Parasitology is the science that studies the phenomenon of parasitism. The main task of such science is to study the relationship between the parasite and the host, 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's consider next what parasites can live in the human body, and what symptoms can arise from various attacks.
The number of people suffering from immunodeficiency has increased, including patients with HIV infection, and also due to advances in medicine related to the use of chemotherapy and developing transplantology.
All this leads to the fact that most diseases (attacks) caused by parasites, which usually occur without complications or without any symptoms at all, can be fatal in people with a weak immune system.
The response to the introduction of parasitic organisms in such patients is very different from the normal response, which leads to the emergence of an acute, atypical form of the disease.
In addition, human population activities trigger global changes in climatic conditions and natural landscapes, which lead to the spread of infection vectors from endemic zones to other areas and regions.
Medical parasitology is divided into several parts depending on the belonging of parasitic organisms to various groups: protozoan parasites, helminth parasites, arthropod parasites, etc. Therefore, science is divided into:
- Medical protozoology (study of parasitic protozoa, symptoms and treatment of protozoa);
- Medical helminthology (the study of parasitic 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, where 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.
Parasites do not kill their hosts immediately; first it must eat it repeatedly. During evolution, parasites have developed special interaction mechanisms with their hosts, which ensure the vital activity of all parasite species.
External natural conditions affect the parasite not directly, but indirectly, through the host.
The phenomenon of parasitism is quite widespread on this planet. Parasites can belong to any systematic group of all kingdoms of organisms. Any type of organism except viruses can be a "home" for parasites.
In this case, the individual parasite itself becomes a host for the parasite of another animal classification group.
Parasitocenosis is the total number of parasitic organisms living simultaneously in a host. The causative agents of these diseases are parasitic organisms specific to different host species.
Parasites that live 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 pathogenic.
Parasites in the human body have a negative effect on it through several mechanisms:
- Damage to cells and tissues;
- Effects on immune defense mechanisms and antibody production by the host;
- Sensitivity of the host organism (hypersensitivity);
- Toxic effects of metabolic products of the parasite.
The developmental cycle of a parasite is the total number of morphological phases of an organism's development, as well as indications 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; adult phase, sexually mature individuals.
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.
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 main symptoms of protozoa, helminthiasis and invasion caused by other animal organisms.
Due to the need to adhere to the lifestyle of the parasite, three types of parasitism are distinguished:
- False parasitism. The accidental introduction of free-living individuals into the host, which may be viable for some time and which are capable of disrupting the normal processes of its life. False parasites are immediately released into the environment (for example, in feces) or die after a short period. False parasitism exists in some leeches, which accidentally enter the human nasal cavity, 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 an organism 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 able to develop outside living organisms and when entering them accidentally (the causative agent of myiasis).
- True parasitism. This type of parasitism includes helminths, fleas, ticks, etc.
| Associated with the host body | |
|---|---|
| Ectoparasites | They live on the surface of the integument, feeding on blood cells and the upper layer of the skin. |
| Endoparasites | They live in the tissues, cells and cavities of their host. They can be located only in one of the organs, but can move to nearby ones, also causing damage |
| According to the duration of the relationship | |
| Temporary parasite | Often they are ectoparasites; their relationship is usually short-lived |
| Stationary parasites | For such parasites, the host is also a kind of "home". The lifestyle of this parasite is divided into two types: periodic (the parasite spends part of the time in the host) and permanent. |
| By specialty | |
| Polyspecific | Able to transform different types of hosts, because it feeds on blood, epidermis and other tissues that exist in different types of living things |
| Monospecific | Able to parasitize only certain species (species) of the host |
Concept of owner
A host is a living organism that the parasite uses as a source of nutrients and a place to live. Most individual parasites can change hosts, which is due to the presence of several stages during the parasite's life.
The definitive host (as opposed to primary, definitive, final) is the 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 parasite lives or a phase that reproduces only asexually.
Reservoir hosts - in which the parasite is viable, increases in number, but does not mature yet.
Parasitic diseases can be anthroponoses (the source of the disease and the host are humans), anthropozoonoses (the source and the host are humans and animals) and zoonoses (the source and the host are animals).
Many infections are called natural focal infections, when pathogens move between wild animals in a given area.
