Parasitology is a science that studies the phenomenon of parasitism. The main task of this science is to study the relationship between parasites and hosts, their mutual influence, which also depends on environmental factors.
Due to the increase in population migration (the development of tourism, due to the increase in the number of people arriving from different countries), the role of the science of parasitism in the health care of the modern world has increased several times. Let us next consider which parasites can live in the human body and what symptoms can arise from various infestations.
The number of people with immunodeficiency has increased, including patients with HIV infection, and also due to advances in medicine associated with the use of chemotherapy and the development of transplantology.
All this leads to the fact that most diseases (infestations) caused by parasites, which usually occur without complications or without any symptoms, can be fatal in people with a weakened immune system.
The response to the introduction of parasitic organisms in these patients differs greatly from the usual reaction, which leads to the appearance of acute and atypical forms of the disease.
In addition, human population activity causes global changes in climatic conditions and the natural landscape, which leads to the spread of infection vectors from endemic areas to other areas and regions.
Medical parasitology is divided into several sections depending on the belonging of parasitic organisms to various groups: protozoan parasites, helminth parasites, parasitic arthropods, etc. Thus, science is divided into:
- Medical protozoology (study of parasitic protozoa, symptoms and treatment of protozoa);
- Medical helminthology (study of parasitic helminths, symptoms and treatment of helminth infections);
- Parasitic entomology (study of parasitic arthropods).
Relationships between organisms
Parasitism is a special form of relationship between organisms of different species, in which one of them (the parasite) uses the other (the host) as a permanent or temporary place of life, as well as a source of food.
The parasite does not kill its host immediately; you must first feed on it repeatedly. During evolution, parasites have developed special mechanisms of interaction with their hosts, which ensure the vital activity of all parasitic species.
External natural conditions affect parasites not directly, but indirectly through hosts.
The phenomenon of parasitism is quite widespread on the planet. Parasites can belong to any systematic group of all kingdoms of organisms. Any type of organism, except viruses, can become a "home" for parasites.
In this case, the parasitic individuals themselves become hosts for parasites of other groups of classification animals.
Parasitocenosis is the total number of absolutely all parasitic organisms living simultaneously in the host. The causative agent of the disease is specific parasitic organisms of different host species.
The parasites that live inside their host not only feed, but also cause various diseases that can lead to the death of the affected person. This phenomenon is called pathogenicity.
Parasites in the human body have a negative effect on it through several mechanisms:
- Damage to cells and tissues;
- Impact on immune defense mechanisms and antibody production by the host;
- Sensitization of the host organism (hypersensitivity);
- Poisonous effect of metabolic products of parasites.
The development cycle of a parasite is the total number of morphological phases of the organism's development, as well as an indication of the habitat of each phase, the route of infection and transmission.
For example, in the development of parasitic worms the following phases are distinguished: invasive phase – entry into the host's body; larval formation phase; Phase of an adult and sexually mature individual.
Invasive diseases (infestations) are diseases caused by parasitic organisms. Invasive human diseases are divided into protozoa (caused by protozoa), helminthiasis (parasitic worms), and diseases caused by arthropod parasitism.
The symptoms of parasites in the human body are so diverse that it makes no sense to consider them as a whole. Therefore, below we will consider the symptoms of the main protozoa, helminthiasis and invasions caused by other animal organisms.
Due to the need to follow a parasitic lifestyle, three types of parasitism are distinguished:
- False parasitism. The accidental entry of a free-living individual into the host, which may be viable for some time and which is capable of altering the normal processes of its life. False parasites are soon released into the environment (e. g. in feces) or die shortly after. False parasitism is inherent in some leeches, which accidentally enter the nasal cavity of people, where they live and cause bleeding, in mites and their eggs, which enter the stomach and are then excreted in excrement, and in some amoebas.
- Facultative parasitism is the ability of organisms to live with and without a host. The viability of the parasite lasts longer than in the first case. This type is characteristic of fly larvae that are capable of developing outside a living organism and when they accidentally enter it (causative agents of myiasis).
- True parasitism. This type of parasitism includes helminths, fleas, lice, etc.
| In relation to the host's body. | |
|---|---|
| Ectoparasites | They live on the surface of the integument and feed on blood cells and the upper layers of the skin. |
| endoparasites | They live within the tissues, cells and cavities of their hosts. They can be located only in one of the organs, but they are capable of moving to nearby ones, also causing damage. |
| By duration of contact | |
| temporary parasite | Most of the time they are ectoparasites; Their contact is usually short-lived. |
| stationary parasite | For these parasites, hosts are also a kind of "home. "This parasitic method of life is divided into two types: periodic (the parasite spends part of the time in the host) and permanent. |
| By specificity | |
| Polyspecific | Able to change different types of hosts, since they feed on blood, epidermis and other tissues inherent to many types of living beings. |
| Monospecific | Able to parasitize only certain species (species) of hosts |
The concept of owner.
