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 depends on environmental factors.
The role of the science of parasitism in the health care of the modern world has increased several times due to the increase in population migration (due to the development of tourism and the increase in the number of visitors from different countries). Let's then consider what parasites can live in the human body and what symptoms can arise from various infestations.
The number of people with immunodeficiency, including those infected with HIV, has increased, as have medical advances in 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, can be fatal in people with weakened immune systems.
In such patients, the reaction to the injection of parasitic organisms is very different from the usual reaction, which leads to the emergence of acute, atypical forms of the disease.
Also, human population activities cause global changes in climatic conditions and natural landscape, which lead to the spread of infection vectors from endemic areas to other areas and regions.
Medical parasitology is divided into several sections depending on the affiliation of parasitic organisms 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 helminth worms, symptoms and treatment of helminth infections);
- Parasitic entomology (the study of parasitic arthropods).
Relationships between organisms
Parasitism is a special way of communication between different types of organisms, one of which (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 the host immediately, it must first feed on it repeatedly. During evolution, parasites have developed special mechanisms of interaction with their hosts that ensure the life activity of all parasite species.
External natural conditions affect parasites not directly, but indirectly, through their 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 other than viruses can be a "home" for parasites.
At this time, the parasitic individuals themselves become hosts for parasites of other classification groups of animals.
Parasitocenosis is the total number of 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 inside the host not only feed, but also cause various diseases that can lead to the death of the patient. This phenomenon is called pathogenicity.
Parasites in the human body have a negative effect on it through several mechanisms:
- Damage to cells and tissues;
- Effect on immune defense mechanisms and antibody production by the host;
- Sensitization of the host organism (high sensitivity);
- Toxic effect of metabolic products of parasites.
The developmental cycle of the parasite is the total number of morphological phases of the organism's development, as well as 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; stage of larval formation; the stage of an adult, sexually mature individual.
Invasive diseases (invasions) are diseases caused by parasitic organisms. Invasive human diseases are divided into diseases caused by protozoa (caused by protozoa), helminthoses (parasitic worms) and arthropods.
Symptoms 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 invasions caused by the main protozoa, helminthosis and other animal organisms.
Three types of parasitism are distinguished according to the need to follow a parasitic lifestyle:
- False parasitism. The accidental entry into the host of a free-living individual capable of living for a period of time and disrupting the normal processes of its life. Pseudoparasites are soon released into the environment (e. g. in faeces) or die after a short time. False parasitism is characteristic of some leeches that accidentally enter the nasal cavity of humans and live and cause bleeding, ticks and their eggs that enter the stomach and are then excreted in the feces, 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 can develop outside the living organism and accidentally enter it (causing miosis).
- 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 bark, feeding on blood cells and the upper layers of the skin. |
| Endoparasites | They live in the tissues, cells and cavities of their hosts. They can be located only in one of the organs, but they can pass to nearby ones and cause their damage. |
| With contact period | |
| A temporary parasite | Often they are ectoparasites, their contact is usually short-lived |
| A stationary parasite | Hosts are also a kind of "home" for such parasites. This mode of parasitic lifestyle is divided into two types: periodic (the parasite spends part of its time in the host) and permanent. |
| Due to specificity | |
| Polyspecific | As it feeds on the blood, epidermis and other tissues characteristic of many species of living things, it can change hosts of different species. |
| Monospecific | It can parasitize only certain species (species) of the host |
Concept of the owner
A host is a living organism that a parasite uses as a food source and habitat. Most of the parasite individuals can change the host, which is due to the fact that there are several stages during the life of the parasite.
The definitive host (otherwise primary, definitive, final) is the organism in which the parasite lives in its adult phase and can reproduce sexually.
An intermediate host is the host in which the larval phase of the parasite lives, or the phase that reproduces only sexually.
Reservoir owner - the parasite is viable in it, increases in number, but does not mature further.
Parasitic diseases can be anthroponoses (the source and hosts of the disease are humans), anthropozoonoses (the sources and hosts are both humans and animals), and zoonoses (the sources and hosts are animals).
Many infections are called natural foci infections when pathogens move between wild animals in a given area.
Diagnostic methods of parasitic infections
You cannot get rid of "parasites in the body" with a "magic pill" or folk remedies, you can do even more harm to yourself. First, you need to understand what occupation a person is subjected to. Macroscopic, microscopic and immunological methods are used to diagnose invasive diseases.
Macroscopic methods allow identifying infectious agents on external surfaces or feces of an affected person.