Methods for diagnosing parasitic infections
You cannot get rid of "parasites in the body" using "magic pills" or folk remedies; you can cause greater damage to yourself. First, you need to understand the type of aggression a person has. To diagnose invasive diseases, macroscopic, microscopic and immunological methods are used.
Macroscopic techniques make it possible to identify infectious agents on external surfaces or in the feces of an affected person.
Microscopic methods also allow to identify parasites in blood smears, tissue fluids, muscle tissue biopsies, as well as in sputum, feces, gastric and duodenal contents.
In the study of parasitology, optical and electron microscopy methods using light and electron microscopy are used. Here, the diagnosis is, first of all, based on in-depth knowledge of the morphological structure of the infectious agent, methods of preparation, fixation and staining of smear preparations.
Microscopic results depend on the choice of pathological material, its nature, the time of collection from the onset of symptoms, and the period of examination from the moment the material is received.
Immunological diagnostic methods include serological and allergic reactions. Serological tests are used for:
- To establish the type of organism, toxins, antigens using immune diagnostic sera;
- To determine the nature of antibodies in blood serum using diagnostic antigens.
Basic serological reactions are agglutination, precipitation, lysis, complement fixation, neutralization and others. Methods using labeled antibodies are also known: immunofluorescence reaction, enzyme-linked immunosorbent assay, immunoblotting, radioimmunoassay.
Nucleic acid hybridization and polymerase chain reaction methods have found widespread use in diagnostics.
The issue 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 human and animal excreta pollution.
- It is necessary to improve the populated areas and toilets.
- It is necessary to carry out sanitary supervision over the territory 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 in slaughterhouses, meat processing plants, markets, and livestock farms.
- It is necessary to identify and treat the carrier of the infection.
- It is necessary to protect people from damage by arthropods and to promote knowledge about the 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 the source of infection. Personal prevention is very important: hygiene measures, annual medical check-ups, proper preparation for tourist trips, solving chemoprophylaxis issues.
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).
Its size is not more than one millimeter, it is found everywhere and in all corners of the planet. Protozoan parasites are also divided into ectoparasites and endoparasites.
Characteristics of protozoa:
- The body consists of a single cell, which performs the functions of both the cell and the organism as a whole. The shape of the body can be changed: 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: dense outer (ectoplasm) and inner (endoplasm). The cytoplasm may contain one or more nuclei.
- Nutrients enter in various ways: through pinocytosis (absorption), phagocytosis (active feeding), osmosis (swallowing of substances due to concentration differences), active transition through the membrane.
- Gas exchange occurs throughout the cell due to the osmotic component. Waste materials are also removed from the entire cell surface and with the help of digestive vacuoles.
- Unicellular organisms reproduce sexually and asexually.
- Unicellular organisms have various tools for movement: pseudopodia, flagella and cilia. They can respond to stimuli due to photo-, chemo- and thermotaxis and other mechanisms.
- Under unfavorable conditions, parasitic protozoa turn into cysts, that is, they are covered with a dense capsule. In the cystic state, the life process stops.
Under favorable conditions, the cyst sheds its shell and changes into a vegetative form, which continues an active life.
Detection of parasitic protozoa in material from patients is almost without difficulty. Usually a smear and an additional drop of thick blood are examined.
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 structure.
Currently, all protozoa have been classified into the Protista kingdom, which includes seven types, of which only three are of medical importance.
Subgenus Sarcodae
Sarcodidae cell shape changes; the cell membrane forms a protrusion, which can then return to its original shape, called a pseudopod.
Because of them, cells move. Sarcodidae live completely everywhere: soil, fresh water bodies, sea. Infectious diseases caused by Sarcodidae are common worldwide, but are more commonly found in tropical and subtropical regions.
Pathogenic amoeboid sarcoid most often affects the human digestive system; these are intestinal parasites. Free-living amoebas from other orders also cause serious infections if accidentally ingested and settle in the human body.
To diagnose amoebiasis, microscopic examination of feces is used. It contains a vegetative or cystic form of sarcode. When examining preparations from feces using a specially heated table, it is possible to detect amoeba pseudopodia and their forward movement.