The host is a living organism that the parasite uses as a source of nutrients and a place to live. Most parasitic individuals can change hosts, which is due to the presence of several stages during the life of the parasite.
The definitive host (otherwise the main, definitive, last) is an organism where the parasite lives in the adult phase and can reproduce sexually.
An intermediate host is a host within which the larval stage of the parasites lives or a stage that reproduces only asexually.
Reservoir host: within which the parasite is viable, increases in number, but does not mature further.
Parasitic diseases can be anthroponoses (the sources of the disease and hosts are humans), anthropozoonosis (the sources and hosts are both humans and animals), and zoonoses (the sources and hosts are animals).
Many infections are called natural focal infections, when pathogens move among wild animals in a given area.
Methods for diagnosing parasitic infections.
You can't get rid of "parasites in the body" with a "magic pill" or home remedies; You can cause even more damage to yourself. First, you need to understand what kind of invasion a person has. Macroscopic, microscopic and immunological methods are used to diagnose invasive diseases.
Macroscopic techniques allow infectious agents to be identified on the external surfaces or in the feces of an affected person.
Microscopic methods also allow parasites to be identified in blood smears, tissue fluids, muscle tissue biopsies, as well as in sputum, feces, and gastric and duodenal contents.
Optical and electron microscopy methods using optical and electron microscopes are used in parasitological studies. Here the diagnosis is based, first of all, on deep knowledge of the morphological structures of infectious agents, methods of preparation, fixation and staining of smears.
The results of microscopy depend on the choice of pathological materials, their nature, the time of collection from the onset of symptoms and the period of examination from the moment the material was received.
Immunological diagnostic methods include serological and allergic reactions. Serological tests are used to:
- Establish the type of organisms, toxins, antigens using immunological diagnostic sera;
- Determine the nature of antibodies in blood serum using diagnostic antigens.
The basic serological reactions are agglutination, precipitation, lysis, complement binding, neutralization and other reactions. Methods for using labeled antibodies are also known: immunofluorescence reactions, enzyme-linked immunosorbent assay, immunoblotting, radioimmunoassay.
Nucleic acid hybridization and polymerase chain reaction methods have found widespread use in diagnosis.
Prevention issues and anti-epidemic measures.
Preventive measures for all parasitic diseases can be summarized as:
- It is necessary to protect soil and water sources from contamination with human and animal excrement.
- It is necessary to improve populated areas and toilets.
- It is necessary to exercise health surveillance over the territories and the water supply of populated areas, as well as over the production, transportation and sale of food products.
- It is important to carry out veterinary and sanitary supervision in slaughterhouses, meat processing plants, markets and livestock farms.
- It is necessary to identify and treat carriers of infections.
- It is necessary to protect people from harm caused by arthropods and promote knowledge about personal prevention of parasitic diseases.
Anti-epidemic measures include active detection of infected people and carriers, registration and treatment of infected people, hospitalization and medical examination if necessary, neutralization or destruction of sources of infection. Personal prevention is of great importance: hygiene measures, annual medical examination, proper preparation for tourist trips, solving the problem of chemoprophylaxis.
Chemoprophylaxis, that is, the administration of anthelmintic drugs in risk groups and endemic areas 1 or 2 times a year, was developed by the WHO for disadvantaged and developing countries.
General properties of protozoa.
Protozoa are single-celled organisms that have a nucleus (eukaryotes).
The size does not exceed one millimeter, they are found everywhere and in every corner of the planet. Parasitic forms of protozoa are also divided into ectoparasites and endoparasites.
Characteristics of protozoa:
- The body is made up of a cell, which performs the function of both the cell and the organism as a whole. The shape of the body can be varied: variable, elongated or fusiform.
- Some protozoa are covered only by a cell membrane, while others have an elastic membrane called a pellicle.
- The cellular cytoplasm is divided into: dense outer (ectoplasm) and inner (endoplasm). The cytoplasm may contain one or more nuclei.
- Nutrients enter in various ways: through pinocytosis (absorption), phagocytosis (active food), osmosis (ingestion of substances due to a difference in concentration), active transition through the membrane.
- Gas exchange occurs throughout the cell due to the osmotic component. Waste products are also released from the entire surface of the cell and with the help of digestive vacuoles.
- Unicellular organisms reproduce both sexually and asexually.
- Unicellular organisms have several movement devices: pseudopodia, flagella and cilia. They can respond to stimuli due to photo, chemo and thermotaxis and other mechanisms.
- In poor conditions, parasitic protozoa turn into cysts, that is, they become covered with a dense capsule. In a cystic state, the life process stops.
