Parasitology is a science that studies the phenomenon of parasitism. The main task of this kind of science is to investigate the relationship between parasites and host organisms and their effect on each other, which also depends on environmental factors.
Due to the increase in population migration (due to the development of tourism and 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 multiplied. In the following, let's see what parasites can live in the human body and what symptoms can be caused by different infections.
The number of immunocompromised people has increased, including the number of people infected with HIV, due to the development of medicine related to the use of chemotherapy and the development of transplantology.
All of this leads to the fact that most parasitic diseases (infections), which are usually uncomplicated or asymptomatic, can be fatal in people with a weakened immune system.
In such patients, the response to the introduction of parasitic organisms differs greatly from the usual response, leading to the appearance of acute, atypical forms of the disease.
The activity of the human population also provokes global changes in climatic conditions and the natural landscape, which leads to the spread of infection vectors from endemic zones to other areas and regions.
Medical parasitology is divided into several parts depending on whether the parasitic organisms belong to different groups: protozoan parasites, helminth parasites, parasitic arthropods, etc. Thus, science is divided into:
- Medical protozoology (examination of parasitic protozoa, symptoms and treatment of protozoa);
- Medical helminthology (examination of parasitic worms, symptoms and treatment of worm infections);
- Parasitic entomology (study of parasitic arthropods).
Relationships between living things
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 permanent or temporary place of residence and as a source of food.
The parasite does not kill its host immediately, it must first feed on it repeatedly. During evolution, parasites have developed special mechanisms of interaction with their hosts that ensure the vital activity of all parasite species.
The external natural conditions do not affect the parasites directly, but indirectly, through the host organisms.
The phenomenon of parasitism is quite widespread on the planet. Parasites can belong to any systematic group in any kingdom of organisms. Except for viruses, any type of organism can become a "home" for parasites.
In this case, the parasitic individuals themselves become the hosts of parasites belonging to other classification groups of animals.
The parasitocenosis is the total number of absolutely all parasitic organisms living simultaneously in the host. The causative agent of the disease are parasitic organisms characteristic of different host species.
Parasites living 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 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 host antibody production;
- Sensitization of the host (hypersensitivity);
- The 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 indication of the habitat of each phase, the route of infection and spread.
For example, the following phases are distinguished in the development of parasitic worms: invasive phase – entry into the host; larval stage; the phase of an adult, sexually mature individual.
Invasive diseases (infections) are diseases caused by parasitic organisms. Invasive human diseases are divided into protozoa (caused by protozoa), helminthiasis (parasitic worms) and arthropod parasitic diseases.
Signs of parasites in the human body are so diverse that it makes no sense to consider them as a whole. Therefore, the main protozoa, helminthiasis and the symptoms of invasion by other animal organisms will be examined below.
Due to the need to adhere to the parasitic lifestyle, we distinguish three types of parasitism:
- False parasitism. The accidental introduction of a free-living individual into the host organism, which may be viable for a period of time, and which is capable of disrupting its normal life processes. False parasites are quickly released into the environment (e. g. in faeces) or die within a short time. Pseudoparasitism is characteristic of some leeches that accidentally enter the nasal cavity of humans where they live and cause bleeding, mites and their eggs that enter the stomach and are excreted in the feces, and some amoebas.
- Facultative parasitism is the ability of organisms to live with or without a host. The viability of the parasite lasts longer than in the first case. This type is typical of fly larvae that can develop outside the living organism and accidentally enter them (the causative agents of myiasis).
- True parasitism. These types of parasites include helminths, fleas, lice, etc.
| Relative to the host | |
|---|---|
| Ectoparasites | They live on the surface of the skin tissue, 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 only be located in one organ, but they can move to nearby organs, causing damage |
| According to the duration of the contact | |
| A temporary parasite | Most often, they are ectoparasites, and their contact is usually short-lived |
| Stationary parasite | For such parasites, hosts are also a kind of "home". This method of parasitic lifestyle is divided into two types: periodic (the parasite spends part of the time in the host's body) and permanent. |
| By specificity | |
| Polyspecific | Able to alter different types of host as they feed on blood, epithelium, and other tissues found in a wide variety of organisms |
| Monospecific | It can only parasitize certain host species (species). |
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 are able to change hosts, which is due to the fact that the parasite is present in several stages during its life.
The definitive host (in other words, the main, definitive, last) is an 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 parasites lives, or a stage that only reproduces asexually.
Reservoir host – in which the parasite is viable, reproduces, 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 known as natural outbreaks, when pathogens move among wildlife in an area.
Methods of diagnosing parasitic infections
It is not possible to get rid of "parasites in the body" with "magic pills" or folk remedies, we can cause even greater damage to ourselves. First of all, you need to understand what kind of invasion a person has. Macroscopic, microscopic and immunological methods are used to diagnose invasive diseases.
Macroscopic techniques allow the identification of infectious agents on the external surface or in the feces of the affected person.
