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 and their influence on each other, which also depends on environmental factors.
Due to increasing population migration (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. Next, let's consider what parasites can live in the human body and what symptoms can occur with different 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 of this means that most diseases caused by parasites (infestations), which usually have no complications or no symptoms at all, can be fatal in people with weakened immune systems.
The reaction 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.
In addition, the activity of the human population leads to global changes in climatic conditions and the natural landscape, which leads to the spread of infectious vectors from endemic areas to other areas and regions.
Medical parasitology is divided into several sections depending on the belonging of parasitic organisms to different groups: protozoan parasites, helminth parasites, parasitic arthropods, etc. Thus, the science is divided into:
- Medical protozoology (study of parasitic protozoa, symptoms and treatment of protozoa);
- Medical helminthology (examination of parasitic helminths, symptoms and treatment of helminth infections);
- Parasitic entomology (study of parasitic arthropods).
Relationships between organisms
Parasitism is a special type of relationship between organisms of different species, in which one of them (the parasite) uses the other (the host) as a place of permanent or temporary life, as well as a source of food.
The parasite does not kill its host immediately; he must first feed on it repeatedly. In the course of evolution, parasites have developed special mechanisms of interaction with their hosts, which ensure the vital activity of all species of parasites.
External natural conditions do not affect parasites directly, but indirectly through the hosts.
The phenomenon of parasitism is widespread on the planet. Parasites can belong to any systematic group of any kingdom of organisms. Any type of organism other than viruses can become a "home" for parasites.
In this case, the parasitic individuals themselves become hosts for parasites from other groups of animals.
Parasitocenosis is the total number of absolutely all parasitic organisms living in the host at the same time. The causative agent of the disease is parasitic organisms specific to different host species.
Parasites living in 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 negatively affect it through various mechanisms:
- damage to cells and tissues;
- Effects on immune defense mechanisms and antibody production by the host;
- Sensitization of the host organism (hypersensitivity);
- Toxic effects of parasite metabolic products.
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, in the development of parasitic worms, the following phases are distinguished: invasive phase - penetration into the host's body; larval formation phase; Phase of an adult, sexually mature individual.
Invasive diseases (infestations) are diseases caused by parasitic organisms. Invasive human diseases are divided into protozoa (they are caused by protozoa), helminthiases (parasitic worms) and diseases caused by arthropod parasitism.
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 consider the symptoms of the main protozoa, helminthiasis and invasions by other animal organisms.
Due to the need to maintain a parasitic lifestyle, three types of parasitism are distinguished:
- False parasitism. The accidental entry into the host of a free-living individual that may be viable for some time and may disrupt the normal life processes of its host. False parasites quickly enter the environment (e. g. via feces) or die after a short 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 the excrement, and some amoebas.
- Facultative parasitism is the ability of organisms to live both with and without a host. The parasite's viability lasts longer than in the first case. This type is characteristic of fly larvae that can develop outside a living organism and upon accidental penetration into it (causative agent 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 skin and feed on blood cells and the upper layers of the skin. |
| Endoparasites | They live in the tissues, cells and cavities of their hosts. They can only be in one of the organs, but can also move into neighboring organs and cause damage there as well |
| By contact duration | |
| Temporary parasite | Most commonly these are ectoparasites; Their contact is usually short-lived |
| Stationary parasite | For such parasites, the hosts are also a kind of "home". This type of parasitic lifestyle is divided into two types: periodic (the parasite spends part of the time in the host) and permanent |
| By specificity | |
| Polyspecific | Can change different types of hosts, as they feed on blood, epidermis and other tissues inherent in many types of living things |
| Monospecific | Can only parasitize certain types (species) of hosts |
The concept of the owner
The host is a living organism that the parasite uses as a source of nutrients and habitat. Most parasitic individuals can change hosts, which is due to the presence of multiple stages in the parasite's life.
The definitive host (otherwise main, final host, final) is an organism in which the parasite lives in the adult stage and can reproduce sexually.
An intermediate host is a host in which the larval phase lives on parasites or a phase that reproduces only asexually.
Reservoir host - in it the parasite is viable, increases in number, but does not mature further.
Parasitic diseases can be anthroponoses (sources of disease and hosts are humans), anthropozoonoses (sources of disease and hosts are both humans and animals), and zoonoses (sources of disease and hosts are animals).
