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 influence on each other, which also depends on environmental factors.
Due to the increase in 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 tomany times. Next, let's see what parasites can live in the human body and what symptoms can result from various infestations.
The number of immunocompromised people has increased, including patients infected with HIV, but also due to medical advances 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 weakened immune systems.
The response to the introduction of parasitic organisms in these patients differs significantly 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 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 whether parasitic organisms belong 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 (study of parasitic helminthic worms, symptoms and treatment of helminthic infections);
- Parasitic entomology (study of parasitic arthropods).
Relationships between organizations
Parasitism is a particular mode 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 as a source of food.
The parasite does not immediately kill its host; he must first feed on it several times. In the course of 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 from all kingdoms of organisms. Any type of organism, with the exception of viruses, can become a "home" for parasites.
In this case, the parasitic individuals themselves become hosts to parasites from other 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 present in the human body have a negative effect on it through several mechanisms:
- Cell and tissue damage;
- Impact on immune defense mechanisms and antibody production by the host;
- Sensitization of the host organism (hypersensitivity);
- Toxic effect of metabolic products of parasites.
The developmental 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, the following phases are distinguished in the development of parasitic worms: invasive phase – entry into the body of the host; 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 (they are caused by protozoa), helminthiasis (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, we will next examine 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 host, which may be viable for some time and is capable of disrupting the normal processes of its life. False parasites are quickly released into the environment (e. g. in feces) or die after a short time. False parasitism is inherent in some leeches that accidentally enter the nasal cavity of people where they live and cause bleeding, in mites and their eggs, which enter the stomach and are subsequently excreted in feces, as well as insome amoebae.
- 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 capable of developing outside a living organism and accidentally penetrating it (causative agents of myiasis).
- A real parasitism. This type of parasitism includes helminths, fleas, lice, etc.
| Relative 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 only be localized in one of the organs, but are able to move to nearby organs, also causing their damage. |
| By contact duration | |
| Temporary parasite | These are most often ectoparasites; their contact is generally short-lived |
| Stationary parasite | For these parasites, the hosts are also a kind of "home". This parasitic lifestyle is divided into two types: periodic (the parasite spends part of the time with the host) and permanent. |
| By specificity | |
| Polyspecific | Able to change different types of hosts, as they feed on blood, epidermis and other tissues inherent in many types of living beings |
| Monospecific | Capable of parasitizing only certain species (species) of hosts |
The notion 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 (if not the main, definitive, last) is an organism in which the parasite lives in the adult phase and can reproduce sexually.
An intermediate host is a host in which the larval phase of the parasites lives or a phase 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), anthropozoonoses (sources and hosts are both humans and animals) and zoonoses (sources and hosts are both humans and animals). animals).
Many infections are called natural focal infections, when pathogens move between wildlife 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 more serious damage to yourself. First of all, you need to understand what kind of invasion a person is experiencing. To diagnose invasive diseases, macroscopic, microscopic and immunological methods are used.
Macroscopic techniques can identify infectious agents on external surfaces or in the stool 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, optical and electron microscopy methods using optical and electron microscopes are used. Here, diagnosis is based primarily on in-depth 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 examination period from the time 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 immune 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 others. Methods for using labeled antibodies are also known: immunofluorescence reactions, enzyme immunoassay, immunoblot, radioimmunological test.
Nucleic acid hybridization and polymerase chain reaction methods have been widely used in diagnosis.
Prevention issues and anti-epidemic measures
Preventive measures against all parasitic diseases can be summarized as follows:
- It is necessary to protect soils and water sources from contamination by human and animal excrement.
- There is a need to improve populated areas and toilets.
- It is necessary to ensure sanitary monitoring of territories and water supply to populated areas, as well as the production, transportation and sale of food products.
- It is important to carry out veterinary and health 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 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 1-2 times a year, was developed by the WHO for disadvantaged and developing countries.
General properties of protozoa
Protozoa are single-celled organisms with a nucleus (eukaryotes).
Their size does not exceed a millimeter, they are found everywhere and in the four corners of the planet. Parasitic forms of protozoa are also divided into ectoparasites and endoparasites.
Characteristics of protozoa:
- The body is made up of a single cell, which performs both the function of a cell and that of 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 cell cytoplasm is divided into: dense external (ectoplasm) and internal (endoplasm). The cytoplasm may contain one or more nuclei.
- Nutrients penetrate in different ways: by pinocytosis (absorption), phagocytosis (active feeding), 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.
- Single-celled organisms reproduce sexually and asexually.
- Unicellular organisms have various movement devices: pseudopodia, flagella and cilia. They can respond to stimuli due to photo, chemo and thermotaxis and other mechanisms.
- Under poor conditions, parasitic protozoa transform into a cyst, that is, they become covered with a dense capsule. In a cystic state, the vital process stops.
Under favorable conditions, the cyst loses its shell and transforms into a vegetative form which continues its active life.
Detection of parasitic protozoa in patient materials presents virtually no difficulty. Usually a smear and additionally a thick drop of blood are examined.
Feces are usually examined fresh using a warming table. To detect amoebic cysts, Lugol's solution is added to the stool, which stains the internal structures.
At present, all protozoa have been classified into the kingdom Protista, which includes seven types, of which only three are of medical importance.
