Parasitology is a science that studies the phenomenon of parasitism. The main task of such science is to study the relationship between parasites and hosts, their influence on each other, 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 coming from different countries), the role of the science of parasitism in the health care of the modern world has increased several times. Let's then consider what parasites can live in the human body and what symptoms can arise from various infections.
The number of immunodeficient people has increased, including patients with HIV infection, as well as due to advances in medicine related to the use of chemotherapy and the development of transplantology.
All this leads to the fact that most diseases (infections) 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 such patients differs greatly from the usual response, which leads to the appearance of acute, atypical forms of the disease.
Also, the activity of the human population provokes 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 affiliation of parasitic organisms to different 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 (the study of parasitic helminth worms, symptoms and treatment of helminth infections);
- Parasitic entomology (the study of parasitic arthropods).
Relationships between organisms
Parasitism is a special way of relationship between organisms of different species, in which one of them (the parasite) uses the other (the host) as a place for permanent or temporary life, as well as as a source of food.
The parasite does not kill its host immediately; it must first be fed 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 the 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 animal classification groups.
Parasitocoenosis is the total number of absolutely all parasitic organisms living at the same time in the host. The causative agent of the disease are parasitic organisms specific to different host species.
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 production of antibodies by the host;
- Sensitization of the host organism (hypersensitivity);
- The poisonous effect of metabolic products of parasites.
The development cycle of a parasite is the total number of morphological stages of the organism's development, as well as an indicator of the habitat of each stage, the route of infection and transmission.
For example, the following stages are distinguished in the development of parasitic worms: invasive stage - entry into the body of the host; stage of larval formation; the stage of an adult, sexually mature individual.
Invasive diseases (infections) 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.
Signs of parasites in the human body are so different that it makes no sense to consider them as a whole. Therefore, in the following we will consider the symptoms of the main protozoa, helminthiasis and invasions caused by other animal organisms.
Due to the need to adhere to a parasitic lifestyle, three types of parasitism are distinguished:
- False parasitism. The accidental entry of a free individual into the shelter, which may be viable for some time and which is capable of disrupting the normal processes of his life. False parasites are quickly released into the environment (for example, in feces) or die after a short period of time. False parasitism is inherent in some leeches, which accidentally enter the nasal cavity of humans, where they live and cause bleeding, mites and their eggs, which enter the stomach and are then excreted in the feces, and some amoebas.
- Facultative parasitism is the ability of organisms to live with and without a host. The persistence of the parasite lasts longer than in the first case. This type is characteristic of fly larvae that are able to develop outside a living organism and when they accidentally enter it (the causative agents of myiasis).
- True parasitism. This type of parasitism includes helminths, fleas, lice, etc.
Owner concept
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 stage and can reproduce sexually.
An intermediate host is a host within which the larval stage of the parasite 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 (disease sources and hosts are humans), anthropozonoses (sources and hosts are both humans and animals) and zoonoses (sources and hosts are animals).
Many infections are called natural focal infections, when pathogens move between wild animals in a given area.
Methods for the diagnosis of parasitic infections
You cannot get rid of "parasites in the body" using a "magic pill" or folk remedies; you can cause even greater damage to yourself. First, you need to understand what kind of occupation a person has. Macroscopic, microscopic and immunological methods are used to diagnose invasive diseases.
Macroscopic techniques make it possible to identify infectious agents on external surfaces or in the feces of an infected person.
Microscopic methods also make it possible to identify parasites in blood smears, tissue fluids, muscle tissue biopsies, as well as in saliva, feces, gastric and duodenal contents.
In parasitological studies, optical and electron microscopy methods are used using light and electron microscopes. 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 staining preparations.
Microscopy results depend on the choice of pathological materials, their nature, the time of collection since the onset of symptoms and the period of examination from the moment of obtaining the material.
Immunological diagnostic methods include serological and allergic reactions. Serological tests are used for:
- To determine the type of organisms, toxins, antigens using immune diagnostic serums;
- To determine the nature of antibodies in blood serum using diagnostic antigens.
The basic serological reactions are reactions of agglutination, precipitation, lysis, complement binding, neutralization and others. Methods of using labeled antibodies are also known: immunofluorescence reactions, enzyme-linked immunosorbent assay, immunoblotting, radioimmunoassay.
Nucleic acid hybridization and polymerase chain reaction methods have found wide use in diagnostics.
Issues of preventive and anti-epidemic measures
Preventive measures for all parasitic diseases can be summarized as follows:
- It is necessary to protect land and water sources from contamination by human and animal excreta.
