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 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 what 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 progress in medicine associated with the use of chemotherapy and developing transplantology.
All this leads to the fact that most diseases (infestations) caused by parasites, which usually occur without complications or without any symptoms at all, 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 reaction, 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 vectors of infections from endemic zones 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, and so on. Thus, science is divided into:
- Medical protozoology (study of parasitic protozoa, symptoms and treatment of protozoa);
- Medical helminthology (study of parasitic helminth worms, symptoms and treatment of helminth infections);
- Parasitic entomology (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; first it must 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 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 classification groups of animals.
Parasitocenosis is the total number of absolutely all parasitic organisms that simultaneously live in the host. The causative agent of the disease is parasitic organisms specific to different host species.
Parasites living 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 development of the organism, as well as an indication of the habitat of each phase, the route of infection and transmission.
For example, the following phases are distinguished in the development of parasitic worms: invasive phase – entry into the host’s body; larval formation phase; phase of an adult, sexually mature individual.
Invasive diseases (infestations) are diseases that are caused by parasitic organisms. Invasive human diseases are divided into protozoa (they are caused by protozoa), helminthiases (parasitic worms) and diseases caused by parasitism of arthropods.
The signs of parasites in the human body are so diverse that it makes no sense to consider them as a whole. Therefore, next 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-living individual into the host, which may be viable for some time and which is capable of disrupting the normal processes of its life. False parasites are soon 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 people, where they live and cause bleeding, mites and their eggs, which enter the stomach and are then excreted in excrement, and some amoebas.
- Facultative parasitism is the ability of organisms to live both 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 accidentally entering 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, feeding on blood cells and the upper layers of the skin. |
| Endoparasites | They live inside the tissues, cells and cavities of their hosts. They can be located only in one of the organs, but are able to move to nearby ones, also causing their damage |
| By duration of contact | |
| Temporary parasite | Most often they are ectoparasites; their contact is usually short-lived |
| Stationary parasite | For such parasites, the hosts are also a kind of "home". This method of parasitic lifestyle is divided into two types: periodic (the parasite spends part of the time in the host) and permanent |
| By specificity | |
| Polyspecific | Capable of changing different types of hosts, as they feed on blood, epidermis and other tissues inherent in many types of living beings |
| Monospecific | Able to parasitize only certain species (species) of hosts |
The concept of the 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 phase of parasites lives or a phase that reproduces only asexually.
Reservoir host - inside which the parasite is viable, increases in number, but does not mature further.
Parasitic diseases can be anthroponoses (sources of the disease and hosts are humans), anthropozoonoses (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 certain area.
Methods for diagnosing 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 invasion a person has. To diagnose invasive diseases, macroscopic, microscopic and immunological methods are used.
Macroscopic techniques make it possible to identify infectious agents on the outer surfaces or in the feces of an affected person.
Microscopic methods also make it possible to identify parasites in blood smears, tissue fluids, muscle tissue biopsies, as well as in sputum, feces, gastric and duodenal contents.
In parasitological studies, methods of optical and electron microscopy using light and electron microscopes are used. Here, diagnosis is, first of all, based on deep knowledge of the morphological structures of infectious agents, methods of preparation, fixation and staining of smear preparations.
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 for:
- To establish the type of organisms, toxins, antigens using immune diagnostic sera;
- To determine the nature of antibodies in blood serum using diagnostic antigens.
The basic serological reactions are the 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 widespread use in diagnostics.
Issues of prevention and anti-epidemic measures
Preventive measures for all parasitic diseases can be summarized as follows:
- It is necessary to protect soil and water sources from contamination of human and animal excrement.
- It is necessary to improve populated areas and toilets.
- It is necessary to carry out sanitary supervision over the territories and 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 at 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 on 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 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 WHO for disadvantaged and developing countries.
General properties of Protozoa
Protozoa are single-celled organisms that have a nucleus (eukaryotes).
The size is no 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.
Features of protozoa:
- The body is made up of one cell, which performs the function of both the cell and the organism as a whole. The body shape can be varied: variable, elongated or spindle-shaped.
- Some protozoa are covered only with a cell membrane, while others have an elastic membrane called a pellicle.
- The cell cytoplasm is divided into: outer dense (ectoplasm) and inner (endoplasm). The cytoplasm may contain one or more nuclei.
