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 mutual influence, 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 healthcare of the modern world has increased several times. Let us now consider what parasites can live in the human body and what symptoms can result from various infestations.
The number of people with immunodeficiency has increased, including patients with HIV infection, and also due to medical advances associated with the use of chemotherapy and the development of transplantation.
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 such patients differs markedly from the usual reaction, which leads to the appearance of acute, atypical forms of the disease.
Furthermore, human population activity causes 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 whether parasitic organisms belong to various groups: protozoan parasites, helminth parasites, parasitic arthropods, and so on. Therefore 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 helminth infections);
- Parasitic entomology (study of parasitic arthropods).
Relationships between organisms
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 a source of food.
The parasite does not immediately kill its host; first he must 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 parasite species.
External natural conditions influence 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 same parasitic individuals become hosts of 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 specific parasitic organisms of 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 in the human body have a negative effect on it through several mechanisms:
- Damage to cells and tissues;
- Impact on immune defense mechanisms and on 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 stages of the organism's development, as well as an indication of the habitat of each stage, the route of infection and transmission.
For example, in the development of parasitic worms the following phases are distinguished: invasive phase – entry into the host's body; larval formation phase; stage of an adult, sexually mature individual.
Invasive diseases (infestations) are diseases caused by parasitic organisms. Invasive human diseases are divided into protozoan (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, we will next 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 into the host of a free-living individual, which may be viable for a time and which is capable of disrupting its normal life processes. False parasites are soon released into the environment (e. g. in feces) or die after a short period of time. False parasitism is inherent in some leeches, which accidentally enter the nasal cavity of people, where they live and cause bleeding, in mites and their eggs, which enter the stomach and are then expelled in the form of excrement, and in some amoebae.
- 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 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 can only be found in one of the organs, but they are able to move into nearby ones, also causing damage |
| By duration of contact | |
| Temporary parasite | Very often these are ectoparasites; their contact is usually short-lived |
| Stationary parasite | For these parasites, hosts are also a kind of "home". This method of parasitic life is divided into two types: periodic (the parasite spends part of the time in the host) and permanent |
| For specificity | |
| Polyspecific | Capable of changing different types of hosts, since they feed on blood, epidermis and other tissues inherent in many types of living things |
| Monospecific | Able to parasitize only some species (species) of hosts |
The concept 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 (otherwise main, definitive, last) is an organism where the parasite lives in the adult phase and can reproduce sexually.
An intermediate host is a host within which the parasite's larval phase lives or a phase that reproduces only asexually.
Reservoir host - within which the parasite is viable, increases in numbers, but does not mature further.
Parasitic diseases can be anthroponoses (source and host of the disease are humans), anthropozoonoses (source and host are both humans and animals) and zoonoses (source and host are animals).
Many infections are called natural focal infections, when pathogens move among wild animals in a certain area.
Methods for the diagnosis of parasitic infections
You cannot get rid of "parasites in the body" using a "magic pill" or folk remedies; you can cause even more damage to yourself. 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 make it possible to identify infectious agents on external surfaces or in the feces of an affected person.
Microscopic methods also allow you to identify parasites in blood smears, tissue fluids, biopsies of muscle tissues, as well as 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 mainly based on deep 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 collection time from the onset of symptoms and the examination period from the moment the material was received.
Immunological diagnostic methods include serological and allergic reactions. Serological tests are used for:
- 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 the reactions of agglutination, precipitation, lysis, complement binding, neutralization and others. Methods of using labeled antibodies are also known: immunofluorescence reactions, enzyme-linked immunosorbent assay, immunoblotting, radioimmunoassay.
Nucleic acid hybridization and polymerase chain reaction methods have found widespread use in diagnostics.
Problems 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.
- Populated areas and sanitation need to be improved.
- It is necessary to carry out sanitary control on the territories and water supply of populated areas, as well as on the production, transportation and sale of food products.
- It is important to carry out veterinary and health checks in slaughterhouses, meat processing plants, markets and farms.
- It is necessary to identify and treat carriers of infections.
- It is necessary to protect people from arthropod damage 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, resolution of the problem of chemoprophylaxis.
Chemoprophylaxis, i. e. 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 unicellular organisms with a nucleus (eukaryotes).
The size is no more than a millimeter, they are found everywhere and in all corners of the planet. The parasitic forms of protozoa are also divided into ectoparasites and endoparasites.
Characteristics of protozoa:
- The body consists 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 protozoans 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 enter in various ways: through pinocytosis (absorption), phagocytosis (active feeding), osmosis (ingestion of substances due to a difference in concentration), active transition across the membrane.
- Gas exchange occurs throughout the cell due to the osmotic component. Waste products are also released from across the surface of the cell and with the help of digestive vacuoles.
- Single-celled organisms reproduce both sexually and asexually.
- Unicellular organisms have various devices for movement: 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 a cystic state, the life process stops.
Under favorable conditions, the cyst loses its shell and turns into a vegetative form, which continues active life.
Detection of parasitic protozoa in a patient's materials presents almost no difficulty. Usually a smear and additionally a thick drop of blood are examined.
Stools are usually examined fresh using a heated table. To identify amoebic cysts, Lugol's solution is added to the feces, which colors the internal structures.
Currently all protozoa have been classified into the kingdom Protista, which includes seven types, of which only three are of medical importance.
