Major human parasites and diseases they cause

Human parasites can inhabit all organ systems. The vital activity of helminths can be a prerequisite for the development of cancer, and microscopic fungi and mites lead to allergies.

The human body can be inhabited by at least 300 parasitic species, including representatives of bacteria, viruses, protozoa, microscopic fungi, helminths (parasitic worms) and individual arthropods. These organisms not only consume nutrients absorbed by the host, but also poison it with the products of their vital activity. In accordance with the cannons of modern medicine, the concept of the "parasite" does not apply to pre-nuclear (prokaryotic) organisms: bacteria and viruses. It characterizes protozoa, fungi, worms and arthropods that live in the host's body and live exclusively on it.


Human and animal organisms are a fertile environment for the life of microscopic fungi and protozoa. Not visible to the naked eye, they damage the skin and internal organs.

Parasitic protozoa

An infection caused by a protozoon is called a protozoon. Such diseases are widespread in both tropical areas and temperate latitudes. About 50 species of protozoa parasitize in human organs and tissues. You can become infected through sexual contact, food, or insect bites.

Giardiasis is very common. Up to 40% of children and 10% of adults have this pathology. The preferred habitat for lamblia is the small intestine. The disease can be accompanied by indigestion and allergic reactions, although it is often asymptomatic. The pathogen is transmitted through the digestive tract - with uncooked water and contaminated food.

According to various sources, 30 to 50% of the world's population is infected with toxoplasmosis. Its pathogen often lives in the host's organism without clinical manifestations. Toxoplasma poses the greatest danger to pregnant women: it causes intrauterine fetal death or severe malformations. The infection occurs through contact with domestic mammals (cats, rabbits, rodents) and through the consumption of undercooked meat.

The most common sexually transmitted infection is protozoa. That is trichomoniasis. Every year more than 150 million people are infected worldwide. The manifestations of the disease are determined by which organs are affected. In women, Trichomonas lives in the vagina and causes inflammation, accompanied by urethritis. In men, the protozoa affects the prostate, seminal vesicles, in severe cases leading to prostatitis, although more often the infection is asymptomatic.

In tropical regions, diseases such as malaria, leishmaniasis, Chagas disease and sleeping sickness are well known. Your pathogens are plasmodia, leishmania or trypanosomes. Parasites are transmitted by blood-sucking insects: mosquitoes, tsetse flies, triatoms. By biting sick animals or humans, they acquire and distribute the causative agents of these diseases.

Parasitic fungi

About 100 species of mushrooms are known to be quite dangerous to humans. Your optimal living space are warm and humid areas of the body, for example the interdigital spaces. However, these organisms can also infect the skin and other areas of the human body.

Fungi of the species Trichophyton, Microsporum, Epidermophyton cause dermatomycosis: ringworm and pityriasis versicolor, lesions of the feet, scalp, rarely mucous membranes. The causative agents of these diseases can be transmitted from animals or sick people to humans. In severe cases, bacterial infections occur in dermatomycosis.

Molds and their spores are no less harmful to humans. They cause diseases like this:

  • penicellosis;
  • mucosa;
  • Aspergillosis.

These pathologies are invariably characterized by inflammation of all parts of the respiratory tract, otitis media and various allergic reactions. In severe cases, parasitic fungi cause pneumonia and bronchial asthma. People with compromised immunity and chronic illness are most susceptible to yeast infections.


The preferred habitat for parasitic worms is the digestive tract of humans and animals, where they feed on the host's digested food, bile and blood. All helminths belong to the following classes:

  • roundworms (nematodes);
  • flatworms (tapeworms and leeches).

Flat parasitic worms

Eggs and larvae of trematodes (flatworm flakes) most often get into the human body with raw water, unwashed greens, meat and fish that have not been adequately heat-treated. Here's how it works:

  • hepatic;
  • Chinese
  • giant;
  • lanceolate leeches;
  • cat accident.

Sometimes a person becomes infected through direct contact: the larvae of tropical parasites of schistosomes pierce the skin of people who swim in fresh water, and then get into the bloodstream, where they live and feed on erythrocytes.

Most trematodes affect the liver, gallbladder and ducts of these organs and cause diseases - trematodes. The environment for the life of a pulmonary flow are muscles, subcutaneous adipose tissue, the brain, but above all the lungs. The disease caused by these helminths is called paragonimiasis. The small trematode metagonium lives in the small intestine, which leads to metagonimosis.

Leeches are small - their flat, leaf-shaped body does not exceed 10 cm - but the consequences of their stay in the bodies of animals and humans are fatal. Long-term parasitism of these helminths can lead to the development of cancer, cirrhosis, and gallstone disease.

In contrast to trematodes, the body of tapeworms (cestodes) can be several tens of meters long. The main route of infection with cestodes is through food. These helminths get into the human body with uncooked meat and fish. The main environment for the development of cestodes is the small intestine, in which adult worms live, while the larval forms live in the parenchymal organs (liver, lungs, spleen).

Of all tapeworms, the following are the most common:

  • bullish tapeworm;
  • Echinococcus;
  • wide band;
  • pork tapeworm;
  • alveococci.

Round parasitic worms

Diseases caused by parasitic roundworms - nematodes - rank first among all helminthiases in terms of the frequency of development. Most adult parasites live in the intestines, but at certain stages in their life they can migrate to the muscles, lungs, heart, and throat. The following nematodes are common in the human population:

  • pinworms;
  • roundworm;
  • Toxocars;
  • Trichinella;
  • hookworms;
  • Strongyle.

Eggs and larvae of roundworms enter the human body through food and water. Nematodes such as hookworms and strongyles invade the host's body by themselves. These helminths are mainly found in the tropics.

The ubiquitous nematodes are pinworms, roundworms and toxocaras. The former most often affects children and causes enterobiasis - the most common helminthiasis. Dogs are carriers of Toxocara, although these nematodes can infect humans as well. Roundworms live in humans and are not dangerous to most animals, with the exception of pigs.

Arthropod parasites

Cestodes, trematodes and parasitic nematodes are adapted to live in the internal organs of their hosts. In contrast, most of the parasitic arthropods live on the surface of the body. Most often, a person becomes infected with lice and mites, the causative agents of demodicosis and scabies. These parasites are dangerous because they can transmit pathogenic bacteria and rickettsiae that cause Volyn fever, typhoid fever, and relapse fever.

Lice drink human blood and parasitic mites live on human skin. Scabies itching gnaws through the passages, Demodex lives in the hair follicles and ducts of the sebum glands. The vital activity of these parasites leads to allergies, accompanied by a rash, reddening of the skin and itching.

The world in which we live is developing rapidly, the standard of living is rising steadily and today it seems to many that parasitic diseases are the lot of the inhabitants of third world countries. However, population migration leads to the spread of such pathologies beyond natural centers of gravity. In this regard, it is important to remember the basic rules of hygiene, compliance with which will help prevent infection.