What are parasites: types and classification

Knowing the routes of entry of parasites into the body, it is possible to take preventive measures in contact with possible sources of infection. What are helminths, as intestinal parasites, is known to many. However, the common man is less aware of the species that live in the circulatory system, subcutaneous lymph, muscles, brain and internal organs.

All types of parasites in the human body are classified into representatives: protozoa, flat and round worms, arthropods and their larvae.Viruses, pathogenic bacteria and fungi can be classified as parasites, but they are distinguished into a separate group. Infectious diseases are divided into: viral, fungal, bacterial and parasitic. The classification of human parasites includes - a unique species of fish (common vandellia), capable of penetrating the human urethra (random host).

Parasitism and its types

Who are parasites? These are organisms living at the expense of another individual, not genetically related to it and entering into antagonistic relationships, that is, interfering with life. The concept of parasitism should not be extrapolated to microorganisms that live inside the body without causing it special harm. In nature, there are plant and animal parasites, depending on the type of host. During the functioning of this way of life, the parasite and host system constantly works. The task of the first: to live off the second, without killing him for a long time.

Classification of parasites by type:

1. Localization sites: external and internal parasites (exo- and endoparasites).
2. By way of life: constantly parasitic (obligate) and free-living forms, which under certain conditions begin to exist at the expense of another organism (facultative parasites).
3. By the timing of contact with the host: temporary and permanent parasites (stationary and periodic).

In the food chain, animal parasites are usually second- or third-order consumers, as they feed on herbivores or carnivores. The way the parasite feeds deprives the host of nutrients and / or leads to the destruction of cells and tissues. Host antagonism often occurs because dangerous inhabitants release toxic metabolic products. This leads to certain symptoms (allergies, disorders of the digestive system, signs of damage to various internal organs).

Viruses

Viruses are intracellular parasites of a protein-genetic structure. Due to the materials of the cell, they reproduce themselves. The virus is an obligate parasite.

According to the classification, depending on the type of genetic material, RNA and DNA-containing viruses are isolated. Intracellular agents of the first group include:

1. Enteroviruses. They multiply in the digestive tract, cause problems in various human organs.
2. Rhinoviruses. Causative agents of ARVI.
3. Influenza, rabies and tick-borne encephalitis viruses.
4. Papillomaviruses.

The second group includes: adenoviruses (cause acute respiratory infections), herpes and smallpox pathogens.

Viruses, entering the target cell, subordinate its processes to themselves, integrate into the genetic material or localize in the cytoplasm, then replicate (multiply). Then, cell death occurs as a result of lysis, apoptosis, or distortion of the membrane structure. Some representatives (papillomaviruses, Epstein-Barr virus) are capable of causing the degeneration of cells into malignant ones.

How viruses penetrate inside:

1. Airborne.
2. Through the gastrointestinal tract when drinking water and eating food.
3. Through the skin and external mucous membranes, such as the conjunctiva of the eye.
4. By means of arthropod vectors (insects, ticks).
5. As a result of the use of non-sterile medical devices (syringes, pipettes).

Each virus is adapted to a specific cell, distinguishes the target with the help of receptors.

Bacteria

Among bacteria, rickettsiae, intracellular parasites, occupy a special position. These are the most primitive representatives that resemble viruses. In humans, these microorganisms cause: typhus, tick-borne rickettsiosis, Rocky Mountain spotted fever. People become infected with rickettsiae through the bites of ticks, fleas, lice.

Other intracellular parasites of chlamydia cause one of the most common venereal diseases (chlamydia) and cause serious eye inflammation, pneumonia of infants, and enteritis.

Dangerous bacteria include:

1. Salmonella - the causative agents of typhoid fever.
2. Tetanus stick.
3. A pale spirochete that causes syphilis, due to a difficult diagnosis of the disease, which leads to a delay in treatment.
4. Pneumococci, which can cause pneumonia and, less commonly, bacterial meningitis.
5. Tuberculosis bacillus, which may not manifest itself for a long time, and then turn into an open form.
6. Escherichia coli due to its ability to acquire antibiotic resistance. Causes gastroenteritis, rarely meningitis and urinary tract infection.

External parasites such as Staphylococcus aureus are known among bacteria, causing a wide range of skin infections. The most dangerous consequences of its activity: pneumonia, meningitis, osteomyelitis, endocarditis, severe shock due to exposure to bacterial toxins and sepsis (in everyday life it is called blood poisoning).

Mushrooms

Disease-causing fungi - human parasites are better protected from the effects of drugs than bacteria. The most common fungal disease is candidiasis (thrush), localized on various mucous membranes with a weakened immune system. Mushrooms of the genus Candida live in the body of any healthy person and bring tangible harm only if the protective function fails. Conditionally pathogenic bacteria and fungi are a borderline group of microorganisms between non-pathogenic and pathogenic categories. Therefore, as a rule, they are not classified as parasites.

