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 (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 healthcare in the modern world has increased several times. Let's consider below which 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 medical progress 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 a weakened immune system.
The response to the introduction of parasitic organisms in these patients differs greatly from the usual reaction, which leads to the appearance of acute and atypical forms of the disease.
Furthermore, the activity of the human population causes 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 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 helminthic infections);
- Parasitic entomology (study of parasitic arthropods).
Relationships between organisms
Parasitism is a special form 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 a source of food.
The parasite does not kill its host immediately; first he 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 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, except viruses, can become a "home" for parasites.
In this case, the parasitic individuals themselves become hosts for parasites from other animal classification groups.
Parasitocenosis is the total number of absolutely all parasitic organisms living simultaneously in the host. The causative agent of the disease are specific parasitic organisms from different host species.
The 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 the production of antibodies 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 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 in the development of parasitic worms are distinguished: invasive phase – entry into the host's body; larval formation phase; stage of a sexually mature adult individual.
Invasive diseases (infestations) 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.
The signs of parasites in the human body are so diverse that it makes no sense to consider them as a whole. Therefore, below 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 disturbing the normal life processes of the host. The false parasites are soon released into the environment (e. g. in feces) or die after a short time. False parasitism is inherent in some leeches, which accidentally enter people's nasal cavities, 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 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 may only be located in one of the organs, but they are capable of moving to the next ones, also causing damage. |
| By duration of contact | |
| Temporary parasite | Most of the time they are ectoparasites; your contact is usually short-lived |
| Stationary parasite | For these parasites, hosts are also a kind of "home". This method of parasitic lifestyle is divided into two types: periodic (the parasite spends part of its 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 to different types of living beings |
| Monospecific | Able to parasitize only certain species (species) of hosts |
The owner's 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 parasite's life.
The definitive host (otherwise, main, definitive, last) is an organism where the parasite lives as an adult and can reproduce sexually.
An intermediate host is a host within which the larval stage of parasites 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 (the sources of the disease and hosts are humans), anthropozoonosis (the sources and hosts are humans and animals) and zoonoses (the sources and hosts 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 a "magic pill" or folk remedies; you can do even greater harm to yourself. First, you need to understand what type of invasion a person suffers from. 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 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 are used using optical and electron microscopes. Here, the diagnosis is based, first of all, on in-depth knowledge of the morphological structures of infectious agents, methods of preparation, fixation and staining of smears.
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 of receipt of the material.
Immunological diagnostic methods include serological and allergic reactions. Serological tests are used to:
- Establish the type of organisms, toxins, antigens using immunological diagnostic sera;
- To determine the nature of antibodies in blood serum using diagnostic antigens.
The basic serological reactions are agglutination, precipitation, lysis, complement binding, neutralization and other reactions. Methods for using labeled antibodies are also known: immunofluorescence reactions, immunoenzymatic assay, immunoblotting, radioimmunoassay.
Nucleic acid hybridization and polymerase chain reaction methods have been widely used in diagnostics.
Prevention issues 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 excreta.
- It is necessary to improve populated areas and bathrooms.
- Sanitary inspection of territories and the water supply of populated areas, as well as the production, transport and sale of food products, is necessary.
- It is important to carry out veterinary and health inspections in slaughterhouses, slaughterhouses, markets and livestock farms.
- It is necessary to identify and treat carriers of infections.
- It is necessary to protect people from damage 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, adequate preparation for tourist trips, resolving 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 properties of protozoa
Protozoa are single-celled organisms that have a nucleus (eukaryotes).
The size is no more than a millimeter, they are found everywhere and in every corner of the planet. The parasitic forms of protozoa are also divided into ectoparasites and endoparasites.
Characteristics of protozoa:
- The body is made up of a cell, which performs the function of both the cell and 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 outer (ectoplasm) and inner (endoplasm). The cytoplasm may contain one or more nuclei.
- Nutrients enter in several ways: by pinocytosis (absorption), phagocytosis (active feeding), osmosis (ingestion of substances due to the 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 several movement devices: pseudopods, flagella and cilia. They can respond to stimuli due to photo-, chemo- and thermotaxis and other mechanisms.
- In poor conditions, parasitic protozoa transform into cysts, that is, they are covered by a dense capsule. In the cystic state, the vital process is interrupted.
Under favorable conditions, the cyst loses its shell and takes on 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, additionally, a thick drop of blood are usually examined.