Many infections are referred to as natural focal infections when pathogens move between wild animals in a specific area.
Methods for diagnosing parasitic infections
You cannot get rid of "parasites in the body" with a "magic pill" or folk remedies; You can cause yourself even greater harm. 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 the identification of infectious agents on the external surfaces or in the feces of an affected person.
Microscopic methods also allow the identification of 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 are used using light and electron microscopes. The diagnosis is based primarily on in-depth knowledge of the morphological structures of infectious pathogens, methods for producing, fixing and staining smear preparations.
The results of microscopy depend on the choice of pathological material, its type, the time of collection from the onset of symptoms and the examination period from the time of receipt of the material.
Immunological diagnostic methods include serological and allergic reactions. Serological tests are used for:
- Determination of the type of organisms, toxins and antigens using immunodiagnostic sera;
- Determination of the type of antibodies in blood serum using diagnostic antigens.
The basic serological reactions are the reactions agglutination, precipitation, lysis, complement fixation, neutralization and others. Methods for using labeled antibodies are also known: immunofluorescence reactions, enzyme immunoassay, immunoblotting, radioimmunoassay.
Methods of nucleic acid hybridization and polymerase chain reaction 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 by human and animal excrement.
- It is necessary to improve populated areas and toilets.
- It is necessary to carry out sanitary supervision of the territories and water supply of populated areas, as well as the production, transportation and sale of food.
- 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 infection.
- It is necessary to protect people from arthropod damage and promote knowledge of personal prevention of parasitic diseases.
Anti-epidemic measures include active detection of infected persons and carriers, registration and treatment of infected persons, hospitalization and, if necessary, medical examination, and 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, i. e. the administration of anthelmintics in risk groups and endemic areas once or twice a year, was developed by the WHO for disadvantaged and developing countries.
General characteristics of protozoa
Protozoa are single-celled organisms with a cell nucleus (eukaryotes).
The size is no more than a 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 that performs the function of both the cell and the entire organism. The body shape can be varied: variable, elongated or fusiform.
- Some protozoa are covered only with a cell membrane, while others have an elastic membrane called a pellicle.
- The cell cytoplasm is divided into: external dense (ectoplasm) and internal (endoplasm). The cytoplasm may contain one or more nuclei.
- Nutrients enter in various ways: through pinocytosis (absorption), phagocytosis (active absorption of food), osmosis (absorption of substances due to a difference in concentration), active passage through the membrane.
- Due to the osmotic component, gas exchange occurs throughout the cell. Waste products are also released from the entire cell surface and with the help of digestive vacuoles.
- Single-celled organisms reproduce both sexually and asexually.
- Single-celled organisms have various locomotor devices: 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 the cystic state the life process stops.
Under favorable conditions, the cyst sheds its shell and turns into a vegetative form, continuing its active life.
The detection of parasitic protozoa in materials from a patient presents almost no difficulties. As a rule, a smear and also a thick drop of blood are examined.
The feces are usually examined fresh on the warming table. To detect amoebic cysts, Lugol's solution is added to the stool, which stains the internal structures.
At this point, all protozoa were assigned to the kingdom Protista, which includes seven species, only three of which are of medical importance.
Subtype Sarcodae
The shape of the Sarcodidae cell changes; the cell membrane forms projections that can then return to their original shape, called pseudopodia.
The cell moves through them. Sarcodidae live absolutely everywhere: soil, freshwater bodies, seas. Infectious diseases caused by Sarcodidae are widespread throughout the world but are more common in the tropics and subtropics.
Pathogenic amoebic sarcodes most commonly affect the human digestive system; These are intestinal parasites. Free-living amoebas of other orders also cause serious infections if accidentally ingested and become established in the human body.
To diagnose amebiasis, a microscopic examination of the stool is performed. They contain vegetative or cystic forms of the sarcode. When examining fecal preparations using a special heating table, it is possible to detect pseudopodia of amoebae and their forward movements.
To treat amebiasis, drugs are used that are divided into groups: contact, acting on forms living in the intestinal lumen, and systemic tissue amoebicides, acting on amoebas that have penetrated the tissues 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 risk of abscess rupture. The following table describes the major parasitic protozoa of the subtype Sarcodidae.