Microscopic methods make it possible to identify parasites in blood smears, tissue fluids, muscle tissue biopsies, as well as in sputum, feces, stomach and duodenal contents.
During the parasitological examinations, light and electron microscopic optical and electron microscopic methods are used. Here, the diagnosis is primarily based on in-depth knowledge of the morphological structure of infectious agents, the methods of preparation, fixation and staining of smear preparations.
The result of the microscopic examination depends on the choice and nature of the pathological material, the time of the appearance of the symptoms, the time of collection, and the duration of the examination from the receipt of the material.
Immunological diagnostic methods include serological and allergic reactions. Serological tests are used to:
- Determination of the type of organisms, toxins, antigens with the help of immunodiagnostic serums;
- Determination of the nature of antibodies in blood serum using diagnostic antigens.
The basic serological reactions are agglutination, precipitation, lysis, complement fixation, neutralization and others. Methods of using labeled antibodies are also known: immunofluorescence reactions, enzyme-linked immunosorbent assay, immunoblot, 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 must be protected from contamination by human and animal excreta.
- Residential areas and toilets need to be repaired.
- Sanitary surveillance must be carried out over the territory and water supply of inhabited areas, as well as over the production, transport and sale of food.
- It is important to carry out animal health surveillance in slaughterhouses, meat processing plants, markets and livestock farms.
- It is necessary to identify and treat the carriers of the infection.
- Protect people from harm caused by arthropods and promote knowledge of 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, proper preparation for tourist trips, solving the issue of chemoprophylaxis.
Chemoprophylaxis, i. e. the administration of anthelmintics 1-2 times a year in risk groups and endemic areas, was developed by the WHO for disadvantaged and developing countries.
General properties of protozoa
Protozoa are single-celled organisms that have a nucleus (eukaryotes).
Their size does not exceed one millimeter, they can be found everywhere and in every corner of the planet. 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 spindle-shaped.
- Some protozoans are covered only by a cell membrane, while others have a flexible membrane called a pellicle.
- The cytoplasm of the cell is divided into: outer dense (ectoplasm) and inner (endoplasm). The cytoplasm may contain one or more nuclei.
- Nutrients enter in several ways: pinocytosis (absorption), phagocytosis (active eating), osmosis (swallowing substances due to a difference in concentration), active transition through the membrane.
- Gas exchange takes place 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 cavities.
- Unicellular organisms reproduce both sexually and asexually.
- Unicellular organisms have various means of locomotion: pseudopodia, flagella, and cilia. They are able to respond to stimuli caused by photo-, chemo- and thermotaxis and other mechanisms.
- Under adverse conditions, the parasitic protozoans turn into a cyst, i. e. they are covered by a dense capsule. In the cystic state, the life process stops.
Under favorable conditions, the cyst sheds its shell and transforms into a vegetative form that continues its active life.
The detection of parasitic protozoa in material from the patient causes almost no difficulties. A smear and a thick drop of blood are usually examined.
Feces are usually examined fresh using a heated table. To detect amoebic cysts, Lugol's solution is added to the stool, which stains the internal structures.
Currently, all protozoa are classified into the kingdom Protista, which includes seven types, only three of which are of medical importance.
Subtype Sarcodeae
Sarcodidae cells change shape, the cell membrane forms protrusions, which can then return to their original form, called pseudopods.
They make the cell move. Sarcodidae live everywhere: in soil, fresh water bodies, seas. Infectious diseases caused by Sarcodidae are distributed throughout the world, but are more commonly found in the tropics and subtropics.
Pathogenic amoeboid sarcoids most often affect the digestive system of humans; these are intestinal parasites. Free-living amoebae belonging to other orders also cause serious infections if accidentally ingested 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 excrement preparations with a special heated table, it is possible to detect the pseudopodia and advanced movement of amoebas.
For the treatment of amebiasis, drugs are used, which are divided into groups: contact, which act on forms living in the intestinal lumen, and systemic tissue amoebicides, which act on amoebae that have penetrated into the tissue of the intestine and other organs.
In addition to the treatment, the liver abscess is suctioned if chemotherapy is ineffective or there is a risk of the abscess rupturing. The table below describes the main parasitic protozoans in the subphylum Sarcodidae.
Flagellates subtribe
Representatives of the flagellar subtype have, in addition to the cytoplasmic membrane, a pellicle (such a shell provides a permanent shape) and flagella (one or more).
The flagellum contains contractile fibers that allow movement. Some representatives of flagellates have a wavy membrane, inside which the flagellum/flagellum lies without going beyond its borders.
The flagellum originates from the kinetosome, which stores energy. Inside some flagellates there is an axostyle - a dense cord inside the body that provides support.