Microscopic methods also allow identification of parasites in blood smears, tissue fluids, muscle tissue biopsies, as well as in sputum, feces, stomach and duodenum.
Optical and electron microscopy methods are used in parasitological studies using light and electron microscopes. Here, the diagnosis is primarily based on in-depth knowledge of the morphological structures of infectious agents, preparation, fixation and staining of smears.
The results of microscopy depend on the selection of pathological materials, their nature, the time of collection from the onset of symptoms, and the examination period from the moment the material is taken.
Immunological diagnostic methods include serological and allergic reactions. Serological tests are used for:
- To determine the type of organisms, toxins, antigens using immunodiagnostic sera;
- To determine the nature of antibodies in blood serum using diagnostic antigens.
The main serological reactions are agglutination, precipitation, lysis, binding of complements, neutralization, etc. reactions. Methods of using labeled antibodies are also known: immunofluorescence reactions, enzyme-linked immunosorbent assay, immunoblotting, radioimmunoassay.
Nucleic acid hybridization and polymerase chain reaction methods are widely used in diagnostics.
Issues of prevention and anti-epidemic measures
Preventive measures for all parasitic diseases can be summarized as follows:
- Soil and water sources should be protected from contamination by human and animal feces.
- It is necessary to improve living quarters and toilets.
- It is necessary to carry out sanitary control of the water supply of territories and settlements, as well as the production, transportation and sale of food products.
- It is important to carry out veterinary-sanitary control in slaughterhouses, meat processing plants, markets, livestock farms.
- Carriers of infections should be identified and treated.
- It is necessary to protect people from the damage of arthropods and promote knowledge on individual prevention of parasitic diseases.
Anti-epidemic measures include active detection of infected persons and carriers, registration and treatment of infected persons, 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, taking anthelmintic drugs 1 or 2 times a year in risk groups and endemic areas, was developed by WHO for disadvantaged and developing countries.
General characteristics of protozoa
Protozoa are unicellular organisms (eukaryotes) with a nucleus.
Their size does not exceed one 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 organism as a whole. The body shape can be different: variable, elongated or spindle-shaped.
- Some protozoa are covered only by a cell membrane, while others have a flexible membrane called a pellicle.
- The cell cytoplasm is divided into: outer dense (ectoplasm) and inner (endoplasm). There may be one or more nuclei in the cytoplasm.
- Nutrients enter in different ways: pinocytosis (absorption), phagocytosis (active eating), osmosis (absorption of substances due to concentration difference), active passage through the membrane.
- Thanks to the osmotic component, gas exchange occurs throughout the cell. Waste products are also removed 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 through photo-, chemo- and thermotaxis and other mechanisms.
- In poor conditions, the parasite turns into a protozoan cyst, that is, it is 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 that continues an active life.
Detection of parasitic protozoa in the patient's materials is almost no difficulty. Usually a smear and additionally a thick drop of blood is examined.
Stool is 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 time, all protozoa were classified into the kingdom Protista, which consisted of seven species, of which only three were of medical importance.
Subgenus Sarcodae
Sarcodidae cells change shape, the cell membrane forms protrusions, which can later return to their original shape called pseudopods.
Thanks to them, the cell moves. Sarcodidae live absolutely everywhere: soil, freshwater bodies, seas. Infectious diseases caused by Sarcodidae are distributed worldwide, but are more common in the tropics and subtropics.
Pathogenic amoeboid sarcoids mostly affect the digestive system of humans, they are intestinal parasites. Free-living amoebae of other orders also cause serious infections when accidentally introduced and colonized in the human body.
Microscopic examination of feces is used to diagnose amoebiasis. They contain vegetative or cystic forms of sarcoid. When examining stool preparations using a special heated table, it is possible to detect the pseudopodia of amoebas and their forward movements.
Drugs divided into groups are used to treat amebiasis: systemic tissue amoebicides, which affect forms living in the intestinal lumen, and systemic amoebicides, which affect amoebae that penetrate the tissue of the intestine and other organs.
In addition to treatment, liver abscess aspiration is performed when chemotherapy is ineffective or there is a threat of abscess rupture. The table below describes the main parasitic protozoa of the subphylum Sarcodidae.
Subphylum Flagellates
Representatives of the flagellar subtype, in addition to the cytoplasmic membrane, have a pellicle (such a shell provides a stable shape) and flagella (one or more).
The flagellum has contractile fibrils that allow it to move. Some representatives of flagella have a wavy membrane, inside which the flagellum/flagella is located without going beyond its boundaries.