Subtype Sarcodae
The cell shape of Sarcodids changes; the cell membrane forms protuberances, which can then return to their original shape, called pseudopodia.
Because of them, the cell moves. Sarcodids live absolutely everywhere: soil, freshwater bodies, seas. Infectious diseases caused by sarcodids are common throughout the world, but are most often found in tropical and subtropical areas.
Pathogenic amoeboid sarcodes most often affect the digestive system of people; these are intestinal parasites. Free-living amoebae of other orders also cause serious infections if accidentally ingested and settle in the human body.
Microscopic examination of feces is used to diagnose amoebiasis. They contain vegetative or cystic forms of sarcode. When examining preparations from feces using a special heated 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, which act on the forms that live in the intestinal lumen, and systemic tissue amoebae, which act on amoebae 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 risk of rupture of the abscess. The following table describes the main parasitic protozoa 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 more).
The flagellum contains contractile fibrils that allow it to move. Some representatives of the flagellates have a wavy membrane, inside which the flagellum/flagellum lies without going beyond its limits.
The flagellum originates from 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 flagellated subtype are presented in the table below.
| Representative/Locations | Symptoms | Diagnostics |
|---|---|---|
| Giardia (Lamblia intestinalis or Giardia lamblia) / Duodenum and small intestine | Nausea, heartburn, abdominal pain, flatulence, heartburn, diarrhea, body poisoning, exhaustion | Microscopy of the contents of the duodenum, stool examination, ELISA for 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 patient's liquid feces |
| Trichomonas vaginalis (Trichomonas vaginalis) / Vagina, cervical canal, urethra - in women. Urethra, prostate, testicles - in men | Affected, urethritis in women, itching, burning in the genital area, yellow foamy discharge from the vagina. Asymptomatic carriage, urethritis, prostatitis in men | Vaginal discharge in women, urethral discharge and prostatic discharge in men, PCR, culture |
| Oral trichomonas (Trichomonas tenax)/ Oral cavity, respiratory tract, tonsils, gums | Caries, periodontal disease, ENT diseases | Imprint stains, culture |
| African trypanosomes (Trypanosoma brucei gambiense and Trypanosoma brucei rhodesiense)/ Skin at the point of penetration, lymph nodes in the neck and back of the head, blood flow | Attacks of fever, painful lymph nodes, rash, headache, drowsiness, tremors in limbs, paralysis, slurred speech, coma, seizures, 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 | Swelling of the skin at the site of penetration, enlargement of nearby lymph nodes, swelling of the eyelids, enlargement of the parotid lymph nodes. The acute form in newborns causes damage to the heart and brain with fatal outcomes. The chronic form in adults sick during 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 phase |
| Cutaneous leishmaniasis (Leishmania tropica)/Skin | Lump on the skin, enlarged 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 tissue from the bottom of the ulcer with Romanovsky-Giemsa staining, RIF, RSK, ELISA |
| Mucocutaneous leishmaniasis (Leishmania braziliensis) / Skin and mucous membranes | Skin lump, swollen regional lymph nodes, skin ulceration, scar formation. 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, 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 | Enlarged liver, spleen, anemia, tiredness, intoxication, intestinal bleeding, diarrhea, grayish spots on the face and head, death | Detection in smears from biopsies of spleen, lymph nodes, bone marrow, RIA, ELISA, RSK |
Sporozoa
Sporozoans have no moving organs. They consume 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 the shape of their body and have a pellicle. Motor maneuvers are performed due to the huge 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, ensuring complete digestion of nutrients. The undigested parts of the food come out through the dust, a special formation at the extremity of the body. The symptoms that can occur when these parasites are present in the intestine are presented in the table below.
| Pathogen | Location | Symptoms | Diagnostics |
|---|---|---|---|
| Balantidium coli | Colon | Fever, intoxication, abdominal pain, diarrhea with mucus and blood, nausea, vomiting. Asymptomatic, carrier of cysts | Detection in stool, colon biopsies |
The treatment of balantidiasis involves 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 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 carry out their activity in the digestive tract of people, others can attack parenchymal organs, blood and genitourinary system.
The spread of helminths depends on the working activity of the population, the eating habits of the various population groups 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 geohelminth eggs or larvae it is necessary for them 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 a replacement host, and to acquire pathogenic properties, their eggs must enter an intermediate and sometimes an additional host. These are cattle, pork 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 intestine (intestinal helminthiasis), in the biliary tract and liver, in the bloodstream, in the central nervous system and in the eyes, in the skin, in muscles, etc. Intestinal parasites occur in humans more often than tissue.
In the pathogenesis of helminthiasis, the appearance of allergic reactions and a severe degenerative process are of considerable importance. They appear due to the large number of antigens that worms have.
Other factors of pathogenesis include the direct influence of enzymes forming larval forms and adult individuals. In the later stages of the development of the worm, the mechanical factor and the direct traumatic effect of the fixation 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 feces, sputum, and duodenal juice.
Serological reactions, radiographic examinations and ultrasound also play an important role in the diagnosis of helminthiasis.
In general, approximately three hundred species of pathogenic worms have been found in humans, of which twenty-eight are the most widespread: 12 species of trematodes, 8 species of tapeworms, 8 species of nematodes.