Pathogenic micellial fungi are human parasites that often cause diseases of the outer integument:

1. Keratomycosis. Reproduction of fungi occurs in the keratinized zone of the epidermis or on the hair cuticles (trichosporium nodosum, versicolor versicolor).
2. Dermatophytosis. Pathogens affect not only the epidermis, but also the dermis, nails and hair (ringworm, scab).
3. Deep mycoses. Damage to the skin and nearby tissues, as well as internal organs. These include histoplasmosis - a severe systemic fungal disease and aspergillosis - damage to the mucous membranes and skin caused by aspergillus.

The classic sources of bacterial and fungal infections are sick people, animals, soil, dirty water and food.

Protozoa

Protozoa are another unicellular parasite along with bacteria and fungi. What protozoan parasites of a person are isolated depending on the systematic position?

1. Some types of amoebas are facultative parasites. The most famous is dysentery amoeba, which enters the human body in the form of a cyst (resting form). The causative agent enters the large intestine (luminal form), then penetrates into the mucous membrane and affects various internal organs with the blood stream. Amoebae are aquatic organisms, therefore the main source of infection with them is dirty water. Acanthamoeba keratitis is a rare eye disease called acanthamoeba keratitis, which has become more frequent due to the rise in popularity of contact lenses.
2. Flagellates (Leishmania, Giardia, Trichomonas). Trichomoniasis is the most common disease of the genitourinary system, dangerous for its complications (infertility, prostatitis, premature birth, etc. ).
3. Apicomplexes (Sporozoans). With the exception of colpodellids, the group includes only obligate parasites (Toxoplasma, Plasmodium malaria, Cryptosporidium, Coccidia, sarcocysts). Sporozoan cysts enter the body after being bitten by insects, eating infected animals or drinking water.
4. Ciliates. For humans, balantidia is dangerous, provoking diarrhea and ulcers in the intestinal wall as a result of activity in the large intestine. Ciliates are the largest pathogenic unicellular organisms.

The simplest human parasites cause protozoal infections (protozoses). What parasites live in the human nervous system among the protozoa? For example, the causative agents of toxoplasmosis and cerebral malaria. Among amoebas, the facultative parasite Neglerius Fowler is capable of infecting the nervous system.

Multicellular

Multicellular parasites include flatworms, roundworms, arachnids, and insects. The former, as a rule, settle inside a person (in various systems and internal organs), and certain species migrate or penetrate (rishta, larvae of Gnathostoma spinigerum and hookworms, schistosomes) into the subcutaneous layer. Worms is the collective colloquial name of all worms that cause helminthic infestations (helminthiases).

Common diseases caused by flatworms

Group of trematodes (digenetic flukes):

1. Opisthorchiasis. Causative agents: types of liver flukes, for example, feline and Siberian fluke. Infection occurs as a result of eating infected river fish, poorly processed thermally.
2. Fascioliasis. Caused by hepatic and giant flukes. Infection occurs through the consumption of contaminated water or coastal grass.
3. Schistosomiasis. The causative agents of schistosomes (blood fluke, in particular) live mainly in hot climates. They penetrate the skin by contact with water.
4. Paragonimiasis. The cause of the disease is a pulmonary fluke, which is found in hot climates. A worm-infected and poorly processed thermally freshwater crab or crab is dangerous.

The life cycle of the parasite from the group of trematodes is complex, including several larval stages and gastropods as intermediate carriers. Flukes are animal parasites of vertebrates, acting as temporary and permanent hosts. Separate larval stages are able to develop without fertilization. Flukes' devices for fixing and feeding inside the host are suckers.

Tapeworms are obligate parasites of the human small intestine. Their body consists of segments (proglottids), which periodically break off and come out along with the fertilized eggs. The life cycle stages of tapeworms necessarily include the finna (blister worm), which forms in a temporary owner. The permanent host swallows the Finn, which develops into a tapered (adult) form. The structural features of tapeworms are the absence of a digestive system and the absorption of nutrients by the entire surface.

Most common:

1. Bovine tapeworm (unarmed tapeworm) causes teniarinhoses disease. Infection occurs through the meat of cattle, the muscles of which are contained by the Finns, formed in the body after the animals swallowed eggs with food.
2. Pork tapeworm (armed tapeworm) is the causative agent of cysticercosis (Finn stage) and teniasis (adult). In addition to the suckers, the helminth is equipped with a rim of hooks. A person can simultaneously perform the function of an intermediate and permanent owner.
3. The broad tapeworm causes diphyllobothriasis. Intermediate hosts are copepods and fish. A person can become infected through insufficiently salted caviar and poorly cooked or fried freshwater fish.

The parasites feed on blood and tissue (flukes) or digested food (tapeworms).

