The simplest human parasites: table

Human parasites are represented by different groups, one of which is protozoa. They are capable of causing disease of varying severity, and these microorganisms are not as easy to diagnose as groups with more complex organization. For convenience, in the article they are presented in a table with the main characteristics.


The simplest include organisms with a primitive organization, which are combined in the phylum of protozoa. It has more than 15, 000 species, and some of them lead a parasitic life in the human body. All of them are characterized by small sizes, they can only be seen under a microscope, and it is impossible to notice them with the naked eye.

Many of the simplest parasites have an extremely primitive structure. Once inside the host's body, they begin to multiply. Sometimes this happens by splitting into two halves, and sometimes by multiple splitting. In the latter case, the disease progresses rapidly, symptoms quickly appear, sometimes even eventually leading to the death of a person.

Features of biology

The organism of human protozoan parasites consists of two main parts: the nucleus and the cytoplasm, in which all the other organelles are found. The kernel can be one or more.

Protozoa have the ability to form a cyst if the environmental conditions become unfavorable. Due to this, they are able to remain viable for a long time, remaining motionless and going without nutrients. As soon as the conditions return to normal, the shell of the cyst is destroyed and the microorganism continues its normal functioning. Encystment also allows parasites to spread successfully from one organism to another.

All protozoa are divided into several categories based on anatomy, mode of movement, and other characteristics:

  • flagella;
  • sarcode
  • sporozoa
  • ciliates.

Within each group, there are species for which humans are the intermediate or definitive host.

Main Types

Parasites of the protozoan type cause many diseases and parasitize different organs. For convenience, they are presented in the table.

Last name Infected body parts Method of infection Symptoms
Balantidia lower intestine Eating raw pork or water with cysts Balantidose is often accompanied by diarrhea. White mucus and bloody secretions appear in the feces. The colonic mucosa ulcerates, and in such cases bleeding may increase. With the progression of the disease, exhaustion of a person occurs, in rare cases it can lead to death.
mouth amoeba Oral cavity, gingival pockets, dental plaque A person becomes infected by kissing a carrier, using dirty dishes and eating contaminated food. It rarely affects people who do not have pathological lesions in the oral cavity. In inflammation, the buccal amoeba feeds on epithelium, microbes, leukocytes and erythrocyte cells. May cause periodontal disease.
dysenteric amoeba Through the bloodstream, it enters the lungs, liver, heart, genitals and kidneys. Settles in the intestinal lumen Ingestion with food or water In some cases, the disease is asymptomatic. If the dysenteric amoeba attacks the intestinal walls, the pathogenic stage begins. It is characterized by colitis, tissue necrosis, liver damage, abscesses may appear. Very serious consequences cause metastasis to the brain and other organs. Possible fatal outcome. Sometimes the disease takes a recurring course. Rarely self-healing occurs
Intestinal giardia Duodenum and bile ducts. oral route Giardia sticks to the mucosal epithelium and damages nutrient absorption. Inflammation of the mucous membrane and constant diarrhea develop. If the infection covers the bile ducts, a yellowing of the skin appears. Some people develop immunity to intestinal Giardia, especially in countries with tropical climates.
Trichomonas vaginalis In women - on the vaginal mucosa, in men - in the epidermis of the prostate and in the urethra During sexual intercourse, as well as during childbirth from mother to child Trichomoniasis is manifested by foamy discharge, itching and burning on the mucous membrane of the genitals, pain during intercourse, the appearance of bloody discharge from the urethra, etc. A complication of trichomoniasis is inflammation of the vulva due to protozoan activity, cystitis, prostatitis and infertility
Trypanosoma brussei Cerebrospinal fluid and the brain After being bitten by a tsetse fly, which is an intermediate host Begins with fever and swollen lymph nodes, continues with listlessness, an irresistible desire to sleep, muscle paralysis and exhaustion. If left untreated, coma and death occur.
Cutaneous leishmania Contact with a sick person or animal On the skin, most often on the face or hands The incubation period lasts from 2 months to 5 years, after which a brownish dense nodule appears at the site of the insect bite. It increases, then a purulent ulcer opens in its place. The disease lasts up to several years, then the final wound healing occurs. Complications can be disorders of the heart, kidneys and adrenal glands.
Toxoplasma Infected pets, mainly cats, sometimes infection occurs when eating food containing protozoa Liver, heart, eyes, brain In the congenital form - multiple pathologies of fetal development, early death, mental retardation, multiple infections. Acquired toxoplasmosis causes high fever, enlarged liver, headache, vomiting, seizures. Often takes a chronic course with increased fatigue and eye damage. Rarely occurs in a latent form
Isospora From a person infected by faecal-oral transmission small intestine epithelium The incubation period lasts about 10 days. Then the body temperature rises, vomiting and diarrhea appear. The disease is acute for a week or two, then recovery occurs
Cryptosporidia oral route Intestinal epithelial tissues Incubation lasts about a week, then diarrhea begins, possibly with spotting inclusions. The stomach can hurt, fever appears, signs of dehydration are possible. With an insufficient immune status of the patient, the infection can affect other organs: lungs, pancreas, stomach, etc.

Are verses the simplest

Sometimes you can hear the phrase that the patient is infected with the simplest worms. It should be understood that protozoa are exclusively unicellular microorganisms, in extreme cases organizing colonies. But they are never multicellular like worms and helminths.

In protozoa, all processes occur in the cell cytoplasm and cell nuclei, while in worms the anatomical organization is much more complicated: they have differentiated organs that perform particular physiological functions. Therefore, it is fundamentally wrong to classify worms as protozoa.

human protozoan parasite

Sometimes helminths are called the simplest parasites compared to insects: bedbugs, lice, etc. , because the latter are much higher in the evolutionary scale. In this interpretation, the name worms is allowed as protozoa.