Parasitology is a science that studies the phenomenon of parasitism. The main task of such science is the study of 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 coming from different countries), the role of the science of parasitism in the health care of the modern world has increased many times. Let's then consider which parasites can live in the human body and which symptoms can arise from various infestations.
The number of people with immunodeficiency has increased, including patients with HIV infection, but also due to medical advances related to 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 such patients differs greatly from the usual reaction, which leads to the appearance of acute, atypical forms of the disease.
Also, human population activity causes global changes in climate conditions and natural landscape, which leads to the spread of infection vectors from endemic zones 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. So, 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 (the study of parasitic arthropods).
Relationships between organisms
Parasitism is a special way of relationship between organisms of different species, in which 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.
The parasite does not kill its host immediately; first it must be fed 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 the host.
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 a virus can become a "home" for parasites.
In this case, the parasitic individuals themselves become hosts for parasites of other classification groups of animals.
Parasitocenosis is the total number of absolutely all parasitic organisms that live in the host at the same time. The causative agent of the disease is parasitic organisms specific to different host species.
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 negatively affect it through several mechanisms:
- Cell and tissue damage;
- Influence on immune defense mechanisms and production of antibodies by the host;
- Sensitization of the host organism (hypersensitivity);
- The toxic effect of metabolic products of parasites.
The parasite development cycle 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; the stage of larval formation; the stage of an adult, sexually mature person.
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.
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 invasion caused by other animal organisms.
Due to the need to adhere to a parasitic lifestyle, three types of parasitism are distinguished:
- False parasitism. Accidental entry of a free-living individual into a host, which may be viable for some time and which may disrupt the normal processes of its life. False parasites are soon released into the environment (for example, in feces) or die after a short period of time. False parasitism is characteristic of some leeches, which accidentally enter the nasal cavity of people, 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 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 of a living organism and when they accidentally enter it (causing agents of myiasis).
- Real parasitism. This type of parasitism includes helminths, fleas, lice, etc.
| In relation to the host 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 be located only in one of the organs, but they are able to move to nearby ones, causing their damage. |
| By duration of contact | |
| A temporary parasite | Most often they are ectoparasites, their contact is usually short-lived |
| Stationary parasite | For such parasites, hosts are also a kind of "home". This way of parasitic lifestyle is divided into two types: periodic (the parasite spends part of the time in the host) and permanent |
| By specificity | |
| Polyspecific | Able to change different types of hosts, because they feed on the blood, epidermis and other tissues characteristic of many types of living things |
| Monospecific | Capable of parasitizing only certain host species (species). |
Owner 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 final host (otherwise the main, final, last) 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 stage of the parasite 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 (sources and hosts of the disease are humans), anthropozoonoses (sources and hosts are both humans and animals) and zoonoses (sources and hosts are animals).
Many infections are called natural focal infections, when pathogens move between wild animals in a certain area.
Methods for diagnosing parasitic infections
You cannot get rid of "parasites in the body" with a "magic pill" or folk remedies, you can cause even more damage to yourself. First, you need to understand what kind of invasion the person has. Macroscopic, microscopic and immunological methods are used to diagnose invasive diseases.
Macroscopic techniques enable the identification of infectious agents on external surfaces or in the feces of a sick person.
Microscopic methods also enable the identification of parasites in blood smears, tissue fluids, muscle tissue biopsies, as well as in sputum, feces, gastric and duodenal contents.
Parasitological research uses optical and electron microscopy methods using a light and electron microscope. Here, the diagnosis is, first of all, based on deep knowledge of the morphological structures of infectious agents, methods of preparation, fixation and staining of smear preparations.
Microscopy results depend on the choice of pathological material, their nature, the time of collection from the onset of symptoms and the examination period from the moment of receipt of the material.
Immunological diagnostic methods include serological and allergic reactions. Serological tests are used to:
- Determine the type of organisms, toxins, antigens using immunodiagnostic serums;
- Determine the nature of antibodies in blood serum using diagnostic antigens.
Basic serological reactions are reactions of agglutination, precipitation, lysis, binding of complement, neutralization and others. Methods of using labeled antibodies are also known: immunofluorescent reactions, enzyme immunosorbent assay, immunoblotting, radioimmunoassay.
Nucleic acid hybridization and polymerase chain reaction methods have found wide use in diagnostics.
Issues of preventive 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 feces.
- Settlements and toilets need to be improved.
- It is necessary to carry out sanitary supervision over the territories and water supply of inhabited places, as well as over the production, transport and sale of food products.
- It is important to carry out veterinary and sanitary supervision in slaughterhouses, meat processing factories, markets and livestock farms.
- It is necessary to identify and treat carriers of infections.
- It is necessary to protect people from damage from arthropods and to promote knowledge about personal prevention of parasitic diseases.
Anti-epidemic measures include active detection of infected persons and carriers, registration and treatment of the infected, hospitalization and medical examination if necessary, neutralization or destruction of the source of infection. Personal prevention is of great importance: hygienic measures, annual medical examination, proper preparation for tourist trips, solving the issue of chemoprophylaxis.
Chemoprophylaxis, i. e. administration of anthelmintics in risk groups and endemic areas 1 or 2 times a year, was developed by the WHO for vulnerable and developing countries.
