Main human parasites and the diseases they cause

Human parasites can inhabit all organ systems. The vital activity of helminths can become 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), individual arthropods. These organisms not only consume nutrients assimilated by the host, but also poison it with the products of their vital activity. In accordance with the canons of modern medicine, the concept of "parasite" does not apply to prenuclear organisms (prokaryotes): bacteria and viruses. It characterizes protozoa, fungi, worms, arthropods that live in the body of the host and subsist there exclusively.


Human and animal organisms provide a fertile environment for the life of microscopic fungi, as well as protozoa. Indistinguishable by the naked eye, they cause skin and internal lesions.

Parasitic protozoa

An infection caused by a protozoan is called a protozoan. These diseases are prevalent in tropical areas as well as in temperate latitudes. About 50 species of protozoa parasitize human organs and tissues. They 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 digestive disorders, allergic reactions, although it is often asymptomatic. The pathogen is transmitted through food - with unboiled 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 body of the host without any clinical manifestation. Toxoplasma represents the greatest danger for pregnant women: it causes intrauterine fetal death or severe malformations. Infection occurs through contact with domestic mammals (cats, rabbits, rodents) and through consumption of uncooked meat.

The most common sexually transmitted infection is the protozoan. It's trichomoniasis. More than 150 million people are infected worldwide each year. Manifestations of the disease are determined by the affected organs. In women, Trichomonas lives in the vagina, causing inflammation, accompanied by urethritis. In humans, the protozoan affects the prostate, seminal vesicles, in severe cases leading to prostatitis, although most often the infection is asymptomatic.

In tropical regions, diseases such as malaria, leishmaniasis, Chagas disease and sleeping sickness are widely known. Their responsible agents are respectively plasmodia, leishmania and trypanosomes. The parasites are carried by blood-sucking insects: mosquitoes, tsetse flies, triatomaceous bugs. By biting sick animals or people, they acquire and distribute the agents responsible for these diseases.

Parasitic fungi

About 100 species of fungi are known to be very dangerous to humans. Their optimal habitat is warm and humid areas of the body, for example interdigital spaces. However, these organisms can also infect the skin and other areas of the human body.

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

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

  • ;
  • mucosis;
  • aspergillosis.

These pathologies are characterized by inflammation of all parts of the respiratory tract without exception, otitis media and various allergic reactions. In severe cases, parasitic fungi cause pneumonia as well as bronchial asthma. People with weakened immunity and chronic illnesses are most susceptible to fungal 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 moats).

Flat parasitic worms

Eggs and larvae of trematodes (tapeworms) most often enter the human body with raw water, unwashed green vegetables, insufficiently heat-treated meat and fish. Here's how:

  • hepatic;
  • Chinese
  • giant
  • ;
  • lanceolate moat;
  • lucky cat.

Sometimes a person is infected by direct contact: the larvae of tropical schistosome parasites pierce the skin of people swimming in fresh water, then enter the bloodstream, where they live and feed onerythrocytes.

Most trematodes affect the liver, gallbladder and the ducts of these organs, causing disease - trematodes. The environment for the life of a lung fluke consists of muscles, subcutaneous adipose tissue, the brain, but especially the lungs. The disease caused by these helminths is called paragonimiasis. The small trematode metagonium lives in the small intestine, causing metagonimosis.

Moats are small in size - their flat, leaf-shaped body does not exceed 10 cm - however, 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.

Unlike trematodes, the body of tapeworms (cestodes) can reach tens of meters in length. The main route of infection with cestodes is through food. These helminths enter the human body with uncooked meat and fish. The main environment for the development of cestodes is the small intestine, in which the adult worms live, while the larval forms live in the parenchymal organs (liver, lungs, spleen).

Of all the tapeworms, the most common are:

  • bullish tapeworm;
  • echinococcus;
  • wide ribbon;
  • pork tapeworm;
  • alveococcus.

Round parasitic worms

Diseases caused by parasitic roundworms - nematodes - rank number one among all helminths in terms of frequency of development. The habitat of most adult parasites is the intestines, but at certain stages in their life they can migrate to the muscles, lungs, heart, and pharynx. In the human population, the following nematodes are widespread:

  • ;
  • roundworm;
  • toxocars;
  • Trichinella;
  • hookworms
  • ;
  • Strongylids.

The eggs and larvae of roundworms enter the human body through food and water. Nematodes such as hookworms and strongylids invade the host body on their own. These helminths are mainly found in the tropics.

The ubiquitous nematodes are pinworms, roundworms and toxocaras. The first most often affect children, causing enterobiosis - 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, except pigs.

Arthropod parasites

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

Lice drink human blood, and parasitic mites live on human skin. Itchy scabies eats away at the passages therein, demodex lives in the hair follicles and ducts of the sebaceous glands. The vital activity of these parasites leads to allergies, which are accompanied by rashes, redness of the skin and itching.

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