The flagellum originates from the energy-harvesting kinetosome. Some flagellates have an axostyle - a tight cord that provides support inside the body.
The main symptoms and signs of infection by representatives of the flagellate subspecies 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 the determination of antibodies against Giardia |
| Intestinal Trichomonas (Trichomonas hominis/intestinalis)/ Lower small intestine, large intestine | Colitis, enterocolitis, cholecystitis, diarrhea | Detection of vegetative forms and cysts in the liquid feces of the patient |
| 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 | Tracking spots, culture |
| African trypanosomes (Trypanosoma brucei gambiense and Trypanosoma brucei rhodesiense)/ Skin, neck and back of the head lymph nodes at the site of penetration, blood circulation | Fever attacks, painful lymph nodes, skin rash, headache, drowsiness, tremors, paralysis, slurred speech, coma, convulsions, fatigue, acute heart failure, death | Examination of the bite site, biopsy of lymph nodes. Wright or Romanowski-Giemsa-stained thick drop and blood smear method, 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 the nearby lymph nodes, swelling of the eyelids, enlargement of the parotid lymph nodes. In newborns, the acute form damages the heart and brain with fatal outcome. Chronic form in adults who were sick in childhood - arrhythmia, extrasystole, expansion of the large intestine with wall hypertrophy, expansion of the esophagus, myxedema, paralysis. | Microscopy of blood smear, 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 | Nodule on the skin, enlargement of regional lymph nodes, ulceration of the nodule with the formation of "dry" or "wet" painless ulcers, daughter lesions, scar on the skin after healing | Microscopy of the tissue from the bottom of the ulcer with Romanovski-Giemsa stain, RIF, RSK, ELISA |
| Mucocutaneous leishmaniasis (Leishmania braziliensis) / Skin and mucous membranes | Skin nodule, enlarged regional lymph nodes, skin ulcer, scar formation. In the mucous membranes - painless deforming lesions of the mouth and nose, ulcers on the tongue, mucous membrane of the cheeks and nose, 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 spleen, liver, bone marrow, lymph nodes | Enlarged liver, spleen, anemia, fatigue, intoxication, intestinal bleeding, diarrhea, grayish spots on face and head, death | Detection of smears from spleen, lymph nodes, bone marrow, RIA, ELISA, RSK biopsies |
Sporozoa
Sporozoa do not have movement organs. They consume nutrients in 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 tochoplamosis are prescribed 3 million units of spiromycin three times a day for fourteen to twenty days.
Parasitic cilia
Cilia do not change the shape of their body and have a pellicle. Motor maneuvers are carried out due to the large number of cilia covering the entire cell.
Ciliates have two nuclei: one is large, responsible for cell metabolism, and the other is small, which transmits genetic information.
Ciliates have an organized digestive system: cytostome is the mouth of the cell, cytopharynx is the pharynx of the cell. Digestive enzymes are gradually released from vacuoles, which ensures complete digestion of nutrients. Undigested parts of food come out through dust, a special formation at the end of the body. Symptoms that may occur when these parasites are in the intestines are presented in the table below.
| Pathogenic | Localization | Symptoms | Diagnostics |
|---|---|---|---|
| Balantidium coli | Colon | Fever, intoxication, abdominal pain, mucous and bloody diarrhea, nausea, vomiting. Asymptomatic, cyst carrier | Detection in stool, colon biopsies |
Treatment of balantidiasis includes the appointment 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 of the worms work in the digestive system of humans, others can attack parenchymal organs, blood and genitourinary system.
The spread of helminths depends on the labor activity of the population, the eating habits of different population groups, and the economic situation of the country. The following helminthoses are the most common in our country.
Helminth diseases are divided into geohelminthosis and biohelminthosis. 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 spend their life cycle with an alternate host, and their eggs must enter an intermediate and sometimes an additional host to acquire pathogenic properties. These are bovine, pork tapeworm, opistorchis, 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. more often in humans than cloth.
The appearance of allergic reactions and severe degenerative process is of great importance in the pathogenesis of helminthiasis. They appear due to the large number of antigens that worms have.
Other factors of pathogenesis include the direct effect of enzymes that produce larval forms and adults. In the later stages of worm development, the mechanical factor and the direct traumatic effect of fixation organs play an important role.
Diagnoses are usually confirmed by interview, clinical picture of the disease, 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 helminthiasis.
In general, about three hundred types of pathogenic worms have been found in humans, of which twenty-eight types are the most common: 12 types of trematodes, 8 types of cestodes, 8 types of nematodes.