Subphylum flagellates
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 more).
The flagellum contains contractile fibrils that allow it to move. Some representatives of the flagellates have a wave-shaped membrane, inside which the flagella/flagellum is located without extending beyond its boundaries.
The flagellum emanates 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 shown in the table below.
| Representatives/Localizations | Symptoms | diagnosis |
|---|---|---|
| Giardia (Lamblia intestinalis or Giardia lamblia) / duodenum and small intestine | Nausea, heartburn, stomach pain, bloating, heartburn, diarrhea, body intoxication, exhaustion | Microscopy of duodenal contents, 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 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, frothy 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, periodontitis, ENT diseases | Imprint smears, culture |
| African trypanosomes (Trypanosoma brucei gambiense and Trypanosoma brucei rhodesiense)/skin at the site of invasion, lymph nodes in the neck and back of the head, blood circulation | Fever attacks, painful lymph nodes, rash, headache, drowsiness, tremor 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 according to 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 neighboring lymph nodes, swelling of the eyelids, enlargement of the parotid lymph nodes. The acute form leads to heart and brain damage with fatal outcomes in newborns. The chronic form in adults who were ill in childhood - arrhythmia, extrasystole, expansion of the large intestine 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 insects from the patient's body and detection of trypanosomes in the feces), infection of laboratory animals - in the chronic stage |
| Cutaneous leishmaniasis (Leishmania tropica)/skin | Lumps on the skin, enlargement of regional lymph nodes, ulceration of the node with formation of "dry" or "wet" painless ulcers, daughter lesions, scar on the skin after healing | Microscopy of tissue from the bottom of the ulcer using Romanovsky-Giemsa staining, RIF, RSK, ELISA |
| Mucocutaneous leishmaniasis (Leishmania braziliensis) / skin and mucous membranes | Skin nodules, enlarged regional lymph nodes, skin ulcers, scarring. 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, throat, 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, poisoning, bleeding in the intestines, diarrhea, gray patches on the face and head, death | Detection in smears from biopsies of spleen, lymph nodes, bone marrow, RIA, ELISA, RSK |
Sporozoa
Sporozoans have no movement organs. They consume nutrients throughout the body and often exhibit intracellular parasitism. The sporozoa include the pathogens 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 for fourteen to twenty days.
Parasitic ciliates
Ciliates do not change their body shape and have a membrane. Due to the large number of cilia covering the entire cell, motor maneuvers are performed.
Ciliates have two nuclei: a large one, which is responsible for cell metabolism, and a small one, which transmits genetic 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 are excreted through the powder, a special formation at the end of the body. The symptoms that may occur when these parasites are present in the intestines are listed in the table below.
| pathogen | Localization | Symptoms | diagnosis |
|---|---|---|---|
| Balantidium coli | colon | Fever, poisoning, abdominal pain, diarrhea with mucus and blood, nausea, vomiting. Asymptomatic, cyst carriers | Detection in feces, colon biopsies |
Treatment of balantidiasis includes the prescription of antibacterial and antiprotozoal drugs according to one of the following schemes.
General characteristics of helminths
Helminthology is the science of worms (helminths) that parasitize the bodies of other animals, the diseases they cause, and 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 widespread everywhere.
Most worms carry out their activity in the human digestive tract, others can attack parenchymal organs, blood and the urogenital system.
The spread of helminths depends on the work activity of the population, the dietary habits of different groups of the population and the economic situation 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 must stay 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 surrogate host, and in order to acquire pathogenic properties, their eggs must enter an intermediate host and sometimes an additional host. These are beef, pork tapeworms, 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 intestine (intestinal worm), bile ducts and liver, blood circulation, central nervous system and eyes, skin, muscles, etc. Intestinal parasites are more common in humans than substances.
In the pathogenesis of helminthiases, the occurrence of allergic reactions and a severe degenerative process is of significant importance. They arise due to the large number of antigens that worms possess.
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 an interview, the clinical picture of the disease and the detection of eggs, larvae, fragments or adult worms in feces, sputum and duodenal juice.
Serological reactions, X-rays 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, of which twenty-eight species are the most widespread: 12 species of trematodes, 8 species of cestodes, 8 species of nematodes.