Sarcodes subtype
The shape of the Sarcodidae cell changes; the cell membrane forms protrusions, which can then return to their original shape, called pseudopodia.
Thanks to them, the cell moves. Sarcodidae live absolutely everywhere: soils, bodies of fresh water, seas. Infectious diseases caused by Sarcodidae are common worldwide, but are more common in tropical and subtropical regions.
Pathogenic amoeboid sarcodes most commonly affect the digestive system of humans; they are intestinal parasites. Free-living amoebas of other orders also cause serious infections if they are accidentally ingested and take up residence 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 heating table, it is possible to detect the pseudopodia of amoebae and their forward movements.
To treat amoebiasis, drugs are used that are divided into groups: contact agents, which act on forms living in the intestinal lumen, and systemic tissue amoebicides, which act on amoebae that have penetrated into the tissues of the intestinal tract. 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 rupture of the abscess. The table below describes the main parasitic protozoa of the Sarcodidae subtype.
Flagellates of the subphylum
Representatives of the flagellar subtype, in addition to the cytoplasmic membrane, have a pellicle (such a shell gives a constant shape) and flagella (one or more).
The flagellum contains contractile fibrils that allow it to move. Some representatives of flagellates have a wavy membrane, inside which the flagellum/flagellum is located without going beyond its boundaries.
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 with representatives of the flagellate subtype are presented in the table below.
| Representative/Locations | Symptoms | Diagnostic |
|---|---|---|
| Giardia (Lamblia intestinalis or Giardia lamblia) / Duodenum and small intestine | Nausea, heartburn, abdominal pain, flatulence, heartburn, diarrhea, body intoxication, exhaustion | Microscopy of duodenal contents, stool examination, ELISA for anti-Giardia antibodies |
| 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 stools |
| 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 prostatic secretion in men, PCR, culture |
| Oral trichomonas (Trichomonas tenax)/ Oral cavity, respiratory tract, tonsils, gums | Caries, periodontal diseases, ENT diseases | Fingerprint smear, 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, sore lymph nodes, rash, headache, drowsiness, tremors, paralysis, slurred speech, coma, convulsions, exhaustion, acute heart failure, death | Examination of the bite site, lymph node biopsy. Thick drop and 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 | Skin swelling at the site of penetration, enlargement of nearby lymph nodes, swelling of the eyelids, enlargement of parotid lymph nodes. The acute form in newborns causes heart and brain damage that can lead to death. The chronic form in adults sick in childhood - arrhythmia, extrasystole, dilatation of the colon with enlargement of the wall, enlargement of the esophagus, myxedema, paralysis | Microscopy of blood smears, biopsy samples of lymph nodes, spleen and other organs - for acute form. Serological studies, xenodiagnosis (feeding uninfected insects from the patient's body and detecting trypanosomes in their feces), infection of laboratory animals - for 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, scar on the skin after healing | Microscopy of tissues from the bottom of the ulcer with Romanovsky-Giemsa staining, RIF, RSK, ELISA |
| Mucocutaneous leishmaniasis (Leishmania braziliensis) / Skin and mucous membranes | Skin nodule, regional lymph node enlargement, skin ulceration, scar formation. On the mucous membranes - painless deforming lesions of the mouth and nose, ulcers of the tongue, mucous membranes of the cheeks and nose, destruction of the nasal septum, hard palate, pharynx, fever, weight loss, addition of infectionsbacterial | Microscopy of ulcer discharge, 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, intestinal bleeding, diarrhea, gray spots on face and head, death | Detection in biopsy smears of the spleen, lymph nodes, bone marrow, RIA, ELISA, RSK |
Sporozoa
Sporozoans do not have movement organs. 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 film. Motor maneuvers are carried out thanks to the large number of cilia covering the entire cell.
Ciliates have two nuclei: a large one, responsible for cellular 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 powder, a special formation located at the end of the body. Symptoms that can occur when these parasites are present in the intestines are shown in the table below.
| Pathogen | Location | Symptoms | Diagnostic |
|---|---|---|---|
| Balantidium coli | Colon | Fever, intoxication, abdominal pain, diarrhea with mucus and blood, nausea, vomiting. Asymptomatic, cyst carrier | Detection in stools, colon biopsies |
Treatment of balantidiasis includes the prescription of antibacterial and antiprotozoal drugs according to one of the following treatment 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 helminthic 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 the genitourinary system.
The spread of helminths depends on the professional activity of the population, the dietary habits of different population groups and the economic situation in 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 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 to acquire pathogenic properties, their eggs must penetrate an intermediate and sometimes additional host. These are bovine tapeworm, pork tapeworm, 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 intestines (intestinal helminthiasis), bile ducts and liver, blood circulation, central nervous system and eyes, skin, muscles, etc. Intestinal parasites occur in humans more often than tissue.
In the pathogenesis of helminthiasis, the occurrence of allergic reactions and a serious degenerative process is of considerable importance. They appear 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. At later stages of worm development, the mechanical factor and the direct traumatic effect of the attachment 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 stool, sputum, and duodenal juice.
Serological reactions, radiographic and ultrasound examinations also play an important role in the diagnosis of helminthiasis.
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.