- Nutrients enter in various ways: through pinocytosis (absorption), phagocytosis (active eating), 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 various devices for movement: pseudopodia, flagella and cilia. They can respond to stimuli due to photo-, chemo- and thermotaxis and other mechanisms.
- Under poor conditions, parasitic protozoa turn into a cyst, that is, they become 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 active life.
Detection of parasitic protozoa in materials from a patient presents almost no difficulties. Usually a smear and additionally a thick drop of blood are examined.
Feces 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.
At this point in time, 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 the Sarcodidae cell changes; the cell membrane forms protrusions, which can then return to their original form, called pseudopods.
Due 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 more often found in the tropics and subtropics.
Pathogenic amoeboid sarcodes most often affect the digestive system of people; these are intestinal parasites. Amoebas of other orders that live freely also cause serious infections if accidentally ingested and settle in the human body.
To diagnose amoebiasis, microscopic examination of stool is used. They contain vegetative or cystic forms of sarcode. When examining preparations from feces using a special heated table, it is possible to detect pseudopodia of amoebas and their forward movements.
To treat amebiasis, drugs are used, which are divided into groups: contact, which act on forms living in the intestinal lumen, and systemic tissue amoebicides, which act on 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 abscess rupture. The table below 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 shell provides 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, inside which the flagellum/flagellum lies without going beyond its limits.
The flagellum starts from the kinetosome, which stores energy. Inside some flagellates there 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.
| Representative/ Localizations | Symptoms | Diagnostics |
|---|---|---|
| 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 for 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 feces |
| 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 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, ENT diseases | Imprint 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, bloodstream | Attacks of fever, painful lymph nodes, skin rash, headache, drowsiness, tremors of limbs, paralysis, slurred speech, coma, convulsions, exhaustion, acute heart failure, death | Examination of the bite site, lymph node biopsy. Method of thick drop and blood smear, stained by Wright or Romanovsky-Giemsa, examination of cerebrospinal fluid. Infection of laboratory animals, RSK, RIF, ELISA |
| American trypanosomiasis (Trypanosoma cruzi)/ Blood | Skin swelling 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 ill in childhood - arrhythmia, extrasystole, dilation of the colon with wall hypertrophy, 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 bugs 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 "dry" or "wet" painless ulcers, daughter lesions, scar on the skin after healing | Microscopy of 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. 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 discharge from ulcers, biopsy of damaged organs, RSK, RNGA |
| Visceral leishmaniasis (Leishmania donovani)/ Cells of the spleen, liver, bone marrow, lymph nodes | Enlarged liver, spleen, anemia, exhaustion, intoxication, hemorrhages in the intestines, diarrhea, grayish spots on the face and head, death | Detection in smears from biopsies of the spleen, lymph nodes, bone marrow, RIA, ELISA, RSK |
Sporozoans
Sporozoans have no 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 toxoplamosis 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 pellicle. Motor maneuvers are carried out due to the huge number of cilia covering the entire cell.
Ciliates have two nuclei: one large, 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 released gradually from the vacuoles, which ensures complete digestion of nutrients. Undigested parts of food exit through the powder, a special formation at the end of the body. Symptoms that may occur when these parasites are present in the intestines are presented in the table below.
| Pathogen | Localization | Symptoms | Diagnostics |
|---|---|---|---|
| Balantidium coli | Colon | Fever, intoxication, abdominal pain, diarrhea with mucus and blood, nausea, vomiting. Asymptomatic, cyst carrier | 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.
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 people, others can attack parenchymal organs, blood, and the genitourinary system.
The spread of helminths depends on the labor activity of the population, the eating habits of various population groups, and the economic state of the country. The following helminthiases 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 need to be in the external environment to mature and acquire pathogenic properties. These are roundworms, whipworms, necators and others.
Biohelminths go through their life cycle with a replacement host, and in order to acquire pathogenic properties, their eggs need to get inside an intermediate and sometimes an additional host. These are bovine, pork tapeworm, 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, bloodstream, central nervous system and eyes, skin, muscles, etc. Intestinal parasites occur in humans more often thanfabric.
In the pathogenesis of helminthiases, the appearance 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 worm development, the mechanical factor and the direct traumatic effect of the fixation organs play an important role.
Diagnoses are 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-ray and ultrasound examinations 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 most widespread: 12 species of trematodes, 8 species of cestodes, 8 species of nematodes.