To treat amebiasis, drugs are used, which are divided into groups: contacts, which act on forms that live in the intestinal lumen, and systemic tissue amoebicides, which act on amoebas 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 threat of abscess rupture. The table below describes the main parasitic protozoa of the Sarcodidae subtype.
Subphylum Flagellates
Representatives of the flagella subtype, in addition to the cytoplasmic membrane, have a pellicle (such a shell gives a fixed shape) and flagella (one or many).
The flagellum contains contractile fibrils that allow it to move. Some representatives of flagellates have a corrugated membrane, inside which the flagellum/flagellum is located without going beyond its limits.
The flagellum originates from the kinetosome, which stores energy. In some flagellates there is an axostyle - a dense cord in the body that provides support.
The main symptoms and signs of infection by representatives of the flagellate subtype are presented in the table below.
| Representation/ Localization | symptoms | Diagnostics |
|---|---|---|
| Giardia (Lamblia intestinalis or Giardia lamblia) / Duodenum and small intestine | Nausea, heartburn, stomach ache, flatulence, heartburn, diarrhea, motion sickness, fatigue | Microscopy of duodenal contents, stool examination, ELISA for antibodies to Giardia |
| Trichomonas usus (Trichomonas hominis/intestinalis)/ Lower small intestine, large intestine | Colitis, enterocolitis, cholecystitis, diarrhea | Detection of vegetative and cystic forms in liquid feces of patients |
| 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, periodontal disease, ENT disease | Trace 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, bloodstream | Fever attacks, painful lymph nodes, skin rash, headache, drowsiness, tremors, paralysis, slurred speech, coma, seizures, fatigue, acute heart failure, death | Bite site examination, lymph node biopsy. Thick drop method 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 | Swelling of the skin 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 damage to the heart and brain with fatal results. Chronic form in adults who were sick in childhood - arrhythmia, extrasystole, colonic dilatation with wall hypertrophy, esophageal enlargement, 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), laboratory animal infections - for the chronic stage |
| Cutaneous leishmaniasis (Leishmania tropica)/Skin | Nodules on the skin, enlargement of regional lymph nodes, nodal ulcers with the formation of painless "dry" or "wet" ulcers, daughter wounds, scars on the skin after healing | Tissue microscopy from the bottom of the ulcer with Romanovsky-Giemsa staining, RIF, RSK, ELISA |
| Mucocutaneous Leishmaniasis (Leishmania braziliensis) / Skin and mucous membranes | Skin nodules, enlarged regional lymph nodes, skin ulcers, scar formation. On the mucous membranes - painless deformities 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, increased bacterial infection | 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, fatigue, hangover, intestinal bleeding, diarrhea, gray spots on face and head, death | Detection in smears from biopsy of spleen, lymph nodes, bone marrow, RIA, ELISA, RSK |
Sporozoa
Sporozoa have no locomotor organs. They take up 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 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 their body shape and have pellicle. Motor maneuvers are performed because a large number of cilia cover the entire cell.
Ciliates have two nuclei: a large one, 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 vacuole, which ensures complete digestion of nutrients. The undigested part of food comes out through powder, a special formation at the end of the body. Symptoms that may occur when this parasite is present in the intestine are shown in the table below.
| Pathogens | Localization | symptoms | Diagnostics |
|---|---|---|---|
| Balantidium coli | colon | Fever, hangover, stomach ache, diarrhea with mucus and blood, nausea, vomiting. Asymptomatic, cyst carrier | Detection in stool, colon biopsy |
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 human digestive tract, 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 state of the country's economy. 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 alternate hosts, and to acquire pathogenic properties, the eggs have to enter intermediate and sometimes additional hosts. These are cattle, pig 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), bile ducts and liver, bloodstream, central nervous system and eyes, skin, muscles, etc. Intestinal parasites occur in humans more often than in cloth.
In the pathogenesis of helminthiases, the appearance of severe allergic reactions and degenerative processes is very important. They appear because of the large number of antigens that worms have.
Other pathogenesis factors include the direct influence of enzymes that form larval and adult individuals. In the final stages of worm development, mechanical factors and direct traumatic effects of the fixation organ play an important role.
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-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 are the most widespread: 12 species of trematodes, 8 species of cestodes, 8 species of nematodes.