Feces are usually examined fresh on a heated table. To detect amoebic cysts, Lugol's solution is added to the stool, which stains the internal structures.
At this time, all protozoa have been classified into the kingdom Protista, which includes seven types, only three of which are of medical importance.
Subtype Sarcodae
The cell shape of Sarcodidae changes; the cell membrane forms protrusions, which can then return to their original shape, called pseudopodia.
Due to them, the cell moves. Sarcodids live anywhere: soil, freshwater bodies, seas. Infectious diseases caused by Sarcodidae are common throughout the world, but are most often found in the tropics and subtropics.
Pathogenic amoeboid sarcodes most often affect people's digestive systems; these are intestinal parasites. Amoebas from other orders that live freely also cause serious infections if accidentally ingested and settle in the human body.
To diagnose amoebiasis, microscopic examination of feces is used. They contain vegetative or cystic forms of sarcodium. By examining fecal preparations on a special heated table, it is possible to detect amoeba pseudopods 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 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 rupture of the abscess. The table below describes the main protozoan parasites 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 several).
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 limits.
The flagellum begins at the kinetosome, which stores energy. Inside some flagellates there is an axostyle - a dense cord within the body that provides support.
The main symptoms and signs of infection by representatives of the flagellate subtype are presented in the following table.
| Representative/Locations | Symptoms | Diagnosis |
|---|---|---|
| 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 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 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, yellow frothy vaginal discharge. 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 | Impression 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 | Fever attacks, painful lymph nodes, rash, headache, drowsiness, limb tremors, paralysis, slurred speech, coma, convulsions, exhaustion, acute heart failure, death | Examination of the bite site, 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. The chronic form in adults who suffered in childhood - arrhythmia, extrasystole, dilation of the colon with hypertrophy of the wall, 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 of uninfected insects from the patient's body and detection of trypanosomes in their feces), infection of laboratory animals - for the chronic stage |
| Cutaneous leishmaniasis (Leishmania tropica)/Skin | Lump on the skin, enlargement of regional lymph nodes, ulceration of the lymph node with the formation of painless "dry" or "wet" ulcers, daughter lesions, scarring 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 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 secretion from ulcers, biopsy of damaged organs, RSK, RNGA |
| Visceral leishmaniasis (Leishmania donovani)/ Cells of the spleen, liver, bone marrow, lymph nodes | Enlargement of the liver, spleen, anemia, exhaustion, intoxication, hemorrhages in the intestines, diarrhea, gray spots on the face and head, death | Detection in smears from biopsies of spleen, lymph nodes, bone marrow, RIA, ELISA, RSK |
Sporozoa
Sporozoa do not have movement organs. They consume nutrients throughout the body and often exhibit intracellular parasitism. Sporozoa include the causative agents of malaria and toxoplasma. Toxoplasmosis is most dangerous for pregnant women and people with proven immunodeficiency (for example, against the background of HIV infection).
Pregnant women with toxoplasmosis are given 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 film. Motor maneuvers are carried out due to the large number of cilia that cover 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. The undigested parts of the food come out through the dust, a special formation at the end of the body. The symptoms that may occur when these parasites are present in the intestine are presented in the table below.
| Pathogen | Location | Symptoms | Diagnosis |
|---|---|---|---|
| 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 prescribing antibacterial and antiprotozoal medications according to one of the following regimens.
General characteristics of helminths
Helminthology is the science of worms (helminths) that parasitize the bodies 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 act in people's digestive tract, others can attack parenchymal organs, blood and genitourinary system.
The spread of helminths depends on the population's work activity, the eating habits of different population groups and the country's economic situation. The following helminthiases are the most common in our country.
Helminth diseases are divided into geohelminthiasis and biohelminthiasis. For geohelminth eggs or larvae to develop, they need to be in the external environment to mature and acquire pathogenic properties. They are roundworms, whipworms, necadores and others.
Biohelminths go through their life cycle with a substitute host and, to acquire pathogenic properties, their eggs need to enter an intermediate host and, sometimes, an additional host. These are cattle, pork tapeworm, opistorchis, 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, bloodstream, central nervous system and eyes, skin, muscles, etc. in humans more often than tissue.
In the pathogenesis of helminthiasis, the appearance of allergic reactions and a severe degenerative process is of considerable importance. They appear due to the large number of antigens that the worms have.
Other pathogenesis factors 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 attachment organs play an important role.
The 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, 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.