What are protozoa?

In medical language, protozoa are a group of diverse unicellular organisms. Together with unicellular fungi and algae and mushrooms, they form the subkingdom of all unicellular organisms with a cell nucleus (protists). While algae and fungi belong to the plant kingdom, protozoa are counted as animal unicellular organisms and can differ considerably in size and morphology.

Protozoa are heterotrophic organisms, which means that they require substances from other organisms for their metabolism. Generally, commensal, mutualistic and parasitic forms of protozoa are distinguished from each other. As pathogens in humans and animals, the parasitic forms of protozoa play an important role and can trigger numerous diseases (protozoonoses). These include, for example, the tropical disease malaria or amoebic dysentery.

Which protozoa cause which disease?

Important causative agents of protozoan diseases are, for example, the following pathogens:

• Entamoeba histolytica: This pathogen can cause amoebic dysentery,
• Balantidium coli, Giardia intestinalis, Cryptosporidium: possible pathogens of various intestinal diseases caused by protozoa,
• Plasmodium falciparum: considered the causative agent of malaria tropica,
• Plasmodium vivax: considered to be the causative agent of malaria tertiana,
• Plasmodium malariae: considered the causative agent of malaria quartana,
• Plasmodium ovale or simian plasmodia: causative agent of parasitologically confirmed malaria,
• Leishmania: caused by the pathogen leishmaniasis,
• Trypanosomiasis gambiensis, Trypanosomiasis rhodesiensis: considered to be the causative agents of African trypanosomiasis,
• Trypanosoma cruzi: causative agent of Chagas disease,
• Toxoplasma gondii: causative agent of toxoplasmosis,
• Pneumocystis carinii, Pneumocystis jirovecii: causative agent of pneumocystosis,
• Babesi spec., Acantamoeba spec., Naegleria fowleri: causative agents of other protozoan diseases

What happens during a protozoal infection and how does it manifest itself?

In a protozoal infection (protozoonosis), protozoa enter the organism, multiply and cause a disease caused by parasites. A protozoal infection can develop different symptoms depending on the parasite that triggers it. Generally, however, a protozoan infection manifests itself through flu-like symptoms, fever and general fatigue and malaise. Those affected may also have an increased heart rate and be irritable. If nausea, vomiting and weight loss are added, possibly accompanied by discomfort in the stomach area such as abdominal pain, flatulence, diarrhoea and bleeding from the rectum, these are clear signs of a protozoal infection.

The most common protozoan infections and their symptoms are presented below:

• Amoebic dysentery: After a few days of the incubation period, the patient complains of very frequent bowel movements, which can amount to several dozen times a day with violent cramps. If amoebic dysentery remains untreated, it can even lead to death.
• Malaria tropica:manifests itself in a rhythmic course of fever. If neurological complications occur, it can even lead to impaired consciousness. Malaria tropica can lead to death under certain circumstances.
• Lamblia infection:is caused by Giardia lamblia pathogens. A lamblia infection does not cause any noticeable symptoms, which is why the disease can easily go unnoticed. Only occasional discomfort in the stomach area, such as pressure pain, weight loss or diarrhoea, can indicate the disease.
• African sleeping sickness:The disease is characterised by two phases. The first phase may be accompanied by intermittent fevers, headaches, joint pain, itching and severe swelling of the lymph nodes. In a second phase, the so-called neurological phase, the parasite invades the central nervous system. This leads to a disturbed sleep-wake cycle, which has given the disease its name. African sleeping sickness is fatal without medical treatment.

What are the causes of protozoal infection in humans?

A protozoal infection is caused by pathogenic microorganisms that use humans as host organisms. There are many different microorganisms that can cause protozoal infections. Generally, infection with protozoa can occur through the ingestion of contaminated food. But contaminated drinking water and/or bathing water can also lead to an infection.

How is a protozoal infection diagnosed?

A protozoan infection can be diagnosed by microscopic methods. For example, African sleeping sickness is diagnosed by microscopic identification of the causative pathogen, trypanosomes, from a tissue sample. However, diagnostic detection via trypanosome-specific antibodies, for example by means of a blood test, is also possible.

Since protozoan infections have flu-like symptoms, it is often difficult to make a quick and early diagnosis. However, this is extremely important, as many protozoan infections can even lead to death if left untreated. Many protozoan infections can be treated well with antibiotics. If treatment is started early, there are usually no complications to worry about.

When should a doctor be consulted?

In any case, a doctor should be consulted if a protozoan infection is suspected, as these diseases usually do not heal on their own. A doctor should therefore be consulted as soon as the first flu-like symptoms appear. A protonzoal infection must be treated with medication.

How is a protonzoal infection treated?

In most cases, protonzoal infections are treated with antibiotics. For example, amoebic dysentery can be treated with metronidazole, tetracyclines or chloroquine. Malaria, on the other hand, can be treated with quinine. In the case of African sleeping sickness, inpatient treatment is necessary.

What is the after-treatment of a protozoan infection?

Protozoa can potentially infect all organs. Despite successful treatment of a protozoan infection, it is therefore possible that some protozoa remain in the body. Regular follow-up examinations are therefore absolutely necessary for a complete cure. If, for example, the mucous membranes were affected, smears of the mucous membranes and blood tests should be taken at regular intervals. Within the blood test, it is important to measure the organ values. In this way, a possible organ infestation as a long-term consequence of the infection can be ruled out or detected at an early stage. If the organ values are insufficient, tissue samples (biopsies) of the respective organ should also be taken.

How can a protozoan infection be prevented?

A protozoan infection can be prevented primarily by avoiding the epidemiologically relevant areas. However, protozoal infections can also be prevented as best as possible by cooking food thoroughly, boiling drinking water, using mosquito nets and anti-insect medication in the relevant risk regions. Malaria can also be prevented as far as possible by taking appropriate prophylactic medication. However, it is important to note that the drugs do not offer complete protection.