Under favorable conditions, the cyst detaches from its shell and turns into a vegetative form, which continues an active life.
The detection of parasitic protozoa in materials from a patient presents almost no difficulties. Usually a smear is examined and, in addition, a thick drop of blood.
Stools are usually examined fresh using a heated table. To detect amoebic cysts, Lugol's solution is added to the stool, which stains the internal structures.
To date, all protozoa have been classified into the kingdom Protista, which includes seven types, of which only three are of medical importance.
Subtype Sarcodae
The shape of Sarcodidae cells changes; The cell membrane forms protuberances, which can then return to their original shape, called pseudopodia.
Thanks to them, the cell moves. Sarcodidae live absolutely everywhere: soil, fresh water bodies, seas. Infectious diseases caused by Sarcodidae are common throughout the world, but are most commonly found in the tropics and subtropics.
Pathogenic amoeboid sarcods most frequently affect the digestive system of people; They are intestinal parasites. Free-living amoebas of other orders also cause serious infections if accidentally ingested and deposited in the human body.
To diagnose amebiasis, a microscopic examination of feces is used. They contain vegetative or cystic forms of sarcode. When examining stool preparations using a special heated table, it is possible to detect pseudopodia of amoebae and their forward movements.
For the treatment of amebiasis, drugs are used, which are divided into groups: contact, which act on the forms that live in the intestinal lumen, and systemic tissue amoebicides, which act on the amoebas that have penetrated the tissue of the intestine and other organs.
In addition to treatment, aspiration of the liver abscess is performed if chemotherapy is ineffective or there is a threat of rupture of the abscess. The following table describes the main parasitic protozoa of the Sarcodidae subtype.
Subphylum flagellates
Representatives of the flagellar subtype, in addition to the cytoplasmic membrane, have a pellicle (such a layer provides a constant shape) and flagella (one or many).
The flagellum contains contractile fibrils that allow it to move. Some representatives of the flagellates have an undulating membrane, within which the flagellum/flagella is located without exceeding its limits.
The flagellum starts from the kinetosome, which stores energy. Within some flagellates is an axostyle, a dense cord within the body that provides support.
The main symptoms and signs of infection by representatives of the flagellate subtype are presented in the following table.
| Representative/Locations | Symptoms | Diagnosis |
|---|---|---|
| Giardia (Lamblia intestinalis or Giardia lamblia) / Duodenum and small intestine | Nausea, heartburn, abdominal pain, flatulence, heartburn, diarrhea, body intoxication, exhaustion. | Microscopy of the contents of the duodenum, examination of feces, ELISA to detect antibodies to Giardia. |
| Intestinal trichomonas (Trichomonas hominis/intestinalis)/ Lower small intestine, large intestine | Colitis, enterocolitis, cholecystitis, diarrhea. | Detection of vegetative forms and cysts in the patient's liquid stool. |
| Trichomonas vaginalis (Trichomonas vaginalis) / Vagina, cervical canal, urethra - in women. Urethra, prostate, testicles - in men | Colpitis, urethritis in women, itching, burning in the genital area, yellow foamy discharge from the vagina. Asymptomatic carrier, urethritis, prostatitis in men. | Vaginal discharge in women, urethral discharge and prostate secretion in men, PCR, culture. |
| Oral trichomonas (Trichomonas tenax)/ Oral cavity, respiratory tract, tonsils, gums | Caries, periodontal disease, otorhinolaryngological diseases. | Imprint smear, culture |
| African trypanosoma (Trypanosoma brucei gambiense and Trypanosoma brucei rhodesiense)/ Skin at the site of penetration, lymph nodes of the neck and neck, bloodstream | Attacks of fever, painful lymph nodes, rash, headache, drowsiness, tremors in extremities, paralysis, slurred speech, coma, seizures, exhaustion, acute heart failure, death. | Examination of the bite site, lymph node biopsy. Thick blood smear method, stained by Wright or Romanovsky-Giemsa, examination of cerebrospinal fluid. Infection of laboratory animals, RSK, RIF, ELISA |
| American trypanosomiasis (Trypanosoma cruzi)/ Blood | Swelling of the skin at the site of penetration, enlargement of nearby lymph nodes, swelling of the eyelids, enlargement of the parotid lymph nodes. The acute form in newborns causes damage to the heart and brain with a fatal outcome. The chronic form in adults who were sick in childhood: arrhythmia, extrasystole, dilation of the colon with hypertrophy of the wall, enlargement of the esophagus, myxedema, paralysis. | Microscopy of blood smears, biopsy samples of lymph nodes, spleen and other organs, for the acute form. Serological studies, xenodiagnosis (feeding uninfected insects from the patient's body and detecting trypanosomes in their feces), infection of laboratory animals, for the chronic stage. |