- It is necessary to improve the residential areas and toilets.
- It is necessary to carry out sanitary supervision over the territories and water supply of residential areas, as well as over the production, transportation and sale of food products.
- It is important to carry out veterinary and sanitary surveillance 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 damage by arthropods and to promote knowledge about personal prevention of parasitic diseases.
Anti-epidemic measures include active detection of infected persons and carriers, registration and treatment of infected persons, hospitalization and medical examination if necessary, neutralization or destruction of sources of infection. Personal prevention is of great importance: hygienic measures, annual medical examination, proper preparation for tourist trips, solving the issue 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 characteristics of protozoa
Protozoa are unicellular organisms that have a nucleus (eukaryotes).
The size is not more than one millimeter, they are found everywhere and in all corners of the planet. Parasitic forms of protozoa are also divided into ectoparasites and endoparasites.
Characteristics of protozoa:
- The body consists of a cell, which performs the function of both the cell and the organism as a whole. The shape of the body can be different: variable, elongated or finger-shaped.
- Some protozoa are covered with only a cell membrane, while others have an elastic membrane called a pellicle.
- The cell cytoplasm is divided into: dense outer (ectoplasm) and inner (endoplasm). The cytoplasm may contain one or more nuclei.
- Nutrients enter in different ways: through pinocytosis (absorption), phagocytosis (active eating), osmosis (swallowing of substances due to a change in concentration), active passage through the membrane.
- Gas exchange occurs throughout the cell due to the osmotic component. Waste products are also released from the entire cell surface and with the help of digestive vacuoles.
- Unicellular organisms reproduce both sexually and asexually.
- Unicellular organisms have various devices for movement: pseudopodia, flagella and cilia. They can respond to stimuli due to photo-, chemotherapy and thermotaxis and other mechanisms.
- In bad conditions, the parasitic protozoa turn into a cyst, that is, they are covered with a dense capsule. In a cystic state, the life process stops.
Under favorable conditions, the cyst sheds its shell and turns into a vegetative form, which continues its active life.
The detection of parasitic protozoa in materials from a patient presents almost no difficulties. A smear and also a thick spot of blood is usually examined.
Faeces are usually examined fresh using a hot table. To detect amoebic cysts, Lugol's solution is added to the stool, which stains the internal structures.
At this point in time, all protozoa are classified into the kingdom Protista, which includes seven species, of which only three are of medical importance.
Subphylum Sarcodae
Sarcodidae cell shape varies; the cell membrane forms protrusions, which can then return to their original shape, called a pseudopod.
Thanks to them, the cell moves. Sarcodidae live absolutely everywhere: land, fresh waters, seas. Infectious diseases caused by Sarcodidae are common throughout the world, but are most often found in the tropics and subtropics.
Pathogenic amoeboid sarcoids most commonly affect the digestive system of humans; these are intestinal parasites. Free-living amoebae of other orders also cause serious infections if accidentally ingested and placed in the human body.
To diagnose amoebiasis, microscopic examination of stool is used. They contain vegetative or cystic forms of sarcoid. When examining feces preparations using a special heated table, it is possible to detect the pseudopodia of amoebas and their forward movements.
For the treatment of amoebiasis, medications are used, which are divided into groups: contact, which act on forms that live in the intestinal lumen, and systemic tissue amoebicides, which act on amoebae that have penetrated the intestinal tissue and other organs.
In addition to treatment, liver abscess aspiration is performed if chemotherapy is ineffective or there is a risk of abscess rupture. The table below describes the main parasitic protozoa of the subphylum Sarcodidae.
Subphylum Flagellate
Representatives of the flagellar subtype, in addition to the cytoplasmic membrane, have a pellicle (such a shell ensures a constant shape) and flagella (one or many).
The flagellum contains contractile fibrils that allow it to move. Some representatives of flagellates have an undulating membrane, within which the flagellum/flagellum extends without going beyond its borders.
The flagellum starts from the kinetosome, which stores energy. Inside some flagellates is an axostyle - a dense cord inside the body that provides support.