The main symptoms and signs of infection caused by representatives of the flagellate subtype are presented in the table below.
| Representative/ Localizations | Symptoms | Diagnostics |
|---|---|---|
| Giardia (Lamblia intestinalis or Giardia lamblia) / Duodenum and small intestine | Nausea, heartburn, abdominal pain, bloating, heartburn, diarrhea, body poisoning, exhaustion | Microscopic examination of the contents of the duodenum, stool examination, ELISA for the detection 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 patient's liquid feces |
| Trichomonas vaginalis (Trichomonas vaginalis) / Vagina, cervical canal, urethra - in women. Urethra, prostate, testes - in men | Colpitis, urethritis in women, itching, burning sensation in the genital area, foamy yellow discharge from the vagina. Asymptomatic pregnancy, urethritis, prostatitis in men | Vaginal discharge in women, urethral discharge and prostate secretion in men, PCR, culture |
| Oral Trichomonas (Trichomonas tenax)/ Oral cavity, airways, tonsils, gums | Tooth decay, periodontal disease, ear-nose-throat diseases | Impression smears, culture |
| African trypanosomes (Trypanosoma brucei gambiense and Trypanosoma brucei rhodesiense)/ Skin at the site of penetration, lymph nodes at the back of the neck and head, bloodstream | Fever attacks, painful lymph nodes, 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 by Wright or Romanovsky-Giemsa, examination of cerebrospinal fluid. Infection of laboratory animals, RSK, RIF, ELISA |
| American trypanosomiasis (Trypanosoma cruzi)/ Blood | Skin swelling at the site of penetration, enlargement of nearby lymph nodes, swelling of the eyelids, enlargement of parotid lymph nodes. The acute form causes fatal damage to the heart and brain in newborns. Chronic form of adults who became ill in childhood - arrhythmia, extrasystole, colon dilatation with wall hypertrophy, esophageal enlargement, myxedema, paralysis | Microscopy of biopsy samples of blood smears, lymph nodes, spleen and other organs - in acute form. Serological tests, xenodiagnosis (feeding uninfected bugs from the patient's body and detection of trypanosomes in feces), infection of laboratory animals - in the chronic stage |
| Cutaneous leishmaniasis (Leishmania tropica)/Skin | Lump on the skin, enlargement of regional lymph nodes, ulceration of the node with the formation of "dry" or "wet" painless ulcers, macular changes, post-healing scar on the skin | Microscopic examination of the tissue from the bottom of the ulcer with Romanovsky-Giemsa staining, 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 membrane of the cheeks and nose, damage to the nasal septum, hard palate, pharynx, fever, weight loss, development of bacterial infections | Microscopic examination of discharge from ulcers, biopsy of damaged organs, RSK, RNGA |
| Visceral leishmaniasis (Leishmania donovani) / Cells of spleen, liver, bone marrow, lymph nodes | Liver and spleen enlargement, anemia, exhaustion, poisoning, intestinal bleeding, diarrhea, gray spots on the face and head, death | Detection in smears taken from spleen, lymph nodes, bone marrow, RIA, ELISA, RSK biopsies |
Sporozoa
Sporozoa do not have locomotor 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 patients 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 for fourteen to twenty days.
Parasitic cilia
Ciliates do not change their body shape and have a pellicle. Motor maneuvers are performed due to the large number of cilia covering the entire cell.
Ciliates have two nuclei: a large one responsible for cell metabolism and a small one that 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. Undigested food particles leave through the dust, which is a special formation at the end of the body. The table below shows the symptoms that can occur when these parasites are present in the intestines.
| Pathogen | Localization | Symptoms | Diagnostics |
|---|---|---|---|
| Balantidium coli | Colon | Fever, poisoning, abdominal pain, 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 schemes below.
General characteristics of helminths
Helminthology is the science of worms (worms) that parasitize the bodies of other animals, the diseases they cause, and methods of diagnosis, prevention, and treatment.
The helminth fauna is the total number of helminths identified in all humans. Unlike diseases caused by protozoa (protozoa), helminthic diseases are not common everywhere.
Most worms work in the digestive system of humans, while others can attack parenchymal organs, the blood and the urinary system.
The spread of intestinal worms depends on the population's labor activity, the eating habits of different population groups, and the country's economic situation. The following helminthiasis are the most common in our country.
Helminthic diseases are divided into geohelminthiasis and biohelminthiasis. In order for the eggs or larvae of geohelminths to develop, they must be in the external environment to mature and acquire pathogenic properties. These are roundworms, whipworms, necators and others.
Biohelminths live out their life cycle with an alternate host, and in order to acquire pathogenic properties, their eggs must transfer to an intermediate host and sometimes to an additional host. 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 more often in humans than in tissue.
In the pathogenesis of helminthiasis, the appearance of allergic reactions and severe degenerative processes are of great importance. They appear due to the large number of antigens of worms.
Additional factors in pathogenesis include the direct effect of enzymes that form larval forms and adults. In the later stages of the worms' development, the mechanical factor and the direct traumatic effect of the attachment organs play an important role.
The diagnosis is usually confirmed by an interview, the clinical picture of the disease, and the detection of eggs, larvae, fragments, or adult worms in feces, sputum, and duodenal fluid.
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 common: 12 species of trematodes, 8 species of cestodes, and 8 species of nematodes.