Major human parasites and diseases caused by them

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 the 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 (prokaryotic) organisms: bacteria and viruses. It characterizes protozoa, mushrooms, worms, arthropods that live in the host's body, subsisting exclusively on it.


Human and animal organisms are a fertile environment for the life of microscopic fungi, as well as protozoa. Indiscernible to the naked eye, they cause damage to the skin and internal organs.

Parasitic protozoa

An infection that is caused by a protozoan is called protozoal. Such diseases are widespread in tropical areas as well as in temperate latitudes. About 50 species of protozoa parasitize in human organs and tissues. They can be infected through sexual contact, food or insect bites.

Giardiasis is very widespread. Up to 40% of children and 10% of adults have this pathology. The favorite 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 by the alimentary route - with unboiled water and contaminated food.

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

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

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

Parasitic fungi

About 100 species of fungi are known to be quite dangerous for humans. Their optimal habitat is warm and moist 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 to humans from animals or sick people. In severe cases, bacterial infections join dermatomycosis.

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

  • penicellosis;
  • 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 diseases are most susceptible to fungal infections.


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

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

Flat parasitic worms

Eggs and larvae of trematodes (flatworm flukes) most often enter the human body with raw water, unwashed greens, not sufficiently heat-treated meat and fish. This is how:

  • hepatic;
  • Chinese
  • giant;
  • lanceolate flukes;
  • cat fluke.

Sometimes a person becomes infected through direct contact: the larvae of tropical parasites of schistosomes pierce the skin of people swimming in fresh water, then enter the bloodstream, in which they live and feed on erythrocytes.

Most trematodes affect the liver, gallbladder, and the ducts of these organs, causing diseases - trematodes. The environment for the life of a pulmonary fluke is muscles, subcutaneous fatty tissue, the brain, but above all, the lungs. The disease caused by this helminth is called paragonimiasis. The small trematode metagonium lives in the small intestine, leading to metagonimosis.

Flukes are small in size - their flat, leaf-shaped body does not exceed 10 cm - however, the consequences of their stay in the body 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 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 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 ribbon;
  • pork tapeworm;
  • alveococcus.

Round parasitic worms

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

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

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

The ubiquitous nematodes are pinworms, roundworms and toxocaras. The former most often affect children, causing enterobiasis - the most common helminthiasis. Dogs are carriers of Toxocara, although these nematodes can also infect humans. 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 parasitic arthropods live on the surface of the body. Most often, a person becomes infected with lice and mites that cause demodicosis and scabies. These parasites are dangerous because they can carry pathogenic bacteria and rickettsia, causing Volyn fever, typhus and relapsing fever.

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

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