The simplest parasite is an organism adapted to invade and live in the cells and tissues of other organisms. The simplest parasites cannot live in an open environment on their own like other protozoa, but must invade another organism's body to receive protection and nutrition.
The simplest parasites and their varieties
The simplest organisms are eukaryotic systems that exist as structurally and functionally independent individual cells (including those species that are gregarious or that form colonies). Protozoa develop relatively complex subcellular characteristics (membranes and organelles) that allow them to survive in harsh environmental conditions. Most protozoa are microscopic organisms and only a few of them grow big enough to be visible to the naked eye. Like single-celled eukaryotes, they move to survive, feed and reproduce.
There are some of the simpler parasites that cause problems. They are present in our food, soil and water and can make us very sick if they get inside us.
Each different protozoan parasite can cause different diseases in our bodies. Some of them can cause serious illnesses of the respiratory tract (air passage from the nose to the lungs) and the central nervous system (brain, cranial nerves and spinal cord), while others live in the intestines, causing symptoms such as diarrhea and are not deadly.
There are four types of protozoan parasites, which are classified according to how they move:
- sarcodes are a group of amoebas that move using pseudopods and contractions that change the shape of their cells;
- mastigophores move with the help of flagella;
- the siliophores use eyelashes;
- sporozoans are immobile when they are in their mature stage.
Life cycles of protozoan parasites
Most protozoa have enormous reproductive potential because they have a short generation time, undergo rapid sequential development, and produce large numbers of offspring either asexually or sexually. These characteristics are responsible for many of the simplest infections, quickly causing the acute symptoms of the disease.
The developmental stages of parasitic protozoa that occur within the host generally consist of feeding trophozoites and can be found intracellularly (within host cells) or extracellularly (in hollow organs, body fluids, or internodes between cells). Although trophozoites are ideal for their parasitic mode of existence, they are not very resistant to external environmental conditions and do not survive long outside their hosts. To pass from host to host, parasitic protozoa use one of four main modes of transmission: direct, fecal-oral, transmissible, and predator-to-prey.
Ways of transmission of protozoan parasites to humans
- Direct transmission of parasites through intimate contact with the body - sexually (eg Trichomonas talked about fungi, which cause trichomoniasis in humans).
- Faecal-oral transmission of ecologically stable stages of cysts - parasites pass in the feces of one host and are transmitted with food or water to another (eg, Entamoeba histolytica, Giardia duodenalis and Balantidium coli are all forms of fecal cysts that lead to dysentery, giardiasis and balantidiosis amoebas).
- Transmission occurs when the parasites are ingested by blood-sucking arthropods (insects or arachnids) and passed on to new hosts by a sting (eg, Trypanosoma brucei, transmitted by tsetse flies and causing sleeping sickness, and Plasmodium spp. haemosporidia, transmitted by mosquitoes and causing malaria).
- Predator-to-prey transmission occurs when the simplest parasite gets trapped in the victim's tissues (eg, a cow, goat, pig) and is eaten by a predator (in our case, a person).
The simplest human parasites and the diseases they cause
Acanthamoeba. This parasite infects a person's eyes or brain and causes exogenous amoebiasis. He can live anywhere in the world. People can catch it when cleaning contact lenses with tap water.
Babesia. It infects red blood cells and causes a disease called babesiosis. Different types of parasites live in different parts of the world. It is transmitted by ticks when bitten.
Balantidium (Balantidium coli). It lives in the intestinal mucosa, causing ciliated dysentery, also called balantidiosis.
Blastocystis (Blastocystis). This parasite infects the host's gut. It enters humans through ingestion of food contaminated with human or animal feces. The disease caused by this parasite is called blastocytosis.
Cryptosporidium (Cryptosporidium). It lives in the human intestine. Distributed worldwide. It enters the human body through ingestion of food contaminated with human or animal feces.
Dysentery amoeba (Entamoeba histolytica). This simpler parasite causes intestinal amoebiasis. Most often found in areas with high population density, poor sanitation and tropical regions. It is transmitted via the fecal-oral route.
Giardia lamblia. It lives in the lumen of the small intestine. If people consume food or water contaminated with feces, dormant Giardia cysts can infect the body, causing intestinal giardiasis. It is especially dangerous for children and requires mandatory adherence to the treatment regimen.
Isospore (Isospora belli). It affects the epithelial cells of the small intestine. Distributed worldwide. It is transmitted via the fecal-oral route and is the causative agent of isosporia.
Leishmania. It parasites a person's skin and internal organs. It exists around the world in various forms. Transmitted by some types of mosquitoes when bitten.
Negleria (Naegleria fowleri). It causes primary amoebic meningoencephalitis as it lives in the human brain. Infection occurs through contaminated soil, swimming pools and contaminated water.
Plasmodium (Plasmodium falciparum, P. vivax, P. ovale, P. malariae). The parasites penetrate red blood cells and cause malaria. They exist in tropical regions where Anopheles, also known as the anopheles mosquito, are transported.
Rhinosporidium seeberi. It multiplies in the nose and nasopharynx, growing as spores. It exists in India and Sri Lanka. People who swim in public waters can become infected with the parasite when the nasal mucosa comes into contact with contaminated material.
Toxoplasma (Toxoplasma gondii). It affects the liver, heart, eyes and brain. A common parasite around the world. People can become infected after eating raw or undercooked pork, lamb, goat, or milk. It can also exist in contaminated food or soil due to cat feces. The disease caused by this parasite is called toxoplasmosis or parasitic pneumonia.
Trichomonas (Trichomonas vaginalis). It infects the female urogenital tract. Symptoms vary in men and women. It is the causative agent of trichomoniasis, a sexually transmitted infection.
Trypanosomes (Trypanosoma brucei, Trypanosoma cruzi). The first type of parasite affects the central nervous system, blood and lymph. It is transmitted by the tsetse fly and causes so-called sleeping sickness. The second parasite causes Chagas disease, affecting the blood, muscles, nerves, heart, esophagus and intestines. It is also transmitted by insect bites.
How to treat infections caused by protozoan parasites in humans?
The treatment plan for a protozoan parasite infection will depend on the specific diagnosis. Your doctor will usually prescribe medication, for example, to treat trichomoniasis, giardiasis or cryptosporidiosis. Medications are not normally prescribed for toxoplasmosis unless conditions exist for it in the form of pregnancy, some other illness, or a long-term severe infection.
Your doctor may also recommend other treatments to help relieve your symptoms. For example, many parasitic infections can cause diarrhea, which often leads to dehydration. Therefore, when treating an infection caused by parasitic protozoa, it is generally recommended to drink plenty of fluids to make up for the loss in the body.
How can protozoan parasites be prevented?
There are several steps you can take to reduce your risk of getting a parasitic infection:
- practicing safe sex using a condom;
- wash your hands regularly, especially after handling raw food or faeces;
- Cook food at the recommended internal temperature.
- drink clean water, including bottled water, when traveling;
- avoid swallowing water from lakes, streams or ponds;
- avoid cat litter and feces during pregnancy.
If you suspect you have a parasitic infection, make an appointment with your doctor. They can help diagnose the cause of your symptoms and recommend a treatment plan. The sooner you start treatment, the sooner you can help stop the infection from spreading to others.