Roundworms

What common types of parasites in humans are roundworms (nematodes)?

1. Ascaris. Ascariasis includes migratory (larval) and intestinal (adult) stages. The larva penetrates the wall of the small intestine, moves to the lungs, bypassing the liver and heart, successively passing through the molting stages. It enters the mouth, is swallowed again and becomes an adult in the small intestine.
2. Pinworm. The causative agent of enterobiasis feeds in the final and initial zones of the small and large intestine, multiplies in the ileum. Females lay eggs in the anal folds, causing severe itching.
3. Vlasoglav is the cause of trichocephalosis. These parasites in the human body invade the mucous membrane of the initial section of the large intestine and feed on tissue fluid and blood.
4. Trichinella causes a dangerous disease of trichinosis. In severe cases, the nervous system is damaged. These are real killers, whose larvae penetrate the wall of the small intestine and are carried throughout the body. Mostly they get into the striated muscles, they can penetrate into the eyes, causing pain and swelling of the face, into the lungs, leading to a cough. Until now, no cure has been invented for a complete recovery.
5. Toksokara. Distinguish between larval (occurs more often) and imaginal (intestinal) toxocariasis. The invasion is characterized by the severity of allergic reactions. The larvae spread throughout the body, getting into the tissues, encapsulating and forming granulomas.
6. Hookworm is more common in the tropics and subtropics. With hookworm infection, the worms inside the intestine secrete proteolytic enzymes that destroy the walls and reduce blood clotting. Parasites inside a person appear as a result of the introduction of larvae through the skin from contaminated water.
7. Escherichia coli and related species are tropical parasites. The disease they cause, strongyloidosis, can be asymptomatic for decades. With reduced immunity, carriers of the worm are at high risk of death (60-85%).
8. Rishta is a subtropical helminth that causes dracunculiasis. The larvae penetrate the intestinal wall. The females reach the subcutaneous layer, and when the host is in the water, they expel the larvae through the skin. The temporary host is a copepod crayfish.

The peculiarities of the habitat of parasites affect the ways they enter the body: contact with contaminated water or land, with carriers of larval stages inhabiting them. Many representatives of roundworms do not have intermediate hosts and belong to geohelminths. Infection with them mainly occurs through contaminated water, unwashed hands, fruits or vegetables, as well as through the consumption of meat from wild animals.

Treatment and dire consequences of helminthiasis

An important way to diagnose helminthiasis is a blood test. Eosinophils (a type of white blood cell) found in high concentration along with other signs of infection indicate the presence of a worm and a number of pathogenic protozoa in the body. How are helminthiases treated? Drugs are used to relieve symptoms and specific treatment. Antiallergic (desensitizing) and detoxification therapy is used. Basically, drugs are administered by infusion (using a dropper), sometimes injections are used:

1. A drug that replaces plasma and removes the effects of toxins.
2. Isotonic glucose solution and saline.
3. Vitamins C and B6.
4. Sodium bicarbonate (soda), calcium chloride or gluconate.
5. Preparations used at elevated temperatures.
6. Hormonal drugs are used in difficult situations (with hepatitis or allergic myocarditis). Potassium intake is combined with them.
7. Preparations for heart failure and edema.

There is evidence that certain parasite worms, such as the pygmy tapeworm, can cause cancer. Stem cells of larvae can degenerate into cancerous ones. Parasites can indirectly cause cancer by weakening the immune system. Interesting data were obtained in the study of the effect of trematodes affecting the liver. As a result of exposure to waste flukes, ordinary cells can turn into cancerous cells. Parasites are mainly localized in the digestive system, but their larvae are able to penetrate into various internal organs. For example, in the kidneys (echinococcosis, schistosomiasis), heart muscle (cysticercosis, hookworm disease), liver (echinococcosis). Parasite worms in humans often affect the nervous system. Known cysticercosis, echinococcosis, alveococcosis and schistosomiasis of the brain.

Arthropods

The order of insects includes such well-known ectoparasites as fleas, bed bugs, blood-sucking dipterans. Unlike lice, these are temporary parasites, that is, they live inconstantly with the help of the host. Arthropod parasites in the order of arachnids include the well-known scabies mite. Mating of male and female occurs on the surface of the epithelium. The parasites in the human body then lay their eggs in the keratin layer of the skin, causing severe itching. Many people know what ixodid ticks are. These are arthropod parasites from the order of arachnids, including the most famous representative of the taiga tick - a carrier of dangerous infections (tick-borne encephalitis, Lyme disease). Among the blood-sucking dipterans, there are: non-malaria and malaria mosquitoes, mosquitoes, midges, biting midges, horseflies and real flies. These arthropod parasites can cause a strong allergic response, and are also carriers of dangerous viral and bacterial infections. Some flies, in particular gadflies, lay larvae under human skin, causing myiasis. The larvae are able to penetrate into the body.