affected should not smoke and drink little or no alcohol. In order to stabilize the body weight again, healthy, fiber-rich meals with lots of fresh fruit and vegetables should be eaten regularly.

A healthy lifestyle also includes a regular sleep-wake cycle with enough sleep. Stress should be avoided during this time. It is also advisable to drink plenty of water during this time. It helps eliminate toxins and other excess substances from the body. Other detoxifying measures such as saunas, steam baths and sweaty sports are also helpful. Doctors and non- medical practitioners who specialize in naturopathic medicine will advise you on other options for detoxification.