The main symptoms and signs of infection by representatives of the flagellate subtype are presented in the table below.
| Representatives/ Locations | Symptoms | Diagnosing |
|---|---|---|
| Giardia (Lamblia intestinalis or Giardia lamblia) / Duodenum and small intestine | Nausea, heartburn, abdominal pain, bloating, heartburn, diarrhea, body intoxication, exhaustion | Microscopy of the contents of the duodenum, stool examination, ELISA for Giardia antibodies |
| Trichomonas intestinale (Trichomonas hominis/intestinalis)/ Lower small intestine, large intestine | Colitis, enterocolitis, cholecystitis, diarrhea | Detection of vegetative forms and cysts in liquid feces of the patient |
| 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, foamy yellow discharge from the vagina. Asymptomatic carriage, urethritis, prostatitis in men | Vaginal secretions in women, secretions from the urethra and prostate secretion in men, PCR, culture |
| Oral Trichomonas (Trichomonas tenax)/ Oral cavity, respiratory tract, tonsils, gums | Caries, periodontal diseases, ENT diseases | Sealing smears, culture |
| African trypanosomes (Trypanosoma brucei gambiense and Trypanosoma brucei rhodesiense)/ Skin at the site of penetration, lymph nodes of the neck and back of the head, blood circulation | Fever attacks, painful lymph nodes, skin rash, headache, drowsiness, tremors, paralysis, slurred speech, coma, convulsions, exhaustion, acute heart failure, death | Examination of the bite site, lymph node biopsy. The method of thick drop and blood staining, 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 the 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. Chronic form in adults who were sick in childhood - arrhythmia, extrasystole, expansion of the large intestine with hypertrophy of the wall, enlargement of the esophagus, myxedema, paralysis. | Microscopy of blood spots, biopsy samples of lymph nodes, spleen and other organs - for the acute form. Serological studies, xenodiagnosis (eating uninfected insects from the patient's body and detecting trypanosomes in their feces), infection of laboratory animals - for the chronic phase |
| Cutaneous leishmaniasis (Leishmania tropica)/Skin | Nodule on the skin, enlargement of the regional lymph nodes, ulceration of the node with the formation of painless "dry" or "wet" ulcers, daughter lesions, scar on the skin after healing. | Microscopy of the tissue from the bottom of the ulcer 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. In the mucosa - painless deforming lesions of the mouth and nose, ulcers on the tongue, mucous membranes of the cheeks and nose, destruction of the nasal septum, hard palate, pharynx, fever, weight loss, increase in bacterial infections. | Microscopy of discharge from ulcers, biopsy of damaged organs, RSK, RNGA |
| Visceral leishmaniasis (Leishmania donovani)/ Cells of spleen, liver, bone marrow, lymph nodes | Enlarged liver, spleen, anemia, exhaustion, intoxication, intestinal hemorrhage, diarrhea, gray spots on face and head, death | Detection in stains from biopsies of the spleen, lymph nodes, bone marrow, RIA, ELISA, RSK |
Sporozoa
Sporozoa do not have organs of movement. They consume nutrients throughout the body and often exhibit intracellular parasitism. Sporozoans 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 their body shape and have a pellicle. Motor maneuvers are performed due to the large number of cilia that cover the entire cell.
Ciliates have two nuclei: a large one, responsible for cell metabolism, and a 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, which ensures complete digestion of nutrients. Undigested parts of food come out through the dust, a special formation at the bottom of the body. Symptoms that may appear when these parasites are present in the intestine are shown in the table below.
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 common everywhere.
Most worms carry out their activity in the digestive tract of humans, others can attack 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 helminthiasis are the most common in our country.
Helminthic diseases are divided into geohelminthiasis and biohelminthiasis. For the development of eggs or larvae of geohelminths, they must be in the external environment to mature and acquire pathogenic properties. These are roundworms, whipworms, nematodes and others.
Biohelminths spend their life cycle with an alternate host, and to acquire pathogenic properties, their eggs must be introduced into an intermediate and sometimes additional host. These are cattle, pig tape, opisthorchis, fasciola and others.
The localization of parasitic worms or their larval forms in the human body is very diverse: in the small and large intestines (intestinal helminthiasis), biliary tract and liver, blood circulation, central nervous system and eyes, skin, muscles, etc. . Intestinal parasites appear. in people more often than fabrics.
In the pathogenesis of helminthiasis, the occurrence of allergic reactions and a severe degenerative process is of considerable importance. They appear due to the large number of antigens that worms have.
Other factors of pathogenesis include the direct influence of enzymes that form larval forms and adult individuals. In the later stages of the development of worms, the mechanical factor and the direct traumatic effect of the fixation organs play an important role.
Diagnoses are usually confirmed by the interview, the clinical picture of the disease and the detection of eggs, larvae, fragments or adult worms in feces, sputum and duodenal fluid.
Serological reactions, X-ray and ultrasound examinations also play an important role in the diagnosis of helminthiasis.
In general, about three hundred types of pathogenic worms have been found in humans, of which twenty-eight types are the most widespread: 12 types of trematodes, 8 types of cestodes, 8 types of nematodes.