| Cutaneous leishmaniasis (Leishmania tropica)/Skin | Nodule on the skin, enlargement of regional lymph nodes, ulceration of the node with the formation of painless "dry" or "wet" ulcers, daughter lesions, scars on the skin after healing. | Tissue microscopy of the ulcer fund with Romanovsky-Giemsa staining, RIF, RSK, ELISA |
| Mucocutaneous leishmaniasis (Leishmania braziliensis) / Skin and mucous membranes | Skin nodule, enlarged regional lymph nodes, skin ulceration, scar formation. On the mucous membranes: painless deforming lesions of the mouth and nose, ulcers on the tongue, mucous membrane of the cheeks and nose, destruction of the nasal septum, hard palate, pharynx, fever, weight loss, addition of bacterial infections. | Microscopy of ulcer secretion, biopsy of damaged organs, RSK, RNGA |
| Visceral leishmaniasis (Leishmania donovani)/ Cells of the spleen, liver, bone marrow, lymph nodes | Enlargement of the liver, spleen, anemia, exhaustion, poisoning, bleeding in the intestines, diarrhea, grayish spots on the face and head, death. | Detection in smears of biopsies of spleen, lymph nodes, bone marrow, RIA, ELISA, RSK |
Sporozoans
Sporozoans do not have organs of movement. They consume nutrients throughout the body and often exhibit intracellular parasitism. Sporozoa include the causative agents of malaria and toxoplasma. Toxoplasmosis is more dangerous for pregnant women and people with proven immunodeficiency (for example, against the background of HIV infection).
Pregnant women with toxoplasmosis are prescribed 3 million units of spiromycin three times a day, every day for fourteen to twenty days.
parasitic ciliates
Ciliates do not change the shape of their body and have a film. Motor maneuvers are carried out due to the large number of cilia that cover the entire cell.
Ciliates have two nuclei: a large one, responsible for cellular metabolism, and another small one, which transmits hereditary information.
Ciliates have an organized digestive system: the cytostome is the mouth of the cell, the cytopharynx is the pharynx of the cell. Digestive enzymes are gradually released from the vacuoles, ensuring complete digestion of nutrients. Undigested parts of food leave through dust, a special formation at the end of the body. The symptoms that may occur when these parasites are present in the intestines are presented in the following table.
| Pathogen | Location | Symptoms | Diagnosis |
|---|---|---|---|
| Balantidium coli | Colon | Fever, poisoning, abdominal pain, diarrhea with mucus and blood, nausea, vomiting. Asymptomatic, carrier of cyst. | Detection in feces, colon biopsies. |
Treatment of balantidiasis includes the prescription of antibacterial and antiprotozoal drugs according to one of the following regimens.
General characteristics of helminths.
Helminthology is the science of worms (helminths) that parasitize the body of other animals, the diseases they cause, as well as methods of diagnosis, prevention and treatment.
The helminth fauna is the totality of all helminths identified in humans. Helminthic diseases, unlike diseases caused by protozoa (protozoa), are not found everywhere.
Most worms carry out their activity in the digestive tract of people, others can attack the parenchymal organs, blood and genitourinary system.
The spread of helminths depends on the work activity of the population, the eating habits of different population groups and the economic situation of the country. The following helminthiases are the most common in our country.
Helminthic diseases are divided into soil-transmitted helminthiases and biohelminthiases. For the development of eggs or larvae of geohelminths, they need to be in the external environment to mature and acquire pathogenic properties. These are roundworms, whipworms, nectars and others.
Biohelminths go through their life cycle with a substitute host, and to acquire pathogenic properties, their eggs need to enter an intermediate and sometimes additional host. These are bovine, porcine, opisthorchis, fasciola and others.
The location of parasitic worms or their larval forms in the human body is very diverse: in the small and large intestine (intestinal helminthiasis), in the bile ducts and liver, in the bloodstream, in the central nervous system and in the eyes, the skin, the muscles, etc. in humans more frequently than fabric.
In the pathogenesis of helminthiases, the occurrence of allergic reactions and a severe degenerative process is of considerable importance. They appear due to the large amount of antigens that the worms have.
Other pathogenesis factors include the direct influence of enzymes that form larval and adult forms. In the later stages of worm development, the mechanical factor and the direct traumatic effect of the fixation organs play an important role.
The diagnosis is usually confirmed by interview, clinical picture of the disease and detection of eggs, larvae, fragments or adult worms in feces, sputum and duodenal juice.
Serological reactions, x-rays and ultrasound also play an important role in the diagnosis of helminthiases.
In general, about three hundred species of pathogenic worms have been found in humans, twenty-eight species of which are the most common: 12 species of trematodes, 8 species of cestodes, 8 species of nematodes.