General properties of protozoa
Protozoa are unicellular organisms that have a nucleus (eukaryotes).
The size is not larger than 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 one cell, which performs the function of both the cell and the organism as a whole. The shape of the body can be different: variable, elongated or spindle-shaped.
- Some protozoa are covered only by a cell membrane, while others have an elastic membrane called a pellicle.
- Cell cytoplasm is divided into: outer dense (ectoplasm) and inner (endoplasm). Cytoplasm may contain one or more nuclei.
- Nutrients enter in different ways: pinocytosis (absorption), phagocytosis (active eating), osmosis (swallowing substances due to the difference in concentration), active passage through the membrane.
- Gas exchange takes place throughout the cell due to the osmotic component. Waste products are also released from the entire cell surface and with the help of digestive vacuoles.
- Unicellular organisms reproduce both sexually and asexually.
- Unicellular organisms have different devices for movement: pseudopodia, flagella and cilia. They can respond to stimuli due to photo-, chemo- and thermotaxis and other mechanisms.
- In bad conditions, the parasitic protozoa turn into a cyst, i. e. they are 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, which continues an active life.
Detection of parasitic protozoa in patient materials presents almost no difficulties. A swab and an additional 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 are classified in the kingdom Protista, which includes seven types, of which only three are of medical importance.
Subphylum Sarcodae
Sarcodidae cell shape changes; the cell membrane forms protrusions, which can then return to their original shape, called pseudopods.
They make the cell move. Sarcodidae live absolutely everywhere: soil, fresh water, seas. Infectious diseases caused by Sarcodidae are common throughout the world, but are more commonly found in the tropics and subtropics.
Pathogenic amoeboid sarcoids most often affect the digestive system of humans, and they are intestinal parasites. Free-living amoebae of other orders also cause serious infections if they are accidentally ingested and become lodged in the human body.
A microscopic examination of the stool is used to diagnose amoebiasis. They contain vegetative or cystic forms of sarcode. During examination of stool preparations using a special heated table, it is possible to detect amoeba pseudopodia and their forward movement.
For the treatment of amoebiasis, drugs are used that 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 into 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 abscess rupture. The table below describes the main parasitic protozoa of the subphylum Sarcodidae.
Subphylum Flagellati
Representatives of the flagellar subtype, in addition to the cytoplasmic membrane, have a pellicle (such a shell gives a permanent 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 lies, without crossing its borders.
The flagellum starts from the kinetosome, which stores energy. Inside some flagellates is an axostyle - a thick cord inside the body that provides support.
The main symptoms and signs of infection in representatives of the flagellate subtype are shown in the table below.
| Representative/Localization | 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 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, foamy yellow discharge from the vagina. Asymptomatic carrying, 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 | Imprint smears, culture |
| African trypanosomes (Trypanosoma brucei gambiense and Trypanosoma brucei rhodesiense)/ Skin at the point 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, convulsions, exhaustion, acute heart failure, death | Examination of the bite site, lymph node biopsy. Thick drop and blood smear method, stained according to 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 a fatal outcome. Chronic form in adults who were ill in childhood - arrhythmia, extrasystole, dilation of the colon with wall hypertrophy, 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 uninfected bugs 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 node 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 staining according to Romanovski-Gimza, RIF, RSK, ELISA |
| Mucocutaneous leishmaniasis (Leishmania braziliensis) / Skin and mucous membranes | Skin lump, enlarged regional lymph nodes, skin ulceration, scar formation. On the mucous membranes - painless deforming lesions 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, addition of bacterial infections | Microscopic 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, exhaustion, intoxication, intestinal bleeding, diarrhea, grayish spots on face and head, death | Detection in biopsy smears of the spleen, lymph nodes, bone marrow, RIA, ELISA, RSK |
Sporozoans
Protozoans do not have organs for movement. 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 toxoplasmosis are prescribed 3 million units of spiromycin three times a day, every day for fourteen to twenty days.
Parasitic eyelashes
Ciliates do not change their body shape and have a pellicle. Motor maneuvers are performed due to the huge 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 vacuole, which ensures complete digestion of nutrients. Undigested parts of food come out through the powder, a special formation at the end of the body. The symptoms that can occur when these parasites are present in the intestines are shown in the table below.
| Pathogen | Localization | Symptoms | Diagnostics |
|---|---|---|---|
| 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 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.
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 of the 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 work activity of the population, the eating habits of different population groups and the economic state of the country. The following helminthiasis are the most common in our country.
Helminthic diseases are divided into geohelminthiasis and biohelminthiasis. For the development of geohelminth eggs or larvae, they need to be in the external environment to mature and acquire pathogenic properties. These are roundworms, whipworms, nekators and others.
Biohelminths go through their life cycle with an alternate host, and in order to acquire pathogenic properties, their eggs must enter an intermediate and sometimes an additional host. These are beef, 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), biliary tract 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 helminthiasis, the appearance of allergic reactions and a severe degenerative process is significant. They appear due to the large number of antigens that worms have.
Other factors of pathogenesis include the direct influence of enzymes that form larval forms and adults. In the later stages of worm development, the mechanical factor and the direct traumatic effect of the fixation organ 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, X-ray 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.